The Pre-Surface Water and Ocean Topography (Pre-SWOT) Hydrology is part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Program. MEaSUREs, develops consistent global- and continental-scale Earth System Data Records by supporting projects that produce data using proven algorithms and input.
The Pre-SWOT Hydrology 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.
The contents of this project span three objectives:
Surface water dynamics information is necessary in order to support various monitoring programs as well as scientific objectives, however is often scarce and difficult to access in many regions due to geographic constraints, budgetary limitations, or closed data policies. As a result our ability to understand the global surface water balance is limited (Lettenmaier and Famiglietti, 2006, Gao, 2015). The recent advent of freely available remotely sensed data products has now provided users with access to high-quality, analysis-ready data at adequate spatial and temporal resolutions for surface water dynamic analysis. As a result the hydrology community has been active in estimation surface area, surface height, and/or storage metrics for lakes and reservoirs for various regions, however there is no comprehensive, long term, and publicly available database of lake and reservoir altimetry, area, and storage time series estimates. It is in this context that this project has produced those datasets with the highest feasible quality data using pre-SWOT remotely sensed data.
Lake Heights Users' Guide
Lake Surface Area Users' Guide
Lake Storage Users' Guide
River Heights Users' Guide
Gao, H. (2015). Satellite Remote Sensing of Large Lakes and Reservoirs: from Elevation and Area to Storage. Wiley Interdisciplinary Reviews: Water. 2, 147–157. doi:10.1002/wat2.1065.
Lettenmaier D.P., and Famiglietti J.S. (2006). Water from on high. Nature, 444, 562-563. doi:10.1038/444562a.
Coss S., et al. (2019). Global River Radar Altimetry Time Series (GRRATS): New River Elevation Earth Science Data Records for the Hydrologic Community. Earth System Science Data. doi:10.5194/essd-2019-84.