|Paper title||High resolution satellite altimetry for river level estimation|
|Form of presentation||Poster|
Using satellite altimetry over poorly gauged basins where in situ data are scarce can be very beneficial for river monitoring, which is becoming more important due to increasing challenges with managing freshwater resources in a world affected by climate change and economic growth. As the resolution of satellite altimeters increases, the potential for their use grows. When CryoSat-2 was launched by ESA in 2010, the 300 m along track resolution of the Synthetic Aperture Radar (SAR) data allowed for the study of rivers much narrower compared to what was possible for missions such as Envisat, where only Low Resolution Mode (LRM) data were available. However, the resolution of SAR altimetry is still not high enough to monitor narrow rivers and rivers in mountainous areas.
In recent years, the Fully Focused SAR (FF-SAR) processing has been used to increase the along-track resolution further, all the way down to half the antenna length (Egido et al., 2017). The FF-SAR processing can be applied to all SAR altimeter missions, i.e. CryoSat-2, Sentinel-3 and Sentinel-6/Jason-CS. It has previously been shown that that FF-SAR processing can be used to obtain water levels for objects of just a few meters in width (Kleinherenbrink et al., 2020).
Satellite altimetry also includes height measurements from lidar measurements. In 2018, NASA launched the ICESat-2 satellite carrying the Advanced Topographic Laser Altimeter System (ATLAS) which uses a green laser to estimate the distance between the satellite and the point of reflection on the ground. ATLAS detects every single photon that finds its way back to the instrument after reflection. The along-track resolution of ICESat-2 is around 0.7 m but depends on the number of detected photons. For highly specular surfaces the resolution is much higher, and in some cases it might be lower.
Here, we compare the respective pros and cons of FF SAR Sentinel-3 and ICESat-2 altimetry over the Yellow River basin in China and other rivers that are challenging for SAR and LRM altimetry.
We present river levels derived from Sentinel-3 data using the processor provided by the SMAP FFSAR CLS/ESA/CNES project and river levels from the ATL03 and ATL13 ICESat-2 products and compare these with available in situ data.