ASTER Satellite Data Research Articles

Extraction of Weak Information of Altered Minerals in the Lala Copper Mine, Sichuan Province, China Based on the ASTER and GF-5 Satellite Data

Extraction of Weak Information of Altered Minerals in the Lala Copper Mine, Sichuan Province, China Based on the ASTER and GF-5 Satellite Data

The geochemistry, origin, and hydrothermal alteration mapping associated with the gold-bearing quartz veins at Hamash district, South Eastern Desert, Egypt

Integrating diverse techniques and datasets, significantly enhances the accurate identification of various mineral deposits. This work aims to determine different types of mineral deposits in the Hamash district (Southern Eastern Desert, Egypt) by combining structural features (derived from ALOS PALSAR DEM), alteration zones (detected using ASTER and Sentinel-2), and ore mineralogy. Multispectral imaging, such as ASTER and Sentinel-2 satellite data, provides a cost-effective and efficient tool for lithological and hydrothermal alteration mapping utilizing selective band ratios (SBR), directed principal component analysis (DPCA), feature-oriented false-color composites (FFCC), and constrained energy minimization (CEM). The deductions drawn from the analysis of ASTER and Sentinel 2 satellite data are solidly corroborated through meticulous investigations of pre-existing lithological maps in the study area, on-site validation via fieldwork, and robust laboratory analysis, attesting to reliable results. Validation of remote sensing results was performed through field observations, petrographic investigations, X-ray diffraction technique (XRD), and SEM–EDX analyses. Based on ore mineralogy derived from XRD and SEM results the quartz-vein-associated ore minerals in the Hamash district include chalcopyrite, pyrite, hematite, goethite, bornite, covellite, and gold. According to the present paragenesis, the mineralization in the study area is classified into three types: sulfide mineralized zone, transitional zone, and supergene zone. Using an ore microscope, our studies identified that the alteration zones include gold-bearing sulfide minerals as well as the minerals goethite and malachite. In gold-bearing quartz samples, the concentrations of Cu, As, Ag, and Sb are positively correlated with Au at the degree of shear deformation. According to data gathered from the fire assay results, Au content varied from 0.027 to 57.20 ppm, along with Cu (10–6484 ppm), Ag (0.5–20.5 ppm), As (5–2046 ppm), Zn (3–1095 ppm), Pb (2–1383 ppm), and Sb (5–23). Our results confirmed that the Hamash region is one of the most important gold-bearing sites, with gold concentrations ranging from 0.027 up to 57.20 ppm. Furthermore, the current contribution highlighted four stages in the paragenetic sequence of the recorded ores, including magmatic, metamorphic, hydrothermal, and supergene by origin, indicating a considered similarity with the known Egyptian gold sites regarding host rocks, mineralization style, alteration assemblage, and several ore mineral conditions.

Evaluating the Use of a Contextual Information Extraction Technique to Identify Mineralized Zones in a Semi-Arid Environment from Aster Satellite Data

Identification of regions of mineralization by traditional techniques where spectral information of pixel alone is applied during classification, either at pixel or sub-pixel level, is usually accompanied by some level of un-satisfaction. Impulse noises that are usually experienced in digital images from sudden sharp disturbances in the signal degrade the output. This effect often referred to as the salt and pepper noise could further cause information loss, and change the colour of an RGB image. The use of filters (median and morphological) has not totally eliminated the effects. Object-based methods came in with higher filter smoothers to make it better yet, there is potential limitation because of possible negative impact of under segmentation. The errors of under-segmentation cannot be adjusted within a unit of features, which apparently affect the potential accuracy of the entire classification. Thus, this study evaluates the contribution of the contextual information to reduce the effects of noise in the data for effective mineral identification. Rule-based technique was applied for information extraction from a threshold values derived from band ratio (BR) transformation operations on ASTER data. The result indicates clay has the highest mineral density of 47% in the study area, with silicate having the least (3%), among others. This study provides a robust test for contextual cues as anticipated to be most effective and shall contribute towards reducing environmental impacts and protecting biodiversity which is one of the major aspects of sustainable development in relation to mining and mineral processing

Detection of iron-bearing mineral assemblages in Nainarmalai granulite region, south India, based on satellite image processing and geochemical anomalies.

