基于EOS/MODIS的若尔盖高原湿地定量遥感研究

The Wetlands in Zoig Plateau Derived from Quantitative Remote Sensing Based on EOS/MODIS

研究旨在探讨EOS/MODIS影像提取若尔盖高原湿地信息的定量遥感方法.先计算MODIS影像的NDVI并将其线性变换到0～255;然后经多次试验确定区分湿地与非湿地的MODIS-NDVI阀值,并用人机交互式调整的方法消除误判像元及云的干扰,再多次试验得到区分湿地内部沼泽地和水体的阀值;通过统计不同类型湿地像元数计算湿地面积.研究表明,若尔盖高原湿地空间分布和面积具有季节差异,这与该地区降水和气温季节变化相关;采用MODIS-NDVI阀值并结合人机交互式调整的方法提取若尔盖高原夏半年的湿地信息是可行的,精度达到82%,而利用该方法提取冬半年湿地信息效果不甚理想,冬半年的MODIS影像湿地判识方法有待进一步探讨.

The method is discussed to extract the data of wetlands in Zoig Plateau by using quantitative remote sensing. First, NDVI is calculated based on ETM band 4 and 3. Through random sample, it is discovered that ETM-NDVI value has obvious difference among water, grassland and marsh in the Zoig Plateau, which provides a theoretic foundation for extracting the wetland data from MODIS image using NDVI method of valve value. Secondly, the MODIS image, including MODIS Band 6 being registrated to Band 1 and Band 2, is pretreated and NDVI is calculated and normalized from 0 to 255. Thirdly, the wetlands are judged and their area is calculated. By the way of human-computer interaction, MODIS-NDVI valve value, which can discriminate wetlands from others, is confirmed through many tests, and the pixel, which is judged incorrectly or disturbed by cloud, is eliminated, and then the valve value, which can discriminate the water and the marshes among the wetlands, is confirmed by using the same method. Lastly, area of the wetlands is calculated by summing up the number of different pixel. This study shows that there are seasonal differences in spatial distribution and area of wetlands in Zoig Plateau, dependent on precipitation and air temperature. It is feasible to extract spatial distribution and area of wetlands in Zoig Plateau in summer by the method of MODIS-NDVI valve value with the help of an adjustment based on humancomputer interaction, reaching a precision of 82 %. But those in winter are not satisfactory. Further study how to judge the wetlands from MODIS image is needed.