Vegetation Index-Deduced Crop Coefficient of Wheat (Triticum aestivum) Using Remote Sensing: Case Study on Four Basins of Golestan Province, Iran
Crop coefficient (Kc) is an important factor contributing to estimation of evapotranspiration, and is also used to determine the irrigation schedule. This study investigated and determined the monthly Kc of winter wheat (Triticum aestivum L.) using five vegetation indices (VIs): Normalized Difference Vegetation Index (NDVI), Difference Vegetation Index (DVI), Soil Adjusted Vegetation Index (SAVI), Infrared Percentage Vegetation Index (IPVI), and Ratio Vegetation Index (RVI) of four basins in Golestan province, Iran. 14 Landsat-8 images according to crop growth stage were used to estimate monthly Kc of wheat. VIs were calculated based on infrared and near infrared bands of Landsat 8 images using Geographical Information System (GIS) software. The best VIs were chosen after establishing a regression relationship among these VIs with FAO Kc and Kc that was modified for the study area by the previous research based on R² and Root Mean Square Error (RMSE). The result showed that local modified SAVI with R²= 0.767 and RMSE= 0.174 was the best index to produce monthly wheat Kc maps.
 Akdim, N., Alfieri, S.M., Habib, A., Choukri Elijah Cheruiyot, A., Labbassi, K., and Menenti, M, “Monitoring of Irrigation Schemes by Remote Sensing: Phenology versus Retrieval of Biophysical Variables”, Remote Sensing, 2014, 6, pp. 5815-5851.
 Allen, R.G., Pereira, L.S., Raes, D., Smith, M, “Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements”. FAO Irrigation and Drainage Paper, 56, Rome, Italy, 1998, 300 p.
 Duchemin, B., Hadria, R., Er-Raki, S., Boulet, G., Maisongrande, P., Chehbouni, A., Escadafal, R., Ezzahar, J., Hoedjes, J., Karrou, H., Khabba, S., Mougenot, B., Olioso, A., Rodriguez, J-C., and Simonneaux, V, “Monitoring wheat phenology and irrigation in Central Morocco: on the use of relationship between evapotranspiration, crops coefficients, leaf area index and remotely sensed vegetation indices”. Agricultural Water Manage, 2006, 79, pp. 1-27.
 Farshi, A.A., Shariati, M.R., Jaralahi, R., Ghaemi, M.R., Shabifar, M., Tvalaei, M.M, “An estimate of water requirement of main field crops and orchards in Iran”, 1998, 900 p. (In Persian).
 Jagtap, S.S., Jones, J.W, “Stability of crop coefficients under different climatic and irrigation management practices”, Irrig Sci, 1989, 10, pp. 231–244.
 Justice, C.O., Townshend, J.R.G, “Special issue on the Moderate Resolution Imaging Spectroradiometer (MODIS): A new generation of land surface monitoring”. Remote Sensing Environment, 2002, 83, pp. 1–2.
 Rahimian, M.H., Poormohammadi, S., and Mokhtari, M. H, “Determination of winter wheat crop coeeficient usind Modis-Derives vegetation indices; a case study of the Azadegan plain, Iran”, ICID 21st International Congress on Irrigation and Drainage, 2011, Tehran, Iran. 8 p.
 Zolfagharnejad, H, “Estimation of wheat water requirement using GIS and RS (A case study in four basins of Golestan province: Qaresoo, Mohammad Abad, Zarin Gol and Gharn Abad)”, MSc Dissertation, Gorgan University of Agricultural Sciences and Natural Resources, Iran, 2015, 158 p.