Shuttle Radar Topography Mission Images Research Articles

THE CONTRIBUTION OF REMOTE SENSING AND AEROMAGNETISM TO GOLD PROSPECTING: THE CASE OF THE MEIGANGA ZONE, CAMEROON

In order to optimize gold prospecting in the Meiganga zone located in the Adamaoua region of Cameroon, aeromagnetic and remote sensing prospecting was carried out in the eastern and southern parts. The remote sensing approach on a Landsat 8 OLI/TIRS image highlighted areas of maximum gold concentration. Thus, ferric ion bearing minerals are located in the North-West, silicate minerals bearing ferrous ions are in the Centre while clay minerals are in the North-East and East. The principal component analysis revealed important structural information. The PCA Spatial Map (PC1, PC2, PC3) showed the plutonic formations composed of anatexis and anatexis granites, vegetation cover (at the date of image acquisition: February 22, 2019), areas of permanent water circulation or accumulation, and metamorphic and sedimentary formations namely gneisses, quartzites, schists and superficial clay formations. A Landsat SRTM (Shuttle Radar Topography Mission) image was also used to enhance the lineaments through the Sobel filter to highlight the geomorphological (cliffs, valleys, ...) and topographic (river network, ridge and drainage segment) structures. The aeromagnetic approach was also important. The study of the modified magnetic field (CM) showed 4 ranges: very high, high, medium and low. The Total Magnetic Anomalies (TMI) of the area are subdivided into 2 ranges large positive anomalies (221.1-103.0 nT) located in the lower part of NE-SW orientation, small positive anomalies (103.0-(-)89.7 nT) located in the upper part of NE-SW orientation. The reduced total magnetic anomaly at the equator shows a fairly similar distribution to the total magnetic anomaly with the large positive anomalies in almost the entire lower part. Superimposed on the geological map, Neoproterozoic pre- to syn-tectonic granitoids (C) are superimposed on the large positive anomalies and Neoproterozoic conglomerates, quartzites, sedimentary shales and volcanosedimentary rocks (A) and Neoproterozoic syn-tectonic granitoids (B) are superimposed on the large and small positive anomalies. The grid of the reduced residual equatorial anomaly (ARRE) confirms that the local geology is strongly magnetic (gneiss and quartzite). The filters of the derivatives allowed to establish a map of magnetic lineaments of major orientation N045° and minor orientation N130°. The horizontal gadient superimposed on the local maxima showed the presence of deep structures oriented NE-SW. The analytical signal superimposed on the local maxima highlights the metamorphic basement consisting of rocks with strong magnetism. The application of Euler deconvolution localizes the depth of the sources of linear anomalies.

Application of remote sensing in mapping hydrothermally altered zones in a highly vegetative area - A case study of Lolgorien, Narok County, Kenya

Objective: To map areas of possible hydrothermal alteration using remote sensing technology; To map geological structures controlling mineralisation using remote sensing; To carryout field mapping to ground truth the features identified by remote sensed data. Methods: Landsat 8 Operational Land Imager (OLI) and Shuttle Radar Topography Mission (SRTM) remote sensed images were downloaded from USGS website. Landsat images were processed using band ratios, band composites, principal component analysis techniques in ArcGIS to map areas of possible hydrothermal alteration. SRTM image was analysed using hillshade analysis technique in ArcGIS to map geological structural features controlling mineralisation. Findings: The study found that in several areas especially Southern, South Eastern, Central and North Western part of Lolgorien, there is a possibility of hydrothermal alteration as spectral signatures associated with iron oxide and clay minerals were identified. It was also found that areas with possibility of hydrothermal alteration are also associated with relatively large number of lineaments. It was also found that Southern and South-Eastern part of Lolgorien are also associated with numerous artisanal mines proving the fact that indeed gold mineralisation may be found in these places. However, due to thick vegetation cover, mapping of different types of lithological units found in Lolgorien was not possible. Novelty/Application: The application of remote sensed technology helped in identification of new areas of possible mineralisation such as Central and North-Western parts of Lolgorien which despite having similar geological properties (in terms of lineament density and hydrothermal alteration) have never been exploited for gold or other minerals. Keywords: Hydrothermal alteration; Landsat 8 (OLI); SRTM; Iron oxide; clay minerals; remote sensing

