Estimation of open field burned area using remote sensing and geographic information system (case study, Sarpol Zahab county)

Plant residues can contribute to nutrient fertility in soil, increase soil organic matter concentration, maintain water in soil, reduce evaporation, stimulate microbial activity, increase grain size, decrease temperature fluctuations, improve the characteristics Physical, chemical and biological properties and improve soil plowing power. Crop residue burning is the factors affecting the emission of greenhouse gases and air pollutants. It is one of the fast and low-cost land preparation methods. This action causes environmental issues, as well as leads to changes in vegetation and soil. Hence, attention to this issue can be important in raising awareness and preventing the increase of its disadvantages. This research was carried out in order to estimate the area of agricultural land that post-harvest crop residue was burned, in the province of Kermanshah, Sarapul-Zahab

Field sampling operations were carried out on burned and unburned fields and their geographic coordinates were recorded. As a result, 255 burned fields and 163 non- burned fields were recorded. Considering the size of the grazing area of the study area, which is often smaller than 5 hectares, in this research, the images of LANDSAT 8, OIL / TIRS sensor with 30 m spatial resolution were obtained from the studied area. After atmospheric correction by FLAASH method, for selecting the best contrast, the contrast enhancement methods of optimum index factor (OIF), Principal Component Analysis (PCA) and Minimum Noise Fraction (MNF) were used. The classification of images was done using the maximum likelihood method.

The results showed that the minimum values of the bands 1 and 2 were negative, so the data were normalized and the negative values of the bands was corrected. Based on the results obtained from the optimum index factor (OIF), the combination of bands 7, 5, 1 for all the examined dates, was chosen as the best band combination. After band combination based on the OIF index the burnt lands were separated by dark gray color and the vegetation of the cultivated lands were also separated by green color. The city and water could also be recognized in this image. The results of PCA and MNF Contrast enhancement methods also showed that the use of these methods, like the OIF band combination method, leads to a good enhancement of ground features in the images. After applying the maximum likelihood method to objects classification, The accuracy of the classification was evaluated by checking the correlation between the observed values (burnt and unburnt fields) and the classified values (burnt and unburnt places resulting from the image classification process). The methods of OIF and MNF (coefficients of Phi= 0.80, Cramer's V= 0.80 and Contingency Coefficient = 0.62) had significant correlations and more accurate than the PCA method (coefficients of Phi= 0.68, Cramer's V= 0.68 and Contingency Coefficient = 0.56). Accordingly, the area of irrigated agricultural field which burned after harvest was estimated at 7380 hectares, which included 56 percent of the County’s total irrigated field.

Based on the obtained results, the use of LANDSAT 8 satellite images can be used with high accuracy to identify burnt lands using enhancement methods OIF and MNF. A high percentage of irrigated lands in Sarpol Zahab city were burned in late spring and early summer for the next cultivation land preparation. In the long term, this can endanger the stability of production in agricultural ecosystems and also cause the release of greenhouse gases and various pollutants into the atmosphere, which in turn can cause air pollution and increase health problems for the inhabitants, which requires more attention of managers in this regard.