Sentinel-3A changes its acquisition mode over Victoria Land glaciers, in Antarctica

Antarctica glaciers are sentinels of climate change, and their variations are scrutinized by climate scientists all over the world. Recently, Sentinel-3 SRAL has changed its acquisition mode from Closed-Loop mode to Open-Loop mode, a capability that has demonstrated very efficient measurement acquisition performance over continental waters. The acquisition mode change is active since December 9^th, 2021 and is set for some specific locations over the Priestley and Aviator glaciers, located in Victoria Land, Antarctica.

The Open-Loop Tracking Command (OLTC) tables onboard Sentinel-3 SRAL are used to set the reception window of radar waveforms reflected by the Earth’s surface.

Over Antarctica, 10 glacier targets have been added in the on-board OLTC Tables. These targets are in the Victoria Land region, a mountainous region with glaciers. This area was, up until December 2021, covered in Closed-Loop mode but tracking loss was almost systematically observed because of rapid elevation variations of the surface. The Priestley and Aviator glaciers have been covered with dedicated elevation commands under Sentinel-3A ground track and activated on December 9, 2021, at approx. 13:18:34 UTC, during Cycle 79. Table 1 shows the start dates of open-loop mode acquisitions and geographical extent on each ground track. REMA DEM (Howat et al., 2019) has been used to define the glaciers surface elevation to set the reception window of waveforms.

Table 1. First acquisition dates and approximate UTC times for each Sentinel-3A relative orbit number (RON, as seen in the Sentinel-3 product filename) over Antarctica glaciers. The same open-loop data acquisitions re-occur on the designated orbits and latitudes once every repeat cycle (27 days / 385 orbits).

Title: Satellite view of the Antarctica glacier area covered by new targets for Sentinel-3A in Open-Loop mode.

Description: Targeted glaciers used to set new elevation commands for Sentinel-3A SRAL altimeter waveform reception window in Open-Loop Mode are shown (cyan boxes) with corresponding elevation values. Theoretical ground tracks are shown. Corresponding longitude/latitude coordinates are indicated in Table 1

Copyright: Google Satellite, figure design CNES.

The list of targets and corresponding elevation commands are detailed in Table 2:

Table 2. Coordinates of the centers of glacier targets defined in Sentinel-3A OLTC tables in Antarctica. The elevation reference is geoid and used as a proxy to adjust the altimeter reception window.

Sentinel-3A currently holds onboard Open-Loop Tables defined over more than 74,000 inland water targets including a few glaciers (in Antarctica, as previously detailed) as well as some other continental glaciers in South America, Asia, and Europe.

Feel free to share any feedback on these new open loop acquisitions with Sentinel-3 Land Ice experts at s3mpc-stm-landice@groupcls.com.

References

Howat, I. M., Porter, C., Smith, B. E., Noh, M.-J., and Morin, P.: The Reference Elevation Model of Antarctica, The Cryosphere, 13, 665-674, https://doi.org/10.5194/tc-13-665-2019, 2019.