Abstract's details
A Complex Correction for the End-to-End Range Impulse Response of the Sentinel-6 MF Altimeter System
CoAuthors
Event: 2023 Ocean Surface Topography Science Team Meeting
Session: Sentinel-6 Validation Team (S6VT) Meeting
Presentation type: Type Poster
Contribution: not provided
Abstract:
Moving from the work presented at 12th Coastal Altimetry Workshop by Abileah & Vignudelli [REF1], we studied a 256-sample complex correction to the end-to-end range impulse response (RIR) of the Sentinel-6 MF POS4 altimeter system.
This complex correction can calibrate any instrumental and antenna distortions out over the whole mission time (like RIR asymmetries, RIR main-lobe widening, antenna imperfections, etc.) and hence is expected to improve the quality and fidelity of the end-to-end RIR of the Sentinel-6 MF POS4 altimeter system.
The first step of this end-to-end correction consists in the estimation of the amplitude and phase distortions of the POS4 CAL1 internal path. This is performed by means of the POS4 CAL-1 SAR I/Q calibration data, estimating the fast-time (i.e. in range) amplitude and phase distortions over the mission time.
Given the digital architecture of POS4 altimeter, the POS4 CAL1 phase distortions are (as expected) negligible and steady in time, with a peak-to-peak error in Ku-Band of around 1 degree. Instead, the CAL1 amplitude distortion features in Ku-Band an exponential profile with a decay rate which is getting stronger over the time since its peak-to-peak error ranges from 0.15 dB (at BoM, side-B) to 0.4 dB (August-2023).
The second step of the end-to-end correction consists in adding to the afore-said CAL1 distortions the antenna amplitude and phase distortions, as these have been measured in the pre-launch antenna characterization test reports.
The end-to-end complex correction will be the inverse of the estimated CAL1+antenna amplitude and phase distortions.
This complex correction will be applied to a theoretical squared sinc function (i.e. ideal RIR) and compared to the end-to-end RIR currently observed over corner reflector (CR) in Fully-Focused SAR, once this latter one has been averaged for several CR passes.
Potential ways-forward to implement this correction on ground and potential measurement of the reported distortions over natural targets (as Etosha Pan) will be presented.
REF1: R. Abileah, S. Vignudelli: A phase error in Sentinel-3 Individual Echoes, and how to correct the error in post processing, 12th Coastal Altimetry Workshop, Cadiz, 2023
This complex correction can calibrate any instrumental and antenna distortions out over the whole mission time (like RIR asymmetries, RIR main-lobe widening, antenna imperfections, etc.) and hence is expected to improve the quality and fidelity of the end-to-end RIR of the Sentinel-6 MF POS4 altimeter system.
The first step of this end-to-end correction consists in the estimation of the amplitude and phase distortions of the POS4 CAL1 internal path. This is performed by means of the POS4 CAL-1 SAR I/Q calibration data, estimating the fast-time (i.e. in range) amplitude and phase distortions over the mission time.
Given the digital architecture of POS4 altimeter, the POS4 CAL1 phase distortions are (as expected) negligible and steady in time, with a peak-to-peak error in Ku-Band of around 1 degree. Instead, the CAL1 amplitude distortion features in Ku-Band an exponential profile with a decay rate which is getting stronger over the time since its peak-to-peak error ranges from 0.15 dB (at BoM, side-B) to 0.4 dB (August-2023).
The second step of the end-to-end correction consists in adding to the afore-said CAL1 distortions the antenna amplitude and phase distortions, as these have been measured in the pre-launch antenna characterization test reports.
The end-to-end complex correction will be the inverse of the estimated CAL1+antenna amplitude and phase distortions.
This complex correction will be applied to a theoretical squared sinc function (i.e. ideal RIR) and compared to the end-to-end RIR currently observed over corner reflector (CR) in Fully-Focused SAR, once this latter one has been averaged for several CR passes.
Potential ways-forward to implement this correction on ground and potential measurement of the reported distortions over natural targets (as Etosha Pan) will be presented.
REF1: R. Abileah, S. Vignudelli: A phase error in Sentinel-3 Individual Echoes, and how to correct the error in post processing, 12th Coastal Altimetry Workshop, Cadiz, 2023