SRTM Digital Elevation Model Research Articles

A comparative study of automatic drainage network extraction using ASTER GDEM, SRTM DEM and Cartosat-1 DEM in parts of Kosi basin, Bihar, India

The present study attempts to evaluate and compare the different open source 30 m resolution spaceborne digital elevation models (DEM) based on their automatic drainage network extraction efficiency. Digital elevation models from three satellite data i.e., ASTER GDEM, SRTM DEM and Cartosat-1 DEM have been employed for the extraction of stream networks. The study was carried out in the watershed situated in parts of Saharsa, Madhepura and Supaul district along the river Kosi, Bihar. Analysis was performed in ArcMap10.3 software wherein, three different thresholds of flow accumulation were used to assess the comparative evaluation. Morphometric parameters were analysed using geographical information system (GIS). The evaluation and quantification of morphometric parameters provide an effective basis for the comparison of extracted stream networks based on hydrological and morphological characteristics. Comparison and selection of appropriate DEM products for quantitative and qualitative hydrological studies are lacking in the present study area. This comparative study is helpful in selecting suitable DEM products out of the three commonly available free datasets for delineating streams in this floodplain with little variation in elevation and slope. The findings can be beneficial for using appropriate DEM data in various morphometric, prioritization, management and other GIS applications in parts of Kosi basin.

Detection of Crustal Uplift Deformation in Response to Glacier Wastage in Southern Patagonia

The Southern Patagonian Icefield (SPI) is the largest continuous ice mass in the Southern Hemisphere outside Antarctica. It has been shrinking since the Little Ice Age (LIA) period, with increasing rates in recent years. An uplift of crustal deformation in response to this deglaciation process has been expected. The goal of this investigation is to analyze the crustal deformation caused by ice retreat using time-series data from continuous GPS stations (2015–2020) in the northern area of the SPI. For this purpose, we installed two continuous GPS stations on rocky nunataks of the SPI (the GRCS near Greve glacier and the GBCS close by Cerro Gorra Blanca). In addition, ice elevation changes (2000–2019) were analyzed by the co-registration of the SRTM digital elevation model and ICESat elevation data points. The results of the vertical components are positive (36.55 ± 2.58 mm a−1), with a maximum at GBCS, indicating the highest rate of crustal uplift ever continuously recorded in Patagonia; in addition, the mean horizontal velocities reached 11.7 mm a−1 with an azimuth of 43°. The negative ice elevation changes detected in the region have also accelerated in the recent two decades, with a median Δh (elevation change) of −3.36 ± 0.01 m a−1 in the ablation zone. The seasonality of the GPS signals was contrasted with the water levels of the main Patagonian lakes around the SPI, detecting a complex interplay between them. Hence, the study sheds light on the knowledge of the crustal uplift as evidence of the wastage experienced by the SPI glaciers.

Flood Depth Estimation in Agricultural Lands From L and C-Band Synthetic Aperture Radar Images and Digital Elevation Model

Flood depth is one of the important attributes in damage assessment especially in areas where agro-based activities takes place. Assessing impacted region turns out to be exceptionally difficult in the case of low-lying catchments with arable lands, which inundates due to extreme precipitation and flood modelling becomes impossible. Under these circumstances, SAR derived flood maps are valuable in removing different constraints related to flood modelling with high degree of profundity. Depth estimation from non-contact based methods requires, flood boundary as a primary input. However, detecting flood depth in emerging vegetation poses a complex challenge in terms of boundary estimation due to composite signatures that are manifested on SAR data. In this paper, a new approach is proposed to extract flood boundaries by fusing SAR data of two different frequencies, which are sensitive to water level changes. In the first step, wavelet fusion is applied to combine L- and C- band SAR data followed by Otsu’s segmentation method to extract varying levels of flood boundaries. In the second step, SRTM Digital Elevation Model (DEM) with 30m horizontal resolution is used on each boundary for statistical analysis based on which water surface levels are extracted. In the final step, depth levels are calculated from the water surface elevation and DEM. Floodwater Depth Estimation tool (FwDET) derived depth measurements are used to calibrate the statistical thresholds for derived flood depths. The study carried out on 2016 Assam flood event shows maximum flood depth of 1.56 meters in the selected study area and the results are verified with evidence-based ground truth collections which showed RMSE error of 0.25 meters from the measured values.

