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<strong>ASTER</strong> Users Handbook5.0 <strong>ASTER</strong> RadiometryThe <strong>ASTER</strong> Level-1B data are offered in terms of scaled radiance. To convert from DN toradiance at the sensor, the unit conversion coefficients (defined as radiance per 1 DN) are used.Radiance (spectral radiance) is expressed in unit of W/(m 2 *sr*µm). The relation between DNvalues and radiances is shown below:(i)(ii)(iii)(iv)(v)(vi)a DN value of zero is allocated to dummy pixelsa DN value of 1 is allocated to zero radiancea DN value of 254 is allocated to the maximum radiance for VNIR and SWIRbandsa DN value of 4094 is allocated to the maximum radiance for TIR bandsa DN value of 255 is allocated to saturated pixels for VNIR and SWIR bandsa DN value of 4095 is allocated to saturated pixels for TIR bandsThe maximum radiances depend on both the spectral bands and the gain settings and areshown in Table 4.Band No.123N3B4567891011121314Maximum radiance (W/(m 2 *sr*µm)High gain Normal Low Gain 1 Low gain 2Gain170.8427569N/A179.0358477106.8218290106.821829027.58.87.97.555.274.0255.017.615.815.110.558.04N/A 28.1727.7526.9723.3021.3873.323.421.020.114.0610.72N/A73.3103.598.783.862.067.0N/ATable 4: Maximum Radiance Values for all <strong>ASTER</strong> Bands and all Gains.The radiance can be obtained from DN values as follows:Radiance = (DN value – 1) x Unit conversion coefficientTable 5 shows the unit conversion coefficients of each band25
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