Abstract's details
S6 P4 GPP: Fully Focused Delay-Doppler Processing applied on RAW and RMC data- Preliminary results
CoAuthors
Event: 2018 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Measurement and Retracking
Presentation type: Type Poster
Contribution: not provided
Abstract:
During the last decade the radar altimetry has entered in its golden age as demonstrated by the different number of missions (Jason-2/-3, CryoSat-2, Saral/Altika, Sentinel-3) currently operating and the forthcoming ones (Sentinel-6). The relatively new operational synthetic aperture radar (SAR) mode in CryoSat-2 and Sentinel-3 missions, opened a new paradigm in the capabilities that can offer an altimetric radar mission. In this line, lessons learned from classical 2-D SAR focusing are exploited to evaluate the imaging-like capability of delay-Doppler altimetric radar mounted on future Sentinel-6 over coastal areas. In this way, the altimetric product gets closer to the conventional SAR imaging data, but in the altimeter case a “strip-like” image is obtained compared to the classical SAR image.
Conventional delay-Doppler processor (DDP) coherently integrates a series of pulses to provide specific Doppler beams focused to a specific location, which after being correctly aligned (compensating for the slant-range variation, among others) provide several looks that can be incoherently averaged, increasing the performance in terms of geophysical retrieval (increasing the signal-to-noise ratio-SNR). The fully focused DDP (FF-DDP) moves one step ahead and intends to coherently integrate such information to get an even higher along-track resolution with an improved SNR and the available number of beams [RD-1].
In order to achieve such imaging capability, the azimuth or along-track phase modulation needs to be compensated for. The relative movement between the scene and the satellite creates a chirp-like modulation in the along-track dimension (quadratic phase response), and so an azimuth compression needs to be performed (once range migration has been compensated) to obtain a fully focused SAR strip, analogous to the well-known range compression (where a specific chirp pulse is compressed).
Sentinel-6 Poseidon-4 radar altimeter includes various innovations, among which we have the new on-board capability or processing called RMC, a Range Migration Correction applied on-board with a priori fixed orbit parameters, and performed to reduce the amount of data to download.
A particular concern is the processing of the FF-DDP technique with the RMC data.
The main objective of this presentation is to provide a general description of the algorithmical implementation of the FF-DDP. This will confer the SAR altimetric product a very high resolution (in the order of 0.6 m) of great interest for Coastal and In-land Altimetry, providing much higher number of looks that can be averaged to improve the altimetric performance as anticipated by Raney in [RD-2]. The operation of this processing chain will be demonstrated with simulated data provided by ESA-ESTEC considering both input data from RAW and RMC modes (undoing the on-board RMC processing). Main stress will be devoted to the evaluation over transponder data to validate the FF-DDP chain, *showing the impact of using RMC data compared to RAW data*. Initial results of processing ocean simulated data with the FF-DDP may be included.
References:
[RD-1] A. Egido and W. H. F. Smith, "Fully Focused SAR Altimetry: Theory and Applications," in IEEE Transactions on Geoscience and Remote Sensing, vol. 55, no. 1, pp. 392-406, Jan. 2017.
[RD-2] Curlander, John C., and Robert N. McDonough. Synthetic aperture radar. New York, NY, USA: John Wiley & Sons, 1991.
Conventional delay-Doppler processor (DDP) coherently integrates a series of pulses to provide specific Doppler beams focused to a specific location, which after being correctly aligned (compensating for the slant-range variation, among others) provide several looks that can be incoherently averaged, increasing the performance in terms of geophysical retrieval (increasing the signal-to-noise ratio-SNR). The fully focused DDP (FF-DDP) moves one step ahead and intends to coherently integrate such information to get an even higher along-track resolution with an improved SNR and the available number of beams [RD-1].
In order to achieve such imaging capability, the azimuth or along-track phase modulation needs to be compensated for. The relative movement between the scene and the satellite creates a chirp-like modulation in the along-track dimension (quadratic phase response), and so an azimuth compression needs to be performed (once range migration has been compensated) to obtain a fully focused SAR strip, analogous to the well-known range compression (where a specific chirp pulse is compressed).
Sentinel-6 Poseidon-4 radar altimeter includes various innovations, among which we have the new on-board capability or processing called RMC, a Range Migration Correction applied on-board with a priori fixed orbit parameters, and performed to reduce the amount of data to download.
A particular concern is the processing of the FF-DDP technique with the RMC data.
The main objective of this presentation is to provide a general description of the algorithmical implementation of the FF-DDP. This will confer the SAR altimetric product a very high resolution (in the order of 0.6 m) of great interest for Coastal and In-land Altimetry, providing much higher number of looks that can be averaged to improve the altimetric performance as anticipated by Raney in [RD-2]. The operation of this processing chain will be demonstrated with simulated data provided by ESA-ESTEC considering both input data from RAW and RMC modes (undoing the on-board RMC processing). Main stress will be devoted to the evaluation over transponder data to validate the FF-DDP chain, *showing the impact of using RMC data compared to RAW data*. Initial results of processing ocean simulated data with the FF-DDP may be included.
References:
[RD-1] A. Egido and W. H. F. Smith, "Fully Focused SAR Altimetry: Theory and Applications," in IEEE Transactions on Geoscience and Remote Sensing, vol. 55, no. 1, pp. 392-406, Jan. 2017.
[RD-2] Curlander, John C., and Robert N. McDonough. Synthetic aperture radar. New York, NY, USA: John Wiley & Sons, 1991.