Abstract's details
Improved SAR-mode ocean retrievals from new Cryosat-2 processing schemes
CoAuthors
Event: 2015 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Measurement and retracking (SAR and LRM)
Presentation type: Type Oral
Contribution: PDF file
Abstract:
New SAR-mode processing schemes enabling a more efficient exploitation of the capabilities of the SIRAL altimeter compared to those obtained with the actual Cryosat-2 ground processing, have been investigated and analyzed thanks to easy-to-use and versatile tools developed in CNES/CLS premises.
It has been clearly demonstrated that the actual SAR-mode performances are not optimized since the current method does not take maximum advantage from the Doppler processing. This observed limited improvement is due to the fact that in a stack, the contributing beams to the final averaged waveform have different mean shapes related to the looking angle of measurement, leading to an effective number of looks that is lower than the number of beams. This number has been computed theoretically and is consistent with the actual SAR retracking estimation noise.
It is thus essential to develop alternative methods allowing a better processing to improve the range noise reduction and ensure maximized scientific returns from Cryosat-2 data, but also from the upcoming Sentinel-3 and Sentinel-6 missions.
Different processing approaches have been then recently studied with Cryosat-2 data showing potential improvement of the SAR altimetric measurements’ precision over ocean, at the expense of a slightly lower spatial resolution for some of the proposed solutions. For each SAR/Doppler processing scheme, a data set of at least one-month duration has been produced over open ocean and their performances assessed through the use of common validation tools and protocols via comparison with operational-like data products (generated with CNES processor CPP). The aim is to determine whether the new processing schemes have a potential impact in operational use or not.
We will present the principle of these methods, and their benefits will be displayed.
It has been clearly demonstrated that the actual SAR-mode performances are not optimized since the current method does not take maximum advantage from the Doppler processing. This observed limited improvement is due to the fact that in a stack, the contributing beams to the final averaged waveform have different mean shapes related to the looking angle of measurement, leading to an effective number of looks that is lower than the number of beams. This number has been computed theoretically and is consistent with the actual SAR retracking estimation noise.
It is thus essential to develop alternative methods allowing a better processing to improve the range noise reduction and ensure maximized scientific returns from Cryosat-2 data, but also from the upcoming Sentinel-3 and Sentinel-6 missions.
Different processing approaches have been then recently studied with Cryosat-2 data showing potential improvement of the SAR altimetric measurements’ precision over ocean, at the expense of a slightly lower spatial resolution for some of the proposed solutions. For each SAR/Doppler processing scheme, a data set of at least one-month duration has been produced over open ocean and their performances assessed through the use of common validation tools and protocols via comparison with operational-like data products (generated with CNES processor CPP). The aim is to determine whether the new processing schemes have a potential impact in operational use or not.
We will present the principle of these methods, and their benefits will be displayed.