Although India's large iron ore reserves are well known, there are still few studies and research on iron ore prospecting in smaller deposits or the deposits with lower grade. Remote sensing concepts are useful to target for mineral exploration, since it covers a large area at low cost. In this research spectral remote sensing and digital image processing of ASTER data to locate and delineate the regions with iron oxide-bearing soils in granulite terrain at Nainnarmalai (southern India) that has hypothetical reserve 8.2 million tons of iron in sub-surface banded magnetite quartzites. The image-based study component involved pre-processing atmospheric correction and processing of the image data reminiscent of band ratio and band mixture to locate iron-bearing soils. We used blending of bands 5/3 + 1/2 to delineate ferrous iron oxide, band combination of 2/1 to delineate ferric iron oxide, and band ratio of 5/4 to delineate the lateritic soil. Further, the linear spectral unmixing outcome of ASRER data was evaluated concerning the ground truth of geochemical compositions of samples from the study area. Our results showed that image processing of the ASTER satellite data has the potential to delineate ferric, ferrous, and lateritic mineral assemblages in the iron-bearing soils with minimal requirement of ground truth verification. This research work aided in increasing trust in the use of space-based data for mineral prospecting. Image processing has demonstrated that ASTER data can be used to enhance iron ore exploration and the discovery of new mineralized areas.

Multithematic Geoscience Data Integration for Identification of Mineral Potential Areas in Parts of Central Indian Precambrian Craton

Abstract The paper highlights the results of multi-thematic geoscience data integration involving geological, geophysical, geochemical and remote sensing data sets, for an area of 4000 Sq. Km in parts of Precambrian Bastar craton, Chhattisgarh. The present team has been able to identify two discrete mineral potential areas for base metal sulphides, Sn, W and REE in sheared and altered felsic volcanics in Kotra-Bhansula area and for gold in propylitically altered meta basalts in Bhursatola-Khampura area. The dataset utilized during collation and integration includes (i) high resolution aeromagnetic data (ii) 1:50000 geological data covering litho-structural and mineralisation attributes (iii) 1:50 k geochemical data for 61 elements (iv) multispectral ASTER satellite data and its derivative alteration maps. Thematic data and derivative maps were studied and interpreted for evaluation of concerned parameters for estimating their role in mineralisation. The data integration has been implemented in three steps beginning with GIS based spatial modelling using Fuzzy logic method resulting into production of mineral favourability map, followed by detailed field evaluation and characterization of the identified mineral favourability areas. Eventual identification of potential areas was based on synthesis of modelling output, field outcome and laboratory results of analyses carried out on critical samples collected from mineral favourability areas. The identified two mineral potential areas are recommended for further detailed exploration for gold, base metal, Sn, W and REE through surface and sub-surface probing.

Reflectance spectroscopy and ASTER mapping of aeolian dunes of Shaqra and Tharmada Provinces, Saudi Arabia: Field validation and laboratory confirmation

ABSTRACT Spatial variability of grain sizes and mapping of aeolian dunes is important to study the sand erosion, transport, and dune movement and to understand the dune encroachment and land degradation. This study examines the grain size statistical parameters and mineralogical composition of 68 sand samples collected from 17 crescentic dunes and assesses the source and depositional environment of these dunes. The analyses of samples for grain sizes resulted that the sands are characteristics to fine with an average size of 2.28 Φ and classified as moderately well-sorted(0.59 Φ), mesokurtic (0.97 Φ), and fine to coarsely skewed (0.14 Φ). X-Ray Diffraction shows that the dunes are deposited mainly by quartz, calcite, and haematite. The occurrence of absorption features near 0.5, 0.9, and 2.22 μm confirm the presence of such iron and aluminosilicate minerals in the dunes. The dunes of the provinces were mapped using TIR bands of ASTER satellite data by Carbonate index (CI) and Quartz index (QI). A good agreement among the results of grain size analyses, spectral measurements, mineralogical studies, and mapping of dunes with the field observations suggests that the sand deposits in the study area have a diversity of sources in the aeolian environment.

