Accurate measurements of terrain elevation are crucial for many ecological applications. In this study, we sought
to assess new global three-dimensional Earth observation data acquired by the spaceborne Light Detection and
Ranging (LiDAR) missions Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) and Global Ecosystem Dynamics
Investigation (GEDI). For this, we examined the “ATLAS/ICESat-2 L3A Land and Vegetation Height”, version 5
(20 × 14 m and 100 × 14 m segments) and the “GEDI Level 2A Footprint Elevation and Height Metrics”, version
2 (25 m circle). We conducted our analysis across four land cover classes (bare soil, herbaceous, forest, savanna),
and six forest types (temperate broad-leaved, temperate needle-leaved, temperate mixed, tropical upland,
tropical floodplain, and tropical secondary forest). For assessment of terrain elevation estimates from spaceborne
LiDAR data we used high resolution airborne data. Our results indicate that both LiDAR missions provide accurate terrain elevation estimates across different land cover classes and forest types with mean error less than 1
m, except in tropical forests. However, using a GEDI algorithm with a lower signal end threshold (e.g., algorithm
5) can improve the accuracy of terrain elevation estimates for tropical upland forests. Specific environmental
parameters (terrain slope, canopy height and canopy cover) and sensor parameters (GEDI degrade flags, terrain
estimation algorithm; ICESat-2 number of terrain photons, terrain uncertainty) can be applied to improve the
accuracy of ICESat-2 and GEDI-based terrain estimates. Although the goodness-of-fit statistics from the two
spaceborne LiDARs are not directly comparable since they possess different footprint sizes (100 × 14 m segment
or 20 × 14 m segment vs. 25 m circle), we observed similar trends on the impact of terrain slope, canopy cover
and canopy height for both sensors. Terrain slope strongly impacts the accuracy of both ICESat-2 and GEDI
terrain elevation estimates for both forested and non-forested areas. In the case of GEDI the impact of slope is,
however, partly caused by horizontal geolocation error. Moreover, dense canopies (i.e., canopy cover higher than
90%) affect the accuracy of spaceborne LiDAR terrain estimates, while canopy height does not, when considering
samples over flat terrains. Our analysis of the accuracy and precision of current versions of spaceborne LiDAR
products for different vegetation types and environmental conditions provides insights on parameter selection
and estimated uncertainty to inform users of these key global datasets.
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Wetlands Water Level Measurements From the New Generation of Satellite Laser Altimeters: Systematic Spatial‐Temporal Evaluation of ICESat‐2 and GEDI Missions Over the South Florida Everglades
The ICESat‐2 and GEDI missions were launched in 2018, becoming the new generation of space‐borne laser altimeters. These missions provide unprecedented global geodetic elevations, opening great opportunities for water level monitoring. The potential of these altimeters has been demonstrated in open‐water environments such as lakes, rivers, and reservoirs. However, detailed evaluations in vegetated environments, such as wetlands, floodplains, and other areas not constrained by water canal networks, are essential for continued improvement and further hydrological application. 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 and 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.
more » « less- Award ID(s):
- 2025954
- PAR ID:
- 10576976
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Water Resources Research
- Volume:
- 60
- Issue:
- 3
- ISSN:
- 0043-1397
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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