ANÁLISE MORFOMÉTRICA E DO USO DA TERRA DA BACIA HIDROGRÁFICA DO CÓRREGO DA ONÇA, PRESIDENTE PRUDENTE- SP

O presente trabalho visa analisar as características morfométricas e do uso da terra na bacia hidrográfica do córrego da Onça, no município de Presidente Prudente- SP, como subsídio ao planejamento ambiental da área em questão. O estudo parte do pressuposto teórico metodológico exposto por Christofoletti (1980), sendo analisados dados referentes ás características morfométricas: linear, areal e hipsométricas da bacia e ainda de suas relações com u uso da terra Os dados base foram extraídos de imagens Shuttle Radar Topography Mission- SRTM, os quais foram processados nos softwares Arc Gis 10.3 e Google Earth, e então, calculados os valores morfométricos, já o mapeamento do uso da terra foi realizado com o uso de imagens de satélite Landsat 7 e 8. A partir dos resultados quantitativos obtidos, a bacia hidrográfica do córrego da Onça foi classifica como de drenagem dendrítica, possuindo hierarquia de drenagem de 4ª ordem. Sua classificação como retangular, de forma alongada, lhe concede certa estabilidade quanto ao risco de cheias, considerando sua média de precipitação anual, sem eventos extremos. A baixa densidade de drenagem e o médio índice de rugosidade do relevo reforçam o caráter de estabilidade da bacia à picos de cheias, entretanto, a predominância de solos suscetíveis a erosão, além do processo de ocupação inadequada da área, demonstram a necessidade de procedimentos de uso e manejo da terra de modo sustentável. Dessa forma a metodologia aplicada e os resultados obtidos têm se mostrado importantes como ferramenta ao planejamento ambiental e consequentemente na atenuação de impactos ambientais adversos.

The Fractal Geometry of the River Network and Neotectonics of South Sikhote-Alin

The proposed complex Parameter of River Network Self-similarity (PRNS), which is a combination of the exponents in the equations for distribution of channel lengths, the fractal dimension of channels, and the fractal dimension of points of change of the order of the channel, matches neotectonic movements more accurately. A comprehensive analysis of the self-similarity of the southern Sikhote-Alin River network model derived from the Digital Elevation Model (DEM) based on the Shuttle Radar Topography Mission image (SRTM) has been performed. Comparison of the results of morphostructural and fractal analyses showed the good consistency of these two methods. The relative PRNS maxima coincide with areas with the largest amplitude of ascending neotectonic movements (increment of relief), while the minima coincide with the areas either with the lowest increment of relief or with greatest erosion rates. Most of the crustal earthquakes are confined to the boundaries between PRNS relative maxima and minima, that is, uplifts are surrounded by seismic areas, which is due to the block nature of neotectonic vertical movements.

Estimating Mangrove Above-Ground Biomass Loss Due to Deforestation in Malaysian Northern Borneo between 2000 and 2015 Using SRTM and Landsat Images

Mangrove forests are highly productive ecosystems and play an important role in the global carbon cycle. We used Shuttle Radar Topography Mission (SRTM) elevation data to estimate mangrove above-ground biomass (AGB) in Sabah, Malaysian northern Borneo. We developed a tree-level approach to deal with the substantial temporal discrepancy between the SRTM data and the mangrove’s field measurements. We predicted the annual growth of diameter at breast height and adjusted the field measurements to the SRTM data acquisition year to estimate the field AGB. A canopy height model (CHM) was derived by correcting the SRTM data with ground elevation. Regression analyses between the estimated AGB and SRTM CHM produced an estimation model (R2: 0.61) with a root mean square error (RMSE) of 8.24 Mg ha−1 (RMSE%: 5.47). We then quantified the mangrove forest loss based on supervised classification of multitemporal Landsat images. More than 25,000 ha of mangrove forest had disappeared between 2000 and 2015. This has resulted in a significant decrease of about 3.96 million Mg of mangrove AGB in Sabah during the study period. As SRTM elevation data has a near-global coverage, this approach can be used to map the historical AGB of mangroves, especially in Southeast Asia, to promote mangrove carbon stock conservation.