Mapping sequences and mineral deposits in poorly exposed lithologies of inaccessible regions in Azad Jammu and Kashmir using SVM with ASTER satellite data

Mapping sequences and mineral deposits in poorly exposed lithologies of inaccessible regions in Azad Jammu and Kashmir using SVM with ASTER satellite data

Mapping of Hydrothermal Alteration Zones in the Kelâat M’Gouna Region Using Airborne Gamma-Ray Spectrometry and Remote Sensing Data: Mining Implications (Eastern Anti-Atlas, Morocco)

The mapping of hydrothermal alteration zones associated with mineralization is of paramount importance in searching for metal deposits. For this purpose, targeting alteration zones by analyzing airborne geophysical and satellite imagery provides accurate and reliable results. In the Kelâat M’Gouna inlier, located in the Saghro Massif of the Moroccan Anti Atlas, natural gamma-ray spectrometry and ASTER satellite data were used to map hydrothermal alteration zones. Natural gamma-ray spectrometry data were processed to produce maps of Potassium (K in %), Uranium (eU in ppm), Thorium (eTh in ppm) and ratios of K/eTh and K/eU. In addition, four-band ratios were computed, on ASTER data, to map the distribution of clay minerals, phyllitic minerals, propylitic minerals, and iron oxides. The combined results obtained from geophysical and satellite data were further exploited by fuzzy logic modelling using the Geographic Information System (GIS) to generate a mineral prospectivity map. Seven hydrothermal alteration zones likely to be favorable for mineralization have been identified. They show a spatial correlation with (i) known surface prospects and mineral occurrences, (ii) the granite-encasing contact zone, and (iii) the fault zones (Sidi Flah and Tagmout faults). This research therefore provides important information on the prospecting of mineral potential in the study area.

The discovery of structural elements and zones of hydrothermal alterations by using ASTER satellite data in the margins of Gadabay and Murovdag ore districts (Lesser Caucasus, Azerbaijan)


 
 
 The article considers the discovery of structural elements, zones of hydrothermal alterations and mineralization in the margins of Gadabay and Murovdag regions and the study of prospective areas for mineralization characterized by them by using ASTER satellite data. The main purpose of the research is the definition of the lithological composition of rocks, ring and linear structures and zones of hydrothermal alterations with the help of remote-sensing methods and by better technological development of special radiometric data. In order to detect the lithological composition of associated rocks of alteration zone of endogenous ores, 14 channel data of ASTER has been used. By using stereoscopic images obtained from ASTER data, it was determined that hydrothermal alterations are mainly represented by alunitization, kaolinization, sericitization, silication, pyropilitization and silification in the studied ore regions. These changes were shown to be characteristic for copper-porphyry, gold- copper pyrite, copper-polymetal and gold-copper-porphyry deposits. Strip ratios, principal component analysis (PCA), minimum of noise fraction (MNF) and selection method for least squares (LS) have been used to map hydrothermal alteration zones. The ring structures detected in the area, different fault fractures and lineaments are assessed as favourable geological structural factors for alteration and mineralization. The results obtained by ASTER image analysis confirm the presence of derivative minerals which are considered to be the product of hydrothermal alterations which are densely concentrated (kalium spathization, kaolinization, serictization, pyrophyllitization, alunitization) has been confirmed. The points each with private coordinates have been determined (defined) within separate areas with the help of remote data and relevant anomalous maps prepared. These points are considered favourable geological condition in terms of the type and intensity of hydrothermal alterations in the area. Such areas are considered a sign of indirect search significant for the detection of copper-polymetallic, copper-porphyry, copper-pyrite and gold-pyrite type of mineralization with epithermal origin in the region.
 
