The ESA Approach to Envisat Calibration and Validation

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The ESA Approach to Envisat Calibration and
Validation

• Evert Attema
• Earth Sciences Division
• ESA / ESTEC
• Noordwijk, The Netherlands
• E-Mail Evert.Attema_at_esa.int

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The Environmental Satellite Envisat

• The Environmental Satellite Envisat
• ESAs 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

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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.

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instrument calibration data calibration geophysica
l calibration
data release to user community
raw data
geophysical variable estimate
Envisat
validation comparison
feed-back to calibration (if needed) quality
statement
observed scene
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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

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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)

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Envisat Calibration and Validation Coordination
Approach
ENVISAT CALIBRATION AND VALIDATION
INSTRUMENT CALIBRATION ALGORITHM VERIFICATION
PRECISE ORBIT DETERMINATION
VALIDATION
ASAR MERIS RA2/MWR AATSR MIPAS GOMOS SCIAMACHY

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

• POD for
• DORIS LRR

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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)

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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

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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)

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Radar Altimeter-2 (RA-2)

• measurements of ocean topographysurface wind
  speedsignificant wave height
• monitor sea ice, polar ice sheets, land surface
  elevation, geological structuresurface
  characteristics
• footprint 1.7km, improved instrument derived
  from ERS-1 and -2 Radar Altimeter

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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
  _at_ 23.8 and 36.5GHz (differential measurement
  principle)

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RA-2/MWR Calibration TeamRA-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

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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

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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)

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MERIS Calibration TeamAATSR 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

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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)

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Sylt
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Elbe- Estuary
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300
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0
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Suspended Matter mg/l
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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

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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

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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

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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

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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

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

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

Spectral Resolution FWHM 0.0338 cm-1
Secondary peak height 17.5
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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

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Atmospheric Chemistry Validation Team (ACVT) -
continued
MOPITT

• 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

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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)

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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

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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

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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
  Launchanalysis, 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)

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Summary

• Schedule
• Envisat Launch October 2001
• Calibration during the Commissioning Phase L to
  L6
• Validation starting during Commissioning Phase
  concentrated activities during Commissioning
  Phase until L9 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 PIs of AO proposals
• Envisat web page http//envisat.esa.int