Area estimation of saffron cultivation using satellite images and time difference method (case study: Fazl Village in Nishabur County of Iran)

Estimating crop area is a key factor for crop monitoring and agricultural management. Having annual information on crop acreage and production change is necessary for agricultural decision-makers and planners. In recent years, the cultivation of saffron in Nishabur has received more attention by farmers due to low water requirements and its good income. Planning for the marketing of this strategic product and the provision of agricultural inputs for saffron requires that the information of the area under its cultivation be estimated accurately. The aim of this study was to monitor changes in cultivated areas and to estimate the saffron area using satellite imagery with different spatial resolutions and time series normalized different vegetation indexes (NDVITs). Using Landsat 8 satellite images and time difference methods based on plant phenology estimate the areas under cultivation of saffron was estimated in Fazl Village of Nishabur County. A satellite image of June 17, 2016, related to the plant's dormant phase and another on January 11, 2017, for the vegetative growth stage of saffron was prepared. Using different vegetation indices, saffron cultivation was distinguished from other agricultural products and estimated at 497 hectares with an overall accuracy of 72% and a kappa value of 71%. Also, the results indicated that the accuracy of this method depended on the patch area of agricultural lands, such that in areas less than 2000 square meters, the user's accuracy was 44 percent, in lands with an area between 2000 and 5000 square meters, the accuracy was 66 percent, while in farms between half to one-hectare, the accuracy reached 80% and in lands more than one hectare, the accuracy was 89%. The results of this research indicated that the use method is suitable for estimating the area under the cultivation of saffron and we suggest its examination in other parts of the country.