جستجوی مقالات مرتبط با کلیدواژه « spectral angle mapping » در نشریات گروه « زمین شناسی »

The Skavagh study area is located in the western of the Alborz-Azarbaijan folded belt. The dominant rocks in this area are volcanic and volcanic-sedimentary rocks with the Eocene-Oligocene age which have covered most of the area. As well, the late Oligocene intrusive bodies with intermediate composition have cut the rocky units of the area. Generally, metal mineralization in the Skavagh area is copper and manganese which has occurred in the Eocene volcanic and volcanic-sediments rocks. In this research, satellite images of Sentinel 2 and Landsat 8 have been used to perform different methods of supervised classification and prepare a geological map. In this study, after performing the necessary pre-processing, the supervised classification of the images was carried out in different ways, and finally, by conducting field studies, the best method was selected based on the geological evidence. Finally, after calculating the error matrix, the accuracy of the data, Kappa coefficient and by comparing with the index samples and sampling and the thin sections of the geology, the method was validated. After sampling and statistical analysis, it was determined that the spectral angle mapping method showed the best match with the geological units of the region.

In this study, processing and interpretation methods in remote sensing such as visual and spectral analysis have been performed on the ASTER (advanced spaceborne thermal emission and reflection radiometer) data from Zarshuran gold area, and as a result, the alteration zones in the area have been identified. Then, the results of two-dimensional and three-dimensional modeling of Induced Polarization (IP) and resistivity data, using geological information, alteration and mineralization from the core drilling have been interpreted. Eventually, optimal locations for exploratory drilling have been proposed.

Development of advanced tools in remote sensing and geophysical exploration during recent decades indicates the necessity and importance of these tools in industry. In this paper, ASTER sensor imagery and geoelectrical data have been used in order to determine alteration zones, analyze mineralization system and identify the hidden mineralization in Zarshuran gold mine located in the north of the city of Takab, northwest of Iran. For this purpose, a variety of imageprocessing methods are used. IP and resistivity methods have an important role for exploration of metallic ore deposits. To achieve good results from these methods as well as minimizing the noise in the study area, it is necessary to select appropriate electrode array type for carrying out IP and resistivity surveys. For this purpose, IP and resistivity field operations over 17 parallel survey lines using the pole-dipole array have been made to identify the location of goldmineralization in the area.

In order to identify alteration zones, image processing methods such as BR (band ratio), PCA (principal component analysis), LS-Fit (linear band prediction) and SAM (spectral angle mapping) using ENVI software were applied on the ASTER images from the study area. After collecting IP and resistivity data in the area, two-dimensional and threedimensional smooth inverse modeling were carried out on the data using Res2dinv and Res3dinv software packages, and for better visualization, the results were demonstrated in Voxler and Rock Works software packages.

Identification of alteration zones in the study area using remote sensing and image processing methods, and interpretation of the geophysical inverse modeling results using geological and drilling information in the area have been led to the identification of gold mineralized zones or deposits in three-dimensional form. Eventually, based on the whole results, optimal locations for exploratory drilling have been proposed. An outcome of this research is that applying both the remote sensing and geophysics data can be led to improve the accuracy of the results. As the obtained geophysical anomalies at the end of some survey lines have been open, therefore, it is suggested to continue geophysical operations at the end of these survey lines. For better display of gold mineralization, it is also recommended to carry out geophysical operations on a number of survey lines perpendicular to main parallel survey lines. As the acquired considerable IP values in the study area can be due to metallic minerals as well clay minerals, therefore, it is recommended that some samples to be taken from drillings or excavations in the area, and then, to be analyzed by x-ray diffraction (XRD) equipment to determine the amount and type of possible metallic or clay minerals in the samples.

The Torud - Chah Shirin volcanic-plutonic complex is located in the western part of Sabzevar Metallogenic Belt and in the south of Moaleman city in the Semnan province. The presence of several mineral occurrences, especially base metal veins of epithermal origin has increased the economic importance of the magmatic complex for geological studies. The intrusionof igneous acidic to intermediate bodies in the volcanic rocks of the area has caused different alternation and mineralization in some parts of the area. In this research, various images processing methods such as false color composites (FCC), band ratios (BR) and spectral angle mapping (SAM) were performed on ASTER L1B VNIR+SWIR dataset, for discrimination of alteration zones in the Torud-Chah shirin magmatic arc. Alteration minerals like kaolinite, illite alunite, pyrophyllite, sericite, chlorite, epidote and calcite, which are associated with argillic, advanced argillic, phyllic and prophyllitic zones were recognized by processing aster dataset and highlighted altered area throughout the range. According to the field studies and XRD analysis, accuracy the results of spectral angle mapping and Band Ratio Logical Operator Algorithms evaluated by confusion matrix and kappa coefficient. Accuracy assessment shows an overall accuracy of 72% and 68% and a kappa coefficient of 0.627 and 0.6 respectively for spectralangle mapping and Band Ratio Logical Operator Algorithms for enhancing argillic and phyllic alteration zones in the study area. Therefore, the results show spectral angle mapping method achieved better results in compared to Band Ratio Logical Operator Algorithms.

Various atmospheric correction algorithms were performed on ASTER L1B VNIR SWIR datasets, and the results were compared with calibrated AST-07 dataset to introduce the best method. Neyriz ophiolite was chosen as a test area for this purpose. ASTER VNIR SWIR datasets were calibrated to apparent reflectance using two techniques: 1-Absolute atmospheric correction methods including ATCOR-2 (Atmospheric correction), ATCOR-3 (Atmospheric and Topographic correction); 2- Relative atmospheric correction methods that included IARR (Internal Average Relative Reflectance), FF (Flat Field), EL (Empirical Line), LR (Log Residuals), DOS (Dark Object Subtraction), AR (Apparent Reflectance) and COS (t). Results were evaluated by principal components analysis (Image-based algorithm) and spectral angle mapping (spectrum-based algorithm). Field spectra were used as end-members and confusion matrix was used for comparing the results of spectral angle mapping. Results of calibrated images showed that applied methods could be ranked in descending order according to the achieved accuracy of enhancing rock units as ATCOR-3, AST-07، IARR، LR, SWIR data set (L1B) and other methods had low accuracy for enhancing rock units.