CALIBRATION/VALIDATION  of  ERS-2  ALTIMETRY

  Jerome BENVENISTE
  European Space Agency/ESRIN
  Via Galileo Galilei,
  I-00044 Frascati Rome, Italy
  (Jerome.Benveniste@esrin.esa.it)

  A Commissioning Working Group has been constituted in order to
  commission and calibrate the Radar Altimeter (RA) and Microwave
  Radiometer (MWR) on ERS-2. The activities covered by this Group are:
      - RA instrument in-orbit functional verification
      - Validation and use of the ERS-2 RA Fast Delivery products
      - RA instrument calibration using the Fast Delivery products
  (URA/QLOPR)
      - RA instrument calibration using the Final Precision products (OPR)
      - MWR-2 instrument calibration
      - Coordination with PRARE commissioning activities at GFZ-Potsdam.

  (1) Calibration of Range
  The RA calibration method is based on the global comparison of ERS-1 and
  ERS-2 data at crossover points, along collinear tracks, as well as
  comparison of Mean Sea Surface models produced from the two altimeters.
  Cross-calibration of ERS-1 and ERS-2 range for Ice mode is also
  performed with a specific set of ice mode data over ocean. A preliminary
  electromagnetic bias for ERS-2 and a datation bias was estimated. The
  objective was to get an estimate of the relative bias between ERS-1 and
  ERS-2 with an error bar of less than 5 cm with 3 35-day cycles of data.

  (2) Calibration of Sigma-Nought / Wind Speed
  Two methods were envisaged to get calibration coefficients, with error
  estimates: a statistical comparisons of ERS-1 versus ERS-2 sigma-nought
  and a statistical comparison of ERS-1 and ERS-2 wind speed with ECMWF
  wind and in-situ data

  (3) Calibration of Significant Wave Height.
  Three methods were envisaged to get calibration coefficients, with error
  estimates: a comparison with the WAM model, with buoys and with ERS-1.

  The ERS-2 RA & MWR Commissioning Working Group have performing the work
  described above and have reviewed the results. Concerning the range, the
  Fast Delivery data, as well as the Precision OPR data-but with better
  precision, show that the relative range bias is not significantly
  different from zero. The ERS-2 sigma-nought is aligned on ERS-1 and
  calibration coefficients have been estimated for SWH.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry