Radiometric Calibration Options for ACRES Landsat 5 TM products

An improved relative radiometric calibration procedure is available for ACRES Landsat 5 TM products. The improved method implements radiometric calibration of TM reflective band image data through a time-dependent calibration Look-Up Table (LUT). This method is different from the only technique previously available for ACRES products that used data from Internal Calibration (IC) lamps on a scene-by-scene basis for radiometric correction. The LUT method models the detector gain as a time-dependant function to account for inconsistencies in the IC lamps over time.

The four options for radiometric calibration that are now available to customers ordering Landsat 5 TM products are:

• National Aeronautics and Space Administration (NASA)
• Canadian Centre for Remote Sensing (CCRS)
• CCRS LUT
• NASA LUT

The NASA and CCRS relative calibration methods differ in the technique used for de-striping the image.

The CCRS method uses a reference detector for each band to match the brightness values of the other detectors in conjunction with scene statistics in the multi-spectral bands. In this method, de-striping corrections are calculated and applied independently to forward and reverse scans.

The NASA method averages the brightness values for all detectors in the multi-spectral bands and also matches the scene statistics in the forward and reverse scans. This method reduces banding artefacts in the image.

The NASA LUT-based radiometric calibration algorithm is the default option for ACRES Landsat 5 TM products. The IC-based algorithms used by the CCRS and NASA methods will continue to be supported by ACRES although they are not recommended. The new LUT-based approach for radiometric correction will only apply to the Landsat 5 TM reflective bands 1-5 and 7.

ACRES will continue to use the IC-based approach recommended by NASA for radiometric correction of the thermal band (TM band 6), as the behaviour of this band is as expected and its calibration is accurate to within 1°C.