A study published in Geophysical Research Letters finds that commercial satellite imagery often outperforms public data sets when identifying surface water, but public data sets may be better at detecting water hidden by forest cover, according to a statement released on Mar. 27.
The findings are important because mapping surface water accurately helps researchers monitor rivers, streams, and small bodies of water, which play a role in understanding flood dynamics and environmental changes. The choice between commercial and public satellite imagery can affect the detail and reliability of these maps.
Researchers compared PlanetBasemap, a high-resolution commercial data set, with the Dynamic Surface Water Extent (DSWE), a publicly available product from the United States Geological Survey Landsat program. Mollie Gaines, lead author of the study at North Carolina State University, said that “Planet Basemap’s higher resolution made it more capable of detecting small bodies of water.” She explained: “The Planet data is approximately four-meter resolution, which means that each pixel is approximately a four-by-four-meter square. That leads to a much more detailed image compared to the DSWE’s 30-meter resolution. We’re seeing that the commercial data set often identifies more of the smaller water bodies, as well as river extents.”
However, Gaines said this advantage shifts during times when dense vegetation covers waterways: “The Planet Scope data…is limited to red, blue and green…and near infrared,” she said. “DSWE includes the shortwave infrared band, which is the best option for this kind of water detection.” Including all three DSWE “confidence classes” further improved its ability to detect winding streams or rivers obscured by plants.
Gaines concluded: “When studying very small bodies of water like ponds, the commercial data is the more reliable product…But if you’re looking at a larger study area, the publicly available product is a really good option.” The research was supported by NASA FINESST Grant 80NSSC21K1606 and NASA CSDA Grant 80NSSC24K0053.
The paper titled “Impact of spatial scale on optical Earth observation-derived seasonal surface water extents” also included co-authors from NC State University; Planet Labs Inc.; and Colombia Institute of Hydrology, Meteorology and Environmental Studies.
