Search Results (40)

Preprocessing Synthetic Aperture Radar (SAR) data is a crucial initial stage in leveraging SAR data for remote sensing applications. Terrain correction, both radiometric and geometric, and the detection of layover/shadow areas hold significant importance when SAR data are collected over mountainous regions. This study aims at investigating the impact of the Digital Elevation Model (DEM) used for terrain correction (radiometric and geometric) and for mapping layover/shadow areas on windthrow detection using COSMO SkyMed SAR images. The terrain correction was done using a radiometric and geometric terrain correction algorithm. Specifically, we evaluated five different DEMs: (i–ii) a digital terrain model and a digital surface model derived from airborne LiDAR flights; (iii) the ALOS Global Digital Surface Model; (iv) the Copernicus global DEM; and (v) the Shuttle Radar Topography Mission (SRTM) DEM. All five DEMs were resampled at 2 m and 30 m pixel spacing, obtaining a total of 10 DEMs. The terrain-corrected COSMO SkyMed SAR images were employed for windthrow detection in a forested area in the north of Italy. The findings revealed significant variations in windthrow detection across the ten corrections. The detailed LiDAR-derived terrain model (i.e., DTM at 2 m pixel spacing) emerged as the optimal choice for both pixel spacings considered. Full article

In this work, TiO₂ spherical nanoparticles with a mean diameter of 10.08 nm (SD = 4.54 nm) were synthesized using Aloe vera extract. Rutile, brookite, and anatase crystalline phases were identified. The surface morphology of a carbon paste electrode does not change in the presence of nanoparticles; however, the surface chemical composition does. The voltammetric response to dicresyl dithiophosphate was higher when the electrode was modified with TiO₂ nanoparticles. After an electrochemical response study from pH 1.0 to 12.0, pH 7.0 was selected for the electroanalysis. The electroactive area of the modified sensor was 0.036 cm², while it was 0.026 cm² for the bare electrode. The oxidation process showed mixed adsorption-diffusion control. The charge transfer resistance of the modified sensor (530.1 Ω, SD = 4.08 Ω) was much lower than that of the bare electrode (4298 Ω, SD = 8.53 Ω). The linear quantitative range by square wave voltammetry was from 5 to 150 μmol/L, with a limit of detection of 1.89 μmol/L and a limit of quantification of 6.26 μmol/L under optimal pulse parameters of 50 Hz frequency, 1 mV step potential, and 25 mV pulse amplitude. The sensor response was repeatable and reproducible over 30 days. The results on real flotation and synthetically contaminated soil samples were statistically equivalent to those obtained by UV-vis spectrophotometry. A dithiocarbamate showed an interfering effect on the sensor response to dithiophosphate. Full article

This article presents a low-cost insurance system developed for smallholder farms in disaster-prone regions, primarily using free Earth observation (EO) data and free open source software’s (FOSS), collectively termed “sustainable geoinformatics.” The study examined 30 farms in Risaralda Department, Colombia. A digital elevation model (12.5 m pixels) from the ALOS PALSAR satellite sensor was used with a geographic information system (GIS) to map the terrain, drainage, and geohazards of each farming district. Google Earth Engine (GEE) was used to carry out time-series analysis of 15 EO and weather datasets for 1998 to 2020. This analysis enabled the levels of risk from hydrometeorological hazards to be determined for each farm of the study, providing key data for the setting of insurance premiums. A parametric insurance product was developed using a proprietary mobile phone app that collected GPS-tagged, time-stamped mobile phone photos to verify crop damage, with further verification of crop health also provided by daily near-real-time satellite imagery (e.g., PlanetScope with 3 m pixels). Machine learning was used for feature identification with the photos and the satellite imagery. Key features of this insurance system are its low operational cost and rapid damage verification relative to conventional approaches to farm insurance. This relatively fast, low-cost, and affordable approach to insurance for small-scale farming enhances sustainable development by enabling policyholder farmers to recover more quickly from disasters. Full article

