| Paper: | FR-P1.3 |
| Session: | Instrument Calibration I |
| Time: | Friday, March 30, 14:00 - 14:20 |
| Presentation: |
Oral
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| Topic: |
Sensor calibration: |
| Title: |
SMOS CALIBRATION: TOWARDS A THIRD MISSION REPROCESSING |
| Authors: |
Roger Oliva; Zenithal Blue Technologies for ESA-ESAC | | |
| | Manuel Martin-Neira; ESA-ESTEC | | |
| | Joseph Tenerelli; Ocean Data Lab | | |
| | Ignasi Corbella; Polythecnical University of Catalonia | | |
| | Josep Closa; Airbus Defence and Space - Madrid | | |
| | Juha Kainulainen; Harp Technologies Ltd. | | |
| Abstract: |
The SMOS mission has been in-orbit for over 8 years now, providing for the first time and for this entire time, the longest record of space-sensed soil moisture and ocean salinity measurement, as well as new applications such as measurements of thin ice thickness and surface ocean winds in storms. During this time the SMOS mission has had two mission Reprocessing, and is currently preparing for the third one. A key objective for the third Mission Reprocessing is to improve even further the stability of the measurements. This abstract shows the methodology followed to achieve better stability and its current status.
The difficulty in trying to improve the calibration relies in differentiating instrument related problems to model errors, and also understanding what the origin of the instrument instabilities is.
In order to improve the instrument stability in view of a third mission reprocessing, the SMOS team has applied a new methodology that uses data analytic techniques over a large database of the satellite related available information to determine the origin of the instabilities, and then act on each of them. The process:
1) Compared and correlated the biases with hundreds of parameters, including telemetry, calibration and geophysical information. This step indicated which parameters were more likely to induce the biases.
2) Assessed the contribution of each of this bias candidates to the overall bias error. This problem is similar to resolving a signal decomposition in non-orthogonal basis, in order to account for the contribution of each of the involved signals.
This method determined that SMOS instabilities contributors are mainly 5: The gain of the SMOS reference radiometer (Tna), the external thermal variability at the tip of SMOS antennas (Tp7) and its gradient, and model errors related to the reflected galactic signal and the total electron content in the atmosphere.
The SMOS team used this information to re-assess the calibration procedures. The investigations conveyed over the past year are introducing new changes in the algorithm to improve SMOS calibration:
- Use of a fixed value for the SMOS reference radiometer.
- The refinement of the antenna losses values.
- A correction to incorporate a thermal lag in one of the thermistor measurements are among the initial tests performed.
- The use of a SMOS-derived Sky map.
- And new methods to improve the TEC retrieval.
The first results show that SMOS stability can be qualitatively improved again for a future mission reprocessing. It has been estimated that the standard deviation of the error is reduced by more than half globally.
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