DIODE/DEM (OLTC) tracking mode performances over inland waters.

Mathilde Cancet (NOVELTIS, France)


Sandrine Bijac (NOVELTIS, France); Emmanuel Augé (NOVELTIS, France); Eric Jeansou (NOVELTIS, France); François Boy (CNES, France); Jean-Damien Desjonquères (CNES, France); Nicolas Picot (CNES, France)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Instrument Processing: Measurement and retracking (SAR and LRM)

Presentation type: Type Poster

The tracking loop mode called "DIODE/DEM", or OLTC (Open Loop Tracking Command), has been developed in order to obtain a larger number of exploitable radar waveforms over areas of interest where the autonomous traker (e.g. median) has lower performances than in the open ocean. The considered areas of interest are: coastal zones, continental ice caps and continental waters: rivers, lakes, reservoirs...

The principle of the OLTC mode is to drive the altimeter with a priori information available on-board: real-time estimates of the satellite orbit with the DIODE navigator, and theoretical height of the sub-satellite point provided by a Digital Elevation Model (DEM) stored in an on-board memory and previously sampled along the satellite track. The sampled DEM is prepared pre-launch by assembling various elevation datasets: a mean sea surface for the ocean and the coastal zones, a global DEM for the continental areas (ACE), inland water elevations from the HYDROWEB data base for the water bodies already observed by altimetry. For the water bodies not present in HYDROWEB, the water height is taken from the ACE DEM.
The OLTC mode is declared performing well if it permits to collect exploitable radar signal with waveform samples correctly located in the range window for further exploitation (retracking).

For Jason-2, the OLTC mode was switched-on for one cycle (cycle 34, Desjonquères 2010), and recently two cycles have been acquired (cycles 209 and cycle 220). In this study, we analysed the performances of the OLTC mode on the most recent Jason-2 cycles, over continental waters.
Mathilde Cancet