Digital elevation models (DEMs) are widely used in digital terrain analysis, global change research, digital Earth applications, and studies concerning natural disasters. In this investigation, a thorough examination and comparison of five open-source DEMs (ALOS PALSAR, SRTM1 DEM, SRTM3 DEM, NASADEM, and ASTER GDEM V3) was carried out, with a focus on the Chongqing region as a specific case study. By utilizing ICESat-2 ATL08 data for validation and employing a random forest model to refine terrain variables such as slope, aspect, land cover, and landform type, a study was undertaken to assess the precision of DEM data. Research indicates that spatial resolution significantly impacts the accuracy of DEMs. ALOS PALSAR demonstrated satisfactory performance, reducing the corrected root mean square error (RMSE) from 13.29 m to 9.15 m. The implementation of the random forest model resulted in a significant improvement in the accuracy of the 30 m resolution NASADEM product. This improvement was supported by a decrease in the RMSE from 38.24 m to 9.77 m, demonstrating a significant 74.45% enhancement in accuracy. Consequently, the ALOS PALSAR and NASADEM datasets are considered the preferred data sources for mountainous urban areas. Furthermore, the study established a clear relationship between the precision of DEMs and slope, demonstrating a consistent decline in precision as slope steepness increases. The influence of aspect on accuracy was considered to be relatively minor, while vegetated areas and medium-to-high-relief mountainous terrains were identified as the main challenges in attaining accuracy in the DEMs. This study offers valuable insights into selecting DEM datasets for complex terrains in mountainous urban areas, highlighting the critical importance of choosing the appropriate DEM data for scientific research. Full article

The subway alleviates the traffic pressure in the city but also brings the potential risk of land subsidence. The land subsidence caused by the subway is a global problem that seriously affects the safety of subway operations and surrounding buildings. Therefore, it is very important to carry out long-term deformation monitoring on the subway system. StaMPS-PS is a time-series Interferometric Synthetic Aperture Radar (InSAR) technique that serves as an effective means for monitoring urban ground subsidence. However, the accuracy of external (Digital Elevation Models) DEM will affect the accuracy of StaMPS-PS monitoring, and previous studies have mostly used SRTM-1 arc DEM (30 m) as the external DEM. In this study, to obtain a more precise measurement of surface deformation caused by the excavation of the Hohhot subway, a total of 85 scenes of Sentinel-1A data from July 2015 to October 2021, as well as two different resolution digital elevation models (DEMs) (ALOS PALSAR DEM and SRTM-1 arc DEM), were used to calculate and analyze the subsidence along the subway line in Hohhot city. The StaMPS-PS monitoring results showed the ALOS PALSAR DEM, as an external DEM, had higher accuracy, and there was regional subsidence in both the construction processes of Line 1 and Line 2 of the Hohhot subway, with a maximum subsidence rate of −21.1 mm/year. The dynamic changes in subway subsidence were fitted using the Peck formula and the long short-term memory (LSTM) model. The Peck formula results showed the width and maximum subsidence of the settlement troughs gradually expanded during the construction of the subway. The predicted values of the Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE) of the LSTM model were less than 4 mm and 10%, respectively, consistent with the measured results. Furthermore, we discussed the factors that affect settlement along the subway line and the impact of two external DEMs on StaMPS-PS. The study results provide a scientific method for DEM selection and subsidence analysis calculations in the StaMPS-PS monitoring of urban subway subsidence. Full article

