Estimating Paddy Field Evapotranspiration using Remote Sensing Multispectral Images

近年來隨著衛星遙測技術的進步，可有效率的監測與評估環境的變化。於各項環境監測中，水資源議題為台灣所重視，台灣地區降雨量雖然豐沛，但時空分布不均，又因地形特殊，不亦攔截儲存利用，在有限的水資源中又以農業用水佔用水之大宗，作物蒸發散量為推估農業用水量以制定年度灌溉計畫的基本資料，因此蒸發散量於水資源的規劃利用上為不可或缺的重要資料。 研究中以宜蘭縣壯圍鄉之水稻田為研討區域，於2010年一期作期間現地量測數據，並收集中央氣象局測站天氣觀測資料及Landsat 7 ETM+影像，分別使用FAO Penman-Monteith法(FAO-56法)、渦流相關法與ETM+影像進行蒸發散量估算。本研究使用遙測多光譜影像估算潛熱通量偏向SVAT模式的方法，特色為使用遙測影像獲得參數(淨輻射量、土壤熱通量與地表溫度)以及取得容易的地面資料(氣溫、空氣濕度)來推算地表參數(空氣阻力、地表阻力、地表蒸氣壓)，進而推求蒸發散量。 研究結果顯示渦流相關法所得之蒸發散量與前人研究所得結果差異偏大，而FAO- 56法與遙測多光譜影像估算結果相近，且符合過往研究所得之水稻田蒸發散量，顯示本研究使用遙測多光譜影像估算水稻田蒸發散量有不錯的結果。Recently, efficient monitoring of environmental changes has become a reality with the advancement of remote sensing technology. Among all kinds of environmental monitoring, water resources are main issues that are highly concerned in Taiwan. Although Taiwan’s annual rainfall is abundant, the non-uniform distribution both in space and time result in water shortage problem. Agriculture holds the biggest share of water right, and most water use in agricultural is for irrigation, so the crop evapotranspiration is important to water resource planning in agricultural. By selecting the paddy rice field in Yilan city as the site of measurement, three methods including FAO Penman-Monteith method, eddy covariance method, and using Landsat ETM+ are used to evaluate the evapotranspiration during spring and summer of 2010 in the research. The part of using multispectral images in the research is combined with the in-situ surface meteorological measurement, such as air temperature and wind velocity, and use remote sensing data to evaluate the net radiation, soil heat flux, and surface conditions, and these parameters are used to estimate evapotranspiration using an energy balance approach. The results of FAO-56 and using Landsat ETM+ are similar to previous studies and different from eddy covariance. It is shown that using multispectral images to evaluate evapotranspiration of paddy rice is feasible