### 8.2.1.5 Improvement of measurement methodologies for Centre for Aerosol In Situ Measurements

Although it is not an obligation, the Centre for Aerosol In Situ Measurements should work to sustain a high level of performance and to stimulate the advancement of new techniques and methodologies in the in situ aerosol measurement field by:

* Development of strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime (as described in section 3.5.2)

* Development of new technological products and methods (as described in section 3.5.3)

* Development of retrieval algorithms or tools for producing level 1 to 3 data, including the exploitation of instrument synergies (as described in section 3.5.4)

* Organizing regular events (at least once at 2 years) and other forums, in order to exchange knowledge with the NFs and other scientists

* Contributing to CEN, ISO, or similar standardization activities (as described in section 3.3.9)

## 8.2.2 Technical obligations in relation with the ACTRIS Data Centre

### 8.2.2.1 Data production and data products

The final in situ aerosol ACTRIS data products (ACTRIS data Level 1 and Level 2) consist of various aerosol particle properties together with the respective precision and accuracy, metadata and time dependent flags as specified by the DC and in the standard operating procedures.

For the online measurements, raw data (Level 0) at temperature and pressure conditions as provided by the instrument has to be stored together with the relevant standard and calibration measurements and all information and meta data, which is needed to calculate the higher-level data products. Details for the data production are given in the ACTRIS Data Management Plan (D4.2) and the associated data production descriptions and documents provided by the DC and the Centre for Aerosol In Situ Measurements. All data products, pre-products and software tools are version controlled and identified by the associated DC unit.

ACTRIS aerosol in situ data production follows one of **two main workflows, online or offline**.

For the **online workflow**, data production is based on Level 0 data, i.e. all raw data and signals provided by an instrument in its native time resolution and native conditions of temperature and pressure, brought to a harmonized format, and annotated with all metadata and remarks needed in the further data production process. Level 0 data are to be submitted and archived at the DC unless the ACTRIS Data Management Plan (D4.2), with the associated data production descriptions, defines an exception caused by, e.g., large raw data volumes, e.g. aerosol mass spectra. In this case, an alternative storage procedure has to be agreed between the Centre for Aerosol In Situ Measurements and the DC, which meets long-term archive criteria. The Level 0 data submission includes relevant calibration measurements and measurements of traceable standards needed for data quality control, which are flagged as such. From Level 0 data, Level 1 and Level 2 data are produced. Level 1 data are quality-controlled, calibrations are applied, final variable calculated, native time resolution, invalid and quality control measurements removed, and transferred to standard conditions of temperature and pressure where applicable. Level 2
data is averaged Level 1 data to typically hourly averages, with measure of atmospheric variability included. The Level 1 and Level 2 data can be produced either by the NF or the associated DC unit, depending on variable. The distribution of work is included in the associated data production descriptions available from the DC. The quality control step between Levels 0 and 1 can be automatic (real-real time data production) or manual, performed by the NF. Data level identifiers distinguish between data having received automatic or manual QC. The details of the steps producing Level 1 from Level 0, and Level 2 from Level 1, are specified in the associated data production descriptions and the standard operating procedures.

For the offline workflow, the steps of sample medium pre-exposure treatment, exposure, preparation, sampling, and analysis are documented with standard operating procedures and protocols including metadata and remarks in machine-readable form. Items to be included are specified in the associated data production descriptions and the standard operating procedures. The archive for the protocols is located at the NF, its operating protocols coordinated with and approved by the DC and the Centre for Aerosol In Situ Measurements. From these protocols, the Level 2 data products are produced in the temporal resolution determined by the sampling schedule, and transferred to the DC using the tools provided for data submission to ensure required documentation, flagging and metadata. The details of the procedure are specified in the associated data production descriptions.

### 8.2.2.2 Data delivery and quality control

It is compulsory for the NF to produce at least Level 1 (online measurements) and Level 2 (online and offline measurements) data for archiving at the associated DC unit. Archiving of Level 0 data will depend on specific variables. For the submission of aerosol in situ data, required procedures are described in the ACTRIS Data Management Plan (D4.2) and the associated data production descriptions. Manually quality controlled data has to be submitted on a regular, scheduled frequency, at least yearly to the ACTRIS DC following the scheme in the ACTRIS Data Management Plan (D4.2), and associated documents. Submission to the DC has to be done before 31 May, using the submission tools and automatic quality control software available within the DC. Data originators at the NF are responsible for checking the data using the procedures in the associated data production descriptions. Data is then reviewed by the Centre for Aerosol In Situ Measurements and shall be discussed at the annual data quality meeting, in collaboration with the DC. An issue tracker is operated in the process of data evaluation to ensure full documentation and traceability of the data production and quality control process. This comes into place yearly following the initial data submission by stations to the ACTRIS DC. Upon errors, the data has to be re-submitted and shall be reviewed again for compliance with suggested changes.

Whenever possible by measurement principle and connectivity to the station, Level 0 data must be transmitted to the DC in real-real-time (RRT), i.e., latest within 3 hours of measurement, for delivery of an RRT data product for operational services.
data is averaged Level 1 data to typically hourly averages, with measure of atmospheric variability included. The Level 1 and Level 2 data can be produced either by the NF or the associated DC unit, depending on variable. The distribution of work is included in the associated data production descriptions available from the DC. The quality control step between Levels 0 and 1 can be automatic (real-real time data production) or manual, performed by the NF. Data level identifiers distinguish between data having received automatic or manual QC. The details of the steps producing Level 1 from Level 0, and Level 2 from Level 1, are specified in the associated data production descriptions and the standard operating procedures.

For the offline workflow, the steps of sample medium pre-exposure treatment, exposure, preparation, sampling, and analysis are documented with standard operating procedures and protocols including metadata and remarks in machine-readable form. Items to be included are specified in the associated data production descriptions and the standard operating procedures. The archive for the protocols is located at the NF, its operating protocols coordinated with and approved by the DC and the Centre for Aerosol In Situ Measurements. From these protocols, the Level 2 data products are produced in the temporal resolution determined by the sampling schedule, and transferred to the DC using the tools provided for data submission to ensure required documentation, flagging and metadata. The details of the procedure are specified in the associated data production descriptions.

### 8.2.2.2 Data delivery and quality control

It is compulsory for the NF to produce at least Level 1 (online measurements) and Level 2 (online and offline measurements) data for archiving at the associated DC unit. Archiving of Level 0 data will depend on specific variables. For the submission of aerosol in situ data, required procedures are described in the ACTRIS Data Management Plan (D4.2) and the associated data production descriptions. Manually quality controlled data has to be submitted on a regular, scheduled frequency, at least yearly to the ACTRIS DC following the scheme in the ACTRIS Data Management Plan (D4.2), and associated documents. Submission to the DC has to be done before 31 May, using the submission tools and automatic quality control software available within the DC. Data originators at the NF are responsible for checking the data using the procedures in the associated data production descriptions. Data is then reviewed by the Centre for Aerosol In Situ Measurements and shall be discussed at the annual data quality meeting, in collaboration with the DC. An issue tracker is operated in the process of data evaluation to ensure full documentation and traceability of the data production and quality control process. This comes into place yearly following the initial data submission by stations to the ACTRIS DC. Upon errors, the data has to be re-submitted and shall be reviewed again for compliance with suggested changes.

Whenever possible by measurement principle and connectivity to the station, Level 0 data must be transmitted to the DC in real-real-time (RRT), i.e., latest within 3 hours of measurement, for delivery of an RRT data product for operational services.
### 8.2.3 Technical obligations in relation with the Centre for Cloud In Situ Measurements and the Centre for Reactive Trace Gases In Situ Measurements

Currently (2018), there are no technical obligations the Centre for Aerosol In Situ Measurements has to fulfil for other TCs. However, as the six scientific ACTRIS themes partly overlap, there is sometimes the need to agree among two TCs which of the two TCs is responsible for specific operation support or services. For the Centre for Aerosol In Situ Measurements this overlap exists with the Centre for Cloud In Situ Measurements concerning the cloud droplet or ice crystal activation properties of aerosol particles, as well as with the Centre for Reactive Trace Gases In Situ Measurements concerning the transition from gas molecule clusters to aerosol particles.

### 8.2.4 Technical obligations in relation with the ACTRIS users

The Centre for Aerosol In Situ Measurements should commit to provide a minimum amount of user services as described in section 4.

## 8.3 Evaluation of the activity of the Centre for Aerosol In Situ Measurements

Once established and operational, the Centre for Aerosol In Situ Measurements shall be evaluated for its performances, using the following Key Performance Indicators (KPIs):

<table><thead><tr><th>No.</th><th>Criteria</th><th>Indicators</th><th>Score</th><th>Weight</th></tr></thead><tbody><tr><td rowspan="5">1</td><td rowspan="5">Usefulness for ACTRIS NFs</td><td>No. of operation support units provided to ACTRIS NFs for quality assurance and quality control</td><td>1 ... 10</td><td rowspan="5">50%</td></tr><tr><td>No. of operation support units provided to ACTRIS NFs for knowledge transfer and training</td><td>1 ... 10</td></tr><tr><td>No. of operation support units provided to ACTRIS NFs for Improvement of measurement and data processing methodologies</td><td>1 ... 10</td></tr><tr><td>Average score of satisfaction received from NFs</td><td>1 ... 10</td></tr><tr><td>Average of Usefulness for ACTRIS</td><td></td></tr><tr><td rowspan="2">2</td><td rowspan="2">Usefulness for ACTRIS users</td><td>No. of service units provided to ACTRIS users for quality assurance and quality control</td><td>1 ... 10</td><td rowspan="2">20%</td></tr><tr><td>No. of service units provided to ACTRIS users for knowledge transfer and training</td><td>1 ... 10</td></tr></tbody></table>
### 8.2.3 Technical obligations in relation with the Centre for Cloud In Situ Measurements and the Centre for Reactive Trace Gases In Situ Measurements

Currently (2018), there are no technical obligations the Centre for Aerosol In Situ Measurements has to fulfil for other TCs. However, as the six scientific ACTRIS themes partly overlap, there is sometimes the need to agree among two TCs which of the two TCs is responsible for specific operation support or services. For the Centre for Aerosol In Situ Measurements this overlap exists with the Centre for Cloud In Situ Measurements concerning the cloud droplet or ice crystal activation properties of aerosol particles, as well as with the Centre for Reactive Trace Gases In Situ Measurements concerning the transition from gas molecule clusters to aerosol particles.

### 8.2.4 Technical obligations in relation with the ACTRIS users

The Centre for Aerosol In Situ Measurements should commit to provide a minimum amount of user services as described in section 4.

## 8.3 Evaluation of the activity of the Centre for Aerosol In Situ Measurements

Once established and operational, the Centre for Aerosol In Situ Measurements shall be evaluated for its performances, using the following Key Performance Indicators (KPIs):

<table><thead><tr><th>No.</th><th>Criteria</th><th>Indicators</th><th>Score</th><th>Weight</th></tr></thead><tbody><tr><td rowspan="5">1</td><td rowspan="5">Usefulness for ACTRIS NFs</td><td>No. of operation support units provided to ACTRIS NFs for quality assurance and quality control</td><td>1 ... 10</td><td rowspan="5">50%</td></tr><tr><td>No. of operation support units provided to ACTRIS NFs for knowledge transfer and training</td><td>1 ... 10</td></tr><tr><td>No. of operation support units provided to ACTRIS NFs for Improvement of measurement and data processing methodologies</td><td>1 ... 10</td></tr><tr><td>Average score of satisfaction received from NFs</td><td>1 ... 10</td></tr><tr><td>Average of Usefulness for ACTRIS</td><td></td></tr><tr><td rowspan="2">2</td><td rowspan="2">Usefulness for ACTRIS users</td><td>No. of service units provided to ACTRIS users for quality assurance and quality control</td><td>1 ... 10</td><td rowspan="2">20%</td></tr><tr><td>No. of service units provided to ACTRIS users for knowledge transfer and training</td><td>1 ... 10</td></tr></tbody></table>
<table><tbody><tr><td></td><td></td><td>No. of service units provided to ACTRIS users for improvement of measurement and data processing methodologies</td><td>1 ... 10</td><td></td></tr><tr><td></td><td></td><td>Average score of satisfaction received from ACTRIS users</td><td>1 ... 10</td><td></td></tr><tr><td></td><td></td><td>Average of Usefulness for external users</td><td></td><td></td></tr><tr><td rowspan="6">3</td><td rowspan="6">Impact on science and technology</td><td>No. of new technological products, methods and algorithms developed/ improved</td><td>1 ... 10</td><td rowspan="6">15%</td></tr><tr><td>No. of peer-review CF-related papers published</td><td>1 ... 10</td></tr><tr><td>No. of CF-related communications at scientific conferences/workshops</td><td>1 ... 10</td></tr><tr><td>No. of CF-related patents promoted</td><td>1 ... 10</td></tr><tr><td>Average of S&T Impact</td><td></td></tr><tr><td>No. of participations to ACTRIS committees and boards</td><td>1 ... 10</td></tr><tr><td rowspan="4">4</td><td rowspan="4">Integration into ACTRIS-RI</td><td>No. of activities performed in collaboration with other TCs (joint SOPs, joint workshops, etc.)</td><td>1 ... 10</td><td rowspan="4">15%</td></tr><tr><td>Average score of satisfaction received from ACTRIS DC for the contribution to documentation and traceability of data products</td><td>1 ... 10</td></tr><tr><td>Average score of satisfaction received from ACTRIS HO for the quality and readiness of the reports</td><td>1 ... 10</td></tr><tr><td>Average of Integration into ACTRIS-RI</td><td></td></tr><tr><td colspan="4">Total score</td><td></td></tr></tbody></table>
<table><tbody><tr><td></td><td></td><td>No. of service units provided to ACTRIS users for improvement of measurement and data processing methodologies</td><td>1 ... 10</td><td></td></tr><tr><td></td><td></td><td>Average score of satisfaction received from ACTRIS users</td><td>1 ... 10</td><td></td></tr><tr><td></td><td></td><td>Average of Usefulness for external users</td><td></td><td></td></tr><tr><td rowspan="6">3</td><td rowspan="6">Impact on science and technology</td><td>No. of new technological products, methods and algorithms developed/ improved</td><td>1 ... 10</td><td rowspan="6">15%</td></tr><tr><td>No. of peer-review CF-related papers published</td><td>1 ... 10</td></tr><tr><td>No. of CF-related communications at scientific conferences/workshops</td><td>1 ... 10</td></tr><tr><td>No. of CF-related patents promoted</td><td>1 ... 10</td></tr><tr><td>Average of S&T Impact</td><td></td></tr><tr><td>No. of participations to ACTRIS committees and boards</td><td>1 ... 10</td></tr><tr><td rowspan="4">4</td><td rowspan="4">Integration into ACTRIS-RI</td><td>No. of activities performed in collaboration with other TCs (joint SOPs, joint workshops, etc.)</td><td>1 ... 10</td><td rowspan="4">15%</td></tr><tr><td>Average score of satisfaction received from ACTRIS DC for the contribution to documentation and traceability of data products</td><td>1 ... 10</td></tr><tr><td>Average score of satisfaction received from ACTRIS HO for the quality and readiness of the reports</td><td>1 ... 10</td></tr><tr><td>Average of Integration into ACTRIS-RI</td><td></td></tr><tr><td colspan="4">Total score</td><td></td></tr></tbody></table>
## 9 Glossary

**ACTRIS data** - are the ACTRIS variables resulting from measurements that fully comply with the standard operating procedures (SOP), measurement recommendations, and quality guidelines established within ACTRIS.

* **ACTRIS level 0 data:** Raw sensor output, either mV or physical units. Native resolution, metadata necessary for next level.

* **ACTRIS level 1 data:** Calibrated and quality assured data with minimum level of quality control.

* **ACTRIS level 2 data:** Approved and fully quality controlled ACTRIS data product or geophysical variable.

* **ACTRIS level 3 data:** Elaborated ACTRIS data products derived by post-processing of ACTRIS Level 0 -1 -2 data, and data from other sources. The data can be gridded or not.

* **ACTRIS syntheses product (Proper name to be defined later):** Data product from e.g. research activities, not under direct ACTRIS responsibility, but ACTRIS offer repository and access.

**ACTRIS Data Centre (DC)** - the Central Facility responsible for ACTRIS data curation, preservation, and distribution of data, value-added products and tools, and hosting the ACTRIS data portal.

**ACTRIS data originator** - entity operating instruments at a National Facility or Topical Centre, resulting in ACTRIS data and delivering ACTRIS data to the Data Centre.

**ACTRIS data provider** - the Data Centre offering the ACTRIS data and value-added data products and tools to users.

**ACTRIS digital tools and services** - tailored codes and software for processing and visualization of ACTRIS data, production of ACTRIS data products, and for data analysis and research.

**ACTRIS exploratory platform** - National Facility (simulation chambers, laboratories, or mobile facilities) operating on campaign basis and delivering dedicated data to the Data Centre.

**ACTRIS General Assembly (GA)** - a council of ministry- and funding organization representatives of ACTRIS members after ACTRIS legal entity has been established, superior decision-making body of ACTRIS.

**ACTRIS Head Office (HO)** - a Central Facility coordinating and representing ACTRIS, and holding the statutory seat.

**ACTRIS label** - earmarks a data set or a measurement site as ACTRIS data or ACTRIS National Facility.

**ACTRIS observational platform** – ACTRIS National Facility performing long-term, regular observations and delivering standardized data to the Data Centre.

**ACTRIS Topical Centres (TCs)** – a Central Facility offering services and operation support for QA/QC of measurements and data (including training, calibration, QA/QC tools, and development of standard operation and evaluation procedures)
9 Glossary

**ACTRIS data** - are the ACTRIS variables resulting from measurements that fully comply with the standard operating procedures (SOP), measurement recommendations, and quality guidelines established within ACTRIS.

o **ACTRIS level 0 data**: Raw sensor output, either mV or physical units. Native resolution, metadata necessary for next level.

o **ACTRIS level 1 data**: Calibrated and quality assured data with minimum level of quality control.

o **ACTRIS level 2 data**: Approved and fully quality controlled ACTRIS data product or geophysical variable.

o **ACTRIS level 3 data**: Elaborated ACTRIS data products derived by post-processing of ACTRIS Level 0 -1 -2 data, and data from other sources. The data can be gridded or not.

o **ACTRIS syntheses product (Proper name to be defined later)**: Data product from e.g. research activities, not under direct ACTRIS responsibility, but ACTRIS offer repository and access.

**ACTRIS Data Centre (DC)** - the Central Facility responsible for ACTRIS data curation, preservation, and distribution of data, value-added products and tools, and hosting the ACTRIS data portal.

**ACTRIS data originator** - entity operating instruments at a National Facility or Topical Centre, resulting in ACTRIS data and delivering ACTRIS data to the Data Centre.

**ACTRIS data provider** - the Data Centre offering the ACTRIS data and value-added data products and tools to users.

**ACTRIS digital tools and services** - tailored codes and software for processing and visualization of ACTRIS data, production of ACTRIS data products, and for data analysis and research.

**ACTRIS exploratory platform** - National Facility (simulation chambers, laboratories, or mobile facilities) operating on campaign basis and delivering dedicated data to the Data Centre.

**ACTRIS General Assembly (GA)** - a council of ministry- and funding organization representatives of ACTRIS members after ACTRIS legal entity has been established, superior decision-making body of ACTRIS.

**ACTRIS Head Office (HO)** - a Central Facility coordinating and representing ACTRIS, and holding the statutory seat.

**ACTRIS label** - earmarks a data set or a measurement site as ACTRIS data or ACTRIS National Facility.

**ACTRIS observational platform** – ACTRIS National Facility performing long-term, regular observations and delivering standardized data to the Data Centre.

**ACTRIS Topical Centres (TCs)** – a Central Facility offering services and operation support for QA/QC of measurements and data (including training, calibration, QA/QC tools, and development of standard operation and evaluation procedures)
**ACTRIS variables** - the measured atmospheric variables as described in the [ACTRIS Data Management Plan]().

**Central Facility (CF)** - a European level ACTRIS component that offers ACTRIS data or other ACTRIS services to users as well as operation support to ACTRIS National Facilities.

**Central Facility Unit** – part of a Central Facility located at, and operated by a research performing organization (RPO) or by ACTRIS ERIC.

**CF Director** – the person responsible for the coordination and representation of a Central Facility.

**CF Unit Head** – the person responsible for the coordination and representation of a Central Facility unit.

**CF Management Board** – consists of the CF Unit Heads and the CF Director; this board manages the Central Facility.

**Data curation** - the activity that stores, manages and ensures access to all persistent data sets produced within the infrastructure.

**Data traceability** - an unbroken chain of uniquely identified process steps leading from raw data to any kind of processed data, where identification of process steps follows the data.

**In situ measurements** - measured or sampled air and instrument are at the same location and in physical contact. In the context of ACTRIS, in situ measurements of aerosol, cloud, and reactive-trace-gas properties are performed at observational sites near the Earth surface, on mobile surface-based or airborne platforms, and in atmospheric simulation chambers and laboratories.

**Interim ACTRIS Council** - a council of ministry- and funding organization representatives of ACTRIS members before ACTRIS legal entity has been established (during the ACTRIS Preparation and Transition Phase), superior decision-making body of ACTRIS.

**Measurement traceability** - an unbroken chain of comparisons relating an instrument's measurements to a known standard, in the ideal case SI units.

**National Facility (NF)** - an observational or exploratory platform providing data and/or physical access to the platform within ACTRIS.