 

ASTER-Based Remote Sensing Image Analysis for Prospection Criteria of Podiform Chromite at the Khoy Ophiolite (NW Iran)

A single chromite deposit occurrence is found in the serpentinized harzburgite unit of the Khoy ophiolite complex in northwest Iran, which is surrounded by dunite envelopes. This area has mountainous features and extremely rugged topography with difficult access, so prospecting for chromite deposits by conventional geological mapping is challenging. Therefore, using remote sensing techniques is very useful and effective, in terms of saving costs and time, to determine the chromite-bearing zones. This study evaluated the discrimination of chromite-bearing mineralized zones within the Khoy ophiolite complex by analyzing the capabilities of ASTER satellite data. Spectral transformation methods such as optimum index factor (OIF), band ratio (BR), spectral angle mapper (SAM), and principal component analysis (PCA) were applied on the ASTER bands for lithological mapping. Many chromitite lenses are scattered in this ophiolite, but only a few have been explored. ASTER bands contain improved spectral characteristics and higher spatial resolution for detecting serpentinized dunite in ophiolitic complexes. In this study, after the correction of ASTER data, many conventional techniques were used. A specialized optimum index factor RGB (8, 6, 3) was developed using ASTER bands to differentiate lithological units. The color composition of band ratios such as RGB ((4 + 2)/3, (7 + 5)/6, (9 + 7)/8), (4/1, 4/7, 4/5), and (4/3 × 2/3, 3/4, 4/7) produced the best results. The integration of information extracted from the image processing algorithms used in this study mapped most of the lithological units of the Khoy ophiolitic complex and new prospecting targets for chromite exploration were determined. Furthermore, the results were verified by comprehensive fieldwork and previous studies in the study area. The results of this study indicate that the integration of information extracted from the image processing algorithms could be a broadly applicable tool for chromite prospecting and lithological mapping in mountainous and inaccessible regions such as Iranian ophiolitic zones.

Satellite-based lithological characterization of Central Chitral, Karakoram Ranges, Northern Pakistan

The satellite remote sensing method is an important low-cost technique for the identification, mapping, and collecting information on potential areas of surface lithologies in areas of appropriate exposure. Multiple techniques have been developed which are utilized for the geological mapping from satellite data. This study is based on the band ratios and spectral analogue method for identifying and characterizing stratigraphy based on using satellite data. The study area (approx. 20 sq. km) is located in Chitral District which lies in the northwest of Pakistan. This area is based on the Devonian and Quaternary sedimentary and metamorphosed rock. ASTER data was used for the geological characterization in a way that image processed first, and then interpretation was done on the processed image. In this study, ASTER satellite data was atmospherically and radiometrically corrected before the lithological characterization. The spectral analogue method and band combination (532) in RGB image were powerful in distinguishing various rock units. Field survey was carried out to measure the accuracy of the remote sensing–based lithological maps. Accuracy of the produced map was evaluated through calculating the kappa index. Overall accuracy and a thematic accuracy of 84% were achieved for geological formations.

Application of optical and radar satellite images for mapping tectonic lineaments in kerdous inlier of the Anti-Atlas belt, Morocco

Lineament mapping is an important step for lithological and hydrothermal alterations mapping. It is an efficient research task and a part of structural investigation and mineral ore deposits identification. The availability of optical as well as radar remote sensing data, such as Landsat 8 OLI, Terra ASTER and ALOS PALSAR data, allows lineaments mapping at regional and national scale. The accuracy of the obtained results depends strongly on the spatial and spectral resolution of the data. The aim of this study is to compare Landsat 8 OLI, Terra ASTER, and radar ALOS PALSAR satellite data for automatic and manual lineaments extraction. The module Line of PCI Geomatica software was applied on PC1 OLI, PC3 ASTER and HH and HV polarization images to automatically extract geological lineaments. Moreover, the manual extraction was achieved using the RGB color composite of the directional filtered images N - S (0°), NE - SW (45°) and E − W (90°) of the OLI panchromatic band 8. The obtained lineaments from automatic and manual extraction were compared to the faults and photo-geological lineaments digitized from the existing geological map of the study area. The extracted lineaments from PC1 OLI and ALOS PALSAR polarizations images showed the best correlation with faults and photo-geological lineaments. The results indicate that the lineaments extracted from HH and HV polarizations of ALOS PALSAR radar data and PC1 OLI were more efficient for structural lineament mapping.

