Table of Contents

Workshop introduction by Anthony Illingworth

3

Executive Summary

4

Validation Workshop - Session Reports

11

Introduction Session

11

Session 1: ATLID Level 1 and Aerosol product validation

18

ATLID Level 1 Product Validation

19

Aerosol Product Validation

20

Session 2: Observational networks

22

Session 3: Cloud and Precipitation product validation

25

Session 4: Validation Campaigns

31

Session 5: Radiation, and BBR Level 1 and MSI level 1 product validation

38

Session 6: Use of models for validation

41

Workshop introduction by Anthony Illingworth(Emeritus Professor at University of Reading, EarthCARE European Mission Advisory Group Chair)

The launch of the EarthCARE mission is foreseen for March 2023, as all of its four advanced
instruments have now been mounted on the satellite and are undergoing system tests. Two ofthese instruments use an active measurement technique, namely high-spectral-resolution LIDAR
at 355 nm in case of the ATmospheric LIDar (ATLID), and Dopplerised RADAR operating at 94GHz
for the Cloud Profiling Radar (CPR). This active sensing payload is complemented with passive
remote sensing instrumentation, namely the Multi-Spectral Imager (MSI) and the Broad Band
Radiometer (BBR). This specific combination of instruments is aimed at providing unprecedented
insight into the vertical structure of clouds, precipitation, aerosols, and radiative properties in theatmosphere. The validation of the complex and numerous synergistic geophysical retrievals
involved is in turn a daunting task, which requires preparation. As part of this preparation, thus
far 2 workshops have been organised and the present report addresses the recent second ESA
EarthCARE Validation Workshop.
The objectives of this 2nd ESA EarthCARE Validation Workshop were as follows:-

Fostering interactions between the algorithm developers and the validation team.

-Discuss and optimize validation approaches and methods-

Broaden international collaboration beyond the ESA and JAXA validation teams.

All presentations are available at the workshop website:
https://earthcare-val.esa.int/display/EEVP/2nd+ESA+EarthCARE+Validation+Workshop
These extensive presentations and the conclusions drawn from them provide a well-defined road map
for the activities that are needed before the EarthCARE launch.
As the ongoing pandemic required that the workshop was organised as an online event, the decision
was taken to collect inputs from validation teams and from algorithm developers in advance, andexchange this information prior to the workshop. This information was also used by the co-chairs tofoster exchanges during the interactive sessions of the workshop. The workshop was attended by 248
participants.

Executive Summary
The (chronologically) last session of the workshop consisted of summaries of earlier sessions and a
final interactive discussion, followed by closing thoughts by Anthony Illingworth. For the readers’convenience, these summaries are moved forward in this report in the form of the present executive
summary, prior to detailed reporting on each of the domain-specific sessions in the full report.
Validation of the EarthCARE mission is an unprecedented challenge, as it has many data products (44products produced by ESA and various others provided by JAXA) which cover a broad range of
geophysical domains. A further complicating factor is the synergistic manner in which some of theseproducts are generated. In addition the narrow swath of both active instruments presents challenges
of its own, as does the dependence of the measured signals on microphysical properties of theparticles along the beam, that cannot be characterised by remote sensing alone.
A few examples of focal areas for validation effort are aerosol type and size distributions, mixtures ofaerosols, hydrometeor phase and size, ice-crystal characteristics at the cloud top, snowfall in highlatitutes, persistent deep layer of super-cooled water at cloud top, and many many more.
As for resources, by now there is a dense coverage by the various networks and stations, with mostoperating 24/7 with well-established quality control. Airborne measurements are of pivotal
importance especially for EarthCARE, but very expensive.
Focussing on the first stage of validation, namely the commissioning phase, it is important to take into
account the lessons learned from Cloudsat and CALIPSO on the importance of airborne validation
measurements early on. The optimal flight configuration for such campaigns involves tandem flights
along the ground track where one high-level aircraft with the same instruments as the satellite is flying
above an aircraft equipped with in-situ sensors for cloud and aerosol particle characterisation. During
the workshop the significant overlap was highlighted between the needs of EarthCARE in-orbit
validation and the AtmOS (ACCP) sub-orbital component activities that are needed prior to the launchof the AtmOS orbital component.
Of the many lessons learned of, among others, the Aeolus mission, the importance of earliest possible
release of preliminary data to the validation teams stands out. It cannot be stressed enough how much
benefit has been derived from many independent ‘eyes’ looking at these not-yet-consolidated
products. Also the benefits of monitoring of biases and variability in the deviations between lidar andradar observations and corresponding background values from the ECMWF IFS (and hopefully soonCAMS) models has been a lesson learned that should be taken to heart and if possible expanded toinclude even Doppler and MSI/BBR.
Discussions were numerous but highlighted the general need to coordinate the approaches andcommon practices, and to foster collaboration and build bridges to related missions and projects inthe field of aerosol, cloud, precipitation, and radiation observations studies. Another common threadin all sessions was the difficulty of many teams to obtain funding, with prospects for improvement
now that launch date confidence has markedly improved, which in turn should facilitate interactionsof Principal Investigators and ESA with national funding agencies. There was a general request foraccess to Algorithm Theoretical Baselines of level 1 and level 2 products, and a general need for aprocess to identify priority areas and regions for further validation activities.
The following is a compilation of session-specific highlights, recommendations, and open issues aspresented during the closing session. The order is identical to the detailed session reports in the next
part of this report, which in turn matches the chronology of the actual workshop sessions.

ATLID Level 1 product validation
Highlights:●●●

Ground and Space-based ATBs (attenuated backscatter coefficient profiles) can not be directlycompared. In order to validate the L1 ATBs, it will be necessary to use terrestrial based L2
products as a basis for “simulating” the corresponding ATLID ATB profiles (theGround/Aircraft-L1-L2-Space-L1 approach).
Monitoring of ATLID L1 signals by the Met centers (e.g. ECMWF) will be useful. This will build
on efforts now coming on-line for Aeolus.
Fast feedback from and to the Developer, Cal/Val, and Instrument teams will be necessary
especially in the early stages of the mission. For Aeolus, the Cal/Val Wiki was found to be
essential for facilitating rapid communication/feedback.

Recommendations:
●
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L1 ATBD as well as L1 (and L2) test data should be provided to the Cal/Val community as soon
as this year.
Simulated L1 ATLID ATBs from ground-based measurements should be reported in the Cal/Val
data base together with the terrestrial based signals and their inversion products.
The Simulation of L1 ATLID signals using terrestrial (ground/air) lidar data should be done in acoordinated manner. It should be up to the large networks to deal with that issue (e.g. setting
up protocols) as well as setting sensible quality-control standards which can even be adopted
by operators not in the networks. It is strongly recommended that ESA support the networks
in this aspect. At the very least, a “How-to/best-practices” document including all required
ATLID info should be formulated !
Measurements at 355 nm will be prioritized. However, data at other wavelengths can be
useful as well. Data from visible + IR wavelengths can be very useful for validating ATLID
sensitivities as they are good for detecting thin cloud and aerosol boundaries (less Rayleigh
Scattering than at 355n m). Using multi-wavelength systems (+photometers) for aerosol
typing is considered very useful as well as using data bases, as e.g., LIVAS, to transformmeasurements at no-EarthCARE wavelengths to 355 nm..

Further Improvements and needs:●●

Coordination between the networks and ESA including the Cal/Val data center likely needs tobe made more concrete.
The recommendations specified in the previous section should be followed. In particular the
Simulation of L1 ATLID signals should be done in a coordinated manner, for example by thenetworks, and it is recommended that ESA supports the networks, with at least supplying a“How-to/best-practices” to the Cal/Val community. Networks should also harmonise setting
sensible quality-control standards which can even be adopted by operators not in the
networks.

Aerosol product validation
Highlights:
Seven different parameters which need to be validated were discussed (Cloud-discrimination,
layering, extinction/backscatter/AOD (355, 670, 865), depolarization, lidar ratio, Angstrom, aerosol
typing )Recommendations:●●●●

If possible, Lidar systems should be upgraded to include a 355 nm channel (incl. depolarization
capabilities) for validation of EarthCARE & Aeolus.
Other wavelengths (532, 1064nm) can be used for many comparisons, however take care anddescribe how the wavelength conversion is performed.
Having early information on the orbit will advise on network design, e.g. in setting up of
specific stations dedicated for EarthCARE
Campaign data sets can already be used for validation exercises (i.e. HSRL-2, 2021 Tropical
Campaign, NARVAL/NARPEX, STRATEOL, A-LIFE, LOAC).

Further Improvements and needs:●●●

HETEAC is the aerosol model used by the L2 algorithms and needs validation (before and after
launch; especially with airborne in-situ). There is need for information on HETEAC, adescription will be provided soon by the developers.
Common practice has to be documented and shared as well as how the retrievals/profiles
were compared; i.e. For stations that do not belong to any network, quality control
procedures can be based on ACTRIS practice if not yet defined.
The publications of the EarthCARE Level 2 algorithms will be ready by mid 2022 and are eagerly
awaited by the validation teams.

Observational Networks
Highlights:
Continental and global networks have well-established QA/QC procedures, well-defined products andcentral processing chains with NRT capabilities (ACTRIS/EARLINET, AERONET, ACTRIS/Cloudnet,
MPLNET, AD-Net, SKYNET, LALINET…).

Recommendations:●●●●Intercomparisons between the networks should be made using the approach which is mostfeasible (field campaigns, collocated sites, aircraft overflights).
Harmonization of the approaches for EC Cal/Val (collocation criteria, L3 products, statistical
approaches, targets, -conversion…) need to be fostered.
QA/QC support to single stations needs to be provided (access to calibration centres, provision
of QA and processing tools)
It was strongly recommended to include the ARM sites in the EarthCARE Cal/Val.

Therefore it was supposed to collect opportunities for EarthCARE Cal/Val after the workshop andmake this information available.
Further improvements and needs:●●●

Possible improvements of the network strategies and Cal/Val products with respect to makeuse of additional observations for homogeneity and representativity checks (e.g. E-PROFILE,
scanning systems…). Furthermore, it was recommended for the networks to use longobservation periods around overpasses together with trajectory analysis to improvecomparability. Finally, it was highlighted that priority geolocations need to be defined andobservational gaps need to be closed by establishing additional sites or deploying mobile
facilities
Need of fast access to meteorological data for NRT processing, possibility to use X-MET
product
Need of interaction between the network data centres and EVDC to agree on data flows andharvesting of (meta)data

A meeting between ESA atmospheric Validation Data Centre and PIs was announced to be plannedin the near future and was seen as essential by the network PI’s.

Clouds & Precipitation (& CPR L2a) Validation
Highlights:
The community has a wealth of experience from CloudSat/CALIPSO/MODIS and their validation. The
ground networks are mature, advanced and have stable funding. There is strong overlap between the
EarthCARE and AtmOS pre-launch sub-orbital activities.
Recommendations:●●

Validation of cloud-base estimated from EarthCARE synergy (AC-TC) using networks of groundbased ceilometers and lidars.
Validation of EarthCARE detection (AC-TC) and retrieved microphysics (C-CLD, ACM-CAP) of liquid,
supercooled and mixed-phase cloud using ground-based radar-lidar retrievals, and complemented
by microwave radiometers and/or dual-frequency radar techniques to constrain estimates ofliquid water content.

