A refined empirical line approach for reflectance factor retrieval from Landsat-5 TM and Landsat-7 ETM+

The recent launch of Landsat-7 ETM+ extends the uninterrupted stream of TM and ETM+ images to a potential span of 32 years. This exceptional image set will allow long-term studies of natural resources, but will require an ope rational method for converting image digital number (dn) to the temporally comparable surface reflectance factor (rho (s lambda)). A refinement to the empirical line (EL) approach for reflectance factor retrieval (RFR) from t he Landsat-5 and -7 TM and ETM+ has been proposed. The refined empirical li ne (REL) approach requires only one within-scene calibration target, minima l field measurements of that target, and a reasonable estimate of dn for rh o (s lambda) = 0 using a radiative transfer model or values provided by thi s analysis. This study showed that the REL approach worked well for a 10-ye ar Landsat-5 TM and Landsat-7 ETM+ image set in Arizona and rho (s lambda) was retrieved with an estimated accuracy of 0.01. A quantitative approach w as proposed to determine the suitability of a within-scene target for the R EL approach, and based on historical measurements, a variety of targets met the size and brightness requirements for the REL approach. This operationa l approach for RFR should encourage long-term investigations of natural res ources to answer critical questions regarding resource management and effec ts of climate changes. (C) Published by Elsevier Science Inc.