Thermal remote sensing
The increased populations in the world, the growing need for energy and the indiscriminate use of fossil fuels have entered deleterious effects on living organisms and their environments. Renewable energies that do not have a limited life can be considered to be an adequate replacement for fossil energy. Geothermal energy is considered as a kind of renewable energy can meet the needs of increasing demand for energy now and in the future due to its excellent advantages such as relative safety, helping to the environment and cheapness. Given that Iran is located on one of the most favorable tectonic regions of the Earth and has a considerable potential for the geothermal energy, its identification and usage seems necessary. In the process of identifying the geothermal resources different layers are important and remote sensing can play a role in providing some of these information layers in a large scale and an acceptable accuracy. One of these layers is the hydrothermal alteration map of the study area. In this study, hydrothermal alteration areas, the potential area and the geothermal area of Ferdows located in the East of Iran have been examined using the satellite images processing methods. In order to map the alteration zones of area, ETM+ sensor data, Landsat7 taken on January 14th, 2001, 1:50,000 topographic maps of Ferdows and 1:100,000 geological map of the region were used. After pre-processing of satellite images such as geometric and atmospheric corrections, the alteration map of the area was provided using the common methods of image processing including, false color composite images, band ratio, principal component analysis, Crosta technique and least squares fitting. Band ratio RGB (754) was found as the best band combination to produce false color images. Due to the reflection of the iron oxides and clay minerals alongside the electromagnetic spectrum in bands 3 and 5, and their absorption in bands 1 and 7 sensor ETM+, the band ratio images RGB (5/4, 3/1, & 5/7) and RGB (5/7, 3/1, & 4/3) were used. Accordingly in the least squares fitting, band 3 was used to identify the iron oxides and band 7 was used to identify the clay minerals. By applying the principal component and using the Crosta technique the areas prone to hydrothermal alteration were detected. After classification of images from each method, the results were compared with the geological map. Alteration zones obtained by different methods show the same alteration process in each area. Least square fitting has a better compatibility with the geological map. The results show that the remote sensing can be used to provide alteration zone maps in large scales and acceptable accuracy, and in the next step in identifying of geothermal resources.