Flood detection using Sentinel-1 Synthetic Aperture Radar for the Washington Atmospheric River December 2025

Date of Images: Post-Event: June 26, 2025 at 00:59 UTC (about 6:59PM MT) Pre-Event: June 20, 2025 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). Satellite/Sensor: Sentinel-1 /Synthetic Aperture Radar (SAR) Resolution: 10 meters Credits: Dr. Khuong H. Tran (Khuong.tran@nasa.gov) Service URL: WMS Endpoint:

Date of Images: Post-Event: June 26, 2025 at 00:59 UTC (about 6:59PM MT) Pre-Event: June 20, 2025 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). Satellite/Sensor: Sentinel-1 /Synthetic Aperture Radar (SAR) Resolution: 10 meters Credits: Dr. Khuong H. Tran (Khuong.tran@nasa.gov) Service URL: https://gis.earthdata.nasa.gov/portal/home/item.html?id=87d3edc8e19d437da1336481506ff377 WMS Endpoint: https://gis.earthdata.nasa.gov/portal/services/DISASTERS_202506_FIRE_NM/2506_sentinel1_flood/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

Dates of Images: Post-Event: December 17, 2025 Pre-Event: October 13, 2025 Date of Next Image: Unknown Summary: Modified Normalized Difference Water Index (MNDWI) provides a different view of the Earth's surface combining different bands to make water bodies more obvious. This index can be used to identify flooded areas as well as heavily saturated areas. Suggested Use: For mNDWI, areas of existing water, such as a rivers or lakes appear in the darkest green with high values near 1, while dry land appears in the darkest brown with low values near -1. This product can be used to identify potentially flooded areas that can be seen in varying shades of green and light brown depending on the amount of moisture picked up by the satellite. Note: Areas of cloud cover will show up in varying shades of green/blue similar to water. Satellite/Sensor: MultiSpectral Instrument (MSI) on European Space Agency's (ESA) Copernicus Sentinel-2A/2B satellites Resolution: 10 meters Credits: NASA/MSFC, USGS, ESA Copernicus Esri REST Endpoint: See URL to the right. WMS: https://gis.earthdata.nasa.gov/portal/services/DISASTERS_202512_FLOOD_WA/2512_sentinel2_mndwi/ImageServer/WMSServer

Date of Image(s): December 8; December 9; December 12; December 13; December 14; December 15; December 17 Date of Next Image: Typically, there are two daytime images expected each day around 1:00pm EST. Summary: Floodwater derived from Visible Infrared Imaging Radiometer Suite (VIIRS) instrument onboard NASA and NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) satellite. VIIRS floodwater product was produced by NASA SatCORPS Ground Station Observation Network (GSON) low latency system.. The image shows where floodwater was detected from the VIIRS observation. Suggested Usage: The floodwater fraction percentage (1-100%) that contains water Satellite/Sensor/Resolution: 375m spatial resolution VIIRS instrument onboard SNPP Satellite Generated using CSPP v4.1 Credits: Image Credit: NASA Langley SatCORPS Louis Nguyen of NASA Langley SatCORPS: https://satcorps.larc.nasa.gov/new/ NOAA Joint Polar Satellite System (JPSS) VIIRS Data: https://registry.opendata.aws/noaa-jpss/ Additional information on VIIRS Flooding products: https://disasters-geoplatform.hub.arcgis.com/pages/viirs-floodwater-fraction-map/