Characterizing Khetri copper mine environment using geospatial tools

Mines result in land use and land cover (LULC) change due to degradation of natural resources and establishment of new infrastructure for ore extraction and beneficiation. The present study was carried out to, with objectives, (1) characterize LULC change (from 1975 to 2017) in Khetri copper mine region, (2) spatial distribution of pollution indices and (3) spectral response of elemental concentration of soil and groundwater using Landstat and ASTER satellite data. The study was designed to fulfil the objectives and for the same NDVI values were calculated for LULC classification and generated maps were analyzed for landscape pattern. Spatial distribution of pollution indices calculated using geochemical data of soil and groundwater was plotted to understand the impact of contamination on landscape pattern. The correlation of spectral response of Landstat bands with heavy metals concentration was plotted to assess their possible use in quantification of heavy metals. Results show constant increase in settlements, mines and open area while vegetation cover has decreased. Landscape and class level metrics (number of patch, patch density, aggregation index and landscape shape index) indicate increase in the fragmentation of landscape in recent years. Shannon’s Evenness Index indicates increase in uniformity in landscape and it is attributed to loss of vegetation and agriculture patches. Pollution indices, Pollution Load Index for soil is high near the overburden materials and Index of Environmental Risk (IER) and Contamination Index for ground water is high near abandoned mines. Spectral bands 5 and 6 (SWIR 1) show significant negative correlation, and 9 (Cirrus) shows significant positive correlation with metal concentration in soil and water suggesting the possible use of remote sensing in assessment of metal concentration at ground level. Thus, it can be concluded that mines significantly influence the landscape pattern and remote sensing could be used for the assessment and predication of heavy metal contamination at broader scale in a cost-effective way.

The mapping of hydrothermal alteration related to the geothermal activities with remote sensing at Akarcay Basin (Afyonkarahisar), using Aster data

The geothermal energy does not pollute the environment and atmosphere during production and consumption. Akarcay basin (Afyonkarahisar) has significant geothermal potential in Turkey. Geothermal waters in the basin are used for tourism, residential heating, greenhouse, and balneological applications. Hydrothermal alteration zones are essential indicators for the exploration of geothermal fields. In the feasibility studies of geothermal exploratory studies, outcrops of alteration contribute significantly to the exploration studies in investigation of target areas. The use of remote-sensing techniques in the detection of hydrothermal alteration minerals spread over large areas enables large areas to be evaluated holistically, saving both time and economically and achieving effective results. In this study, the Crosta and Spectral Angle Mapping (SAM) techniques were applied to determine the hydrothermal alteration zones by using ASTER satellite data. In this context, samples from hydrothermal alteration zones were collected from the study area. The mineralogical compositions of studied samples were determined by using X-ray diffraction (XRD) method. Alteration zones were also distinguished in similar locations in mapping techniques and XRD method. The results were combined, and the final alteration zones were formed. The alteration zones masked with volcanic and metamorphic rocks in order to be a geothermal indicator of hydrothermal alterations. The existing alteration zones are almost on the existing geothermal fields. As a result of the study, alteration zones were proposed different from the existing alteration zones. It is expected that these zones will be a reference in future geothermal explorations.

