Abstract
Homogeneous surface is usually assumed in aerosol retrieval for the dark target method. Retrieved aerosol optical depth can thus be overestimated. This error will also be propagated into retrieved surface reflectance during atmospheric correction, especially for high spatial resolution of 8 m for FORMOSAT-2 (also known as ROCSAT-2) RSI. The error in retrieved surface reflectance during atmospheric corrections induced by retrieved aerosol optical depth error due to adjacency effect over a dark target is studied in the green and red bands of FORMOSAT-2 RSI. The results show that significant errors in retrieved surface reflectance, i.e., larger than 0.01, may occur in most cases except at low contrast for a bright target. Such an error for a dark target is larger than that for a bright target for given contrast and haziness. Relatively, the error of retrieved surface reflectance is enhanced by the introduced error of aerosol optical depth in atmospheric correction for dark targets. The error can be larger than 35% for dark targets and less than 10% for bright targets. Hence, it is suggested that adjacency effect be considered from aerosol optical depth retrieval to surface reflectance retrieval in atmospheric correction except at low contrast for bright targets.
Highlights
FORMOSAT-2 developed by the National SPace Organization (NSPO) of Taiwan was successfully launched on 21 May 2004
This is due to the fact that atmospheric reflectance increases and the proportion of the scattering attributed to adjacent surface decreases when θv increases
The error in retrieved surface reflectance in atmospheric correction (AC) induced by the error in retrieved aerosol optical depth (AOD) due to adjacency effect (AE) over a dark target (DT) is studied in the green and red bands of FORMOSAT-2 Remote sensing instrument (RSI)
Summary
FORMOSAT-2 ( known as ROCSAT-2) developed by the National SPace Organization (NSPO) of Taiwan was successfully launched on 21 May 2004 (http://www.nspo.gov.tw). Owing to the nature of temporal and spatial variations, aerosol effect is the most difficult part of AC to correct. Aerosol characteristics, such as aerosol optical depth (AOD), size distribution and single scattering albedo, can be observed and determined from sunphotometer (Holben et al 2001; Dubovik et al 2002). The image-based method seems to be the only way to retrieve AOD for operational AC It has been developed in numerous previous studies (Kaufman and Sendra 1988; Liang et al 1997; Ouaidrari and Vermote 1999; Liang et al 2001; Vermote et al 2002; Lyapustin et al 2004). After these parameters are known, retrieval of surface reflectance can be very straightforward (Kaufman 1989)
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