AST_07XT v003

ASTER L2 Surface Reflectance VNIR and Crosstalk Corrected SWIR


PI: U.S./Japan ASTER Science Team

Description

The Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (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 crosstalk corrected product no longer displays blurred images initiated by stray light that caused multiple reflections with the SWIR bands.

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.

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Characteristics

Improvements/Changes from Previous Versions

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:

  • A new option has been added to use MODIS Version 6.1 (MOD07_L2) Temperature, Water Vapor, and Pressure inputs. The default order option will remain as National Centers for Environmental Prediction (NCEP)/Global Data Assimilation System (GDAS).
  • The default for the Ozone input data was switched from NCEP/Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS) to the new Total Ozone Analysis using Solar Backscatter UltraViolet Version 2 (SBUV/2) and TOVS (TOAST)/Earth Probe-Total Ozone Mapping Spectrometer (EPTOMS) option.
  • The Level 2 algorithm has been updated to provide a fall back option for the Temperature/Water Vapor/Pressure and Ozone input selections. Both selections will automatically revert to the next lower input if the selected input is not available.
    • The Temperature/Water Vapor/Pressure input will fall back from MOD07 to NCEP/GDAS then to Climatology.
    • The Ozone input will fall back from TOAST/EPTOMS to OZ_DLY/TOVS then to Climatology.
  • Users can check the OPERATIONALQUALITYFLAGEXPLANATION field in the metadata file of the output product file to see if a fall back has occurred and identify which input source was used to generate the Level 2 product files.
  • Level 2 SWIR outputs are only available for scenes acquired prior to April 2008. Scenes processed after this time contain fill values.

Starting June 23, 2021, radiometric calibration coefficient Version 5 (RCC V5) will be applied to newly observed ASTER data and archived ASTER data products. Details regarding RCC V5 are described in the following journal article.

Tsuchida, S., Yamamoto, H., Kouyama, T., Obata, K., Sakuma, F., Tachikawa, T., Kamei, A., Arai, K., Czapla-Myers, J.S., Biggar, S.F., and Thome, K.J., 2020, Radiometric Degradation Curves for the ASTER VNIR Processing Using Vicarious and Lunar Calibrations: Remote Sensing, v. 12, no. 3, at https://doi.org/10.3390/rs12030427.

As of December 15, 2021, the LP DAAC has implemented changes to ASTER PGE Version 3.4, which will affect all ASTER Level 2 on-demand products. Changes include:

  • Aura Ozone Monitoring Instrument (OMI) has been added as one of the ancillary ozone inputs for any observations made after May 27, 2020. The sequence of fallbacks for ozone will remain the same.
  • Toolkit has been updated from Version 5.2.17 to 5.2.20. Users may notice minor differences between the two versions. Differences may include minuscule changes in digital numbers around the peripheral of the granule and boundaries of a cloud for Surface Reflectance and Surface Radiance (AST07 and AST09) QA Data Plane depending on the Operating System and libraries being used by the user to process the data.

Additionally, Climatology, which is one of the inputs for Ozone and Moisture, Temperature and Pressures (MTP) will be removed from the Earthdata Order Form. It has been observed that PGEs generated with Climatology as an input yield noticeable differences statistically during image and spectral analysis. Climatology will continue to be used as the final default if neither of the first two selectable options are available for Ozone and MTP. Users can check the OPERATIONALQUALITYFLAGEXPLANATION field in the metadata or the output file for atmospheric parameters that were applied.

Collection and Granule

Collection

Characteristic Description
CollectionTerra ASTER
DOI10.5067/ASTER/AST_07XT.003
File Size~94 MB
Temporal ResolutionOther
Temporal Extent2000-03-06 to Present
Spatial ExtentGlobal
Coordinate SystemUniversal Transverse Mercator (UTM)
DatumWorld Geodetic System (WGS84)
File FormatHDF-EOS
Geographic Dimensions~60 km x 60 km

Granule

Characteristic Description
Number of Science Dataset (SDS) Layers9
Columns/Rows4200 (VNIR) and 2100 (SWIR) x 4980 (VNIR) and 2490 (SWIR)
Pixel Size15 m (VNIR) and 30 m (SWIR)

Layers / Variables

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:

  1. Ozone data input: The default for the Ozone input data is the Aura OMI. The fall back option is the Total Ozone Analysis using Solar Backscatter UltraViolet Version 2 (SBUV/2) and TOVS (TOAST)/Earth Probe-Total Ozone Mapping Spectrometer (EPTOMS) option. The second fall back option is the National Centers for Environmental Prediction (NCEP)/Television Infrared Observation Satellite (TIROS) Operational Vertical Sounder (TOVS). The NCEP/TOVS data are acquired from a NOAA satellite and provide the ancillary column ozone data twice daily. If the aforementioned fall back options are not available for a particular time period, the final fall back option is the Naval Research Laboratory's (NRL) Ozone Climatology dataset. Aura OMI data are no longer available as an input for data acquisitions after October 6, 2023. For data acquired after this date, ozone inputs will automatically fall back to climatology ozone inputs. For more details please refer to this news announcement.
  2. Aerosol data input: The NRL Aerosol Climatology ancillary data are the only available input.
  3. Temperature, Atmospheric pressure, and Moisture Profile data inputs: Simultaneously acquired MODIS Version 6.1 (MOD07_L2) Temperature, Water Vapor, and Pressure inputs were added as a new option on October 23, 2019. The default order option will remain as the NCEP-Global Data Assimilation System (GDAS) which is available every 6 hours. The second alternative is the NRL Climatology data which are based on modeling, simulation, and prediction. They are static, monthly, averaged datasets, therefore, used only as a last resort.

Known Issues

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.

Data Anomalies: 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.


About the image

Terra ASTER surface reflectance band 1-2-3n data from the AST_07XT product over Canada on August 2, 2018.

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Documentation

User Guide
Algorithm Theoretical Basis Document (ATBD)
User Handbook
ASTER Order Instructions

Using the Data

Access Data

Citation

DOI: 10.5067/ASTER/AST_07XT.003