**Quality assurance and control:** Quality assurance is process oriented and focuses on defect prevention; quality control is product oriented and focuses on defect identification:

* **Quality Assurance (QA):** The process or set of processes used to ensure the quality of a product (e.g. data series, instrument, sample, measured value of a variable, etc.),

* **Quality Control (QC):** The process and activities of ensuring products and services meet the expectations.

**Remote sensing** - measured air and instrument are not at the same location and not in physical contact. In the context of ACTRIS, active and passive atmospheric remote-sensing techniques for the

<footnote n="1">¹The ACTRIS data management plan and list of variables were approved by ACTRIS-2 scientific steering committee, October 2015. These documents are expected to be refined during ACTRIS-PPP (WP5).</footnote>
**ACTRIS variables** - the measured atmospheric variables as described in the [ACTRIS Data Management Plan]().

**Central Facility (CF)** - a European level ACTRIS component that offers ACTRIS data or other ACTRIS services to users as well as operation support to ACTRIS National Facilities.

**Central Facility Unit** – part of a Central Facility located at, and operated by a research performing organization (RPO) or by ACTRIS ERIC.

**CF Director** – the person responsible for the coordination and representation of a Central Facility.

**CF Unit Head** – the person responsible for the coordination and representation of a Central Facility unit.

**CF Management Board** – consists of the CF Unit Heads and the CF Director; this board manages the Central Facility.

**Data curation** - the activity that stores, manages and ensures access to all persistent data sets produced within the infrastructure.

**Data traceability** - an unbroken chain of uniquely identified process steps leading from raw data to any kind of processed data, where identification of process steps follows the data.

**In situ measurements** - measured or sampled air and instrument are at the same location and in physical contact. In the context of ACTRIS, in situ measurements of aerosol, cloud, and reactive-trace-gas properties are performed at observational sites near the Earth surface, on mobile surface-based or airborne platforms, and in atmospheric simulation chambers and laboratories.

**Interim ACTRIS Council** - a council of ministry- and funding organization representatives of ACTRIS members before ACTRIS legal entity has been established (during the ACTRIS Preparation and Transition Phase), superior decision-making body of ACTRIS.

**Measurement traceability** - an unbroken chain of comparisons relating an instrument's measurements to a known standard, in the ideal case SI units.

**National Facility (NF)** - an observational or exploratory platform providing data and/or physical access to the platform within ACTRIS.

**Quality assurance and control:** Quality assurance is process oriented and focuses on defect prevention; quality control is product oriented and focuses on defect identification:

* **Quality Assurance (QA):** The process or set of processes used to ensure the quality of a product (e.g. data series, instrument, sample, measured value of a variable, etc.),

* **Quality Control (QC):** The process and activities of ensuring products and services meet the expectations.

**Remote sensing** - measured air and instrument are not at the same location and not in physical contact. In the context of ACTRIS, active and passive atmospheric remote-sensing techniques for the

<footnote n="1">¹The ACTRIS data management plan and list of variables were approved by ACTRIS-2 scientific steering committee, October 2015. These documents are expected to be refined during ACTRIS-PPP (WP5).</footnote>
observation of aerosols, clouds, and trace gases are applied at observational sites and on mobile surface-based or airborne platforms.

**RI committee** – consists of up to two representatives from each Central Facility and [three] representatives from the National Facilities Assembly; the RI committee supports the (Interim) Director or Board of Directors in operating the RI.

**Service and Access Management Unit (SAMU)** - a part of ACTRIS Head Office facilitating the access to ACTRIS services.

**User** - a person, a team, or an institution making use of ACTRIS data or other ACTRIS services, including access to ACTRIS facilities.
observation of aerosols, clouds, and trace gases are applied at observational sites and on mobile surface-based or airborne platforms.

**RI committee** – consists of up to two representatives from each Central Facility and [three] representatives from the National Facilities Assembly; the RI committee supports the (Interim) Director or Board of Directors in operating the RI.

**Service and Access Management Unit (SAMU)** - a part of ACTRIS Head Office facilitating the access to ACTRIS services.

**User** - a person, a team, or an institution making use of ACTRIS data or other ACTRIS services, including access to ACTRIS facilities.
# 10 Reference documents

* ACTRIS-PPP proposal

* ACTRIS Data Management Plan, approved by ACTRIS-2 SSC 23 October 2015

* ACTRIS Concept Documents

* ISO 10012:2003: Measurement management systems — Requirements for measurement processes and measuring equipment

* ISO 9000:2015: Quality management systems—Fundamentals and vocabulary

* Baseline document for the Concepts of ACTRIS Central Facilities

* Technical concepts and requirements for ACTRIS Observational Platforms

* Technical concepts and requirements for ACTRIS Exploratory Platforms
10 Reference documents

ACTRIS-PPP proposal

ACTRIS Data Management Plan, approved by ACTRIS-2 SSC 23 October 2015

ACTRIS Concept Documents

ISO 10012:2003: Measurement management systems — Requirements for measurement processes and measuring equipment

ISO 9000:2015: Quality management systems—Fundamentals and vocabulary

Baseline document for the Concepts of ACTRIS Central Facilities

Technical concepts and requirements for ACTRIS Observational Platforms

Technical concepts and requirements for ACTRIS Exploratory Platforms
11 Scientific references

Aalto, P. et al., Physical characterization of aerosol particles during nucleation events. Tellus, Ser. B Chem. Phys. Meteorol. 53, 344–358, 2001.

Ahonen, L. R. et al., First measurements of the number size distribution of 1–2 nm aerosol particles released from manufacturing processes in a cleanroom environment. Aerosol Sci. Technol. 51, 685–693, 2017.

Cavalli, F. et al., towards a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol, Atmos. Meas. Tech., 3, 79-89, https://doi.org/10.5194/amt-3-79-2010, 2010.

Kangasluoma, J. et al., Sub-3 nm particle size and composition dependent response of a nano-CPC battery. Atmos. Meas. Tech. 7, 689–700, 2014.

Kulmala, M. et al., Measurement of the nucleation of atmospheric aerosol particles. Nat. Protoc. 7, 1651–1667, 2012.

Lehtipalo, K. et al., Methods for determining particle size distribution and growth rates between 1 and 0.003 µm using the Particle Size Magnifier. Boreal Env. Res. 19 (suppl., 215–236), 2014.

Manninen, H. E. et al., EUCAARI ion spectrometer measurements at 12 European sites–analysis of new particle formation events. Atmos. Chem. Phys. (2010), doi:10.5194/acp-10-7907-, 2010.

Manninen, H. E. et al., How to reliably detect molecular clusters and nucleation mode particles with Neutral cluster and Air Ion Spectrometer (NAIS). Atmos. Meas. Tech. 9, 3577–3605, 2016.

Pfeifer, S. et al., Intercomparison of 15 aerodynamic particle size spectrometers (APS 3321): uncertainties in particle sizing and number size distribution, Atmos. Meas. Tech., 9, 1545-1551, https://doi.org/10.5194/amt-9-1545-2016, 2016.

Vanhanen, J. et al., Particle Size Magnifier for Nano-CN Detection. Aerosol Sci. Technol. 45, 533–542, 2011.

Wiedensohler, A. et al., Mobility particle size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions. Atmos. Meas. Tech. 5, 657–685, 2012.

Wiedensohler, A. et al., Mobility Particle Size Spectrometers: Calibration Procedures and Measurement Uncertainties. Aerosol Science and Technology, https://doi.org/10.1080/02786826.02782017.01387229, 2017.

Williams, J. et al., The summertime Boreal forest field measurement intensive (HUMPPA-COPEC-2010): an overview of meteorological and chemical influences. Atmos. Chem. Phys. 11, 10599–10618, 2011.
## 11 Scientific references

Aalto, P. et al., Physical characterization of aerosol particles during nucleation events. Tellus, Ser. B Chem. Phys. Meteorol. 53, 344–358, 2001.

Ahonen, L. R. et al., First measurements of the number size distribution of 1–2 nm aerosol particles released from manufacturing processes in a cleanroom environment. Aerosol Sci. Technol. 51, 685–693, 2017.

Cavalli, F. et al., towards a standardised thermal-optical protocol for measuring atmospheric organic and elemental carbon: the EUSAAR protocol, Atmos. Meas. Tech., 3, 79-89, https://doi.org/10.5194/amt-3-79-2010, 2010.

Kangasluoma, J. et al., Sub-3 nm particle size and composition dependent response of a nano-CPC battery. Atmos. Meas. Tech. 7, 689–700, 2014.

Kulmala, M. et al., Measurement of the nucleation of atmospheric aerosol particles. Nat. Protoc. 7, 1651–1667, 2012.

Lehtipalo, K. et al., Methods for determining particle size distribution and growth rates between 1 and 0.003 µm using the Particle Size Magnifier. Boreal Env. Res. 19 (suppl., 215–236), 2014.

Manninen, H. E. et al., EUCAARI ion spectrometer measurements at 12 European sites–analysis of new particle formation events. Atmos. Chem. Phys. (2010), doi:10.5194/acp-10-7907-, 2010.

Manninen, H. E. et al., How to reliably detect molecular clusters and nucleation mode particles with Neutral cluster and Air Ion Spectrometer (NAIS). Atmos. Meas. Tech. 9, 3577–3605, 2016.

Pfeifer, S. et al., Intercomparison of 15 aerodynamic particle size spectrometers (APS 3321): uncertainties in particle sizing and number size distribution, Atmos. Meas. Tech., 9, 1545-1551, https://doi.org/10.5194/amt-9-1545-2016, 2016.

Vanhanen, J. et al., Particle Size Magnifier for Nano-CN Detection. Aerosol Sci. Technol. 45, 533–542, 2011.

Wiedensohler, A. et al., Mobility particle size spectrometers: harmonization of technical standards and data structure to facilitate high quality long-term observations of atmospheric particle number size distributions. Atmos. Meas. Tech. 5, 657–685, 2012.

Wiedensohler, A. et al., Mobility Particle Size Spectrometers: Calibration Procedures and Measurement Uncertainties. Aerosol Science and Technology, https://doi.org/10.1080/02786826.02782017.01387229, 2017.

Williams, J. et al., The summertime Boreal forest field measurement intensive (HUMPPA-COPEC-2010): an overview of meteorological and chemical influences. Atmos. Chem. Phys. 11, 10599–10618, 2011.
# Annex: Provision of the operation support

## Scheduled support

<table><thead><tr><th>Mode</th><th>Type of support</th><th>Specific support</th><th>Frequency</th><th>Comments</th></tr></thead><tbody><tr><td rowspan="2">In situ measurements</td><td>Instrument-specific calibration workshop at TC facility</td><td>Comparison with fixed reference instruments, intercomparison measurements, support for beneficiaries whose instrument under-performed</td><td rowspan="2">Once every 1-3 years, after major upgrades, or after replacement</td><td>TC distributes a schedule one year in advance and agrees with the NFs on potential adjustments of the schedule</td></tr><tr><td>Site performance test with reference instruments operated at NFs</td><td>Round-Robin reference instrument, support for beneficiaries whose instrument under-performed</td><td>TC distributes a schedule one year in advance and agrees with the NFs on potential adjustments of the schedule</td></tr><tr><td>In situ sampling</td><td>Laboratory intercomparison at NFs</td><td>Round-Robin reference samples, support for beneficiaries whose instrument under-performed</td><td>Once every 1-2 years, after major upgrades, or after replacement</td><td>TC distributes a schedule one year in advance and agrees with the NFs on potential adjustments of the schedule</td></tr><tr><td>In situ measurements or sampling</td><td>Training of operators and scientists</td><td>Training on particle measurement and sampling, exercises to access the performance of NFs, training on data evaluation</td><td>Once every 1-2 years</td><td>Mostly co-located with instrument calibration workshops, otherwise specific schools announced on the TC web page and with online registration</td></tr></tbody></table>
# Annex: Provision of the operation support

## Scheduled support

<table><thead><tr><td>Mode</td><td>Type of support</td><td>Specific support</td><td>Frequency</td><td>Comments</td></tr></thead><tbody><tr><td rowspan="2">In situ measurements</td><td>Instrument-specific calibration workshop at TC facility</td><td>Comparison with fixed reference instruments, intercomparison measurements, support for beneficiaries whose instrument under-performed</td><td rowspan="2">Once every 1-3 years, after major upgrades, or after replacement</td><td>TC distributes a schedule one year in advance and agrees with the NFs on potential adjustments of the schedule</td></tr><tr><td>Site performance test with reference instruments operated at NFs</td><td>Round-Robin reference instrument, support for beneficiaries whose instrument under-performed</td><td>TC distributes a schedule one year in advance and agrees with the NFs on potential adjustments of the schedule</td></tr><tr><td>In situ sampling</td><td>Laboratory intercomparison at NFs</td><td>Round-Robin reference samples, support for beneficiaries whose instrument under-performed</td><td>Once every 1-2 years, after major upgrades, or after replacement</td><td>TC distributes a schedule one year in advance and agrees with the NFs on potential adjustments of the schedule</td></tr><tr><td>In situ measurements or sampling</td><td>Training of operators and scientists</td><td>Training on particle measurement and sampling, exercises to access the performance of NFs, training on data evaluation</td><td>Once every 1-2 years</td><td>Mostly co-located with instrument calibration workshops, otherwise specific schools announced on the TC web page and with online registration</td></tr></tbody></table>
Operation support on request

<table><thead><tr><th>Mode</th><th>Type of support</th><th>Specific support</th><th>Comments</th></tr></thead><tbody><tr><td rowspan="6">In situ measurements or sampling</td><td>Measurement guidelines</td><td>Definition and establishment of measurement guidelines and standard operation procedures</td><td>For new instruments and/or new ACTRIS variables, depending on capacity and time schedule, on request by the National Facilities Assembly and the RI Committee</td></tr><tr><td>Quality-assurance criteria and procedures</td><td>Definition of measurement quality-assurance criteria and procedures</td><td>For new instruments and/or new ACTRIS variables, depending on capacity and time schedule, on request by the National Facilities Assembly and the RI Committee</td></tr><tr><td>Instrument calibration</td><td>Development and provision of instrument-specific calibration</td><td>Unscheduled calibration, either at TC or at NF, depending on capacity and time schedule, on request by NFs via SAMU</td></tr><tr><td rowspan="2">Measurement and data tools</td><td>Development and provision of in-house check-up tools</td><td rowspan="2">Depending on capacity and time schedule, on request by the NFs, the DC, the National Facilities Assembly, or the RI Committee</td></tr><tr><td>Development of data evaluation procedures and plausibility tests</td></tr><tr><td>Site performance tests</td><td>Round-Robin test with either reference samples or reference instruments, analysis of samples collected by the NFs</td><td>Unscheduled site performance tests, e.g. after major site upgrades, depending on capacity and time schedule, on request by NFs via SAMU</td></tr><tr><td>Training of operators and scientists</td><td>Training on particle measurement and sampling, exercises to access the performance of NFs, training on data evaluation</td><td>Unscheduled training, depending on capacity and time schedule, on request by NFs or RI Committee</td></tr></tbody></table>
Operation support on request

<table><thead><tr><th>Mode</th><th>Type of support</th><th>Specific support</th><th>Comments</th></tr></thead><tbody><tr><td rowspan="6">In situ measurements or sampling</td><td>Measurement guidelines</td><td>Definition and establishment of measurement guidelines and standard operation procedures</td><td>For new instruments and/or new ACTRIS variables, depending on capacity and time schedule, on request by the National Facilities Assembly and the RI Committee</td></tr><tr><td>Quality-assurance criteria and procedures</td><td>Definition of measurement quality-assurance criteria and procedures</td><td>For new instruments and/or new ACTRIS variables, depending on capacity and time schedule, on request by the National Facilities Assembly and the RI Committee</td></tr><tr><td>Instrument calibration</td><td>Development and provision of instrument-specific calibration</td><td>Unscheduled calibration, either at TC or at NF, depending on capacity and time schedule, on request by NFs via SAMU</td></tr><tr><td rowspan="2">Measurement and data tools</td><td>Development and provision of in-house check-up tools</td><td rowspan="2">Depending on capacity and time schedule, on request by the NFs, the DC, the National Facilities Assembly, or the RI Committee</td></tr><tr><td>Development of data evaluation procedures and plausibility tests</td></tr><tr><td>Site performance tests</td><td>Round-Robin test with either reference samples or reference instruments, analysis of samples collected by the NFs</td><td>Unscheduled site performance tests, e.g. after major site upgrades, depending on capacity and time schedule, on request by NFs via SAMU</td></tr><tr><td>Training of operators and scientists</td><td>Training on particle measurement and sampling, exercises to access the performance of NFs, training on data evaluation</td><td>Unscheduled training, depending on capacity and time schedule, on request by NFs or RI Committee</td></tr></tbody></table>
<table><tr><td rowspan="3">In situ measurements or sampling</td><td>New RI components</td><td>Consultancy for setting-up new observational or exploratory platforms and new instruments at NFs<br/>Testing of new measurement instruments</td><td>Depending on capacity and time schedule, on request by NFs via SAMU</td></tr><tr><td>Data production</td><td>Development of tools for producing level 1 to 3 data, including tools for producing NRT data</td><td>Depending on capacity and time schedule, on request by the DC, the National Facilities Assembly, or the RI Committee</td></tr></table>
<table><tr><td rowspan="3">In situ measurements or sampling</td><td>New RI components</td><td>Consultancy for setting-up new observational or exploratory platforms and new instruments at NFs<br/>Testing of new measurement instruments</td><td>Depending on capacity and time schedule, on request by NFs via SAMU</td></tr><tr><td>Data production</td><td>Development of tools for producing level 1 to 3 data, including tools for producing NRT data</td><td>Depending on capacity and time schedule, on request by the DC, the National Facilities Assembly, or the RI Committee</td></tr></table>
Section 4

Concept of the Centre for Aerosol Remote Sensing

ACTRIS PPP WP 4 task 4.1

22.2.2018

Public
Section 4

Concept of the Centre for Aerosol Remote Sensing

ACTRIS PPP WP 4 task 4.1

22.2.2018

Public
Contents

<table><tr><td>1</td><td>Purpose of the document</td><td>4</td></tr><tr><td>2</td><td>Description and role of the Centre for Aerosol Remote Sensing</td><td>4</td></tr><tr><td>2.1</td><td>Framework</td><td>4</td></tr><tr><td>2.2</td><td>Scientific relevance</td><td>4</td></tr><tr><td>2.3</td><td>Mission</td><td>5</td></tr><tr><td>3</td><td>Operation support provided to ACTRIS National Facilities</td><td>5</td></tr><tr><td>3.1</td><td>Measurement techniques covered by the Centre for Aerosol Remote Sensing, and related ACTRIS variables</td><td>6</td></tr><tr><td>3.1.1</td><td>Aerosol high-power lidar (AHL)</td><td>6</td></tr><tr><td>3.1.2</td><td>Automatic low-power lidar / ceilometer (ALC)</td><td>7</td></tr><tr><td>3.1.3</td><td>Automatic sun/sky/polarized/lunar photometer (ASP)</td><td>8</td></tr><tr><td>3.2</td><td>Estimation of the need</td><td>8</td></tr><tr><td>3.3</td><td>Timeline for implementation of the mandatory operation support</td><td>9</td></tr><tr><td>3.4</td><td>Operation support for quality assurance and quality control</td><td>11</td></tr><tr><td>3.4.1</td><td>Definition and establishment of standard operation procedures</td><td>11</td></tr><tr><td>3.4.2</td><td>Definition of measurement quality-assurance criteria and procedures</td><td>12</td></tr><tr><td>3.4.3</td><td>Development and provision of instrument-specific calibration</td><td>13</td></tr><tr><td>3.4.4</td><td>Development and provision of in-house check-up tools</td><td>15</td></tr><tr><td>3.4.5</td><td>Development of data evaluation procedures and plausibility test</td><td>15</td></tr><tr><td>3.4.6</td><td>Realization of observational site performance audits with reference samples or mobile systems</td><td>16</td></tr><tr><td>3.4.7</td><td>Organization of regular exercises to assess the performances of the NFs, including instrument performance workshops</td><td>17</td></tr><tr><td>3.4.8</td><td>Contribution to documentation and traceability of level 0 to level 3 data products</td><td>17</td></tr><tr><td>3.4.9</td><td>Contribution to CEN, ISO, or similar standardization activities</td><td>18</td></tr><tr><td>3.5</td><td>Operation support for knowledge transfer and training</td><td>18</td></tr><tr><td>3.5.1</td><td>Training of operators and scientists</td><td>18</td></tr><tr><td>3.5.2</td><td>Consultancy for setting-up new observational or exploratory platforms and new instruments at the NFs</td><td>18</td></tr><tr><td>3.6</td><td>Operation support for improvement of measurement methodologies</td><td>19</td></tr><tr><td>3.6.1</td><td>Testing of new measurement instruments and procedures</td><td>19</td></tr><tr><td>3.6.2</td><td>Development of strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime</td><td>19</td></tr><tr><td>3.6.3</td><td>Development of new technological products and methods</td><td>19</td></tr><tr><td>3.6.4</td><td>Development of retrieval algorithms or tools for producing level 1 to 3 data, including the exploitation of instrument synergies</td><td>19</td></tr></table>
Contents

