蒸發散量(Evapotranspiration)在水文循環中扮演著一個非常重要的因素。估算蒸發散量的方法相當多，以往多半都是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，再把經驗公式應用到整個地面區域，並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，因此利用遙測影像推估蒸發散量，可由傳統單點的估算轉而對整個區域面的估算。
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，選用中央大學太空及遙測研究中心所提供的多張MODIS 1D影像。研究結果顯示，在地表參數方面，由模式反演的NDVI，其趨勢與嘉義二期水稻生長曲線相符合。在地表熱通量方面，使用相關係數良好的地表反照率，估算潛熱通量與實地測站比對後，相關係數可達到0.7618。未來可使用MODIS 1D影像進行嘉義地區長時期水稻田潛熱通量的監測，修正並驗證反演模式的準確性。

Evaportranspiration is an important factor in hydrology cycle. Traditionally, it is measured by using basin or empirical formula with meteorology data, while it does not represent the evaportransporation over a regional area. With the advent of improved remote sensing technology, it becomes a surface parameter of research interest in the field of remote sensing.
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. The results showed two aspects, first, the tendency between retrieve NDVI and two rice agriculture cycles is in accordance. Second, comparing latent heat by using good surface albedo with ground measurement, the correlation coefficient is over 0.76. In the future, we can monitor the surface heat fluxes of paddy rice field in Chiayi area, and can correct and confirm the accuracy of the retrieve model.

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