Spectral responses analysis of soybean residues
大豆残茬光谱响应特征研究

Ground refl ectance with different soybean residue covers (SRC) were measured with HR-768 portable spectroradiometer. Coincident with spectrum measurements, soybean residue cover were measured using photographic method. Linear regression analysis was used to evaluate the correlations between soybean residue cover and spectral refl ectance, as well as its f irst order derivative and derived indices (namely ratio index and normalized difference index). Characteristics of spectral responses of soybean residue were analyzed. With relative spectral response functions, bands refl ectance of MODIS, TM, HJ-1B CCD1 and IRS were simulated respectively to establish soybean residue cover estimation model. The results indicate that soybean residue can be distinguished from soil using its unique absorption feature in the spectral range of 2050 nm to 2150 nm and 2250 nm to 2350 nm. The spectral characteristics of soybean residue are similar to that of corn and wheat residue except for an absorption feature in the spectral range of 920 nm to 967 nm. Parameters that are suitable for soybean residue cover estimation were identif ied using hyperspectral data, which includes refl ectance at wavelength of 941.6 nm, f irst derivation of refl ectance at wavelength of 2151.8 nm, normalized difference index between refl ectance at wavelengths of 1461.3 nm and 2404.4 nm, and ratio index between refl ectance at wavelengths of 2247 nm and 608.6 nm. Taking broad band data as data source, ratio index between shortwave infrared refl ectance and red refl ectance performs the best in soybean residue cover estimation.