●

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Insights from multiple-frequency Doppler radars in ground-based and airborne configurations
should be used for ongoing development, evaluation and inter-comparison of cloud andprecipitation retrieval algorithms.
Multiple-frequency radar techniques for constraining the vertical distribution of liquid cloud water
should be developed and evaluated, for use in validating EarthCARE’s synergistic blind zones.
Provide to ESA recommendations and requirements for a commissioning phase aircraft campaign,
including: (a) when to fly within the constraints of the commissioning of EarthCARE instruments
and the possibility of short launch delays; (b) required aircraft instrumentation and flight strategy;and (c) locations and regimes to target.
Coordination on standard procedures for accounting for gaseous, water vapour and liquid water
attenuation from ground-based radars.
Development of tools for transforming between downward- and upward-looking remote sensors
for statistical validation against ground-based networks.
Use ground-based and ship-based microphysical measurements to inform spatio-seasonal changes
in cloud and precipitation microphysical assumptions.
Aircraft remote-sensing with hyperspectral and microwave radiometers in addition to EarthCARElike payloads will be essential to validating the consistent representation of ice microphysics acrossthe spectrum, as well as to assessing the MSI smile effect. Ground-based stations withcomplementary radiation measurements should also be used for validating surface fluxes andheating rates.

Further improvements and needs:●●●

The target classification from active ATLID/CPR synergy suffers from blind zones (e.g. cloudbase, liquid & mixed-phase cloud), with impacts on downstream retrievals including radiation.
There are uncertainties in ice and snow microphysical properties & scattering acrossregions/regimes, and across wavelengths. There is a need for ongoing (perennial) in-situ
measurements.
Cloud & precipitation over the ocean is both of critical importance and difficult to validate(especially rain retrievals leveraging CPR ocean surface return).

Validation Campaigns
Highlights:
Many well characterized airborne (remote sensing and in-situ) and ground-based (incl. mobile
platforms) facilities with well established QA/QC procedures exist. The capability of these facilities for
EC Cal/Val has been proven in pre-launch campaigns for very different aspects and strategies forintercomparison of the different measurements have been developed. Quite a few planned campaigns(in different stages of maturity) have been identified which can serve for EC Cal/Val: E.g., two
integrated campaigns with airborne/ground-based and additional activities with balloons, UVAs andground-stations.
Recommendations:

●
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The potential of combining multiple aircrafts with remote sensing and in-situ instrumentation
should be addressed.
The combination of measurements with lidars and radars at complementary wavelengths isseen as very useful and should be supported. While clearly the EC wavelengths/frequencies
are favored.
Ground-based (campaign and network/permanent sites) and airborne measurements should
be synchronized or combined to use the full synergy of these instruments for EC Cal/Val. In
this way, the products from the different platforms can be intercompared andrepresentativeness of the platform products can be investigated.
Combining remote sensing and in-situ measurements should be done because it is very
powerful. In-situ measurements alone are not favored as the context to the EC products is
missing.
Mobile facilities (some of them are available on demand) should be used to close the gap in
the global observations. Especially, shipborne platforms (there are quite a few RV which canboard remote sensing) should not be forgotten which might be exploited for EC cal/val to close
the observational gaps over the oceans.
L2 algorithms should be brought together with real measurements (previous and scheduled).
This also means to foster the exchange between the different teams.
Teaming up with the ATMOS initiative is seen as very beneficial for both sides.

Further improvements and needs:●●●

Bringing “everything” together is seen as key. The communication between the different PIs
need to be established to combine efforts, e.g. in defining best measurement strategies andalso best locations.
It is still unclear how to deal with funding issues. Some proposed campaign activities arelacking secured funding and thus are yet very uncertain to take place.
Regarding the cal/val schedule of airborne activities, a gap at the beginning of the post-launch
mission was identified. If this is seen as crucial, the question arises how it could be filled. E.g.,
by ground-based measurements or if some opportunities for other airborne measurements
can be identified.

Radiation Product Validation
Highlights:●●●●

Established calibration procedures for MSI and BBR have been proposed
Importance of good communication with instrument providers is an important lesson learned
Importance of continuous monitoring of instrument performances and calibration, and to beready to adapt processing
The design of the BBR looks excellent, and implements solutions to the many problems
encountered on GERB.

Recommendations:

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●
●

Make more use of Invariant Calibration Targets: Rayleigh Calibration, Deep Convective Clouds,
Sun Glint, SST, (Pseudo) Invariant Calibration Sites (PICS) – and continue to do so during theentire mission lifetime
Agree on protocols/procedures/common approaches for comparisons with other Satellite L1
products
Use the moon as calibration target (if at all possible)

Further improvements and needs:
●
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●
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●

Possible improvements of Radiation Cal/Val activities
Establish/develop procedures for continuous monitoring of MSI and BBR L1 products
Develop a procedure for spectral characterisation of MSI bands after launch
Publish data about ground calibration sources (e.g. ground calibration source that should beclose to “science” scenes).
There is a need of access to housekeeping data data for instrument health analysis
Funding has not (yet) been secured for several proposals or partners-->need for discussion between ESA and PIs on instrumental data availability and applied
procedures

ModellingHighlights:●●●●

There are a number of models being used within the cal/val effort (instrument, radiativetransfer, dynamical models).
Data can be used to evaluate models in clever manners, e.g., forward simulators, sampling,statistics.
Methods, and models, could play a role in overall EarthCARE evaluation.
Data can also be used for operational models, e.g., assimilation of lidar, radar.

Suggestions/recommendations:●●●

Consider of use of cal/val data to augment EarthCARE observations for models
Coordinated modelling with campaigns, surface networks: reach out to modellers, AtmOS
Modelling Group as needed?
EarthCARE signal/product simulators to facilitate apple-to-apple model evaluation:
appropriate complexity needs to be considered.

Remaining main issues and further needs:●

Is EarthCARE cal/val data of interest to those evaluating and developing models. Reach out asneeded to groups.

Validation Workshop - Session Reports
In the following reports sections the individual sessions are reported in chronological order

Introduction Session

Title

Presenter

Chairs: A. Illingworth (U.Reading), U. Wandinger (TROPOS) , N. Clerbaux(RMIB)IntroductionMission
SystemWelcomeR. Koopman (ESA)

Workshop opening

D. Gillieron (ESA)& EarthCARE Status

D. Bernaerts (ESA)In-Orbit Characterization, Calibration and Verification of K. Wallace (ESA)BBR and MSI
In-Orbit Characterization, Calibration and Verification of G. Tzeremes (ESA)
ATLID
Chairs: Pavlos Kollias (Stony Brook U.), Luca Baldini (ISAC-CNR)
Algorithms

EarthCARE L2 Validation Needs of the ESA Products
and Algorithms

S. Mason (ECMWF)

Tools

ESA Atmospheric Validation Data Centre

A.M. Fjæraa (NILU)

Atmospheric Virtual Lab

S. Niemeijer (S&T)

E3SIM - EarthCARE Simulator

D. Donovan (KNMI)ICAROHS - Inter-Comparison of Aerosol Retrievals and G.J. van Zadelhoff
Observational Requirements for Multi(KNMI)
Wavelength HSRL Systems

Chairs: J. Fischer (FU Berlin), A. Battaglia (U.Leicester)
QA/QC

Quality Assurance for Earth Observation (QA4EO) concept
and example
J.C. Lambert (BIRA/IASB)
The power of monitoring EarthCARE observations at
ECMWF and preparing towards their assimilation.
M. Fielding (ECMWF)
Fiducial Reference Measurement concept
FRM4Radar Cloud Profiling for Satellite Validation

ECVT

and J. Von Bismarck(ESA)
L. Pfitzenmaier (IGMK)

Validation preparations timeline

New
EVID33 / AOID 51515 Validation of Atlid lidar data withprincipal
ground-based lidars in Northern Sweden
investigator
EVID34 / AOID 51949 WEGN4CARE - Validation ofs
EarthCARE cloud and precipitation products by theWegenerNet 3D Weather Research Facility inSoutheastern Austria

R. Koopman (ESA)

P. Völger (IRF)

G. Kirchengast and J.
Fuchsberger(WegCenter)

EVID35/AOID 60799 Validate Cloud Profiling Radar on
EarthCARE against Aircraft Observations of Cirriform
Cloud
V. Philips (INES)

Rob Koopman opened the introduction session by a brief overview of changes with respect to theprevious workshop, and thanking ESA colleagues Alain Lefebvre (former EarthCARE project manager)
and Damien Maeusli (former EarthCARE mission and system manager) and introduced their respective
successors, Dirk Bernaerts (PM) and Kotska Wallace (Optical payload and mission manager).
Dominique Gillieron explained the context in which EarthCARE is developed, in particular the ESA
Earth Observation programme in collaboration with European and global partners, and in particular
the Earth Explorer programme implementing new missions for scientific research. His presentation
also gave examples of Earth Explorer missions already in orbit, including Aeolus with its major impact
on numerical weather prediction.
Dirk Bernaerts addressed the status of the EarthCARE mission, payload, and ground segment in detail,and stressed that EarthCARE is the most complex Earth Explorer developed thus far both in terms of
payload instrumentation and in terms of data processing complexity. On the payload, the Atmospheric
LIDAR (ATLID) is integrated onto the satellite and has completed all its performance tests andintegration tests. The lifetime tests on a space copy of the laser are ongoing. The Multi-Spectral Imager(MSI) is also integrated onto the satellite and has completed its performance tests and integration
tests. A modification of the baffle is underway to reduce thermal straylight into the thermal infra-red
module. The intervention and subsequent tests can be done with the instrument mounted on thespacecraft.The Broad Band Radiometer (BBR) is also fully integrated and tested, and is awaiting thestart of the system-level test campaign. The JAXA Cloud Profiling Radar (CPR) is mechanically andelectrically integrated on the spacecraft. At present one of its two high-power transmitters (only one
is needed for the functioning of the instrument, the other is backup) is integrated into the instrument,
the second unit is presently being manufactured. The present configuration will allow some systemlevel tests to proceed, and once the spare power transmitter is available, it will be integrated and theremaining system-level tests can be completed. Having all four instruments mounted and theirperformance tested has allowed to further consolidate the EarthCARE schedule with a launch date ofMarch 2023 with a detailed schedule for staggered release of the data products to the validation team,well before the public release.
Kotska Wallace addressed the in-orbit characterisation, calibration, and verification in general, andalso specifically for the BBR and the MSI instrument. The instruments each have a different timelineof checkout and decontamination and characterisation, with ATLID expected to be the last instrument
to enter the phase of nominal observations after approximately 50 days. For BBR, the Long Wave andShort Wave calibration steps were addressed, and also the use of black-body swap for detector
linearity characterisation. For MSI the approaches for the VNS (Visible, NIR, and SWIR-1) camera andTIR (Thermal Infra-Red) camera calibration approaches (involving diffusers and black bodyrespectively) and verification approaches were presented.
Georgios Tzeremes presented the ATLID calibration and verification, in particular the calibrations
performed during routine operations, namely radiometric calibration assessment through backgroundsignal monitoring, spectral cross talk calibration by seeking out “Mie-” and “Rayleigh”-only situations,absolute Rayleigh and Mie co-polar and cross polar calibration again by using nominal measurementswith for each of these calibrations a specific combination of scene selection/filtering (e.g. high ice
clouds), and the application of extra information (e.g. the already characterised known cross talk of apure Rayleigh spectrum into the co-polar channel, or the use of already characterised ground sites).
David Donovan summarized the validation needs for the ATLID products. For that, he gave a briefsummary about ATLID, highlighting its HSR capabilities and detection sensibility. He emphasized that
ATLID L1 products are not directly measured, but are a product of applying instrument response
function and cross-talk correction to the measured signals. He explained the different cross talks(spectral and polarization related) and presented the applied correction scheme and identified thatthe main challenge of validation of L1 products is the validation of expected sensitivity limits and thespectral-polarization cross-talk correction. Following that he stressed the need to validate the valueof the effective Rayleigh Depolarization ratio for ATLID! As spaceborne and ground-based attenuatedbackscatter coefficients cannot be directly compared, Dave Donovan recommended to use highquality terrestrial (inc. airborne) lidar observation of extinction, backscatter and linear depolarization
ratio profiles at 355 nm to “simulate” the EarthCARE attenuated backscatter coefficient profiles.
Finally, he stressed that even though the presentation has focused on the cross-talk problem there
will also be several other less-complex but still important issues to deal with and which should not be
forgotten about: E.g. the altitude assignment and the correct pointing of the instrument.
Rene Preusker presented the validation needs for the MSI. The MSI instrument was briefly introduced,
and he highlighted that the radiometric accuracy required should be better than 10% or 1K,
interchannel accuracy better than 1% or 0.25K and a radiometric stability of 1% or 0.3K/year. A shortreview of the calibration of the MSI - VNS was also presented, daily calibrations will be done over theSouth Polar Region and Dark calibration will be performed at the night side of the orbit. The MSI - TIR
calibration will be performed once per day. A comprehensive list of in-flight needs to be validated waspresented, including, absolute and relative radiometric, linearity, straylight (spectral and spatial),
spectral position, and their dependencies with respect to the FoV and the orbit. René provided
examples of invariant calibration targets, i.e, Rayleigh Calibration, Deep Convective Clouds (DCC),
Liquid Water Clouds (LWC), Sun Glint, the Moon, Sea Surface Temperature (SST) and pseudo invariant
calibration sites. The Simultaneous Nadir Observations (SNO) for intersatellite comparisons using Geosand HR sensors was also proposed for the Calibration / Validation. Closure between the BBR and MSI
measurements in the same platform was recommended. Eventually, Rene underlined some lessons
learned from previous missions, such as: the importance of effort and budget to be allocated to
instrument pre-launch characterisation and knowledge transfer; multi-sensor radiometric intercomparisons; orbital maneuvers to provide view on the moon for stability monitoring, diffusor BRDF
investigations and finally calibration as a never-ending process to be performed throughout the fullmission lifetime and beyond.
Shannon Mason presented a breakdown of the EarthCARE L2 algorithms and summarized thevalidation needs raised by their developers (Table 1). Two kinds of uncertainties were most common:challenges in identifying cloud and aerosol layers and constraining their properties in complex orlayered scenes; and of how the applicability of the physical assumptions underpinning our retrievals
may vary across regions, seasons, and regimes. Finally, a range of validation paradigms were discussedwith examples from EarthCARE's synergistic cloud-aerosol-precipitation retrieval algorithm (ACMCAP), from direct validation of microphysical assumptions using airborne and ground-based in-situ andremotely-sensed measurements, to developing statistical datasets characterising key processes andregimes, and using numerical models and instrument simulators to quantify retrieval uncertainties.
Table 1. Summary of the EarthCARE L2 algorithm development and validation needs
Uncertainty

