A new surface-water mapping process, using a database of satellite imagery spanning many decades, can be applied to map short-term flooding events and long-term surface water trends. There are many possible benefits to this approach, including the opportunity for land-use planners to evaluate cropland susceptibility to water inundation throughout the year.
The new research, released today in the Journal of the American Water Resources Association, shows a method that combines daily imagery to make a composite map identifying large bodies of water because of flooding. These methods complement similar methods for water detection to get a clearer picture of surface water dynamics.
Since flooding events are typically obscured by cloud cover, the new method uses the unique capabilities of each satellite to create a mapping approach that can “see through the clouds” to better inform crop choice and placement to minimize flooding losses.
The Satellites
NASA operates the Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) satellites. The imagery capture from MODIS is at a much lower spatial resolution, but each satellite collects daily images of the entire globe, allowing for more information on the current condition of earth’s surface. The MODIS database includes readily accessible daily imagery from 2003-present.
Landsat, a USGS-operated satellite, acquires high resolution imagery of the earth’s surface every 16 days. The finer resolution provides excellent spatial detail, but the infrequent passes are not always sufficient to regular capture time-sensitive information like flooding events.
MODIS and Landsat are considered optical satellites and can be used to better understand past and current surface water dynamics. In both cases, imagery is less useful if cloud cover obstructs the land surface.
The Method
Taking the best of both satellites’ capabilities, the new method can effectively monitor water continuously over large areas. The addition of maps derived from MODIS satellites can help improve understanding of surface water during the winter. MODIS and Landsat products can also help us understand how surface water changes as a function of streamflow, since each product can be correlated with discharge data gathered at USGS streamgages. Collectively, surface water maps give historical reference to understanding past flooding extents and long-term trends.
For more information, please contact Chris Soulard or check out the article DSWEmod - The production of high-frequency surface water map composites from daily MODIS images (usgs.gov)
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