Search

This study demonstrates the use of ASTER data to map the siltation of the Al-Khod Dam constructed at the lower reaches of Samail Catchment area, north Muscat, Sultanate of Oman. In this study, the decorrelated image of spectral bands 6, 3, and 1 clearly discriminated the distribution of siltation. The occurrence of siltation is confirmed by the detection of minerals using the VNIR-SWIR bands by the Spectral Angle Mapper (SAM) method. In addition, the siltation of the dam is studied for the years 1987 to 2018 using Landsat satellite images. Interpretation of images showed a gradual increase of the siltation. Mapping accuracy for the occurrence of siltation is assessed by a confusion matrix which produced an overall accuracy of 97.88% and Kappa coefficient of 0.98 in the Maximum Likelihood method. Results of image analyses are verified in the field and confirmed through laboratory analyses. The study of spectral absorption characters of field samples using a Portable Infrared Mineral Analyzer (PIMA) showed the presence of OH molecule bearing minerals (clays, serpentines, etc.) and carbonate minerals (calcite and dolomite) in the silt deposits. The occurrence of these minerals is confirmed further by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analyses. [ABSTRACT FROM AUTHOR]

Abstract This study maps hydrothermal alteration of Wadi Tayin Massif of the Sultanate of Oman using the spectral bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the image processing methods namely band ratios, false color composite (FCC), spectral angle mapper (SAM), mixture tuned matched filtering (MTMF) and linear spectral unmixing (LSU) to understand alteration of the upper mantle-lower crust transition zone. The study of FCC image of the spectral bands 8, 4, and 1 in Red (R), Green (G), and Blue (B), respectively, showed the presence of the hydrothermal alteration in shades of purple and brown over the mantle peridotites, dunites, and crustal gabbros. The ASTER band ratios R:9/8, G:4/3, B:2/1 used in this study able to show the occurrence and distribution of alteration in orange distinctly. The SAM, LSU and MTMF image processing methods applied over the region confirmed the presence of alteration and altered minerals in the rocks. The assessment of accuracy for the methods provided the high accuracy of 91.86% and Kappa Coefficient = 0.89 in the LSU method. The image interpretations are studied in the field and the occurrence of alterations are validated by presence of strong serpentinization in the peridotites and dunites, and secondary veins in the micro cracks of gabbros. Laboratory studies showed presence of the serpentinization, iddingsitization, chloritization and development of pargasite in the altered rocks. This study shows application of the ASTER sensor to map hydrothermal alteration found near the fast-spreading oceanic ridge. Graphical abstract Image 1 Highlights • Hydrothermal alteration zone of upper mantle-lower crust transition zone is studied using remote sensing technique. • Hydrothermal altered minerals are detected using SAM method. • Spatial distribution of altered minerals is studied using LSU and MTMF methods. • Application of remote sensing technique is evaluated in the field and through laboratory studies. [ABSTRACT FROM AUTHOR]

Moho and Moho Transition Zone (MTZ) of the Samail ophiolite of Sultanate of Oman are characteristic to potential occurrences of chromite deposit, hydrothermal mineralization and serpentinization. Mapping of Moho and MTZ, and discriminating them in between the mafic and ultramafic rocks in ophiolite sequence are more significant and important. The present study describes the remote sensing spectral characters of minerals and rocks of the Moho and MTZ and discriminates the Moho of Wadi Al Abyad of Nakhl massif, and Wadi Nidab and Wadi Abda regions of Sumail massif in the visible and near infrared (VNIR), and short wavelength infrared (SWIR) spectral regions using low-cost multispectral satellite data of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Results of this study show that the red–green–blue (RGB) color composite images of ASTER spectral bands 8, 3 and 1, and 8, 7 and 4 are able to delineate the Moho and MTZ of the regions. The RGB images of ASTER band ratios (4/8, 4/1, 3/2 * 4/3 and (1 + 3)/2, (4 + 6)/5, (7 + 9)/8) are capable to discriminate the mantle material (ultramafic harzburgites) and crustal rocks (mafic gabbros). The occurrence of such rock types is demonstrated by detection of their minerals using Spectral Angle Mapper (SAM) image processing method. The presence of Moho and MTZ, and associated lithologies are verified in field at Wadi Al Abyad, Wadi Nidab, Wadi Abda, Wadi Tayin, Wadi Fizh and several locations of Nakhl regions of Samail ophiolites. The laboratory study shows the occurrence of typical minerals namely olivine, orthopyroxene and clinopyroxene in the harzburgite and the minerals such as plagioclase, clinopyroxene, hornblende, orthopyroxene and olivine in the layered gabbro. The spectral properties of the rocks are studied using Portable Infrared Mineral Analyzer (PIMA) spectrometer and the occurrences of minerals are confirmed by X-ray diffraction (XRD) analyses. This study demonstrates the sensor capability of ASTER to map Moho and MTZ, and thus it is recommended to the geoscientists and geophysicists working on Moho and MTZ. The satellite image interpretations of Moho and MTZ, and the associated rocks and minerals are consistent with the field research studies carried out in these regions. Our images have potential to map the chromites mineralized zone and dunites (refractory materials) bearing MTZ. [ABSTRACT FROM AUTHOR]