<table><tr><td>1</td><td>Purpose of the document</td><td>4</td></tr><tr><td>2</td><td>Description and role of the Centre for Aerosol Remote Sensing</td><td>4</td></tr><tr><td>2.1</td><td>Framework</td><td>4</td></tr><tr><td>2.2</td><td>Scientific relevance</td><td>4</td></tr><tr><td>2.3</td><td>Mission</td><td>5</td></tr><tr><td>3</td><td>Operation support provided to ACTRIS National Facilities</td><td>5</td></tr><tr><td>3.1</td><td>Measurement techniques covered by the Centre for Aerosol Remote Sensing, and related ACTRIS variables</td><td>6</td></tr><tr><td>3.1.1</td><td>Aerosol high-power lidar (AHL)</td><td>6</td></tr><tr><td>3.1.2</td><td>Automatic low-power lidar / ceilometer (ALC)</td><td>7</td></tr><tr><td>3.1.3</td><td>Automatic sun/sky/polarized/lunar photometer (ASP)</td><td>8</td></tr><tr><td>3.2</td><td>Estimation of the need</td><td>8</td></tr><tr><td>3.3</td><td>Timeline for implementation of the mandatory operation support</td><td>9</td></tr><tr><td>3.4</td><td>Operation support for quality assurance and quality control</td><td>11</td></tr><tr><td>3.4.1</td><td>Definition and establishment of standard operation procedures</td><td>11</td></tr><tr><td>3.4.2</td><td>Definition of measurement quality-assurance criteria and procedures</td><td>12</td></tr><tr><td>3.4.3</td><td>Development and provision of instrument-specific calibration</td><td>13</td></tr><tr><td>3.4.4</td><td>Development and provision of in-house check-up tools</td><td>15</td></tr><tr><td>3.4.5</td><td>Development of data evaluation procedures and plausibility test</td><td>15</td></tr><tr><td>3.4.6</td><td>Realization of observational site performance audits with reference samples or mobile systems</td><td>16</td></tr><tr><td>3.4.7</td><td>Organization of regular exercises to assess the performances of the NFs, including instrument performance workshops</td><td>17</td></tr><tr><td>3.4.8</td><td>Contribution to documentation and traceability of level 0 to level 3 data products</td><td>17</td></tr><tr><td>3.4.9</td><td>Contribution to CEN, ISO, or similar standardization activities</td><td>18</td></tr><tr><td>3.5</td><td>Operation support for knowledge transfer and training</td><td>18</td></tr><tr><td>3.5.1</td><td>Training of operators and scientists</td><td>18</td></tr><tr><td>3.5.2</td><td>Consultancy for setting-up new observational or exploratory platforms and new instruments at the NFs</td><td>18</td></tr><tr><td>3.6</td><td>Operation support for improvement of measurement methodologies</td><td>19</td></tr><tr><td>3.6.1</td><td>Testing of new measurement instruments and procedures</td><td>19</td></tr><tr><td>3.6.2</td><td>Development of strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime</td><td>19</td></tr><tr><td>3.6.3</td><td>Development of new technological products and methods</td><td>19</td></tr><tr><td>3.6.4</td><td>Development of retrieval algorithms or tools for producing level 1 to 3 data, including the exploitation of instrument synergies</td><td>19</td></tr></table>
<table><tr><td>4</td><td>Services provided to ACTRIS users</td><td>20</td></tr><tr><td>4.1</td><td>Estimation of the need</td><td>20</td></tr><tr><td>4.2</td><td>Provision of measurement quality assurance and quality control procedures and tools</td><td>21</td></tr><tr><td>4.3</td><td>Instrument-specific calibration</td><td>21</td></tr><tr><td>4.4</td><td>Knowledge transfer and operator training</td><td>21</td></tr><tr><td>4.5</td><td>Improvement of measurement and retrieval methodologies for aerosols, clouds, and reactive trace gases</td><td>22</td></tr><tr><td>5</td><td>Governance and management structure of the Centre for Aerosol Remote Sensing</td><td>22</td></tr><tr><td>6</td><td>Requirements for the Centre for Aerosol Remote Sensing</td><td>23</td></tr><tr><td>6.1</td><td>General requirements</td><td>23</td></tr><tr><td>6.2</td><td>Technical requirements</td><td>23</td></tr><tr><td>6.2.1</td><td>Facilities</td><td>23</td></tr><tr><td>6.2.1</td><td>Human resources</td><td>25</td></tr><tr><td>6.2.2</td><td>Other requirements</td><td>25</td></tr><tr><td>7</td><td>Basic criteria for the selection of the Centre for Aerosol Remote Sensing</td><td>26</td></tr><tr><td>8</td><td>Obligations of the Centre for Aerosol Remote Sensing</td><td>26</td></tr><tr><td>8.1</td><td>General obligations</td><td>26</td></tr><tr><td>8.2</td><td>Technical obligations</td><td>26</td></tr><tr><td>8.2.1</td><td>Technical obligations in relation with the ACTRIS National Facilities</td><td>26</td></tr><tr><td>8.2.2</td><td>Technical obligations in relation with the ACTRIS Data Centre</td><td>28</td></tr><tr><td>8.2.3</td><td>Technical obligations in relation with the Centre for Cloud Remote Sensing</td><td>31</td></tr><tr><td>8.2.4</td><td>Technical obligations in relation with the ACTRIS users</td><td>31</td></tr><tr><td>8.3</td><td>Evaluation of the activity of the Centre for Aerosol Remote Sensing</td><td>31</td></tr><tr><td colspan="2">List of acronyms</td><td>33</td></tr><tr><td colspan="2">Glossary</td><td>34</td></tr><tr><td colspan="2">Reference documents</td><td>36</td></tr><tr><td colspan="2">Annex: Provision of the operation support</td><td>39</td></tr><tr><td colspan="2">Scheduled support</td><td>39</td></tr><tr><td colspan="2">Operation support on request</td><td>41</td></tr></table>
<table><tr><td>4</td><td>Services provided to ACTRIS users</td><td>20</td></tr><tr><td>4.1</td><td>Estimation of the need</td><td>20</td></tr><tr><td>4.2</td><td>Provision of measurement quality assurance and quality control procedures and tools</td><td>21</td></tr><tr><td>4.3</td><td>Instrument-specific calibration</td><td>21</td></tr><tr><td>4.4</td><td>Knowledge transfer and operator training</td><td>21</td></tr><tr><td>4.5</td><td>Improvement of measurement and retrieval methodologies for aerosols, clouds, and reactive trace gases</td><td>22</td></tr><tr><td>5</td><td>Governance and management structure of the Centre for Aerosol Remote Sensing</td><td>22</td></tr><tr><td>6</td><td>Requirements for the Centre for Aerosol Remote Sensing</td><td>23</td></tr><tr><td>6.1</td><td>General requirements</td><td>23</td></tr><tr><td>6.2</td><td>Technical requirements</td><td>23</td></tr><tr><td>6.2.1</td><td>Facilities</td><td>23</td></tr><tr><td>6.2.1</td><td>Human resources</td><td>25</td></tr><tr><td>6.2.2</td><td>Other requirements</td><td>25</td></tr><tr><td>7</td><td>Basic criteria for the selection of the Centre for Aerosol Remote Sensing</td><td>26</td></tr><tr><td>8</td><td>Obligations of the Centre for Aerosol Remote Sensing</td><td>26</td></tr><tr><td>8.1</td><td>General obligations</td><td>26</td></tr><tr><td>8.2</td><td>Technical obligations</td><td>26</td></tr><tr><td>8.2.1</td><td>Technical obligations in relation with the ACTRIS National Facilities</td><td>26</td></tr><tr><td>8.2.2</td><td>Technical obligations in relation with the ACTRIS Data Centre</td><td>28</td></tr><tr><td>8.2.3</td><td>Technical obligations in relation with the Centre for Cloud Remote Sensing</td><td>31</td></tr><tr><td>8.2.4</td><td>Technical obligations in relation with the ACTRIS users</td><td>31</td></tr><tr><td>8.3</td><td>Evaluation of the activity of the Centre for Aerosol Remote Sensing</td><td>31</td></tr><tr><td colspan="2">List of acronyms</td><td>33</td></tr><tr><td colspan="2">Glossary</td><td>34</td></tr><tr><td colspan="2">Reference documents</td><td>36</td></tr><tr><td colspan="2">Annex: Provision of the operation support</td><td>39</td></tr><tr><td colspan="2">Scheduled support</td><td>39</td></tr><tr><td colspan="2">Operation support on request</td><td>41</td></tr></table>
# 1 Purpose of the document

This document describes the relevance, mission, requirements and obligations of the ACTRIS Centre for
Aerosol Remote Sensing.

# 2 Description and role of the Centre for Aerosol Remote Sensing

## 2.1 Framework

The Centre for Aerosol Remote Sensing (CARS) is one of the six ACTRIS Topical Centres organized around the main scientific themes of ACTRIS: aerosols, clouds, and reactive trace gases, each with a particular focus on either remote sensing or in situ measurement techniques.

The following documents are completing the current concept of the Centre for Aerosol Remote Sensing (CARS):

* The ACTRIS framework is described in the following documents:

* ACTRIS ESFRI proposal

* ACTRIS-PPP project

* ACTRIS Stakeholders Handbook 2017

* ACTRIS Science Case document

* The general rules and principles for the ACTRIS Central Facilities are described in the Baseline document for the Concepts of ACTRIS Central Facilities.

* The measurements techniques operated by the ACTRIS National Facilities for which the operation support should be offered, along with the specific requirements, are described in:

* Technical concepts and requirements for ACTRIS Observational Platforms

* Technical concepts and requirements for ACTRIS Exploratory Platforms

## 2.2 Scientific relevance

ACTRIS science case is described in ACTRIS Stakeholder handbook and ACTRIS Science case document.

In particular for the **Centre for Aerosol Remote Sensing (CARS)**, the focus is on measuring with high accuracy the optical properties of tropospheric and low stratospheric aerosols, and potentially derive their microphysical properties. CARS involves aerosols column and aerosol profiling measurement techniques as well as their synergetic uses at ground-based level.

**Aerosol profile observations** are covered in ACTRIS by automatic low-power lidars and high-power lidars. Due to the differences at the hardware level (e.g. laser power and sounding wavelengths), the data products which can be retrieved from these measurement techniques are essentially different.

* **Automatic low-power lidars and ceilometers (ALC)** are currently used to provide aerosol layering and attenuated backscatter at one wavelength (in IR), information which is used in combination with cloud radars and microwave radiometers to complete the cloud classification at the ACTRIS Cloud Remote Sensing National Facilities. In addition, these parameters could be used to study aerosol nucleation processes that are of great importance for visibility studies. The temporal coverage and low overlap of low power lidar instruments is a valuable add-on used to study the diurnal variation of aerosol layers and to trigger advanced measurements performed using high-
# 1 Purpose of the document

This document describes the relevance, mission, requirements and obligations of the ACTRIS Centre for
Aerosol Remote Sensing.

# 2 Description and role of the Centre for Aerosol Remote Sensing

## 2.1 Framework

The Centre for Aerosol Remote Sensing (CARS) is one of the six ACTRIS Topical Centres organized around the main scientific themes of ACTRIS: aerosols, clouds, and reactive trace gases, each with a particular focus on either remote sensing or in situ measurement techniques.

The following documents are completing the current concept of the Centre for Aerosol Remote Sensing (CARS):

* The ACTRIS framework is described in the following documents:

* ACTRIS ESFRI proposal

* ACTRIS-PPP project

* ACTRIS Stakeholders Handbook 2017

* ACTRIS Science Case document

* The general rules and principles for the ACTRIS Central Facilities are described in the Baseline document for the Concepts of ACTRIS Central Facilities.

* The measurements techniques operated by the ACTRIS National Facilities for which the operation support should be offered, along with the specific requirements, are described in:

* Technical concepts and requirements for ACTRIS Observational Platforms

* Technical concepts and requirements for ACTRIS Exploratory Platforms

## 2.2 Scientific relevance

ACTRIS science case is described in *ACTRIS Stakeholder handbook* and *ACTRIS Science case document*.

In particular for the **Centre for Aerosol Remote Sensing (CARS)**, the focus is on measuring with high accuracy the optical properties of tropospheric and low stratospheric aerosols, and potentially derive their microphysical properties. CARS involves aerosols column and aerosol profiling measurement techniques as well as their synergetic uses at ground-based level.

**Aerosol profile observations** are covered in ACTRIS by automatic low-power lidars and high-power lidars. Due to the differences at the hardware level (e.g. laser power and sounding wavelengths), the data products which can be retrieved from these measurement techniques are essentially different.

* **Automatic low-power lidars and ceilometers (ALC)** are currently used to provide aerosol layering and attenuated backscatter at one wavelength (in IR), information which is used in combination with cloud radars and microwave radiometers to complete the cloud classification at the ACTRIS Cloud Remote Sensing National Facilities. In addition, these parameters could be used to study aerosol nucleation processes that are of great importance for visibility studies. The temporal coverage and low overlap of low power lidar instruments is a valuable add-on used to study the diurnal variation of aerosol layers and to trigger advanced measurements performed using high-
power lidar instruments. Even single wavelength low-power lidars are able to detect high
resolution dynamics of aerosol layers.

*   **Aerosol high-power aerosol lidars (AHL)** are aerosol lidar which thanks to the higher power can provide besides the same quantities reported for the ALL, more quantitative information about the aerosol optical properties. In particular, AHL used to provide profile aerosol optical properties (aerosol backscatter coefficient, aerosol extinction coefficient and aerosol linear depolarization ratio) at one or more wavelengths, allowing subsequent calculation of several spectral parameters (Angstrom exponents, lidar ratios) of the lofted aerosol layers, and therefore aerosol typing.

It is estimated that, with the progress of the technology (especially lasers and detectors), these two
measurement techniques will evolve in the future to a low-cost, low-maintenance, automatic
multiwavelength aerosol profiler. For the moment, however, the procedures for QA/QC, as well as the
algorithms for data processing are instrument-specific and should be treated separately by CARS.

**Aerosol column observations** are covered in ACTRIS by **automatic sun/sky/lunar photometers (ASP)**. The state-of-the-art photometric measurement techniques and associated retrieval techniques provide aerosol properties both directly (e.g. daytime and night time spectral extinction AOD and daytime downward sky angular, spectral and polarized radiance) and indirectly (size distribution, refractive indexes, single scattering albedo, spherical fraction, scattering properties (Dubovik et al., 2000, 2014).

**Synergies between aerosol profile and column observations** are being greatly developed within ACTRIS-1/2 to provide higher-level aerosol variables such as daytime extinction, backscatter, absorption and mass concentration (total, fine, coarse) and columnar aerosols optical and microphysical properties.

## 2.3 Mission

The mission of the Centre for Aerosol Remote Sensing (CARS) is to offer operation support to ACTRIS National Facilities operating aerosol remote sensing instrumentation: high-power aerosol lidars, automatic low-power aerosol lidars, and automatic sun/sky/polarized/lunar photometer.

Additionally, the Centre for Aerosol Remote Sensing should offer specialized services for the above instruments and related ACTRIS variables, to ACTRIS users of various types: academia, business, industry, and public services.

## 3 Operation support provided to ACTRIS National Facilities

The main duty of the Centre for Aerosol Remote Sensing is to permit the operability of the NFs operating high-power aerosol lidars, automatic low-power aerosol lidars, and sun/sky/lunar photometers, and the compliance of their methodologies and products to the requirements of full traceability, high quality and full documentation.

The operation support provided by the Centre for Aerosol Remote Sensing consists of:

a) Procedures and tools for quality assurance and quality control of ACTRIS measurements and data

b) Transfer of knowledge and training to ACTRIS operators

c) Improvement of measurement methodologies
power lidar instruments. Even single wavelength low-power lidars are able to detect high
resolution dynamics of aerosol layers.

*   **Aerosol high-power aerosol lidars (AHL)** are aerosol lidar which thanks to the higher power can provide besides the same quantities reported for the ALL, more quantitative information about the aerosol optical properties. In particular, AHL used to provide profile aerosol optical properties (aerosol backscatter coefficient, aerosol extinction coefficient and aerosol linear depolarization ratio) at one or more wavelengths, allowing subsequent calculation of several spectral parameters (Angstrom exponents, lidar ratios) of the lofted aerosol layers, and therefore aerosol typing.

It is estimated that, with the progress of the technology (especially lasers and detectors), these two
measurement techniques will evolve in the future to a low-cost, low-maintenance, automatic
multiwavelength aerosol profiler. For the moment, however, the procedures for QA/QC, as well as the
algorithms for data processing are instrument-specific and should be treated separately by CARS.

**Aerosol column observations** are covered in ACTRIS by **automatic sun/sky/lunar photometers (ASP)**. The state-of-the-art photometric measurement techniques and associated retrieval techniques provide aerosol properties both directly (e.g. daytime and night time spectral extinction AOD and daytime downward sky angular, spectral and polarized radiance) and indirectly (size distribution, refractive indexes, single scattering albedo, spherical fraction, scattering properties (Dubovik et al., 2000, 2014).

**Synergies between aerosol profile and column observations** are being greatly developed within ACTRIS-1/2 to provide higher-level aerosol variables such as daytime extinction, backscatter, absorption and mass concentration (total, fine, coarse) and columnar aerosols optical and microphysical properties.

**2.3 Mission**

The mission of the Centre for Aerosol Remote Sensing (CARS) is to offer operation support to ACTRIS National Facilities operating aerosol remote sensing instrumentation: high-power aerosol lidars, automatic low-power aerosol lidars, and automatic sun/sky/polarized/lunar photometer.

Additionally, the Centre for Aerosol Remote Sensing should offer specialized services for the above instruments and related ACTRIS variables, to ACTRIS users of various types: academia, business, industry, and public services.

**3 Operation support provided to ACTRIS National Facilities**

The main duty of the Centre for Aerosol Remote Sensing is to permit the operability of the NFs operating high-power aerosol lidars, automatic low-power aerosol lidars, and sun/sky/lunar photometers, and the compliance of their methodologies and products to the requirements of full traceability, high quality and full documentation.

The operation support provided by the Centre for Aerosol Remote Sensing consists of:

a) Procedures and tools for quality assurance and quality control of ACTRIS measurements and data

b) Transfer of knowledge and training to ACTRIS operators

c) Improvement of measurement methodologies
The operation support should be offered to the National Facilities for the measurement techniques described in this concept document, also listed in the *Technical concepts and requirements for ACTRIS Observational Platforms*, and in the *Technical concepts and requirements for ACTRIS Exploratory Platforms*.

The Centre for Aerosol Remote Sensing is obliged to put in place and offer to NFs the specific operation support marked with * in this document. Other operation support described in this document is not mandatory for CARS, but recommended.

The operation support can be scheduled or on request:

* Participation at the scheduled activities is mandatory for the NFs. Measurements performed at NF not following the mandatory actions are not considered as ACTRIS-conform and do not yield ACTRIS data.

* NFs may request operation support which is not scheduled, depending on the identified need.

Specific operation support offered as scheduled or offered on request is detailed in Annex: Provision of the operation support. This annex will be updated each time is necessary (e.g. development of new testing or calibration methods and tools).

The Centre for Aerosol Remote Sensing should operate at the state-of-the-art, fostering the implementation of validated new techniques in ACTRIS. To sustain a high level of performance and to stimulate the advancement of new techniques and methodologies, the Centre for Aerosol Remote Sensing should also contribute to expert collaboration networks.

## 3.1 Measurement techniques covered by the Centre for Aerosol Remote Sensing, and related ACTRIS variables

Measurement techniques covered by the Centre for Aerosol Remote Sensing are described in detail in: *Technical concepts and requirements for ACTRIS Observational Platforms* and *Technical concepts and requirements for ACTRIS Exploratory Platforms*.

### 3.1.1 Aerosol high-power lidar (AHL)

At present, the minimum lidar requirement for effective aerosol profiling includes one elastic channel, one channel at the corresponding inelastic wavelength for aerosol extinction measurement and one channel to measure the aerosol depolarisation (1+1+1 configuration). The particular wavelength of these 3 channels can be in the visible or UV.

With this configuration, the following ACTRIS variables can be retrieved:

* Extensive aerosol optical properties (profiles): linear volume depolarization ratio, backscatter and extinction coefficients (single wavelength)

* Intensive aerosol layer optical properties (partial profiles): particle linear depolarization ratio, lidar ratio (single wavelength)

* Aerosol layer geometrical (height and thickness) and optical properties (extensive and intensive properties, mean-layer values, single wavelength)

A more **advanced setup** comprises three channels at elastic wavelengths, two channels at the corresponding inelastic wavelengths for aerosol extinction measurement, and two channels to measure
The operation support should be offered to the National Facilities for the measurement techniques described in this concept document, also listed in the *Technical concepts and requirements for ACTRIS Observational Platforms*, and in the *Technical concepts and requirements for ACTRIS Exploratory Platforms*.

The Centre for Aerosol Remote Sensing is obliged to put in place and offer to NFs the specific operation support marked with * in this document. Other operation support described in this document is not mandatory for CARS, but recommended.

The operation support can be scheduled or on request:

* Participation at the scheduled activities is mandatory for the NFs. Measurements performed at NF not following the mandatory actions are not considered as ACTRIS-conform and do not yield ACTRIS data.

* NFs may request operation support which is not scheduled, depending on the identified need.

Specific operation support offered as scheduled or offered on request is detailed in Annex: Provision of the operation support. This annex will be updated each time is necessary (e.g. development of new testing or calibration methods and tools).

The Centre for Aerosol Remote Sensing should operate at the state-of-the-art, fostering the implementation of validated new techniques in ACTRIS. To sustain a high level of performance and to stimulate the advancement of new techniques and methodologies, the Centre for Aerosol Remote Sensing should also contribute to expert collaboration networks.

