West Direction Research Articles

Sky-view images aided NLOS detection and suppression for tightly coupled GNSS/INS system in urban canyon areas

Although the global navigation satellite system (GNSS) and inertial navigation system (INS) integration framework has many advantages compared to the standalone GNSS and INS systems, its accuracy can be severely degraded in urban canyon areas, due to non-line-of-sight (NLOS) signals. Detection and suppression of NLOS signals are the key to improving the location accuracy of urban areas. Therefore, this paper proposes a method for NLOS detection using the improved region growing algorithm on sky-view images captured by a fish-eye camera. After obtaining NLOS detection results, this paper constructs a weighted model with an adaptive scale factor to suppress the influence of NLOS signals. Experimental results show that the proposed method can effectively improve the performance of NLOS detection and suppression. On this basis, a tightly coupled GNSS/INS integration system based on an extended Kalman filter is developed and tested on the vehicle equipment. Results show that the proposed method outperforms the traditional GNSS single point positioning (SPP) and tightly coupled GNSS SPP/INS integration on positioning accuracy. The root mean square error can be reduced by 33.7% and 24.6% in the north and east directions respectively. It indicates that the tightly coupled GNSS SPP/INS integration aided by the fish-eye camera has certain research value and potential on positioning in urban canyon areas.

Adaptive event-triggered actor–critic algorithm for optimal 3D formation circumnavigation with relative measurement and an unknown moving target

This paper studies the optimal three-dimensional (3D) formation circumnavigation problem for multiple unmanned aerial vehicles (UAVs) with relative measurement and an unknown moving target. First, the 3D formation circumnavigation errors under the relative measurement and directed topology, that is, the spherical enclosing along the normal direction, the latitude surrounding along the north direction, and the longitude formation along the east direction, are constructed. Then, radial basis function neural networks (RBFNNs) based adaptive estimation is designed for each UAV to approximate the unknown target velocity using relative information. Further, to achieve the optimal energy of 3D formation circumnavigation along the normal, north, and east directions with lowered data transmission cost, an event-triggered actor–critic algorithm is designed under limited neighbor and relative target information. The stability of the whole system is analyzed under continuous sampled and event sampled cases, respectively, and the Zeno phenomenon is excluded. The effectiveness is validated through simulation under cases of with and without random noise. Meanwhile, comparative simulations are performed to validate the system energy and convergence time of the proposed method in contrast with two relevant works.

Determination of long-term deformation behaviours with InSAR data at a dump site of an open-pit coal mine in Turkey

Dump sites with broken overburden layers in surface mines have the risk of instability due to their loose bulk structures. In this study, deformations at a dump site of the Kangal/Kalburçayırı open-pit coal mine and their long-term behaviours were revealed with InSAR data for a total period of 4.5 years. Firstly, 9-periods involving different time ranges were created considering the presence of LiCSAR products. Then, the deformation velocities of each period were calculated by LiCSBAS software using LiCSAR products. The area where high deformations were concentrated from the LiCSBAS result products was determined and divided into 4 zones for more detailed evaluations. At the final stage, the period-deformation velocity graphs were drawn separately for each zone with the data obtained using two different approaches from the deformation velocities of all periods, and long-term deformation behaviours were determined. More reliable future behaviour projections could be made considering the current increasing or decreasing trend of deformation behaviours. It was revealed that vertical deformations at the dump site had an increasing trend in the first periods and a decreasing trend in the later periods. Maximum vertical deformation velocities ranging between −111.4 mm/year and −178.0 mm/year in the first 4 months reached the highest values (ranging from −141.9 mm/year to −261.8 mm/year) at the end of two years and decreased to values ranging from −33.0 mm/year to −44.3 mm/year in the later periods. It was found that horizontal deformation velocities ranged between +0.5 mm/year and +55.4 mm/year in the east–west direction and between −7.0 mm/year and −56.8 mm/year in the west-east direction, were approximately 5 times lower than vertical velocities and did not have a constantly increasing or decreasing trend in any direction. It was observed that deformations exhibited a behaviour resulting from the structural property of the dump bulk material. The results of the evaluations showed that the risk of instability gradually decreased at the dump site. The methodology of this study can enable the determination of similar areas that may pose a threat in a short time, the prioritization of risky areas, the planning of more detailed studies, and taking the necessary measures in a timely manner.

