Abstract
The airborne AirSWOT instrument suite, consisting of an interferometric Ka-band synthetic aperture radar and color-infrared (CIR) camera, was deployed to northern North America in July and August 2017 as part of the NASA Arctic-Boreal Vulnerability Experiment (ABoVE). We present validated, open (i.e., vegetation-free) surface water masks produced from high-resolution (1 m), co-registered AirSWOT CIR imagery using a semi-automated, object-based water classification. The imagery and resulting high-resolution water masks are available as open-access datasets and support interpretation of AirSWOT radar and other coincident ABoVE image products, including LVIS, UAVSAR, AIRMOSS, AVIRIS-NG, and CFIS. These synergies offer promising potential for multi-sensor analysis of Arctic-Boreal surface water bodies. In total, 3167 km2 of open surface water were mapped from 23,380 km2 of flight lines spanning 23 degrees of latitude and broad environmental gradients. Detected water body sizes range from 0.00004 km2 (40 m2) to 15 km2. Power-law extrapolations are commonly used to estimate the abundance of small lakes from coarser resolution imagery, and our mapped water bodies followed power-law distributions, but only for water bodies greater than 0.34 (±0.13) km2 in area. For water bodies exceeding this size threshold, the coefficients of power-law fits vary for different Arctic-Boreal physiographic terrains (wetland, prairie pothole, lowland river valley, thermokarst, and Canadian Shield). Thus, direct mapping using high-resolution imagery remains the most accurate way to estimate the abundance of small surface water bodies. We conclude that empirical scaling relationships, useful for estimating total trace gas exchange and aquatic habitats on Arctic-Boreal landscapes, are uniquely enabled by high-resolution AirSWOT-like mappings and automated detection methods such as those developed here.
Highlights
Accurate mapping of terrestrial surface water bodies is necessary for understanding the hydrologic cycle, energy and biogeochemical cycles, aquatic habitats, and improving earth system models [1].Spatially, the world’s greatest density of surface water bodies is in the Arctic-Boreal regions, and these water bodies change in extent based on climate variability and permafrost presence [2,3,4,5]
Arctic-Boreal Vulnerability Experiment (ABoVE) AirSWOT deployments occurred in two legs, with northbound sorties from North Dakota to Alaska conducted between July 9–21, 2017 and southbound sorties over the same flight lines from August 16–17, 2017 (Figure 1)
CIR imagery would help identify phenomenology issues that should be excluded from spatial averaging of AirSWOT radar data, for example, exclusion of wet sediment bars as noted in Section 3.1, which could introduce height errors if erroneously classified as open water
Summary
Accurate mapping of terrestrial surface water bodies is necessary for understanding the hydrologic cycle, energy and biogeochemical cycles, aquatic habitats, and improving earth system models [1].Spatially, the world’s greatest density of surface water bodies is in the Arctic-Boreal regions, and these water bodies change in extent based on climate variability and permafrost presence [2,3,4,5]. Large-scale satellite-based studies typically produce datasets with 30 m resolution, which limit the observable lakes to 0.002 km (2000 m2) or larger [6,8]. The surface water area distribution has been shown to be a dynamic variable, and some satellite products contain multi-temporal information at both coarse global [11] and detailed regional scales [12]. As it stands, there is no one surface water map suitable for all spatial and temporal scales, and regional maps remain crucial for detailed hydrologic studies
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