比辐射率是多种温度反演算法的重要参数，如单通道算法、分裂窗算法等。比辐射率的方向性决定了地物热辐射的方向性，其角度效应可以导致不同方向上物体辐射亮温存在较大差异。比辐射率0.01的误差能够带来温度约3K的变化。国内外学者提出了多种测量比辐射率的方法，并尝试从比辐射率的定义着手来解决遥感像元上的比辐射率方向性问题。然而，当将研究结论运用到遥感像元时，两方面的问题还需要考虑：(1)地表测量向遥感像元耦合过程中的尺度转换；(2)比辐射率数值的角度效应的定量描述。要研究以上两个问题，需要直接从遥感数据中反演出像元尺度的比辐射率来。 日夜 (Day/Night) 算法是现行MODIS陆面温度和比辐射率产品的主要算法，该算法直接利用MODIS上午星和下午星的两次测量数据反演出中红外和热红外共6个波段的比辐射率数据，从理论上真正实现了陆面温度与比辐射率的分离。MODIS比辐射率产品在±650观测范围可提供高达131个观测角度，为研究比辐射率的角度效应提供了数据支撑。 本文以MODIS提供的地表分类和比辐射率产品为数据源，利用不同的统计方式获得了中国大部分区域及周边地区典型地物的比辐射率在时间上和空间上的变化特征以及角度效应。主要研究结论：(1)地物比辐射率数值在传感器发射前期变动明显，后期趋于稳定；(2)中红外波段比辐射率较热红外波段变化明显；(3) 地物比辐射率随角度变化，多以垂直观测为轴呈对称性。在大角度下，以±450为界，中红外波段的数值逐渐升高，热红外波段数值降低；(4)角度效应导致的比辐射率数值变化维持在0.01~0.03之间。本文还拟合了MODIS像元尺度比辐射率与角度的关系，建立了比辐射率查找表，为改进分裂窗算法和日夜算法提供先验知识。

As an important input, emissivity is used for many algorithms to retrieve land surface temperature (LST), such as the Single Channel Method and the Split-Window Algorithm. It has been proven that the emissivity dominates the directionality of thermal emission. As a result, the angular effects of emissivity always result in significant difference of radiant brightness temperatures in different viewing directions. It was demonstrated that 0.01 emissivity error will cause a 3K error for temperature retrieval. Many scholars have developed the measure methods of emissivity and tried to explain the directionality of emissivity on remotely sensed pixels’ scales by making new definitions of emissivity. However, two factors should be considered before using the current methods on remotely sensed pixels: (1) scaling up from field measurements to remote sensing pixel; (2) the quantitative description of angular effects of emissivity. To study the two problems, it is necessary to retrieve the pixel emissivity directly from remotely sensed data. Day and Night algorithm is one of the current methods to retrieve MODIS land surface temperature and emissivity. It can get 6 bands’ emissivity from Mid-TR to TIR, without any previous knowledge about emissivity, based on two measurements of MODIS sensors on Aqua and Terra respectively. This algorithm has achieved the separation of LST and emissivity in theory. In addition, the MODIS Emissivity Product gives us up to 131 viewing angles from -65 to 65 degree in each scene. That information can support our study on the angular effects of emissivity previously mentioned. This paper will focus on the angular effects of emissivity for several typical cover types’ within China and its surroundings. MODIS Land Cover and LST/Emissivity Products were used. Our main conclusions are: (1) The retrieved emissivity fluctuated during the prophase of MODIS emissivity generation but kept relatively stable in the later; (2) The emissivities in the Mid-TIR bands are less stable than that in the TIR bands; (3) Most emissivity values showed a good symmetry appearance from nadir viewing to ±650. Big viewing angle measurements can increase the emissivity of Mid-TR but decrease that of TIR. The inflexion is located at about ±450 ; (4) The angular effects make the emissivity value of change in a range of 0.01~0.03. In final, we present some models based on the statistical analysis of viewing angles and the emissivity values for some typical cover types. Several Look-Up Tables which can be used in many fields were built. Our research results can provide a priori knowledge about emissivity for advancing Split-Window Algorithm and “Day and Night” Algorithm in the future.