用模型和车载微波辐射仪研究多频率多角度下玉米的散射和衰减特性

在使用被动微波技术反演土壤水分的过程中,为去除植被的影响,通常采用适用于低频的τ-ω模型。为准确评估较高频率下植被的散射和衰减特性,以玉米为例,采用基于光线跟踪原理的双矩阵(Matrix-Doubling)微波辐射模型,研究不同高度的作物在C(6.925GHz)、X(10.65GHz)和Ku(18.7GHz)波段下的单散射反照率和传输率。模型模拟的亮度温度跟车载微波辐射仪的野外实测数据接近。为验证模拟的玉米自身微波辐射,在玉米地上铺设了一层铝箔屏蔽地表的辐射。通过给验证后的模型输入不同的参数,建立一个亮度温度数据库,以模拟自然状态下不同高度玉米的亮度温度。然后把模型模拟的结果,跟相同环境下τ-ω模型得到的结果按最小二乘法进行匹配,从而获得不同高度的玉米在C、X和Ku波段上等效的单散射反照率和传输率。

Scattering and attenuation characteristics of corn at multiple fre-quencies and view angles by model simulation and truck-mounted microwave radiometer

To remove vegetation effect in soil moisture retrieval by passive microwave technique at lower frequencies,the τ-ω model is often used. In order to evaluate the scattering and attenuation characteristics of vegetation at higher frequencies,a Matrix-Doubling microwave emission model based on ray-tracing technique was used on com,to study its single scattering albedo and transmissivity with different height at C (6.925GHz),X (10.65GHz) and Ku (18.7GHz) bands. The comparison between simulation results and the data collected by a truck-mounted microwave radiometer in a field experiment are good. To verify the simulated emission from corn layer only,the ground surface of corn field was placed with an Aluminum foil,so as to mask the emission from the soil. A Brightness Temperature database was setup by assigning a variety of parameters to the verified model,to simulate Brightness Temperature of natural corn field with different height. The results by the Matrix-Doubling model were then matched with those by τ-ω model at the same condition by least-square deviation,so as to retrieve the effective single scattering albedo and transmissivity of corn at C,X and Ku-band.