Method

The multi-sensor system integrates high spatial resolution relative observations of water level changes (SAR phase) with limited coverage ‘absolute’ measurements of water level (altimetry) to generate maps of water levels and water level changes. Optical imagery is used for assessing vegetation type and vegetation conditions to refine the observations.

SAR interferometry – Maps of Relative Water Level Changes (RWLC) in wetlands:

SAR Interferometry (InSAR) measures water-level changes in wetlands with high spatial resolution and centimetric accuracy. However, it only provides Relative Water Level Changes (RWLC), requiring in-situ data for calibration.

Figure 1: SAR interferometry approach. (1) InSAR geometry in wetlands for relative water change detection. (2) Sample interferogram from Sentinel-1 (2021/08/08 – 2021/08/20) showing fringe patterns associated with water level changes between the acquisition dates. The interferogram allows us to generate high spatial resolution maps of relative water level changes in vast wetland areas.

Satellite Altimetry – Along track Absolute Water Level (AWL) observations:

Altimetric observations provide along track absolute water level observations that can be used as a substitute for in-situ data in calibrating InSAR observation over ungauged wetlands.

Figure 2: Satellite Altimetry approach using ICESat-2 laser altimeter. (1) Schematic of the ICESat-2 observation geometry in wetlands for (1)(a) Dry condition and (1)(b) Inundation condition. The Schematic is adapted from the ATBD ICESat-2 ATL08 [Source (Neuenschwander et al., 2021) https://nsidc.org/sites/default/files/documents/technical-reference/icesat2_atl08_atbd_r005.pdf]. (2) Sample ICESat-2 ATL08 ground track for 2021-10-11. (2)(a) Derived water depth for the sample ground track. (2)(b), (c) and (d) subplots present the latitudinal water depth along the ICESat-2 ground tracks (P1, P2, and P3 of panel (a), respectively). The EDEN water depth gauge-based reference is also presented. [Source: (Palomino-Ángel et al., 2024 - manuscript) https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023WR035422 and (Palomino-Ángel et al., 2024 - dataset) https://dataverse.fiu.edu/dataset.xhtml?persistentId=doi:10.34703/gzx1-9v95/4JETAA]