不同含水量土壤高光谱二向性反射特征研究

【目的】探讨高光谱遥感土壤含水量对土壤二向性反射分布函数(bidirectional reflectance distribution function,BRDF)的影响,可为改进土壤含水量高光谱遥感反演机理模型,提高反演精度奠定重要基础。【方法】该研究在室内条件下对含水量为5%~45%(按5%递增)的土样进行多角度光谱测定,分析光源天顶角、观测天顶角、观测方位角及含水量不同对土壤二向性反射特征的影响。【结果与结论】由于土壤表面颗粒之间的相互遮蔽,土壤BRDF随光源天顶角的增加而增大,随观测天顶角的减小而降低,且土壤BRDF随观测天顶角的变化与波长有关。后向散射方向的土壤BRDF最高,前向散射方向的土壤BRDF最小。在400~1 400nm波段范围内,当土壤含水量小于田间持水量时,土壤BRDF值随含水量的增加而降低;大于田间持水量时,土壤BRDF值随含水量的增加而增加。但在波长1 400~2 400nm范围内,不同的观测位置下,土壤含水量不同引起土壤BRDF的变化没有明显规律。

STUDY ON HYPERSPECTRAL BIDIRECTIONAL REFLECTANCE CHARACTERISTICS UNDER DIFFERENT SOIL MOISTURE CONTENTS

Aiming to study the effect of soil moisture contents (SMC) on the soil bidirectional reflectance distribution function (BRDF), which can lay an important foundation for the improvement of SMC hyperspectral inversion mechanism model and accuracy, this paper conducted multi-angle spectrometry measurement to soil samples with different SMC from 5% to 45% (the interval of 5%), analyzed the influences of different light source zenith angle, observing zenith angle, azimuth angle and SMC on soil BRDF. The results showed that because of interaction between soil surface particles, soil BRDF increased with the light source zenith angle increasing and decreased with the observing zenith angle decreasing. The change of soil BRDF with zenith angle was related to the wavelength. The BRDF in backscatter direction was the highest, while it was the lowest in the forward scattering direction. In the range of 400~1400 nm wavelength, soil BRDF declined with SMC rising when SMC was less than the field water holding capacity, but soil BRDF raised with SMC rising when SMC was larger than the field water holding capacity. In the range of 1400~2400 nm wavelength and under different observation position, there was no obvious rules for the change of soil BRDF caused by different SMC.