Remote Sensing Based Estimation of Evapo-Transpiration Using Selected Algorithms; The Case of Wonji Shoa Sugar Cane Estate
No Thumbnail Available
Date
2013-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
The goal of every grower is to practice irrigation management to fulfill water needs profitably, safely, and in an environmentally responsible way. For this, accurate knowledge of the amount of evapotranspiration (ET) is critical. The focus of this study was to estimate and compare the actual evapotranspiration (ETa) of the Wonji Shoa Sugarcane Estate using different remote sensing algorithms. The daily ETa of the sugarcane was estimated and thematically mapped pixel-by-pixel using Surface Energy Balance Algorithm for Land (SEBAL), Simplified Surface Energy Balance (SSEB) and Operational Simplified Surface Energy Balance (SSEBop) algorithms on Landsat7 ETM+ and MODIS images acquired on four days in 2002. The algorithms were based on image processing which uses spatially distributed spectral satellite data (visible, near infrared and thermal infrared) and ground meteorological data to derive the surface energy balance components. The results obtained revealed that the ranges of the daily ETa estimated on January 25, February 26, September 06 and October 08, 2002 using SEBAL were 0.0 - 6.85, 0.0 – 9.36, 0.0 – 3.61, 0.0 – 6.83 mm/day; using SSEB 0.0 - 6.78, 0.0 – 7.81, 0.0 – 3.65, 0.0 – 6.46 mm/day, and SSEBop were 0.05 - 8.25, 0.0 – 8.82, 0.2 – 4.0, 0.0 – 7.40 mm/day, respectively. The Root Mean Square Error (RMSE) values between SSEB and SEBAL, SSEBop and SEBAL, and SSEB and SSEBop were 0.548, 0.548, and 0.99 for January 25, 2002; 0.739, 0.753, and 0.994 for February 26, 2002;0.847, 0.846, and 0.999 for September 06, 2002; 0.573, 0.573, and 1.00 for October 08, 2002, respectively. The standard deviation of ETa over the sugarcane estate showed high spatio-temporal variability perhaps due to soil moisture variability and surface cover. Dry periods exhibit greater variability compared to wetter periods. Generally during the dry season, ET is limited to the well watered sugarcane fields and water storage areas only. During the peak rainy season, ETa was high throughout the entire sugarcane estate. All the three algorithm results showed that generally well watered sugarcane fields in the mid-season growing stage of the crop and water storage areas had higher ETa values compared with the other dry agricultural fields confirming that they consumptively use more water. The evaporation fraction (ETrF) results also followed the same pattern as the daily ETa over the sugarcane estate. Comparison of ETa obtained from the MODIS Product (MOD16) with those obtained from the Landsat based algorithms resulted in a very poor correlation. The total crop and irrigation water requirement and effective rainfall estimated using the Cropwat model were 2468.8, 2061.6 and 423.8 mm/yr for January 2001 planted and 2281.9, 1851.0 and 437.8 mm/yr for March 2001planted sugarcanes, respectively. The mean annual ETa estimated for the whole estate were 107 Mm3, 140 Mm3, 178 Mm3 and 80 Mm3 using SEBAL, SSEB, SSEBop and MOD16, respectively. Though the algorithms need to be validated through field observation, either of these algorithms tested in this study have potential to be used for effective irrigation water management.
Description
Keywords
CWR, ET, IR, Landsat ETM+, MODIS, Remote Sensing, SEBAL, SSEB