Estimation of the total production of the herbage in the Tianshan Mountain Area using remote sensing technology with NDVI similarity zoning

An estimation of the total production of herbage in Xinjiang using remote sensing technology is an effective method for quantitative evaluation of regional animal husbandry productivity. It is time-consuming and cannot cover the whole area of the Tianshan Mountains, although the measured accuracy of the total herbage yield using conventional means is very high. To address this problem, we used MODIS/MOD13Q1 vegetation index products, with 250 m GSD as experimental data and city or county as a basic unit for analysis. The Bhattacharyya distance was used to quantitatively evaluate the distribution of the similarity of the vegetation index in the Tianshan Mountain Area as a study case. The purpose was to obtain an effective remote sensing modeling zoning, and then to construct an estimation model of the total production of herbage with respect to the vegetation index using remote sensing technology. Finally, the spatial distribution and feature analysis of the total herbage yield (fresh weight) in the Tianshan Mountains from the year 2009 to 2015 were determined based on the analysis of the spatial distribution and characteristics obtained under the GIS platform. The results showed the following: the seven modeling zones were derived from an analysis of the mean histogram of NDVI data collected during the optimal period (i.e., July and August each year) of vegetation growth for each city or county in the study area via the Bhattacharyya distance with a threshold greater than 0.5. Secondly, the constructed estimation model of the total production of the herbage showed different fitting relationships to the vegetation index, and there were three forms, including the exponential, power index, and a unary regression equation with the second order. On the whole, the fitting correlation coefficient of the constructed estimation model could reach between 0.754 and 0.836 for each zones. The RMSE value of cross-validation in the northern slope of the Tianshan Mountains-Yili Valley was 2 951 kg·ha-1, and the RMSE value were between 266 and 928 kg·ha-1 in the other zones. This was because more measured samples which total production of the herbage was between 10 000 and 30 000 kg·ha-1 were collected in the zone. Also there was higher total production of the regional herbage in the zone than others.