**3.1 Measurement techniques covered by the Centre for Aerosol Remote Sensing, and related ACTRIS variables**

Measurement techniques covered by the Centre for Aerosol Remote Sensing are described in detail in: *Technical concepts and requirements for ACTRIS Observational Platforms* and *Technical concepts and requirements for ACTRIS Exploratory Platforms*.

**3.1.1 Aerosol high-power lidar (AHL)**

At present, the minimum lidar requirement for effective aerosol profiling includes one elastic channel, one channel at the corresponding inelastic wavelength for aerosol extinction measurement and one channel to measure the aerosol depolarisation (1+1+1 configuration). The particular wavelength of these 3 channels can be in the visible or UV.

With this configuration, the following ACTRIS variables can be retrieved:

* Extensive aerosol optical properties (profiles): linear volume depolarization ratio, backscatter and extinction coefficients (single wavelength)

* Intensive aerosol layer optical properties (partial profiles): particle linear depolarization ratio, lidar ratio (single wavelength)

* Aerosol layer geometrical (height and thickness) and optical properties (extensive and intensive properties, mean-layer values, single wavelength)

A more **advanced setup** comprises three channels at elastic wavelengths, two channels at the corresponding inelastic wavelengths for aerosol extinction measurement, and two channels to measure
the depolarisation at one wavelength (3+2+1 configuration). Such a multi-wavelength polarisation lidar
system for night time and daytime measurements comprises a complex wavelength separation unit.

With this configuration, the following ACTRIS variables can be retrieved:

* Extensive aerosol optical properties (profiles): linear volume depolarization ratio, backscatter and extinction coefficients (multiple wavelengths)

* Intensive aerosol layer optical properties (partial profiles): particle linear depolarization ratio, lidar ratio, backscatter and extinction-related Angstrom exponent (multiple wavelengths)

* Aerosol layer geometrical (height and thickness) and optical properties (extensive and intensive properties, mean-layer values, multiple wavelengths)

* Aerosol type, aerosol microphysical properties (in particular cases and/or by synergy with photometer)

**In future** we expect 3+2+3 and even 3+3+3 setups, which will increase the complexity. Furthermore, it is highly desirable and expected that the detection range will be extended down to 200 m above ground level to include this part of the mixing layer which often contains most of the aerosol. This adds another order of magnitude to the dynamic range of the signals and much higher demands on the mechano-optical design of the lidar with more sources for larger systematic errors.

The collection, harmonisation, and development of standards and calibration techniques started in the framework of EARLINET and ACTRIS, e.g. the calculation of the Rayleigh scattering coefficients, the Rayleigh-fit, the trigger delay determination, the telecover tests, the dark signal subtraction, the specialised lidar pulse generator, and the polarisation calibration (Freudenthaler et al., 2017), mainly in the aim to avoid signal disturbance. These should be considered as a starting base for the QA/QC program of the ACTRIS high-power aerosol lidars.

**This program should be further developed** in order to: a) make these tests easier to be used on a regular basis by the ACTRIS NFs and users; b) establish new tools to quantify the signal disturbances; c) develop an error analysis of the final products which includes and combines systematic and random errors. Also, CARS should **consider future lidar developments** as, e.g., the High-Spectral-Resolution-Lidar (HSRL) technique and the circular depolarisation ratio.

3.1.2 Automatic low-power lidar / ceilometer (ALC)

Automatic low-power aerosol lidars and ceilometers are **elastic backscatter lidars, providing aerosol profiles (attenuated backscatter) at one wavelength (in IR)**. These are mainly commercial systems, usually very robust, eye-safe, operated continuously and unattended, often at remote sites. Most of them are operated by national meteorological services and environmental agencies. Several low-power lidars are operated at ACTRIS NFs, mainly in combination with cloud radars and microwave radiometers to complete the cloud classification. Also, they are used as ancillary instruments to fill gaps in the operation time of high-power lidars or to provide basic knowledge about the vertical structure of the atmosphere at NFs for in-situ measurements of aerosols and trace gases.

The hardware issues are mainly the same as in case of high-power lidars, such as the incomplete overlap
between laser and telescope, electronic background signals, saturation effects. Additionally, some of the
low-power lidars operate at wavelengths which are influenced by water-vapour absorption.
the depolarisation at one wavelength (3+2+1 configuration). Such a multi-wavelength polarisation lidar
system for night time and daytime measurements comprises a complex wavelength separation unit.

With this configuration, the following ACTRIS variables can be retrieved:

* Extensive aerosol optical properties (profiles): linear volume depolarization ratio, backscatter and extinction coefficients (multiple wavelengths)

* Intensive aerosol layer optical properties (partial profiles): particle linear depolarization ratio, lidar ratio, backscatter and extinction-related Angstrom exponent (multiple wavelengths)

* Aerosol layer geometrical (height and thickness) and optical properties (extensive and intensive properties, mean-layer values, multiple wavelengths)

* Aerosol type, aerosol microphysical properties (in particular cases and/or by synergy with photometer)

**In future** we expect 3+2+3 and even 3+3+3 setups, which will increase the complexity. Furthermore, it is highly desirable and expected that the detection range will be extended down to 200 m above ground level to include this part of the mixing layer which often contains most of the aerosol. This adds another order of magnitude to the dynamic range of the signals and much higher demands on the mechano-optical design of the lidar with more sources for larger systematic errors.

The collection, harmonisation, and development of standards and calibration techniques started in the framework of EARLINET and ACTRIS, e.g. the calculation of the Rayleigh scattering coefficients, the Rayleigh-fit, the trigger delay determination, the telecover tests, the dark signal subtraction, the specialised lidar pulse generator, and the polarisation calibration (Freudenthaler et al., 2017), mainly in the aim to avoid signal disturbance. These should be considered as a starting base for the QA/QC program of the ACTRIS high-power aerosol lidars.

**This program should be further developed** in order to: a) make these tests easier to be used on a regular basis by the ACTRIS NFs and users; b) establish new tools to quantify the signal disturbances; c) develop an error analysis of the final products which includes and combines systematic and random errors. Also, CARS should **consider future lidar developments** as, e.g., the High-Spectral-Resolution-Lidar (HSRL) technique and the circular depolarisation ratio.

3.1.2 Automatic low-power lidar / ceilometer (ALC)

Automatic low-power aerosol lidars and ceilometers are **elastic backscatter lidars, providing aerosol profiles (attenuated backscatter) at one wavelength (in IR)**. These are mainly commercial systems, usually very robust, eye-safe, operated continuously and unattended, often at remote sites. Most of them are operated by national meteorological services and environmental agencies. Several low-power lidars are operated at ACTRIS NFs, mainly in combination with cloud radars and microwave radiometers to complete the cloud classification. Also, they are used as ancillary instruments to fill gaps in the operation time of high-power lidars or to provide basic knowledge about the vertical structure of the atmosphere at NFs for in-situ measurements of aerosols and trace gases.

The hardware issues are mainly the same as in case of high-power lidars, such as the incomplete overlap
between laser and telescope, electronic background signals, saturation effects. Additionally, some of the
low-power lidars operate at wavelengths which are influenced by water-vapour absorption.
The calibration and quality assurance procedures which were developed for high-power lidars in ACTRIS and ACTRIS-2 cannot be directly applied to the low-power instruments. Calibration and quality assurance methods for low-power lidars have been recently developed by E-PROFILE community. **These should be considered as a starting base for the QA/QC program of the ACTRIS low-power aerosol lidars.**

In addition, a strong link with QA of AHL is required because both techniques are used to provide attenuated backscatter (intermediary product) for cloud processing.

### 3.1.3 Automatic sun/sky/polarized/lunar photometer (ASP)

The required instrument is a sun/sky/lunar photometer making two basic measurements, direct sun/moon and sky measurements, possibly including linear polarization, both within several programmed sequences or protocols. The direct measurements are currently made in nine spectral bands (340, 380, 440, 500, 670, 870, 940, 1020 and 1640) and will be likely performing with a higher spectral resolution in the future.

ACTRIS-13 projects provides since 2011 a relevant support for (i) QC/QA activity, (ii) the consolidation of a dedicated European sun/sky/moon calibration centre based on French and Spanish complementary TC units, (iii) the integration with aerosol profiles and in situ communities through several ACTRIS Joint Research Activities, (iv) the development, implementation and operation, in the ACTRIS Data Centre, of an advanced processing system producing and delivering added-value information based on GRASP/GARRLIC high performances software (Lopatin et al., 2013; Dubovik et al., 2014). This program should be considered as a starting base for the Centre for Aerosol Remote Sensing in close interaction with Data Centre.

## 3.2 Estimation of the need

<table><thead><tr><th rowspan="3">Measurement technique</th><th colspan="3">Number of instruments/groups<sup>i</sup> to which CARS is providing operational support</th></tr><tr><th rowspan="2">Now (preparatory phase, by 2020)</th><th colspan="2">by 2025</th></tr><tr><th>Min.</th><th>Max.</th></tr></thead><tbody><tr><td>Aerosol high-power lidar (AHL)</td><td>25</td><td>30</td><td>70</td></tr><tr><td>Automatic low-power lidar / ceilometer (ALC)</td><td>15</td><td>20</td><td>25</td></tr><tr><td>Automatic sun/sky/polarized/lunar photometer (ASP)</td><td>25</td><td>30</td><td>70</td></tr></tbody></table>

These numbers refer strictly to the instruments operated by the potential ACTRIS NFs, considering the current ACTRIS partnership and the planned facilities, as described in the ACTRIS Stakeholders Handbook 2017.

<footnote>i A group may be composed of several operators; it is assumed that one person will be trained for one instrument.</footnote>
The calibration and quality assurance procedures which were developed for high-power lidars in ACTRIS and ACTRIS-2 cannot be directly applied to the low-power instruments. Calibration and quality assurance methods for low-power lidars have been recently developed by E-PROFILE community. **These should be considered as a starting base for the QA/QC program of the ACTRIS low-power aerosol lidars.**

In addition, a strong link with QA of AHL is required because both techniques are used to provide attenuated backscatter (intermediary product) for cloud processing.

### 3.1.3 Automatic sun/sky/polarized/lunar photometer (ASP)

The required instrument is a sun/sky/lunar photometer making two basic measurements, direct sun/moon and sky measurements, possibly including linear polarization, both within several programmed sequences or protocols. The direct measurements are currently made in nine spectral bands (340, 380, 440, 500, 670, 870, 940, 1020 and 1640) and will be likely performing with a higher spectral resolution in the future.

ACTRIS-13 projects provides since 2011 a relevant support for (i) QC/QA activity, (ii) the consolidation of a dedicated European sun/sky/moon calibration centre based on French and Spanish complementary TC units, (iii) the integration with aerosol profiles and in situ communities through several ACTRIS Joint Research Activities, (iv) the development, implementation and operation, in the ACTRIS Data Centre, of an advanced processing system producing and delivering added-value information based on GRASP/GARRLIC high performances software (Lopatin et al., 2013; Dubovik et al., 2014). This program should be considered as a starting base for the Centre for Aerosol Remote Sensing in close interaction with Data Centre.

## 3.2 Estimation of the need

<table><thead><tr><th rowspan="3">Measurement technique</th><th colspan="3">Number of instruments/groups<sup>i</sup> to which CARS is providing operational support</th></tr><tr><th rowspan="2">Now (preparatory phase, by 2020)</th><th colspan="2">by 2025</th></tr><tr><th>Min.</th><th>Max.</th></tr></thead><tbody><tr><td>Aerosol high-power lidar (AHL)</td><td>25</td><td>30</td><td>70</td></tr><tr><td>Automatic low-power lidar / ceilometer (ALC)</td><td>15</td><td>20</td><td>25</td></tr><tr><td>Automatic sun/sky/polarized/lunar photometer (ASP)</td><td>25</td><td>30</td><td>70</td></tr></tbody></table>

These numbers refer strictly to the instruments operated by the potential ACTRIS NFs, considering the current ACTRIS partnership and the planned facilities, as described in the ACTRIS Stakeholders Handbook 2017.

<footnote>i A group may be composed of several operators; it is assumed that one person will be trained for one instrument.</footnote>
## 3.3 Timeline for implementation of the mandatory operation support

Considering the ACTRIS roadmap, CARS should consider the following implementation plan for the mandatory operation support (including general tasks, scheduled and on request operation support, see Annex: Provision of the operation support):

<table><thead><tr><th rowspan="2">Operation support</th><th rowspan="2">Type</th><th>Preparation phase</th><th>Implementation phase</th><th>Operation phase</th></tr><tr><th>&lt; 2020</th><th>2020 - 2025</th><th>&gt; 2025</th></tr></thead><tbody><tr><td>SOPs</td><td>General task</td><td>Basic SOPs for operation of the instruments (minimum requirements)</td><td>New SOPs for operation of advanced instruments (optimum setup)</td><td>Updates and new SOPs</td></tr><tr><td rowspan="2">QA criteria & procedures</td><td>General task</td><td>Basic procedures for controlling the quality of the measurements (minimum requirements)</td><td>New procedures for controlling the quality of the advanced measurements (optimum setup)</td><td>Updates and new procedures</td></tr><tr><td>General task</td><td>Quality-assurance criteria for basic measurements (minimum requirements)</td><td>New quality-assurance criteria for advanced measurements (minimum requirements) (optimum setup)</td><td>Updates and new quality-assurance criteria</td></tr><tr><td rowspan="3">Instrument-specific calibration</td><td>On request</td><td>Direct comparison with fixed, state-of-the-art, reference instruments</td><td>Continue as support on request</td><td>Continue as support on request</td></tr><tr><td>On request</td><td>Tests at CARS' laboratories or using remote methods (partially)</td><td>Tests at CARS' laboratories or using remote methods (new)</td><td>Continue as support on request</td></tr><tr><td>On request</td><td></td><td>On-site expert inspection of the instruments</td><td>Continue as support on request</td></tr><tr><td rowspan="2">In-house check-up tools<br>not applicable<br>for ASP</td><td>General task</td><td></td><td>Tools for rapid assessment of critical behaviour of the instrument</td><td>Updates</td></tr><tr><td>General task</td><td></td><td>Software for automatic submission of level 0 data</td><td>Updates</td></tr><tr><td>Data evaluation<br>procedures and<br>plausibility test<br>not applicable<br>for ASP</td><td>General task</td><td></td><td>Software for rapid assessment of the measurements' quality</td><td>Updates</td></tr><tr><td>Site performance audits<br>with reference samples<br>or mobile systems</td><td>Scheduled</td><td>Direct comparison with mobile reference system</td><td>Continue as scheduled activity</td><td>Continue as scheduled activity</td></tr></tbody></table>

ACTRIS PPP (www.actris.eu) is supported by the European Commission under the Horizon 2020 - Research and Innovation Framework Programme, H2020-INFRADEV-2016-2017, Grant Agreement number: 739530
## 3.3 Timeline for implementation of the mandatory operation support

Considering the ACTRIS roadmap, CARS should consider the following implementation plan for the mandatory operation support (including general tasks, scheduled and on request operation support, see Annex: Provision of the operation support):

<table><thead><tr><th rowspan="2">Operation support</th><th rowspan="2">Type</th><th>Preparation phase</th><th>Implementation phase</th><th>Operation phase</th></tr><tr><th>&lt; 2020</th><th>2020 - 2025</th><th>&gt; 2025</th></tr></thead><tbody><tr><td>SOPs</td><td>General task</td><td>Basic SOPs for operation of the instruments (minimum requirements)</td><td>New SOPs for operation of advanced instruments (optimum setup)</td><td>Updates and new SOPs</td></tr><tr><td rowspan="2">QA criteria & procedures</td><td>General task</td><td>Basic procedures for controlling the quality of the measurements (minimum requirements)</td><td>New procedures for controlling the quality of the advanced measurements (optimum setup)</td><td>Updates and new procedures</td></tr><tr><td>General task</td><td>Quality-assurance criteria for basic measurements (minimum requirements)</td><td>New quality-assurance criteria for advanced measurements (minimum requirements) (optimum setup)</td><td>Updates and new quality-assurance criteria</td></tr><tr><td rowspan="3">Instrument-specific calibration</td><td>On request</td><td>Direct comparison with fixed, state-of-the-art, reference instruments</td><td>Continue as support on request</td><td>Continue as support on request</td></tr><tr><td>On request</td><td>Tests at CARS' laboratories or using remote methods (partially)</td><td>Tests at CARS' laboratories or using remote methods (new)</td><td>Continue as support on request</td></tr><tr><td>On request</td><td></td><td>On-site expert inspection of the instruments</td><td>Continue as support on request</td></tr><tr><td rowspan="2">In-house check-up tools<br>not applicable<br>for ASP</td><td>General task</td><td></td><td>Tools for rapid assessment of critical behaviour of the instrument</td><td>Updates</td></tr><tr><td>General task</td><td></td><td>Software for automatic submission of level 0 data</td><td>Updates</td></tr><tr><td>Data evaluation<br>procedures and<br>plausibility test<br>not applicable<br>for ASP</td><td>General task</td><td></td><td>Software for rapid assessment of the measurements' quality</td><td>Updates</td></tr><tr><td>Site performance audits<br>with reference samples<br>or mobile systems</td><td>Scheduled</td><td>Direct comparison with mobile reference system</td><td>Continue as scheduled activity</td><td>Continue as scheduled activity</td></tr></tbody></table>

ACTRIS PPP (www.actris.eu) is supported by the European Commission under the Horizon 2020 - Research and Innovation Framework Programme, H2020-INFRADEV-2016-2017, Grant Agreement number: 739530
Section 4 - Concept of Centre for Aerosol Remote Sensing

<table><thead><tr><th rowspan="2">Operation support</th><th rowspan="2">Type</th><th>Preparation phase</th><th>Implementation phase</th><th>Operation phase</th></tr><tr><th>&lt; 2020</th><th>2020 - 2025</th><th>&gt; 2025</th></tr></thead><tbody><tr><td>not applicable for ALC and ASP</td><td></td><td></td><td></td><td></td></tr><tr><td>Instrument performance workshops<br>not applicable for ASP</td><td>Scheduled</td><td>Annual assessment of the site performance through expert analysis of specific QA test results</td><td>Continue as scheduled activity</td><td>Continue as scheduled activity</td></tr><tr><td>Documentation and traceability</td><td>Scheduled</td><td></td><td>Codification of the results of the QA tests</td><td>Continue as scheduled activity</td></tr><tr><td rowspan="4">Training</td><td>Scheduled</td><td></td><td>Regular training sessions (at least twice per year) on pre-defined subjects</td><td>Continue as scheduled activity</td></tr><tr><td>On request</td><td>Training during parallel activities (direct comparisons, audits, calibration)</td><td>Continue as support on request</td><td>Continue as support on request</td></tr><tr><td>Scheduled</td><td>Documentation available on the CARS website: instrument setup, QC, QA protocols, operation and optimization of the instruments and data management</td><td>Continue as needed</td><td>Continue as needed</td></tr><tr><td>Scheduled</td><td></td><td>Forums, webinars</td><td>Continue as needed</td></tr><tr><td rowspan="2">Consultancy</td><td>On request</td><td>Upgrading of the instruments, establishment of new observing stations, development of new exploratory platforms</td><td>Continue as support on request</td><td>Continue as support on request</td></tr><tr><td>On request</td><td></td><td>Specific observation protocols</td><td>Continue as support on request</td></tr><tr><td>Testing of new and procedures</td><td>On request</td><td></td><td>Testing of prototypes</td><td>Continue as support on request</td></tr></tbody></table>

ACTRIS PPP (www.actris.eu) is supported by the European Commission under the Horizon 2020 - Research and Innovation Framework Programme, H2020-INFRADEV-2016-2017, Grant Agreement number: 739530
Section 4 - Concept of Centre for Aerosol Remote Sensing

<table><thead><tr><th rowspan="2">Operation support</th><th rowspan="2">Type</th><th>Preparation phase</th><th>Implementation phase</th><th>Operation phase</th></tr><tr><th>&lt; 2020</th><th>2020 - 2025</th><th>&gt; 2025</th></tr></thead><tbody><tr><td>not applicable for ALC and ASP</td><td></td><td></td><td></td><td></td></tr><tr><td>Instrument performance workshops<br>not applicable for ASP</td><td>Scheduled</td><td>Annual assessment of the site performance through expert analysis of specific QA test results</td><td>Continue as scheduled activity</td><td>Continue as scheduled activity</td></tr><tr><td>Documentation and traceability</td><td>Scheduled</td><td></td><td>Codification of the results of the QA tests</td><td>Continue as scheduled activity</td></tr><tr><td rowspan="4">Training</td><td>Scheduled</td><td></td><td>Regular training sessions (at least twice per year) on pre-defined subjects</td><td>Continue as scheduled activity</td></tr><tr><td>On request</td><td>Training during parallel activities (direct comparisons, audits, calibration)</td><td>Continue as support on request</td><td>Continue as support on request</td></tr><tr><td>Scheduled</td><td>Documentation available on the CARS website: instrument setup, QC, QA protocols, operation and optimization of the instruments and data management</td><td>Continue as needed</td><td>Continue as needed</td></tr><tr><td>Scheduled</td><td></td><td>Forums, webinars</td><td>Continue as needed</td></tr><tr><td rowspan="2">Consultancy</td><td>On request</td><td>Upgrading of the instruments, establishment of new observing stations, development of new exploratory platforms</td><td>Continue as support on request</td><td>Continue as support on request</td></tr><tr><td>On request</td><td></td><td>Specific observation protocols</td><td>Continue as support on request</td></tr><tr><td>Testing of new and procedures</td><td>On request</td><td></td><td>Testing of prototypes</td><td>Continue as support on request</td></tr></tbody></table>

ACTRIS PPP (www.actris.eu) is supported by the European Commission under the Horizon 2020 - Research and Innovation Framework Programme, H2020-INFRADEV-2016-2017, Grant Agreement number: 739530
## 3.4 Operation support for quality assurance and quality control

### 3.4.1 Definition and establishment of standard operation procedures

The Centre for Aerosol Remote Sensing should develop, document, and distribute the SOPs to the corresponding ACTRIS NFs. Also, CARS should organize specific training sessions to help in the implementation of the SOPs. The actual implementation of the SOPs falls in the responsibility of the NFs.