Recently, it has been shown that the long penetrating polarimetric L-band ALOS is very promising for boreal and subarctic peatland mapping and monitoring. The unique information provided by the Touzi decomposition, and the dominant-scattering-type phase in particular, on peatland subsurface water flow permits an enhanced discrimination of bogs from fens, two peatland classes that can hardly be discriminated using conventional optical remote sensing sensors and C-band polarimetric SAR. In this study, the dominant and medium-scattering phases generated by the Touzi decomposition are investigated for discontinuous permafrost mapping in peatland regions. Polarimetric ALOS2, LiDAR, and field data were collected in the middle of August 2014, at the maximum permafrost thaw conditions, over discontinuous permafrost distributed within wooded palsa bogs and peat plateaus near the Namur Lake (Northern Alberta). The ALOS2 image, which was miscellaneously calibrated with antenna cross talk (−33 dB) much higher than the actual ones, was recalibrated. This led to a reduction of the residual calibration error (down to −43 dB) and permitted a significant improvement of the dominant and medium-scattering-type phase (20${}^{\circ }$ to −30${}^{\circ }$) over peatlands underlain by discontinuous permafrost. The Touzi decomposition, Cloude–Pottier $\alpha$-H incoherent target scattering decomposition, and the HH-VV phase difference were investigated, in addition to the conventional multipolarization (HH, HV, and VV) channels, for discontinuous permafrost mapping using the recalibrated ALOS2 image. A LiDAR-based permafrost classification developed by the Alberta Geological Survey (AGS) was used in conjunction with the field data collected during the ALOS2 image acquisition for the validation of the results. It is shown that the dominant- and scattering-type phases are the only polarimetric parameters which can detect peatland subsurface discontinuous permafrost. The medium-scattering-type phase, ${\varphi }_{s2}$, performs better than the dominant-scattering-type phase, ${\varphi }_{s1}$, and permits a better detection of subsurface discontinuous permafrost in peatland regions. ${\varphi }_{s2}$ also allows for a better discrimination of areas underlain by permafrost from the nonpermafrost areas. The medium Huynen maximum polarization return (m${}_2$) and the minimum degree of polarization (DoP), pmin, can be used to remove the scattering-type phase ambiguities that might occur in areas with deep permafrost (more than 50 cm in depth). The excellent performance of polarimetric PALSAR2 in term of NESZ (−37 dB) permits the demonstration of the very promising L-band long-penetration SAR capabilities for enhanced detection and mapping of relatively deep (up to 50 cm) discontinuous permafrost in peatland regions. Full article

Rural mobility in Africa is an under-researched issue. Rural communities have often suffered from reduced mobility that has hampered their access to essential services and facilities such as education, health care, food, and clean water. In many rural communities, a more affordable mobility option, such as non-motorized mobility (cycling and walking), is the preferred way for people to travel. Apart from its well-known advantages, little is known about the impact of topography and routes on the mobility options adopted by rural communities. Therefore, this study aims to use Digital Elevation Models (DEMs) to analyze the impact of topography and routes on rural mobility patterns at the level of formal and informal cycle track networks in the Bugesera District, focusing on the Nyamata and Mayange sectors, Rwanda. This study used GPS devices given to 50 participants to collect mobility patterns in the two previously mentioned sectors. Then, the study imposed a 30-m buffer on the official road networks of Rwanda collected by the Rwanda Transport Development Agency (RTDA). These data were joined to GPS tracks to highlight official and unofficial roads (tracks that did not fall within the 30-m buffer). In addition, Digital Elevation Models were applied to analyze the SRTM (30 m resolution) and ALOS PALSAR (12.5 m resolution) elevation data of the Bugesera region. The findings revealed an elevation range of 1333 to 1535 for SRTM and 1323 to 1641 for ALOS PALSAR. The study calculated the slope to find the slope percentage (m) and length (m). The findings from the DEMs and the slope calculation revealed that Bugesera has a relatively flat surface, favorable for cycling. The slope percentage was further classified into five levels of slope ranging from steep to very steep. And the Van Zuidam classification results confirmed that Bugesera has “a flat or nearly flat surface, without significant denudation processes”. With a favorable topography and a higher bicycle ownership ratio, residents of the Bugesera district favor cycling in their daily activities more than any district in Rwanda. Cycling in Nyamata or Mayange links residents to areas with higher social, educational, administrative, and economic activities. Full article

The search for adsorbent materials with a certain chemical inertness, mechanical resistance, and high adsorption capacity, as is the case with alumina, is carried out with structural or surface modifications with the addition of additives or metallic salts. This research shows the synthesis, characterization, phase evolution and Cd(II) adsorbent capacity of α-Al₂O₃/Ba-β-Al₂O₃ spheres obtained from α-Al₂O₃ nanopowders by the ion encapsulation method. The formation of the Ba-β-Al₂O₃ phase is manifested at 1500 °C according to the infrared spectrum by the appearance of bands corresponding to AlO₄ bonds and the appearance of peaks corresponding to Ba-O bonds in Raman spectroscopy. XRD determined the presence of BaO·Al₂O₃ at 1000 °C and the formation of Ba-β-Al₂O₃ at 1600 °C. Scanning electron microscopy revealed the presence of spherical grains corresponding to α-Al₂O₃ and hexagonal plates corresponding to β-Al₂O₃ in the spheres treated at 1600 °C. The spheres obtained have dimensions of 4.65 ± 0.30 mm in diameter, weight of 43 ± 2 mg and a surface area of 0.66 m²/g. According to the curve of pH vs. zeta potential, the spheres have an acid character and a negative surface charge of −30 mV at pH 5. Through adsorption studies, an adsorbent capacity of Cd(II) of 59.97 mg/g (87 ppm Cd(II)) was determined at pH 5, and the data were fitted to the pseudo first order, pseudo second order and Freundlich models, with correlation factors of 0.993, 0.987 and 0.998, respectively. Full article

