ABSTRACT

Multi-spectral and diurnal meteorological data from optical-thermal observations of Indian Geostationary satellites were used to estimate country-scale evapotranspiration (ET). In this study radiation and vegetation products from a suite of Indian geostationary satellites, Kalpana-1 (K-1) and Indian National SATellite (INSAT) 3A Charged Couple Detector (CCD), were used. ET was derived as a function of net available energy and evaporative fraction within a single-source energy balance framework. The scaling function for albedo, net radiation and soil heat flux were developed with ground measured data from twenty-three Agro-Met Station (AMS) installed in different agro-climatic zones of India. These scaling functions were applied on the satellite data to derive intermediate inputs for surface energy balance. Further, evaporative fraction was derived from Priestley-Taylor parameter (φ) and day-time net available energy. On regional scale, pixel-by-pixel dynamic φ_i was computed from upper (φ_max) and lower (φ_min) limits of warm and wet edges of thermal inertia-Normalized Difference Vegetation Index (NDVI) triangle. Here, thermal inertia was represented by morning rise in surface brightness temperature (ΔT) between 02:30 and 06:30 Greenwich Mean Time (GMT). The dynamic φ_i with upper and lower limits were computed using ΔT – NDVI triangle. The derived net radiation was validated with AMS measured net radiation at seven agro-climatic zone of India showed Root mean Square Error (RMSE) between 37 and 87 W m⁻². The estimated ET was validated at six agricultural and five natural grassland and wetland vegetation sites with AMS measured ET for a year. The RMSE of 10 days ET sum were varying from 7.50 to 17.70 mm for agricultural and for natural vegetation sites it varies from 8.60 to 13.10 mm. The errors variation among all site is depending on the sub-pixel heterogeneity and difference in K-1 and AMS footprints. The ET sum over agricultural kharif (June to October) and rabi (November to April) season also able distinguish normal and drought year. This study provides a robust methodology for generating near real time ET at country scale from Indian Space Research Organisation (ISRO’s) present and future high-resolution geostationary satellites over India.

摘要

来自印度对地静止卫星的光热观测的多光谱和昼夜气象数据被用于估算国家规模的蒸散量（ET）。在这项研究中，使用了来自印度对地静止卫星套件Kalpana-1（K-1）和印度国家卫星（INSAT）3A带电耦合检测器（CCD）的辐射和植被产品。ET是根据单源能量平衡框架内的净可用能量和蒸发分数的函数得出的。利用安装在印度不同农业气候区的23个农业气象站（AMS）的地面测量数据，开发了反照率，净辐射和土壤热通量的换算函数。这些缩放函数被应用到卫星数据上，以得出用于地表能量平衡的中间输入。更多，φ）和白天的净可用能量。上区域范围内，逐像素动态φ_我是从上（计算φ_最大值）和下限（φ_分钟）温暖和热惯性植被指数（NDVI）三角形的湿边缘的限制。在此，热惯性由格林威治标准时间（GMT）在02:30至06:30之间的表面亮度温度（ΔT）的早晨升高表示。动态φ_我与上限和下限，使用Δ计算Ť– NDVI三角形。推导的净辐射量已通过AMS验证，在印度的七个农业气候区测得的净辐射量均方根误差（RMSE）在37至87 W m ^-2之间。估计的ET在AMS测得的ET范围内，在6个农业和5个天然草地和湿地植被地点得到了验证。ET和10天ET的均方根误差（RMSE）在7.50毫米至17.70毫米之间，对于农业和自然植被站点，其在8.60毫米至13.10毫米之间。所有站点之间的误差变化取决于亚像素异质性以及K-1和AMS占用空间的差异。农业哈里夫（6月至10月）和狂犬病的ET总和（11月至4月）季节还可以区分正常年份和干旱年份。这项研究提供了一种强大的方法，可以通过印度航天研究组织（ISRO's）目前和将来在印度上空的高分辨率对地静止卫星，在国家范围内产生近乎实时的ET。