Atmospheric Correction of Hyperspectral 大气光谱校正.ppt

Atmospheric Correctionof Hyperspectral 刘智深 胡连波 2003.6.25 * * ? Compensation for the shape of the solar spectrum. The measured radiances are divided by solar irradiances above the atmosphere to obtain the apparent reflectance of the surface. ? Compensation for atmospheric gaseous transmission and molecular and aerosol scattering enable apparent reflectances to be converted to scaled surface reflectances ? Scaled surface reflectances can be converted to real surface reflectances after accounting for topographic effects or by assuming that surfaces are lambertian. Atmospheric Correction Measures The Flat Field Correction technique is used to normalize images to an area of known “flat” reflectance (Goetz and Srivastava, 1985; Roberts et al., 1986). The method requires that you locate a large, spectrally flat, spectrally uniform area in the AVIRIS data, usually defined as a Region of Interest (ROI). The radiance spectrum from this area is assumed to be composed of primarily atmospheric effects and the solar spectrum. The average AVIRIS radiance spectrum from the ROI is used as the reference spectrum, which is then divided into the spectrum at each pixel of the image. The result is apparent reflectance data that can be compared with laboratory spectra. Flat Field Correction A CCD imager is composed of a two dimensional array of light sensitive detectors or pixels. The CCD array is mechanically quite stable with the pixels retaining a rigidly fixed geometric relationship. Each pixel within the array, however, has its own unique light sensitivity characteristics. As these characteristics affect camera performance, they must be removed through calibration. The process by which a CCD camera is calibrated is known as Flat Fielding or Shading Correction. Flat fielding can be illustrated in the following equation: IC = [(IR - IB) * M] / (IF - IB) Where IC is the calibrated image; IR is the non-calibrated object exposure; IB is the bias or dark frame; M is