In Near and Middle Eastern archaeology, satellite-derived digital elevation models (DEM) of medium spatial resolution (≥30 m) are mostly used to locate and map archaeological mounds (namely ‘tells’), whereas high resolution DEMs (≤10 m) are still poorly exploited. To fill this gap, the 5 m resolution CartoSat-1 Euro-Maps 3D Digital Surface Model (DSM) is assessed vs. the 30 m Shuttle Radar Topography Mission (SRTM) global DEM, the Advanced Land Observing Satellite (ALOS) World 3D–30 m (AW3D30) and a 10 m COSMO-SkyMed DEM, on a test area in Wasit, southern Iraq, where the high density of tells is yet to be exhaustively documented. A total of 344 sites was mapped, with one order of magnitude improvement compared to previous mapping exercises, existing databases and historical maps. The morphometric analysis not only highlights the reliability of CartoSat-1 DSM height and volume estimates, but also suggests that, in the test area, the volume of a tell can robustly be calculated based on the simple knowledge of its basal area, following a quadratic function. Morphology and elevation of at least 53% irregularly shaped tells were impacted by anthropogenic disturbances. Morphometric indices (e.g., Topographic Position Index, DEViation from mean elevation) are a viable automated method to ease tells detection. When integrated with other satellite datasets (e.g., CORONA, Google Earth, Sentinel-2 imagery), the CartoSat-1 DSM can unveil morphological changes and support condition assessment. In Wasit, agriculture and modern development are among the major threats for tells preservation, alongside looting. Full article

The medicinal administration of Aloe vera gel has become promising in pharmaceutical and cosmetic applications particularly with the development of the nanotechnology concept. Nowadays, effective H. pylori treatment is a global problem; therefore, the development of natural products with nanopolymers such as chitosan nanoparticles (CSNPs) could represent a novel strategy for the treatment of gastric infection of H. pylori. HPLC analysis of A. vera gel indicated the presence of chlorogenic acid as the main constituent (1637.09 µg/mL) with other compounds pyrocatechol (1637.09 µg/mL), catechin (1552.92 µg/mL), naringenin (528.78 µg/mL), rutin (194.39 µg/mL), quercetin (295.25 µg/mL), and cinnamic acid (37.50 µg/mL). CSNPs and A. vera gel incorporated with CSNPs were examined via TEM, indicating mean sizes of 83.46 nm and 36.54 nm, respectively. FTIR spectra showed various and different functional groups in CSNPs, A. vera gel, and A. vera gel incorporated with CSNPs. Two strains of H. pylori were inhibited using A. vera gel with inhibition zones of 16 and 16.5 mm, while A. vera gel incorporated with CSNPs exhibited the highest inhibition zones of 28 and 30 nm with resistant and sensitive strains, respectively. The minimal inhibitory concentration (MIC) was 15.62 and 3.9 µg/mL, while the minimal bactericidal concentration (MBC) was 15.60 and 7.8 µg/mL with MBC/MIC 1 and 2 indexes using A. vera gel and A. vera gel incorporated with CSNPs, respectively, against the resistance strain. DPPH Scavenging (%) of the antioxidant activity exhibited an IC₅₀ of 138.82 μg/mL using A.vera gel extract, and 81.7 μg/mL when A.vera gel was incorporated with CSNPs. A.vera gel incorporated with CSNPs enhanced the hemolysis inhibition (%) compared to using A.vera gel alone. Molecular docking studies through the interaction of chlorogenic acid and pyrocatechol as the main components of A. vera gel and CSNPs with the crystal structure of the H. pylori (4HI0) protein supported the results of anti-H. pylori activity. Full article