All procedures should be developed and updated based on internal requirements and external user feedback, and should be applicable both to NFs and ACTRIS users.

#### 3.4.1.1 Aerosol high-power lidar (AHL)

The standard operation procedures (SOP) should be designed to ensure the correct operation of high-power aerosol lidars operating at the ACTRIS National Facilities, as well as the defined schedule for the observation of aerosol optical properties in the Planetary Boundary Layer up to the lower stratosphere. The SOPs should cover both instrumental and data correction aspects since the two are interlinked, as follows:

* **Measurement set-up:** ordinary and extraordinary schedule, time resolution, spatial resolution

* **Maintenance:** recommended schedule for window cleaning, replacement of optical components, laser maintenance and replacements, dark measurement retrieval, overlap measurements, alignment check-ups.

* **General instrument operation procedures:** signal intensity and distortions, dark correction, daytime operation, lidar alignment

* **Typical procedures for specific lidar channels and product accuracy:** calibration of the depolarization channels, amplification and signal attenuation for the analogue channels, discrimination level for photon counting channels, correction of range dependency, signal distortions for the analogue channels, alignment of the output beam, assessment of lidar mechanical stability.

The SOPs should be based on the previous developments and lessons learnt during EARLINET, EARLINET-ASOS and ACTRIS technical projects (http://www.earlinet.org). The SOPs should foster:

* The observation of aerosol layers throughout the troposphere up to the lower stratosphere, weather permitting (in the absence of precipitation, fog and low clouds), with a resolution of at least 60 s in time and 100 m in height

* The optimal setting of the instruments to run the Single Calculus Chain (signal attenuation, signal linearity, SNR, minimum timeslot)

#### 3.4.1.2 Automatic low-power lidar / ceilometer (ALC)

SOPs for automatic low-power aerosol lidars should provide information for the optimum operation and data analysis of these instruments, operating at NFs and/or ACTRIS users. They should cover the following aspects:

* **Measurement set-up:** optimum hardware setup (e.g. tilt angle), optimum firmware version and settings, time resolution, spatial resolution, frequency of data delivery, data submission protocols, generation of data in common format

* **Maintenance:** recommended schedule for window cleaning, laser replacements, dark measurements, overlap measurements.
## 3.4 Operation support for quality assurance and quality control

### 3.4.1 Definition and establishment of standard operation procedures

The Centre for Aerosol Remote Sensing should develop, document, and distribute the SOPs to the corresponding ACTRIS NFs. Also, CARS should organize specific training sessions to help in the implementation of the SOPs. The actual implementation of the SOPs falls in the responsibility of the NFs.

All procedures should be developed and updated based on internal requirements and external user feedback, and should be applicable both to NFs and ACTRIS users.

#### 3.4.1.1 Aerosol high-power lidar (AHL)

The standard operation procedures (SOP) should be designed to ensure the correct operation of high-power aerosol lidars operating at the ACTRIS National Facilities, as well as the defined schedule for the observation of aerosol optical properties in the Planetary Boundary Layer up to the lower stratosphere. The SOPs should cover both instrumental and data correction aspects since the two are interlinked, as follows:

* **Measurement set-up:** ordinary and extraordinary schedule, time resolution, spatial resolution

* **Maintenance:** recommended schedule for window cleaning, replacement of optical components, laser maintenance and replacements, dark measurement retrieval, overlap measurements, alignment check-ups.

* **General instrument operation procedures:** signal intensity and distortions, dark correction, daytime operation, lidar alignment

* **Typical procedures for specific lidar channels and product accuracy:** calibration of the depolarization channels, amplification and signal attenuation for the analogue channels, discrimination level for photon counting channels, correction of range dependency, signal distortions for the analogue channels, alignment of the output beam, assessment of lidar mechanical stability.

The SOPs should be based on the previous developments and lessons learnt during EARLINET, EARLINET-ASOS and ACTRIS technical projects (http://www.earlinet.org). The SOPs should foster:

* The observation of aerosol layers throughout the troposphere up to the lower stratosphere, weather permitting (in the absence of precipitation, fog and low clouds), with a resolution of at least 60 s in time and 100 m in height

* The optimal setting of the instruments to run the Single Calculus Chain (signal attenuation, signal linearity, SNR, minimum timeslot)

#### 3.4.1.2 Automatic low-power lidar / ceilometer (ALC)

SOPs for automatic low-power aerosol lidars should provide information for the optimum operation and data analysis of these instruments, operating at NFs and/or ACTRIS users. They should cover the following aspects:

* **Measurement set-up:** optimum hardware setup (e.g. tilt angle), optimum firmware version and settings, time resolution, spatial resolution, frequency of data delivery, data submission protocols, generation of data in common format

* **Maintenance:** recommended schedule for window cleaning, laser replacements, dark measurements, overlap measurements.
* **Retrieval and application of correction data:** measurements or statistical retrieval of dark measurements and corresponding correction, measurements or statistical retrieval of overlap correction function and its application, correction of water vapour absorption.

The SOPs should be based on:

* Previous developments and lessons learnt for high-power lidars during previous EARLINET, EARLINET-ASOS, ACTRIS projects, TOPROF and E-profile initiatives

* Statistical analysis of measurements with automatic low-power aerosol lidars in large operational networks

* Intercomparison campaigns (e.g. CeiLinEx2015, Interact) and long-term parallel measurements with a high-power lidar at a testbed site.

The goal of the SOPs is to enable NFs and non-expert operators of ALC networks to provide continuous observations of aerosol profiles throughout the troposphere with best achievable accuracy and known uncertainties.

### 3.4.1.3 Automatic sun/sky/polarized/lunar photometer (ASP)

The SOPs aim at ensuring nominal use of photometers, and should include:

* Full characterization of instrument (for new instrument)

* Remote monitoring of its status

* Quality Check (QC) during operation in the field

* Quality Assurance (QA).

SOPs should strictly be applied to monitor field and reference instruments QC and for calibration. The SOPs covered by CARS are:

* Level 0 data evaluation to detect failures

* Calibration check (at level 1) to evaluate pre- and post-field calibration to monitor instrument degradation

* Inspection of AOD data

* Cloud contamination check.

Calibration should be done regularly: AOD calibration (sun and moon) and radiometric calibration (sky and polarization), every 12 months (in average), for a field instrument and every 3 months, for the reference instrument. CARS should also offer continuity service to prevent stop of observation during calibration phase.

Most SOPs exist and are based on the long experience of worldwide sun/sky/moon photometer network (Smirnov et al., 2000, Holben et al., 2006). These should be updated and new SOPs have to be considered, e.g. adaptation to possible new instrument type in the future, during the implementation phase.

## 3.4.2 Definition of measurement quality-assurance criteria and procedures

### 3.4.2.1 Aerosol high-power lidar (AHL)

CARS should develop, document and distribute to the NFs:

* **Specific procedures for quality assurance:** zero-bin, dark measurements, Rayleigh-fit, telecover tests, Δ90-calibration for the depolarization - starting from the already available guidelines from EARLINET-ASOS and ACTRIS technical projects (Freudenthaler 2006-2016, https://www.meteo.physik.uni-muenchen.de/~stlidar/earlinet_asos/EARLINET-ASOS-NA3-QA.html).
* **Retrieval and application of correction data:** measurements or statistical retrieval of dark measurements and corresponding correction, measurements or statistical retrieval of overlap correction function and its application, correction of water vapour absorption.

The SOPs should be based on:

* Previous developments and lessons learnt for high-power lidars during previous EARLINET, EARLINET-ASOS, ACTRIS projects, TOPROF and E-profile initiatives

* Statistical analysis of measurements with automatic low-power aerosol lidars in large operational networks

* Intercomparison campaigns (e.g. CeiLinEx2015, Interact) and long-term parallel measurements with a high-power lidar at a testbed site.

The goal of the SOPs is to enable NFs and non-expert operators of ALC networks to provide continuous observations of aerosol profiles throughout the troposphere with best achievable accuracy and known uncertainties.

### 3.4.1.3 Automatic sun/sky/polarized/lunar photometer (ASP)

The SOPs aim at ensuring nominal use of photometers, and should include:

* Full characterization of instrument (for new instrument)

* Remote monitoring of its status

* Quality Check (QC) during operation in the field

* Quality Assurance (QA).

SOPs should strictly be applied to monitor field and reference instruments QC and for calibration. The SOPs covered by CARS are:

* Level 0 data evaluation to detect failures

* Calibration check (at level 1) to evaluate pre- and post-field calibration to monitor instrument degradation

* Inspection of AOD data

* Cloud contamination check.

Calibration should be done regularly: AOD calibration (sun and moon) and radiometric calibration (sky and polarization), every 12 months (in average), for a field instrument and every 3 months, for the reference instrument. CARS should also offer continuity service to prevent stop of observation during calibration phase.

Most SOPs exist and are based on the long experience of worldwide sun/sky/moon photometer network (Smirnov et al., 2000, Holben et al., 2006). These should be updated and new SOPs have to be considered, e.g. adaptation to possible new instrument type in the future, during the implementation phase.

## 3.4.2 Definition of measurement quality-assurance criteria and procedures

### 3.4.2.1 Aerosol high-power lidar (AHL)

CARS should develop, document and distribute to the NFs:

* **Specific procedures for quality assurance:** zero-bin, dark measurements, Rayleigh-fit, telecover tests, Δ90-calibration for the depolarization - starting from the already available guidelines from EARLINET-ASOS and ACTRIS technical projects (Freudenthaler 2006-2016, https://www.meteo.physik.uni-muenchen.de/~stlidar/earlinet_asos/EARLINET-ASOS-NA3-QA.html).
These procedures should be used by the NFs for controlling the quality of their
measurements.

* **Quality-assurance criteria** to flag measurements (or parts of the measurements) that are not compliant with the requirements, e.g.: lidar signals with very low SNR, saturated signals, distorted signals, signals with a very limited dynamic range.

Such criteria should be applied by CARS to: (a) assess the performances of the different instruments based on the QA tests performed and/or coordinated by the CARS (see section 3.4.6.1); (b) contribute to documentation and traceability of level 0 to level 3 data products (see section 3.4.8.1).

* **Mathematical methods to determine and combine the different errors** (starting e.g. from Bravo-Aranda et al, 2016 and Freudenthaler, 2016).

* **Methods for further improving the accuracy of the aerosol lidar measurements** addressing the further error sources affecting aerosol lidar measurements.

These techniques will be developed and described in such a way that they can be
generally applied in a homogenous way for different lidar systems.

### 3.4.2.2 Automatic low-power lidar / ceilometer (ALC)

CARS should develop, document and distribute to the NFs:

* **Specific procedures for quality assurance:** electronic background profile (dark measurements or statistical analysis of data); overlap correction (telecover tests, horizontal measurements, or statistical analysis of data); monitoring of temporal variability and trends of instrument specific calibration factors.

Such criteria should be applied by CARS to: (a) assess the performances of the different instruments based on the QA tests performed and/or coordinated by the CARS (see section 3.4.6.2); (b) contribute to documentation and traceability of level 0 to level 3 data products (see section 3.4.8.2).

* **Additional methods for new automatic low-power aerosol lidars** types and new error sources which are not yet known

### 3.4.2.3 Automatic sun/sky/polarized/lunar photometer (ASP)

CARS should develop, document and distribute to the NFs:

* **Quality criteria and procedures,** as defined and in use for long time by AERONET-EU: instrument design, calibration (Holben et al., 2001; Smirnov et al., 2000, Li et al., 2010, 2013, 2016, 2017; Barreto et al., 2013, 2017), maintenance, training, database and network management and aerosol retrievals (Dubovik et al., 2011, 2014)

## 3.4.3 Development and provision of instrument-specific calibration

### 3.4.3.1 Aerosol high-power lidar (AHL)

The calibration of high-power lidars, as in case of all instruments for which a hard reference cannot be
defined, consists of a combination of procedures to characterize the different parts, identify and correct
for systematic biases, check and preserve the optimal setup and the correction factors. In this sense, the
calibration of high-power aerosol lidars is closely linked to the implementation (at the corresponding
ACTRIS NFs) of the standard operation and quality assurance procedures previously described.
These procedures should be used by the NFs for controlling the quality of their
measurements.

* **Quality-assurance criteria** to flag measurements (or parts of the measurements) that are not compliant with the requirements, e.g.: lidar signals with very low SNR, saturated signals, distorted signals, signals with a very limited dynamic range.

Such criteria should be applied by CARS to: (a) assess the performances of the different instruments based on the QA tests performed and/or coordinated by the CARS (see section 3.4.6.1); (b) contribute to documentation and traceability of level 0 to level 3 data products (see section 3.4.8.1).

* **Mathematical methods to determine and combine the different errors** (starting e.g. from Bravo-Aranda et al, 2016 and Freudenthaler, 2016).

* **Methods for further improving the accuracy of the aerosol lidar measurements** addressing the further error sources affecting aerosol lidar measurements.

These techniques will be developed and described in such a way that they can be
generally applied in a homogenous way for different lidar systems.

### 3.4.2.2 Automatic low-power lidar / ceilometer (ALC)

CARS should develop, document and distribute to the NFs:

* **Specific procedures for quality assurance:** electronic background profile (dark measurements or statistical analysis of data); overlap correction (telecover tests, horizontal measurements, or statistical analysis of data); monitoring of temporal variability and trends of instrument specific calibration factors.

Such criteria should be applied by CARS to: (a) assess the performances of the different instruments based on the QA tests performed and/or coordinated by the CARS (see section 3.4.6.2); (b) contribute to documentation and traceability of level 0 to level 3 data products (see section 3.4.8.2).

* **Additional methods for new automatic low-power aerosol lidars** types and new error sources which are not yet known

### 3.4.2.3 Automatic sun/sky/polarized/lunar photometer (ASP)

CARS should develop, document and distribute to the NFs:

* **Quality criteria and procedures,** as defined and in use for long time by AERONET-EU: instrument design, calibration (Holben et al., 2001; Smirnov et al., 2000, Li et al., 2010, 2013, 2016, 2017; Barreto et al., 2013, 2017), maintenance, training, database and network management and aerosol retrievals (Dubovik et al., 2011, 2014)

## 3.4.3 Development and provision of instrument-specific calibration

### 3.4.3.1 Aerosol high-power lidar (AHL)

The calibration of high-power lidars, as in case of all instruments for which a hard reference cannot be
defined, consists of a combination of procedures to characterize the different parts, identify and correct
for systematic biases, check and preserve the optimal setup and the correction factors. In this sense, the
calibration of high-power aerosol lidars is closely linked to the implementation (at the corresponding
ACTRIS NFs) of the standard operation and quality assurance procedures previously described.
CARS should implement and provide to the NFs, on request, the following calibration support for AHLs:

* **Direct comparison** with fixed, state-of-the-art, reference instruments for identifying possible issues that may not be visible by following the QA program.

* **Laboratory tests** to assess key parameters used for retrieving major error sources of the instruments

* **On-site expert visits** to test and debug the instrument, including: test-pulse generator, polarisation calibration lamp setup, equipment to determine the state of the laser polarisation, laser wavelength meter.

* **Expert analysis** of the optical design, and of specific test measurements, to assess and reduce instrumental systematic errors: optical misalignments, design flaws, electronic induced errors, electronic synchronization, mechanical instability, aging effects (electronics and optics)

Calibration support should be provided by CARS after each major upgrade of the instrument, and/or at the duly justified request of the NFs.

### 3.4.3.2 Automatic low-power lidar / ceilometer (ALC)

As in case of high-power lidars, direct calibration of the instrument is closely linked to the implementation of the standard operation and quality assurance procedures previously described.

CARS should implement and provide to the NFs, on regular basis, the following calibration support for ALCs:

* **Statistical analysis** of network data - continuously, in near-real time (where applicable)

CARS should implement and provide to the NFs, on request, the following calibration support for ALCs:

* **Long-term parallel measurements with a reference instrument at a testbed site**, for characterization of effects and sources of uncertainty for characteristic sample instruments, new instrument types, or new firmware versions

* **Laboratory tests**: characterization of laser spectrum for the correction of water vapour absorption; detection of temperature dependencies, inspection of suspicious hardware components

Calibration support on request should be provided by CARS after each replacement of the instrument, and/or at the duly justified request of the NFs.

### 3.4.3.3 Automatic sun/sky/polarized/lunar photometer (ASP)

CARS should implement and provide to the NFs, on regular basis, the following calibration support for ASPs:

* **Direct comparison** with a reference instrument at specific outdoor calibration platforms, for day and night AOD calibration - yearly

* **Laboratory tests**: radiometric calibrations (sky radiance and polarization) - yearly

* **QC/QA monitoring during the operation in the field on a weekly basis**, to detect if instrument needs to be repaired and re-calibrated

* **Continuity Observation Service** during calibration phase using CARS temporary spare instrument or any similar organization to never stop observation.

* **Advanced Calibration Services** should be proposed to improve the calibration in the future (Li et al., 2010, 2013, 2016, 2017; Barreto et al., 2013, 2016, 2017).

More advanced calibration services should be proposed to improve the calibration in the future (Li et al., 2010, 2013, 2016, 2017; Barreto et al., 2013, 2016, 2017).
CARS should implement and provide to the NFs, on request, the following calibration support for AHLs:

* **Direct comparison** with fixed, state-of-the-art, reference instruments for identifying possible issues that may not be visible by following the QA program.

* **Laboratory tests** to assess key parameters used for retrieving major error sources of the instruments

* **On-site expert visits** to test and debug the instrument, including: test-pulse generator, polarisation calibration lamp setup, equipment to determine the state of the laser polarisation, laser wavelength meter.

* **Expert analysis** of the optical design, and of specific test measurements, to assess and reduce instrumental systematic errors: optical misalignments, design flaws, electronic induced errors, electronic synchronization, mechanical instability, aging effects (electronics and optics)

Calibration support should be provided by CARS after each major upgrade of the instrument, and/or at the duly justified request of the NFs.

### 3.4.3.2 Automatic low-power lidar / ceilometer (ALC)

As in case of high-power lidars, direct calibration of the instrument is closely linked to the implementation of the standard operation and quality assurance procedures previously described.

CARS should implement and provide to the NFs, on regular basis, the following calibration support for ALCs:

* **Statistical analysis** of network data - continuously, in near-real time (where applicable)

CARS should implement and provide to the NFs, on request, the following calibration support for ALCs:

* **Long-term parallel measurements with a reference instrument at a testbed site**, for characterization of effects and sources of uncertainty for characteristic sample instruments, new instrument types, or new firmware versions

* **Laboratory tests**: characterization of laser spectrum for the correction of water vapour absorption; detection of temperature dependencies, inspection of suspicious hardware components

Calibration support on request should be provided by CARS after each replacement of the instrument, and/or at the duly justified request of the NFs.

### 3.4.3.3 Automatic sun/sky/polarized/lunar photometer (ASP)

CARS should implement and provide to the NFs, on regular basis, the following calibration support for ASPs:

* **Direct comparison** with a reference instrument at specific outdoor calibration platforms, for day and night AOD calibration - yearly

* **Laboratory tests**: radiometric calibrations (sky radiance and polarization) - yearly

* **QC/QA monitoring during the operation in the field on a weekly basis**, to detect if instrument needs to be repaired and re-calibrated

* **Continuity Observation Service** during calibration phase using CARS temporary spare instrument or any similar organization to never stop observation.

* **Advanced Calibration Services** should be proposed to improve the calibration in the future (Li et al., 2010, 2013, 2016, 2017; Barreto et al., 2013, 2016, 2017).

More advanced calibration services should be proposed to improve the calibration in the future (Li et al., 2010, 2013, 2016, 2017; Barreto et al., 2013, 2016, 2017).
### 3.4.4 Development and provision of in-house check-up tools

#### 3.4.4.1 Aerosol high-power lidar (AHL)

Check-up and preservation of the high-power aerosol lidar calibration is under the responsibility of the NF. In order to facilitate the control of the quality of the measurements performed at the NFs, CARS should develop and distribute in-house check-up tools, as follows:

* **Software tools:**

* For fast and dynamic assessment of the instrument alignment and signal linearity

* For calculation of the depolarization correction factor, overlap function, real time data of range corrected signals, real time aerosol layering, etc.

* For automatic submission of the measurements to the SCC

* **Convertors**

* From the lidar native format to the QA tests format

* From the lidar native format to the Single Calculus Chain (SCC) format

Preferably, these should be developed in an open source programming language (e.g. Python) and, if interaction with the operator is required, user-friendly interface should be embedded. If applicable, the tools should be distributed as pre-installed, upgradeable software toolbox in a plug-and-play hardware key.

#### 3.4.4.2 Automatic low-power lidar / ceilometer (ALC)

Monitoring and preservation of instrument performance is in the responsibility of the NFs.

Most of the check-up tools for internal use are software tools, e.g. for monitoring of variability and trends in calibration factors or housekeeping data, calculation and monitoring of overlap functions. Those software tools should be open source and platform independent.

In order to facilitate the control of the quality of the measurements performed at the NFs, CARS should develop and distribute:

* **Recommendations** for commercial check-up tools (hardware provided by instrument manufacturer for dark measurements), or **'Open source' construction plans** for those tools

* **Software tools for monitoring of instrument performance**

* **Recommendations** of amount of house-keeping data

#### 3.4.4.3 Automatic sun/sky/polarized/lunar photometer (ASP)

**Not applicable.**

Check-up of the ASPs is done centralized by CARS during the annual calibration. In some very rare case, for very remote and not easy to access NF, NF can be asked to perform simple internal check-up.

### 3.4.5 Development of data evaluation procedures and plausibility test

#### 3.4.5.1 Aerosol high-power lidar (AHL)

High-power aerosol lidar (AHL) raw data acquired at NFs are mandatorily processed at the ACTRIS DC using the Single Calculus Chain (SCC).

For preventing collection of measurements of poor quality, CARS should develop and distribute to the NFs tools for on-site data evaluation procedures and plausibility tests, as follows:

* **Software tools** to continuously monitor: signal-to-noise ratio, maximum amplitude of the signals, beam pointing stability and mechanical stability
### 3.4.4 Development and provision of in-house check-up tools

#### 3.4.4.1 Aerosol high-power lidar (AHL)

Check-up and preservation of the high-power aerosol lidar calibration is under the responsibility of the NF. In order to facilitate the control of the quality of the measurements performed at the NFs, CARS should develop and distribute in-house check-up tools, as follows:

* **Software tools:**

* For fast and dynamic assessment of the instrument alignment and signal linearity

* For calculation of the depolarization correction factor, overlap function, real time data of range corrected signals, real time aerosol layering, etc.

* For automatic submission of the measurements to the SCC

* **Convertors**

* From the lidar native format to the QA tests format

* From the lidar native format to the Single Calculus Chain (SCC) format

Preferably, these should be developed in an open source programming language (e.g. Python) and, if interaction with the operator is required, user-friendly interface should be embedded. If applicable, the tools should be distributed as pre-installed, upgradeable software toolbox in a plug-and-play hardware key.

#### 3.4.4.2 Automatic low-power lidar / ceilometer (ALC)

Monitoring and preservation of instrument performance is in the responsibility of the NFs.

Most of the check-up tools for internal use are software tools, e.g. for monitoring of variability and trends in calibration factors or housekeeping data, calculation and monitoring of overlap functions. Those software tools should be open source and platform independent.

In order to facilitate the control of the quality of the measurements performed at the NFs, CARS should develop and distribute:

* **Recommendations** for commercial check-up tools (hardware provided by instrument manufacturer for dark measurements), or **'Open source' construction plans** for those tools

* **Software tools for monitoring of instrument performance**

* **Recommendations** of amount of house-keeping data

#### 3.4.4.3 Automatic sun/sky/polarized/lunar photometer (ASP)

Not applicable.

Check-up of the ASPs is done centralized by CARS during the annual calibration. In some very rare case, for very remote and not easy to access NF, NF can be asked to perform simple internal check-up.

### 3.4.5 Development of data evaluation procedures and plausibility test

#### 3.4.5.1 Aerosol high-power lidar (AHL)

High-power aerosol lidar (AHL) raw data acquired at NFs are mandatorily processed at the ACTRIS DC using the Single Calculus Chain (SCC).

For preventing collection of measurements of poor quality, CARS should develop and distribute to the NFs tools for on-site data evaluation procedures and plausibility tests, as follows:

* **Software tools** to continuously monitor: signal-to-noise ratio, maximum amplitude of the signals, beam pointing stability and mechanical stability
* **Statistical tests** to check the long-term behaviour of electronic distortion (dark signal) and noise levels, to highlight electronic faults.

The data evaluation and plausibility tests are subject of regular updates during the implementation and operation phase. If proven useful, some of the plausibility tests will be transferred to the DC for implementation in the SCC.

### 3.4.5.2 Automatic low-power lidar / ceilometer (ALC)

For preventing collection of measurements of poor quality, CARS should develop and distribute to the NFs tools for on-site data evaluation procedures and plausibility tests, as follows:

* **Software tools:**

* for the monitoring of housekeeping data

* for the long-term analysis of variability and trends in calibration factors and detection range

Those data evaluation and monitoring tools should be provided to the NFs and external user as 'open source' platform independent software tools.

### 3.4.5.3 Automatic sun/sky/polarized/lunar photometer (ASP)

**Not applicable.**

Instrument performances during in the field operation should be monitored in near real time at CARS. Failures and calibration changes are detected, flagged and NF informed when necessary actions are requested to solve technical problem at instrument level.

## 3.4.6 Realization of observational site performance audits with reference samples or mobile systems

### 3.4.6.1 Aerosol high-power lidar (AHL)

CARS should provide (at the time of its full operation) mobile reference lidar systems for direct comparisons:

* **At least two mobile 3+2+3 reference lidar** working at the three elastic (355, 532, and 1064 nm) wavelengths with polarisation sensitivity, and at the two Raman wavelengths (387 and 607 nm) over a detection range from 200 m above ground level to 15 km

In case the technique for a third Raman wavelength evolves in the meantime, it should be included in the mobile instruments.

CARS should maintain, calibrate, and further develop such reference lidar systems as needed according to the advance of the knowledge, techniques, and improved accuracy needs (see Freudenthaler et al., 2016).

### 3.4.6.2 Automatic low-power lidar / ceilometer (ALC)

**Not applicable.**

In case of extremely strong accuracy requirements on instruments at specific NFs, those audits could be covered by the experts and reference system for high-power lidars.

### 3.4.6.3 Automatic sun/sky/polarized/lunar photometer (ASP)

**Not applicable.**
* **Statistical tests** to check the long-term behaviour of electronic distortion (dark signal) and noise levels, to highlight electronic faults.

The data evaluation and plausibility tests are subject of regular updates during the implementation and operation phase. If proven useful, some of the plausibility tests will be transferred to the DC for implementation in the SCC.

### 3.4.5.2 Automatic low-power lidar / ceilometer (ALC)

For preventing collection of measurements of poor quality, CARS should develop and distribute to the NFs tools for on-site data evaluation procedures and plausibility tests, as follows:

* **Software tools:**

* for the monitoring of housekeeping data

* for the long-term analysis of variability and trends in calibration factors and detection range

Those data evaluation and monitoring tools should be provided to the NFs and external user as 'open source' platform independent software tools.

### 3.4.5.3 Automatic sun/sky/polarized/lunar photometer (ASP)

**Not applicable.**

Instrument performances during the field operation should be monitored in near real time at CARS. Failures and calibration changes are detected, flagged and NF informed when necessary actions are requested to solve technical problem at instrument level.

## 3.4.6 Realization of observational site performance audits with reference samples or mobile systems

### 3.4.6.1 Aerosol high-power lidar (AHL)

CARS should provide (at the time of its full operation) mobile reference lidar systems for direct comparisons:

* **At least two mobile 3+2+3 reference lidar** working at the three elastic (355, 532, and 1064 nm) wavelengths with polarisation sensitivity, and at the two Raman wavelengths (387 and 607 nm) over a detection range from 200 m above ground level to 15 km

In case the technique for a third Raman wavelength evolves in the meantime, it should be included in the mobile instruments.

CARS should maintain, calibrate, and further develop such reference lidar systems as needed according to the advance of the knowledge, techniques, and improved accuracy needs (see Freudenthaler et al., 2016).

### 3.4.6.2 Automatic low-power lidar / ceilometer (ALC)

**Not applicable.**

In case of extremely strong accuracy requirements on instruments at specific NFs, those audits could be covered by the experts and reference system for high-power lidars.

### 3.4.6.3 Automatic sun/sky/polarized/lunar photometer (ASP)

**Not applicable.**
Direct comparisons should only be done, each 3-months, between the reference instruments at the different CARS Units.

### 3.4.7 Organization of regular exercises to assess the performances of the NFs, including instrument performance workshops

#### 3.4.7.1 Aerosol high-power lidar (AHL)

Periodically (at least once per year), CARS should organize exercises to assess the performances of the AHLs operating at the corresponding NFs, as follows:

* **Expert analysis of the quality assurance tests:** zero-bin, dark measurements, Rayleigh-fit, telecover tests, Δ90-calibration for the depolarization (Freudenthaler 2006-2016).

The QA tests performed and/or coordinated by the CARS should be codified and embedded into the SCC for the traceability and full documentation of the data quality.

#### 3.4.7.2 Automatic low-power lidar / ceilometer (ALC)

Periodically (at least once per year), CARS should organize exercises to assess the performances of the ALCs operating at the corresponding NFs, as follows:

* **Expert analysis of the quality assurance tests:** dark measurements, overlap functions, signal artefacts, and variability and trends of calibration factors, or any other not yet known source of uncertainties.

#### 3.4.7.3 Automatic sun/sky/polarized/lunar photometer (ASP)

**Not applicable.**

ASPs are fully automatic instruments. Their performances are regularly assessed during the annual calibration.

### 3.4.8 Contribution to documentation and traceability of level 0 to level 3 data products

#### 3.4.8.1 Aerosol high-power lidar (AHL)

CARS should codify in a convenient way the results of the quality assurance program (see sections 3.4.3.1, 3.4.6.1, and 3.4.7.1) and transfer them to the ACTRIS Data Centre. The specific annotation should be agreed with the ACTRIS Data Centre, and should be complete, exhaustive and machine readable.

Additionally, CARS should make available to the ACTRIS Data Centre the full documentation on the standard operation procedures and on the measurement quality-assurance criteria and procedures.

#### 3.4.8.2 Automatic low-power lidar / ceilometer (ALC)

CARS should codify in a convenient way the results of the quality assurance program (see sections 3.4.3.2, 3.4.6.2, and 3.4.7.2) and transfer them to the ACTRIS Data Centre. The specific annotation should be agreed with the ACTRIS Data Centre, and should be complete and exhaustive.

#### 3.4.8.3 Automatic sun/sky/polarized/lunar photometer (ASP)

CARS should codify in a convenient way the results of the quality assurance program (see sections 3.4.3.3, 3.4.6.3, and 3.4.7.3) and transfer them to the ACTRIS Data Centre. The specific annotation should be agreed with the ACTRIS Data Centre, and should be complete and exhaustive.
Direct comparisons should only be done, each 3-months, between the reference instruments at the different CARS Units.

### 3.4.7 Organization of regular exercises to assess the performances of the NFs, including instrument performance workshops

#### 3.4.7.1 Aerosol high-power lidar (AHL)

Periodically (at least once per year), CARS should organize exercises to assess the performances of the AHLs operating at the corresponding NFs, as follows:

* **Expert analysis of the quality assurance tests:** zero-bin, dark measurements, Rayleigh-fit, telecover tests, Δ90-calibration for the depolarization (Freudenthaler 2006-2016).

The QA tests performed and/or coordinated by the CARS should be codified and embedded into the SCC for the traceability and full documentation of the data quality.

#### 3.4.7.2 Automatic low-power lidar / ceilometer (ALC)

Periodically (at least once per year), CARS should organize exercises to assess the performances of the ALCs operating at the corresponding NFs, as follows:

* **Expert analysis of the quality assurance tests:** dark measurements, overlap functions, signal artefacts, and variability and trends of calibration factors, or any other not yet known source of uncertainties.

#### 3.4.7.3 Automatic sun/sky/polarized/lunar photometer (ASP)

**Not applicable.**

ASPs are fully automatic instruments. Their performances are regularly assessed during the annual calibration.

### 3.4.8 Contribution to documentation and traceability of level 0 to level 3 data products

#### 3.4.8.1 Aerosol high-power lidar (AHL)

CARS should codify in a convenient way the results of the quality assurance program (see sections 3.4.3.1, 3.4.6.1, and 3.4.7.1) and transfer them to the ACTRIS Data Centre. The specific annotation should be agreed with the ACTRIS Data Centre, and should be complete, exhaustive and machine readable.

Additionally, CARS should make available to the ACTRIS Data Centre the full documentation on the standard operation procedures and on the measurement quality-assurance criteria and procedures.

#### 3.4.8.2 Automatic low-power lidar / ceilometer (ALC)

CARS should codify in a convenient way the results of the quality assurance program (see sections 3.4.3.2, 3.4.6.2, and 3.4.7.2) and transfer them to the ACTRIS Data Centre. The specific annotation should be agreed with the ACTRIS Data Centre, and should be complete and exhaustive.

#### 3.4.8.3 Automatic sun/sky/polarized/lunar photometer (ASP)

CARS should codify in a convenient way the results of the quality assurance program (see sections 3.4.3.3, 3.4.6.3, and 3.4.7.3) and transfer them to the ACTRIS Data Centre. The specific annotation should be agreed with the ACTRIS Data Centre, and should be complete and exhaustive.
### 3.4.9 Contribution to CEN, ISO, or similar standardization activities

CARS should take the opportunity to send experts as part of the working groups in CEN, ISO or similar standardization activities whenever a related initiative is promoted. Depending on the maturity of the techniques covered by CARS and their potential transfer to the operational activities, CARS should propose to CEN, ISO (or similar) to start the standardization process.

## 3.5 Operation support for knowledge transfer and training

### 3.5.1 Training of operators and scientists

Training of operators and scientists at the ACTRIS NFs which fall under CARS guidance may be required for several cases:

* New operators that need to line up to the internal protocols and quality assurance criteria

* New operators that are inexperienced with data collection and data management

* Experienced operators and scientists facing a potential upgrade of their instrument

* Availability of new SOPs, QA procedures and tools, and/or data evaluation procedures and plausibility tests

* New types or firmware versions available for ALC and/or ASP

The training should be organized on various channels:

* Regular training sessions (at least once per year) on pre-defined subjects

* Training during campaigns for direct comparisons (at the NF or at CARS)

* Transfer of expertise during regular exercises to assess the performances of the NFs

* Transfer of expertise during the on-site expert visits to test and debug the instrument

* Documentation available on the CARS website: instrument setup, QC, QA protocols, operation and optimization of the instruments and data management

* Forums

* Regular WebEx sessions as follow-ups of the face-to-face training (quarterly)

In case of the face-to-face training, the number of participants should not exceed 40, with a ratio of trainers / trainees of min. 10%. The sessions may be organized in different CARS Units, depending on the subjects (required expertise and laboratories for hands-on).

CARS should prepare and distribute the training material to the participants, and collect feed-backs. A list of upcoming training sessions should be available on the CARS website and maintained updated.

Training support may be **scheduled** (for pre-defined subjects and needs) and **on request** (for specific needs of some NFs).

### 3.5.2 Consultancy for setting-up new observational or exploratory platforms and new instruments at the NFs

CARS should offer to the NFs, on request, consultancy regarding the state of the art of the remote sensing techniques, and/or the possibility to integrate the observations, in case of:

* Upgrading of the instruments

* Specific observation protocols

* Establishment of new observing stations

* Development of new exploratory platforms (laboratories and dedicated mobile instruments and facilities operating on campaign basis and following common standards)
### 3.4.9 Contribution to CEN, ISO, or similar standardization activities

CARS should take the opportunity to send experts as part of the working groups in CEN, ISO or similar standardization activities whenever a related initiative is promoted. Depending on the maturity of the techniques covered by CARS and their potential transfer to the operational activities, CARS should propose to CEN, ISO (or similar) to start the standardization process.

## 3.5 Operation support for knowledge transfer and training

### 3.5.1 Training of operators and scientists

Training of operators and scientists at the ACTRIS NFs which fall under CARS guidance may be required for several cases:

* New operators that need to line up to the internal protocols and quality assurance criteria

* New operators that are inexperienced with data collection and data management

* Experienced operators and scientists facing a potential upgrade of their instrument

* Availability of new SOPs, QA procedures and tools, and/or data evaluation procedures and plausibility tests

* New types or firmware versions available for ALC and/or ASP

The training should be organized on various channels:

* Regular training sessions (at least once per year) on pre-defined subjects

* Training during campaigns for direct comparisons (at the NF or at CARS)

* Transfer of expertise during regular exercises to assess the performances of the NFs

* Transfer of expertise during the on-site expert visits to test and debug the instrument

* Documentation available on the CARS website: instrument setup, QC, QA protocols, operation and optimization of the instruments and data management

* Forums

* Regular WebEx sessions as follow-ups of the face-to-face training (quarterly)

In case of the face-to-face training, the number of participants should not exceed 40, with a ratio of trainers / trainees of min. 10%. The sessions may be organized in different CARS Units, depending on the subjects (required expertise and laboratories for hands-on).

CARS should prepare and distribute the training material to the participants, and collect feed-backs. A list of upcoming training sessions should be available on the CARS website and maintained updated.

Training support may be **scheduled** (for pre-defined subjects and needs) and **on request** (for specific needs of some NFs).

### 3.5.2 Consultancy for setting-up new observational or exploratory platforms and new instruments at the NFs

CARS should offer to the NFs, **on request**, consultancy regarding the state of the art of the remote sensing techniques, and/or the possibility to integrate the observations, in case of:

* Upgrading of the instruments

* Specific observation protocols

* Establishment of new observing stations

* Development of new exploratory platforms (laboratories and dedicated mobile instruments and facilities operating on campaign basis and following common standards)
Consultancy may be provided during training sessions, workshops, meetings, site visits, direct comparison campaigns, or electronically via email or forums.

## 3.6 Operation support for improvement of measurement methodologies

### 3.6.1 Testing of new measurement instruments and procedures

CARS should apply all techniques and methods described under 3.4.3 for testing prototypes. CARS should develop further techniques and methods if those are needed for the testing, depending on the capacity of the Centre, available infrastructure and expertise, and costs. Such operation support should be made on request. The application should contain sufficient information to allow the Centre to assess the feasibility of providing this support, as well as an estimation of the added value for the scientific community in general and for ACTRIS in particular.

### 3.6.2 Development of strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime

CARS should develop, when possible, strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime. Such strategies may include:

* Temporary provision of spare parts

* Temporary provision of a spare instrument (mandatory for ASP)

* Negotiation of extended warranty and/or maintenance/service contracts with manufacturers

* Collective purchase of commonly used parts

* Specific operation schedule / protocols, etc.

### 3.6.3 Development of new technological products and methods

New measurement techniques, technological products and methods may be developed by the Centre in collaboration with the NFs. At the request of NFs, or by its own decision, CARS may investigate new technical solutions, experimental set-up and/or upgrades, new algorithms to retrieve new variables, new experimental configuration, approaches to increase accuracy, or integration of observations from different instruments.

Depending on the situation, the Centre may recommend to the RI Committee to decide on the implementation of such new techniques at the RI level. The Centre has no obligation to develop the full set of operation support for such new techniques, unless they are embraced by ACTRIS and implemented as part of the National Facilities.

### 3.6.4 Development of retrieval algorithms or tools for producing level 1 to 3 data, including the exploitation of instrument synergies

#### 3.6.4.1 Aerosol high-power lidar (AHL)

The Single Calculus Chain (SCC) is the centralized processing tool for AHLs, always improving according to new processing requirements and standards developed in the research community.

In view of the further implementation into the SCC, CARS should aim at:

* **developing optimized algorithms** for: extinction calculation (retrieval using vibrational and rotational Raman channels), cloud screening, smoothing, etc.
Consultancy may be provided during training sessions, workshops, meetings, site visits, direct comparison campaigns, or electronically via email or forums.

## 3.6 Operation support for improvement of measurement methodologies

### 3.6.1 Testing of new measurement instruments and procedures

CARS should apply all techniques and methods described under 3.4.3 for testing prototypes. CARS should develop further techniques and methods if those are needed for the testing, depending on the capacity of the Centre, available infrastructure and expertise, and costs. Such operation support should be made on request. The application should contain sufficient information to allow the Centre to assess the feasibility of providing this support, as well as an estimation of the added value for the scientific community in general and for ACTRIS in particular.

### 3.6.2 Development of strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime

CARS should develop, when possible, strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime. Such strategies may include:

* Temporary provision of spare parts

* Temporary provision of a spare instrument (mandatory for ASP)

* Negotiation of extended warranty and/or maintenance/service contracts with manufacturers

* Collective purchase of commonly used parts

* Specific operation schedule / protocols, etc.

### 3.6.3 Development of new technological products and methods

New measurement techniques, technological products and methods may be developed by the Centre in collaboration with the NFs. At the request of NFs, or by its own decision, CARS may investigate new technical solutions, experimental set-up and/or upgrades, new algorithms to retrieve new variables, new experimental configuration, approaches to increase accuracy, or integration of observations from different instruments.

Depending on the situation, the Centre may recommend to the RI Committee to decide on the implementation of such new techniques at the RI level. The Centre has no obligation to develop the full set of operation support for such new techniques, unless they are embraced by ACTRIS and implemented as part of the National Facilities.

### 3.6.4 Development of retrieval algorithms or tools for producing level 1 to 3 data, including the exploitation of instrument synergies

#### 3.6.4.1 Aerosol high-power lidar (AHL)

The Single Calculus Chain (SCC) is the centralized processing tool for AHLs, always improving according to new processing requirements and standards developed in the research community.

In view of the further implementation into the SCC, CARS should aim at:

* **developing optimized algorithms** for: extinction calculation (retrieval using vibrational and rotational Raman channels), cloud screening, smoothing, etc.
* **developing new algorithms** for: high spectral resolution channels, water vapour mixing ratio, calculation of the intensive optical parameters (e.g. Angstrom parameter, Lidar Ratio, colour ratio), estimation of the aerosol type, calculation of the statistical climatological parameters, etc.

