基于ATI和TVDI模型的河北平原土壤湿度遥感反演

Remote sensing inversion of soil moisture in Hebei Plain based on ATI and TVDI models

  • 摘要: 为了进一步提高河北平原土壤湿度时空变化的监测精度, 本文以MODIS数据和实测土壤相对湿度数据为数据源, 按照优势互补的设计思想, 联合应用表观热惯量模型(ATI)和温度植被干旱指数模型(TVDI)反演河北平原地区的土壤相对湿度。在3-5月、10-11月采用基于NDVI=0.2阈值分区分方案的反演方法反演河北平原地区的土壤相对湿度, 其中在每旬NDVI>0.2的区域采用TVDI模型, NDVI≤0.2的区域采用ATI模型, 而6-9月单独使用TVDI模型来反演土壤相对湿度值。在1-2月和12月, 由于植被覆盖度较低和实测土壤相对湿度数据缺测, 采用ATI模型。模拟模型全部通过0.01的显著性检验。研究结果表明, 河北平原地区的土壤相对湿度在年内时间变化上呈现两个由升到降的变化周期, 第1个周期为12月-翌年6月, 其中, 12月-翌年3月为上升, 3-6月为下降, 3月为峰值; 第2个周期为6-12月, 其中, 6-8月上升, 8-12月下降, 8月为峰值; 全年土壤相对湿度的平均最大值出现在8月, 最小值出现在6月。土壤相对湿度的空间分布主要受降水、人工灌溉和土地利用方式的影响, 冀东和沧州滨海平原同期的土壤相对湿度值高于平原其他部分, 春季太行山山前平原和燕山山前平原的土壤相对湿度值相对较高。对3个代表性月份(5月、7月和10月)进行的点对点验证表明, 各月遥感反演结果的平均相对误差分别为21.4%、19.25%和22.22%。可见, 遥感反演的土壤相对湿度和实测土壤相对湿度具有良好的相关性。将本文研究结果和全部用ATI模型和全部用TVDI模型反演的结果进行对比发现, 联合应用ATI和TVDI模型分区反演模型反演的土壤相对湿度的平均相对误差均小于其他两种单一反演模型。

     

    Abstract: Soil moisture, as a strong indicators for soil water content, is a critical element for crop growth in Hebei Plain, one of the main crop production bases in Hebei Province. Scientific monitoring of soil relative moisture in Hebei Plain is vital for sustainable development of agriculture in the province. With respect to research on soil relative moisture monitoring, a series of soil relative moisture inversion models have been established. Inversion models based on thermal inertia and temperature vegetation index have been the most widely used models in recent years. However, the single use of any inversion model has always posed certain limitations in application scope. In terms of the advantages and disadvantages of the above two models, this paper used MODIS data and measured soil relative moisture data to retrieve soil moisture in Hebei Plain by integrating Apparent Thermal Inertia (ATI) model and Temperature Vegetation Dryness Index (TVDI) model. NDVI was employed as the division factor in March, April, May, October and November. TVDI model was used in area with NDVI > 0.2 for each ten days; in the area withNDVI ≤ 0.2, ATI model was used. TVDI model was used alone to retrieve soil relative moisture in June, July, August and September. Because of low vegetation coverage and missing measured soil relative moisture data in January, February and December, ATI model was used to invert soil relative moisture. The models were tested through P value, which was generally less than 0.01 for all the models. The retrieval results showed that soil relative moisture in Hebei Plain had two cycles, which changed from increasing to decreasing in the year. In the first cycle, from December to June of the next year, soil relative moisture increased from December to March and then decreased from March to June, with the maximum value in March. In the second cycle, from June to December, soil relative moisture increased from June to August and then decreased from August to December, with the peak value in August. While the average annual maximum value was in August, the average annual minimum value was in June. The spatial distribution of soil relative moisture was influenced mainly by precipitation, irrigation and land use patterns. During the same period, soil relative moisture in the east Hebei Plain and coastal plain in Cangzhou was relatively higher than that in other regions of the plain. The soil relative moisture in the piedmont plains of Taihang Mountain and Yanshan Mountain was relatively higher in spring. The point-to-point validation of three representative months (May, July, October) showed that the average relative errors of retrieval results were 21.4%, 19.25% and 22.22%, respectively, consistent with what was in the literature. The study showed that soil relative moisture from remote sensing inversion was in good correlation with field-measured data. The average relative error of the union of ATI and TVDI models was less than those from separate ATI and TVDI model.

     

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