Satellite Image Processing by Python and R Using Landsat 9 OLI/TIRS and SRTM DEM Data on Côte d’Ivoire, West Africa

In this paper, we propose an advanced scripting approach using Python and R for satellite image processing and modelling terrain in Côte d'Ivoire, West Africa. Data include Landsat 9 OLI/TIRS C2 L1 and the SRTM digital elevation model (DEM). The EarthPy library of Python and 'raster' and 'terra' packages of R are used as tools for data processing. The methodology includes computing vegetation indices to derive information on vegetation coverage and terrain modelling. Four vegetation indices were computed and visualised using R: the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index 2 (EVI2), Soil-Adjusted Vegetation Index (SAVI) and Atmospherically Resistant Vegetation Index 2 (ARVI2). The SAVI index is demonstrated to be more suitable and better adjusted to the vegetation analysis, which is beneficial for agricultural monitoring in Côte d'Ivoire. The terrain analysis is performed using Python and includes slope, aspect, hillshade and relief modelling with changed parameters for the sun azimuth and angle. The vegetation pattern in Côte d'Ivoire is heterogeneous, which reflects the complexity of the terrain structure. Therefore, the terrain and vegetation data modelling is aimed at the analysis of the relationship between the regional topography and environmental setting in the study area. The upscaled mapping is performed as regional environmental analysis of the Yamoussoukro surroundings and local topographic modelling of the Kossou Lake. The algorithms of the data processing include image resampling, band composition, statistical analysis and map algebra used for calculation of the vegetation indices in Côte d'Ivoire. This study demonstrates the effective application of the advanced programming algorithms in Python and R for satellite image processing.

Thrust Sequence in the Western Fold-and-Thrust Belt of the Indo-Burma Range Determined from Fluvial Profile Analysis and Dynamic Landform Modeling

The Indo-Burma Range (IBR) is a forearc fold-and-thrust belt that evolved under oblique convergence between India and the Burma microplate. IBR convergence is understood to be absorbed by north-striking dextral strike-slip faults and a west-propagating fold-and-thrust belt (FTB), however, the FTB spatio-temporal evolution and its seismic potential remain an area of active research. This study combines geomorphic and kinematic analyses to explore simple thrust-propagation scenarios for the IBR outer belt. We use a 30 × 30 m SRTM digital elevation model and investigate four river basins in the outer belt by extracting antecedent tributaries that cross young, NS-striking antiforms and analyzing their fluvial profiles. To help interpret the profiles, we explore first-order surface dynamics models based on four possible scenarios of the FTB evolution, including cases of sequential propagation, partial reactivation, continuous reactivation, and synchronous thrusting. We compare our modeled stream profiles and knickpoint locations to the IBR river profiles. The shapes of the profiles between knickpoints are most similar to model results of sequential propagation and continuous reactivation of older structures. This suggests that as younger antiforms start rising in the west, the eastern folds are still active. The stream profiles of the synchronous thrusting model also demonstrate similar shapes with the IBR tributaries crossing the westernmost antiforms. Results from a numerical FTB experiment with a weak detachment overlain by stronger sediment layers predicts cyclic periods of frontal ramp propagation and fault reactivation. Overall, our findings suggest alternating periods of FTB propagation and fault reactivation in the outer belt, implying that earthquakes may alternately rupture to the deformation front and/or along splay thrusts in the wedge. The shapes of antecedent stream profiles crossing active FTB may record information about the sequence of ramp propagation and can be studied to inform the kinematic evolution of FTB.