Surface and Subsurface Fracture Zones Modeling Using Automatic Lineament Analysis and Geostatistical Method, with Case Study of Wayang Windu Geothermal Field, West Java, Indonesia

Geological structures such as faults and fractures in a geothermal prospect area might be an indication of a permeable zone for geothermal fluids through fractures that appear inside the rocks. Such geological structures can be identified by lineaments in satellite images and aerial photographs. In this study, we determine the effect of pixel size on the results of automatic lineament extraction and examine the relationship between lineaments at the Wayang Windu geothermal field (WWGF) and nearby geothermal areas, automated lineament results which were extracted from digital elevation models (DEMs) with pixel sizes of 0.5 m, 1 m, 2 m, 3 m, 4 m, 5 m, 10 m, 15 m, and 20 m based on aerial photographs, DEM Nasional (DEMNAS) images, and Shuttle Radar Topography Mission (SRTM) images. Under similar parameters, larger pixel sizes revealed fewer and longer lineaments than smaller pixel sizes. The type of image (i.e., satellite images or aerial photographs) used for lineament extraction did not affect the results. Based on lineament density maps, the lineaments from images with smaller pixels had a wider distribution area than those with larger pixels. Surface geothermal manifestations, such as hot springs, showed good correlation with lineaments found in images with smaller pixel sizes (≤ 5m), which were found in moderate to high lineament density zones. Based on the lineaments extracted from SRTM images, each geothermal field in southern Bandung (Patuha, WWGF, Darajat, Kamojang) had a local geological structure that greatly correlated with the lineament extraction results. All of the lineaments in the geothermal fields were primarily oriented in the NE–SW direction (i.e., N65°E for Patuha, N51°E for WWGF, N57°E for Darajat, and N24°E for Kamojang). Subsurface fracture zone modeling was conducted at WWGF to estimate the permeability zones based on the fracture density from production well data using the Ordinary Kriging (geostatistical) method. The results revealed the direction of subsurface fracture dips and strikes as well as the relationship between subsurface fracture geometries and surface lineament structures. In general, the subsurface fracture zones featured strikes in a NE–SW direction, with dip angles ranging from 74° to 85° and fracture density ranging from 36 to 43 fractures per 10 m. Additionally, the fracture density linearly corresponded to the depth of wellpads. Compared to the surface lineament extraction map, the majority of lineaments were in the NE–SW direction, similar to the major strike of the subsurface fracture zones.

Potential tsunami risk assessment to the city of Alexandria, Egypt.

Tsunami extreme events present a highly significant hazard and considerable risk to the coastal communities. The continued occurrence of tsunami incidents, together with population growth, increases the risk in coastal communities. Two known catastrophic historic tsunamis in Alexandria occurred in the years 365 and 1303AD, with reported wave heights of 1m and 2.9m, respectively. Approximately 5000 people lost their lives and 50,000 homes were destroyed in the city after the earthquake in 365. The 1303 tsunami destroyed the great lighthouse of Alexandria, one of the seven wonders of the ancient world. In order to avoid such events in the future, a detailed knowledge about the tsunami phenomenon and its potential risk is needed. In this paper, the vulnerability and risk to the city of Alexandria will be examined by remote sensing and GIS techniques considering three scenarios. Methodology used depends on building a comprehensive GIS in addition to recent satellite images. After digitizing raster data, it was then stored into a vector format. A digital parcel map was created; attributes (like distance to shore line, elevation, land use/cover, and population) for each polygon were added. Using the Shuttle Radar Topography Mission images, a digital elevation model was created, to test all the tsunami scenarios (based on 5m, 9m, and 20m wave's height). Finally, vulnerability analysis including physical as well as social and economic constraints was executed for the determination of the vulnerability level of elements. Results indicated that Alexandria city is highly vulnerable to tsunami hazard. Very high risk covers the biggest portion of the area in Alexandria (49.16% and 58.71%), followed by high risk (30% and 28.41%), medium risk (13.61% and 7.76%), and low and very low risk (20.82% and 12.88%).

