Results

1. Spatial-temporal evaluation of ICESat-2 and GEDI missions for water level and depth retrievals over the South Florida Everglades:

Here we present results of our recent study using ICESat-2 and GEDI altimetry data for water level and depth retrievals over the entire south Florida Everglades wetlands (Palomino-Ángel et al., 2024 - manuscript https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023WR035422). We developed a systematic accuracy assessment of ICESat-2 ATL08 and GEDI L2A products to monitor spatial-temporal water level and depth dynamics over the South Florida Everglades wetlands. The evaluation was performed on data acquired between 2020–2021, using gauge-based water level and depth estimates as references. The results showed an RMSE of 0.17 m (water level) and 0.15 m (water depth) for ICESat-2 and 0.75 m (water level) and 0.37 m (water depth) for GEDI. The analysis suggested that nighttime acquisitions were more accurate for both missions than daytime ones. The low-power beams achieved slightly higher accuracies than those of the high-power beams over the evaluated wetlands. Water level retrieval was more problematic in densely vegetated areas; however, we derived a correction model based on the leaf area index that improved the accuracy by up to 75% for water depth retrievals from GEDI. Furthermore, the analysis provides new insights to understand the potential of the altimeters in monitoring the spatial-temporal dynamics of water levels in the evaluated wetlands.

Figure 1. Spatial variation of the water depth along different transects. (a) Presents the transect location and direction. Each subplot presents the water depth for the (b) ICESat-2 Transect 1 (I-T1); (c) ICESat-2 Transect 2 (I-T2); (d) GEDI Transect 1 (G-T1); (e) GEDI Transect 1 corrected (G-T1-C); (f) GEDI Transect 2 (G-T2); and (g) GEDI Transect 2 corrected (G-T2-C). The solid black line represents the reference water depth obtained from EDEN. The blue dots represent the ICESat-2 and GEDI observations in strong (SB) and full (FB) beams. The red dots represent ICESat-2 and GEDI observations in weak (WB) and coverage (CB) beams. [Source: (Palomino-Ángel et al., 2024 - manuscript https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023WR035422)]

2. Calibration of InSAR Relative Water Level Changes (RWLC) maps using Altimetry Absolute Water Level (AWL) observations:

We preliminarily tested the calibration methodology using four Long Temporal Baseline Interferograms: (1) Aug-08/2021 - Sept-01/2021 (24 days); (2) Feb-27/2020 - May-21/2020 (84 days); (3) May-28/2021 - Aug-20/2021 (84 days); (4) Feb-21/2021 - May-28/2021 (96 days). We first generated Relative Water Level Change (RWLC) maps using Sentinel-1 data and subsequently calibrated the RWLC maps to obtain Absolute Water Level Changes (AWLC) maps using ICESat-2 observations for calibration (InSAR Calibrated). We compared our results with the Everglades Depth Estimation Network (EDEN) water level surfaces as reference and calculated the difference.

Figure 2. Preliminary Absolute Water Level Change maps generated from Sentinel-1 and ICESat-2 observations for the Water Conservation Area 1 (WCA1) in the Everglades wetlands.