Impact of climate change on spatiotemporal variations in the vegetation cover and hydrology of district Nowshera

Abstract This research seeks to validate climate change in the district of Nowshera, as well as its impact on NDVI (vegetation) and hydrological events such as monsoon rains. Modified Mann-Kendall and Sen's statistics were used to examine climate parameters. Using climate factors and MODIS NDVI (Normalized Difference Vegetation Index) data, regression analysis was used to study a 20-year (2001–2020) spatiotemporal climate-vegetation relationship. Landsat 5 and 7 NDWI (Normalized Difference Water Index) data, as well as SRTM DEM (Digital Elevation Model) data, were used to map extreme weather events such as floods caused by climate change. For mapping and data processing, ArcGIS and R tools were used. The findings revealed significant trends in climate parameters, which has led to climate change in the area, affecting NDVI and water cycles. The NDVI showed a generally good trend, however some places were damaged. Monsoon rain patterns and rates have been substantially disrupted, resulting in flash and fluvial floods. The risk of future floods owing to the Kabul and Indus rivers was shown through watershed delineation, which is compounded by climate change and anthropogenic activities. It is advised that government officials and policymakers establish climate change mitigation plans for regional sustainable development and vegetation restoration.

Quantifying the impacts of DEM uncertainty on clear-sky surface shortwave radiation estimation in typical mountainous areas

Accurate estimation of shortwave radiation in mountains will advance our knowledge of climate change effects, especially on mountain ecosystems. Recently, some approaches have been developed to estimate shortwave radiation parameters in mountains with satellite data, but few attempts were made to understand the impacts of digital elevation model (DEM) uncertainty on estimates. Our study investigates such impacts quantitatively in clear-sky conditions at multiple spatial and temporal scales (30–3000 m, instantaneous to daily). We employed a retrieval algorithm to estimate instantaneous and daily mean clear-sky downward shortwave radiation (DSR) and net shortwave radiation (NSR), as a proxy for our evaluation. The accuracy of our method based on accurate terrain data was verified against in-situ measurements with root-mean-square errors (RMSEs) of 65.9 W/m2 and 65.1 W/m2 for instantaneous DSR and NSR, and 21.2 W/m2 and 22.5 W/m2 for daily mean values, respectively. When using satellite DEM products, the DSR estimation uncertainty could increase by 64.0% for instantaneous values and 46.2% for daily mean values. Using AW3D30 and SRTM DEMs for DSR estimation led to a maximum difference of 16.8% (103.6 W/m2) and 13.0% (25.8W/m2) on instantaneous and daily mean values, respectively. That estimation difference of shortwave radiation decreased with an increase in spatial scale, with RMS deviation lower than 2% for spatial resolution beyond 3000 m. In addition, the evaluation of introducing random errors into AW3D30 DEM showed that the shortwave radiation uncertainty caused by DEM may exceed the algorithm uncertainty itself with DEM mean absolute error (MAE) equaling about 5.0 m. Considering the current DEM accuracy, the impacts of DEM errors on shortwave radiation in mountains cannot be ignored. This study emphasizes the potential impacts of DEM uncertainty on surface shortwave radiation estimation, which is crucial in using satellite-derived datasets for energy balance calculation and climate change applications in mountains.

Route Plans for UAV Aerial Surveys according to Different DEMs in Complex Mountainous Surroundings: A Case Study in the Zheduoshan Mountains, China

Accurate and error-free digital elevation model (DEM) data are a basic guarantee for the safe flight of unmanned aerial vehicles (UAVs) during surveys in the wild, especially in moun-tainous areas with large topographic undulations. Existing free and open-source DEM data gen-erally cover large areas, with relatively high spatial resolutions (~90, 30, and even 12.5 m), but they do not have the advantage of timeliness and cannot accurately reflect current and up-to-date topographical information in the survey area. UAV pre-scanning missions can provide highly accurate and recent terrain data as a reference for UAV route planning and ensure security for subsequent aerial survey missions; however, they are time consuming. In addition, being limited to the electric charge of the UAV, pre-scanning increases the human, financial, and time consumption of field missions, and it is not applicable for field aerial survey missions in reality, unless otherwise specified, especially in harsh environments. In this paper, we used interferometric synthetic aper-ture radar (InSAR) technology to process Sentinel-1a data to obtain the DEMs of the survey area, which were used for route planning, and other free and open-source DEMs were also used for flightline plans. The digital surface models (DSMs) were obtained from the structure of the UAV pre-scan mission images, applying structure for motion (SfM) technology as the elevation reference. Comparing the errors between the InSAR-derived DEMs and the four open-source DEMs based on the reference DSM to analyze the practicability of flight route planning, the results showed that among the four DEMs, the SRTM DEM with a spatial resolution of 30 m performed best, which was considered as the first reference for UAV route plans when the survey area in complex mountainous regions is covered with a poor or inoperative network. The InSAR-derived DEMs from the Sentinel-1 images have great potential value for UAV flight planning, with a large perpendicular baseline and short temporal baseline. This work quantitatively analyzed the errors among the different DEMs and provided a discussion regarding UAV flightline plans based on external DEMs. This can not only effectively reduce the manpower, materials, and time consumption of field operations, improving the efficiency of UAV survey tasks, but it also broadens the use of InSAR technology. Furthermore, with the launch of high-resolution SAR satellites, InSAR-derived DEMs with high spatial and temporal resolutions provide an optimistic and credible strategy for UAV route planning with small errors.

