Validation of ICESat-2 Derived Data Products on Freshwater Lakes: Bathymetry, Diffuse Attenuation Coefficient for Downwelling Irradiance (K_d ), and Particulate Backscatter Coefficient (b _bp)

Abstract

Monitoring large bodies of water, such as the Laurentian Great Lakes in North America, can be challenging and costly. The bathymetry, the diffuse attenuation coefficient for downwelling irradiance (K d ), and the particulate backscattering coefficient (b bp ) are important metrics in monitoring water quality in lakes and have typically been measured in two ways: 1) via in situ sampling campaigns, which are expensive, timeconsuming, and have low spatial resolution, and 2) via passive optical imagery, which can have errors in excess of 50%. Recently, ICESat-2, an active LiDAR-based satellite, has proven effective in deriving the bathymetry, K d , and b bp in the global oceans. However, validation of such metrics has never been done on satellite flyovers taken on the same day as in situ measurements. Likewise, studies on freshwater environments have been limited. Here, we compare in situ data sampled from Lake Michigan and Big Glen Lake between August 13th and 14th, 2021, and results derived from an ICESat-2 flyover in the same region on August 14th, 2021. We find excellent agreement between the in situ values and the satellite-derived values for all three metrics. This suggests that ICESat-2 and other future LiDAR-based satellites will be powerful tools in monitoring large freshwater lakes.

Analysis of ICESat‐2 Data Acquisition Algorithm Parameter Enhancements to Improve Worldwide Bathymetric Coverage

“…We next defined and computed a new metric, which we refer to as the extinction depth index, $${\zeta }_{e}$$: $$${\zeta }_{e}=\frac{{Z}_{sd}}{{Z}_{ref}}$$$ where Z SD is the Secchi depth, and Z ref is the reference depth at the same location, with the latter obtained from the ETOPO2022 data set. Because previous studies have shown that ICESat‐2 is generally capable of bathymetric measurement to ∼1 Secchi depth (Parrish et al., 2019; Watkins et al., 2023), the dimensionless ratio ( ζ e ) can be thought of as an ICESat‐2 bathymetric retrievability index: where ζ e ≥ 1, the seafloor should be detectable by ICESat‐2. Next, we calculated an overall score for bathymetric retrievability by: (a) performing a binary reclassification on the monthly extinction depth ratio raster data sets to be one (a) for cells with a ratio greater than or equal to 1.0 and zero (0) for cells less than 1.0; (b) summing the monthly reclassified rasters; and (c) dividing the sum by 12.…”

“…Post‐launch, as the initial ICESat‐2 data became available, it was evident that ICESat‐2’s bathymetric measurement performance exceeded expectations. Multiple studies confirmed the ability to retrieve bathymetry to ∼1 Secchi depth, or >40 m in very clear waters, with typical accuracies on the order of 0.5 m (Albright & Glennie, 2021; Chen et al., 2021; Le Quilleuc et al., 2022; Parrish et al., 2019; Ranndal et al., 2021; Watkins et al., 2023; Zhang et al., 2022). These bathymetric capabilities were soon shown to be of value for a wide range of science uses, from the study of coral reefs and other sensitive marine habitats to assessment of seafloor morphological change (Herrmann et al., 2022; Le Quilleuc et al., 2022; Selamat et al., 2021; Van An et al., 2023).…”