ASTER L1A data are formally defined as reconstructed, unprocessed instrument data at full resolution. They consist of the image data, the radiometric coefficients, the geometric coefficients and other auxiliary data without applying the coefficients to the image data, thus maintaining original data values. The L1B data are generated by applying these coefficients for radiometric calibration and geometric resampling.

All ASTER data products are stored in a specific implementation of Hierarchical Data Format called HDF-EOS.

Level1 data are processed by combining bands in the following order:

File sizes and image dimensions of ASTER L1A and L1B data sets:

The ASTER Level-1A data set contains image and ancillary data from all 3 sensors (assuming data from all three sensors were collected). The average sizes of these 14 channels or bands for L1A and L1B data sets are:

VNIR and SWIR are 8-bit unsigned integer data, and TIR are 16-bit unsigned integer data.

The image dimensions for an ASTER L1A and L1B data set are:

The areal size of an ASTER Level-1 scene (swatch width) is about 60 km by 60 km. This is only slightly larger for the VNIR 3B image (which is used in generating stereoscopic images for producing DEMs).

ASTER Level-1A dataset

An ASTER Level-1A dataset contains reconstructed, unprocessed instrument digital data derived from the telemetry streams of the 3 telescopes: Visible Near Infrared (VNIR), Shortwave Infrared (SWIR), & Thermal Infrared (TIR).

Data derived from each of these telescopes or sensors are at three different ground resolutions: VNIR at 15 m, SWIR at 30 m, and TIR at 90 m. These depacketized, demultiplexed, and realigned instrument image data have their geometric correction coefficients and radiometric calibration coefficients calculated and appended but not applied.

Level-1A datasets also include corrections for the SWIR parallax, and intra- and inter-telescope registration information. ASTER Level-1A data is produced at the Ground Data System (GDS) in Tokyo, Japan, and sent to the EROS Data Center's (EDC) Distributed Active Archive Center (DAAC) for archiving, distribution, and higher-level processing. GDS and EDG naming conventions differ.

ASTER Level-1B dataset

The ASTER Level-1B product contains radiometrically calibrated and geometrically co-registered data for all the channels acquired previously through the telemetry streams of the 3 different telescopes in Level-1A.

This product is created by applying the radiometric calibration and geometric correction coefficients to the Level-1A data. Both intra-telescope and inter-telescope registration corrections have also been applied relative to the reference band of each sub-system.

The Level-1B product offers the same number of bands at the same resolution as the Level-1A product. Level-1B data are required as the input for generating higher level-2 geophysical products.

These Level-1B data are produced at the Ground Data System (GDS) in Tokyo, Japan, and sent to the EROS Data Center's (EDC) Distributed Active Archive Center (DAAC) for archiving, distribution, and higher-level processing. GDS and EDG naming conventions differ.

ASTER Expedited Data Sets (EDS)

The Expedited ASTER Level-1A data set is produced with the express purpose of providing the ASTER Science Team members data of their particular interest in quick turn-around time from the moment the data are acquired.

This is usually done to support on-going field calibration and validation efforts or to support emergency response to natural disasters when processed Level-1 data with minimum turn-around time would prove beneficial in initial damage or impact assessments.

This data set is expected to be publicly available for a period of 30 days after which time it will be removed from the archive. This is done because the routinely processed (Production Data Set or PDS) version of this data set will be available from Japan in due course for search and order from the LP-DAAC archives.

ASTER Expedited Data Sets (EDS) serve the short-term requirements of a small group of scientists and fulfill immediate imagery needs during times of natural disasters.

The general product description details as described for the Production Data Set version of the ASTER Level-1A Data Set – Reconstructed, Unprocessed Instrument Data apply to the expedited data set with a few notable exceptions. These include:

• Stereo data is not available from the Expedited Level - 1 data set since it does not contain the VNIR 3B (aft-viewing) Band. Therefore DEM data cannot be extracted.

• TIR data quality is expected to be lower than that of the regular PDS data because short-term calibration for TIR is not available. Instead, the long-term calibration is used.

• The Inter-telescope registration quality may be lower than that of PDS. This is because regular PDS data are surrounded by 13 adjacent scenes to ensure sufficient information for inter-telescope registration. However, these 13 adjacent scenes are not transmitted via the expedited pathway, and therefore are not available.

• The geometry of L1BE scenes is slightly different than L1B because the expedited processing uses the raw spacecraft ephemeris data, and the L1B processing uses the refined (post-processed) ephemeris data.

Aster and MadMappers:

The Madmappers Team routinely processes ASTER Level-1A, ASTER Level-1B and  Expedited ASTER Level-1 into products for topographic, spectral and digital elevation model studies. Furthermore MadMappers is capable of processing ASTER Level-1A into ASTER Level-1B by applying the appropriate corrections. By virtue of being able of generating Aster DEM products, orthorectification is also achieved. Furthermore MadMappers is able to schedule data acquisitions for selected study areas in Africa.

Aster products are undoubtedly superior to their Landsat 7 equivalent due to their superb clarity and crispiness.

Software:

Until recently only advanced remote sensing software was the only means to access native Aster data in HDF format. The excellent Globalmapper can now read and convert HDF data into formats suitable to common GIS software.
MadMappers collection comprises of Aster data suitable for use in OziExplorer.

Additional details regarding the instrument, data products etc. can be accessed from:

http://asterweb.jpl.nasa.gov/default.htm

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