基于SPOT5影像的郁闭度反演方法

Study on Canopy Density Retrieval Method from SPOT5

为探讨区域植物措施因子在林地的赋值问题,以重庆市云阳县为研究区,以58个单元实地林地地块郁闭度调查数据为基础,计算了对应地块同期SPOT5影像各波段DN(灰度)均值和DN值标准差,分析了SPOT5影像在林地不同郁闭度下的稳定性。随机选取38个单元调查郁闭度数据,与对应地块同期SPOT5影像各波段DN均值进行回归、相关性分析,建立了不同波段组合反演郁闭度的方法。利用剩余20个单元的调查郁闭度数据进行精度检验。结果表明:SPOT5影像红外、红、绿波段DN均值在不同郁闭度林地地块表现稳定,最大偏离分别为13.8%,15.65%,24.52%,偏离平均值分别为10.11%,10.94%,17.78%;红、绿波段是反演郁闭度的最佳波段组合,拟合方程判定系数R2为0.66。精度检验结果表明,反演结果与实地调查数据正、负向最大偏差为+16.92%,-16.06%,偏差均值为-2.08%。按10%的分级统计,偏离均小于15%,总体精度较高。在反演结果误差为±20%时,植物措施因子赋值的最大误差<10%,可作为区域土壤侵蚀监测时植物措施因子计算的参考。

In order to determine the value of regional factors of biological-control in forest,Yunyang County in Chongqing was selected as the study area.On the basis of investigated canopy density data from 58 forest blocks,we calculated the average and standard deviation of digital number（DN） for each band of corresponded SPOT5,then analyzed the stability of SPOT5 in various forest canopy density.Regression and correlation analysis were taken between 38 different random selected canopy density data and corresponding average DN values of each band for SPOT5,and we established the method of retrieving canopy density by combining different bands.The other 20 investigated canopy density data were applied for accuracy test.Our results showed,the average DN values in infrared red,red and green bands of SPOT5 manifested stable over various canopy density forest blocks,their maximum deviation are 13.8%,15.65%,24.52%,and their average deviation are 10.11%,10.94%,17.78%;red and green bands are the optimal combination for retrieving canopy density,their determination coefficient of fitting equation is 0.66.The accuracy test results showed,the maximum positive and negative deviation between retrieving results and investigation data is ＋16.92%,-16.06%,with an average deviation of-2.08%.According to 10% graduation statistics,the deviation of all the results were less than 15%,the general accuracy is relatively high.While the error of retrieving result was 20%,the maximum error of corresponding factors of biological-control was less than 10%,which can be used as the reference of calculating factors of biological-control in monitoring regional soil erosion.