IMAGE-BASED ATMOSPHERIC CORRECTIONS REVISITED AND IMPROVED

A major benefit of multitemporal, remotely sensed images is their appl icability to change detection over time. Because of concerns about glo bal and environmental change, these data are becoming increasingly mor e important. However, to maximize the usefulness of the data from a mu ltitemporal point of view, an easy-to-use, cost-effective, and accurat e radiometric calibration and correction procedure is needed. The atmo sphere effects the radiance received at the satellite by scattering, a bsorbing, and refracting light; corrections for these effects, as well as for sensor gains and offsets, solar irradiance, and solar zenith a ngles, must be included in radiometric correction procedures that are used to convert satellite-recorded digital counts to ground reflectanc es. To generate acceptable radiometric correction results, a model is required that typically uses in-situ atmospheric measurements and radi ative transfer code (RTC) to correct for atmospheric effects. The main disadvantage of this type of correction procedure is that it requires in-situ field measurements during each satellite overflight. This is unacceptable for many applications and is often impossible, as when us ing historical data or when working in very remote locations. The opti mum radiometric correction procedure is one based solely on the digita l image and requiring no in-situ field measurements during the satelli te overflight. The dark-object subtraction (Dos) method, a strictly im age-based technique, is an attempt to achieve this ideal procedure. Ho wever, the accuracy is nor acceptable for many applications, mostly be cause it corrects only for the additive scattering effect and not for the multiplicative transmittance effect. This paper presents an entire ly image-based procedure that expands on the Dos model by including a simple multiplicative correction for the effect of atmospheric transmi ttance. Two straightforward methods to derive the multiplicative trans mittance-correction coefficient are presented. The COS(TZ) or COST met hod uses the cosine of the solar zenith angle, which, to a first order , is a good approximation of the atmospheric transmittance for the dat es and sites used in this study The default TAUs method uses the avera ge of the transmittance values computed by using in-situ atmospheric f ield measurements made during seven different satellite overflights. P ublished and unpublished data made available for this study by Moran e t al. (1992) are used, and my model results are compared with their re sults. The corrections generated by the entirely image-based COST mode l are as accurate as those generated by the models that used in-situ a tmospheric field measurements and RTC software.