An historical empirical line method for the retrieval of surface reflectance factor from multi-temporal SPOT HRV, HRVIR and HRG multispectral satellite imagery

作者：Clark Barnaby^*; Suomalainen Juha; Pellikka Petri

来源：International Journal of Applied Earth Observation and Geoinformation, 2011, 13(2): 292-307.

DOI：10.1016/j.jag.2010.12.004

• Atmospheric correction
• Empirical line correction
• Reflectance factor retrieval
• SPOT

SPOT satellites have been imaging Earth's surface since SPOT 1 was launched in 1986. It is argued that absolute atmospheric correction is a prerequisite for quantitative remote sensing. Areas where land cover changes are occurring rapidly are also often areas most lacking in situ data which would allow full use of radiative transfer models for reflectance factor retrieval (RFR). Consequently, this study details the proposed historical empirical line method (HELM) for RFR from multi-temporal SPOT imagery. HELM is designed for use in landscape level studies in circumstances where no detailed overpass concurrent atmospheric or meteorological data are available, but where there is field access to the research site(s) and a goniometer or spectrometer is available. SPOT data are complicated by the +/- 27 degrees off-nadir cross track viewing. Calibration to nadir only surface reflectance factor (rho(s)) is denoted as HELM-1, whilst calibration to rho(s) modelling imagery illumination and view geometries is termed HELM-2. Comparisons of field measured rho(s) with those derived from HELM corrected SPOT imagery, covering Helsinki, Finland, and Taita Hills, Kenya, indicated HELM-1 RFR absolute accuracy was +/- 0.02 rho(s) in the visible and near infrared (VIS/NIR) bands and +/- 0.03 rho(s) in the shortwave infrared (SWIR), whilst HELM-2 performance was +/- 0.03 rho(s) in the VIS/NIR and +/- 0.04 rho(s) in the SWIR. This represented band specific relative errors of 10-15%. HELM-1 and HELM-2 RFR were significantly better than at-satellite reflectance (rho(SAT)), indicating HELM was effective in reducing atmospheric effects. However, neither HELM approach reduced variability in mean rho(s) between multi-temporal images, compared to rho(SAT). HELM-1 calibration error is dependent on surface characteristics and scene illumination and view geometry. Based on multiangular rho(s) measurements of vegetation-free ground targets, calibration error was negligible in the forward scattering direction, even at maximum off-nadir view. However, error exceeds 0.02 rho(s) where off-nadir viewing was >= 20 degrees in the backscattering direction within +/- 55 degrees azimuth of the principal plane. Overall, HELM-1 results were commensurate with an identified VIS/NIR 0.02 rho(s) accuracy benchmark. HELM thus increases applicability of SPOT data to quantitative remote sensing studies.

• 出版日期2011-4