The sensitivity of simulated flood depth and area to DEM resolution are acknowledged, but their effects on flood damage and risk estimates are less well understood. This study sought to analyse the relative benefits of using global DEMs of different resolution sizes, 5 m AW3D Standard, 12.5 m ALOS PALSAR and 30 m SRTM, to simulate flood inundation, damage and risk. The HEC-RAS 2D model was adopted for flood simulations, and the Toba River in the Klang River Basin in Malaysia was chosen for the case study. Simulated inundation areas from AW3D coincide the most with reported flooded areas, but the coarser-resolution DEMs did capture some of the reported flooded areas. The inundation area increased as the resolution got finer. As a result, AW3D returned almost double flood damage and risk estimates compared to ALOS PALSAR, and almost quadruple compared to SRTM for building-level damage and risk analysis. The findings indicate that a finer-resolution DEM improves inundation modelling and could provide greater flood damage and risk estimates compared to a coarser DEM. However, DEMs of coarser resolution remain useful in data-scarce regions or for large-scale assessments in efforts to manage flood risk. Full article

Satellite forest inventories are the only feasible way to map Canada’s vast, remote forest regions, such as those in the Northwest Territories (NWT). A method used to create such inventories is the k-nearest neighbour (k-NN) algorithm, which spatially extends information from forest inventory (FI) plots to the entire forest land base using wall-to-wall features typically derived from Landsat data. However, the benefits of integrating L-band synthetic aperture radar (SAR) data, strongly correlated to forest biomass, have not been assessed for Canadian northern boreal forests. Here we describe an optimized multivariate k-NN implementation of a 151,700 km² area in southern NWT that included ca. 2007 Landsat and dual-polarized Phased Array type L-band SAR (PALSAR) data on board the Advanced Land Observing Satellite (ALOS). Five forest attributes were mapped at 30 m cells: stand height, crown closure, stand/total volume and aboveground biomass (AGB). We assessed accuracy gains compared to Landsat-based maps. To circumvent the scarcity of FI plots, we used 3600 footprints from the Geoscience Laser Altimeter System (GLAS) as surrogate FI plots, where forest attributes were estimated using Light Detection and Ranging (LiDAR) metrics as predictors. After optimization, k-NN predicted forest attribute values for each pixel as the average of the 4 nearest (k = 4) surrogate FI plots within the Euclidian space of 9 best features (selected among 6 PALSAR, 10 Landsat, and 6 environmental features). Accuracy comparisons were based on 31 National Forest Inventory ground plots and over 1 million airborne LiDAR plots. Maps that included PALSAR HV backscatter resulted in forest attribute predictions with higher goodness of fit (adj. R²), lower percent mean error (ME%), and percent root mean square error (RMSE%), and lower underestimation for larger attribute values. Predictions were most accurate for conifer stand height (RMSE% = 32.1%, adj. R² = 0.58) and AGB (RMSE% = 47.8%, adj. R² = 0.74), which is much more abundant in the area than mixedwood or broadleaf. Our study demonstrates that optimizing k-NN parameters and feature space, including PALSAR, Landsat, and environmental variables, is a viable approach for inventory mapping of the northern boreal forest regions of Canada. Full article

Trypanosomiasis and leishmaniasis are among the major neglected diseases that affect poor people, mainly in developing countries. In Ethiopia, the latex of Aloe rugosifolia Gilbert & Sebsebe is traditionally used for the treatment of protozoal diseases, among others. In this study, the in vitro antitrypanosomal activity of the leaf latex of A. rugosifolia was evaluated against Trypanosoma congolense field isolate using in vitro motility and in vivo infectivity tests. The latex was also tested against the promastigotes of Leishmania aethiopica and L. donovani clinical isolates using alamar blue assay. Preparative thin-layer chromatography of the latex afforded a naphthalene derivative identified as plicataloside (2,8-O,O-di-(β-D-glucopyranosyl)-1,2,8-trihydroxy-3-methyl-naphthalene) by means of spectroscopic techniques (HRESI-MS, ¹H, ¹³C-NMR). Results of the study demonstrated that at 4.0 mg/mL concentration plicataloside arrested mobility of trypanosomes within 30 min of incubation period. Furthermore, plicataloside completely eliminated subsequent infectivity in mice for 30 days at concentrations of 4.0 and 2.0 mg/mL. Plicataloside also displayed antileishmanial activity against the promastigotes of L. aethopica and L. donovani with IC₅₀ values 14.22 ± 0.41 µg/mL (27.66 ± 0.80 µM) and 18.86 ± 0.03 µg/mL (36.69 ± 0.06 µM), respectively. Thus, plicataloside may be used as a scaffold for the development of novel drugs effective against trypanosomiasis and leishmaniasis. Full article