The Joint Clean Air Actions and air quality spillovers in China

ABSTRACT Facing severe air pollution in its North Plain, the central government of China initiated the Joint Clean Air Action (JCAA) in 2017 to facilitate pollution mitigation efforts across the region. While quite a few studies investigated the effectiveness of this regulation, much less attention is paid to the pollution spillover effects. We empirically examine the effects, and show that 1) air quality in the east of the target cities has been improved due to positive spillover of improved air quality under the JCAA; 2) the beneficiary spillover lasts for two seasons and disappeared in autumn and winter; 3) air quality in the north, south and west directions are almost not changed; 4) wind direction and topography, two determinants of atmospheric transport, have a considerable influence over the spillover effects. Our study provides a fresh perspective to understand the impacts of the JCAA policy and underlines the necessity of taking both pollution and air quality spillover effects into the cost-benefit analysis. Implications: Pollution regulations in one place may increase pollution in other places, as production and emissions are re-allocated under the incentives induced by regional-specific regulations. This phenomenon has long been recognized in the literature as pollution spillover. However, if the relevant production and emissions are not re-allocated, at least not re-allocated in large quantities, local air quality improvement induced by regulations may also benefit the neighboring areas. We call this effect air quality spillover. Both spillover effects should be rigorously evaluated, which is of scientific interest by itself and also contributes to a comprehensive cost-benefit analysis of environmental regulations.

PENERAPAN METODE RESISTIVITAS KONFIGURASI SCHLUMBERGER UNTUK MENDETEKSI PERSEBARAN AIR LINDI (STUDI KASUS TPA TERJUN MARELAN)

Leachate has the potential to be used as organic fertilizer because it contains high levels of minerals and organic matter. In the leachate there are several compounds, namely heavy metal compounds, salts, nitrogen compounds and various types of other organic matter. Leachate leachate also contains very fine suspended matter from the decomposition of microbes, usually consisting of Ca, Mg, Na, K, Fe, Chloride, Sulfate, Phosphate, Zn, Ni, CO2, H2O, N2, NH3, H2S, Organic acids , and H2. This study aims to find out how the subsurface layer in the Medan Marelan Falls Landfill area, the distribution of leachate in the Medan Marelan Falls Landfill. 1D resistivity measurements were only carried out in the Medan Marelan Falls TPA area. The geophysical method used in this study is the Schlumberger configuration. This research was conducted at three points along the 200 meter track. on line I is at a depth of 6.92 m with a resistivity value of 3.16 Ωm with a North to South flow direction. On track II it is at a depth of 1.15 m, 4.53 m, and 22.1 m with a resistivity value of 1.5 Ωm, 2.25 Ωm, and 5.05 Ωm respectively with the North to West flow direction. On track III it is at a depth of 1.19 m, 20.8 m, and 53.9 m with resistivity values of 1.54 Ωm, 3.51 Ωm, and 1.13 Ωm respectively with North to West flow direction. The distribution of leachate at the Medan Marelan Falls TPA which dominates is on track III marked with black to bluish color images.

Potential environmental pollution study by leachate generation and health risk assessment in the vicinity of bandhwari landfill disposal site, National Capital Region, India