Copyright of Sultan Qaboos University Journal for Science is the property of Sultan Qaboos University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Documentation of chemical weathering and CO2 sequestration in the Samail ophiolite massifs of the Sultanate of Oman represents an important case study for Geological Carbon Capture and Storage System (GCCSS). The present research study demonstrates the capability of remote sensing technique for mapping of weathered zones and potential CO2 sequestration area abundances at different scales within peridotites in the northern mountain region of the Samail ophiolite massifs. The carbonate mineral index (CI) applied with other mineral indices to the TIR wavelength region of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) TIR spectral bands 13 and 14 mapped CO2 sequestered minerals along the structural- and wadi-controlled CO2 flowing regions. Peridotites, the source rocks of CO2 sequestration in the study area, were mapped using an ASTER 8, 3 and 1 band combinations. The decorrelated Landsat TM image discriminated the rock types associated with peridotites of ophiolite sequences and delineated the region of weathered and altered serpentinized peridotites in the zone of CO2 sequestration. CO2 sequestration mapping was carried out using Landsat TM satellite data that span 20years (1986, 1998, 2000, 2003 and 2006) to assess the present status of CO2 sequestration in this region. The image interpretations are verified with existing geological maps and through field and laboratory studies. The spectral measurements of carbonate minerals at 1300 to 2500nm with the spectral resolution of ~7nm using a PIMA SP infrared spectrometer in the field and laboratory show the presence of hydroxyl-bearing minerals and carbonates that have spectral absorption features around 1.4μm, 1.9μm and 2.35μm. The strong absorptions around 2.35μm are mainly due to C O bonds in carbonate minerals such as calcite (CaCO3), dolomite (CaMg(CO3)2), magnesite (MgCO3), aragonite (CaCO3) and siderite (FeCO3), which form 15 to 57%, 12 to 53%, 9 to 38%, 11 to 21% and 3 to 8% respectively in the samples. The absorptions around 1.4μm and 1.9μm are caused by hydration effects of hydroxyl minerals including antigorite and montmorillonite present at 10 to 21% and 37 to 81% respectively in the samples. The alterations of serpentinite are evidenced by the presence of antigorite and lizardite minerals. X-ray powder diffraction analyses further confirms the occurrence of CO2 sequestered major carbonate minerals such as aragonite, calcite and dolomite in the samples. The study demonstrates that the ASTER and Landsat TM satellite multispectral sensors are useful to detect the carbonate minerals, to delineate the peridotites and to discriminate the areal abundance of potential CO2 sequestration. This technique is a useful tool to map and monitor the region of CO2 sequestration in well exposed arid and semi-arid regions and to analyze and understand this aspect of the world geological carbon capture and storage system. [Copyright &y& Elsevier]

Highlights: [•] Spectral sensitivity of carbonate rocks are studied using ASTER satellite data. [•] Satellite image spectra of limestones, listwaenites, marls and carbonatites are studied. [•] Evaluated the study in field and laboratory works. [•] The study proved the remote sensing technique is time and cost-effective. [•] The outcome of the study is useful to geologists and exploration communities. [Copyright &y& Elsevier]

