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EDG Data Set Name
ASTER On-Demand L3 DEM and Orthorectified Images
Granule Shortname
AST14DMO
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Data Set Characteristics Area: ~60 km x 60 km (ASTER Level-1A input image) Input Image Resolution: 15, 30, 90 meters Output Image Resolution: DEM: 30 meters Orthorectified Images: 15, 30, 90 meters File Size: ~191 MB Image Dimensions: Varies by scene Map Projection: Universal Transverse Mercator (UTM) Resampling Method: DEM: Bilinear Orthorectified Images: Cubic Convolution Data Format: GeoTIFF |
 This is an Orthorectified ASTER Level-1B image of the northwestern part of Los Angeles County with a backdrop of the Tehachapi mountains. In the lower right is the northwestern end of the San Fernando Valley with Santa Clarita to its north. In the middle right is Castaic Lake with Interstate-5 trending northwest to southeast. Healthy vegetation appears in red in contrast to a couple of burn scars, one in the middle left (north of Simi Valley), while the other one in the north in the Angeles National Forest. |
The ASTER On-Demand L3 DEM and Orthorectified Images form a multi-file product that contains both the Digital Elevation Model (DEM), and the Orthorectified Image products. Each product delivery includes one DEM data file, and fifteen orthorectified data files in GeoTIFF format.
ASTER DEM
The ASTER Digital Elevation Model (DEM) product is generated using bands 3N (nadir-viewing) and 3B (backward-viewing) of an ASTER Level-1A image acquired by the Visible Near Infrared (VNIR) sensor. The VNIR subsystem includes two independent telescopes. Together, they produce stereoscopic data. The spectral range of the Band 3 stereo pair is between 0.78 and 0.86 microns with a base-to-height ratio of 0.6, and an intersection angle of about 27.7. There is a time lag of approximately one minute between the acquisition of the nadir and backward-viewing images. Click here to view a diagram depicting the ASTER VNIR's stereoscopic (nadir and backward-viewing sensors) along-track imaging geometry.
Starting in early summer of 2006, the LP DAAC implemented new production software for efficiently creating quality DEMs. Based on an automated stereo-correlation method, the new software generates a relative DEM without any ground control points (GCPs), based on the ephemeris and attitude data for the ASTER instrument and the Terra spacecraft platform. The new ASTER DEM is a single-band product with 30 meter horizontal postings that is geodetically referenced to the UTM coordinate system, and referenced to the Earth's geoid using the EGM96 geopotential model. Compared to ASTER DEMs previously available from the LP DAAC, users likely will note some differences in ASTER DEMs produced by the new system, because they are now produced automatically, with no manual editing. Larger water bodies are detected and typically have a single value, but they no longer are manually edited. Any failed areas, while infrequent, remain as they occur in the data. Cloudy areas typically appear as bright regions, rather than as manually edited dark areas.
The precision of the new LP DAAC-produced DEMs meets or exceeds accuracy specifications set for the ASTER relative DEMs by the Algorithm Theoretical Basis Document (ATBD). Users likely will find that these DEMs have accuracies approaching those specified in the ATBD for absolute DEMs. Validation testing has shown that the accuracy of the new DEMs is frequently better than 25 meters RMSExyz.
ASTER DEM Product Output Information
| Data Fields | Units | Data Type | Valid Range |
|---|---|---|---|
| Single band | Meters | 16-bit signed integer | -32768 to +3276 |
ASTER Orthorectified Images
The ASTER On-Demand Orthorectified Image products contain imagery transformed from a perspective projection to an orthogonal one. An orthorectified image possesses the geometric characteristics of a map, with near-vertical views for every location. These products are terrain-corrected, provide radiometrically calibrated radiance, and are mapped to the Universal Transverse Mercator coordinate system. The inputs include the following: an ASTER Level-1A Reconstructed Unprocessed Instrument data set; georeferencing information from the ASTER instrument's and Terra platform's ephemeris and attitude data; and an ASTER-derived digital elevation model (DEM). The output product includes fifteen orthorectified ASTER Level-1B calibrated radiance images, one per band, as listed below.