Locations/scenes/regimes

Measurements needed

Products

Macrophysic Aerosol layersdetection•Multiple aerosol layers•Aerosol layers with strong internal
structure•Attributing aerosol plumes at nadir
to features in the across-track
imagery•Ground-based (& scanning?)
and airborne lidars

A-ALD,
AM-ACD, ATCAerosol/cloud
discrimination•Cloud embedded in aerosol layers•Ground-based lidars

A-ALD,
AM-ACD, ATC

Cloud layer
detection andstructure•Multiple cloud layers•Cirrus over liquid cloud•Non-precipitating liquid clouds•Ground-based (& scanning?)
lidars & radiometers

M-CLD, AMCTH, A-TC,
C-TC,
AC-TC

Liquid clouds not•Physical depth of liquid clouds (i.e. •Ground-based
fully resolved bycloud base height)
ceilometers/lidars
radar/lidar synergy •Mixed-phase layers embedded in ice •Multiple-frequency radars to•Liquid (& liquid-topped mixed-phase) constrain W-band attenuation
clouds below optically thick ice clouds •Microwave radiometers for•Warm liquid clouds within cold rain LWP•Aircraft profiles of LWC

A-TC, C-TC,
AC-TC

Ice cloud& snow

CPR surface clutter •Range of surface types
removal•Ground-based radars

C-TC, C-FMR

Snow microphysics •Stratiform vs convective(e.g. PSDs,•Rimed snow
microwave
scattering, density& fallspeed)•Bulk precipitation and particle
imaging measurements at
surface•Profiles of in-situ particle
properties in ice clouds

C-CLD,
ACM-CAP•Cloud-tops across range of•In situ aircraft measurements
temperatures, locations & cloud types •Visible & IR radiances

A-ICE,
ACM-CAP•Range of meteorological conditions

C-CLD, ACMCAP

Ice microphysics(e.g. PSDs, ice
optics, mass-size
rel’n)
Surface snow rate

Liquid cloud How to account for •Deep ice clouds: embedded mixedradiativelyphase layers
important liquid•Layered cloud scenes
clouds not detected •Warm liquid clouds within cold rain
by ATLID
Rain

Relation between
rain rate and drop
size distribution•Warm rain (maritime)•Convective/stratiform rain

Melting layer
structure & radar
attenuation•Dependence on snow properties
aloft•Continuity of mass flux & size
distributions across melting layer

Aerosol

Large AOT
uncertainties overland; sensitivity toaerosolclassification•Range of different land classes(biomes) & ocean•Range of different aerosol classes

Radiation

Detection of and/or •Range of snow-covered surfaces
representation offluxes over snowcovered surfaces•Ground-based radars and insitu at surface•Microwave radiometer for LWP ACM-CAP•Profiles of liquid water content•Ground-based multiplefrequency radars•Dual-pol weather radars overocean
•Ground-based & airborne
multiple-frequency radar

C-CLD,
ACM-CAP•Ground-based, e.g. AERONET(OC)•Ship-based sun photometers,e.g. MAN•Satellite imagers, e.g. MODIS,VIIRS, 3MI•High-latitude ground stations

M-AOT

C-CLD,
ACM-CAP

BM-RAD,BMA-FLX

The recent updates to the functionality of the ESA atmospheric Validation Data Centre (EVDC) were
presented by A.M. Fjæraa (NILU). She mentioned that the data centre served several ESA missions but
also hosted data from networks such as NDACC, EARLINET, PGN, TCCON, COCCON and ACTRIS and isproviding input data for the COPERNICUS Atmosphere Monitoring Service (CAMS). The EVDC hosts
validation data (“correlative data”) and for some missions it also provides access to satellite data withsubsetting and filtering. The full functionality for correlative data handling is available when data are
uploaded in GEOMS format, and support tools for conversion of files to this metadata standard areavailable on the EVDC portal. Also analysis and forecast data files of global gridded meteorologicalparameters from ECMWF are available via the EVDC. The OPOT tool on the EVDC portal provides
overpass information for many missions, including already a hypothetical scenario for EarthCARE. It
should be noted that the actual overpass pattern may shift as the exact position of the EarthCARE
orbit has not been decided yet.

Sander Niemeijer from S[&]T presented the ESA Atmospheric Virtual Lab and in particular the HARP
toolbox that supports intercomparison between EarthCARE data and correlative data, for example
those in the ESA Atmospheric Validation Data Centre (EVDC). He mentioned the upcoming adaptations
for EarthCARE, including ingestion of correlative data and dedicated HARP operations for the cloud
and aerosol domains. HARP is already used operationally for Sentinel 5P systematic validation, at the
EVDC, and in the CAMS service.
David Donovan from KNMI presented after the coffee break the potential role of E3SIM in the Cal/Val
activities. He used the example made in the first talk, to highlight that measured signals from groundand space cannot be directly compared. In that case, E3SIM may help especially when the simple
simulation by high performance ground based data as explained in his first talk is not sufficient totraceback potential problems of ATLID. Nevertheless, using E3SIM is for sure not a simple approach,which can be easily applied by someone. Expert knowledge and practically speaking significant
resources and commitment is needed to run this model. So E3SIM is very powerful but will be used
for a few selected cases and cannot be offered by KNMI as a ``general service’’ to the community.
Following Dave Donnovan’s presentation, Gerd-Jan van Zadelhoff , also from KNMI gave an overview
over ICAROHS for the creation of realistic scenes using E3SIM. He showed various examples andpresented some of the input dtaa. He concluded that simulations will play an important role in ATLID
L1 validations and, like Dave Donovan stated, that the simple approaches should be used first. But if
these simple simulations are not applicable, E3SIM is a powerful but complex toolbox to be used even though it should be always clear that it is not direct validation.
Jean.-Christopher Lambert (BIRA) introduced the framework for Quality Assurance for Earth
Observation (QA4EO) and addressed implementation methods, tools, and examples. The framework
formulates guidelines for establishment of requirements, interoperability, definition of quality
indicators and for quality reporting, and is already applied structurally in many CEOS missions. To
support the workshop objective of common validation approaches, he highlighted a study of validation
practices across domains. As example of QA4EO implementation, Quality Assurance system for EO
Essential Climate Variables was described, namely for NO2
Mark Fielding (ECMWF) presented the developments for monitoring and potential assimilation ofEarthCARE data at ECMWF. Using Aeolus monitoring as an example he explained the power ofmonitoring using assimilation models as it is very sensitive to detection of biases (e.g. the data quality
turned out to have a dependence on primary telescope mirror temperature, which has been correctedby a bespoke correction algorithm). In preparation for EarthCARE data availability, tests have been run
with simulated EarthCARE data and with Cloudsat and CALIPSO data, demonstrating the ability todetect even small biases rapidly. In turn, simulations also suggest a significant impact of the ingestionof EarthCARE lidar backscatter and radar reflectance on the ECMWF cloud model analysis andforecasts.
Jonas von Bismarck (ESA) introduced the concept of Fiducial Reference Measurements (FRM) namely
a suite of independent, fully characterized, and traceable ground measurements that follow theguidelines outlined by the GEO/CEOS Quality Assurance framework for Earth Observation (QA4EO).
The traceability to SI standards should be documented and follow metrology standards and/or
community standards with a well-specified uncertainty budget and community wide practices formeasurements, processing, archiving, accessing, and documentation. He itemised several ongoing
initiatives to work towards such community standards, the “FRM4 ….” projects, as introduction to thefollowing talk on the FRM4Radar project.
Lukas
Pfitzenmeierpresented
the
FRM4Radarproject(https://geomet.unikoeln.de/forschung/frm4radar), a Cloud Profiling Radar Network for Satellite Validation, which targets
to pave the way towards Fiducial Reference Measurements for the EarthCARE Cloud Profiling Radar(CPR) L2 ESA products. The standards and approaches that will be followed consist of complementary
94-GHz radar network measurements as part of Cloudnet, in the same wavelength as the EarthCARE
CPR radar, the fill of geographical gaps in the ground-based network with long term observations, thecoverage of different cloud climate regimes, the development of new cal/val products, the near realtime data processing and visualization with GEOMS data format files, data quality checks (concerning
the received power calibration and the antenna pointing characterization) and data retrievals with the
Cloudnet algorithm. Within the project a simple radar forward model will be developed (to accountfor different sampling, sensitivity and surface clutter between the ground-based and space based
observations) in order to enable a more objective comparison between the CPR and the FRM4Radarmeasurements. The same framework was suggested to be applied to model-CPR comparisons.
The organisation of the upcoming activities of the ECVT was addressed by Rob Koopman (ESA). He
addressed the upcoming workshops and planned and possible dedicated/topical online events in
between, and introduced the organisational subgroups for the validation team, which were alreadyreflected in the workshop agenda. The interactive portal was already intensely used as preparation
tool and confirmation was obtained that also co-investigators of the ECVT principal investigators will
be provided with access to the portal. In closing the EarthCARE validation effort was placed into thebroader context of multi-mission aerosol, cloud&precipitation, and radiation product validation.
Scientific effort on EarthCARE validation builds heavily on experience with earlier missions and will behighly relevant to already planned upcoming missions beyond EarthCARE. This was also reflected in
the workshop agenda with lessons-learned and forward looking presentations.
Peter Völger (IRF) opened the brief introductions of those projects that joined the ECVT after the Bonnworkshop, by presenting the plans for the IRF lidar system at Kiruna and the in-situ samping of cloudparticles with a balloon-borne particle imager. The project is aimed at validation of cirrus and Polar
Stratospheric Clouds
Gottfried Kirchengast and Jürgen Fuchsberger (WEGC of the University of Graz) introduced the dense
network of 156 climate stations on almost a regular grid covering 22km x 16km including at selected
stations precipitation radars, microwave and infra-red radiometers, and GNSS water vapour
measurements. The project seeks to validate cloud base height, convective classification and melting
layer base and top heights with the cloud radar and liquid water content and path with theradiometers. The combination of Xband weather radar and ground-based precipitation data willvalidate the rain rate, rain water content, raindrop number concentration and diameter, the rain
classification and the convective classification
As preview of his later presentation in the model session Vaughan Philips (INES) introduced the plans
to validate the microphysical assumptions of the algorithms by inferring ascent from EarthCARE, byusing aircraft data flying through cirriform clouds during EarthCARE overpasses.

