Center for Earth Observation

...supporting the remote sensing needs of the University

What is ASTER?

The ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) sensor is an imaging instrument flown on the Terra satellite which was launched in December 1999.  ASTER has been designed to acquire land surface temperature, emisivity, reflectance, and elevation data and is a cooperative effort between NASA and the Japanese Ministry of Economy, Trade, and Industry (METI).  As of April 1, 2016 these date are being distributed free of charge. 

You can learn more about the ASTER program at:  http://asterweb.jpl.nasa.gov/ or view this hour-long NASA ASTER YouTube video.

This document does not cover the 30m ASTER Global Elevation Dataset.  You can find information about the ASTER GDEM data in the DEM FAQ on this site.

An ASTER scene covers an area of approximately 60 km by 60 km and data is acquired simultaneously at three resolutions.
VNIR - 15m spatial resolution - 3 bands at Green, Red, and Near InfraRed wavelengths
        - for the AST_L1B dataset only, there is also a backward viewing band 3B.
SWIR - 30m spatial resolution - 6 bands between 1.65 and 2.40 micrometers
TIR    - 90m spatial resolution - 5 bands between 8.29 and 11.13 micrometers

Note:  Since April 2008 the ASTER SWIR sensor has been subjected to abnormally high temperature abnormalities and these bands should not be used.  The VNIR and TIR data are fine.

The images are georeferenced to the WGS-84 datum and Universal Transverse Mercator projection.  Data are acquired when tasked and the telescopes on the ASTER sensor can be pointed to each side to expand data collection opportunities.  As a result, images do not have regular and repeating path and row footprints as many other sensors have.  This can provide a challenge when searching for imagery over time.

As of the spring of 2016 the primary full ASTER individual dataset is the AST_L1T: ASTER Level 1 Precision Terrain Corrected Registered At-Sensor Radiance product.  The AST_L1T product has a very high level of geometric correction and the scenes are distributed with a North-Up orientation.  All prior ASTER scenes have been reprocessed to this data format.  A complete ASTER scene consists of 14 bands of data as described above.  In addition you can select full resolution browse images in GeoTIFF format suitable for use in GIS programs along with several Quality Assurance files.  You should read the USGS AST_L1T product page for full dataset details. 

The earlier ASTER version AST_L1B: ASTER Level 1B Registered Radiance at the Sensor product includes the backward viewing NIR band labeled 3B and is delivered in the along-track orientation.  These scenes should be rotated so north is up.  This is described in the FAQ Importing ASTER with ENVI.

There are several ASTER products derived from individual scenes such as temperature, emissivity, and reflectance.  You can view the full list of products, as well as individual product documentation sheets at: https://lpdaac.usgs.gov/dataset_discovery/aster/aster_products_table.  Each product has unique scaling factors and fill values that are described in the product documentation.  For example, the AST_08 Surface Kinetic Temperature product has a valid data range from 200 to 3200 and must be multiplied by 0.1 to restore the values to degrees Kelvin.

Note:  If you are considering working with the AST_07: ASTER Surface Reflectance VNIR and SWIR product prior to April 2008, you may want to consider using the AST_07XT: ASTER Surface Reflectance VNIR and Crosstalk Corrected SWIR product instead.  One SWIR band has defective shielding, leading to light leakage to other SWIR bands.  This is referred to as Crosstalk.  An algorithm has been developed to remove this aberration.

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