利用空載多波段資料推求水稻田蒸發散量之研究

Abstract

利用空載高解析度、可見光與熱紅外光多波段資料，配合地面氣象站所量測得的氣象資料，針對台中縣霧峰鄉農試所的試驗田區進行蒸發散量估計。推估方法基於地表能量平衡方程式，反演的地表參數包含反照率（albedo）、地表溫度及標準差植被指數（Normalized Difference vegetation Index ; NDVI）。其中，對於地表溫度的部分，係利用NDVI推求熱紅外光波段的放射率，再利用史蒂夫波茲曼定律將亮溫( Brightness temperature）轉換為地表溫度。至於潛熱通量與可感熱的分配，則以乾、濕控制條件配合推求。本研究中，利用2003 年04 月28 號蒐集到具有充分乾、濕控制條件的影像，經由乾、濕控制像元決定了乾、濕控制曲線，並依該曲線決定影像中各像元潛熱通量與可感熱的分配比值，進而決定潛熱通量與可感熱通量，並與現場量測值做比較。證實透過多波段遙測資料推估潛熱通量與可感熱通量是可行的方法，更為水文循環提供了良好的蒸發散量空間資訊。 This paper presents a retrieval scheme for the remote sensing of evapotranspiration (ET) over rice paddy. To perform the retrieval, high-resolution airborne imagery of multi-spectral visible and thermal infrared data, and ground-based meteorological measurements are utilized. The ET retrieval scheme is based on the basic principal of surface energy budget, which is a result of balance among longwave and shortwave radiation, latent heat, sensible heat, and energy flux into the ground. To partition the latent and sensible heat fluxes of interest from the energy balance equation, three basic parameters are of most concern, including albedo, surface temperature, and normalized difference vegetation index (NDVI). The NDVI and albedo can be easily derived from the visible and near infrared spectral data, while the surface temperature can be determined through the analysis of the infrared data with the Stefan Boltzmann law. From the airborne imagery taken on 28 April 2003, we observe very good dry and wet pixels that can be easily corresponded to the radiation and evaporation controlled criteria, respectively, and, hence, for the further use in defining the evaporative fraction needed to partition sensible and latent heat fluxes from the net energy flux. The derived ET is compared with the in situ measurements.