بیلان انرژی سطح

In determining the evapotranspiration (ET) of a crop species, factors such as type, crop density, growth stage, climate of the region, physicochemical characteristics and soil fertility, have a significant effect. Therefore, it has a significant complexity. In recent years, new technologies are used to estimate ET, such as surface energy balance algorithm for land (SEBAL), which estimates actual evapotranspiration, using satellite data and some ground data. The purpose of this research is to estimate the actual ET and water requirement of Rosa damascena using SEBAL during three crop growth years in a part of the Shahrekord high plain.

The studied farm with an area of 16.38 ha is located in the Shahrekord plain, Karoun watershed. The remote sensing data included 42 cloud-free images of Landsat 7 and Landsat 8 satellites (2017, 2018, and 2019). The growth period lasted from the beginning of April to the end of November of each crop year. Images were processed in ERDAS Imagine 2015 software for radiometric correction and subsequent calculations using SEBAL algorithm. In order to estimate the actual evapotranspiration, the energy balance equation is used. For this purpose, all energy fluxes such as, Rn: the net incoming radiation flux to the considered surface, H: the sensible heat flux, G0: the soil heat flux and lET: the latent heat flux of evapotranspiration should be taken into account. The first step in the SEBAL process is to calculate the net radiation flux of the Rn. The second, soil heat flux G0 that is the rate of heat capacity in the soil and vegetation resulting from heat conduction or heat energy used to heat or cools the volume of the soil mass. The third is to calculate sensible heat flux (H) is the rate of heat loss to the air by conduction and convection phenomena, which is caused by the thermal difference. In SEBAL process, two "anchor" pixels are used to create boundary conditions for energy balance. These include as "cold (wet)" and "warm (dry)" pixels that are determined in the study area. A cold pixel is selected at the surface of open water or the surface covered by a well-watered alfalfa crop. It is assumed that the temperature of the surface and the temperature of the air near the surface are the same in this pixel. The "warm" pixel is selected in dry agricultural lands and its ET is considered zero. It is necessary for SEBAL model to establishing a linear equation between the surface temperature (Ts) and the air-surface temperature difference (dT) for each pixel using hot (dry) and cold (wet) pixels.

Based on the results of three years of research in a 16.38 hectare Golmohammadi farm in the Shahrekord plain, using the Sabal algorithm and the number of 42 images on the days of Landsat 7 and Landsat 8 satellites passing, as well as using the modified Penman-Mantith-Fao mathematical relationship. It was found that the amount of evaporation and transpiration of hollyhocks in the studied area was on average 1043.8 mm during the growth period. According to the results of other researchers, which have been conducted using lysimeter data and field studies, it necessarily requires higher costs than remote sensing methods. In this research, the ability of the Sabal algorithm (as one of the best remote sensing algorithms) to estimate evaporation And the actual transpiration and determination of the water requirement of the chrysanthemum plant with a low cost and an easy method compared to the results of other researchers, which were done with difficult and expensive lysimetric methods, were proved and it is suitable to be used for other plant species and in other geographical areas. Results showed that actual evapotranspiration value of rose crop (ETC) obtained from the SEBAL during the three years of experiment were 1089.4, 1021.3, and 1020.6 mm per growth period. In the same period, reference crop evapotranspiration (ET0) values were 1214.8, 1100.5, and 1135.5 mm during the growth period, respectively. In other words, average value for ETC was 1043.8 mm in growth period.

Based on the results of three years of research in a 16.38 hectare Golmohammadi farm in the Shahrekord plain, using the Sabal algorithm and the number of 42 images on the days of Landsat 7 and Landsat 8 satellites passing, as well as using the modified Penman-Mantith-Fao mathematical relationship. It was found that the amount of evaporation and transpiration of hollyhocks in the studied area was on average 1043.8 mm during the growth period. According to the results of other researchers, which have been conducted using lysimeter data and field studies, it necessarily requires higher costs than remote sensing methods. In this research, the ability of the Sabal algorithm (as one of the best remote sensing algorithms) to estimate evaporation And the actual transpiration and determination of the water requirement of the chrysanthemum plant with a low cost and an easy method compared to the results of other researchers, which were done with difficult and expensive lysimetric methods, were proved and it is suitable to be used for other plant species and in other geographical areas.

Estimation of actual evapotranspiration (Eta) at the basin-scale using SEBAL, as one of the commonly used satellite-based models, are affected by uncertainties associated with the selection of the anchor pixels, satellite sensors, and the spatial extent of the input satellite images. This study was conducted to investigate the impacts of aforementioned uncertainties on the actual evapotranspiration estimates in Urmia Plain (in the northwest of Iran) using MODIS and Landsat8 satellite imaginaries and the PySEBAL and MPySEBAL (Modified version) models. Validation results using lysimetric data during 2010-2011, showed that MPySEBAL (with cold pixels on well-irrigated vegetation) has less RMSE up to 70% as compared to PySEBAL model. Moreover, in the heterogeneous areas such as Urmia Plain, MODIS data with less spatial resolution leads to a 33 percent overestimation of daily Eta compared to Landsat 8 results. Furthermore, introducing a satellite image at its original extent rather than cropping the study area will result an uncertainty in the daily Eta estimates up to 8%. Comparing the relative impacts of the three sources of uncertainties indicated that the selection of the anchor pixels based on the surface temperature and NDVI thresholds, the spatial resolution of the sensors, and the spatial extent of the input images introduce the largest uncertainties respectively. Findings of this study can be used to enhance the accuracy of satellite-based Eta models and estimation of the irrigation water consumption from filed to basin scales.

Freshwater lakes are considered one of limited water resources that in recent decades are faced with many problems of quality and quantity. Proper management of these resources requires accurate information of component of the water budget. Evaporation as most unknown term of water budget, have a large share of water losses. To have precise information on the spatial and temporal distribution contribute to principles of qualitative and quantitative planning at water resources. Chanimeh’s artificial reservoirs are located in the east part of the country, with an area 141 Km2 was selected as case study. In this research, evaporation rate were estimated by SEBAL model and using meteorological data and satellite images of MODIS. Pan method applied in the region was used as reference method. As a result, the mapping of evaporation by 25*250 m spatial resolution was obtained. In point compare SEBAL model results with pan observed amount, the model correlation coefficient R, 0.74 and the error average percentage, ±14.5 and RMSD is equal to 2.95 mm. The mean latent heat flux and evaporation in average daily rate for the 202th of Julian days of 2012 year from water surface are equal 308 W/m2 and 13 mm per day, respectively.