Abstract's details
Assesment of E1 phase for Sentinel-3 and Jason-3 in Open Loop tracking command mode
CoAuthors
Event: 2016 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Measurement and retracking (SAR and LRM)
Presentation type: Type Poster
Contribution: not provided
Abstract:
The autonomous median trackers on-board the satellite altimetry missions have lower performances in the coastal zones and over the continental ice caps and waters (rivers, lakes, reservoirs), mainly because of the land contamination in the radar waveforms and steep topography. As the number of satellite altimetry applications in these regions has significantly grown for a decade, some techniques have been developed in order to answer these new user requirements. In particular, the DIODE/DEM or OLTC (Open Loop Tracking Command) mode has been implemented with the objective to obtain a larger number of exploitable radar waveforms over these areas of interest for the SRAL altimeter on board Sentinel-3 and the Poseidon-3B altimeter on board Jason-3.
The principle of the OLTC (Open Loop Tracking Command) mode consists in driving 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 point located under the satellite, provided by a Digital Elevation Model (DEM) stored in the on-board memory and previously sampled along the satellite track. The sampled DEM is prepared pre-launch by assembling various elevations data: a Mean Sea Surface for the ocean and coastal zones, a global DEM for continental areas, inland water elevations from specific databases and specific DEM over ice caps where available.
Validation tools have been developed by CNES and NOVELTIS in order to assess the performance of the OLTC mode versus the autonomous tracking mode in near real time, for the inland waters and for the continental ice caps. These tools will be operated during the Sentinel-3 and Jason-3 lifetime. A first review has been done to assess the performance of both missions during the whole E1 phase, for all the cycles available in OLTC mode. As Jason-3 operates in either mode depending on the cycles, we are able to compare closed-loop tracking commands with open-loop ones. For Sentinel-3, all the considered cycles (from cycle 4) were operated in the OLTC mode and the comparison with closed-loop tracking commands is not possible. Some diagnostics based on the echo quality have been defined that provide some quick visualization of the OLTC performances. First results demonstrate the interest of the OLTC mode for both missions. Very good results are obtained over the waterbodies and rivers in the defined areas of interest. These results encourage us to work closely with the users and inland waters experts to enlarge lakes and rivers coverage in the OLTC mode to provide better acquisitions where closed-loop mode is not enough efficient.
The performance over ice caps margins (Greenland, Antarctica) was also analyzed for the Sentinel-3 mission. At this stage, it is too early to conclude whether the OLTC mode improves the altimeter performance over ice compared to the closed-loop mode and recommendation has been made to operate the Sentinel-3 altimeter in closed-loop mode in order to better understand how the altimeter tracks these surfaces (strong slopes, seasonal variations).
This communication will present the performance results for Sentinel-3 and Jason-3.
The principle of the OLTC (Open Loop Tracking Command) mode consists in driving 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 point located under the satellite, provided by a Digital Elevation Model (DEM) stored in the on-board memory and previously sampled along the satellite track. The sampled DEM is prepared pre-launch by assembling various elevations data: a Mean Sea Surface for the ocean and coastal zones, a global DEM for continental areas, inland water elevations from specific databases and specific DEM over ice caps where available.
Validation tools have been developed by CNES and NOVELTIS in order to assess the performance of the OLTC mode versus the autonomous tracking mode in near real time, for the inland waters and for the continental ice caps. These tools will be operated during the Sentinel-3 and Jason-3 lifetime. A first review has been done to assess the performance of both missions during the whole E1 phase, for all the cycles available in OLTC mode. As Jason-3 operates in either mode depending on the cycles, we are able to compare closed-loop tracking commands with open-loop ones. For Sentinel-3, all the considered cycles (from cycle 4) were operated in the OLTC mode and the comparison with closed-loop tracking commands is not possible. Some diagnostics based on the echo quality have been defined that provide some quick visualization of the OLTC performances. First results demonstrate the interest of the OLTC mode for both missions. Very good results are obtained over the waterbodies and rivers in the defined areas of interest. These results encourage us to work closely with the users and inland waters experts to enlarge lakes and rivers coverage in the OLTC mode to provide better acquisitions where closed-loop mode is not enough efficient.
The performance over ice caps margins (Greenland, Antarctica) was also analyzed for the Sentinel-3 mission. At this stage, it is too early to conclude whether the OLTC mode improves the altimeter performance over ice compared to the closed-loop mode and recommendation has been made to operate the Sentinel-3 altimeter in closed-loop mode in order to better understand how the altimeter tracks these surfaces (strong slopes, seasonal variations).
This communication will present the performance results for Sentinel-3 and Jason-3.