This study demonstrates the capability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor data to remotely map industrial carbonate rocks known as the ‘Oman exotics’ of the Sultanate of Oman. We measured reflectance spectra of marble using a PIMA™ spectrometer and studied their spectral absorptions distinguishing calcite from spectral absorptions of dolomite of the same region. The spectral band 8 of ASTER is processed by simple decorrelation stretch image processing method to map the exotic limestone rock of the Nakhl region, Oman. Results showed that carbonate rocks displayed distinctive tonal variation on the image. A comparative study with the spectral band 7 of Landsat 7 (ETM+) does not discriminate the calcite-bearing marbles and associated carbonate formations in the studied area. ASTER data were also processed by the application of the Maximum Likelihood Classification (MLC), Spectral Angle Mapper (SAM) and Spectral Information Divergence (SID) image classification algorithms. The results were assessed by the production of a confusion matrix. The study shows the capability of visible near infrared (VNIR) and shortwave infrared (SWIR) spectral bands of the ASTER sensor and potential of the image processing methods to remotely identify industrial carbonate rocks and we recommend this technique to similar regions of the world. [ABSTRACT FROM AUTHOR]

Aeolian deposit in part of the Arabian Desert is mapped using ASTER data to understand desertification, land encroachment, and degradation, and to assess agricultural development in arid regions. In this study, the interpretation of emissive spectra of sand deposits showed the presence of triplet absorptions in emissivity between 8 and 9.50 μm and studied with ASTER spectral bands to map the deposits. The ASTER quartz index (QI) images used to study the Abu Samra region, Qatar from 2000 to 2021 showed significant changes in desertification and land degradation. Analysis of temporal variability of deposits between 2000 and 2021 using ASTER band 12 by Parallelepiped image classification showed a decreasing trend from 9.70% to 2.94% in their distributions due to erosion and transportation. The changes are studied using FCC images (R:1; G:2; B:3) and hill-shaded images of 2000 and 2021. The results are confirmed from FCC (R:14; G:12; B:11) and Google Earth satellite images which showed the occurrence of sabkhas in 1985 and their disappearance from 2015, and the presence of agriculture in 2000 and their absence from 2005. The changes in desertification, land degradation, and agricultural development are verified in the field and evidenced. The grain size analysis of samples by ASTM method showed aeolian deposits have very fine to very coarse (63–2000 μm) sand types with silts of <3%. The samples analyzed by XRD and SEM-EDX methods showed the occurrence of dolomite, calcite, quartz, feldspar, and gypsum minerals with high sphericity and sub-angular to well-rounded characters and suggested transportations of grains from long distances. The geochemical elements analyses of samples reflected the chemistry of carbonates, aluminosilicates, and evaporites minerals which could have been derived from the carbonate, shale and sandstone formations, and sabkhas that occurred in Qatar and the Arabian Peninsula. [Display omitted] • Aeolian deposit of the Arabian Desert was mapped using TIR bands of satellite data. • Changes in desertification and land degradation are studied between 2000 and 2021. • Image studies showed a decreasing trend in desertification from 9.70% to 2.94%. • Sphericity, minerals, and chemical composition of aeolian deposits are documented. • Satellite sensor and QI index capabilities are demonstrated to map aeolian deposits. [ABSTRACT FROM AUTHOR]

Abstract: Economically viable chromite deposit occurrences are widespread in the ultramafic rocks of Semail ophiolite massifs of the northern Oman Mountains, particularly in the basal dunite and harzburgite unit of the mantle section. Geological mapping of this region is challenging, primarily due to difficult access, complexity of structures, and lack of resolution and areal integrity of lithological differentiation using conventional mapping techniques. The present research study evaluates the discrimination and occurrence of chromites bearing mineralized zones within ophiolites by analyzing the capabilities of Landsat TM and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data; using a number of selected methods including decorrelated stretching, different band rationing and Principal Component Analysis image processing techniques exist in the scientific literature. The study results show that the processed VNIR and SWIR spectral wavelength regions are promising in detecting the areas of potential chromite bearing mineralized zones within the ophiolite region, and proved to be successful for mapping of serpentinized harzburgite containing chromites. Exploration geologists, industrialists and mine owners are advised to adopt this technique and avoid the limits in filed data alone for more exploration and exploitation of areas having chromite deposits in arid region elsewhere. [Copyright &y& Elsevier]