10.5067/ASTER/AST_L1A.003
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This is an ASTER Level-1A 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.
Users are advised that ASTER SWIR data acquired from late April 2008 to the present exhibit anomalous saturation of values and anomalous striping. This effect is also present for some prior acquisition periods. Please refer to the ASTER SWIR User Advisory Document for more details.
The ASTER instrument aboard the Terra satellite has a complement of three different telescopes with varying pointing capabilities. ASTER data are primarily acquired and processed in support of a global mapping mission, and based on Data Acquisition Requests (DARs) from authorized users. ASTER Level-1 data are produced at the Ground Data System (GDS) facility of Japan Space Systems in Tokyo, Japan, and subsequently sent to the Land Processes (LP) Distributed Active Archive Center (DAAC) for archiving, distribution, and higher-level product generation. The ASTER Level-1A data set contains reconstructed, instrument digital numbers (DNs) derived from the telemetry streams of the 3 telescopes: Visible Near Infrared (VNIR), Shortwave Infrared (SWIR), and Thermal Infrared (TIR). The Level-1A data contains depacketized, demultiplexed, and realigned instrument image data with their geometric correction coefficients and radiometric calibration coefficients calculated and appended but not applied. It also includes corrections for the SWIR parallax, and intra- and inter-telescope registration information.
An ASTER Level-1A data set contains raw digital numbers (DNs) quantized as 8-bit unsigned integers. To convert these to scaled or calibrated DNs, the ASTER Level-1A DNs are converted on a detector-by- detector basis using the Slope/Inclination (A), Gain (G) and Offset (D) values from the Radiometric Conversion Coefficients (RCC) table that is appended with the Level-1A data set in the HDF-EOS file. The RCC information determines how the Level-1A DNs are converted into Level-1B calibrated DNs. The gain and offset information in the RCC table are used in that conversion. Information from both the On-Board and Vicarious Calibration sources are used in the generation of RCC table.
The RCC table is one of several ancillary tables bundled with the ASTER Level-1A data. It contains three columns (Structure of the RCC table):
VNIR and SWIR | TIR |
D: Offset | D: Offset |
A: Slope/Inclination | A: Slope/Inclination |
G: Gain | C: Nonlinear Coefficient |
These three sets of values are provided for each sensor, band (channel) and detector. Each row corresponds to a specific detector. For example, the RCC table for the VNIR bands would include the offset, slope/inclination, and gain columns for each of the 4100 detectors for bands 1, 2, and 3N, and 5000 detectors of band 3B. This is consistent with VNIRs pushbroom sensor configuration flying in the along-track direction. The Detector- Pixel Position Relationship diagram depicts the relationship between the detector number and the image pixel position. Note that this relationship is reversed for the VNIR and SWIR bands. The detector number 1 corresponds to the left-end column pixel for VNIR bands while it corresponds to the right-end column pixel for the SWIR bands.
ASTER Level-1A DNs can be converted to at-sensor radiance thus:
LVNIR, SWIR = AV/G + D
LTIR = AV + CV2 + D
Area | ~60 km x 60 km |
Image Dimensions - VNIR | 4200 rows x 4100 columns |
Image Dimensions - VNIR (3B) | 5400 rows x 5000 columns |
Image Dimensions - SWIR | 2100 rows x 2048 columns |
Image Dimensions - TIR | 700 rows x 700 columns |
File Size Total | 110 MB |
File Size - VNIR (1, 2, 3N) | ~50 MB |
File Size - VNIR (3B) | ~30 MB |
File Size - SWIR (4 through 9) | ~25MB |
File Size - TIR (10 through 14) | ~5 MB |
Spatial Resolution - VNIR | 15 m |
Spatial Resolution - SWIR | 30 m |
Spatial Resolution - TIR | 90 m |
Data Format | HDF-EOS or GeoTIFF |
Vgroup Data Fields | 15 |
VNIR (15 Meters) Rotation
Vgroup Data Fields/ Spectral Range (µm) |
Units | Data Type | Valid Range |
Telescope Pointing Capability |
Band 1 (0.52–0.60) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-24 |
Band 2 (0.63–0.69) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-24 |
Band 3N (0.78–0.86) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-24 |
Band 3B (0.78–0.86) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-24 |
SWIR (30 Meters) Rotation
Vgroup Data Fields/ Spectral Range (µm) |
Units | Data Type | Valid Range |
Telescope Pointing Capability |
Band 4 (1.600–1.700) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-8.55 |
Band 5 (2.145–2.185) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-8.55 |
Band 6 (2.185–2.225) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-8.55 |
Band 7 (2.235–2.285) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-8.55 |
Band 8 (2.295–2.365) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-8.55 |
Band 9 (2.360–2.430) | Digital Counts | 8-bit unsigned integer | 0–255 | +/-8.55 |
TIR (90 Meters) Rotation
Vgroup Data Fields/ Spectral Range (µm) |
Units | Data Type | Valid Range |
Telescope Pointing Capability |
Band 10 (8.125–8.475) | Digital Counts | 16-bit unsigned integer | 0–65535 | +/-8.55 |
Band 11 (8.475–8.825) | Digital Counts | 16-bit unsigned integer | 0–65535 | +/-8.55 |
Band 12 (8.925–9.275) | Digital Counts | 16-bit unsigned integer | 0–65535 | +/-8.55 |
Band 13 (10.25–10.95) | Digital Counts | 16-bit unsigned integer | 0–65535 | +/-8.55 |
Band 14 (10.95–11.65) | Digital Counts | 16-bit unsigned integer | 0–65535 | +/-8.55 |
The following is a brief description of a subset of key metadata attributes that are embedded in the HDF header in both ASTER Level-1A and Level-1B data sets:
SCENE FOUR CORNERS (Under ProductMetadata.0/SceneInformation): Provides coordinate information on the four corners of an ASTER scene. These include the upper-left, upper-right, lower-left, and lower-right coordinate values for latitude and longitude in floating point decimal degrees.
