Abstract's details
Sentinel-3A, Jason-3 and AltiKa instrumental drifts and their impacts on geophysical estimates
CoAuthors
Event: 2019 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Measurement and Retracking
Presentation type: Type Oral
Contribution: PDF file
Abstract:
Measuring sea surface height from space is a challenging exercise. Even if the measurement principle is simple in theory (a difference between the satellite altitude and the measured altimeter range), a large set of corrections must be applied to satellite measurements so as to manage all potential errors. Instrumental corrections are one of the most important and essential correction set to be accounted for. Radar altimeters are designed and calibrated on ground before the satellite launch but then, are not perfectly stable over time. Once in flight, the altimeter is subjected to extreme conditions impacting its electronics components that are monitored via the instrumental impulse response. The evolutions of the instrument behavior must then be accounted for in order to ensure the measurement quality and stability, in particular for climate application purpose.
In all altimeter missions, instrumental calibrations are regularly performed (several times per day) in order to monitor the instrument PTR (and also the low pass filter of the RX chain). In each altimeter ground segment, the PTR monitoring is exploited to derive instrumental corrections that are applied on the altimeter range (the internal path delay correction) and the backscatter coefficient (PTR total power). These two instrumental corrections allow to correct altimeter measurements from any instrumental drift if and only if the altimeter PTR is symmetric (the PTR has a squared sinc shape). From previous studies conducted in the frame of the Sentinel-3 Mission Performance Center, it has been shown that the PTR symmetry of the Sentinel-3A radar altimeter (SRAL) is changing, impacting geophysical measurements, sigma naught, sea level but also significant wave height measurements.
In this study we propose to compare Sentinel-3A, Jason-3 and AltiKa PTR drifts/evolutions and to assess how geophysical estimates are impacted by the instrumental ageing.
This analysis is of particular importance to be certain that the Sentinel-6 ground processing chains are well designed to guaranty an accurate measurement of the global mean sea level trend. This is a major requirement of the Sentinel-6 mission.
In all altimeter missions, instrumental calibrations are regularly performed (several times per day) in order to monitor the instrument PTR (and also the low pass filter of the RX chain). In each altimeter ground segment, the PTR monitoring is exploited to derive instrumental corrections that are applied on the altimeter range (the internal path delay correction) and the backscatter coefficient (PTR total power). These two instrumental corrections allow to correct altimeter measurements from any instrumental drift if and only if the altimeter PTR is symmetric (the PTR has a squared sinc shape). From previous studies conducted in the frame of the Sentinel-3 Mission Performance Center, it has been shown that the PTR symmetry of the Sentinel-3A radar altimeter (SRAL) is changing, impacting geophysical measurements, sigma naught, sea level but also significant wave height measurements.
In this study we propose to compare Sentinel-3A, Jason-3 and AltiKa PTR drifts/evolutions and to assess how geophysical estimates are impacted by the instrumental ageing.
This analysis is of particular importance to be certain that the Sentinel-6 ground processing chains are well designed to guaranty an accurate measurement of the global mean sea level trend. This is a major requirement of the Sentinel-6 mission.