Session 1: ATLID Level 1 and Aerosol product validation
Chairs: U. Wandinger, H. Baars, D. Donovan, G.-J. Zadelhoff, M. Haarig , N. Docter, M. Eisinger
This session opened the sequence of sessions discussing the validation approaches applicable to a
specific domain. This particular session was dedicated to validation of the ATLID Level 1 product, andthe second part of this session focused on the ESA aerosol products (single and multi-sensor products.
Presentation summary
Title

Presenter

Lessons learned from Aeolus Cal/Val and the DISC

Oliver Reitebuch DLR

Lessons learned from CALIPSO

Dave
NASA

Winker-

The ACCP orbital component

Dave
NASA

Winker-

ACCP suborbital component - Aerosol

Jens Redemann Univ. of Oklahoma

O. Reitebuch (DLR) presented the Aeolus mission and its highlights. He stressed the great importanceof DISC for a successful mission especially due to the close cooperation between scientists, ESA andindustry. DISC includes the algorithm and processor development, instrument monitoring and productquality assessment. He reported on how the processor chain is updated every 6 months according to
the actual findings of the Cal/Val teams and the DISC. He also stresses that Aeolus and EarthCARE (EC)benefit from each other. EC feature mask has been implemented in Aeolus, Dave Donovan's OEM will
be implemented in the September 2021 Aeolus data processing chain release.
Concerning validation, he states that ground based measurements are key and there is a need forroutine observations by active teams which need national fundings. Funding of expert Cal/Val teams
is crucial for the Cal/Val and should be well prepared. The VIRES tool proved to be very powerful. A
modern communication strategy including the cal/val wiki page and confluence is key. The main
lessons learnt from Aeolus are:
●
●
●
●
●

Monitoring tools for instrument parameters and products are essential after launchMany unexpected behaviours --> continuous commissioning phase
DISC is crucial
Strong support from Cal/Val teams is essential for mission success. He proposes a joint Aeolus
validation in preparation of EC
Benefit between EC and Aeolus and in support of an operational follow-on mission of Aeolus

Recommendation: EC Cal/Val teams should join Aeolus Cal/Val! It was further discussed that thealready existing synthesis reports of Aeolus could be used as input, i.e. , as template for EC.
Dave Winker (NASA) talked about the lessons learned from CALIPSO and especially stated thatcalibration is a never ending process. After each data release, validation efforts are ongoing. He also
stated that the first targeted validation campaign was one month post launch. Here, a gap for EC wasseen as currently no dedicated airborne campaign in the commissioning phase is foreseen. He also
considered the continuous HSRL underflight as useful to check the Calipso calibration over time. Direct
L2 validation is considered to be difficult. He considered as validation resources ground-based
networks (Aeronet, Earlinet, ADnet), satellite comparisons (MODIS, MLS, AIRS, CALIOP vs IIR), targeted
and continuing airborne campaigns, and large field campaigns. He also emphasized that a global data
set needs global validation: There are “empty areas” in terms of validation capabilities like thesouthern oceans. On the other hand, validation tends to be only one of many objectives in a scientificcampaign (airborne or ground or both). Therefore satellite2satellite validation is considered to be as
always useful. It also was discussed that retrieval consistency checks are very useful as well as theinter-comparison of the algorithms from multiple retrievals based on independent assumptions.
During the discussion, Ulla Wandinger recommended that one should make the best possible use ofother scientific campaigns not yet targeted for EC Cal/Val but could make a valuable contribution.
In his second talk David Winkler presented the ACCP orbital component which is now called ATMOS.
He presented that the dual-orbit concept was recommended to NASA headquarters and that they are
now entering Pre-phase A. ATMOS or fromer ACCP has 3 main elements, the orbital one, the suborbital one and modelling. This holistic view on a mission is considered to be a main achievement
already. They aim to determine the size and number of aerosols due to the HSR and polarimeter
capabilities. Lifetime is officially to be 3 to 5 years.
Jens Redemann (Univ. of Oklahoma) later presented the suborbital (in ESA language: the Cal/Val) of
ATMOS. He highlighted that suborbital activities are an integral part of ACCP mission as already Dave
Winker has done and that a process mission like ATMOS can be done only when suborbital science isdone. He also stressed the spectrum of implementation strategies from ground-based to multiaircrafts with emphasis on strong intra-agency, inter-agency, and international partnerships withmaking use of existing networks, regional supersites, and targeted campaigns. Thus, use of existingdata sets and foster relationships with partners is key. The real sub-orbital work, e.g. first pre-studies
for ATMOS will start not earlier than Spring 2022.

ATLID Level 1 Product Validation
Highlights:
Ground and Space based attenuated backscatter profiles (ATBs) cannot be directly compared. In orderto validate the L1 ATBs of EC,it will be necessary to use terrestrial based L2 products as a basis for“simulating” the corresponding ATLID ATB profiles (the Ground/Aircraft-L1 L2Space-L1 approach).
Monitoring of ATLID L1 signals by the Met centers (e.g. ECMWF) will be useful. This will build on efforts
now coming on-line for Aeolus. Might be particular useful to identify “rogue” profiles.

Fast feedback will be necessary especially in the early stages of the mission. Therefore also preliminary
data from the Cal/Val teams is beneficial and should be fostered to be delivered as soon as possible.
Not only data delivering but also own investigations are very welcome and should be communicatedto ESA. For Aeolus, the Cal/Val Wiki was found to be essential for facilitating rapid
communication/feedback.
Recommendations:
●
●
●
●

●

●

The Level 1 ATBD as well as the L1 (and L2) simulated data should be provided to the Cal/Val
community (ECVT) as soon as this year.
Real L1 data should be made available to Cal/Val teams as soon as possible after launch
Predicted L1 ATLID ATBs should be reported in the Cal/Val database as well as the terrestrialbased signals and inversion products.
The simulation of L1 ATLID signals using terrestrial (ground/air) lidar data should be done in acoordinated manner. One option would be to have the networks deal with (as well as setting
sensible quality-control standards which can even be adopted by operators not in the
networks). It is recommended that ESA support the networks in this aspect. At the very least,a “How-to/best-practices” document including all required ATLID info should be formulated !
Cal/Val (correlaive) lidar measurements at 355 nm will be prioritized. However, data at otherwavelengths can be useful. Green + IR data can be very useful for validating ATLID sensitivities
as they are good for detecting thin cloud and aerosol boundaries (less Rayleigh Scattering thanat 355 nm). Green + UV mapping using multi-wavelength systems (+photometers), aerosol
typing and, e.g., LIVAS database info may be useful.
Dave Winker is recommending that calibration should be done between 35 and 40 km (asdone now for Calipso) and by using Merra-2

Further Improvements and needs:●●

Coordination between the networks and ESA including Cal/Val data center likely needs to bemade more concrete.
The recommendations specified in the previous section should be followed. In particular: The
Simulation of L1 ATLID signals should be done in a coordinated manner.

For the L1 validation, measurements at the wavelength of 355 nm are needed. Whereas L2 validation
could make use of input at other wavelengths, especially 532 nm, as well, although 355 nm are
prefered. L1 validation also needs measurement covering the stratosphere. Coordinated underflights
are seen as key, while from ground-based remote-sensing measurements the long-term observations
are considered especially useful.
The L1 ATBD is on the way to be available to Cal/Val teams. The L1&L2 test data should follow to help
the Cal/Val teams in getting familiar with the data structure. A Wiki/Confluence is a crucial tool forfast feedback from Cal/Val teams during the whole mission.

Aerosol Product Validation
Highlights:

The algorithm developers defined the following validation needs for the aerosol L2 products:
1. Aerosol-cloud
discrimination
Here lidar measurements at any wavelength are welcome. Longer wavelengths are more
powerful in the separation of aerosol and cloud layers as they are less affected by Rayleighscattering. Model data such as from ECMWF could be used to check for cloud probability. The
cloud forecast is included in X-MET and can be used.
2. Layering/layerheights
Hlidar measurements at any wavelength are welcome. Longer wavelengths are more powerfulin the detection of aerosol layers as they are less affected by Rayleigh scattering. For validation
layer height a different (stricter) colocation criteria might be used as for e.g. the lidar ratio.
3. Aerosol
Extinction/backsatter&
AOD
The aerosol optical depth is not just needed at 355 nm, but as well at 670 and 865 nm to
validate the MSI retrieval. The extinction coefficient could be transferred from otherwavelengths using the Ångström exponent provided by AERONET.
4. Lidarratio
A Raman or HSR lidar is necessary to measure independently the extinction coefficient and toprovide the lidar ratio. Measurements at 355 nm are prefered as the spectral behavior of thelidar ratio depends on aerosol type and age.
5. Depolarization
ratio
For the particle linear depolarization ratio, measurements at 355 nm are prefered as the
spectral slope in the 355 - 532 nm range depends on aerosol type. A good aerosol typing isneeded to use the correct relationship. Note that Aeolus measures the circular depolarization
ratio.
6. Ångström
exponent(AE)
The AE should be considered as a diagnostic quantity as it is estimated from retrieved AOTs at
355, 670 and 865 nm.
7. Aerosol
typingVarious aerosol typing schemes are available in literature. The definition of the aerosol types
should be clearly communicated, as there might be significant differences (typing based on
origin, emission source, physical properties etc.). For EarthCARE, the HETEAC scheme is used.
Nevertheless, a typing for validation can originate from a combination of lidar ratio anddepolarization ratio at 355, 532 and/or 1064 nm (HSRL or Raman lidar) or airborne (thisincludes UAV) in-situ data inside the aerosol layer (e.g., effective diameter, refractive index)
combined with lidar profiles for layer information if available.
Recommendations:
If possible, upgrade your Lidar systems to 355 nm including a depolarization channel for validation ofEarthCARE & Aeolus.
Other wavelengths (532, 1064nm) can be used for many comparisons, however take care and describe
how the wavelength conversion is performed.
Having early info on the orbit will advise on network design and enable the setup of specific stations.

Campaign data sets can already be used for validation exercises (i.e., HSRL-2, 2021 Tropical Campaign(now called A-TAC), NARVAL/NARPEX, STRATEOL, A-LIFE, LOAC).
Trajectory analysis in combination with ground-based observation shall be used for analysing therepresentativeness. Co-location is only one criteria. For different products (e.g. layering, clouddetection) stricter co-location criterion might be applied than to others (lidar ratio).
Heritage from the ESA project to validate sentinel-3 AOD can be used for the validation of the EC AOD.
Further Improvements and needs:
HETEAC is the aerosol model used by the L2 algorithms. It is worth to remind that HETEAC is made forradiative closure of EC and thus estimates aerosol microphysical properties. Thus, HEATEC needs
validation. This should already be done before launch, especially with collocated airborne in-situ andlidar observations (ground-based or airborne). This effort should be continued after launch as well byadding airborne in-situ observations of the aerosol effective diameter and refractive index to thevalidation strategies by ground-based lidar stations and airborne lidar systems. For underflights withan EarthCARE-like payload, a second aircraft should be considered to measure inside the aerosol (andcloud) layers.
There is need for information on HETEAC, a describing publication will be provided soon (anconference proceedings paper is already available here: doi.org/10.1051/epjconf/201611901004).
HETEAC information should be made available on confluence. The L2 algorithm publications will beready by mid 2022.
For own Cal/Val investigations, the common practice has to be documented and shared as well as how
the retrievals/profiles were compared; i.e. QC can be linked to ACTRIS practice if not defined yet. The
QA/QC should follow the network guidelines, e.g., the ACTRIS/EARLINET calibration procedures. Thesestandards are open to everybody.