SCENE CENTER (Under ProductMetadata.0/SceneInformation): This pair of geodetic latitude and longitude coordinates denote the center of the reference band (VNIR Band-2 (for VNIR, SWIR and TIR), or SWIR Band-6 (for SWIR and TIR only), or TIR Band-11 (for TIR only)) in floating point decimal degrees.
FLYING DIRECTION (Under ProductMetadata.0/SceneInformation): This specifies the satellite flight direction at the time of observation. An AS denotes ascending direction for daytime scenes while DE denotes descending direction for nighttime scenes. Alternatively, positive solar elevation angles indicate daytime scenes while negative solar elevation angles indicate nighttime scenes. Note: This information along with geographic location and acquisition time are used to calculate a Day-Night flag (not available in the Level-1 HDF metadata) attribute for all the higher-level products, except the ASTER DEM product (located in both the HDF and ECS metadata files). That attribute also includes a third option called Both for scenes falling in the day-night and night-day cusps.
SOLAR DIRECTION (Under ProductMetadata.0/SceneInformation): This attribute defines the sun direction as seen from the scene center, and includes two values. The first value is the SOLAR AZIMUTH angle in degrees (values can range between 0 and 360) measured eastward from North. The second value is the SOLARELEVATION angle in degrees (values can range between <= -90 to <= 90).
POINTING ANGLES (Under ProductMetadata.0/PointingAngles): This provides the pointing angle values for each of the three sensors (VNIR, SWIR, and TIR) in floating point decimal degrees. They range from +/- 24 telescope rotation for VNIR to +/- 8.55 pointing mirror rotation and scan mirror rotation for SWIR and VNIR sensors respectively.
MAP ORIENTATION ANGLE (Under ProductMetadata.0/SceneInformation): This denotes the angle of rotation between the path-oriented image and the transformed map-projected coordinates. Ranging from -180 to +180, it provides the amount by which the ASTER Level-1B image is rotated from True North.
RADIOMETRIC DATABASE VERSION (Under ProductMetadata.0/GainInformation): This provides the version number of the radiometric correction coefficients that were used to generate the Radiometric Correction Tables.
GEOMETRIC DATABASE VERSION (Under ProductMetadata.0/GainInformation): This provides the version number of the geometric correction coefficients that were used to generate the Geometric Correction Tables.
ACQUISITION DATE AND TIME (Under CoreMetadata.0/SingleDateTime): Calendar Date (YYYYMMDD) provides the acquisition date while TimeOfDay (HHMMSSSSSSZ) provides the acquisition time in Coordinated Universal Time (UTC).
PRODUCTION DATE AND TIME (Under CoreMetadata.0/ProductionDateTime): This provides the production date (YYYYMMDD) and time (HHMMSSSSS local time) of the ASTER scene.
Attributes Not Supported in the HDF Metadata: Consult diagram on solar and satellite orbital geometry components.
SOLAR ZENITH ANGLE: Solar zenith angle is the complementary angle to the solar elevation angle. In other words, it equals 90 degrees minus the solar elevation angle.
SATELLITE ZENITH ANGLE: The satellite zenith angle is the complementary angle to the satellite elevation angle. In other words, it equals 90 degrees minus the satellite elevation angle.
SATELLITE AZIMUTH AND ELEVATION ANGLES: The satellite azimuth and elevation angles are not provided in the HDF metadata. They can be calculated using the satellite position, and line-of-sight vector information that are provided in the parameter tables in the HDF metadata. The following link provides a list of all the orbital geometry parameter tables, their dimensions and other details: ASTER Level-1A Orbital Geometry Parameters.
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For information on how to cite and acknowledge LP DAAC data, please see our Citing Our Data page at https://lpdaac.usgs.gov/citing_our_data.
The full archive record for this data product is available through the Earthdata Search Client interface.
Please find a link to (and information about) this data access tool on the Data Access Section of this Web Site.
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