1
RA-2/MWR/DORIS Session Instrument, Level 1b and
Absolute Calibrations by M. Roca et al.

• Instrument and Level 1b overview
• Absolute Range Calibration preliminary results
  and next steps
• Absolute Sigma-0 Calibration results and future
  plans

 
2
Instrument and Level 1b Overview

• Instrument
• All parameter optimised by the Calibration review
  (last modification in September)
• Instrument Performance have since been excellent
  !
• Level 1b
• Correction for datation and range bias was
  verified. Implementation in the IPF since v4.53.
• Further correction in the sigma-0 computation
  implemented in the reference processor. To be in
  the next version of the IPF.
• Modification of the PTR computation also included
  in the reference processor. To be in the next
  version of the IPF.

3
Absolute Range Calibration

• Regional calibration for maximum precision
• Co-ordinated campaign using
• Buoys
• Tide Gauges
• Modelling
• Permanent sites for long term monitoring

4
Absolute Range Calibration - Preliminary Results

• A total of in-situ measurements
• 44 measurements of light GPS buoys (IEEC/ICM)
• 2 moored GPS buoys (IfGN), with a total of 16
  passes each
• 6 coastal tide gauges (IMEDEA, ICM, LEGOS,
  SHOM)
• Propagation of in-situ measurements towards the
  satellite tracks through geophysical models.
• Dedicated corrections to be applied to the
  altimeter estimated range (from Level 2 products)
  provided by several groups
• short arc orbits, by DEOS
• atmospheric correction (with ECMWF and on-ground
  MWR), by TOS

5
Absolute Range Calibration - Preliminary Results
bias estimation 41 cm ? quoted error 6 cm ?
Objectives for EGU, April2003

• include coastal tide gauges in the bias
  estimation once errors in the MSS model at the
  coast have been reduced
• improved ionospheric correction
• new model for sea state bias developed by CLS to
  be applied
• formal computation of the error
• error to be reduced to 1 cm, as per requirement.
• Long term monitoring with Casablanca oil platform
  and Eivissa TG.

6
Sigma-0 Absolute Calibration

• Absolute Sigma-0 calibration never been attempted
• Scientific needs demonstrated
• Requirement
• 0.5 dB
• 0.1 dB stability over
• 3 years
• Dedicated transponder developed at ESTEC

7
Sigma-0 - Absolute Calibration Results

• Transponder calibrated
• RCS 75.08 dB m2
• rss 0.11 dB and
• stability 0.06 dB.
• RA-2 power bias 0.831 dB
• Estimated error 0.28 dB
• Further improvement is expected with the analysis
  bias with the we need to retrieve more passes.
• Future a site will be identified in the vicinity
  of ESRIN, where the TRP will be located for
  further measurement, and eventually, drift
  monitoring.