Session 2: Observational networks
Chairs: Jonas v. Bismarck, Luca Baldini, Ulla Wandinger“In this session, validation considerations for networks were discussed, including application of
network standards to non/not-yet networked stations.”
The session was dedicated to the well-established continental and global lidar, radar and photometer
networks. These networks have long-term experience in supporting satellite Cal/Val activities andtheir own dedicated quality-assurance measures and processing chains. Lessons learned fromprevious activities were introduced, and the networks presented their efforts in preparing EarthCARE
Cal/Val activities.
Title

PresenterLessons learned from the validation of Aeolus L2A product with Nikos Siomos - NOAEARLINET
Perspectives on ground validation from the NASA/JAXA Global S. Joseph Munchak
Precipitation Measurement Mission- NASAACTRIS Aerosol Remote Sensing in support of EarthCARE Cal/Val

Doina
INOE

Nicolae-

ACTRIS Cloud Remote Sensing in support of EarthCARE Cal/Val

Ewan O'Connor FMI

MPLNET observations in support of EarthCARE Cal/Val

Judd Welton - NASA

Approaches to intercalibration/QA/QC and other network aspects of Tomoaki Nishizawa
AD-Net and SKYNET systems- NIESLALINET network approaches for QA/QC, validation and data
Eduardo Landulfo handling
IPEN
Presentation summary
Ulla Wandinger introduced the scope of the session, consisting of short (10-min) presentations
followed by a discussion.
Nikos Siomos (NOA) introduced the EARLINET Cal/Val activities. EARLINET is part of ACTRIS andinvolved in the validation of Aeolus L2A products. Data collection is conducted for orbits within 100
km and ±3hours. Own threshold-based criteria have been developed for data quality checks of Aeolus,
but more sophisticated approaches are under development. Data flags developed for Aeolus haveincreased the correlation between EARLINET and Aeolus estimates, especially for estimates collected
at 2 km above the ground. Specific strategies are under development for identification of Saharandust. EARLINET data are converted to Aeolus-like profiles (as Aeolus is measuring only the co-polar
component of the backscatter). Cloud flagging is considered to be key.
S. Joseph Munchak (NASA) summarized the lesson learned from the GPM ground validation
programme. GPM Ground Validation (GV) is based on three main components, namely Direct GV(involving operational network for statistical comparisons), Physical GV (based on field campaigns toinvestigate physical assumptions of algorithms), Integrated GV (to assess the impact of products).
Fields campaigns were conducted in both pre- and post-launch phases. GV includes two supersites(Wallops and Marquette) and relies heavily on ground-based weather radar belonging to operational
networks, both in the US and outside the US. Conclusions stress the importance of a link between GV
outcomes and product release. Phasing of campaigns is important for this purpose. Interaction

between the algorithm developers and the Cal/Val teams is seen as very important. Data collection
and analysis need to balance, thus dedicated resources need to be available.
Doina Nicolae (INOE) illustrated the structure of Aerosol Remote Sensing (ARS) in ACTRIS, based on
three components, namely ARES (the ARS Data Centre Unit, in charge of data processing and productrelease), CARS (Centre for ARS, for establishing the technical procedures and quality assurance foracquisition and instrument managements) and the ARS national facilities. Today ACTRIS ARS comprises
30 Aerosol stations, for 2025 51 Aerosol stations are foreseen. It mainly includes aerosol lidars(EARLINET) and sun photometer (AERONET-EUROPE). The measurements collected in several nodesof the network are processed with a central processing chain, from data collection to quality assuranceof geophysical products. Especially important is the traceability of data. The network has experiencein supporting Cal/Val campaigns (Aeolus, CATS, and CALIPSO, the latter from 2006) and has
coordinated 19 campaigns. A specific effort is being devoted to developing a specific workflow for EC.
For this purpose, access to NWP data in near real time is necessary as well as a direct transfer of theoverpass information from ESA/EVDC to ACTRIS.
Ewan O'Connor (FMI) illustrated the capability of ACTRIS Cloud Remote Sensing (CRS) in theperspective of supporting EC Cal/Val. The network has developed common practice for calibration
procedures and for geophysical product retrieval. Shown are 16 sites of the network. From the pointof instrumentation, the network is not homogenous, using instruments of the same class, but fromdifferent manufacturers, and also in terms of wavelengths used. Coordination is assured by two
structures, CCRES (Centre for CRS) focused on procedures for running sites (including calibration andmonitoring of calibration, carried out also using properties of natural targets, such as for Doppler
velocities used to verify the vertical pointing of radars, but also external measurements, such as
disdrometers) and CLU (the CRS Data Centre Unit) focused on products and their evaluation. Recently,
graphical tools to facilitate the display of key functioning parameters have been made available. Other
procedures have been developed to mitigate attenuation effects due to both propagation and radome
wetting. ACTRIS CRS has strong expertise in validation of clouds in numerical weather prediction andglobal circulation models.
Judd Welton (NASA) introduced MPLNET, a worldwide lidar network for global backscattermeasurements designed following the AERONET model, running since 2000. It is composed of 75 sites(7 more in the future) co-located with AERONET. The procedures (QA/QC) adopted for the network
are well established and described in papers published since 2002-2003. An upgrade to polarization
was defined in 2007 and completed in 2016. New procedures and products are illustrated inconference papers and a journal article is in preparation. An overview of version 3 products wasprovided which can be tailored for EC. For EarthCARE validation they will target only wavelength
independent products: cloud height, cloud phase, aerosol height, surface attached mixed layer top
and top of atmosphere cloud radiative effect (TOA CRE ). L1 and L1.5 products are provided in nearreal time. Some locations are in common with EARLINET and LALINET. Inter-network validation isforeseen (also with AD-Net). MPL-NET offered to set up new sites dedicated for EC Cal/Val -waiting
for input concerning priority regions from the EC community (i.e., EURO-MAG?).
Tomoaki Nishizawa (NIES) described two networks, AD-Net (lidar) and SKYNET (sun photometer), thelatter present in both Asian countries and Europe. Ad-Net consists of Raman lidars and HSRL lidars,
partly equipped with 355 nm depol capabilities. For both networks, procedures for calibration ofinstruments have been established and applied. Products suitable for EC validation were presented. A
data centre for SKYNET is under construction and includes products for EC validation.
Eduardo Landulfo (IPEN) introduced the Latin America Lidar Network (LALINET) and the specificaspects that are of interest for monitoring in South America, namely forest fires, biomass burning andvolcanic ashes. A specific example involving ground-based measurements and satellite measurements
was shown. 14 stations in Latin America are existent (5 more than originally proposed for EC
validation), many co-located with AERONET.. Many of these lidars have 355 nm capabilities, but depol
is available at 532 nm only. Coincidence criteria are based on 3 hours and 120 km distance to theoverpass. Passive satellite data is used to analysis representativeness. QA/QC procedures are similar
to those used by EARLINET as both networks collaborate. Umbrella projects to create join frameworks
would be highly desirable.
Discussion summary
The Discussion was introduced by Ulla Wandinger who summarized in a couple of slides items fordiscussion in the session or for future discussion. The necessity to harmonize and intercalibrate thedifferent network approaches was discussed. Doina Nicolae pointed out that ACTRIS can support
other programs, including campaigns and internetwork calibration with, e.g., with mobile platforms
via ATMO ACCESS. Specific field campaigns can benefit from this experience, for a better usage ofmobile instruments, through guidance on sites and installation. Silke Groß highlighted that aircraft
can be used for network intercomparison. In principle, it was emphasized that networks andcampaigns should be connected in both directions. S. Joseph Munchak was asked to clarify the role ofoperation weather radar network for EC. In spite of the difference in wavelength, there are rooms for
employment especially for estimating and mitigating effects of W-band attenuation.
Recommendations:●●●●Collect opportunities for funding and support schemes but also for common measurements
and common sites.
Efforts should be undertaken to check representativeness of a ground-based site.
Define gaps observation gaps in the view of EC Cal/Val and beyond.
Provide all networks with ECMWF meteorological fields (mainly p and T) for their Cal/Val
stations to assure the same input for the retrievals.

Session 3: Cloud and Precipitation product validation
Chairs: Pavlos Kollias, Alessandro Battaglia, Shannon Mason, Eleni Marinou
This session focused on validation of the CPR-only (L2a) and synergistic (L2b) cloud and precipitation
products.
Title

Presenter

CloudSat Cal/Val lessons learned & intro to ACCP and its Jay Mace, Univ. of Utah, USA
Suborbital program with emphasis to Cal/Val
Summary of inputs from Principal Investigators

Eleni Marinou, National
Observatory of Athens, Greece

Summary of the algorithm needs with respect to clouds and Shannon Mason, ECMWF, UK
CPR for Level 2

Presentation summary
J. Mace (University of Utah) provided a survey of cloud and precipitation validation campaigns from the ATrain, followed by an update on the AtmOS mission and plans for its suborbital component. E. Marinou(National Observatory of Athens) consolidated input from Cal/Val PIs and gave an overview of the capacityand distribution of Cal/Val facilities and activities planned for EarthCARE. S. Mason (ECMWF) summarized
validation needs from the perspective of the developers of level-2 cloud and precipitation retrieval
algorithms (Table 2).

Table 2 Summary of L2 algorithm development needs for the cloud products
Uncertainty
CPR L2aLocations/scenes/regimes

Measurements needed

Products

Antenna pointing
correction•Ice clouds at all latitudes•CFADs of reflectivity andDoppler velocity from groundbased radars

C-APC, CCD

Doppler
decomposition:
sedimentation + air
motion•Unrimed/rimed snow
•Drizzle/rain•Convective/stratiform; other sourcesof vertical motion•Multiple-frequency Doppler
radars•In-situ measurements

C-CD•Cloud embedded in aerosol layers•Ground-based lidars•Collocated in-situ aerosol
sampling

A-ALD,
AM-ACD,
A-TC•Multiple cloud layers•Cirrus over liquid cloud•Non-precipitating liquid clouds•Ground-based (& scanning?)
lidars & radiometers

M-CLD,
AM-CTH, ATC,
C-TC, ACTC
M-CM

Macrophysic Aerosol/cloud
discriminations
Cloud layer
detection andstructure

Cloud spatial scales •Cumulus & stratocumulus clouds•Land/sea, day/night, boundary layer
conditions, etc.

