| 摘要: | 在台灣水資源總量中，農業用水高達其中73%，而又有一半以上的用水量是用於水稻田的灌溉，因此探討水稻的蒸發散行為，就成為一項重要的課題。估算蒸發散量的方法相當多，利用蒸發皿量測單點的蒸發散量，或是利用氣象資料經相關公式推估單點的潛勢蒸發散量，常無法反應出區域性的實際狀況，近年來，由於遙測技術的進步，利用遙測影像推估大面積區域的蒸發行為，就顯得較為重要。 本研究的研究方法就是利用衛星影像配合地面氣象站所量測得的氣象資料(風速、氣溫等)，進行地表熱通量的估計，地表熱通量包括土壤熱通量、可感熱通量及潛熱通量。推估方法基於地表能量平衡演算法，依據大氣不穩定的修正模式初步推估潛熱通量與可感熱通量，再利用乾、濕控制曲線結合，求出蒸發散比值，獲得最終的潛熱通量與可感熱通量。 在衛星影像的使用上，則選用中央大學太空及遙測研究中心所提供的MODIS 1D影像，自行反演地表參數，以及下載美國USGS網站所提供的MODIS地表參數產品，分別輸入模式估算地表熱通量，初步成果發現，利用MODIS 1D影像所演算的地表熱通量，較接近實際地面測站的觀測值。因此，本研究則應用2006年多張MODIS 1D的影像，針對當年第一、二期水稻田的潛熱通量的估算，與實地測站比對後，相關係數可達到0.6。相信未來可配合MODIS 1D的影像，進行嘉義地區長時期水稻田潛熱通量的監測，並對水稻田的總用水量監控有所幫助。 In Taiwan, approximately 73% of the total water resource is been used for agricultural purposes. Among the 73% of agricultural water usage, more than half of the water is used for the paddy rice irrigation. As a result, it is important to evaluate the evapotranspiration characteristic of the paddy rice fields. Traditionally, evapotranspiration is measured by using basin or empirical function with surface meteorological data. However, these methods only measure points and may not effectively address the evapotranspiration over a large spatial domain. To resolve such issue, using remote sensing technology to estimate the evapotranspiration becomes an interest field, as the remote sensing technology has the advantage of acquiring large surface data instantaneously and the data can be used to retrieve surface parameters, as well as thermal prosperities. The research presented here is to use satellite images in conjunction with the in-situ surface meteorological measurement, such as temperature and wind velocity, to estimate the surface heat fluxes that include soil heat flux, sensible heat flux, and latent heat flux. This method is based on surface energy balance to estimate the surface heat fluxes. Once the heat fluxes has been determined, the evaporation then can be derived from radiation and evaporation controlled lines. The satellite data used for this study are the MODIS level 1D image obtaining from CSRSR (Center of Space and Remote Sensing Research), National Central University. In additional, derivative products of the MODIS sensor from USGS/NASA were also obtained for comparative study. The result shows that using MODIS level 1D data as input parameters produces better result and is closer to the ground measurement. Hence, the MODIS level 1D data were used to study the surface heat fluxes of two rice agricultural cycles in 2006. With the correlation coefficient over 0.60, the result shows a potential in estimating the surface heat fluxes of paddy rice fields in Chiayi area, and can be helpful to control the water used to irrigate the paddy rice. |