Quality Assessment of TanDEM-X DEM 12m Using GNSS-RTK and Airborne IFSAR DEM: A Case Study of Tuba Island, Langkawi

Digital elevation models (DEMs) have been recognized as a primary spatial dataset and essential for numerous scientific applications. The advent of TerraSAR-X for digital elevation measurement (TanDEM-X) has opened a new potential to obtain an accurate DEM. Nowadays, the demand/use of TanDEM-X DEM in scientific applications has become increasingly popular as it offers an alternative to the widely used DEMs: ASTER and SRTM DEM. Although many researches have been conducted to assess the performance of the TanDEM-X DEM at different locations in the world, however, only several multi-regional studies have been performed in Malaysian region. Currently, there are two types of DEMs published by DLR i.e., non-open access (12m and 30m resolution) and open access (90m resolution). In this article, the accuracy of TanDEM-X 12m has been comprehensively and systematically evaluated using 1284 GNSS-RTK control points over Tuba Island and airborne IFSAR-DEM as a reference height. Besides, four available global DEMs: TanDEM-X 90m, AW3D30 DEM, SRTM DEM, and ASTER DEM have also been evaluated to identify the accuracy of TanDEM-X DEM 12m. Based on the evaluation using GNSS-RTK points, TanDEM-X 12m exhibits the highest accuracy with an RMSE of ±1.553m. Unexpectedly, AW3D30 DEM shows a better performance compared to TanDEM-X 90m with RMSE of ±1.964m, followed by SRTM DEM with RMSE of ±3.296m Meanwhile, ASTER DEM exhibits the lowest accuracy with RMSE of ±4.100m The comparison of TanDEM-X 12m and the well-known DEM, SRTM DEM with airborne IFSAR-DEM shows the opposite results. Based on the topographic profile at flat and forest area, the SRTM-DEM exhibits better accuracy than TanDEM-X 12m

The Spatiotemporal Change of Xiao Qaidam Lake from 1990 to 2020 and Its Potential Hazards

In the climatic context of warming and humidification in Northwest China, most lakes in Qinghai Province experienced a rising water level and expanding area, inundating grassland and infrastructure around lakes, and even extreme events such as lake outburst floods. Based on Landsat TM/ETM+/OLI and GF PMS images, lake water level data, SRTM digital elevation model (DEM), GlobeLand30 and meteorological data used in this study, we analyzed the area change of Xiao Qaidam Lake in Qaidam Basin with its causes, factors and potential hazards. The results show that the area of Xiao Qaidam Lake increased by 60.42 km2 (85.43%) from 1990 to 2020, which can be roughly divided into three stages: fluctuation decline in 1990–2001 (−1.89 km2/a); relatively stable in 2002–2014; and rapid expansion in 2015–2020 (8.54 km2/a). In 2020, the water level and water volume of Xiao Qaidam Lake increased by 3.62 m and 0.39 km3, respectively, compared with 2015, resulting in the inundation of an area of 54.55 km2 of grassland around the lake and a direct threat to the Liuge and Dexiao Expressways. Both the increase in annual precipitation (12.63 mm/10a) and the decrease in potential evapotranspiration (−13.38 mm/10a) since 1990 are the main reasons for the rapid expansion of Xiao Qaidam Lake, and the increasing trend of climate warming and humidification will lead to the continuous expansion of Xiao Qaidam Lake in the next decades. According to the water volume growth rate from 2015 to 2020, it is predicted that by 2024 the area and water level of Xiao Qaidam Lake will reach 154 km2 and 3180 m, respectively, and part of Liuge and Dexiao Expressways will be submerged. Therefore, it is urgent to strengthen the monitoring of Xiao Qaidam Lake and formulate corresponding disaster prevention and reduction measures.

