An extension to the <i>like-value</i> procedure is proposed for calibrating multitemporal sequences of TM and ETM+ imagery to absolute reflectance values. The procedure described differs from the
conventional approach by using a calibrated reference image and constraining the line of best fit to pass through the modeled digital number (<i>DN</i>) for a target with zero surface flectance. It was demonstrated that the resulting lines calibrate image <i>DN</i>s to surface reflectance values by simultaneously correcting for the additive and multiplicative components of the sensor output that result from changes in sensor response, solar position and atmospheric effects over time. In a comparison to reference image reflectances, the precision of the procedure was shown to be very good for the visible spectral bands but poorer for the infrared bands. Generally errors in retrieval were within the range considered acceptable for most practical applications. For the data used in the analysis, the procedure was shown to be insensitive to uncertainty in input parameters required to model path <i>DN</i>.