Abstract
A simple atmospheric correction model (SACM) for ROCSAT-2 RSI data is presented. Gaseous transmission and Rayleigh optical depth are simplified as analytic functions. Rayleigh and aerosol scattering are determined using lookup tables. Results indicate the SACM not only quite accurately reproduces top-of-atmosphere reflectance computed by the 6S model (Vermote et al. 1997), but also does so faster than 6S. The results of the inverse application of SACM also indicate that the error of surface reflectance can be greatly reduced even in hazy sky if the adjacency effect is corrected. Future studies and possible improvements are also highlighted.
Highlights
The ROCSAT-2 satellite will be launched in the end of 2003 to image over Taiwan and the surrounding area daily for various applications, such as agriculture, land use and disaster monitoring (Lee et al 2002)
The performance of simple atmospheric correction model (SACM) is evaluated in terms of maximum relative error (MRE) and root mean square error with respect to 6S
The MRE is defined as IOOIXi -X68I !X68 and rmse = (Xi -X68 )2 /(N -1), with Xi derived by SACM and X6s according to 6S
Summary
The ROCSAT-2 satellite will be launched in the end of 2003 to image over Taiwan and the surrounding area daily for various applications, such as agriculture, land use and disaster monitoring (Lee et al 2002). Since SACM utilizes simplified functions for gas eous transmission and Rayleigh optical depth and lookup tables for atmospheric scattering, it can rapidly (several hundred times faster than 6S) and accurately (-0.001) reproduce TOA reflectance. SACM is based on the 6S radiative transfer model, whose outputs are considered to deter mine simplified functions for gaseous transmission and Rayleigh optical depth, and lookup tables for Rayleigh and aerosol scattering. It considers various altitudes (but not on sloped terrain) and can correct the adjacency effect. All of the transmission functions and scattering lookup tables of the various gases and aerosol are computed by 6S and spectrally integrated with the sensor response functions for the four bands of ROCSAT-2 RSI. Only the continental aerosol model is considered here
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