The role of topographic-derived hydrological variables in explaining plant species distributions in Amazonia

ABSTRACT In Amazonian terra-firme non inundated forests, local floristic composition and species occurrence are explained by water availability as determined by topographic conditions. Topographic complexity can render these conditions quite variable across the landscape and the effects on plant ecological responses are difficult to document. We used a set of topographically defined hydrological metrics to evaluate community composition and single-species responses of four plant groups [pteridophytes (ferns and lycophytes), Melastomataceae, palms (Arecaceae) and Zingiberales] to topographic conditions in the middle Juruá River region, in western Brazilian Amazonia. The area spans two geological formations (Içá and Solimões) with contrasting topography. River terraces are also found along the main rivers in the area. Local topographic conditions were approximated by height above the nearest drainage (HAND), slope, and Strahler´s drainage order, all obtained from a SRTM digital elevation model (DEM). Data were analyzed using linear and generalized linear mixed models and regression trees. HAND was most successful in explaining floristic composition for all plant groups, except for Melastomataceae, and was more important in the hilly Içá formation than in the Solimões. Individual occurrences of 57% species were predicted by at least one of the topographic variables, suggesting a marked habitat specialization along topographic gradients. For these species, response models using SRTM-DEM-derived variables gave similar results than models using field-measured topography only. Our results suggest that topographical variables estimated from remote sensing can be used to predict local variation in the structure of plant communities in tropical forests.

Application of Unmanned Aerial Vehicle DEM in flood modeling and comparison with global DEMs: Case study of Atrak River Basin, Iran.

Digital Elevation Models (DEMs) play a significant role in hydraulic modeling and flood risk management. This study initially investigated the effect of Unmanned Aerial Vehicle (UAV) DEM resolutions, ranging from 1m to 30m, on flood characteristics, including the inundation area, mean flow depth, and mean flow velocity. Then, the errors of flood characteristics for global DEMs, comprising ALOS (30m), ASTER (30m), SRTM (30m), and TDX (12m) were quantified using UAV DEM measurements. For these purposes, the HEC-RAS 2D model in steady-state conditions was used to simulate the flood with return periods of 5- to 200 years along 20km reach of Atrak River located in northeastern Iran. Results indicated when UAV DEM resolution decreased from 1m to 30m, inundation area and mean flow depth increased 17.0% (R2=0.94) and 10.2% (R2=0.96) respectively, while mean flow velocity decreased 16.8% (R2=-0.94). Validation of the hydraulic modeling using the modified normalized difference water index demonstrated that the HEC-RAS 2D model in conjunction with UAV DEM simulates the flood with ⁓92% accuracy. Comparing the global DEMs with UAV DEM showed that the root mean square error (RMSE) values of the flow depth for ASTER, SRTM, ALOS, and TDX DEMs were 1.77, 1.12, 1.02, and 0.93m, and the RMSE values of the flow velocity for the same DEMs were 0.81, 0.66, 0.55, and 0.47m/s, respectively. Furthermore, TDX DEM with a 6.15% error in the inundation area was the nearest to UAV measurements. Overall, TDX DEM revealed a better performance in hydraulic modeling of the fluvial flood characteristics. Hence, it is recommended for environments where high-resolution topography data is scarce. The results of this study could potentially serve as a guideline for selecting global DEMs for hydraulic simulations.

