AST_09T v003

ASTER L2 Surface Radiance TIR


PI: U.S./Japan ASTER Science Team

Description

The ASTER Surface Radiance TIR (AST_09T) is generated using the five Thermal Infrared (TIR) bands (acquired either during the day or night time) between 8 and 12 µm spectral range. It provides surface-leaving radiance for the TIR bands at a spatial resolution of 90 meters, which includes both surface-emitted and surface-reflected components. It also provides the downwelling sky irradiance values (in W/m2/µm) for each of the TIR bands. This product is atmospherically corrected, and the surface-leaving radiance is of known accuracy and valid only for clear-sky scenes (cloud-free pixels). This atmospherically corrected product provides the input for generating two other higher-level products: surface spectral emissivity and surface kinetic temperature.

The algorithm to correct atmospheric effects involves two elements: 1) it uses a radiative transfer model which is capable of estimating the magnitude of atmospheric emission, absorption, and scattering. It uses the Moderate Resolution Transmittance Code (MODTRAN) radiative transfer model, which calculates atmospheric transmittance and radiance for frequencies from 0 to 50,000 cmˉ¹ at moderate spectral resolution. 2) It identifies and incorporates all the necessary atmospheric parameters applicable to the location and time for which the measurements require correction. These include temperature, water vapor, elevation, ozone, and aerosols.

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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.

Collection and Granule

Collection

Characteristic Description
CollectionTerra ASTER
DOI10.5067/ASTER/AST_09T.003
File Size~14 MB
Temporal ResolutionOther
Temporal Extent2000-03-04 to Present
Spatial ExtentGlobal
Coordinate SystemUniversal Transverse Mercator (UTM)
DatumWorld Geodetic System (WGS84)
File FormatHDF-EOS or GeoTIFF
Geographic Dimensions~60 km x 60 km

Granule

Characteristic Description
Number of Science Dataset (SDS) Layers5
Columns/Rows700 x 830
Pixel Size90 m

Layers

SDS Name Description Units Data Type Fill Value No Data Value Valid Range Scale Factor
TIR_Band10 90 meter resolution TIR Band 10 (8.125 to 8.475 µm) W/m²/sr/μm 16-bit signed integer N/A N/A 0 to 3000 0.006882
TIR_Band11 90 meter resolution TIR Band 11 (8.475 to 8.825 µm) W/m²/sr/μm 16-bit signed integer N/A N/A 0 to 3000 0.006780
TIR_Band12 90 meter resolution TIR Band 12 (8.925 to 9.275 µm) W/m²/sr/μm 16-bit signed integer N/A N/A 0 to 3000 0.006590
TIR_Band13 90 meter resolution TIR Band 13 (10.25 to 10.95 µm) W/m²/sr/μm 16-bit signed integer N/A N/A 0 to 3000 0.005693
TIR_Band14 90 meter resolution TIR Band 14 (10.95 to 11.65 µm) W/m²/sr/μm 16-bit signed integer N/A N/A 0 to 3000 0.005225

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 new Total Ozone Analysis using Solar Backscatter UltraViolet Version 2 (SBUV/2) and TOVS (TOAST)/Earth Probe-Total Ozone Mapping Spectrometer (EPTOMS) option. The 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 provides the ancillary column ozone data twice daily. The second fall back option is the Naval Research Laboratory's (NRL) Ozone Climatology dataset.
  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.

Documentation

Using the Data

E-Learning

View from NASA Terra's Zoom Lens: All About the ASTER Sensor

Tools

Citation

DOI: 10.5067/ASTER/AST_09T.003

About the Image

Terra ASTER surface radiance TIR band 10 data from the AST_09T product over Canada on August 2, 2018.

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