# Presentation: 588679

## The ESA Approach to Envisat Calibration and Validation

*Evert Attema*
*Earth Sciences Division*
*ESA / ESTEC*
*Noordwijk, The Netherlands*
*E-Mail: Evert.Attema@esa.int *

## The Environmental Satellite Envisat

**The Environmental Satellite Envisat**

**The Environmental Satellite Envisat**
**ESA’s largest Earth observation mission so far**
**Launcher: Ariane-5**
**Orbit: near-polar at 98.5o inclination**
**Ready for Launch in October 2001**
**Atmospheric variables measured by**
- MERIS, MWR (meteorology)
- GOMOS, MIPAS, SCIAMACHY (chemistry)
**Land surface variables measured by**
- AATSR, MERIS
**Marine variables measured by**
- AATSR, ASAR, MERIS, RA-2

## CEOS Definitions

**CEOS Definitions**

**Calibration **
***is the process of quantitatively defining the system response to known, controlled signal inputs.***
**Validation**
***is the process of assessing by independent means the quality of the data products derived from the system outputs.***

## Envisat

**observed scene**

**Envisat**

**instrument calibration**
**data calibration**
**geophysical  calibration**

**raw data**

**geophysical variable**
**estimate**

**validation**
**=**
**comparison**

**feed-back to calibration**
**(if needed)**
**quality statement**

**data release to**
**user community**

## CALIBRATION AND VALIDATION OBJECTIVES

**Calibration**
- Full in-flight calibration and re-characterisation of the instrument.
- Complete verification of the L1b processor
- First upgrade of the Level 1b ground processor by the end of the Commissioning Phase
- Routine calibration operations by the end of the Commissioning Phase
**Validation**
- Level 2 algorithm verification providing data products with consistent geophysical behaviour by the end of the Commissioning Phase
- Data quality assessment at a Validation Workshop 9 months after launch based on a sufficiently large number of correlative measurements of sufficient quality covering large areas and a wide range of conditions under strict data quality control using established, well-defined techniques
- Recommendations for long-term validation

## Envisat Data Products

**Envisat Data Products**

**Engineering Variables (Level 1b)**
- Radiance, Transmittance, Reflectance, Radar Backscattering Coefficient, Radar Echo Time Delay
**Atmospheric Variables (Level 2)**
- Profiles of Pressure, Temperature, O3, H2O, NO2, NO3, H2O, CH4, HNO3
- Columns of O3, NO2, H2O, N2O, CO, CH4, OClO, H2CO, SO2
- Aerosol Extinction, Optical Thickness, Type, Absorption Indicator
- Cloud Cover Fraction, Cloud Top Height & Pressure, Cloud Albedo and Optical Thickness
**   ****Land Surface Variables (Level 2)**
- Vegetation Index, Reflectance, Surface Temperature & Pressure
**   ****Marine Variables (Level 2)**
- Significant Wave Height, Wind Speed , Sea Surface Temperature
- Water-leaving Reflectance, Yellow Substance, Chlorophyll, Suspended Matter, PAR (fluorescence)

## Envisat Calibration and Validation Coordination Approach

**INSTRUMENT CALIBRATION**
**ALGORITHM VERIFICATION**

**ASAR**
**MERIS**
**RA2/MWR**
**AATSR**
**MIPAS**
**GOMOS**
**SCIAMACHY**

**ASAR**
**RA2/MWR**
**MAVT for**
**MERIS & AATSR**
**ACVT for**
**MIPAS, GOMOS & SCIAMACHY**

**ENVISAT CALIBRATION AND VALIDATION**

**PRECISE ORBIT **
**DETERMINATION**

**VALIDATION**

**POD for**
**DORIS & LRR**** **

## Activities are being Co-ordinated via ESA Calibration and Validation Teams consisting of ESA staff and contractors (e.g. Expert Support Laboratories) and Principal Investigators of the Envisat Announcement of Opportunity

**ASAR Calibration & Validation Team**
**RA-2/MWR Calibration Team**
**RA-2/MWR Validation & Cross-Calibration Team(CCVT)**
**MERIS Calibration Team**
**AATSR Calibration & Algorithm Verification Team**
**MERIS (& AATSR) Validation Team(MAVT)**
**MIPAS Calibration & Algorithm Verification Team**
**GOMOS Calibration & Algorithm Verification Team**
**SCIAMACHY Calibration & Algorithm Verification Team**
**Atmospheric Chemistry Validation Team(ACVT)**
**Precise Orbit Determination Team(POD)**

## Advanced Synthetic Aperture Radar (ASAR)

**Advanced Synthetic Aperture Radar (ASAR)**

**Coherent, active phased array SAR**
**Operated at C-band (5.331 GHz)**
**Active phase array antenna**
**Image modes**
- Seven predetermined swaths
- Vertically or horizontally polarised radiation for transmit and receive
- Wide swath options using scansar
**Wave mode**
- Same swaths and polarisations as image mode
- Small areas of the ocean are imaged at regular intervals along the swath  low data rate for on-board storage