Effects of fast urbanization and development in metropolitan cities is the production of massive amounts of waste from households and industries. Dumping of waste at an unengineered landfill site creates environmental issues. Generated leachate from such landfill is having potential to pollute the surrounding environment including groundwater. To understand the groundwater pollution by the effect of landfill leachate and health risk assessment for humans, four leachate samples and thirty-six groundwater samples were collected from different sources of groundwater from close proximity of Bandhwari Landfill site located in National Capital Region, Delhi. EC and SO42− values of Leachate samples i. e L-1 and L-2 are 42.5 mS/cm and 55.4 mS/cm; 1916.4 mg/l and 1931 mg/l respectively. Leachate pollution Index (LPI) values signifies that landfill leachate is having moderate potential for contamination. The dominance of average ionic species concentration of major cations in groundwater is given as Ca2+>Na+>Mg2+>K+ and major anion as HCO3− > Cl− > SO42− > NO3− > F−. As per Water Quality Index (WQI), 67% of samples lies in excellent category, 17% of samples falling in good category, whereas around 6% of groundwater samples lies in poor category, very poor category and unsuitable category. Landfill leachate and groundwater sample from North East direction are having high concentration of tritium i.e. 8.11 ± 0.40 TU and 3.03 ± 0.29 TU, respectively. Leachate samples from leachate pond-1 and leachate pond-2 are showing quite high Cl−/Br− ratio i. e 342 and 320. 86 respectively. But groundwater samples are exhibiting Cl−/Br− ratio in the range of 173.68 to 108.75. This represents leaching of salts from solid decomposed waste from landfill. Both non-carcinogenic and carcinogenic risk (CRing) were calculated for children and adult. Hazard Index (HI) values are higher than reference value i. e > 1 in the children (in 23% samples) as compare to the adult. These are mainly associated with Co, Cd and Pb. CRing of groundwater sample due to the presence of As, Ni, Cr and Cd falling in the range of 10−6 and 10−4 showing high risk to cancer per 10, 00, 000 million people by ingestion. However there is no significant cancer risk by dermal exposure by all metals in all groundwater samples. Groundwater pollution appears to be limited to the close vicinity in South and North-East direction.

Evaluation of Groundwater Potentiality and Subsurface Structural Setting by Using Geophysical Data in Wadi Hubuna, Southwest Najran, Saudi Arabia

A geophysical study was conducted to explore the shallow groundwater aquifer and to identify the subsurface structure on the basis of resistivity and geomagnetic surveys. The study area is situated in the southwestern portion of Saudi Arabia, southwest of the Najran region. The total intensity magnetic map is reduced to the northern magnetic pole. The estimated mean depths of the regional and residual magnetic sources are 3 km and 1.4 km respectively. Eighty vertical electrical soundings were measured using the Schlumberger configuration with AB/2 spacing of up to 700 m. Four geoelectrical layers were identified, and could be described from ground surface to deeper layers as the following: The first layer encompasses wadi deposits with true resistivity values ranging from 452 Ω.m to 1353 Ω.m and thicknesses of 2-4 m. The second layer is comprised of dry fine to medium grain-sized deposits with true resistivity values ranging from 104 Ω.m to 451 Ω.m, and thickness varying between 2 and 16 m. The third layer consists of water-bearing friable deposits beside the topmost part of the underlying weathered (fractured) basement. The true resistivity of this layer ranges from 22 Ω.m to 188 Ω.m, whereas the thickness of this layer is highly variable and ranges from 5 to 35 m. Generally, the resistivity values and the thickness of these three layers exhibit an increasing trend toward the main wadi stream. A fourth layer was also detected and is represented by a thin clay layer directly overlying the hard rocks of the basement complex. The dominant tectonic trends controlling the shallower parts are N-S and NNW-SSE. Meanwhile, the structural trend controlling the deeper parts is NE-SW, E-W, and. NNE-SSW. The ideal areas for drilling wells, according to the interpreted cross-sections, are along the main stream of Wadi hubuna and other small wadis, as well as the lower portions of the wadi in the extreme east direction.

