توسعه الگوریتم SM-SEBAL به منظور محاسبه تبخیر و تعرق واقعی به کمک سنجش از دور
محورهای موضوعی : برگرفته از پایان نامهفرهاد میرزایی 1 , محمدرضا کشاورز 2 , مجید وظیفه دوست 3
1 - دانشیار و عضو هیئت علمی آبیاری و آبادانی دانشکده کشاورزی و منابع طبیعی دانشگاه تهران
2 - فارغ التحصیل دکتری آبیاری و آبادانی دانشکده کشاورزی و منابع طبیعی دانشگاه تهران
3 - عضو هیئت علمی مهندسی آب دانشکده کشاورزی دانشگاه گیلان
کلید واژه: سنجش از دور, سبال, تبخیر و تعرق, M-SEBAL, SM-SEBAL,
چکیده مقاله :
روش Sufrace Energy BALance (SEBAL)یکی از پر‌کاربردترین روش‌های تعیین تبخیر و تعرق واقعی به کمک سنجش از دور است. با این حال فرض خطی بودن رابطه اختلاف دما و دمای سطح زمین و نیز استفاده از دو پیکسل گرم و سرد که توسط کاربر شناسایی می‌شوند از نقاط ضعف این روش محسوب می‌شود. روش Modified SEBAL (M-SEBAL) علاوه بر اصلاح این مشکل، دو مفهوم جدید لبه سرد و گرم را جایگزین پیکسل‌های سرد و گرم می‌کند که تاثیر بسزایی در افزایش دقت و نیز خودکارسازی اجرای الگوریتم و عدم نیاز به کاربر ماهر دارد. با این حال تعیین لبه گرم نیاز به محاسبات زیاد و در نتیجه بالا رفتن زمان محاسبه و امکان خطای محاسباتی دارد. در این تحقیق، شکلی ساده شده از روش M-SEBAL با نام Simplified M-SEBAL (SM-SEBAL) توسعه یافته است و نتایج حاصل از اجرای سه روش بر روی بیش از 300 لایه تصویری MODIS با داده‌های لایسیمتری و نیز داده‌های زمینی بیلان انرژی مزرعه تحقیقاتی دانشگاه تهران واقع در کرج مقایسه شده است. نتایج حاصل از اجرای سه الگوریتم نشان می‌دهد که الگوریتم SEBAL تبخیر و تعرق را بیش برآورد و دو الگوریتم دیگر آنرا اندکی کم برآورد می‌کنند. بیشترین خطای محاسبه شار گرمای محسوس مربوط به روش M-SEBAL با 87/33 درصد و کمترین میزان خطا مربوط به نتایج روش SEBAL (23/11 درصد) می‌باشد. با این حال حداکثر خطا در مقادیر تبخیر تعرق روزانه در نتایج روش SEBAL (56/3 درصد) و کمترین میزان خطا در روش SM-SEBAL ( 18/1 درصد) مشاهده شد.
The algorithm of Sufrace Energy BALance (SEBAL) is one of the most widely used methods for determining actual evapotranspiration through remote sensing. However, assuming a linear relationship between temperature difference (dT) and land surface temperature (LST) and the visual identification of hot and cold pixels are the weak points of the method. Modified SEBAL (M-SEBAL) on the other hand, replaces two new concepts as hot and cold edges, with a significant impact on increasing the accuracy and automation of the execution of the algorithm and removing the need for skilled user. Although, determining the warm edge requires high computing and thus increase in computing time and possible errors. In this study, a simplified form of the M-SEBAL (SM-SEBAL) is developed and the results of executing of the three method on MODIS images and comparing the results with the observed data are shown. Results show that SEBAL overstimates the ET values and M-SEBAL and SM-SEBAL underestimate the same values. The highest sensible heat flux calculation error comes from M-SEBAL (33.87%) and SEBAL shows the lowest error rate (11.23%). The highest error in the calculation of the latent heat (LE) retrives from M-SEBAL (11.66%) and the lowest error rate retrives from SEBAL (5.05%). However, the maximum daily evapotranspiration observed error was for SEBAL (3.56%) and the lowest error was retrived from SM-SEBAL (1.81%) and then M-SEBAL (2.47%). In addition, the time required to perform SEBAL algorithm is up to four times more than the time needed to run other two algorithms.
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