The Aresys FF-SAR Service for Cryosat-2 at ESA GPOD

Michele Scagliola (Aresys, Via Privata Flumendosa 16, 20132 Milano, Italy)


Marco Restano (SERCO c/o ESA/ESRIN, Italy); Mauro Arcorace (Progressive Systems/ESRIN, Frascati, Italy, Italy); Marco Fornari (ESA-ESTEC Keplerlaan 1, PO Box 299, NL-2200 AG Noordwijk, The Netherlands); Giovanni Sabatino (Progressive Systems/ESRIN, Frascati, Italy, Italy); Jérôme Benveniste (ESA-ESRIN, Largo Galileo Galilei 1, 00044 Frascati, Italy, Italy)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Outreach, Education and Altimetric Data Services

Presentation type: Type Forum

The Fully-Focused SAR (FF-SAR) processing, introduced in Egido and Smith, 2016, allows obtaining a maximum resolution of 0.5 m in the along-track direction. It provides significant benefits for inland water altimetry investigations allowing the successful investigation of small canals (Kleinherenbrink, 2020) that typically cannot be analyzed by using unfocused Delay-Doppler SAR (DD-SAR) data (about 300 m resolution in the along-track direction).

In its development, two major limitations were associated with the FF-SAR processing: 1) the presence of evenly spaced high sidelobes in the PTR due to the close-loop burst mode implemented in Sentinel-3 & Cryosat-2 altimeter payloads, used for initial FF-SAR investigations, and 2) the heavy computational burden with respect to the unfocused DD-SAR processing.

The first limitation can be overcome by designing the radar system differently and adopting an open-loop transmission scheme as, for instance, the one implemented in the altimeter payload of the Sentinel-6 Michael Freilich mission, scheduled for this year.
The second limitation has been addressed in research works following Egido and Smith, 2016 indicating that an improvement in terms of computational burden can be achieved by adopting algorithms in the frequency domain (Guccione et al., 2018).

Being the role of FF-SAR for future inland water altimetry well understood, along with the possibility to see it implemented with reduced drawbacks during the future Sentinel-6 Michael Freilich mission, a collaboration has started between the ESA GPOD Team, already hosting the successful SARvatore services portfolio for unfocused SAR & SARin altimetry, and Aresys.

Aresys has developed a generic FF-SAR prototype processor, that is able to process data acquisition from different instruments and exploiting the frequency-domain Omega-K algorithm. The Aresys's FFSAR prototype processor for CryoSat allows users to process, on line and on demand, low-level CryoSat FBR products in SAR mode up to FF-SAR Level-1 products with self-customized options. Additionally a wide set of processing parameters is configurable, allowing as an example to select the along-track resolution or to obtain FFSAR multilooked waveforms at the desired posting rate.

The collaboration led to the creation of a new service for the processing of CryoSat Baseline D data in FF-SAR mode. Users will be able selecting the following options: 1) range oversampling factor, 2) bandwidth factor (responsible for the along-track resolution value) and 3) multi-look posting rate (1Hz-500Hz). Geophysical corrections and L2 estimates from a threshold peak retracker are also part of the output package to ease the analysis of end-users.

In this presentation, the Aresys FF-SAR prototype processor is described and the outcome of some preliminary validation activities, performed by the ESA-ESRIN Altimetry Team, are reported. At present, a research group, involving inland water altimetry researchers, has been formed. The service is scheduled to open to all GPOD users in the first semester of 2021. Future evolutions may include the extension of the service to Sentinel-3 and Sentinel-6 data.
Michele Scagliola
Aresys, Via Privata Flumendosa 16, 20132 Milano