Abstract's details
Sentinel-6 MF Poseidon-4 Radar Altimeter In-Flight Calibration and Performances Monitoring
CoAuthors
Event: 2022 Ocean Surface Topography Science Team Meeting
Session: Sentinel-6 Validation Team (S6VT) feedbacks
Presentation type: Type Poster
Contribution: PDF file
Abstract:
Poseidon-4 is a dual frequency redundant radar altimeter, embarked on board of European Commission Copernicus Programme Sentinel-6 MF satellite, which represents a significant breakthrough with respect to its predecessors Jason-class altimeters thanks to its digital architecture (based on an on-board digital matched-filtering) and to novel internal calibrations modes.
In this work, we assess Poseidon-4 main instrumental improvements and performances, with the presentation of the more important outcomes from the In-Flight internal calibration modes and from an external calibration analysis over a transponder.
The instrumental performances of the radar altimeter, as verified from its internal calibrations, are excellent: Poseidon-4 delivers a range/azimuth instrument impulse response with the highest quality and fidelity in the age of space-borne radar altimetry and its thermal noise response is almost at level of random noise, and this both for its nominal and redundant side.
A significant power decay of the level of the transmitted power in Ku Band has been detected both for the nominal and redundant side, which will not lead anyhow to a violation of the mission requirement of the minimum signal-to-noise ratio over ocean at the end of the expected satellite life (5.5 years).
The novel CAL1 ECHO-CAL calibration mode allows to characterize very precisely the sensitivity of the instrument impulse response to the in-orbit temperature variations: this has been estimated to be of +0.3 mm for the range and of +0.01 dB for the power in Ku Band. Furthermore, the novel CAL1 INSTR mode successfully allows the monitoring of the transmitted chirp and, in case, to update the chirp replica used on-board for the pulse compression in order to recover for any significant degradation in the impulse response quality during the course of the mission life.
The PTR sidelobes in Ku Band do not evolve in a perfect symmetrical manner between the left-hand side and right-hand side but some deviations have been registered for side-A (0.5 mm and 0.025 dB after 10 months). The impact of these dis-symmetries on the range measurement stability will be analyzed in a separate work (S6PP science results, abstract submitted in the same session).
The external calibration by transponder analysis highlights a very small end-to-end range bias and a time-tag bias.
In this work, we assess Poseidon-4 main instrumental improvements and performances, with the presentation of the more important outcomes from the In-Flight internal calibration modes and from an external calibration analysis over a transponder.
The instrumental performances of the radar altimeter, as verified from its internal calibrations, are excellent: Poseidon-4 delivers a range/azimuth instrument impulse response with the highest quality and fidelity in the age of space-borne radar altimetry and its thermal noise response is almost at level of random noise, and this both for its nominal and redundant side.
A significant power decay of the level of the transmitted power in Ku Band has been detected both for the nominal and redundant side, which will not lead anyhow to a violation of the mission requirement of the minimum signal-to-noise ratio over ocean at the end of the expected satellite life (5.5 years).
The novel CAL1 ECHO-CAL calibration mode allows to characterize very precisely the sensitivity of the instrument impulse response to the in-orbit temperature variations: this has been estimated to be of +0.3 mm for the range and of +0.01 dB for the power in Ku Band. Furthermore, the novel CAL1 INSTR mode successfully allows the monitoring of the transmitted chirp and, in case, to update the chirp replica used on-board for the pulse compression in order to recover for any significant degradation in the impulse response quality during the course of the mission life.
The PTR sidelobes in Ku Band do not evolve in a perfect symmetrical manner between the left-hand side and right-hand side but some deviations have been registered for side-A (0.5 mm and 0.025 dB after 10 months). The impact of these dis-symmetries on the range measurement stability will be analyzed in a separate work (S6PP science results, abstract submitted in the same session).
The external calibration by transponder analysis highlights a very small end-to-end range bias and a time-tag bias.