•High-resolution satellite
imagery

Liquid clouds not•Physical depth of liquid clouds (i.e.
fully resolved bycloud base height)
radar/lidar synergy •Mixed-phase layers embedded in ice•Liquid (& liquid-topped mixed-phase)clouds below optically thick ice clouds•Warm liquid clouds within cold rain

•Ground-based
ceilometers/lidars•Multiple-frequency radars toconstrain W-band attenuation•Microwave radiometers for
LWP•Aircraft profiles of LWC

A-TC, C-TC,
AC-TC

CPR surface clutter •Range of surface types
removal•Ground-based radars

C-TC, CFMR

Ice cloud& snow

Snow microphysics •Stratiform vs convective(e.g. PSDs,•Rimed snow
microwave
scattering, density &fallspeed)•Bulk precipitation and particle
imaging measurements at
surface•Profiles of in-situ particle
properties in ice clouds

C-CLD,
ACM-CAPIce microphysics(e.g. PSDs, ice
optics, mass-size
rel’n)•Cloud-tops across range of•In situ aircraft measurements
temperatures, locations & cloud types •Visible & IR radiances

A-ICE,
ACM-CAP

Surface snow rate

•Range of meteorological conditions

C-CLD,
ACM-CAP

Liquid cloud How to account for •Deep ice clouds: embedded mixedradiativelyphase layers
important liquid•Layered cloud scenes
clouds not detected •Warm liquid clouds within cold rain
by ATLID
Relation between •Warm rain (maritime)Rain
rain rate and drop •Convective/stratiform rainsize distribution
Melting layer
structure & radar
attenuation•Ground-based radars and insitu at surface•Microwave radiometer for
ACM-CAP
LWP•Profiles of liquid water content•Can models help train
assumptions?
•Ground-based multipleC-CLD,
frequency radars
ACM-CAP•Dual-pol weather radars over
ocean

•Dependence on snow properties aloft •Ground-based & airborne•Continuity of mass flux & size
multiple-frequency radar
distributions across melting layer

C-CLD,
ACM-CAPTARGET CLASSIFICATION
J. Mace reminded us that a novel result of CloudSat and CALIPSO flying in formation—and a foundational
concept of EarthCARE—is the near-complete view of the atmospheric profile provided by the synergy ofradar and lidar. The target classification and associated hydrometeor layer boundaries are an important“zeroth order” cloud and precipitation product, as well as forming the essential basis for microphysicalretrievals. An early objective of the CloudSat/CALIPSO Cal/Val activities was to confirm the performance ofthe synergistic radar/lidar observations using airborne observations. Such comparisons are great forevaluating the performance of the target classification in complex, layered and precipitating cloud scenes,
where the extinction of the lidar signal at the top-most layer of cloud very frequently means that the
distribution of liquid and mixed-phase clouds, and especially cloud-base height, are unknown. These
synergistic blind zones make it difficult to exploit passive and integrated measurements in synergistic
retrievals and contribute to uncertainties in EarthCARE radiative transfer products.
Today, surface-based networks such as the US ARM and EU ACTRIS observatories provide well establishednetworks with routine synergistic observations from radars, lidars, radiometers and surface sensors andused for statistical validation of EarthCARE target classification and microphysical products. For example,
ceilometer and lidar networks will enable widespread statistical validation of cloud-base height; surfacebased observations of rainfall rate and precipitation type can be used to validate our precipitation target
classification. Complementary information from microwave radiometers will allow for more robust
identification of liquid and mixed-phase cloud that cannot be identified with active remote-sensing.
Recommendations:-

Validation of cloud-base estimated from EarthCARE synergy (AC-TC) using networks of ground-based
ceilometers and lidars.

-

Validation of EarthCARE detection (AC-TC) and retrieved microphysics (C-CLD, ACM-CAP) of liquid,
supercooled and mixed-phase cloud using ground-based radar-lidar retrievals, and complemented by
microwave radiometers and/or dual-frequency radar techniques to constrain estimates of liquidwater content.

MULTIPLE-FREQUENCY RADARS
Additional insights into cloud and precipitation are facilitated by the addition of lower-frequency Doppler
radars that are less attenuated than the W-band radars of CloudSat and EarthCARE and provide
complementary scattering and sizing information in snow and rain. Some existing multiple-frequency radar
campaigns datasets provide valuable resources for evaluating EarthCARE cloud and precipitation retrievals.
J. Mace highlighted the TC4 campaign (Costa Rica, 2007), which employed dual-frequency Doppler radars,
lidar, and multispectral, microwave, and broadband radiometers aboard the high-altitude ER-2 aircraft,creating a high-quality dataset that includes EarthCARE-like instrumentation and, with its multiplefrequency Doppler radars, prefigures plans for the AtmOS satellites. The BAECC campaign at Hyytiälä,
Finland (2014) combined triple-frequency Doppler radars alongside microwave radiometers and groundbased in situ measurements; this field campaign and ongoing measurements from the Hyytiälä supersite
have provided the basis for many process studies and radar retrievals of mixed-phase cloud and melting,rimed, and aggregate snowfall. S. Mason showed examples of the ACM-CAP retrieval algorithm applied toboth datasets, using multiple-frequency radars to improve and evaluate retrievals of rain drop size
distribution, and rimed snow.
Recommendations:--Insights from multiple-frequency Doppler radars in ground-based and airborne configurations should
be used for ongoing development, evaluation and inter-comparison of cloud and precipitation
retrieval algorithms.
Multiple-frequency radar techniques for constraining the vertical distribution of liquid cloud water
should be developed and evaluated, for use in validating EarthCARE’s synergistic blind zones.

AIRCRAFT CAMPAIGNS
J. Mace was unequivocal that the greatest contribution to CloudSat/CALIPSO retrieval algorithms from field
campaigns was from systematic and collocated in-situ cloud microphysical measurements, which areessential for developing and evaluating priors and covariance matrices. The AtmOS operational groundsegment will include systematic measurements along key “corridors”, similar to the SPartICus campaign
which included 21 CloudSat/CALIPSO under flights and a total of 200 flight hours over the continental US.
One of the innovations for CloudSat/CALIPSO Cal/Val field campaigns was the capacity to coordinate
multiple aircraft for remote-sensing and in-situ measurements along the satellite track. Direct
CloudSat/CALIPSO underflights from the CCVEx campaign were achieved within months of launch and werecritical to validating radar-lidar synergy for hydrometeor detection, and for diagnosing and quantifying theeffects of multiple scattering on the CloudSat radar. Proposals for aircraft campaigns for EarthCARE Cal/Val
included remote-sensing and in-situ measurements from the LATMOS, DLR and FAAM aircraft, with 4
campaigns proposed between October 2023 and 2025. This highlighted an apparent gap in Cal/Val aircraft
campaigns planned for the EarthCARE commissioning phase (March to October 2023). While the pre-launch
AtmOS suborbital program will overlap with EarthCARE, plans for specific field campaigns are not yet
finalised.

Figure 1 Direct validation of CloudSat radar reflectivity factor using airborne cloud radar aboard ER-2
during CCVEx. This comparison helped quantify the effects of multiple scattering on CloudSat CPR.
Figure reproduced from Battaglia et al, 2008, JGR-Atmospheres.
Recommendations:-

Provide to ESA recommendations and requirements for a commissioning phase aircraft campaign,
including: (a) when to fly within the constraints of the commissioning of EarthCARE instruments andthe possibility of short launch delays; (b) required aircraft instrumentation and flight strategy; and (c)locations and regimes to target.

GROUND-BASED STATIONS AND NETWORKS
E. Marinou provided a quick overview of the existing ground-based in-situ and remote-sensing stations for
EarthCARE cloud and precipitation Cal/Val activities. The surface-based facilities include around 50 radars,
more than 100 lidars, and over 400 ceilometers, as well as weather radar networks in the USA and Finland.
These mature and stable networks provide standardized instrumentation, calibration and data processing.
These supersites and networks constitute a resource for statistical validation of hydrometeor detection
and microphysical retrievals that was not available at the launch of CloudSat/CALIPSO, but have since beenused for robust validation of cloud and precipitation detection, retrievals, and radiative transfer modellingfrom those satellites (e.g. Protat, A. et al, 2014, JAMC). While a paucity of stations throughout Australasia
was noted, especially given the importance of Cape Grim, Tasmania for long-term Southern Ocean aerosol
measurements, the density of high-quality network sites over Europe presents obvious opportunities forstatistical validation across large spatial scales.

The systematic use of ground-based remote-sensors to validate spaceborne measurements requires thedevelopment of a standard way of accounting for the different viewing geometries, and the effects ofattenuation of cloud radars and extinction of lidars. The uncertain vertical distribution of liquid cloud is aproblem to which multiple-frequency ground-based radars stand to make a significant contribution, but inmany circumstances a relatively forward-model could be used to transform between upward- anddownward-looking remote-sensors in order to better exploit ground-based networks for validation ofEarthCARE.

Figure 2 Global map of ground-based lidar and radar stations (not including NEXRAD and FMI
weather radars).
Recommendations:-

Coordination on standard procedures for accounting for gaseous, water vapour and liquid water
attenuation from ground-based radars.
Development of tools for transforming between downward- and upward-looking remote sensors forstatistical validation against ground-based networks.

VALIDATION OVER OCEANS
While large ground-based measurement networks provide widespread, if not evenly distributed, capacity
for systematic validation of cloud and precipitation retrievals over land, the large part of global cloud andprecipitation occurring over the oceans are much harder to validate. CPR path-integrated attenuation(PIA)—critical to constraining rain retrievals—is estimated from the ocean surface return, making
EarthCARE rain retrievals especially difficult to validate. Snow is more readily validated over land at groundbased sites with both in-situ and remote-sensing measurements, but the microphysics of snow and mixedphase precipitation over ocean are also poorly constrained by observations. This reinforces the importanceof widespread in-situ aircraft measurements for validating cloud microphysics over a range of locations andcloud regimes. For precipitation microphysics, the systematic collection of ship-based measurements may

be a critical product for statistical validation (Klepp et al., 2018), and especially for informing priors andcovariances in retrieval algorithms. Experience of in-situ and remote-sensed measurements of clouds andaerosols over the Southern Ocean reinforce the need for resolving regional and even seasonal
microphysical differences in these priors. Evaluation against other retrievals may include statisticalevaluation against polarimetric weather radars in coastal locations (e.g., NEXRAD) or GPM satellite
retrievals.
Recommendations:-

Use ground-based and ship-based microphysical measurements to inform spatio-seasonal changes incloud and precipitation microphysical assumptions.

CLOUD AND RADIATION
EarthCARE’s cloud detection and microphysical retrievals will be represented in the radiative transfer(ACM-RT) product, and their quality will be evaluated in the top-of-atmosphere radiative closure
assessment (ACMB-DF). The passive cloud retrievals (M-CLD), active (A-ICE and C-CLD) and synergistic cloudand precipitation retrievals (ACM-CAP) may each made different assumptions about the radiative
properties of ice clouds. Aircraft remote-sensing with hyperspectral and microwave radiometers in
addition to EarthCARE-like payloads will be essential to validating the consistent representation of ice
microphysics across the spectrum, as well as to assessing the MSI smile effect. Ground-based stations withcomplementary radiation measurements should also be used for validating surface fluxes and heating
rates.

Discussion summary
The discussion period covered a breadth of topics related to the EarthCARE Cal/Val activities.
The participants discussed the need to coordinate and harmonized data records from surface-based
observatories and the need for funding to do this. In addition, funding is needed for analyzing past
field campaign datasets such as those collected by NASA’s airborne platforms. Regarding data
standardization and requirements for L2 Cal/Val activities, the new EarthCARE L2 activity called
CARDINAL contains an early task led by P. Kollias that aims to outline data needs for L2 Cal/Val
activities.
The participants expressed the need to coordinate with the AtmOS suborbital program for Cal/Val
activities post-launch.
The participants discussed the role of numerical weather prediction models in EarthCARE Cal/Val
activities in a way similar to how ECMWF helped the Aeolus mission.

