New look for the Altimetry OLTC website!

21 April 2023

An interactive website to view and contribute to Sentinel-3 and Sentinel-6-MF OLTC for inland waters measurement

The website, developed by Noveltis for ESA, offers the possibility to display the Open-Loop Tracking Command (OLTC) tables for inland water targets currently onboard ESA Sentinel-3 SRAL altimeters, as well as the Copernicus Sentinel-6-MF Poseidon-4 altimeter. The addition of Sentinel-6-MF is one of the new features of this latest release and brings the total number of hydrological targets displayed to ~180,000 worldwide.

An interactive map allows visitors to navigate and display elevation commands defined over lakes, reservoirs and rivers overflown by the three nadir altimeters.

In addition to the improvement of the general layout of the website, several visualization tools have been added to enhance the OLTC website experience: choice of map layout, display of satellite ground tracks, filter by target type...

Screenshot of the OLTC website new display

Outside of these hydrological targets, the elevation command defined in the OLTC table is set to the mean continental surface elevation, so that the altimeter constantly tracks the Earth’s surface.

Call for hydrology users’ contributions

Users wishing to further contribute to OLTC contents may sign up and have access to additional functionalities: once logged in, they have the possibility to submit modifications of existing elevations as well as requesting new targets that may not yet be defined in the onboard OLTC tables.

For example, adding a target over a river or a lake, in order to enhance the OLTC contents and make sure that the altimeter will acquire quality echoes over the defined targets. Requests may be submitted directly using the "Contribute" tool on the right panel or by sending a list of targets to the OLTC database management committee.

We encourage scientists and Sentinel users to visit the website and contact us via the Contact form for further questions.

Background information on the Open-Loop mode

The Open-Loop Tracking Command (OLTC) represents a major evolution of the altimeter tracking function that was first developed for Jason-2 and SARAL/Altika missions as probative mode (called Diode/DEM mode).Taking into account this experience, this tracking mode's efficiency has been proven and it is now stated as operational mode for Jason-3, Sentinel-3 and Sentinel-6-Michael-Freilich missions.

On Sentinel-3, areas of interest define where SRAL is operated in OLTC mode. Outside these areas, SRAL altimeters operate in Close-Loop mode (i.e. autonomous tracking mode), with no a priori elevation information used to set the echo reception window.

On Sentinel-6-MF, Poseidon-4 nominally operates in OLTC mode over all oceans and continental surfaces.

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