Structural controls on formation of the Xiayu vein-hosted Ag–Pb–Zn–Au orefield during intracontinental extension along the southern margin of the North China Craton

The Xiayu Ag–Pb–Zn–Au deposit, situated in the Early Cretaceous Xiong’er shan area on the southern edge of the North China Craton, comprises the Haopinggou, Shagou, Tieluping, and Houzhanggou deposits, making it the largest Ag producer in the southern North China Craton. Despite significant research efforts, the connection between extensional faults and vein–hosted Ag–Pb–Zn–Au deposits in this area is still not well understood. To address this issue, we introduce new structural data, fault–slip data analysis, and information on epithermal Ag–Pb–Zn–Au mineralization. Two separate paleo–stress inversion methods were applied to determine that the region was affected by two discrete stress fields: E–W transtension and NW–SE transtension. Our palaeostress reconstruction indicates that transtensional tectonics would have affected the emplacement of fault–fill veins (stage I) and extensional veins (stage II). Both types of geometric veins show two distinct stages of formation. The first stage (I) involves the development of quartz–pyrite within hydraulic breccia, transitioning into crack–seal laminated shear veins. These likely formed during a period of regional extension in an east–west direction. The second stage (II) features the deposition of undeformed quartz–sphalerite–galena within pre–existing dilational sites near newly formed normal faults or stage I veins. This second stage likely occurred during a regional extension in a northwest–southeast direction.

Study and simulation of concentrating irradiance in box solar cooker with tracking reflectors

In this work a design of solar cooker with mirror reflectors has been studied for two tracking modes and his performances are analyzed by the simulation of collected energy on the absorber of the cooker. The box of the cooker receives the solar radiation both directly and by reflection from the mirror reflectors. The plane mirrors with high optical reflectivity allows sun tracking in the north south direction (for seasonal tracking) as well as in the east west direction (for tracking during the day) by moving theses reflectors with the correct angles. Adding reflectors improves the performances of the cooker, which is interesting in particular in winter, where the elevation of the sun is relatively low. The combination of north-south and east-west facing mirror reflectors are favorable for more energy collection, the cooker is enabling to cook during the day and around the year.

Balancing urban expansion with a focus on ecological security: A case study of Zhaotong City, China

The conflict between socio-economic development and ecological environmental protection presents a significant challenge to achieving regional and urban sustainable development. In Zhaotong City, Yunnan Province, China, this conflict arises from the interplay between urban expansion and ecological environmental protection land, creating a fundamental tension between built-up and non-built-up ecosystems. This study focuses on investigating the spatial characteristics of expansion, constructing an ecological security pattern based on ecosystem service functions and sensitivity, and utilizing integrated models to simulate urban expansion paths and analyze their formation mechanisms. The results highlight that Zhaotong City has undergone rapid urban expansion, characterized by linear growth surrounding the central city, specifically in the east, north, and west directions. The expansion between urban areas exhibits a discontinuous dotted-star distribution, with concentrated urbanization and a distinct urban boundary observed in Zhaoyang District. In contrast, other areas experience scattered expansion, indicative of random land encroachment. Through simulation, three primary urban expansion axes are identified: the western town sprawl belt, central town development axis, and resource-rich town corridor. Ecological conflicts primarily arise in Zhaoyang District, Zhenxiong County, and Yanjin County. By combining these findings, the study analyzes the scenario pattern of urban expansion evolution in Zhaotong City, revealing a transition from the spreading spillover expansion of a single center (Zhaoyang and Ludian) during the circle expansion phase to a polycentric expansion and spreading spillover pattern centered around Zhaoyang District along three primary axial radial paths. In conclusion, this study contributes to our understanding of the challenges posed by the conflict between socio-economic development and ecological environmental protection in Zhaotong City. The findings underscore the importance of integrating ecological considerations into urban planning processes and highlight the need for sustainable development practices to achieve a harmonious coexistence between urban expansion and ecological security. The insights gained from this research offer guidance for fostering sustainable urban development in Zhaotong City and beyond.

Monitoring Pollution and the Trend of Air Quality in Brick Factories in the Nahrawan Region and its Impact on Baghdad, Using Remote Sensing Data

One of the most significant environmental issues facing the planet today is air pollution. Due to development in industry and population density, air pollution has lately gotten worse. Like many developing nations, Iraq suffers from air pollution, particularly in its urban areas with heavy industry. Our research was carried out in Baghdad's Al-Nahrawan neighbourhood. Recently, ground surveys and remote sensing were used to study the monitoring of air pollution. In order to extract different gaseous and particle data, Earth Data source, Google Earth Engine (GEE), and Geographic Information Systems (GIS) software were all employed. The findings demonstrated that there is a significant positive connection between data collected by ground-based devices and remote sensing platforms. The brick manufacturers' operations in the region's northwest and west directions from Baghdad were plainly having an impact on the region of Al-air Nahrawan's quality. As a result, residents in the area are more likely to contract illnesses caused by pollution.

