USGS EROS Archive - Radar - IFSAR Orthorectified Radar Image (ORI) Alaska
Science Center Objects
Interferometric Synthetic Aperture Radar (IFSAR) data were used to generate an Orthorectified Radar Image (ORI) product for Alaska (2010-2012).
The U.S. Geological Survey (USGS) National Geospatial Program (NGP) developed the Alaska Mapping Initiative (AMI) to collaborate with State and other Federal partners in Alaska to acquire 3-dimensional elevation data to improve statewide topographic mapping products. AMI coordinates Federal activities through the Alaska Mapping Executive Committee (AMEC) and State efforts through Alaska’s Statewide Digital Mapping Initiative (SDMI) to ensure a unified approach for consistent data acquisition and enhancement of topographic data products.
AMI attained interferometric synthetic aperture radar (IFSAR) data to generate digital map products. This radar mapping technology is an effective tool for collecting data under challenging circumstances such as cloud cover, extreme weather conditions, rugged terrain, and remote locations. Airborne IFSAR data were flown over south-central Alaska in summer 2010 and over northwestern Alaska in 2012. Additional areas may become available as projects are inspected for quality and released for dissemination. A coverage map in EarthExplorer indicates the extent of distributable data.
IFSAR Alaska ORI Products
An Orthorectified Radar Image (ORI) is a grayscale image of the earth’s surface that is similar in appearance to a black-and-white photograph. The image is based on the intensity of radar signals transmitted from the aircraft during data acquisition. Radar uses electromagnetic energy which is unaffected by darkness and is able to penetrate most clouds. IFSAR is an effective technology for preparing clear, sharp image maps of haze and cloud-covered areas. The radar signal strikes the terrain at an oblique angle which accentuates landscape details. Topographic features, such as subtle faults and folds, may be more clearly seen on radar imagery than on conventional aerial photographs or satellite images.
IFSAR data were contracted through two separate vendors to meet a resolution of 5 meters or less for ORI products. Since the project was split between vendors, data are available at either 2.5-meter or 0.625-meter resolution depending on vendor and area of coverage.
The USGS Earth Resources Observation and Science (EROS) Center distributes IFSAR ORI Alaska product in Georeferenced Tagged Image File Format (GeoTIFF). Images are available in 15-minute by 15-minute tiles and have been orthorectified to match the spatial accuracy of a map.
|Projection||Alaska Albers Conical Equal Area|
|Resolution||0.625-meter or 2.5-meter, depending on region and vendor|
|Horizontal Accuracy||< 5.682-meter Root Mean Square Error (RMSE) for x and y|
|Raster Size||15 minute tiles|
|Voids||< 5% per tile|
|File Size||50 - 100 megabytes for 2.5-meter resolution data
1.0 - 1.5 Gigabytes for 0.625-meter resolution data
Coverage Maps indicating the availability of IFSAR ORI Alaska products are available for download.
- USGS Alaska Mapping Initiative
- Alaska’s Statewide Digital Mapping Initiative
- Alaska Mapping Executive Committee
- USGS Factsheet - The 3D Elevation Program – Summary for Alaska
- IFSAR Orthorectified Radar Image (ORI) Alaska Digital Object Identifier (DOI) number: 10.5066/F7CJ8CSF
EarthExplorer can be used to search, preview, and download IFSAR ORI Alaska data. The collection is located under the Radar category.
Digital Surface Model (DSM) and Digital Terrain Model (DTM) products were also generated from the IFSAR data and are available through EarthExplorer under the digital elevation category. These collections share the same browse images so please note that the level of detail in the ORI is much greater than observed in the browse image.