Note: The Observatory uses an automatically generated 14 day accumulation of the MODIS NRT daily water to show current conditions. This is necessary to provide the most complete geographic coverage under conditions of intermittent cloud cover.
This map incorporates data from an automated MODIS 250 m flood processor using NASA LANCE data. See appropriate Surface Water Record display for more information, links to those component data, and technical description.We acknowledge the Land Atmosphere Near-real time Capability for EOS (LANCE) system operated by NASA/GSFC, and also the NASA Applications and Earth Sciences programs, which support development and improvements to the MODIS NRT flood processor.
Click here for access to the archived long term GIS file record for this map sheet.
Click here for access to the automated daily .shp file GIS record (record commences in 2011; enhanced cloud shadow filtering was initiated in early 2012).
Landsat 8 data, when used (available on request), are provided by the United States Geological Survey Hazards Data Distribution System (http://hdds.usgs.gov/hdds2/). Landsat 8 is jointly managed by NASA and the United States Geological Survey.
Method of Landsat water/land classification and map production: 1) Landsat bands 3 (green), 0.53-0.59; 5 (near infrared), 085.-0.88; and 6, (short-wave infrared), 1.57-1.65, of the Operational Land Imager (OLI) sensor are used to produce a color composite for quality control purposes. 2) The following processing steps are performed to produce classified water pixels: a) Using Envi™, an NDVI-like product is produced: band 3-band 5/band 3 + band 5. b) Water pixels are identified via a threshold: "water" = < -.04 of this ratio result, c) GIS (.shp files) are then produced within Envi™ and outline the preliminary water areas. d). Within GIS software, the polygons are displayed over the tif image, and evident cloud shadow-sourced and other error polygons are manually deleted. This method is designed for rapid, operator-assisted transformation of Landsat image data into water map information. The band 3/ band 5 information when processed in this way avoids most cloud shadow (false positives) and provides sensitive water/land discrimination.
At selected locations, a time series of satellite microwave-based daily river discharge measurements are available. These define the estimated recurrence interval of mapped flooding. Click on the colored dots in the online Current Conditions display. Yellow dots: low flow (<50 % mean daily runoff for this date); Blue dots: normal flow; Purple dots: moderate flooding (>1.33 yr recurrence); Red, major flooding (> 5 yr recurrence). See River Watch Global Display for more information. We may add sites for this region soon.
MAP SYMBOLOGY