Identification of depositional landforms in environment of confluence of the Branco and Grande rivers, west region of Bahia State (Brazil): by trend surface

ABSTRACTThe geomorphological understanding may lead to the evolution understanding and the processes that characterize the fluvial view at the Quaternary. Changes that happened in the fluvial systems are registered at the terraces and fluvial areas. In this way, the confluence stretch of the Branco and Grande rivers has paleochannels, abandoned meanders and lakes that denote the evolution of both channels. Therefore, this study aims to understand how these geomorphologies are placed in the area using as a resource provided by the remote sensing. It was used then the Shuttle Radar Topography Mission image in order to apply the trend surface model, which shows the light flotation of the area, in other words, positive values – high spots in the relief, and negative values – low spots. Through this observation, it was possible to identify the terraces and the areas of the low plain. The results were also described by the morphostratigraphic analysis that is important in order to validate the data applied by the geoprocessing analysis. Besides, the data inferred in the elaboration of a morphologies base chat placed in the fluvial portion.

DINÂMICA E CARACTERIZAÇÃO FLUVIAL DA BACIA DO RIACHO GRANDE, SERRA TALHADA – PE: ABORDAGEM DA CONECTIVIDADE DA PAISAGEM

doi: 10.12957/geouerj.2016.15456 The water scarcity problem in Pernambuco semiarid encourages scientific research that aim to understanding the behavior of integrated semiarid river systems, relating the physical system of basins to antropic systems. This perspective the present study characterized the fluvial dynamics of Riacho Grande basin, located in the Sertao de Pernambuco region, applying an integrated manner the proposal of landscape connectivity and rivers styles, generating useful background information for management of water resources at the local scale. Therefore, it was identified the land uses, from data obtained in the field work with the support of GPS and use of QuickBird and SRTM (Shuttle Radar Topography Mission) images; understanding its dynamics and relating them to water infiltration capacity retained in the soil and runoff. The calculation of runoff flow volume was performed by using data extracted from the Agritempo data platform, for the period 1993-2012, through water balance daily sequential. It was identified in the Riacho Grande basin 3 main classes of land use, associated, with the texture and soil structure, the volume of runoff flow in the area. The analysis also identified the drainage impediments, able to retain the drained flow making it impossible them from reaching the network channels. Between main transmission impediments was identified a large number of dams, roads paved and unpaved and floodplains. Finally, the characterization of the channels from the primary analysis of river styles.

Mass loss from glaciers in the Chinese Altai Mountains between 1959 and 2008 revealed based on historical maps, SRTM, and ASTER images

Mass loss of glaciers in the Chinese Altai was detected using geodetic methods based on topographical maps (1959), the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) (2000), and the Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) stereo images (2008). The results indicate that a continued and accelerating shrinkage has occurred in the Chinese Altai Mountains during the last 50 years, with mass deficits of 0.43 ± 0.02 and 0.54 ± 0.13 m a−1 water equivalent (w.e.) during the periods 1959–1999 and 1999–2008, respectively. Overall, the Chinese Altai Mountains have lost 7.06 ± 0.44 km3 in ice volume (equivalent to −0.43 ± 0.03 m a−1 w.e.) from 1959–2008. The spatial heterogeneity in mass loss was potentially affected by comprehensive changes in temperature and precipitation, and had a substantial correlation with glacier size and topographic settings. Comparison shows that in the Chinese Altai Mountains glaciers have experienced a more rapid mass loss than those in the Tianshan and northwestern Tibetan Plateau (TP), and the mass balance of glaciers was slightly less negative relative to those in the Russian Altai, Himalaya, and southern TP.