Analysis of the water‐vapor sources in rainstorm processes in Tianjin city based on the trajectory method

AbstractTianjin, one of the four municipalities in China, is the eastern gate of the capital city of Beijing and is of great socioeconomic importance. When rainstorms attack Tianjin, urban flooding often occurs due to the dense river network, well‐developed water system and flat terrain. In this study, the source analysis of water vapor in rainstorm processes in Tianjin during 2012–2020 is conducted based on the moisture source attribution method, and the PyTrajector and HYSPLIT softwares. Then, the evolution characteristics of rainstorms in Tianjin are investigated. The results show that the rainstorm water‐vapor sources in Tianjin city can be roughly divided into four directions. The west and southwest directions are the main source, which contribute about 89% of the water vapor to the rainstorms. For heavy rainstorm, the water vapor from the southwest direction contributes about 60%, which is larger than that of rainstorm. The southwest direction is the main water vapor source of heavy rainstorm in Tianjin and has the main effect on the water vapor fluctuations during heavy rainstorm. For the more hazardous extraordinary rainstorm, the water vapor from the southwest direction occupies an even larger proportion (74.3%). The annual total rainstorm precipitation in Tianjin city in 2012 was more than that in common years, and this is mainly due to the anomalous increase of water vapor from the southwest direction. This result further indicates that the annual total rainstorm precipitation in Tianjin is mainly influenced by the water vapor from the southwest direction. This study reveals that the majority of rainstorm in Tianjin originates from the western and southwestern directions, but significant heavy rainstorm events in Tianjin are particularly influenced by moisture from the southwestern direction. This research holds crucial implications not only for meteorological and water resource management in Tianjin but also provides valuable insights for global urban flood risk studies.

Transition prospects to sustainable development of the Kamchatka Krai in the Russian Federation

The transition to sustainable development remains an urgent task both at the national and regional levels. For the regions of the Far East in Russia this issue is of particular relevance due to the high amount of natural capital they have and the vulnerability of local ecosystems. In the article on the example of one of the regions of the Far East (Kamchatka Krai) possible directions for the transition to a model of sustainable and balanced development are identified. The purpose of this study is to evaluate alternatives for such a transition using simulation tools. In the course of the work a characteristic of the region was presented with the main components’ assessment of natural, human and physical capital. At the same time the definition of a complex regional balance is formulated as a regional projection of sustainability and a space of opportunities for the optimal use of all types of capital. The complex regional balance consists of ecologicaleconomic, ecological-social and socio-economic components. Based on the language of algorithmic networks, a simulation model complex for sustainable balanced development of the region has been developed, on which a series of experiments has been run. The results obtained make it possible to focus on the preferential development of human capital and on the support of innovation as the preferred option for the transition to a model of sustainability and integrated regional balance.

A Parallax Shift Effect Correction Based on Cloud Top Height for FY-4A Lightning Mapping Imager (LMI)

The Lightning Mapping Imager (LMI) onboard the Fengyun-4A (FY-4A) satellite is the first independently developed satellite-borne lightning imager in China. It enables continuous lightning detection in China and surrounding areas, regardless of weather conditions. The FY-4A LMI uses a Charge-Coupled Device (CCD) array for lightning detection, and the accuracy of lightning positioning is influenced by cloud top height (CTH). In this study, we proposed an ellipsoid CTH parallax correction (ECPC) model for lightning positioning applicable to FY-4A LMI. The model utilizes CTH data from the Advanced Geosynchronous Radiation Imager (AGRI) on FY-4A to correct the lightning positioning data. According to the model, when the CTH is 12 km, the maximum deviation in lightning positioning caused by CTH in Beijing is approximately 0.1177° in the east–west direction and 0.0530° in the north–south direction, corresponding to a horizontal deviation of 13.1558 km, which exceeds the size of a single ground detection unit of the geostationary satellite lightning imager. Therefore, it is necessary to be corrected. A comparison with data from the Beijing Broadband Lightning Network (BLNET) and radar data shows that the corrected LMI data exhibit spatial distribution that is closer to the simultaneous BLNET lightning positioning data. The coordinate differences between the two datasets are significantly reduced, indicating higher consistency with radar data. The correction algorithm decreases the LMI lightning location deviation caused by CTH, thereby improving the accuracy and reliability of satellite lightning positioning data. The proposed ECPC model can be used for the real-time correction of lightning data when CTH is obtained at the same time, and it can be also used for the post-correction of space-based lightning detection with other cloud top height data.

