基于NDVI的新疆荒漠地区植被覆盖度遥感估算经验模型研究

Remote sensing estimation models for vegetation coverage in desert regions of Xinjiang based on NDVI

新疆荒漠地区植被覆盖度遥感估算模型十分缺乏,给荒漠化监测等相关工作带来很大不便,开展植被覆盖度遥感估算经验模型研究,对于促进和完善相关地区的生态监测及研究工作具有积极的现实意义。通过对阜康市北部沙漠南缘和克拉玛依市中部平原荒漠进行无人机航拍,利用无人机遥感提取(光合)植被信息,并将无人机航拍影像的植被覆盖度统计单元与高分辨率卫星影像像元在空间上直接相对应,获取在高分辨率卫星影像像元尺度上的植被盖度,然后通过植被覆盖度和空间上与其相对应的源自高分辨率卫星影像的NDVI数据的拟合关系,建立基于源自高分二号影像的NDVI的阜康北部沙漠植被覆盖度遥感估算线性模型以及基于源自ZY1-02C影像的NDVI的克拉玛依平原荒漠植被覆盖度遥感估算二次多项式模型。研究中所采用的无人机遥感与卫星遥感相结合、植被覆盖度统计单元与卫星像元在空间上直接对应的方法,可避免以往相关工作中常以点位测量数据代表卫星像元数据所带来的不确定性。由于所用卫星影像的NDVI数据稳定性相对不足等原因,所建立的遥感估算模型的估算精度尚相对偏低,有待于今后进一步的工作加以改进。

The lack of remote sensing estimation models in vegetation coverage for desert regions of Xinjiang,China has brought great inconvenience to desertification monitoring and other related work.It is of positive and practical significance to study the empirical models for remote sensing estimation of vegetation coverage for promoting and improving ecological monitoring abilities in relevant areas.In this study,unmanned aerial vehicle(UAV) photography was firstly carried out in typical desert regions in Xinjiang,vegetation information(photosynthesis) was extracted by UAV images.Secondly,vegetation coverage was obtained at the pixel scale of high resolution satellite image by making the statistical units of vegetation coverage directly correspond to the pixels of high resolution satellite image in space.Lastly,based on the fitting relationship between vegetation coverage and the corresponding NDVI data derived from high resolution satellite images,the empirical models were established for estimating vegetation coverage of typical desert regions in Xinjiang.The deserts in the southern margin of the northern part of Fukang City and in the central plain of Karamay City were chosen as aerial shooting areas respectively.The relative flight height was set to 6-7 m and the ground resolution was 0.002-0.003 m.Satellite images which were shot on the same day and the day before UAV photographing,were selected and purchased for generating NDVI data.Agisoft Photoscan software was used for UAV image processing,ENVI and ArcGIS software packages were used for satellite remote sensing image processing and spatial analysis,Origin software was used for fitting analysis of data series and the vegetation information of UAV images was extracted by VDVI index.As a result,a linear model(y=149.86x-13.449,R^2=0.735 3) was established for remote sensing estimation of vegetation coverage in northern sandy desert in Fukang based on NDVI derived from GF2 satellite image and a quadratic polynomial model(y=97.397x^2+80.837x-5.210 9,R^2=0.818) was established for remote sensing estimation of vegetation coverage in plain desert in Karamay based on NDVI derived from ZY1-02 C satellite image.These models might provide necessary foundation and basis for monitoring and research of land use and land cover change,ecological environment change,desertification(or sandy desertification),vegetation mapping and other related work in Xinjiang.The combination of UAV images and satellite remotely sensed data and the spatial direct correspondence between vegetation coverage statistical unit and satellite pixel,could avoid the uncertainty caused by the process of representing vegetation coverage of satellite pixel with manual measurement data at different points in the previous related work.The proposed method made the spatial matching between vegetation coverage and satellite image pixels relatively more intuitive and accurate in the process of constructing remote sensing estimation model of vegetation coverage and it also provided an idea for similar work.