Correlation of lineaments (magnetic and topographic) and Phanerozoic brittle structures with Precambrian shear zones from the basement of the Paraná Basin, Santa Catarina State, Brazil

The objective of this article is to characterize the main directions of structures of the Parana Basin, to define the relation of deep structures (magnetic lineaments) with superficial structures [lineaments obtained over Shuttle Radar Topography Mission (SRTM) images] and analyse reactivated structures in the Phanerozoic. The magnetic lineaments at the Eastern edge of the Parana Basin, in the central-southern region of the Santa Catarina State, show a main orientation pattern NE-SW and secondarily NNE-SSW. The NE-SW pattern reflects a framework of the ductile structures of the Santa Catarina Shield that continues in the substratum of the basin. The structural NNE pattern appears in the south of the Major Gercino Shear Zone (MGSZ) and the NE pattern appears in the north of this structure. The data obtained shows that the structural NE-SW pattern of the basin, present in the MGSZ and Itajai-Perimbo Shear Zone as well as in the Tijucas Terrain (Brusque Metamorphic Complex) in Santa Catarina, clearly extends underneath the Gondwanic sequence of the Parana Basin in the region. Among the products obtained by geophysical data processing in this work, what propitiated the best definition and distinction of the magnetic structures was the tilt angle of the total horizontal gradient (TAHG) method. However, the great flight line spacing of one of the geophysical projects (7 km) makes the identification of small magnetic structures difficult, particularly in N-S and E-W directions. Such structural directions are referred to in the previous works and were confirmed through the interpretation of SRTM images and studies of brittle structures in the field.

ESTUDO COMPARATIVO ENTRE IMAGENS SRTM E CARTAS DO EXÉRCITO PARA ESTUDO PLANO ALTIMÉTRICO EM BACIAS HIDROGRÁFICAS

The mapping of the Brazilian territory does not have full coverage. One way to solve this gap is through the use of satellite images. One of these products are the images SRTM (Shuttle Radar Topography Mission), which have very important information for environmental studies. Yet still lacks theoretical foundation regarding the reliability of this basemap. Thus, this study aims to compare the information on SRTM altimetry in the images with the information contained in topographic maps made by the brazilian army in the 70s. Was studied the watershed Arroio do Veado located between the cities of Santa Maria and Silveira Martins, in the transition zone between Central Depression and Serra Geral Plateau, in the Rio Grande do Sul state, southern Brazil. Using the ArcGIS software were extracted contour lines that served as bases and then generated the digital terrain model and slope map of the basin. It was observed that the data resulting from the two cartographic databases are very similar using a map scale 1: 50 000 applied to watersheds with one area circa the 4,000 hectares. Was concluded, with these conditions may be used SRTM images, useful, handling and wide coverage in Brazil.

Comparative evaluation of horizontal accuracy of elevations of selected ground control points from ASTER and SRTM DEM with respect to CARTOSAT-1 DEM: a case study of Shahjahanpur district, Uttar Pradesh, India

Digital elevation model (DEM) data of Shuttle Radar Topography Mission (SRTM) are distributed at a horizontal resolution of 90 m (30 m only for US) for the world, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEM data provide 30 m horizontal resolution, while CARTOSAT-1 (IRS-P5) gives 2.6 m horizontal resolution for global coverage. SRTM and ASTER data are available freely but 2.6 m CARTOSAT-1 data are costly. Hence, through this study, we found out a horizontal accuracy for selected ground control points (GCPs) from SRTM and ASTER with respect to CARTOSAT-1 DEM to implement this result (observed from horizontal accuracy) for those areas where the 2.6-m horizontal resolution data are not available. In addition to this, the present study helps in providing a benchmark against which the future DEM products (with horizontal resolution less than CARTOSAT-1) with respect to CARTOSAT-1 DEM can be evaluated. The original SRTM image contained voids that were represented digitally as −140; such voids were initially filled using the measured values of elevation for obtaining accurate DEM. Horizontal accuracy analysis between SRTM- and ASTER-derived DEMs with respect to CARTOSAT-1 (IRS-P5) DEM allowed a qualitative assessment of the horizontal component of the error, and the appropriable statistical measures were used to estimate their horizontal accuracies. The horizontal accuracy for ASTER and SRTM DEM with respect to CARTOSAT-1 were evaluated using the root mean square error (RMSE) and relative root mean square error (R-RMSE). The results from this study revealed that the average RMSE of 20 selected GCPs was 2.17 for SRTM and 2.817 for ASTER, which are also validated using R-RMSE test which proves that SRTM data have good horizontal accuracy than ASTER with respect to CARTOSAT-1 because the average R-RMSE of 20 GCPs was 3.7 × 10−4 and 5.3 × 10−4 for SRTM and ASTER, respectively.