* **developing new techniques and procedures** for determination and, where possible, correction of instrumental uncertainties.

### 3.6.4.2 Automatic low-power lidar / ceilometer (ALC)

ALCs measurements are generally used for cloud studies, therefore development of new algorithms is generally covered by the cloud remote sensing component of ACTRIS. However, state-of-the-art instruments have a large potential to fill observational gaps in the network of high-power lidars with respect to aerosols.

In view of a potential use of aerosol information provided by the ALCs, CARS should aim at:

* **developing new algorithms** for calculation of: cloud base height, top height of atmospheric boundary layer, automatic detection of volcanic ash layers, etc.

### 3.6.4.3 Automatic sun/sky/polarized/lunar photometer (ASP)

CARS is in charge with the retrieval of Level 1-to-Level 2 stand-alone retrieval for ASPs. Level 3 data and higher based on GARRLIC/GRASP high performance retrieval software should be obtained at the ACTRIS Data Centre.

In view of future implementation of advanced retrievals, CARS should aim at:

* **developing uncertainty calculation** for Level 1-to-Level 2 data

* **developing updated/adjusted algorithms** for Level 1-to-Level 2 data for new instruments (wavelength, spectral resolution, angular and temporal samplings, etc.).

* **implementing existing algorithm exploiting** synergy of ASP with single ALC or multi-wavelength AHLs

* **developing new algorithms** for Level 3 data and higher, based on GRASP/GARRLIC to exploit new synergy of ASP, ALCs, AHLs with in situ and satellite

## 4 Services provided to ACTRIS users

The operation support offered by the Centre for Aerosol Remote Sensing should also reply to the need of ACTRIS users in the assessment of the aerosol remote sensing instruments and products. A large number of users is expected by research community which are not part of ACTRIS, both in Europe and worldwide. The services offered to ACTRIS users and in particular to the private sector will be an innovation driver for the aerosol remote sensing community as a whole, with a potential positive feedback for ACTRIS.

The Service and Access Management Unit (SAMU) should be considered as the single point of entry for user access to all CARS services. The access is regulated by both the ACTRIS access policy and the ACTRIS data policy, and will not be detailed in this document.

### 4.1 Estimation of the need

CARS expects various types of users: individual academic and private users, national and worldwide networks (AERONET, E-PROFILE, GAW, ICOS, UK and Chinese MET-Offices, SONET, EARLINET, MPLNET, LALINET, etc.), private sector (mostly SMEs), etc. Users are mostly located in Europe, South America, Africa and Asia. Most of them are expected to be regular users requesting calibration, maintenance and access to aerosol variables through the processing of field instrument data. Some users, leading other networks,
* **developing new algorithms** for: high spectral resolution channels, water vapour mixing ratio, calculation of the intensive optical parameters (e.g. Angstrom parameter, Lidar Ratio, colour ratio), estimation of the aerosol type, calculation of the statistical climatological parameters, etc.

* **developing new techniques and procedures** for determination and, where possible, correction of instrumental uncertainties.

### 3.6.4.2 Automatic low-power lidar / ceilometer (ALC)

ALCs measurements are generally used for cloud studies, therefore development of new algorithms is generally covered by the cloud remote sensing component of ACTRIS. However, state-of-the-art instruments have a large potential to fill observational gaps in the network of high-power lidars with respect to aerosols.

In view of a potential use of aerosol information provided by the ALCs, CARS should aim at:

* **developing new algorithms** for calculation of: cloud base height, top height of atmospheric boundary layer, automatic detection of volcanic ash layers, etc.

### 3.6.4.3 Automatic sun/sky/polarized/lunar photometer (ASP)

CARS is in charge with the retrieval of Level 1-to-Level 2 stand-alone retrieval for ASPs. Level 3 data and higher based on GARRLIC/GRASP high performance retrieval software should be obtained at the ACTRIS Data Centre.

In view of future implementation of advanced retrievals, CARS should aim at:

* **developing uncertainty calculation** for Level 1-to-Level 2 data

* **developing updated/adjusted algorithms** for Level 1-to-Level 2 data for new instruments (wavelength, spectral resolution, angular and temporal samplings, etc.).

* **implementing existing algorithm exploiting** synergy of ASP with single ALC or multi-wavelength AHLs

* **developing new algorithms** for Level 3 data and higher, based on GRASP/GARRLIC to exploit new synergy of ASP, ALCs, AHLs with in situ and satellite

## 4 Services provided to ACTRIS users

The operation support offered by the Centre for Aerosol Remote Sensing should also reply to the need of ACTRIS users in the assessment of the aerosol remote sensing instruments and products. A large number of users is expected by research community which are not part of ACTRIS, both in Europe and worldwide. The services offered to ACTRIS users and in particular to the private sector will be an innovation driver for the aerosol remote sensing community as a whole, with a potential positive feedback for ACTRIS.

The Service and Access Management Unit (SAMU) should be considered as the single point of entry for user access to all CARS services. The access is regulated by both the ACTRIS access policy and the ACTRIS data policy, and will not be detailed in this document.

### 4.1 Estimation of the need

CARS expects various types of users: individual academic and private users, national and worldwide networks (AERONET, E-PROFILE, GAW, ICOS, UK and Chinese MET-Offices, SONET, EARLINET, MPLNET, LALINET, etc.), private sector (mostly SMEs), etc. Users are mostly located in Europe, South America, Africa and Asia. Most of them are expected to be regular users requesting calibration, maintenance and access to aerosol variables through the processing of field instrument data. Some users, leading other networks,
can request regularly the calibration of reference instrument, which is particularly relevant to develop traceability at international level.

An estimation of the number of users who could benefit from the services of CARS is presented below.

<table><thead><tr><th rowspan="2">Type of ACTRIS user</th><th rowspan="2">Measurement technique</th><th colspan="3">Number of users to which ACTRIS is providing services</th></tr><tr><th>Now (in the preparatory phase, by 2020)</th><th colspan="2">by 2025</th></tr><tr><th></th><th></th><th></th><th>Min.</th><th>Max.</th></tr></thead><tbody><tr><td rowspan="4">Academia</td><td><strong>Total</strong></td><td>92</td><td>92</td><td>145</td></tr><tr><td>Aerosol high-power lidar</td><td>7</td><td>7</td><td>15</td></tr><tr><td>Automatic low-power lidar / ceilometer</td><td>30</td><td>30</td><td>60</td></tr><tr><td>Automatic sun/sky/lunar photometer</td><td>55</td><td>55</td><td>70</td></tr><tr><td rowspan="4">Business & industry</td><td><strong>Total</strong></td><td>10</td><td>10</td><td>20</td></tr><tr><td>Aerosol high-power lidar</td><td>1</td><td>1</td><td>2</td></tr><tr><td>Automatic low-power lidar / ceilometer</td><td>15<sup>2</sup></td><td>15<sup>iv</sup></td><td>27<sup>iv</sup></td></tr><tr><td>Automatic sun/sky/lunar photometer</td><td>2</td><td>2</td><td>5</td></tr><tr><td rowspan="4">Public services</td><td><strong>Total</strong></td><td>31</td><td>31</td><td>50</td></tr><tr><td>Aerosol high-power lidar</td><td>10</td><td>10</td><td>15</td></tr><tr><td>Automatic low-power lidar / ceilometer</td><td>10<sup>3</sup></td><td>10<sup>v</sup></td><td>20<sup>v</sup></td></tr><tr><td>Automatic sun/sky/lunar photometer</td><td>11</td><td>11</td><td>15</td></tr></tbody></table>

These numbers refer strictly to users (institutional), excluding ACTRIS NFs. The numbers should be revised at a later stage, according to the estimations in *User requirements* document.

## 4.2 Provision of measurement quality assurance and quality control procedures and tools

All procedures and tools which are provided as operational support to ACTRIS NFs should also be offered to ACTRIS users - as far as the capacities of the Centre allows. It is not foreseen to develop customized tools (other than those developed in support of the ACTRIS NFs) for the ACTRIS users.

## 4.3 Instrument-specific calibration

All of the calibration methods developed at CARS should be offered as services to ACTRIS users. No custom methods should be developed for the ACTRIS users.

## 4.4 Knowledge transfer and operator training

Out of the knowledge transfer and training activities foreseen as operational support to NFs, the following should be also offered to ACTRIS users, on request:

* Consultancy for instrument set-up - for new users or users not familiarized with the new instruments

* Training regarding the retrieved aerosol variables - for new users or users not familiarized with the new variables

<footnote n="2">² Commercial operators of ALC networks (e.g. heli rescue)</footnote>

<footnote n="3">³ National organizations which operate networks of up to 100 ALCs</footnote>
can request regularly the calibration of reference instrument, which is particularly relevant to develop traceability at international level.

An estimation of the number of users who could benefit from the services of CARS is presented below.

<table><thead><tr><th rowspan="2">Type of ACTRIS user</th><th rowspan="2">Measurement technique</th><th colspan="3">Number of users to which ACTRIS is providing services</th></tr><tr><th>Now (in the preparatory phase, by 2020)</th><th colspan="2">by 2025</th></tr><tr><th></th><th></th><th></th><th>Min.</th><th>Max.</th></tr></thead><tbody><tr><td rowspan="4">Academia</td><td><strong>Total</strong></td><td>92</td><td>92</td><td>145</td></tr><tr><td>Aerosol high-power lidar</td><td>7</td><td>7</td><td>15</td></tr><tr><td>Automatic low-power lidar / ceilometer</td><td>30</td><td>30</td><td>60</td></tr><tr><td>Automatic sun/sky/lunar photometer</td><td>55</td><td>55</td><td>70</td></tr><tr><td rowspan="4">Business & industry</td><td><strong>Total</strong></td><td>10</td><td>10</td><td>20</td></tr><tr><td>Aerosol high-power lidar</td><td>1</td><td>1</td><td>2</td></tr><tr><td>Automatic low-power lidar / ceilometer</td><td>15<sup>2</sup></td><td>15<sup>iv</sup></td><td>27<sup>iv</sup></td></tr><tr><td>Automatic sun/sky/lunar photometer</td><td>2</td><td>2</td><td>5</td></tr><tr><td rowspan="4">Public services</td><td><strong>Total</strong></td><td>31</td><td>31</td><td>50</td></tr><tr><td>Aerosol high-power lidar</td><td>10</td><td>10</td><td>15</td></tr><tr><td>Automatic low-power lidar / ceilometer</td><td>10<sup>3</sup></td><td>10<sup>v</sup></td><td>20<sup>v</sup></td></tr><tr><td>Automatic sun/sky/lunar photometer</td><td>11</td><td>11</td><td>15</td></tr></tbody></table>

These numbers refer strictly to users (institutional), excluding ACTRIS NFs. The numbers should be revised at a later stage, according to the estimations in *User requirements* document.

## 4.2 Provision of measurement quality assurance and quality control procedures and tools

All procedures and tools which are provided as operational support to ACTRIS NFs should also be offered to ACTRIS users - as far as the capacities of the Centre allows. It is not foreseen to develop customized tools (other than those developed in support of the ACTRIS NFs) for the ACTRIS users.

## 4.3 Instrument-specific calibration

All of the calibration methods developed at CARS should be offered as services to ACTRIS users. No custom methods should be developed for the ACTRIS users.

## 4.4 Knowledge transfer and operator training

Out of the knowledge transfer and training activities foreseen as operational support to NFs, the following should be also offered to ACTRIS users, on request:

* Consultancy for instrument set-up - for new users or users not familiarized with the new instruments

* Training regarding the retrieved aerosol variables - for new users or users not familiarized with the new variables

<footnote n="2">² Commercial operators of ALC networks (e.g. heli rescue)</footnote>

<footnote n="3">³ National organizations which operate networks of up to 100 ALCs</footnote>
* Training for the implementation of SOPs (maintenance, general instrument operation procedures, retrieval and application of correction data) – for new users or users not familiarized with the new SOPs

* Transfer of knowledge regarding new measurement techniques, technological solutions, retrieval algorithms – for all kind of users

The dissemination of knowledge should be organized by CARS for the ACTRIS users through the following channels:

* Publication of related documents (e.g. SOPs, training material) through the ACTRIS portal

* Publication of general achievements (e.g. methodologies) in scientific papers

* Technical and scientific expert and user meetings

* On request access to CARS for specific training

## 4.5 Improvement of measurement and retrieval methodologies for aerosols, clouds, and reactive trace gases

CARS should actively be in contact with instrument manufacturers in order to assess the applicability of their related products for the scientific purposes of the NFs, discuss latest developments and needs, necessary and possible improvements and standards, and develop solutions for new measurement methods.

Interaction of the Centre with the instrument manufacturers may take place during conferences and exhibits, dedicated workshops and meetings, as well as part of joint projects.

Both for measurement and retrievals, the user must provide sufficient information to assess the feasibility of providing this support, as well as an estimation of the added value for the scientific community in general, and for ACTRIS in particular with respect to the minimum requirements.

# 5 Governance and management structure of the Centre for Aerosol Remote Sensing

The Units of the Centre for Aerosol Remote Sensing shall be organized according to the specific role of the CF, assuring that the CF complies with the requirements and obligations described in sections 6 and 8 of this document, and considering the general principles described in the *Baseline document for the concept of the Central Facilities*. The Centre for Aerosol Remote Sensing shall be organized such that:

* It has a well-defined structure of Units,

* It has a well-defined decision-making process,

* It is coordinated by a CF Director and managed by a CF Management Board, which consists of the CF Director and the CF Unit Heads,

* It has clear and cost-efficient task sharing between the Units,

* It has a risk management strategy,

* It participates in the ACTRIS decision making by sending representative(s) to the ACTRIS legal entity bodies, e.g. to the RI committee.
* Training for the implementation of SOPs (maintenance, general instrument operation procedures, retrieval and application of correction data) – for new users or users not familiarized with the new SOPs

* Transfer of knowledge regarding new measurement techniques, technological solutions, retrieval algorithms – for all kind of users

The dissemination of knowledge should be organized by CARS for the ACTRIS users through the following channels:

* Publication of related documents (e.g. SOPs, training material) through the ACTRIS portal

* Publication of general achievements (e.g. methodologies) in scientific papers

* Technical and scientific expert and user meetings

* On request access to CARS for specific training

## 4.5 Improvement of measurement and retrieval methodologies for aerosols, clouds, and reactive trace gases

CARS should actively be in contact with instrument manufacturers in order to assess the applicability of their related products for the scientific purposes of the NFs, discuss latest developments and needs, necessary and possible improvements and standards, and develop solutions for new measurement methods.

Interaction of the Centre with the instrument manufacturers may take place during conferences and exhibits, dedicated workshops and meetings, as well as part of joint projects.

Both for measurement and retrievals, the user must provide sufficient information to assess the feasibility of providing this support, as well as an estimation of the added value for the scientific community in general, and for ACTRIS in particular with respect to the minimum requirements.

# 5 Governance and management structure of the Centre for Aerosol Remote Sensing

The Units of the Centre for Aerosol Remote Sensing shall be organized according to the specific role of the CF, assuring that the CF complies with the requirements and obligations described in sections 6 and 8 of this document, and considering the general principles described in the *Baseline document for the concept of the Central Facilities*. The Centre for Aerosol Remote Sensing shall be organized such that:

* It has a well-defined structure of Units,

* It has a well-defined decision-making process,

* It is coordinated by a CF Director and managed by a CF Management Board, which consists of the CF Director and the CF Unit Heads,

* It has clear and cost-efficient task sharing between the Units,

* It has a risk management strategy,

* It participates in the ACTRIS decision making by sending representative(s) to the ACTRIS legal entity bodies, e.g. to the RI committee.
# 6 Requirements for the Centre for Aerosol Remote Sensing

## 6.1 General requirements

In order to be labelled as the Centre for Aerosol Remote Sensing, the candidate shall:

* Commit for long-term operation, at least 10 years starting with the next year after the implementation as a CF,

* Set-up an appropriate structure of Units, to ensure an adequate functionality of the CF, cost-effective operation, and scalability with respect to the user demands and advancement of the state-of-the art technology,

* Demonstrate the capacity (in terms of material and personnel resources), to ensure the provision of the needed services and operation support, as described in section 6.2

* Provide a feasible implementation and operation plan for the first five years, starting with the next year after the selection as CF,

* Commit to provide a minimum amount of user services, as described in section 4

* Commit to provide the mandatory operation support to the ACTRIS NFs, as described in section 3.

## 6.2 Technical requirements

### 6.2.1 Facilities

In view of the operation support and service provision CARS should have / put in place:

<table><thead><tr><th></th><th>Spaces</th><th>Instrumentation</th><th>IT infrastructure</th></tr></thead><tbody><tr><th>AHL</th><td><ul><li>Indoor laboratories: at least 50 m² air temperature stabilized lidar operation lab with access to sky (roof window) for two lidar systems; at least 30 m² air temperature stabilized optical lab with at least 10 m² clean room cabin ISO 6; at least 20 m² electronic lab; All with water supply, electrical power line filter and electrical grounding.</li><li>Outdoor space to simultaneously operate at least 3 lidar systems, power supply and internet connection;</li></ul></td><td><ul><li>At least 1 lidar (3 beta + 2 alpha + 3 delta), dynamic range 200 m to 20 km; complemented by ancillary instrumentation (meteorology)</li><li>At least 3 mobile lidars (3 beta + 2 alpha + 3 delta), dynamic range 200 m to 15 km</li><li>Optical laboratory for characterization of lidar blocks (optics and electronics, lasers)</li></ul></td><td><ul><li>Computers</li><li>Internet connection</li><li>Storage capability for QA annotation in machine readable format</li><li>Software (general lidar data analysis software (elastic inversion, Raman inversion, linear and circular depolarisation ratio) adaptable to all possible raw data formats, but especially SCC format.</li><li>Teleconference tools</li></ul></td></tr><tr><th>ALC</th><td><ul><li>Outdoor laboratories with enough capacity (electrical power, space) to simultaneously operate further 5-10 other low power lidars during campaigns and permission to operate the</li></ul></td><td><ul><li>Reference lidar(s) which <ul><li>covers the wavelength range of the low-power lidars,</li><li>with depolarization option</li></ul></li></ul></td><td><ul><li>Computer infrastructure for statistical error retrievals</li><li>Sufficient internet bandwidth and data storage and</li></ul></td></tr></tbody></table>
# 6 Requirements for the Centre for Aerosol Remote Sensing

## 6.1 General requirements

In order to be labelled as the Centre for Aerosol Remote Sensing, the candidate shall:

* Commit for long-term operation, at least 10 years starting with the next year after the implementation as a CF,

* Set-up an appropriate structure of Units, to ensure an adequate functionality of the CF, cost-effective operation, and scalability with respect to the user demands and advancement of the state-of-the art technology,

* Demonstrate the capacity (in terms of material and personnel resources), to ensure the provision of the needed services and operation support, as described in section 6.2

* Provide a feasible implementation and operation plan for the first five years, starting with the next year after the selection as CF,

* Commit to provide a minimum amount of user services, as described in section 4

* Commit to provide the mandatory operation support to the ACTRIS NFs, as described in section 3.

