Identification of salt domes in Ravar region, Kerman province by using the radar Polarimetry technique of Palsar images and analyzing Sentinel-2 and Aster multispectral images

In addition to tourist attractions, salt domes are one of the most interesting geomorphic phenomena having different mineral resources and can in some cases act as an oil reservoir  and oil trap. It is very important to identify them. Iran is very rich in evaporative deposits and also shows a unique abundance of emerged/outcropped salt domes. Most of the known salt domes are distributed in the south of  Zagros and the Persian Gulf region. But they have also been reported in the other parts of Iran, including the Great Desert, Garmsar, Qom and the Ravar region. So far, no special study has been done on the salt domes of the Ravar region, so that only a few domes in the northern and eastern parts of Ravar have been mentioned. without specifying their location on the map. Therefore, the necessity for further study of this area is specified. The main purpose of this study is to identify the salt domes found/outcropped in the area of Ravar city, Kerman province, by using new remote sensing methods and using  radar and multispectral images.

 There are several ways to process multi-dimensional images that the analysis of the principle components and the false color combination are the most important ones. We will explain how  these methods  have been used in the present study. Aster thermal sensor bands were used to produce the false color combination, so that the mentioned minerals were exposed/highlighted by placing the 12, 11 and 13 bands in the red, green and blue channels respectively, Studies on the use of the main components analysis technique for Sentinel 2 satellite images to detect soil and rock salinity show that the false color combinations of PC7, PC6 and PC2, in red, green and green channels respectively is very suitable for this purpose. This is done in the same way in this study.

 By performing atmospheric corrections on the multi-spectral images of Sentinel 2, the analysis of the main components was performed on it, as a result of which, the corresponding image was divided into 12 components. Using the three main components 2, 6 and 7, a false color combination was prepared. The results show that the different stone units are highlighted with different colors. Meanwhile, according to previous studies and by examining different colors and comparing and matching it with the geological map of the study area, it was specified that the light pink color indicates the salt units in the study area, This has been proven by field studies. It is noteworthy that in addition to determining the salt domes, the pink areas also show the secondary salts caused by weathering and erosion of these domes. Since the composition of the salt domes displayed in the Ravar salt basin varies so that some of these domes are dominated by salt minerals and polyalite, and others by sulfate minerals such as gypsum and Carbonate minerals such as anhydrite form the dominant mineral, different satellite images can be used to highlight the dominant minerals of each group in terms of their characteristics and spectral behavior. Thus Aster images were also used. Therefore, according to the specific spectral behavior of anhydrite and gypsum minerals in the thermal spectrum range, special color combinations can be combined to recognize salt domes by placing bands 12, 11 and 13 in the red, green and blue channels, respectively. As shown in this result, the salt domes having the dominant gypsum and anhydrite mineral are marked by light white. By performing the radar polarimetry technique and applying the CPR index, the relevant images were prepared. As mentioned earlier, CPR image suffering is closely related to the type and spectral behavior of different levels, In order to better analyze the images, the data suffering  were normalized between 0 and 1. The closer these numbers are to the number one, the greater the roughness is due to surface erosion. As a result, the areas that are red in the image are usually very eroded.

 The results of this study show that evaporative minerals and salt domes can be identified by using radar polarimetry method. In this study, with the application of CPR index, salt domes with red color were highlighted. In addition, due to the specific spectral behavior of the anhydrite and gypsum minerals in the thermal spectrum range, with the color combination of bands 12, 11 and 13, ASTER images of light-colored salt domes were identified. Also, the existing salt units in the study area were identified by using the three main components 2, 6 and 7 prepared from Sentinel 2 images,. Based on the obtained results, 27 salt domes were identified in the study area, which are in good agreement with the usual structural mechanism of salt domes creation. In addition, the accuracy of the results were confirmed by field survey.