Session 4: Validation Campaigns
Chairs: Silke Groß, Julien Delanoë, Dirk Schüttemeyer

This session was dedicated to campaign activities in preparation of the EarthCARE mission and to
campaigns as opportunities for future EarthCARE validation. Four presentations were given:
Title

Presenter

Introduction to ESA campaigns and Pre-launch lessons learned

Silke Groß - DLR
Julien Delanoë - LATMOS

CCREST, an example for a science/validation campaign on Stuart Fox - UKMO
validation of several missions combined with general science
Latest status and future plans for in-situ

Wolde Mengistu - NRC

Opportunities for dedicated or piggy back campaigns

Silke Groß - DLR
Dirk Schuettemeyer - ESA

Presentation summary
Silke Groß and Julien Delanoë presented the lessons learned from ESA Pre-Launch campaign activities.
Four main points were addressed with those campaigns:(1) Airborne measurements were used to compare lidar and radar measurements form aircraft andfrom satellite (A-Train). Macro-physical properties were compared to evaluate effects due tosensitivity and resolution. Cirrus clouds and shallow marine convection were in the focus. Small scale
structures are unlikely to be fully resolved from the satellite measurements leading to a potential shift
in the overall analysis and should thus be treated with care. Direct comparisons of satellite andairborne lidar measurements of height and location of the observed structures showed a good
collocation agreement of +/- 600 seconds. In addition to the lidar alone studies, the synergistic radarlidar algorithm was implemented and tested on HALO lidar-radar measurements. The results werecompared to the same scenes from satellite measurements to study wavelength and resolution
effects.
(2) Tandem flight with radar-lidar measurements at different wavelengths were performed on two
different aircrafts; the German HALO and the French Falcon20. The synergistic algorithm was further
developed and tested with respect to its multi-wavelength capability of the synergistic algorithm. It is
now possible to use different combinations and different resolutions, which is crucial to directlycompare measurements from different platforms. Directly measured variables (L1) of the different
platforms as well as derived properties (L2) were compared to characterize the impact of different
wavelengths/resolution/sensitivity. Experience could be gained for coordinated multi-aircraft satellite
underpasses, and first strategies for future EarthCARE validation could be developed and tested.
(3) Closure analysis including hyper spectral imager and in-situ measurements were performed.
Radiative closure with Hyperspectral Imager measurements show the capability of further information

to identify situations in which the synergistic approach fails, and may help to overcome this issue.
Coordinated in-situ measurements could prove the overall good performance of the algorithms andidentified reasons for its failure in other situations.
(4) The pre-launch campaign activities further focused on a performance check of the aerosol
classification and the link of remote sensing measurements to microphysical properties. In generalmeasurements of the lidar ratio and the particle linear depolarization ratio can be used for aerosol
typing. The linked and derived microphysical properties showed good agreement with in-situ
measured microphysical properties.
The following campaign needs and gaps were identified from the pre-launch studies:--

Airborne in-situ and ground-based lidar measurements should be brought together to test L2
algorithms or to look at the sensitivity.
There is a need for more in-situ measurements (prior information – covariance matrix/validation)
There are some occasions where the retrieval doesn't work, but we have a very limited number ofmeasurements. Closure studies are a valuable tool to check the performance of the algorithm. Moreclosure studies should be performed.
Airborne campaign data should be used for L2 retrievals (one gap: to investigate the impact of theused ice microphysical properties).

Suart Fox presented ideas for CCREST campaign and thus showed an example how science campaigns
could provide opportunities for combination with cal/val activities. The main goal of the campaign isto characterize cirrus and ice cloud across the spectrum (PIs: A. Baran/S. Fox) with the focus on:
diversity of ice crystal size and shape, mass-dimension/area-dimension, shape of the particle size
distribution (small and large modes) to bring realistic microphysics and optical model across the
spectrum, issues having consistency between measurements in mid-far IR, and to reduce theuncertainty in global average shortwave. During the campaign multiple aircrafts (FAAM/DLR
F20/ATR42) shall be involved, combining in-situ and active/passive remote sensing. The campaign isplanned for March 2024 with its base still to be decided. Possible locations are Iceland, UK, NE-US,
Kiruna. Target of 3-4 weeks of campaign. The interest of using passive and active measurements would
be ideal for EarthCare and FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring –ESA mission EE9). Possible coordinated tracks with EC could be performed, but it is unlikely to fly underclear sky conditions. Ice clouds are targeted in this campaign and flight altitude shall be, if possible,
above them so the tropopause must be low. Overflights of Chilbolton depend on the selected area for
the flights.
Mengistu Wolde presents their experiences from in-situ measurements. In addition to the in-situ
instrumentation, NRC Convair is also equipped with remote sensing instrumentation: X, Ka, W band
radars including polarisation diversity (following WIVERN), 355 nm lidar system and radiometers foraerosol and cloud measurements. The team has already performed a few campaigns: e.g.
CloudSat/CALIPSO validation, for GPM/ WIVERN, RadSnow (in-situ + 3 frequencies). New instruments(optical probes) for better measurements in flights were added: AERI, HiSRAMS, SPE, HVPS-4. Theirfocus is on in-situ measurements with new instruments (including bulk measurements): SPEC HVPS4(2022), NRC cIKP (2022), HISRAMS (2021), CVI inlet (2022), Artium HIS (2021) both PSD and images

In addition they have ground-based systems which could also be used for EarthCARE validation:
Climate Sentinel Station in Ottawa (2021). Campaign activities are planned for 2021-2022 but nothingplanned later on yet.
Silke Gross summarized the proposals related to EarthCARE calibration/validation campaigns. A
number of ground-based field campaigns are planned; e.g. in the Mediterranean or in the highlatitudes, balloon-borne and UAV measurements available on selected locations. Measurements withlidar and radar (+ceilometer) available in Antarctica during the first phase of EarthCARE.
Airborne campaign activities
AOID

PI

activities

38018

Marenco1-2 potential ad hoc research flights High-latitudes
compatible with other experiments (CCREST) and UK
with FAAM; preferentially combinedwith multiple aircraft

CCREST winter2023/2024

Airborne campaign dedicated to EC Portugal (tbd)validation (ECVAL) with EarthCARElike payload on HALO – potential of
combined ATR42 measurements(Delanoë)Summer 2024

Airborne campaign with 2-3 Barbados
dedicated cal/val flights with
EarthCARE-like payload on HALO
(TOOC)

Summer 2024

Airbornelidar
andin-situ High-Latitudes
measurements on HALO during
ASCCI and HALO-south

2025

38188

Wandinger

locationtime

UK in summer
2023

NZ
38810

Delanoë

2025

Airborne EarthCARE-like + in-situ High-latitudes
measurements (CCREST + NAWDIC)
as opportunity campaign

Winter2023/2024

Extra-tropical NA
Nicolae
Stachlewska/ Airborne campaign with MULTIPLY Romania(multi-wavelength HSRL) system Mediterranean(ESA project)2025/

39821

Qu

Airborne measurements

60799

Phillips

Airborne radar measurements incombination with satellites

Campaign activities with balloons and UAVs
AOID

PI

activities

location

38810

Delanoë

Balloon-borne radar X + W-Band TBD
radar

38809

RenardBalloon-borne lidar measurements

39067

Hu

UAV
measurementswith Chinese South Sea
dropsondes, radiometer and THz
Radar and lidar for cloud
observations

Every summer

51515

Völger

Balloon-borne in-situ measurements Northern Sweden(in combination with ground-based
lidar)

On occasiontime

LaunchFrancetime
2023/2024

site

in

Ground-based campaigns
AOID

PI

activities

location

38810

Delanoë

Mobile ground systems – BASTA (W- mobile
Band radar) and BALI (scanning
BASTA + ulidar)

Already running(on demand)

Scanning C-Band (POLDIRAD) and W- Southern Germany Starting 2022
Band (BASTA) radar
38623

GenthonCeilometer measurements

Antarctica

38909

Gausa

Radar and lidar measurements

Northern Norway

Voelker

Lidar measurements (in combination Northern Sweden
with balloon in-situ measurements)

ongoing
On occasion

3918338188

AmiridisGround-based PANGEA station Eastern(lidar, cloud radar, MWR, Radiation) Mediterranean

SicardLidar deployments during different
campaigns

Stachlewska

Lidar measurements in Poland and Eastern
possibility for campaign participation Mediterraneanin Romania

ongoing

Wandinger

Cloud Radar, MW-Lidar,
Radiation measurements

ongoing

MWR, Cape Verde

Balloon-borne in-situ measurements Melpitz(in combination with ground-based
lidar)

ongoingongoing

Two airborne campaigns are proposed:--

Flying the MULTIPLY lidar on the Romanian aircraft (~2024) in connection to the ongoing network
activities and the campaign activities in the Eastern Mediterranean. First ideas of a possible campaign
were evolved but no fixed plans yet. The consortiums proposing a dedicated campaign in the Eastern
Mediterranian comprises TROPOS, ECoE, Cyprus Institute, INOE and NOA. A focus on aerosol opticaland microphysical properties and thus aerosol typing is made. Funding for the overall campaign is stillneeded.
Having HALO and ATR42 flying out of Portugal (Location can still be changed); Portugal as base for theaircrafts would provide the possibility to perform validation measurements in different aerosol/cloud
situations. Ground-based measurements are in the reach of the aircrafts. Overpasses should beplanned for a general characterization of the situation and for inter-comparisons. HALO is available
for this campaign and the schedule is already confirmed. The plans are quite advanced.

In the presentation general thoughts, that came up by reviewing the updated proposals and from thesummary of the 1st Cal/Val workshop were mentioned:-

Many activities are proposed to be performed in the mid- or high latitudes
TOOC (HALO airborne measurements in combination with ground-based and ship-borne
measurements) as an opportunity campaign is one of the few campaigns in the (sub-)tropic regions.
Multi-aircraft campaigns (with different wavelengths of the lidar and radar measurements andcombined remote sensing and in-situ information) are needed.
Connecting airborne measurements with ground-based stations is a crucial thing in the validation
process. Mobile facilities should be placed at strategic locations or be used for inter-calibration
Flights over land and over the ocean are needed to test the performance of the EarthCARE algorithms
with respect to different surfaces.
Funding of the campaign activities is often still open and the proposed activities may change
depending on funding.
There is no dedicated airborne validation campaign planned directly post launch.

-The possibility of doing campaigns from the home bases during commissioning should be explored

Needs were identified from the L2 developer related to campaign cal/val activities that was mentioned
in the previous sessions:-

Lidar measurements of Mie and Rayleigh signal preferable at 355 nm
Simultaneous lidar measurements of low depol and high depol measurements
Depolarization measurements at 355 nm. Measurements at 532 nm would work as well but might add
potentially additional uncertainties due to conversion.
Macro-physical properties (PBL height, multi-layer aerosol scenarios, broken clouds and aerosols,
multi-layer cloud scenarios) must be addressed.
L2 algorithms should be run with airborne and ground-based measurements.
Simulation of non-EC products should be performed, e.g. to compare with measurements at different
wavelengths
Information of extinction and IWC/LWC are needed for simulations and closure
AOT measurements from ground (e.g. AERONET) and satellite (e.g. MODIS, VIIRS, …)Ground-based remote sensing measurements located along flight track
Imager measurements
Synoptic observations
In-situ measurements (underflights along EC flight track)
Airborne microwave measurements
Polarization radar measurements and precipitation radar scans

Questions that were raised during the campaign discussion:-

How can we best combine airborne and ground-based measurements (+ satellites?)
Which are the best locations for (ground-based) measurements?
Which / how many mobile facilities would be available?
How can we best combine remote sensing and in-situ measurements (airborne + ground-based)?
Which regions are missing? And how can the gaps be filled?

Discussion summary
After the presentation an extensive discussion started. The main points of the discussion were:---

Shipborne measurements (like the POLARSTERN or the METEOR) should also be considered for
EarthCARE calibration/validation. It was also discussed about the Australian RV – Alain Protat is thecontact; Rob Koopman is already in touch with him. METEOR will most probably be deployed during
TOOC, and there are also planes to have shipborne measurements during the ECVAL campaign.
It was highlighted that in-situ and remote sensing is very powerful. In situ and no remote sensing
makes it difficult to place the in-situ measurements in context.
In connection of the proposed Cal/Val campaign in the Eastern mediterrainian, it was mentioned that
the Cyprus Institute has strong interest to participate with its UAV fleet for in-situ observations.
Furthermore it was highlighted that Limassol will become a permanent aerosol and cloud remotesensing station starting in 2022.
Once the EarthCARE orbit pattern will be decided, ACTRIS can propose a more detailed plan; e.g. fixed
observation sites in combination with mobile platforms (many with complex instrumentation foraerosols and clouds).