Volumetric change analysis of the Cauvery delta topography using radar remote sensing

Geomorphology refers to the study of the Earth’s physical land surface features. Digital Elevation Model (DEM) is a digital imagery where each pixel represents elevation value above or below mean sea level. The availability of DEM allows analysis of landscape morphology and related processes in terms of geomorphometry. DEM of Difference (DoD) techniques are used to estimate the elevation variations and volumetric changes over time. The volumetric change of terrain in the Cauvery delta (CD) for the past two decades is estimated using DoD algorithm by utilizing freely available moderate spatial resolution SRTM, PALSAR and Sentinel 1A DEMs which are derived by radar remote sensing technique. A detailed assessment of individual DEM’s errors and propagating errors into the DoD are estimated using the field elevation points measured by Real-Time Kinematic (RTK) Global Positioning System (GPS). The default errors in the SRTM, PALSAR and Sentinel 1A DEMs are observed with Root Mean Square Error (RMSE) of 3.33, 3.11 and 3.04 m respectively. The erosion and accretion rates determined are 25 and 30 million m3 / decade correspondingly. The total volume of sediment load due to erosion and accretion is 50 and 60 million m3 respectively during 2000–2020. Further the net area affected due to deposition (69 %) is higher than the total area affected due to erosion (30%). This study presents decadal sediment budget and rate of annual change due to erosion/accretion in the CD.

An Assessment of the GEDI Lasers’ Capabilities in Detecting Canopy Tops and Their Penetration in a Densely Vegetated, Tropical Area

The Global Ecosystem Dynamics Investigation (GEDI), specifically designed to measure vertical forest structures, has acquired, since April 2019, more than 35 billion waveforms of Earth’s surface on a nearly global scale. GEDI is equipped with 3 identical 1064 nm lasers with a power of 10 mJ per shot, where 1 laser is split into 2 lasers, resulting in two 5 mJ coverage lasers and two 10 mJ full-power lasers. In this study, we evaluate the potential of GEDI’s four lasers to penetrate through canopies and detect the ground, and their capabilities to detect the top of the canopies over a tropical forest (in French Guiana) characterized by a dense canopy cover and tall trees. The accurate detection of both of these surfaces is the first step in characterizing vertical forest structures. The SRTM Digital Elevation Model (DEM) is used as a reference point for elevations while a canopy height model (CHM), derived from airborne and spaceborne LiDAR data, is used as a reference for canopy heights. In addition, the ground and canopy-top elevations estimated from NASA’s Land, Vegetation, and Ice Sensor (LVIS, 1064 nm full-waveform LiDAR, 5 mJ per shot, ~8 km altitude) are used as a benchmark for comparison with GEDI’s lasers. Results indicate that GEDI’s coverage and full-power lasers, even after the application of a preliminary filter that removes around 50% of acquisitions, tend to underestimate tree heights in densely vegetated, tall forests. Moreover, GEDI’s coverage lasers also exhibited a lower level of performance in comparison to both the full-power lasers and LVIS. Overall, the average estimated maximum canopy heights (RH100) for a CHM greater than 30 m was 24.4 m with the coverage lasers, 32.1 m with the full-power lasers, and 36.7 m with LVIS. The analysis of shots with high-beam sensitivity (sensitivity ≥ 98%) showed that they tend to have a better probability of reaching the ground and have better detection of canopy tops for both GEDI laser types. Nonetheless, GEDI’s coverage lasers still showed an underestimation of canopy heights with an average RH100 of 29.8 m, while for GEDI’s full-power lasers and LVIS, the average RH100 was 35.2 m and 37.7 m, respectively. Finally, the assessment of the acquisition time on the detection of the ground return and the top of the canopies showed that, for the coverage lasers, solar noise could affect the detection of the ground return as acquisitions made during early mornings or late afternoons have more penetration than shots acquired between 8 a.m. and 4 p.m. The effect of acquisition time on the detection of the tops of canopies showed that solar noise slightly affected the coverage lasers. Regarding the full-power lasers, the acquisition time of the shots seem to affect neither the penetration of the lasers, nor the detection of the tops of canopies.

