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• I. Product Description
• II. Converting Level-1A DNs to Scaled DNs
• III. Level-1A Spectral Band Information
• IV. Key Embedded HDF Metadata Attributes
• V. Ordering Information
• VI. Data-Related Documentation
• VII. Contact Information

EDG Data Set Name ASTER L1A Reconstructed Unprocessed Instrument Data Granule Shortname AST_L1A Data Set Characteristics Area: ~60 km x 60 km Image Dimensions: VNIR: 4200 rows x 4100 columns VNIR (3B): 5400 rows x 5000 columns SWIR: 2100 rows x 2048 columns TIR: 700 rows x 700 columns File Size: VNIR (1, 2, 3N) = ~ 50 Mb VNIR (3B) = ~ 30 Mb SWIR (4-9) = ~ 25 Mb TIR (10-14) = ~ 5 Mb Total = 110 Megabytes Spatial Resolution: VNIR = 15 m SWIR = 30 m TIR = 90 m Data Format: Hierarchical Data Format-Earth Observing System (HDF-EOS) GeoTIFF Vgroup Data Fields: 15

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.

I. Product Description

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 the Earth Remote Sensing Data Analysis Center (ERSDAC) 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. The EOS Data Gateway (EDG) provides GDS-produced Level-1A browse images for each of the three sensors, and allows users to view and/or request these images.

II. Converting Level-1A DNs to Scaled DNs

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 VNIR’s 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.

• L: Scaled Radiance (in w/m²/sr/µm)
• A: Linear Coefficient
• C: Non-linear Coefficient
• G: Gain
• D: Offset
• V: Signal (DN value)

III. Level-1A Spectral Band Information

The Vgroup HDF object field describes the swath-based image data sets for each of the three sensor systems.

IV. Key Embedded HDF Metadata Attributes

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 SOLAR ELEVATION 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.

V. Ordering Information

EOS Data Gateway Search Tips

Data Center:	LPDAAC
Sensor:	ASTER
Dataset:	ASTER L1A Reconstructed Unprocessed Instrument Data
Geographic Extent:	Type latitude/longitude range or delineate a geographic search window
Temporal Extent:	March 4, 2000 to present

VI. Data-Related Documentation

Product Information

Release Notes (http://asterweb.jpl.nasa.gov/content/03_data/01_Data_Products/aster_expedited_data.htm)

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 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)

VII. Contact Information

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