Summary: The Advanced Rapid Imaging and Analysis (ARIA) and Observational Products for End-Users from Remote Sensing Analysis (OPERA) teams at NASA's Jet Propulsion Laboratory and California Institute of Technology created maps of surface water extent impacted by the flooding caused by Atmospheric Rivers in the Pacific Northwest starting on December 8, 2025 using the OPERA Dynamic Surface Water Extent from Sentinel-1 (DSWx-S1). The results posted here are preliminary and unvalidated results, primarily intended to aid the field response and provide a rough first look at the inundation extent. The ARIA-share website has always focused on posting preliminary results as fast as possible for disaster response. All information is provisional for use under emergency response guidelines. These data are provided with absolutely no warranty of any kind. Use at your own risk. OPERA DSWx-S1 The OPERA DSWx-S1 was used to identify surface water for the flooding event. The images provided are a mosaic of OPERA DSWx-S1 products, producing a composite image for each date. The mosaicking applied prioritized pixels classified as open surface water and inundated vegetation to preserve water pixels in regions of product granule overlap. The images are provided as GeoTIFF files. Water (WTR) Layer Description: Masked interpreted water classification layer. This represents pixel-wise classification into one of three water classes (not water, open water and inundated vegetation), masks (HAND mask and layover/shadow mask), or no data classes. Water (WTR) Layer Values: 0: Not Water - an area with valid data that is not open water (class 1), inundated vegetation (class 3), height above nearest drainage masked (class 250), or layover/shadow masked (class 251). Masking can result in "not water" (class 0) where land cover masking is applied (suggested color: #ffffff) 1: Open Water - an area that is entirely water and unobstructed to the sensor, including obstructions by vegetation, terrain, and buildings. (suggested color: #0000ff) 3: Inundated vegetation - an area that is considered inundated, extracted from the high value in dual polarization ratio and the wetland class in land cover map. (suggested color: #00ff00) 250: Height Above Nearest Drainage (HAND) masked - an area where topographic height is higher than the HAND threshold (suggested color: #c8c8c8) 251: Layover/shadow masked - an area identified as layover or shadow computed from the geometry of the digital elevation model and sensor. The area is directly copied from input burst RTC-S1 products (suggested color: #808080) 255: No data (suggested color: transparent) Water Gain Description: Water gain classification layer. This represents pixel-wise classification into water gain and no change/water loss, as well as no data classes. Water Gain Layer Values:0: No Change or Water Loss- an area that had no change (e.g., open water in both images) or water loss (e.g., open water to not water). Masked pixels from HAND and Layover/Shadow are set to No data. (suggested color: #ffffff) 1: Water Gain - an area that gained water in the most recent image. This includes change from Not Water to Inundated Vegetation, Not Water to Open Water, and Inundated Vegetation to Open Water. (suggested color: #ff15e4) Satellite/Sensor: Synthetic Aperture Radar (SAR) instrument on European Space Agency's (ESA) Sentinel-1A/C satellite. Resolution: 30 meters OPERA DSWx-S1 data availability The post-processed products are available to download at https://aria-share.jpl.nasa.gov/20251210-PacificNorthwest-AtmRiver/DSWx-S1//. The OPERA DSWx-S1 products have been in production since September 2024, are freely distributed to the public via NASA's Physical Oceanography Distributed Active Archive Center (PO.DAAC), and can be downloaded through NASA's Earthdata search. For more information about the Dynamic Surface Water eXtent product suite, please refer to the DSWx Product page: https://www.jpl.nasa.gov/go/opera/products/dswx-product-suite. For more information about the Caltech-JPL ARIA project, visit https://aria.jpl.nasa.gov. For more information about the JPL OPERA project, visit https://www.jpl.nasa.gov/go/opera/. Product POCs: Cole Speed (cole.speed@jpl.nasa.gov) Mary Grace Bato (bato@jpl.nasa.gov) Ines Fenni (ines.fenni@jpl.nasa.gov) Emre Havazli (emre.havazli@jpl.nasa.gov) Alexander Handwerger (alexander.handwerger@jpl.nasa.gov) WMS Endpoint: https://gis.earthdata.nasa.gov/portal/services/DISASTERS_202512_FLOOD_WA/2512_opera_dswx_s1/MapServer/WMSServer Data Download: https://aria-share.jpl.nasa.gov/20251210-PacificNorthwest-AtmRiver/DSWx-S1/ Credits: Sentinel-1 data were accessed through the Copernicus Open Hub and the Alaska Satellite Facility server. The product contains modified Copernicus Sentinel data (2025), processed by the European Space Agency and analyzed by the NASA-JPL/Caltech ARIA and OPERA team. The products are produced as part of the OPERA project, which is funded by NASA to address remote sensing needs identified by the Satellite Needs Working Group, and managed by NASA's Jet Propulsion Laboratory. NASA JPL-Caltech ARIA/OPERA Team ==================  Image acquisition times in UTC (local): 2025-12-17 2:00AM (local Pacific Time: 2025-12-16 6:00PM),  2025-12-15 2:00AM (local Pacific Time: 2025-12-14 6:00PM),  2025-12-14 2:00PM (local Pacific Time: 2025-12-14 6:00AM),  2025-12-11 2:00AM (local Pacific Time: 2025-12-10 6:00PM),  2025-12-10 2:00AM (local Pacific Time: 2025-12-09 6:00PM),  2025-12-07 2:00PM (local Pacific Time: 2025-12-07 6:00AM),  2025-12-05 2:00AM (local Pacific Time: 2025-12-04 6:00PM),   2025-12-02 2:00PM (local Pacific Time: 2025-12-02 6:00AM),  2025-11-29 2:00AM (local Pacific Time: 2025-11-28 6:00PM),   2025-11-28 2:00AM (local Pacific Time: 2025-11-27 6:00PM)  Last Update 23 Dec. 2025