Convergent solutions for retracking conventional and Delay Doppler altimeter echoes

Pierre Thibaut (CLS, France)


Fanny Piras (CLS, France); Jean Christophe Poisson (CLS, France); Thomas Moreau (CLS, France); Jérémie Aublanc (CLS, France); Laiba Amarouche (CLS, France); Abderrahim Halimi (Heriot-Watt University, United Kingdom); François Boy (CNES, France); Amandine Guillot (CNES, France); Sophie Le Gac (CNES, France); Nicolas Picot (CNES, France)

Event: 2017 Ocean Surface Topography Science Team Meeting

Session: Instrument Processing: Measurement and Retracking

Presentation type: Type Oral

During the last years, different teams have devoted huge efforts to improve retracking algorithms for both conventional and Delay Doppler echoes. Recently, for LRM measurements, CLS has developed and successfully validated a new solution called "Adaptive Retracker", implementing a new waveform model and a Nelder Mead optimization method with exact likelihood criterion. Dramatic improvements in the estimation performances over ocean have been shown (respectively 10% and 60% of noise reduction on range and significant wave height, in addition to the reduction of biases in range and SWH estimations). This solution has been presented at the last Eumetsat Conference in 2016 and at the OSTST in La Rochelle, 2016. For non oceanic areas (sea ice and inland water areas), a new model accounting for the roughness of the ocean surface has been introduced to ensure the continuity of estimations from typical Brownian ocean waveforms to peaky waveforms acquired over the leads in the Arctic ocean for example.

Similar developments have been conducted at CLS for retracking the Delay Doppler measurements (Cryosat-2 and Sentinel-3). The roughness parameter has been introduced in both our numerical solution and in the analytical model developed by A. Halimi during his PhD thesis. Consistency between these two solutions is quite perfect allowing us to include such models in our estimation process. As for the conventional LRM retracker, a numerical solution accounting for the real point target response of the instrument, has been privileged with the benefits already seen for conventional altimetry.

The aim of this paper is to present the consistency of this approach and the main figures of performances obtained with such methods (model and estimation algorithm) in both SAR and LRM modes. It will be shown how current (Cryosat-2 and Sentinel-3A) and future missions (Sentinel-3B and Sentinel-6) could benefit from such powerful method that has already proved its worth for conventional missions (Jason-3). Illustrations over different surfaces will be discussed.

Oral presentation show times:

RoomStart DateEnd Date
Symphony Ballroom IV Tue, Oct 24 2017,11:00 Tue, Oct 24 2017,11:15
Pierre Thibaut