To Study the Hydrological System and Watershed by Using Remote Sensing (RS) and Geographic Information System (GIS) in Kannad Taluka, Aurangabad District, MS, India

The current study in this research focuses on the importance of the digital elevation model (DEM) and satellite images to evaluate and interpret the relative parameters of watersheds in Kannad taluka, Aurangabad district, India. Watersheds in the area were identified and calculated using the SRTM DEM through ARCGIS 10.8 software. Kannad shows a first to fourth-order drainage network which is of dendritic type, which indicates a sign of the structural lack of control and homogeneity of the watersheds in Kannad taluka. The basin’s mean bifurcation ratio is found to be 1.47 which indicates that the drainage network pattern is not much influenced by geological structures. Based on the hydrological assessment on the watershed scale, the present study reveals that the SRTM DEM is the most accurate application compared to other techniques. As visual or manual identification and evaluation are difficult and may not provide a holistic view of watersheds, modern tools of RS and GIS were used to study the watershed of Kannad taluka. There was lack of published reports on watersheds by using the RS and GIS and work undertaken.

The complexities of assessing volcanic hazards along the Cameroon Volcanic Line using spatial distribution of monogenetic volcanoes

Volcanic eruptions represent hazards for local communities and infrastructure. Monogenetic volcanoes (usually) erupt only once, and then volcanic activity moves to another location, making quantitative assessment of eruptive hazards challenging. Spatio-temporal patterns in the occurrence of these eruptions may provide valuable information on locations more likely to host future eruptions within monogenetic volcanic fields. While the eruption histories of many stratovolcanoes along the Cameroon Volcanic Line (CVL) are relatively well studied, only fragmentary data exist on the distribution and timing of this region's extensive monogenetic volcanism (scoria cones, tuff rings, maars). Here, we present for the first time a catalog of monogenetic vents on the CVL. These were identified by their characteristic morphologies using field knowledge, the global SRTM Digital Elevation Model (30 m resolution), and satellite imagery. More than ~1100 scoria cones and 50 maars/tuff rings were identified and divided into eight monogenetic volcanic fields based on the visual assessment of clustering and geological information. Spatial analyses show a large range of areal densities between the volcanic fields from >0.2 km−2 to 0.02 km−2 from the southwest towards the northeast. This finding is in general agreement with previous observations, indicating closely spaced and smaller edifices typical of fissure-fed eruptions on the flanks of Bioko and Mt. Cameroon in the southwest, and a more focused plumbing system resulting in larger edifices of lower spatial density towards the northeast. Spatial patterns were smoothed via kernel density estimates (KDE) using the Summed Asymptotic Mean Squared Error (SAMSE) bandwidth estimator, the results of which may provide an uncertainty range for a first-order hazard assessment of vent opening probability along the CVL. Due to the scarce chronological data and the complex structural controls across the region, it was not possible to estimate the number of vents formed during the same eruptive events. Similarly, the percentage of hidden (buried, eroded) vents could not be assessed with any acceptable statistical certainty. Furthermore, the impact of different approaches (convex hull, minimum area rectangle and ellipse, KDE isopaches) to define volcanic field boundaries on the spatial distribution of vents was tested. While the KDE boundary definition appears to reflect the structure of a monogenetic volcanic field better than other approaches, no ideal boundary definition was found. Finally, the dimension of scoria cones (approximated by their basal diameters) across the CVL was contrasted to the specific geodynamic setting. This region presents a complex problem for volcanic hazard analysis that cannot be solved through basic statistical methods and, thus, provides a potential testbed for novel, multi-disciplinary approaches.