--

Following this comment a discussion about the EarthCARE’s tracks started. The main question was if
it is possible to move them to be better collocated with highly import sites? How does this work for
AEOLUS? And which radius (50km?) should be applied as 'direct' overpass? The latter one depends on
the topic; e.g. cloud or aerosol. For aerosols it further depends on the region; in Africa it is not so
crucial, over europe 100km can make a big difference. According to Michael Eisinger no ideal setting
was identified so far. David Donovan suggested developing a cost function (weighting what thestations have to offer from their measurements). Oliver Reitebuch mentioned that a cost (weighting)function was used to fix the AEOLUS track as well. Aeolus L2A colocation criteria is 100 km. Usually for
AEOLUS collocation is considered within a 30 km distance.
Patric Seifert: highlighted the opportunity for deployments of mobile sites, such as LACROS, even forrather short periods (2-8 weeks) to defined locations. This can be done via trans-national accessprocedures, which are currently under development. For example, the LACROS site could be put
directly below the swath of EarthCare, e.g., in a coastal or mountainous region which is of interest for
Cal/Val. ESA could apply for the deployment of the LACROS mobile station. – Rob Koopman takes
action https://www.atmo-access.eu/.

Session 5: Radiation, and BBR Level 1 and MSI level 1
product validation
Chairs: Jürgen Fischer (FUB), Tobias Wehr (ESA), Michael Eisinger (ESA), Almudena Velazquez (RMIB)
and Nicolas Clerbaux (RMIB).
Title

Presenter

MMP - Monitoring MSI/EarthCARE L1 Performances using
concomitant intercalibration and stand-alone approaches

Dr. Noelle Scott Laboratoire de
Météorologie Dynamique

Geostationary Earth Radiation Budget (GERB) - Lessons
learnedDr. Jacqueline E. Russell- Imperial College
LondonLessons Learned from CERES

Kory Priestley - NASA
Langley Research Center

Presentation summary
The Cal/Val of the MSI level 1 data (M-NOM and M-RGR) is addressed in 3 activities: Monitoring
MSI/EarthCARE L1 performances using concomitant intercalibration and stand-alone approaches(MMP, lead by Noelle Scott at LMD), the German Initiative for the Validation of EarthCARE (Ulla
Wandinger, Tropos, Leipzig, Germany) and the Validation of EarthCARE Product in China (Xiuqing Hu,
National Satellite Meteorological Center, Beijing, China). Within GIVE, MSI Cal/val is addressed more
specifically by FUB (J. Fischer, R. Preusker) and comprises: (i) inter-comparison of different satellite
aerosol products and additional radiative transfer simulations are further used to interpret the MSI
Level 1 radiance measurements, (ii) comparisons of validated aerosol products from OLCI and SLSTR(long operational perspective of the European Sentinel-3 series), and (iii)The EarthCARE BMA-FLX

product will also be compared to fluxes that are estimated from MSG-SEVIRI radiance measurements(DLR contribution in GIVE). As regards to the Validation of EarthCARE products in China, synchronousradiometric calibration experiment will be conducted at China Dunhuang (China Radiation Calibration
Site) CRCS site for the visible and near infrared bands of MSI. Finally, the MSI long-term stability canbe monitored by using the Dunhuang desert site
A first invited talk was given by Dr. Noelle Scott (LMD, Palaiseau, France) about calibration of optical
instruments. She proposed two concomitant approaches: a relative (sometimes referred to as intercalibration or observation-to-observation) approach and a "stand alone" (observation to simulation)
approach. The selected method should use: all geographical regions and seasons, as well as
land/sea/day/night scenes, clear/cloudy/aerosols scenes, thus encompassing a broad range ofbrightness temperatures. The shown simulations were performed with the 4A/OP model fed withadequate descriptions of the atmospheric and surface state. The talk stressed the complementarity ofthe two approaches. In terms of “Lessons learned”, Noelle stressed the importance to pay the highest
attention to permanently quality control not only the observations but also the models and auxiliary
data sets. It is also important to stay in close contact and interact with PIs and all human actors/teams
in charge of the observations or of the processing of the observations (L1, L2, …). Getting feedback
from PIs is of paramount importance and (using) reprocessed data (L1, L2, …) is part of the game. The
talk was illustrated with results from the IIR/Calipso intercomparison with MODIS-Aqua and
MSG/SEVIRI.
The Cal/Val of the BBR level 1 and 2 is specifically addressed in 4 proposals. First activity is from the
CERES team at NASA Langley. Second comprises GERB partners (Imperial College London, RMIB) in
collaboration with the CERES instrument team and the University of Valencia (in charge of field
campaigns at the Valencia Anchor station). Third proposal, from the National Satellite MeteorologicalCenter, China, proposes the comparison of the BBR with FY-3 instruments. The fourth proposal,
ACROSS (lead by Vassilis Amiridis) will implement various tools and algorithms to retrieve synergistic
products and implement radiation closure studies.
A second invited talk was given by Dr. Kory Priestley on the lessons learned for CERES. He shared thelarge experience of the CERES team on ERB measurements (7 instruments since 1997, 6 of them still
flying). His first recommendation was to Calibrate as much as possible since calibration is crucial tountangle instrument artifacts from climate signals. He stressed from CERES experience that it is very
important to make sure that the spectral content of the calibration sources adequately represents thescience targets. Experience of the darkening of the SW channels when pointing in the forward looking
direction for CERES was shared. A very comprehensive list of recommendations was provided in histalk, including pre-launch, post-launch and Data Product Release Strategy. In particular: increase
weighting / influence of Radiometric Performance in cost/schedule trades, maintain positive / open
relationship with hardware provider, re-verify your ground targets frequently, establish collaborations
with international agencies such as NIST, implement automated Data Acquisition System on
Calibration Chamber, do not point optics in “forward” looking direction, provide additional SW
spectral characterization capability (important for the unfiltering and LW calculation), minimize
possibility of contamination and develop inspection and cleaning procedures, science team has a
Lifecycle responsibility, establish a calibration team early and hold regular reviews, understandrequirement traceability, be adept at responding to change (the instrument won’t work exactly as inthe testing environment), keep a good communication between the engineers and scientists, develop
logical and well understood approach to data release, minimize Editions / Versions of Data, use Data
Quality Summaries for the community.
A third invited talk was given by Dr Jacqueline Russell who nicely summarized the “lessons learned”
from the GERB instruments cal/val activities. The talk started with a summary of the GERB
measurements and onboard calibration, showing it some strengths and some limitations of theapproaches. Then, Dr Russell introduced many unexpected signals and instrument / satellite effects.
Finally, the power and difficulties of inter-instrument in-orbit comparisons and checks was discussed.
In summary, it was stressed that instruments and satellites do not behave as expected. Flexibility andrevisiting processing may be necessary. Inter-instrument in-orbit comparisons are extremely usefulalthough not definitive. Differences in processing and footprint can lead to systematics, whilst
temporal and angular matches are more likely to be noise. Tracking SW aging is not straightforward
and, if significant, allows for adaptations in processing to correct aging. Another point of summary is
the difficult ground to orbit calibration transfer (particularly in the SW). However, in orbit tests forconsistency can be sufficient to indicate that ground calibration analysis needs to be revisited. As for
the MSI, vicarious targets and quality checks are important throughout the mission life and are usefulto evaluate processing and provide inter instrument comparison for ideal cases, identifying systematicchanges and gross offsets. As Kory, Jacqui stressed that there will be things you don’t expect and that
communication with the instrument team is likely to be needed to understand and solve some issues
and that we can expect to update the processing and revisit the Cal/val plans. Some errors and effects
only get highlighted by use or time and thus maintain communication with the instrument team andenable baseline values to be revisited. There will be changes to the instrument over time you have todeal with to maintain data quality. From the GERB mission, it is clear that some artefacts that were
never expected could occur years into a mission and this stresses the importance of continuous quality
monitoring.
Discussion summary
A strong interest was shown in obtaining confirmation from the Mission and Optical Payload Manager(Kotska Wallace) about the foreseen calibration procedures and the performed on-groundcharacterizations. This stressed the importance for the Cal/Val teams to get detailed information on
the activities done and foreseen by ESA and industry. As it was already largely discussed during thetalks, several interventions stressed the importance of good communication with instrument
providers and the importance of continuous monitoring of instrument performances and calibration,and to be ready to adapt processing. It was also discussed how the drift of the Aqua spacecraft(currently at 13:30 ECT but that is going to drift later in the afternoon from 2022 onward) could lead
to better matching with EarthCARE. This would allow good matching, not only between MODIS andthe MSI, but also between the CERES FM3/FM4 and the BBR.
Recommendations: From the presentations and the discussion, the co-chairs of the session haveproposed the following recommendations. First, an extensive use of invariant calibration targets
should be foreseen: Rayleigh calibration, deep convective clouds, sun glint, SST, (pseudo) invariant
calibration sites . A second recommendation is to agree on procedures/protocols for intercomparisonof satellites L1 data. Lunar observations are also recommended, even if this looks especially difficult

for EarthCARE with its long trailing solar panel (21 m²). Finally, preparations in view of a continuous
calibration effort during the full mission lifetime are absolutely recommended.

Session 6: Use of models for validation
Chairs: Tobias Wehr and Jason Cole
Title

Presenter

Introduction

J. Cole (ECCC)

Vertical velocity in storms

V. Phillips (INES)

Cal/Cal campaigns and synergies for desert dust modeling studies

V. Amiridis (NOA)

Considerations for using radar observations to guide numerical K. Lamer (BNL)model development
NWP model evaluation using ACTRIS cloud profiling

E. O’Connor (FMI)

Presentation summary
J. Cole introduced the session. The presentations include using models for calibration/validation andusing sub-orbital and space-based measurements to improve and evaluate models and model
simulations.
V. Phillips presented a proposal to use a convective storm model to validate statistics of verticalvelocity and ice cloud properties using aircraft and space-based observations. In turn, the convective
storm model will be used in combination with EarthCARE data to study the global distribution of
convection and relationships with lightning and its land/sea contrast.
V. Amiridis illustrated how ATLID measurements could be used to improve desert dust products andprocesses through climatological dust property and dust deposition products, new dust
parameterizations and radiative closure studies. The utility of ATLID for assimilation was highlighted
since one could use backscatter profiles for aerosol mass and in a new approach lidar ratio to improveaerosol optical properties. A suggestion was made to consider calibration/validation efforts in thecontext of broader community in scientific studies.
K. Lamer presented the use of surface and space-based observations, mainly radar, to evaluate low
and high resolution models. It was shown that instrument simulators, with appropriate level of detailand considering including instrument sensitivities, are important for like with like comparisons. In
addition to instrument simulators, one needs to consider sampling in time and space between the
instruments and model and should also consider appropriate evaluation metrics.

E. O’Connor continued the discussion about the use of observations to evaluate models, highlighting
the need to consider representativeness, e.g., a 2D sample from EarthCARE instead of the 3D model
field or observations of atmosphere advected over a fixed surface site. By sampling models in a similarmanner as the observations, including filtering data to account for known sensitivities and issues plus
using statistical, rather than case-by-case, evaluation, issues due to mismatches in sampling between
observations can be reduced.
Discussion summary
The discussion was limited due to time constraints. A summary of information from the session andproposals, use of models include instrument models/simulators and multiple scattering models as wellas radiative transfer models for radiative closure studies. Model systems are planning to use
EarthCARE data, e.g., ECMWF, which can be used to monitor the changes in the data.
Given the significant amount of sub-orbital observations being taken, including in-situ aircraft andsurface-based observations, a question is if this data can be used for model evaluation anddevelopment. This could include coordinated model studies overlapping surface sites and aircraft
campaigns.