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• I. Product Description
• II. Level-1B Spectral Band Information
• III. Key Embedded HDF Metadata Attributes
• IV. Converting ASTER Level-1B Calibrated Radiance to At-Sensor Radiance
• V. Ordering Information
• VI. Data-Related Documentation
• VII. Contact Information

EDG Data Set Name ASTER L1B Registered Radiance at the Sensor Granule Shortname AST_L1B Data Set Characteristics Area: ~60 km x 60 km Image Dimensions: VNIR: 4200 rows x 4980 columns VNIR (3B): 4600 rows x 4980 columns SWIR: 2100 rows x 2490 columns TIR: 700 rows x 830 columns File Size: VNIR (1,2,3N) = ~ 60 Mb VNIR (3B) = ~ 22 Mb SWIR (4-9) = ~ 30 Mb TIR (10-14) = ~ 6 Mb Total = 118 Megabytes Spatial Resolution: VNIR = 15 m SWIR = 30 m TIR = 90 m Projection: Universal Transverse Mercator (UTM) Data Format: Hierarchical Data Format-Earth Observing System (HDF-EOS) GeoTIFF Vgroup Data Fields: 15

This is an 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.

I. Product Description

The ASTER Level-1B Registered Radiance at the Sensor product contains radiometrically calibrated and geometrically co-registered data for the acquired channels of the three different telescopes of Level-1A data. The Level-1B data set is produced by applying the radiometric calibration and geometric correction coefficients to the Level-1A. Both intra-telescope and inter-telescope registration correction for all the bands are accomplished relative to the reference band for each sub-system (Bands 2, 6, and 11). The Level-1B radiance data set offers the same number of bands at the same resolution as the Level-1A, and provides the input for generating a number of derived Level-2 geophysical products. Since March 2000, the Ground Data System (GDS) facility in Tokyo, Japan produced the Level-1B data sets, and sent them to the Land Processes (LP) Distributed Active Archive Center (DAAC) for archiving, distribution, and higher-level processing. That practice has changed to an on-demand paradigm as explained in the next section.

II. Level-1B Spectral Band Information

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

III. 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.

IV. Converting ASTER Level-1B Calibrated Radiance to At-Sensor Radiance

The ASTER Level-1B data set contains radiometrically calibrated DNs (in units of watts per meter² per steradian per micrometer) quantized as 8-bit unsigned integers for the VNIR and SWIR bands, and 16-bit unsigned integers for the TIR bands. Notwithstanding the fact that the long name of an ASTER Level-1B is defined “Registered Radiance at the Sensor” they still are only scaled or calibrated radiances. These scaled DNs are converted to at-sensor radiance using the Unit Conversion Coefficients (UCC) in the following manner:

Radiance = (DN value – 1) * Unit Conversion Coefficient                                                                 (1)

This is a standard method to integerize the radiance values with a backfill of zero values. UCC values are provided for each channel in the embedded HDF metadata under the UNITCONVERSIONCOEFFICIENT Group, INCL Object of the Product Metadata for each sensor.

The UCCs provide the inclination or slope values in units of watts/meter²/steradian/micrometer per DN. The following table provides the UCC information. They are also published in the ASTER User Handbook (pp 25-26).

ASTER Unit Conversion Coefficients (watts/meter²/steradian/micrometer)/DN

The ASTER Level-1 processing at GDS, Japan keeps the minimum and maximum radiance of the Level-1B data set constant over time. This explains why the inclination (slope) and offset scaling factors also have remained practically constant over time.

V. Ordering Information

Starting on May 24, 2006, all ASTER Level-1B data sets are offered on an on-demand basis. Therefore, you can pick any ASTER Level-1A data set from the LP DAAC archive for processing to Level-1B via the EOS Data Gateway. Initially, only data acquired after March 22, 2003 will be available through GloVis due to incompatibility of the smaller browse images associated with those data. For additional details, please consult the following URL: http://lpdaac.usgs.gov/news/news_aster_051506.asp

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

Order Data through the USGS Global Visualization Viewer (GloVis)
http://LPDAAC.usgs.gov/aster/glovis.asp

VI. Data-Related Documentation

Release Notes
http://www.gds.aster.ersdac.or.jp/gds_www2002/service_e/set_service_e.html

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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