Two successive field trials were carried out at the experimental farm of the Agriculture Department of Fayoum University, Fayoum, Egypt, to investigate the sole or dual interaction effect of applying a foliar spray of Aloe saponaria extract (Ae) or potassium silicate (KSi) on reducing the stressful salinity impacts on the development, yield, and features of roselle (Hibiscus sabdariffa L.) plants. Both Ae or KSi were used at three rates: 0% (0 cm³ L⁻¹), 0.5% (5 cm³ L⁻¹), and 1% (10 cm³ L⁻¹) and 0, 30, and 60 g L⁻¹, respectively. Three rates of salinity, measured by the electrical conductivity of a saturated soil extract (ECe), were also used: normal soil (ECe < 4 dS/m) (S1); moderately-saline soil (ECe: 4–8 dS/m) (S2); and highly-saline soil (ECe: 8–16 dS/m) (S3). The lowest level of salinity yielded the highest levels of all traits except for pH, chloride, and sodium. Ae at 0.5% increased the values of total soluble sugars, total free amino acids, potassium, anthocyanin, a single-photon avalanche diode, stem diameter, fruit number, and fresh weight, whereas 1% of Ae resulted in the highest plant height, chlorophyll fluorescence (Fv/Fm), performance index, relative water content, membrane stability index, proline, total soluble sugars, and acidity. KSi either at 30 or 60 g L⁻¹ greatly increased these abovementioned attributes. Fruit number and fruit fresh weight per plant also increased significantly with the combination of Ae at 1% and KSi at 30 g L⁻¹ under normal soil conditions. Full article

“Tells” are archaeological mounds formed by deposition of large amounts of anthropogenic material and sediments over thousands of years and are the most important and prominent features in Near and Middle Eastern archaeological landscapes. In the last decade, archaeologists have exploited free-access global digital elevation model (DEM) datasets at medium resolution (i.e., up to 30 m) to map tells on a supra-regional scale and pinpoint tentative tell sites. Instead, the potential of satellite DEMs at higher resolution for this task was yet to be demonstrated. To this purpose, the 3 m resolution imaging capability allowed by the Italian Space Agency’s COSMO-SkyMed Synthetic Aperture Radar (SAR) constellation in StripMap HIMAGE mode was used in this study to generate DEM products of enhanced resolution to undertake, for the first time, a systematic mapping of tells and archaeological deposits. The demonstration is run at regional scale in the Governorate of Wasit in central Iraq, where the literature suggested a high density of sites, despite knowledge gaps about their location and spatial distribution. Accuracy assessment of the COSMO-SkyMed DEM is provided with respect to the most commonly used SRTM and ALOS World 3D DEMs. Owing to the 10 m posting and the consequent enhanced observation capability, the COSMO-SkyMed DEM proves capable to detect both well preserved and levelled or disturbed tells, standing out for more than 4 m from the surrounding landscape. Through the integration with CORONA KH-4B tiles, 1950s Soviet maps and recent Sentinel-2 multispectral images, the expert-led visual identification and manual mapping in the GIS environment led to localization of tens of sites that were not previously mapped, alongside the computation of a figure as up-to-date as February 2019 of the survived tells, with those affected by looting. Finally, this evidence is used to recognize hot-spot areas of potential concern for the conservation of tells. To this purpose, we upgraded the spatial resolution of the observations up to 1 m by using the Enhanced Spotlight mode to collect a bespoke time series. The change detection tests undertaken on selected clusters of disturbed tells prove how a dedicated monitoring activity may allow a regular observation of the impacts due to anthropogenic disturbance (e.g., road and canal constructions or ploughing). Full article