Extraction Of Alteration Information From Remote Sensing Data In The Gongchangling District, Liaoning Province

Using remote sensing data can quickly extract alteration information related to mineralization,and using this alteration anomaly information can delineate and predict the prospecting area,providing a reliable reference for conventional ore prospecting work.However,in areas with high vegetation coverage,whether the interference of vegetation information on alteration information extraction can be minimized has a great impact on the results of alteration information extraction and the delineation of metallogenic prospects.In this paper,Gongchangling District of Liaoning Province is taken as the research area.There are many kinds of mineral resources in this area,among which iron ore resources are the most abundant,but the vegetation coverage in this area is high,which brings great difficulties to extract alteration information from remote sensing.In order to solve this problem,Landsat 8 and ASTER are used as data sources,vegetation index and water index masking method are used to reduce the disturbance information of vegetation and water body in the study area.Combined with the basic geological data and field geological survey information of the study area,the ratio-principal component analysis and principal component analysis are used to extract the remote sensing mineralization alteration information in the study area.First,the remote sensing data are pre-processed by radiation calibration,atmospheric correction and clipping,and the clipped image is used as the base map of remote sensing alteration information extraction.Because the study area contains a large number of vegetation and a small amount of water disturbance,it is necessary to remove disturbance from the bottom map of the study area before extracting alteration information.When removing vegetation disturbance,vegetation and water information in the study area are identified by NDVI and improved MNDWI.The threshold range of vegetation and water is selected by statistical analysis,and then the mask range of vegetation and water information is established by the threshold.Finally,the purpose of removing vegetation and water disturbance is achieved.Based on the alteration information of rocks and minerals in the study area,the spectra of minerals related to iron-stained and hydroxyl-altered minerals are selected from USGS spectral library and resampled to ASTER and Landsat8 data in the study area.The spectral characteristics of iron-stained and hydroxyl-altered minerals in ASTER and Landsat8 data bands are analyzed.According to the spectral characteristics of iron-stained and hydroxyl altered minerals,the main component bands are selected to prepare for the next extraction of alteration information.According to the characteristic bands of iron dyeing and hydroxyl spectrum,principal component analysis and ratio-principal component analysis were used to calculate and analyze the alteration information in the study area.According to the eigenvector matrix,the principal component containing the information of iron staining or hydroxyl alteration is selected,and then the principal component image is processed by 3×3 Gauss low-pass filtering and digital stretching.Finally,the principal component threshold method is used to extract the abnormal information of the alteration in the study area.In this study,Landsat8 and ASTER remote sensing data were used to extract the distribution of iron staining and hydroxyl alteration information in Gongchangling District,Liaoning Province.The results of alteration information distribution show that iron staining and hydroxyl alteration information extracted from Landsat 8 data are mainly distributed in Quaternary and Gongchangling mining areas.Based on the analysis of basic geological data,the alteration information distributed in Quaternary area is mostly pseudo-anomaly caused by the interference of QuaternarySediment.The information of hydroxyl and iron staining and alteration distributed in No.1 and No.2 mining areas of Gongchangling Mine is basically consistent with the distribution of exposed wall rocks on the surface of the mining area.This also proves to some extent that the alteration information extracted in this study has certain accuracy.