Comparative evaluation of Cartosat-1 and SRTM imageries for digital elevation modelling

Digital Elevation Models (DEM) of a hilly–valley region are prepared using stereo images of Cartosat-1 and Shuttle Radar Topography Mission (SRTM) images. The procedure of ortho-image generation from Cartosat-1 stereo images and the estimation of ground features from ortho-image are elaborated in the paper. Comparison of DEMs prepared from both images is discussed in terms of the quality of ground features detection, hydrological applications and geometrical calculations. It is found that DEM prepared from Cartosat-1 images are more accurate in the valley region and hence it is better suited for hydrological applications. On the contrary, for hilly region, SRTM images produce better DEM. However, if ground control points and Rational Polynomial Coefficients can be obtained in the hilly region, more accurate DEM can be prepared using Cartosat-1 stereo images.

Land Cover Classification of Hail—Saudi Arabia Using Remote Sensing

A set of five satellite images from the Landsat satellite, Moderate Resolution Imaging Spectroradiometer (MODIS) and the Shuttle Radar Topography Mission (SRTM) sensors has been operated to analyze land cover and topography of the Hail region, Saudi Arabia. Image processing techniques included unsupervised classification for clustering four land cover units in the MODIS image, namely: plains, sand dunes, mountains, and cultivated lands. The SRTM image was classified to produce a thematic topographic map with 100 m elevation interval. The normalized difference vegetation index (NDVI) was applied in the Landsat images as a proxy to the change of agricultural land in Hail between 1972 and 2000. Results showed that Hail region occurs at a high plateau. Minimum elevation occurs at its northeastern corner and peaks occur at the southwestern side. The surface area of Hail is estimated at 115,690 km2. The majority of Hail area is represented by plains and sand dunes. Cultivated lands increased from 9500 ha in 1972 to 139,000 ha in 2010.

The impact of misregistration on SRTM and DEM image differences

Image differences between Shuttle Radar Topography Mission (SRTM) data and other Digital Elevation Models (DEMs) are often performed for either accuracy assessment or for estimating vegetation height across the landscape. It has been widely assumed that the effect of sub-pixel misregistration between the two models on resultant image differences is negligible, yet this has not previously been tested in detail. The aim of this study was to determine the impact that various levels of misregistration have on image differences between SRTM and DEMs. First, very accurate image co-registration was performed at two study sites between higher resolution DEMs and SRTM data, and then image differences (SRTM–DEM) were performed after various levels of misregistration were systematically introduced into the SRTM data. It was found that: (1) misregistration caused an erroneous and dominant correlation between elevation difference and aspect across the landscape; (2) the direction of the misregistration defined the direction of this erroneous and systematic elevation difference; (3) for sub-pixel misregistration the error due solely to misregistration was greater than, or equal to the true difference between the two models for substantial proportions of the landscape (e.g., greater than 33% of the area for a half-pixel misregistration); and (4) the strength of the erroneous relationship with aspect was enhanced by steeper terrain. Spatial comparisons of DEMs were found to be sensitive to even sub-pixel misregistration between the two models, which resulted in a strong erroneous correlation with aspect. This misregistration induced correlation with aspect is not likely specific to SRTM data only; we expect it to be a generic relationship present in any DEM image difference analysis.