PPP_Mansoura: an open-source software for multi-constellation GNSS processing

Abstract PPP_Mansoura is a new software that can process multi-GNSS data work on MATLAB environment and linked with C# in the preprocessing stage. It gives highly accurate results and provides a results file for each epoch, and the users can choose the GNSS system they want to run with the primary systems (GPS or GLONASS) and all this with simple MATLAB Code. For testing the software, we processed the raw data (RINEX 3) from 17 MGEX stations for 24 h data during 1-week with a 30-s interval time and submitted it to the new software and PPPH software. The averaged positioning errors obtained from PPP_Mansoura and PPPH were 5.14 mm and 6.9 mm respectively, for the East direction, 11.6 mm and 14 mm for the North direction, and 14.56 mm and 20.4 mm respectively for the Up direction, the averaged convergence time obtained from PPP_Mansoura and PPPH were 35.3 min and 54.47 min, so the results show that PPP_Mansoura give results with high accuracy can be comparable with PPP standards results and PPP software results.

Influence of Transparent Envelope Parameters on Office Building Energy Use Intensity in the Different Thermal Climate Regions of China

The role of the transparent envelope in energy savings is crucial as it accounts for a significant proportion of the total energy loss (between 30 and 40%). This paper focuses on the identification of reasonable parameters for the transparent envelope in different climatic regions. To achieve this goal, typical urban office buildings from four different climatic regions are used as research objects. A total of 1600 scenarios were simulated to investigate the variation of energy use intensity, including transparent envelope parameters, meteorological parameters and different types of glazing. The results show that for south-facing transparent envelope facades, type D glazing is the most energy efficient in severe cold regions, type C in colder regions and type B in the other two climatic regions. No solar shading is required in the very cold region. Horizontal shading can be an effective method for saving energy in colder climates, while comprehensive shading can be beneficial in other regions. Deep shading is particularly energy efficient if it meets lighting requirements. For example, in Guangzhou, energy savings of 13.46%, 15.47%, 7.01% and 7.02% can be achieved in the east, west, south and north directions, respectively, using B-type glazing and a comprehensive shading depth of 900 mm.

Elevation-Wise and Direction-Wise Distribution of Land Surface Temperature in Jeju Island using Landsat 7 Data

In the present research, the Land Surface Temperature (LST) has been calculated from Landsat 7 data of Jeju Island to understand the spatial distribution of temperature on the island which would be strongly related to the ecological characteristics of the island. The dates were selected based on seasons (winter and summer) March 12 and September 19, 2020, respectively. Results calculated from a thermal band of Landsat 7 revealed the temperature variations on the island. Winter temperature varies from -3.7 to 31 oC while the summer season temperature varies from 20.6 to 43.1 oC. The surface temperature was also calculated at elevations of 100m and 500m for both seasons. It was found that on 100 m elevation, in winter the North and South directions have the same temperature, comparatively, in summer the North direction has a 0.97 oC higher temperature than the South. The East direction showed a 0.55 oC higher temperature as compared to the West in winter but in the summer season the case was opposite and the West had a 1.46 oC higher surface temperature than the East. Interestingly at 100 m height in summer, the North, and West has also the same temperature (34.25 oC). In the second case, on 500 m height for all four directions, the LST was compared and results showed that the South has 0.58 and 1.52 oC higher temperatures in winter and summer seasons respectively from the North. On the contrary, the West has 3.33 and 0.5 oC higher temperatures than the East in winter and summer seasons respectively. It revealed that seasons and altitude have a great impact on the LST in different cardinal directions of the island. From the results, it can be assumed that the island's ecological diversity would be strongly related to the geographical distribution of temperature.