ASTER Orthorectified Product Output Information
| Spectral Range (µm) | Units | Data Type | Valid Range | Unit Conversion Coefficient* |
|---|---|---|---|---|
| VNIR (15 Meters) | Normal Gain | |||
| Band 1 (0.52 - 0.60) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 1.688 |
| Band 2 (0.63 - 0.69) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 1.415 |
| Band 3N (0.78 - 0.86) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 0.862 |
| Band 3B (0.78 - 0.86) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 0.862 |
| SWIR (30 Meters) | ||||
| Band 4 (1.600 - 1.700) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 0.2174 |
| Band 5 (2.145 - 2.185) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 0.0696 |
| Band 6 (2.185 - 2.225) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 0.0625 |
| Band 7 (2.235 - 2.285) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 0.0597 |
| Band 8 (2.295 - 2.365) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 0.0417 |
| Band 9 (2.360 - 2.430) | w/m2/sr/µm | 8-bit unsigned integer | 0 - 255 | 0.0318 |
| TIR (90 Meters) | ||||
| Band 10 (8.125 - 8.475) | w/m2/sr/µm | 16-bit unsigned integer | 0 - 65535 | 6.882 x 10-3 |
| Band 11 (8.475 - 8.825) | w/m2/sr/µm | 16-bit unsigned integer | 0 - 65535 | 6.780 x 10-3 |
| Band 12 (8.925 - 9.275) | w/m2/sr/µm | 16-bit unsigned integer | 0 - 65535 | 6.590 x 10-3 |
| Band 13 (10.25 - 10.95) | w/m2/sr/µm | 16-bit unsigned integer | 0 - 65535 | 5.693 x 10-3 |
| Band 14 (10.95 - 11.65) | w/m2/sr/µm | 16-bit unsigned integer | 0 - 65535 | 5.225 x 10-3 |
*Unit Conversion Coefficient (UCC) values are provided for each channel in the encapsulated ASTER Level-1 metadata under the UNITCONVERSIONCOEFFICIENT Group, and within the INCL Object of the Product Metadata for each sensor. UCC provide the slope or inclination values in units of watts/meter2/steradian/micrometer per DN.
Differences between an ASTER Level-1B data set and ASTER Orthorectified Images
- ASTER Level-1B data consist of calibrated radiance in a path-oriented UTM projection, whereas ASTER orthorectified images are presented in a north-up UTM projection. ASTER orthorectified images possess the geometric characteristics of a map with near-vertical views for every location, and they also are terrain-corrected.
- ASTER L1B image dimensions for each of the three sensor systems (VNIR, SWIR, and TIR) are different because of their different spatial resolutions; those image dimensions remain constant from one L1B scene to another. However, ASTER orthorectified image dimensions can vary from scene to scene. This is because the image dimensions of the ASTER Digital Elevation Model (DEM) used in the orthorectification process can vary, and the DEM’s image dimensions define the output dimensions for each of the three sensor’s orthorectified images.
- The ASTER Level-1B data set is provided in a single multi-file packaged Hierarchical Data Format (HDF) with specific EOS conventions. The ASTER orthorectified image file format is GeoTIFF. The file includes fifteen orthorectified ASTER Level-1B calibrated radiance images, one for each band. These image files are compressed and provided to the user in a single zip file.
Ordering ASTER DEM and Orthorectified Images
The ASTER On-Demand L3 Orthorectified product is produced by first selecting an ASTER Level-1A input data set through the EOS Data Gateway. An ASTER DEM is produced, and is also used as an input to the process of generating the orthorectified products. The ordering process and procedures are described in the following tutorial: http://lpdaac.usgs.gov/tutorial/.
Product-Related Documentation
ASTER User Handbook
http://asterweb.jpl.nasa.gov/content/03_data/04_Documents/aster_user_guide_v2.pdf
ASTER Level-1 Users Guide
http://www.science.aster.ersdac.or.jp/en/documnts/users_guide/index.html
ASTER Level-1 Data Products Specification
http://asterweb.jpl.nasa.gov/content/03_data/04_Documents/ASTER_L1_Product_Spec_Ver_1.3_July01.pdf
ASTER Higher-Level Product User Guide
http://asterweb.jpl.nasa.gov/content/03_data/04_Documents/ASTERHigherLevelUserGuideVer2May01.pdf
ASTER Level-1 ATBD
http://eospso.gsfc.nasa.gov/eos_homepage/for_scientists/atbd/docs/ASTER/atbd-ast-01.pdf
EOS Data Products Handbook (Volume 1, Revised 2004)
http://eospso.gsfc.nasa.gov/ftp_docs/data_products_1.pdf
ASTER JPL Web Page
http://asterweb.jpl.nasa.gov/data_products.asp
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LP DAAC User Services U.S. Geological Survey (USGS) Earth Resources Observation and Science Center (EROS) 47914 252nd Street Sioux Falls, SD 57198-0001 |
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