The Pre-Surface Water and Ocean Topography (Pre-SWOT) Hydrology MEaSUREs project provides precursor SWOT products for global hydrologic changes from a combination of satellite imagery and multi-mission satellite radar altimetry data, including virtual river station heights, lake/reservoir surface water area extent, and lake/reservoir water height spanning from 1992 (TOPEX-Poseidon launch) to present, with the potential to be extended up to the launch of the SWOT mission planned for 2021. This project focuses on the development of Earth Systems Data Records (ESDRs) for surface-water storage change dynamics throughout the world with up to 349 targets, especially at resolutions and quality relevant to human use and which are largely absent from current global hydrology models. Lakes and reservoirs (larger than ~100 km2) and rivers (wider than ~900 m) are included in the initial project scope, with an emphasis on targets that were clearly distinguishable from other nearby water bodies for improved accuracy of both elevation and surface area estimates. More specifically, we use data produced by multiple satellite altimetry missions (TOPEX-Poseidon, Jason-1, Jason-2, Jason-3, and ENVISAT) beginning in 1992 onwards, with surface water area extent estimates derived from Terra/Aqua MODIS from 2000 onwards. Surface-water storage change dynamics were produced using both surface area and altimetry (i.e., hypsometry) and was able to be estimated during periods when either of the variables was not available, provided that there was a strong surface area/altimetry relationship during overlapping periods.
Figure 1. Location of the global lake and reservoir targets (blue bubbles, by average lake/reservoir size).
Figure 2. The GRRATS dataset and evaluation results. Maximum NSE (best fit) plotted in yellow to red (shown on all rivers with gage data) and qualitative grades plotted in teal to dark purple. In both cases, darker colors indicate better evaluation results.