A remote sensing approach for assessing the invasion of Najas marina in Madu Ganga Estuary, Sri Lanka

The present study was carried out to determine the distribution of Najas marina , an invasive floral species in the Ramsar site of Madu Ganga Estuary in Sri Lanka using ASTER satellite data. Cloud free ASTER imageries of Madu Ganga Estuary with 15 m resolution were atmospherically corrected using the FLAASH in ENVI software. The NDVI was calculated and unsupervised classification was applied for the study site for each image and the distribution maps of N. marina were developed from 2007 to 2014. Methodology was validated using in situ data, which were collected in 2014 with monthly intervals parallel to ASTER overpass. The derived distribution maps indicated that N. marina was distributed in about 31% of the estuary in April 2014. The highest densities were mostly found in bay areas and peripheral areas. Maps developed for December 2007, December 2009 and December 2013 indicated that there is a temporal variation in the distribution of N. marina over the years. The overall distribution of N. marina has decreased from December 2007 to December 2009 and increased from December 2009 to April 2014. Low water levels and stagnation of water appears to be conducive for the variation of this species. These factors should be taken into consideration when managing the invasion of N. marina in this economically and ecologically important estuary.

Characterization of microseepage-induced diagenetic changes in the Upper-Red Formation, Qom region, Iran. Part I: Outcrop, geochemical, and remote sensing studies

This article explores the footprints of hydrocarbon microseepage in the Upper-Red Formation covering the Alborz petroleum reservoir in the Saveh-Qom basin, Iran. The adopted multidisciplinary approach combines field observation and sampling, detailed petrographical and geochemical analysis, and remote sensing mapping using Sentinel-2 and ASTER satellite data. The study revealed significant changes in the microseepage-affected zones when contrasted to unaffected lithofacies and led to the establishment of a new array of mineralogical and geochemical indicators for the phenomenon. These comprise partial bleaching of the red-beds, secondary goethite coatings, diagenetic clay minerals (e.g. illite-smectite, chlorite), and pervasive calcite, silica, and gypsum cementations. In terms of geochemistry, the major oxides, particularly the ratio of CaO + K 2 O/Na 2 O + MgO + CaO + K 2 O proved to be a reliable index for distinguishing microseepage-prone areas. Based on isotopic studies, a combination of three sources of carbon, comprising oxidized hydrocarbons, was recognized in the carbonate cements; yet the strata were shown to be moderately flushed by percolating fluids. Satellite remote sensing was successful in mapping reservoir-scale footprints of the microseepage systems. It indicated that the extent of the induced alterations, and thereby the outline of the underlying reservoir, is much larger than previously known. Overall, the secondary changes were shown to be a function of the geochemistry of the host-rock, the local environmental variables (i.e. climate and hydrogeology), and the 3D architecture of the trap. The substantiated indicators carry direct implications for onshore microseepage targeting and hold high potential to help reduce the exploration and development risks in frontier and mature basins. • The footprints of petroleum microseepage were shown to be traceable at multiple scales. • The structural geology has governed the extent, locality, and intensity of the anomalies. • The extent of the reservoir was indicated to be larger than what was previously envisaged.

Remote sensing of urban thermal environments within local climate zones: A case study of two high-density subtropical Chinese cities

A comprehensive understanding of urban thermal environments is vital for improving urban planning and design strategies to mitigate the urban heat island effect as part of sustainable development. This study investigates the fine-scale thermal environment within high density cities using multi-sourced open satellite data. The whole urban area was first classified based on the urban features such as building morphology and land cover, using the local climate zone scheme; then the thermal performance of different local climate zones was assessed using thermal satellite data. Experiments conducted in two high-density Chinese cities indicated that different urban structures have contrasting thermal conditions in the daytime and nighttime. Furthermore, the utility of different satellite data for detecting and monitoring intra-urban thermal environments was assessed. It was found that Landsat and ASTER satellite data have similar performance, and both datasets perform better than MODIS data, which tend to underestimate urban heat islands. The findings of this study can provide a fast and efficient way to understand the thermal environment within high-density cities, which will allow for better planning to improve urban thermal conditions and ensure more sustainable development.