## ASAR Calibration and Validation Team

**ASAR Calibration and Validation Team**

**Instrument In-flight Calibration**
**Processor Verification ****(Level 1b and Level 2)**
**Calibration and Validation Variables**
- Image quality of Radar imagery (radiometry, geometry, polarimetry)
- Directional ocean spectrum
- Significant wave height
- Wind speed & direction
**Proposed Methods**
- Imaging transponders and stable natural targets
- Airborne radar underflights
- Buoy data and model assimilation for wind & wave products
- Comparisons with other satellites: ERS-2, RADARSAT, TOPEX/POSEIDON, JASON, GFO, Envisat(RA-2)

## Radar Altimeter-2 (RA-2)

**Radar Altimeter-2 (RA-2)**

**measurements of ocean topography****surface wind speed****significant wave height**
**monitor sea ice, ****polar ice sheets, ****land surface elevation, geological structure****surface characteristics**
**footprint 1.7km, ****improved instrument derived from ERS-1 and -2 Radar Altimeter**

## Microwave Radiometer (MWR)

**major objective: measurement of integrated atmospheric water vapour column and cloud liquid water content, as correction terms for RA-2**
**dual-channel nadir-pointing Dicke-type radiometer @ 23.8 and 36.5GHz (differential measurement principle)**

## RA-2/MWR Calibration TeamRA-2/MWR Validation & Cross-Calibration Team

**RA-2/MWR Calibration Team****RA-2/MWR Validation & Cross-Calibration Team**

**Instrument In-flight Calibration**
**Processor Verification ****(Level 1b and Level 2)**
**Calibration and Validation Variables**
- RA-2: range, significant wave height, wind speed
- MWR: water vapour and liquid water content
**Proposed Methods**
- Ground-based stations/transponders and sondes
- Buoys/tide gauges
- GPS data
- Satellite data (ERS, TOPEX/POSEIDON, JASON, GEOSAT Follow-On
- Algorithm verification

## MEdium Resolution Imaging Spectrometer Instrument (MERIS)

**MEdium Resolution Imaging Spectrometer Instrument (MERIS)**

**Pushbroom imaging spectrometer**
**Ground spatial resolution **
- 300m / 1200m
**15 spectral bands in VIS and NIR**
**Primary objectives: **
- measurement of chlorophyll concentrations for open ocean  and coastal waters
- measurement of ocean colour
** ****Secondary objectives: **
- cloud top height, water vapour total column, aerosol over land

## Advanced Along Track Scanning Radiometer (AATSR)

**Advanced Along Track Scanning Radiometer (AATSR)**

**IR channels **
- 1.6, 3.7, 10.7 and 12 microns
**VIS channels **
- 0.87, 0.67 and 0.55 microns
**Two-angle viewing geometry**
**Conical scan**
**Resolution: 1x1km2 at nadir**
**Primary objective: **
- continuation of ERS-1, -2 ATSR data sets of precise (~0.3K) sea surface temperature (thermal IR channels)
**Secondary objective: **
- land surfaces, particularly vegetation biomass, moisture, health and growth stage (visible channels)

## MERIS Calibration TeamAATSR Calibration & Algorithm Verification Team

**Instrument In-flight Calibration**
**Vicarious Calibration ******** desert sites, clouds, rayleigh scattering over clear water**
**Processor Verification (Level 1b and Level 2)**
**AATSR is the responsibility of the instrument provider but activities are coordinated at technical level**

## MERIS and AATSR Validation Team (MAVT)

**50**

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**Elbe-**
**Estuary**

**Sylt**

**Suspended Matter [mg/l]**

**MERIS**** and AATSR Validation Team (MAVT)**

**Measurement Variables for Ocean/Land**
- Radiance and reflectance
- Concentrations of chlorophyll suspended matter and yellow substance
- Vegetation indices
**Proposed Methods and Facilities**
- Optical buoys
- Research cruises and other vessels
- Towed instrumentation
- In-situ sampling
- Airborne spectrometer underflights
- Comparison with other satellites (POLDER, VEGETATION, AVHRR)

## MERIS and AATSR Validation Team (MAVT) - continued

**Atmospheric Measurement Variables**
- Cloud cover
- Cloud top pressure,
- Cloud optical thickness and albedo
- Water vapour, aerosol
**Proposed Methods and Facilities**
- sun and sky scanning spectral radiometers (AERONET, CIMEL)
- Radio sounding, GPS, microwave radiometers and LIDAR
- Comparison with POLDER and the Envisat instruments AATSR, SCIAMACHY and MWR

## MERIS and AATSR Validation Team (MAVT) - continued

**MERIS and ****AATSR**** Validation Team (MAVT) ***- continued*

**Validation Variables**
- Top of atmosphere (TOA) brightness
- Surface temperature for land and ocean
- Cloud top temperature
**Proposed Methods**
- Comparisons with other satellites POLDER, VEGETATION
- Research cruises
- SST buoys
- Sun/sky radiometers
- Algorithm verification and development

## MIPAS

**Fourier transform IR spectrometer (685-2410cm-1) providing vertical profiles of p, T, O3, H2O, CH4, N2O, HNO3 at a vertical resolution of 3-4km**

