ra-2/mwr/doris session instrument, level 1b and absolute calibrations by m. roca et al

ENVISAT Validation Review - ESRIN - 9–13 Dec 2002 - RA2/MWR/DORIS

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


Instrument and Level 1b OverviewInstrument:* 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.


* Regional calibration for maximum precision

* Co-ordinated campaign using:• Buoys• Tide Gauges• Modelling

* Permanent sites for long term monitoring

Absolute Range Calibration


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


Absolute Range Calibration - Preliminary Results

• 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.

-1

-0.5

0

0.5

1

1.5

19160 19180 19200 19220 19240 19260 19280 19300

CasablancaFTB2FTB4ICM

bias estimation = 41 cm ?quoted error = 6 cm ?

Objectives for EGU, April’2003:


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


Sigma-0 - Absolute Calibration Results* Transponder calibrated

– RCS = 75.08 dB m^2;– rss = 0.11 dB; and – stability = 0.06 dB.

RA-2 power bias = + 0.831 dBEstimated 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.

Measured Received Power vs Theoretical Power

y = -0.0027x2 + 0.1643x + 21.953

y = -0.0025x2 + 0.1443x + 23.3

21

22

23

24

25

26

27

1 6 11 16 21 26 31 36 41 46 51 56 61 66data_blocks

power [dB]

Theor_power Eval_area_pw Poly. (Theor_power) Poly. (Eval_area_pw)

ra-2/mwr/doris session instrument, level 1b and absolute calibrations by m. roca et al

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