目标物的二向性反射特性,无论是在遥感模型还是在遥感反演中都扮演着重要的角色,因此,选用正确的方法获得自然条件下目标物的二向性反射特性是遥感定量分析的基石。长期以来,人们往往用在自然条件下（即太阳直射光和天空漫射光同时存在）测得的双向反射率因子（Bidirectional Reflectance Factor,BRF）作为对目标物反射特性的表述,但定义BRF时,对外来辐射环境（即入射辐射亮度的空间分布函数）没有做出明确的规定,事实上,这样测得的BRF值与辐射环境有关,用它来描述目标物的反射特性是不妥当的。本文通过野外测量证实了上述观点,还证明了双向反射率分布函数（Bidirectional Reflectance Distribution Function,BRDF）与辐射环境无关的事实。同时本文也为读者提供了一种获得野外实测目标物BRDF的方法。实验证明,使用该方法能较准确地获得目标物在自然条件下的BRDF。

The bidirectional reflective characteristic of objects plays an important role not only in models of remote sensing but also in inversion,consequently,it is the base of quantitative analysis in remote sensing that chooses the appropriate method of acquiring the bidirectional reflective characteristic of ocjects in natural environment.For a long period,BRF(Bidirectional Reflectance Factor) acquired in natural environment is taken as the expression of bidirectional reflective characteristic of objects,but the definition of BRF doesn't prescribe radiant circumstances explicitly.Actually,BRF acquired in natural environment is related to radiant environment,so it is unsuitable to describe the reflective characteristic of objects with BRF.This viewpoint is testified in this paper by field data,meanwhile,we established the truth that BRDF(Bidirectional Reflectance Distribution Function) has nothing to do with the radiant environment.This paper provides a new method of acquiring BRDF data of objects in natural environment in order to arouse more pondering over the difference between BRDF and BRF.As it is indicated in the result of the experiments,with this method,we can acquire BRDF of objects in natural environment exactly.