Aquatic scientists and water resource managers require information on the dynamics of surface water extent. Surface water extent is modulated by weather and climate, stream network hydrology, and geological processes such as isostatic rebound. Land use, ecosystem and service management, and overall water management are also impacted by changes in surface water extent.
The Landsat Collection 2 (C2) Level-3 Dynamic Surface Water Extent (DSWE) product provides raster layers that represent surface water inundation per-pixel in Landsat data. C2 DSWE contains six acquisition-based raster data products relating to the existence of surface water.
Available for Landsat 4-5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), and Landsat 8 Operational Land Imager (OLI) data, C2 DSWE products are generated from Landsat Collection 2 U.S. Analysis Ready Data (ARD) Surface Reflectance data, and use the cloud, cloud shadow, and snow information provided in the “QA_PIXEL” band. Landsat 9 DSWE products will become available later in 2022.
The Landsat C2 DWSE product is processed to 30-meter spatial resolution in Albers Equal Area (AEA) projection using the World Geodetic System 1984 (WGS84) datum and gridded to the ARD tiling scheme consisting of fixed 5000-meter squared non-overlapping tiles.
NOTE: This page provides basic information about the Landsat C2 DSWE products. Please refer to the Landsat Collection 2 Level-3 Dynamic Surface Water Extent Data Format Control Book for more descriptive information.
The C2 DSWE product is available for the conterminous U.S., Alaska, and Hawaii and for the following date ranges:
- Landsat 8 OLI: April 2013 to present
- Landsat 7 ETM+: July 1999 to April 2022
- Landsat 5 TM: March 1984 to May 2012
- Landsat 4 TM: November 1982 to December 1992
Landsat 9 C2 DSWE products will become available later in 2022.
Collection 2 Dynamic Surface Water Extent Product Improvements
Several improvements were made to the Collection 2 DSWE product. Overall, there is excellent agreement in the High Confidence Water Class between C1 and C2. The changes made in C2 DSWE are described below.
- Landsat C2 DSWE uses the Collection 2 Digital Elevation Model (DEM)
- Land Cover Mask (LCMASK) was added into the Interpreted Layer (INTR) masking (see map below)
- The INTR is masked wherever a threshold based on the Otsu method indicates shaded area and LCMASK does NOT indicate water/wetland. Tiles with low terrain relief are excluded from Otsu thresholding.
- Specific classes in INTR layer are masked if LCMASK indicates developed urban area.
- For additional information about land cover masking rules, please refer to Collection 2 DSWE Algorithm Description Document.
- The Interpreted layer with mask applied (INWM) has been split into two bands: Interpreted Layer with Some Masks Applied (INTSM) and Interpreted Layer with All Masks Applied (INWAM). (See Bands table below)
- Replaced the static Hillshade (SHADE) threshold with dynamic Otsu threshold for commission masking
- The Percent Slope (SLOPE) thresholds in Interpreted Layer (INTR) masking was removed, so the SLOPE band is removed from C2 DSWE package.
The map below displays the Land Cover Mask (LCMASK) added into the Interpreted Layer (INTR) masking in Landsat C2 DSWE. Click map to view larger version.
File Specifications of Landsat Collection 2 Dynamic Surface Water Extent (DSWE) Products
Interpreted Layer with
some masks applied
Interpreted Layer with
all masks applied
Landsat C2 DSWE products include six raster layers and an .xml metadata file relating to the existence and condition of surface water. The files included in C2 DSWE products are listed below.
- Diagnostic layer (DIAG) – Raster Layer: Provides the results of the five diagnostic tests used to determine the probability of water presence in each pixel.
Delivered file name: tileID_DIAG.TIF
- Interpreted layer (INTR) – Raster Layer: Provides the recoded results of the five diagnostic tests to identify specific surface water conditions.
Delivered file name: tileID_INTR.TIF
- Interpreted Layer with Some Masks Applied (INTSM) – Raster Layer: Like the interpreted layer “INTR” but is screened for terrain, snow, and land cover conditions.
Delivered file name: tileID_INTSM.TIF
- Interpreted Layer with All Masks Applied (INWAM) – Raster Layer: Similar to the interpreted layer “INTSM” but applies cloud and cloud shadow information from the Level 2 Quality Assessment (QA_PIXEL) layer.
Delivered file name: tileID_INWAM.TIF
- Mask (MASK) – Raster Layer: Indicates where cloud, cloud shadow, and/or snow are true, where the Otsu threshold indicated shade, or where the land cover map specifies that the location is not water.
Delivered file name: tileID_MASK.TIF
- Hillshade (SHADE) – Raster Layer: Represents the extent of terrain-produced shadow for each pixel.
Delivered file name: tileID_SHADE.TIF
- Metadata – XML file: Metadata file
Delivered file name: tileID_DSWE.XML
Caveats and Constraints
- Overcorrection of aerosol path radiance over water in Landsat 8 Collection 2 Surface Reflectance near clouds or other bright targets may adversely impact the quality of DSWE science product. Initial analysis showed that the C2 Landsat 8 DSWE may erroneously classify a pixel as non-water as a result of overcorrected Surface Reflectance over water. For additional information please see the Landsat Collection 2 Known Issues webpage.
Under low solar illumination condition where water pixels are flagged as shaded in the MASK band (SHADE ≤ Otsu threshold), the INTSM and INWAM bands may erroneously classify the water pixels as "Not Water" (see this example image). The issue mainly impacts the open ocean waters that are not covered by the land cover mask. In clear sky condition (see Cloud and Shadow bits in MASK), the INTR band will provide a more accurate interpretation for these pixels.
- Some undesired artifacts in Landsat Collection 2 Digital Elevation Model (DEM) may get propagated to the INTSM and INWAM bands. This image is an example off the coast of Akun Island in Alaska (tile H009V0012) where lines of low elevation show up as "Not Water" in the INTSM and INWAM bands. For additional information about Collection 2 DEM please visit https://doi.org/10.3390/rs12233909.
Please refer to Landsat Surface Reflectance Quality Assessment (QA) bands for pixel-level condition and validity flags and when using the Landsat Dynamic Surface Water Extent product.
Landsat C2 DSWE products are available for download from EarthExplorer. The data are located under the Landsat category, Landsat Collection 2 Level-3 Science Products subcategory, and listed as Landsat 4-8 C2 Dynamic Surface Water Extent.
Visit the Landsat Data Access webpage for information about downloading C2 DSWE products.
Landsat Collection 2 Dynamic Surface Water Extent Digital Object Identifier (DOI): 10.5066/P9DPWBUS
There are no restrictions on the use of Landsat Collection 2 Level-3 Science Products. It is not a requirement of data use, but the following citation may be used in publication or presentation materials to acknowledge the USGS as a data source and to credit the original research.
Landsat Collection 2 Level-3 Dynamic Surface Water Extent (DSWE) Science Products courtesy of the U.S. Geological Survey.
Jones, J.W., 2019. Improved Automated Detection of Subpixel-Scale Inundation—Revised Dynamic Surface Water Extent (DSWE) Partial Surface Water Tests. Remote Sens., 11, 374 https://doi.org/10.3390/rs11040374.
Jones, J. W. (2015). Efficient wetland surface water detection and monitoring via Landsat: Comparison within situ data from the Everglades Depth Estimation Network. Remote Sensing, 7(9), 12503-12538. http://dx.doi.org/10.3390/rs70912503.