Sentinel-1 Water Extent and Water Extent Difference for the Texas Floods, May 2024

Dates of Images: 4/30/2024, 5/7/2024, 5/12/2024 Date of Next Image: Varies by region, typically 12 days since previous pass. Summary: The Alaska Satellite Facility has developed surface water extent products of the Sentinel-1A/B Synthetic Aperture Radar (SAR) instrument. These images can be used to see where water is located at the time of the satellite overpass. This product shows all water detected and does not differentiate between normal water and flood water. To determine where flooding may have occurred, combine this layer with a reference water layer. The water extent difference maps shown here were created by subtracting the water extent of the first date from the water extent of the second date to show what changes, if any, occurred in the water extent. Suggested Use: Water extent difference: Light Blue: Water Present in the Second Date Only Dark Blue: Water Present in Both Dates Orange: Water Present in the First Date Only Satellite/Sensor: Synthetic Aperture Radar on European Space Agency's (ESA) Copernicus Sentinel-1A satellite Resolution: 30 meters Service URL: WMS Endpoint:

Dates of Images: 4/30/2024, 5/7/2024 Date of Next Image: Varies by region, typically 12 days since previous pass. Set time slider to most recent interval and click on area of interest to identify date of last pass. Summary: The Alaska Satellite Facility has developed false color Red, Green, Blue (RGB) and Radiometrically Terrain-Correct (RTC) composites of the Sentinel-1A/B Synthetic Aperture Radar (SAR) instrument which assigns the co- and cross-polarization information to a channel in the composite. When used to support a flooding event, areas in blue denotes water present at the time of the satellite overpass before or after the start of the flooding event. Sentinel-1 RGB Decomposition of RTC VV and VH imagery over United States coastlines. Blue areas have low returns in VV and VH (smooth surfaces such as calm water, but also frozen/crusted soil or dry sand), Green areas have high returns in VH (volume scatterers such as vegetation or some types of snow/ice), and Red areas have relatively high VV returns and relatively low VH returns (such as urban or sparsely vegetated areas). Suggested Use: In this image, water appears in blue, vegetated areas in shades of green and urban areas in bright orange. It is recommended to use this product with ancillary information to derive flooded areas. Satellite/Sensor: Synthetic Aperture Radar on European Space Agency's (ESA) Copernicus Sentinel-1A satellite Resolution: 30 meters Service URL: https://gis.earthdata.nasa.gov/portal/home/item.html?id=e893329c61b6428bbe903d3452a8ba0a WMS Endpoint: https://gis.earthdata.nasa.gov/portal/services/DISASTERS_202405_FLOOD_TX/2408_sentinel1/ImageServer/WMSServer

Date of Images: 2/4/2023, 2/5/2023, 2/9/2023, 2/10/2023 Date of Next Image: None Expected Summary: The Alaska Satellite Facility has developed water extent images using the Sentinel-1A/B Synthetic Aperture Radar (SAR) instrument. These images can be used to see where water is located at the time of the satellite overpass. This product shows all water detected and does not differentiate between normal water and flood water. To determine where flooding may have occurred, combine this layer with a reference water layer. Additional SAR Information Suggested Use: This product shows all water detected and does not differentiate between normal water and flood water. To determine where flooding may have occurred, combine this layer with a reference water layer. Satellite/Sensor: Synthetic Aperture Radar on European Space Agency's (ESA) Copernicus Sentinel-1A satellite Resolution: 30 meters Credits: Sentinel data used in this derived product, contains modified Copernicus Sentinel data (2023), processed by ESA, Alaska Satellite Facility, NASA MSFC Service URL: WMS Endpoint:

Dates of Images: Pre-Event: 11/4/2024, 11/6/2024, 11/11/2024 Post-Event: 11/16/2024, 11/18/2024, 11/23/2024 Date of Next Image: Varies by region, typically 12 days since previous pass. Set time slider to most recent interval and click on area of interest to identify date of last pass. Summary: The Alaska Satellite Facility has developed surface water extent products of the Sentinel-1A/B Synthetic Aperture Radar (SAR) instrument which assigns the co- and cross-polarization information to a channel in the composite. When used to support a flooding event, areas in blue denotes water present at the time of the satellite overpass before or after the start of the flooding event. Suggested Use: In the Water Extent images, data is classified from the above imagery shows water, including flooded areas, as blue. Satellite/Sensor: Synthetic Aperture Radar on European Space Agency's (ESA) Copernicus Sentinel-1A satellite Resolution: 20 meters Service URL: https://gis.earthdata.nasa.gov/portal/home/item.html?id=bd843e5aa9a84bca9a7f0181d293a164 WMS Endpoint:  https://gis.earthdata.nasa.gov/portal/services/DISASTERS_202411_TROPICALSTORM_SARA/2430_sentinel1_water/ImageServer/WMSServer

Date of Images: 2/4/2023, 2/5/2023, 2/9/2023, 2/10/2023, 2/16/2023, 2/17/2023 Date of Next Image: None Expected Summary: The Alaska Satellite Facility has developed water extent images using the Sentinel-1A/B Synthetic Aperture Radar (SAR) instrument. These images can be used to see where water is located at the time of the satellite overpass. This product shows all water detected and does not differentiate between normal water and flood water. To determine where flooding may have occurred, combine this layer with a reference water layer. Additional SAR Information Suggested Use: This product shows all water detected and does not differentiate between normal water and flood water. To determine where flooding may have occurred, combine this layer with a reference water layer. Satellite/Sensor: Synthetic Aperture Radar on European Space Agency's (ESA) Copernicus Sentinel-1A satellite Resolution: 30 meters Credits: Sentinel data used in this derived product, contains modified Copernicus Sentinel data (2023), processed by ESA, Alaska Satellite Facility, NASA MSFC Service URL: https://gis.earthdata.nasa.gov/portal/home/item.html?id=c9225c80d734497a8a8509383feb65b8 WMS Endpoint: https://gis.earthdata.nasa.gov/portal/services/DISASTERS_202302_EARTHQUAKE_TURKIYE/2302_sentinel1_water/ImageServer/WMSServer

Dates of Images: Post-Event: July 18, 2026 Pre-Event: May 1 to July 1, 2026 Date of Next Image: Unknown Summary: We developed a rapid-response workflow to map flooded areas during this emergency event using multi-temporal Sentinel-1 SAR data. Sentinel-1’s SAR backscatter characteristics are particularly effective for detecting surface water: water surfaces typically exhibit low backscatter, whereas non-water areas show higher backscatter. Leveraging this physical property, we distinguished between water and non-water surfaces from both pre- and post-flood observations. To highlight flood-induced surface changes, we computed the differenced co-polarized VV backscatter (dVV = VV_post – VV_pre). This change detection technique enhances the visibility of newly inundated areas. We then applied a simple threshold to the dVV image to separate flooded from non-flooded areas. Suggested Use: The final output is a binary raster product, where pixels with a value of 1 represent flooded areas (dark blue color). A permanent water body layer and a binary layer incorporating land cover are also included. Satellite/Sensor: Sentinel-1 /Synthetic Aperture Radar (SAR) Resolution: 10 meters Credits: Dr. Khuong H. Tran (Khuong.tran@nasa.gov) Esri REST Endpoint: See URL section on right side of page