Estimation of LST from multi-sensor thermal remote sensing data and evaluating the influence of sensor characteristics.

ABSTRACTRemote sensing science has proven fruitful for land surface temperature (LST) determination contrary to other techniques used especially for the rugged terrain like the Himalayan mountain system. In this study, an attempt has been made to estimate the land surface temperature in parts of Chenab basin, Jammu & Kashmir, by using Landsat-7 ETM+, TM, and Terra ASTER satellite data. The current study basically utilizes different surface temperature estimation techniques i.e. Reference Channel Method (RCM), Emissivity Normalization Method (ENM), Classification based and Stefan Boltzmann’s approach to inter-compare various temperature estimation techniques and to examine the influence of the difference in sensor characteristics on the estimated surface temperature on a glacier terrain. For the effect of spatial resolution variation in the determined (LST) values for ETM+ and TM was estimated and for radiometric resolution, effect comparison was carried between the ETM+ and ASTER-derived LST image. Furthermore, an effect of spatial resolution has been quantified and has been evaluated successfully due to the fact that two sensors used for the purpose did not differ much in their characteristics features.

Evidence for a lava lake on Mt. Michael volcano, Saunders Island (South Sandwich Islands) from Landsat, Sentinel-2 and ASTER satellite imagery

Mt. Michael is an active stratovolcano on Saunders Island in the South Sandwich Islands; a remote, oceanic island arc in the southern Atlantic Ocean, bordering the Southern Ocean. The arc contains the only active volcanoes in the South Georgia and South Sandwich Islands British Overseas Territory, yet little is known of their activity. Despite lava lakes being extremely rare with only a few global examples, previous analyses of satellite AVHRR imagery of Mt. Michael in the 1990s showed persistent thermal anomalies not associated with magma overflowing the crater. This suggested the existence of a lava lake inside Mt. Michael's crater. However, their study relied on 1 km resolution imagery, and there have been no long-term investigations to determine if this is a persistent feature.In-situ observations of Mt. Michael are extremely difficult given the location. We used Landsat, Sentinel-2 and ASTER satellite data to monitor activity and detect thermal anomalies within the crater. Persistent volcanic plumes and eruptions were identified throughout the thirty-year period studied. On all 15 occasions that a suitable satellite image was available a thermal anomaly within the crater was detected in the high transmissivity shortwave infrared bands (SWIR) centred on 1.65 μm and 2.2 μm. Pixel-integrated surface temperatures over the crater floor yield temperatures of 284–419 °C; comparable to lava lakes elsewhere. Unmixing these temperatures using the dual-band method reveals a molten lava component at basaltic temperatures (989–1279 °C) among a cooler crust. This is the first evidence for a lava lake within Mt. Michael from data that can resolve the crater floor, and the first evidence for magmatic temperatures. As thermal anomalies were detected in all images showing the crater, we suggest that the lava lake is a common and persistent feature.

Accuracy Assessment of Digital Elevation Model (DEM) Data Obtained from ASTER Satellite in Flat Land

It is important to investigate the accuracy of Digital Elevation Models (DEMs) because of their crucial impact on all engineering and scientific disciplines. Photogrammetry, traditional surveying, remote sensing systems and satellite whole DEMs output methods. In this paper include the DEM data produced by the ASTER satellite (Band near-infrared wavelength region from 0.78 to 0.86 μm), where tested and evaluation DEM data for an area of 100 square kilometers in Al-Shtra city. The technique used to evaluate was twofold: first method was to use statistical methods; second method is to take advantage of applied linear transformation equation to detect the gap between Z-DEM and Z-Global Navigation Satellite System (GNSS) (which represents reality (. The result of a root means square error (RMSE) is 5.087m, where it was calculated based on the observed data in the field using GNSS. And standard deviation error (SDT err) was 5.088 m, while after applied linear transformation equation the RMSE reduction to about 80%, which indicates a large bias between the Z-DEM and Z-GPS.