## GOMOS: stellar occultation instrument, UV-VIS (250-675nm), NIR (756-773nm, 926-952nm)

**GOMOS: stellar occultation instrument, ****UV-VIS (250-675nm), NIR (756-773nm, 926-952nm)**

**Stratospheric & Mesospheric O3 Profiles (major objective)**** **
**Profiles of **
- NO2, NO3, H2O
- aerosol
- high resolution temperature
**at a vertical resolution of 1.7km and better, depending on occultation obliqueness**

## SCIAMACHY

**SCIAMACHY**

**Spectrometer (UV, VIS, IR)**
**AO Instrument**
**Various Operational Modes**
- limb
- nadir
- solar & lunar occultation
**Vertical Columns and Profiles of**
- ozone and various trace gases
- cloud cover and cloud top height
- aerosol absorption

## Calibration & Algorithm Verification Teams for the Atmospheric Chemistry Instruments MIPAS, GOMOS and SCIAMACHY

**Secondary peak height 17.5%**

**Spectral Resolution:**
**FWHM =0.0338 cm****-1**

**Calibration & Algorithm Verification Teams for the ****Atmospheric Chemistry Instruments MIPAS, GOMOS and SCIAMACHY**

**Instrument In-flight ****Calibration **
**Processor Verification ****(Level 1b and Level 2)**

## Atmospheric Chemistry Validation Team (ACVT)

**Ground-based instruments**
- Ozone and radio soundings
- Lidars
- UV-VIS spectrometers
- Fourier transform spectrometers and radiometers
- Microwave radiometers
**Aircraft Measurements and ****Dedicated Balloon Campaigns**
- ‘small’ and ‘large’ balloons
- M55 ‘Geophysica’
- DLR Falcon

## Atmospheric Chemistry Validation Team (ACVT) - continued

**Atmospheric Chemistry Validation Team (ACVT) ***- continued*

**Satellite Measurements**
- AMSR, AMSU, AVHRR, ATSR2, GOME, HALOE, HIRLDS,
- METEOSAT, MOPITT, OMI, OSIRIS, POAM III, POLDER,
- SABER, SAGE II, SAGE III, SBUV, SMR, SUSIM, SOLSPEC,TOMS
**Model Assimilation ****	**
-  assimilation in transport/dynamic models & meteorological models
-  assimilation in chemistry-transport models including active chemistry
-  comparison to assimilated TOMS & SBUV/2

## Precise Orbit Determination Team (POD)

**Orbit Calibration and Validation ****using DORIS ( Doppler Orbitography and ****Radiopositioning Integrated by Satellite) **
**Satellite tracking system using network ****of ground-based beacons and Lidars**
**Orbit determination with accuracy of ****the order of centimetres**
**On-board processing for real-time ****satellite position (accuracy about 10 cm)**

## Supporting Activities

**Data storage facility at NILU in Norway**
- Provision of data storage / data access for correlative measurements
- Access for all calibration and validation participants
**ECMWF**
- Technical support of Envisat mission
- Contribution to validation and long-loop monitoring of meteo products from ASAR, RA-2, MWR, GOMOS, MIPAS, SCIAMACHY
- Support through data assimilation and analysis using NWP facilities
- Furthermore, ECMWF provides meteorogical data for Envisat data product generation

## Envisat Calibration and Validation Funding Approach

**Combination of ESA contracts and Announcement of Opportunity(AO) Contributions**** **
**AO PIs have Free Access to Data, no Funding **** **
**Engineering Calibration Primarily under ESA contract with Additional Support by AO PIs**** **
**Geophysical Validation Primarily by AO PIs but for Cal/Val co-funding Negotiated with ESA Member States**

## Calibration and Validation Schedule

**Selection of AO proposals****	****	****	****	****End 1998**
**Formation of validation teams****	****	****	****Mid 1999**
**Rehearsals****	****	****	****	****	****	****2000/2001**
**Start of commissioning phase, data acquisition ****	****Launch****analysis, calibration****	****	****	**
**End commissioning phase ****	****	****	****	****L + 6 months**
- L1b fully verified, L2 preliminarily validated
- release of data to the general public
**Validation workshop****	**** ****	****	****	****L + 9 months**
- L2 preliminary validation consolidated
**First data processor update****	****	****	****L + 12 months**
**Long-term validation****	****	****	****	****Phase E (Operation)**

## Summary

**Summary**

**Schedule:**
- Envisat Launch: October 2001
- Calibration during the Commissioning Phase: L to L+6
- Validation starting during Commissioning Phase; concentrated activities during Commissioning Phase until ~L+9; long-term validation during mission Phase E
- no release of data to general public during commissioning phase
**Calibration and Validation Activities**
- ESA calibration and algorithm verification groups for each individual instrument
- ESA validation groups: ACVT, MAVT (MERIS/AATSR), RA-2/MWR(CCVT), ASAR, POD
- Group composition: ESA with contractors (ESLs) and PI’s of AO proposals
**Envisat web page: http://envisat.esa.int**