## 6.2 Technical requirements

### 6.2.1 Facilities

In view of the operation support and service provision CARS should have / put in place:

<table><thead><tr><th></th><th>Spaces</th><th>Instrumentation</th><th>IT infrastructure</th></tr></thead><tbody><tr><th>AHL</th><td><ul><li>Indoor laboratories: at least 50 m² air temperature stabilized lidar operation lab with access to sky (roof window) for two lidar systems; at least 30 m² air temperature stabilized optical lab with at least 10 m² clean room cabin ISO 6; at least 20 m² electronic lab; All with water supply, electrical power line filter and electrical grounding.</li><li>Outdoor space to simultaneously operate at least 3 lidar systems, power supply and internet connection;</li></ul></td><td><ul><li>At least 1 lidar (3 beta + 2 alpha + 3 delta), dynamic range 200 m to 20 km; complemented by ancillary instrumentation (meteorology)</li><li>At least 3 mobile lidars (3 beta + 2 alpha + 3 delta), dynamic range 200 m to 15 km</li><li>Optical laboratory for characterization of lidar blocks (optics and electronics, lasers)</li></ul></td><td><ul><li>Computers</li><li>Internet connection</li><li>Storage capability for QA annotation in machine readable format</li><li>Software (general lidar data analysis software (elastic inversion, Raman inversion, linear and circular depolarisation ratio) adaptable to all possible raw data formats, but especially SCC format.</li><li>Teleconference tools</li></ul></td></tr><tr><th>ALC</th><td><ul><li>Outdoor laboratories with enough capacity (electrical power, space) to simultaneously operate further 5-10 other low power lidars during campaigns and permission to operate the</li></ul></td><td><ul><li>Reference lidar(s) which <ul><li>covers the wavelength range of the low-power lidars,</li><li>with depolarization option</li></ul></li></ul></td><td><ul><li>Computer infrastructure for statistical error retrievals</li><li>Sufficient internet bandwidth and data storage and</li></ul></td></tr></tbody></table>
<table><tr><td></td><td>reference lidar(s) and test instruments (eye safety issues) and additional (reference and ancillary) instrumentation<ul><li>Offices (at least for 2 people)</li><li>Meeting room for training purposes (at least for 10 people)</li></ul></td><td><ul><li>is fully certified as ACTRIS high-power lidar</li><li>covers an altitude range between lower ABL and tropopause</li><li>operated continuously</li><li>Ancillary measurements<ul><li>Sun/moon photometer which covers the wavelength range of the low-power lidars.</li><li>Water vapour profile measurements</li></ul></li><li>At least 1 (better two) of the most commonly used types of low-power lidars</li></ul></td><td>processing capacities.</td></tr><tr><td>ASP</td><td><ul><li>Outdoor laboratories: platforms (4) for transferring sun-calibration and performing functional tests:<ul><li>one at high-altitude (with easy access)</li><li>2 at medium-altitude</li><li>all with clean atmospheric situation and good weather conditions</li><li>geographically distributed in N and S Europe</li></ul></li><li>Indoor laboratories (3) for characterization, maintenance and repair, calibration in radiance and polarization and control of sensitivity to temperature</li><li>Offices / meeting rooms (at least for 10 people)</li></ul></td><td><ul><li>Reference sun/sky/moon photometers to enable calibration transfer, by 3 lines, of about 10 x (robot + data logger) each, to receive field instruments to be calibrated in AOD (absolute error &lt; 0.01) and tested</li><li>At least one calibrated integrating spheres for sky radiance calibration (relative error &lt; 3%)</li><li>Specific linear polarizing system to calibrate polarization (absolute error &lt; 0.005)</li><li>Thermal chambers to measure temperature sensitivity</li><li>Solar simulator to adjust solar tracking system</li><li>Mobile reference photometer for internal and external radiance traceability between calibration</li><li>Spectrometers to control filter transmission</li></ul></td><td><ul><li>Dedicated data storage and computing capacities</li></ul></td></tr></table>
<table><tr><td></td><td>reference lidar(s) and test instruments (eye safety issues) and additional (reference and ancillary) instrumentation<ul><li>Offices (at least for 2 people)</li><li>Meeting room for training purposes (at least for 10 people)</li></ul></td><td><ul><li>is fully certified as ACTRIS high-power lidar</li><li>covers an altitude range between lower ABL and tropopause</li><li>operated continuously</li><li>Ancillary measurements<ul><li>Sun/moon photometer which covers the wavelength range of the low-power lidars.</li><li>Water vapour profile measurements</li></ul></li><li>At least 1 (better two) of the most commonly used types of low-power lidars</li></ul></td><td>processing capacities.</td></tr><tr><td>ASP</td><td><ul><li>Outdoor laboratories: platforms (4) for transferring sun-calibration and performing functional tests:<ul><li>one at high-altitude (with easy access)</li><li>2 at medium-altitude</li><li>all with clean atmospheric situation and good weather conditions</li><li>geographically distributed in N and S Europe</li></ul></li><li>Indoor laboratories (3) for characterization, maintenance and repair, calibration in radiance and polarization and control of sensitivity to temperature</li><li>Offices / meeting rooms (at least for 10 people)</li></ul></td><td><ul><li>Reference sun/sky/moon photometers to enable calibration transfer, by 3 lines, of about 10 x (robot + data logger) each, to receive field instruments to be calibrated in AOD (absolute error &lt; 0.01) and tested</li><li>At least one calibrated integrating spheres for sky radiance calibration (relative error &lt; 3%)</li><li>Specific linear polarizing system to calibrate polarization (absolute error &lt; 0.005)</li><li>Thermal chambers to measure temperature sensitivity</li><li>Solar simulator to adjust solar tracking system</li><li>Mobile reference photometer for internal and external radiance traceability between calibration</li><li>Spectrometers to control filter transmission</li></ul></td><td><ul><li>Dedicated data storage and computing capacities</li></ul></td></tr></table>
<table><tr><td></td><td><ul><li>A dedicated set of reference mobile sun/sky/moon photometers to be involved in field campaign or inter-comparison exercises</li><li>Sky-imager and lidar as complementary instruments</li></ul></td><td></td></tr></table>

## 6.2.1 Human resources

In view of the operation support and service provision CARS should have / employ:

<table><thead><tr><th rowspan="2"></th><th colspan="3">Scientific & technical staff</th><th colspan="3">Management & administration staff</th></tr><tr><th>Scientific expert</th><th>Qualified operator</th><th>Technician</th><th>Expert manager</th><th>Qualified officer</th><th>Administrative assistant</th></tr></thead><tbody><tr><th>AHL</th><td>5</td><td>3</td><td>2</td><td>0.75</td><td>0.75</td><td></td></tr><tr><th>ALC</th><td>1</td><td>2</td><td>0.5</td><td>0.25</td><td>0.25</td><td></td></tr><tr><th>ASP</th><td>2</td><td>4</td><td>2.5</td><td>0.75</td><td>0.25</td><td></td></tr></tbody></table>

The estimation of the needed human resource has been performed on the basis of the proposed activities and of the ACTRIS-2 and national efforts (reference year =2016). Numbers are expressed in FTE units.

The scientific and technical staff should have the necessary expertise to operate the facilities, instruments and IT infrastructure of CARS at the state of the art, and to develop and provide the operation support and services described above. As a minimum they should have:

* expert scientists: >5 years of experience in related field

* engineer/qualified operator/engineer: >3 years of experience

* technician: > 1 year of experience

* expert manager, qualified officer, and administrative assistance: at least 3 years of experience in the administrative area.

## 6.2.2 Other requirements

The improvement of the retrieval algorithms for the ASPs, ALCs, AHLs synergies by CARS, requires in addition from other CFs, the following:

* Easy access to cloud-free QC SCC level 1 data

* Water vapour profiles as ancillary data to analyse atmospheric situation.

* Back-trajectories associated to each retrieval
<table><tr><td></td><td><ul><li>A dedicated set of reference mobile sun/sky/moon photometers to be involved in field campaign or inter-comparison exercises</li><li>Sky-imager and lidar as complementary instruments</li></ul></td><td></td></tr></table>

## 6.2.1 Human resources

In view of the operation support and service provision CARS should have / employ:

<table><thead><tr><th rowspan="2"></th><th colspan="3">Scientific & technical staff</th><th colspan="3">Management & administration staff</th></tr><tr><th>Scientific expert</th><th>Qualified operator</th><th>Technician</th><th>Expert manager</th><th>Qualified officer</th><th>Administrative assistant</th></tr></thead><tbody><tr><th>AHL</th><td>5</td><td>3</td><td>2</td><td>0.75</td><td>0.75</td><td></td></tr><tr><th>ALC</th><td>1</td><td>2</td><td>0.5</td><td>0.25</td><td>0.25</td><td></td></tr><tr><th>ASP</th><td>2</td><td>4</td><td>2.5</td><td>0.75</td><td>0.25</td><td></td></tr></tbody></table>

The estimation of the needed human resource has been performed on the basis of the proposed activities and of the ACTRIS-2 and national efforts (reference year =2016). Numbers are expressed in FTE units.

The scientific and technical staff should have the necessary expertise to operate the facilities, instruments and IT infrastructure of CARS at the state of the art, and to develop and provide the operation support and services described above. As a minimum they should have:

* expert scientists: >5 years of experience in related field

* engineer/qualified operator/engineer: >3 years of experience

* technician: > 1 year of experience

* expert manager, qualified officer, and administrative assistance: at least 3 years of experience in the administrative area.

## 6.2.2 Other requirements

The improvement of the retrieval algorithms for the ASPs, ALCs, AHLs synergies by CARS, requires in addition from other CFs, the following:

* Easy access to cloud-free QC SCC level 1 data

* Water vapour profiles as ancillary data to analyse atmospheric situation.

* Back-trajectories associated to each retrieval
# 7 Basic criteria for the selection of the Centre for Aerosol Remote Sensing

The applications to host the Centre for Aerosol Remote Sensing are evaluated against a set of criteria covering:

* The level of commitment for long-term operation

* The capacity to provide the operational support and the services described in sections 3 and 4

* The availability of the necessary laboratories, instruments, equipment

* The availability of human resources (no., expertise)

* The efficiency in providing the operational support and the services

* The feasibility of the implementation plan (costs, resources, timeline)

* The feasibility of the operation plan (methodology, costs per service)

* The level of maturity

* Status of the development of the Units

* No. of existing users

* Adequacy of the decision-making

* Risk management strategy

These criteria will be detailed in the associated call documents.

# 8 Obligations of the Centre for Aerosol Remote Sensing

## 8.1 General obligations

The following general obligations shall apply to the Centre for Aerosol Remote Sensing while operational:

* To organize its activities in a cost-efficient way, timely, and with high quality,

* To actively participate in the governance and sustainable development of ACTRIS,

* To provide services to users, according to the access procedures, availability of time, and material resources,

* To provide operation support to the NFs, according to the identified needs, agreed schedules, and procedures,

* To implement efficient user interaction activities by:

* Organizing workshops, to interact with users,

* Collecting user feed-backs,

* Maintaining the CF and ACTRIS websites,

* To document its activities, accesses provided, key performance indicators, and finances, and provide this information to the HO,

* To contribute to minimize and assess the uncertainties related to data and data products, according to their role and in collaboration with each other.

## 8.2 Technical obligations

### 8.2.1 Technical obligations in relation with the ACTRIS National Facilities

Technical obligations of the Centre for Aerosol Remote Sensing in relation with the ACTRIS National Facilities refer strictly to the measurement techniques described in this concept document and in *Technical concepts and requirements for ACTRIS Observational Platforms*. The operation of other techniques at the NFs does not imply a technical obligation for the Centre for Aerosol Remote Sensing to provide operation support. New techniques / instrument types are only accepted as ACTRIS instruments
# 7 Basic criteria for the selection of the Centre for Aerosol Remote Sensing

The applications to host the Centre for Aerosol Remote Sensing are evaluated against a set of criteria covering:

* The level of commitment for long-term operation

* The capacity to provide the operational support and the services described in sections 3 and 4

* The availability of the necessary laboratories, instruments, equipment

* The availability of human resources (no., expertise)

* The efficiency in providing the operational support and the services

* The feasibility of the implementation plan (costs, resources, timeline)

* The feasibility of the operation plan (methodology, costs per service)

* The level of maturity

* Status of the development of the Units

* No. of existing users

* Adequacy of the decision-making

* Risk management strategy

These criteria will be detailed in the associated call documents.

# 8 Obligations of the Centre for Aerosol Remote Sensing

## 8.1 General obligations

The following general obligations shall apply to the Centre for Aerosol Remote Sensing while operational:

* To organize its activities in a cost-efficient way, timely, and with high quality,

* To actively participate in the governance and sustainable development of ACTRIS,

* To provide services to users, according to the access procedures, availability of time, and material resources,

* To provide operation support to the NFs, according to the identified needs, agreed schedules, and procedures,

* To implement efficient user interaction activities by:

* Organizing workshops, to interact with users,

* Collecting user feed-backs,

* Maintaining the CF and ACTRIS websites,

* To document its activities, accesses provided, key performance indicators, and finances, and provide this information to the HO,

* To contribute to minimize and assess the uncertainties related to data and data products, according to their role and in collaboration with each other.

## 8.2 Technical obligations

### 8.2.1 Technical obligations in relation with the ACTRIS National Facilities

Technical obligations of the Centre for Aerosol Remote Sensing in relation with the ACTRIS National Facilities refer strictly to the measurement techniques described in this concept document and in *Technical concepts and requirements for ACTRIS Observational Platforms*. The operation of other techniques at the NFs does not imply a technical obligation for the Centre for Aerosol Remote Sensing to provide operation support. New techniques / instrument types are only accepted as ACTRIS instruments
after the approval of the RI Committee and after the development of the associated QA procedures by
the CF.

ACTRIS NFs are responsible for controlling the quality of their measurements by:

a) Applying the SOPs and QA procedures, and using in a proper manner the in-house check-up tools developed by CARS

b) Participating to all scheduled QA activities described in Annex: Provision of the operation support - Scheduled support

c) Notifying CARS, and requesting access to specialized services described in Annex: Provision of the operation support - Operation support on request, whenever the instrument is not performing well or a major upgrade has been made

CARS, on the other hand, is responsible to provide the mandatory operation support to all corresponding
NFs, and maintain a continuous collaboration with the operators and scientists at the NFs, in order to
facilitate the control of the measurements quality.

8.2.1.1 Guidelines, quality assurance criteria and procedures

The Centre for Aerosol Remote Sensing is responsible for the quality assurance procedures and guidelines of the ACTRIS measurements conducted at the NFs (high and low power aerosol lidars, sun/sky/lunar photometers). For this, CARS should implement the following operation support for each of the measurement technique under its topics:

* Definition and establishment of standard operation procedures (as described in section 3.4.1)

* Definition of measurement quality-assurance criteria and procedures (as described in section 3.4.2)

All the procedures, guidelines, quality assurance criteria, plausibility tests, etc. should be documented and accessible to all related NFs. Specific training sessions with the related NF operators should be organized to ensure a smooth and correct implementation of the above.

8.2.1.2 Tools, tests and consultancy for quality control of the measurements

It is duty of the Centre for Aerosol Remote Sensing to assist the related NFs in the quality control of their
measurements by providing the following operation support for each of the measurement techniques
under its topics:

* Development and provision of instrument-specific calibration (as described in section 3.4.3)

* Development and provision of in-house check-up tools (as described in section 3.4.4)

* Development of data evaluation procedures and plausibility test (as described in section 3.4.5)

* Consultancy for setting-up new observational or exploratory platforms and new instruments at the NFs (as described in sections 3.5.2)

* Testing of new measurement instruments and procedures (as described in sections 3.6.1)

This operation support should be offered to the related NFs whenever there is a need, or a significant
progress in the development of these tools, and accompanied by the appropriate training.

8.2.1.3 Assessment of performances, measurement flagging

The Centre for Aerosol Remote Sensing is mandated to assist the Data Centre and the related NFs in the
quality control of the measurements and data, by:

* Realization of observational site performance audits with reference samples or mobile systems (as described in section 3.4.6)
after the approval of the RI Committee and after the development of the associated QA procedures by
the CF.

ACTRIS NFs are responsible for controlling the quality of their measurements by:

a) Applying the SOPs and QA procedures, and using in a proper manner the in-house check-up tools developed by CARS

b) Participating to all scheduled QA activities described in Annex: Provision of the operation support - Scheduled support

c) Notifying CARS, and requesting access to specialized services described in Annex: Provision of the operation support - Operation support on request, whenever the instrument is not performing well or a major upgrade has been made

CARS, on the other hand, is responsible to provide the mandatory operation support to all corresponding
NFs, and maintain a continuous collaboration with the operators and scientists at the NFs, in order to
facilitate the control of the measurements quality.

8.2.1.1 Guidelines, quality assurance criteria and procedures

The Centre for Aerosol Remote Sensing is responsible for the quality assurance procedures and guidelines of the ACTRIS measurements conducted at the NFs (high and low power aerosol lidars, sun/sky/lunar photometers). For this, CARS should implement the following operation support for each of the measurement technique under its topics:

* Definition and establishment of standard operation procedures (as described in section 3.4.1)

* Definition of measurement quality-assurance criteria and procedures (as described in section 3.4.2)

All the procedures, guidelines, quality assurance criteria, plausibility tests, etc. should be documented and accessible to all related NFs. Specific training sessions with the related NF operators should be organized to ensure a smooth and correct implementation of the above.

8.2.1.2 Tools, tests and consultancy for quality control of the measurements

It is duty of the Centre for Aerosol Remote Sensing to assist the related NFs in the quality control of their
measurements by providing the following operation support for each of the measurement techniques
under its topics:

* Development and provision of instrument-specific calibration (as described in section 3.4.3)

* Development and provision of in-house check-up tools (as described in section 3.4.4)

* Development of data evaluation procedures and plausibility test (as described in section 3.4.5)

* Consultancy for setting-up new observational or exploratory platforms and new instruments at the NFs (as described in sections 3.5.2)

* Testing of new measurement instruments and procedures (as described in sections 3.6.1)

This operation support should be offered to the related NFs whenever there is a need, or a significant
progress in the development of these tools, and accompanied by the appropriate training.

8.2.1.3 Assessment of performances, measurement flagging

The Centre for Aerosol Remote Sensing is mandated to assist the Data Centre and the related NFs in the
quality control of the measurements and data, by:

* Realization of observational site performance audits with reference samples or mobile systems (as described in section 3.4.6)
* Organizing regular exercises to assess the performances of the NFs, including instrument performance workshops (as described in section 3.4.7)

* Contributing to documentation and traceability of level 0 to level 3 data products (as described in section 3.4.8)

The activities involving directly the NFs operating high and low power lidars, sun/sky/lunar photometers should be scheduled by CARS and provided regularly. The corresponding NFs should participate in these activities according to the plan proposed by the Centre for Aerosol Remote Sensing and agreed together with the ACTRIS Scientific Advisory Board (SAB).

### 8.2.1.4 Transfer of knowledge and training

In addition to the training organized for the implementation of guidelines, procedures, and tools developed in support of the quality control of the measurements, the Centre for Aerosol Remote Sensing should organize training sessions with the NFs operating high and low power lidars, sun/sky/lunar photometers as needed (see sections 3.5.1).

### 8.2.1.5 Improvement of measurement methodologies for aerosol remote sensing

Although it is not an obligation, the Centre for Aerosol Remote Sensing should work to sustain a high level of performance and to stimulate the advancement of new techniques and methodologies in the aerosol remote sensing field by:

* Development of strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime (as described in sections 3.6.1)

* Development of new technological products and methods (as described in sections 3.6.3)

* Development of retrieval algorithms or tools for producing level 1 to 3 data, including the exploitation of instrument synergies (as described in section 3.6.4)

* Organizing regular events (at least once at 2 years) and other forums, in order to exchange knowledge with the NFs and other scientists

* Contributing to CEN, ISO, or similar standardization activities (as described in section 3.4.9)

## 8.2.2 Technical obligations in relation with the ACTRIS Data Centre

The following general share of responsibilities between the Centre for Aerosol Remote Sensing and the ACTRIS Data Centre applies:

<table><thead><tr><td>Responsibilities at CARS</td><td>Responsibilities at ACTRIS DC</td></tr></thead><tbody><tr><td>The Centre for Aerosol Remote Sensing is responsible for developing and facilitating the implementation of the QA/QC procedures and tools at the ACTRIS NFs operating high- and low-power aerosol lidars and automatic sun/sky/polarized/lunar photometers, in order to allow the respective NFs to keep control on the quality of their measurements (level 0 data)</td><td>ACTRIS Data Centre is responsible for the QC of the ACTRIS data produced from the respective measurements (level 1 to level 3 data), which are made available through the ACTRIS data portal</td></tr><tr><td>The Centre for Aerosol Remote Sensing is responsible for auditing the ACTRIS NFs operating high- and low-power aerosol lidars</td><td>ACTRIS Data Centre is responsible for the traceability and full documentation of the data quality of the ACTRIS data produced by</td></tr></tbody></table>
* Organizing regular exercises to assess the performances of the NFs, including instrument performance workshops (as described in section 3.4.7)

* Contributing to documentation and traceability of level 0 to level 3 data products (as described in section 3.4.8)

The activities involving directly the NFs operating high and low power lidars, sun/sky/lunar photometers should be scheduled by CARS and provided regularly. The corresponding NFs should participate in these activities according to the plan proposed by the Centre for Aerosol Remote Sensing and agreed together with the ACTRIS Scientific Advisory Board (SAB).

### 8.2.1.4 Transfer of knowledge and training

In addition to the training organized for the implementation of guidelines, procedures, and tools developed in support of the quality control of the measurements, the Centre for Aerosol Remote Sensing should organize training sessions with the NFs operating high and low power lidars, sun/sky/lunar photometers as needed (see sections 3.5.1).

### 8.2.1.5 Improvement of measurement methodologies for aerosol remote sensing

Although it is not an obligation, the Centre for Aerosol Remote Sensing should work to sustain a high level of performance and to stimulate the advancement of new techniques and methodologies in the aerosol remote sensing field by:

* Development of strategies to increase the duty cycle of instruments operated at the NFs, to reduce breakdown and maintenance downtime (as described in sections 3.6.1)

* Development of new technological products and methods (as described in sections 3.6.3)

* Development of retrieval algorithms or tools for producing level 1 to 3 data, including the exploitation of instrument synergies (as described in section 3.6.4)

* Organizing regular events (at least once at 2 years) and other forums, in order to exchange knowledge with the NFs and other scientists

* Contributing to CEN, ISO, or similar standardization activities (as described in section 3.4.9)

## 8.2.2 Technical obligations in relation with the ACTRIS Data Centre

The following general share of responsibilities between the Centre for Aerosol Remote Sensing and the ACTRIS Data Centre applies:

<table><thead><tr><td>Responsibilities at CARS</td><td>Responsibilities at ACTRIS DC</td></tr></thead><tbody><tr><td>The Centre for Aerosol Remote Sensing is responsible for developing and facilitating the implementation of the QA/QC procedures and tools at the ACTRIS NFs operating high- and low-power aerosol lidars and automatic sun/sky/polarized/lunar photometers, in order to allow the respective NFs to keep control on the quality of their measurements (level 0 data)</td><td>ACTRIS Data Centre is responsible for the QC of the ACTRIS data produced from the respective measurements (level 1 to level 3 data), which are made available through the ACTRIS data portal</td></tr><tr><td>The Centre for Aerosol Remote Sensing is responsible for auditing the ACTRIS NFs operating high- and low-power aerosol lidars</td><td>ACTRIS Data Centre is responsible for the traceability and full documentation of the data quality of the ACTRIS data produced by</td></tr></tbody></table>