The ASTER Surface Reflectance VNIR and Crosstalk Corrected SWIR (AST_07XT) dataset contains measures of the fraction of incoming solar radiation reflected from the Earth’s surface to the ASTER instrument corrected for atmospheric effects and viewing geometry for both the Visible and Near Infrared (VNIR) and Shortwave Infrared (SWIR) sensors. Each product delivery includes two Hierarchical Data Format - Earth Observing System (HDF-EOS) files: one for the VNIR, and the other for the SWIR. They are distinguished from one another by a one-second difference in the production time that appears as part of the file name. Both the VNIR and SWIR data are atmospherically corrected and are generated using the bands of the corresponding ASTER L1B image.
AST_07XT is a multi-file product that contains atmospherically corrected data for both the VNIR and SWIR sensors.
The ASTER L2 Surface Reflectance VNIR and Crosstalk Corrected SWIR data product is only available through NASA’s Earthdata Search. The ASTER Order Instructions provide step-by-step directions for ordering this product.
The Science Scalable Scripts-based Science Processor for Missions (S4PM) Version 3.4 algorithm has additional input data options that provide better input data coverage (simultaneously acquired MODIS data versus 6-hourly modeled NCEP input data) and consequently more accurate Level 2 output data. The updated algorithm includes the following improvements:
|File Size||~94 MB|
|Temporal Extent||2000-03-06 to Present|
|Coordinate System||Universal Transverse Mercator (UTM)|
|Datum||World Geodetic System (WGS84)|
|Geographic Dimensions||~60 km x 60 km|
|Number of Science Dataset (SDS) Layers||9|
|Columns/Rows||4200 (VNIR) and 2100 (SWIR) x 4980 (VNIR) and 2490 (SWIR)|
|Pixel Size||15 m (VNIR) and 30 m (SWIR)|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor|
|VNIR_Band 1||15 meter resolution VNIR Band 1 (0.52 to 0.60 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
|VNIR_Band2||15 meter resolution VNIR Band 2 (0.63 to 0.69 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
|VNIR_Band3N||15 meter resolution VNIR Band 3 (0.78 to 0.86 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
|SWIR_Band4||30 meter resolution SWIR Band 4 (1.600 to 1.700 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
|SWIR_Band5||30 meter resolution SWIR Band 5 (2.145 to 2.185 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
|SWIR_Band6||30 meter resolution SWIR Band 6 (2.185 to 2.225 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
|SWIR_Band 7||30 meter resolution SWIR Band 7 (2.235 to 2.285 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
|SWIR_Band 8||30 meter resolution SWIR Band 8 (2.295 to 2.365 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
|SWIR_Band 9||30 meter resolution SWIR Band 9 (2.360 to 2.430 µm)||N/A||16-bit signed integer||N/A||N/A||0 to 1000||0.001|
There are three groups of ancillary data inputs used in the atmospheric correction of ASTER Level 2 products:
SWIR Crosstalk Correction The ASTER SWIR sensor is affected by a crosstalk signal scattering problem, a phenomenon discovered after the launch of ASTER aboard the Terra platform in December 1999. The SWIR detector contains 2048 Pt-Si (platinum-silicide) arrays for each of its six spectral bands. There are six pairs of staggered linear CCD arrays for each band that are spaced 1.33 µm apart in the band order 7, 8, 9, 4, 5, and 6. In front of each CCD array pair, there are interference filters that spectrally separate the radiation reflected from the Earth.
Users are advised that ASTER SWIR data acquired from 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.