Further understanding and a case of three-scale spectrum of the winter wheat

The reflective spectrum of winter-wheat shows different features with different observed scale, which is important to accurate application of remote sensing. But in many cases, people didn't consider that and the errors were resulted. In this article, firstly the definition of three-scale: material, endmember and pixel was further explained based the previous definition, and the ground measuring data and Omis aerial image of winter wheat of Shunyi, a city in Beijing, explained the difference of three-scale spectrum. To understand the relationship between three-scale spectrums, two methods were used: physical model and statistical method. At the canopy scale, the wheat can be thought as the mixture of leaf and soil. This mixture is nonlinear, the SAIL model, which is based on radiation transfer formula, can be used to simulate the canopy spectrum with the leaf spectrum as input. Mixed pixels and atmosphere effect are the main factors for the difference between canopy and pixel spectrum. But at aerial scale, the wheat canopy is homogeneous and we found for the Omis image, the spectrum of wheat in the same region with changing window is changing in very small extend.