|
Radiometric Scaling Parameters for Landsat 7 ETM+ Level 1G Products The LMIN's and LMAX's are a representation of how the output Landsat ETM+ Level 1G data products are scaled in radiance units. The LMIN corresponds to the radiance at the minimum quantized and calibrated data digital number (QCALMIN), which is typically "1" or "0" and LMAX corresponds to the radiance at the maximum quantized and calibrated data digital number(QCALMAX), typically "255". Reflective bands: The LMIN's are set so that a "zero radiance" scene will still be on scale in the 8 bit output product, even with sensor noise included. LMIN should result in "zero " radiance being about 5 DN in low gain and 7.5 DN in high gain. The LMAX's are set so that LMAX corresponds to slightly less than the saturation radiance of the most sensitive detector. This is done so that in the output product all "pixels" saturate at the same radiance. Currently the LMAX is set to be 0.99 of the pre-launch saturation radiance of the most sensitive detector in each band. Normally, there is no need to change the LMIN's or LMAX's, unless something changes drastically on the instrument. If the sensitivity of the instrument increases, which is not expected, there is no need to change the LMIN and LMAX values. If the sensitivity decreases, the LMAX values can be increased which in turn increases the usable dynamic range of the product (this will not occur unless the change is large). The changes that have taken place to date have been mostly due to the adoption of "improved" pre-launch gains for the instrument that have, in effect, "increased" its sensitivity. The Landsat Project Science Office also detected a few errors in the original numbers, which were corrected. |