Geospatial modeling for selection of optimum sites for hybrid solar-wind energy in Assiut Governorate, Egypt

Renewable energy resources are strategic solutions to develop remote urban areas, provide accessibility, meet the growing energy needs, prevent and mitigate adverse environmental impacts of anthropogenic activities. The purpose of the current research paper is to map and designate optimal sites for locating new hybrid solar and wind farms that fulfill suitability criteria for photovoltaic power plants and wind power in Assiut Governorate. SRTM digital elevation model was processed using the ESRI ArcGIS Area solar radiation tool to estimate and map insolation across the landscape on the topographic surface. Same data (SRTM DEM) was used together with the average wind speed map at elevation 50 m to calculate the wind power density. A geospatial model was designed based on three criteria sets covering three themes: first energy resource (climate and topography), second least cost (infrastructure and third, environmental constraints. The Analytic Hierarchy Process, Weighted Linear Combination and Binary overlay methods were applied, resulting in three sub-models. Such were further combined to produce the solar radiation and the wind power suitability indices separately. The solar radiation index values were reclassified; zones with a minimum threshold of 4 kw/m2/day were selected. From such zones, twenty optimum solar sites were selected based on a minimum area threshold. To identify potential wind zones, a minimum of wind power density equivalent to 220 W/m2 was considered. Results reveal that six potential solar sites exist within the potential wind energy zones; such sites were finally selected as candidates for allocation of hybrid solar-wind power stations.

Environmental hazards of land use/land cover dynamics using data observation techniques and GIS: case study of Guyuan watershed, China

Agricultural production system is extensively impacted by dynamics of land use. In the present paper, dynamics of land use and land cover (LULC) and environmental factors such as digital elevation model (DEM), slope, vegetation cover, soil type, and aspect were assessed to simulate the potential hazard in the watershed area at the southern part of Ningxia, Guyuan. This area was selected due to its wealthy fertile soils; thus, it provides food for multiple regions. Guyuan, Shilitan, and Yangcao cities were chosen as case studies. Multispectral Gaofen (GF) 2 satellite images and SRTM DEM were processed to produce environmental variables to assess the probable risks. In Shilitan watershed, very dense vegetation showed an increase from 14.6 to 22.1% and in Yangcao from 5.65 to 9.46% at 2005 and 2019, respectively, which protects the watershed area from flood and land degradation. However, spare vegetation recorded a decrease during the investigated period in two watershed areas. Hence, soil with little vegetative cover is more vulnerable to erosion, degradation runoff, and inconsequential water retention. DEM analyses showed that higher degree of segmentation leads to more degradation and damage of agricultural lands which adversely affects food security of the city. Results of the present study help policy makers, planners, and other accompanying development workers to apply the best suitable land use management options to protect Guyuan watershed.

Slight change of glaciers in the Pamir over the period 2000–2017

ABSTRACT Glaciers in the Pamir are the water tower of arid Central Asia, and more than 50 million people depend on meltwater from them. Many studies have reported glacier changes in the Pamir, but the glacier inventories employed in the previous investigations are both outdated and lack comparability. In this study, we present a new multitemporal glacier inventory for the Pamir based primarily on the Landsat ETM+/OLI scenes from the period around 2000 and 2017. Glacier outlines in 2000 and 2017 were delineated manually using Landsat images, SRTM digital elevation model (DEM), and high-resolution Google Earth images, using the same criteria and methods. We mapped 12,186 glaciers covering 10,396.20 ± 421.16 km2 in 2017 for the Pamir and demonstrated that the Pamir lost 124.28 ± 81.33 km2 of its glacier areas with a shrinkage rate of 1.17 ± 0.77 percent or 0.07 ± 0.05 percent·a−1 from 2000 to 2017. Based on the new inventories and the existing elevation change data sets of High Mountain Asia (HMA) from 2000 to 2016, we calculated a weaker glacier mass loss of −0.05 ± 0.06 m w.e. a−1. Spatial heterogeneity of glacier changes has been found in both the area and mass balance, but our results still suggest that the Pamir glaciers changed slightly since 2000.

Extraction of drainage Characteristics and Morphometric analysis using GIS and SRTM Digital Elevation Model Data in Sathyavedu area, Chittoor District, Andhra Pradesh, India

The aim of the present study is to extraction of the drainage characteristics from SRTM 30M resolution data processed in Arc GIS 10.1and develops the different maps such as Drainage fill, flow accumulation, stream link, flow direction, stream order map. The study area stream order map shows 5 orders. Most of the stream area flow in the direction of North West to south west and it determine the less porosity and permeability due to presence of the granite schist, quartzite's and laterite group of rocks and SRTM DEM with spatial resolution of 30m.