Retrieval of Tropospheric NO2 Vertical Column Densities from Ground-Based MAX-DOAS Measurements in Lhasa, a City on the Tibetan Plateau

In order to investigate the abundance of and temporal variation in nitrogen dioxide (NO2) in the troposphere and validate the corresponding satellite products during a normal year and the lockdown period of coronavirus disease 2019 (COVID-19) in Lhasa, a city on the Tibetan Plateau (TP), ground-based remote-sensing measurements captured by applying multi-axis differential optical absorption spectroscopy (MAX-DOAS) were recorded from August 2021 to March 2023 at the Lhasa site (91.14°E, 29.66°N; 3552.5 m altitude). The NO2 differential slant column densities (dSCDs) were retrieved from the spectra of scattered solar light at different elevation angles. Then, the tropospheric NO2 vertical column densities (VCDs) were calculated with the geometric approximation method. Based on the retrieved tropospheric NO2 VCDs, we found that the pattern of monthly variation in tropospheric NO2 VCDs in Lhasa presented two peaks, one in winter and one around May. According to the monthly means of tropospheric NO2 VCDs during the COVID-19 lockdown, the NO2 background level in Lhasa was estimated to be 0.53 × 1015 molecules·cm−2. For diurnal variations in tropospheric NO2 VCDs, the morning and evening peaks disappeared during the COVID-19 lockdown period. The east–west direction (i.e., along the river valley) was the main path of NO2 transport and dispersion in Lhasa, but the tropospheric NO2 VCDs were little dependent on the wind direction or wind speed during the COVID-19 lockdown. The correlation coefficient of tropospheric NO2 VCDs was R = 0.33 (R = 0.43), with the averaged relative deviation of −28% (99%) for the TROPOMI (GEMS) relative to ground-based MAX-DOAS. The monthly deviations of tropospheric NO2 VCDs between ground-based MAX-DOAS and the satellite showed a dependence on NO2 abundance, with the maxima of the monthly positive deviations during the COVID-19 lockdown period. The GEMS could not capture the strong and systematic diurnal variation in tropospheric NO2 VCDs in the “normal” year well. During the COVID-19 lockdown, the GEMS (>2 × 1015 molecules·cm−2) overestimated the hourly levels measured by ground-based MAX-DOAS (<1.6 × 1015 molecules·cm−2). As a whole, these results are beneficial to understanding the influences of anthropogenic activities on NO2 background levels in Lhasa and to learning the accuracy of satellite products over the TP, with its high altitude and complex terrain.

Detection of optical emission from the supernova remnant G7.7–3.7

ABSTRACT We present the first optical study of the supernova remnant (SNR) G7.7–3.7, with the aim of determining its evolutionary phase since it has been suggested to be the remnant of SN 386 AD. We obtained narrow-band images in the filters H α + [N ii], H β, [O iii], [S ii] that revealed faint optical emission in the southern region of the SNR consisting of two filaments elongated in the east–west direction aligned with the X-ray emitting region of the remnant. The filaments were seen in H α + [N ii], [O iii] images and marginally in the [S ii] images, with a non-detection in H β. Long-slit spectroscopy of the three regions along one filament revealed large ratios of [S ii]/H α = (1.6–2.5), consistent with that expected for a shock-heated SNR. The [S ii] doublet ratio observed in two of the regions implies an upper limit for the electron density of the gas, with estimates falling below 400 cm−3 and 600 cm−3 in the respective areas. We discuss potential physical mechanisms that formed the observed optical filaments and we suggest that most likely they resulted by a collision of the SNR with a dense circumstellar shell lying at the southern region of the remnant.

Assessment of landfill site suitability using GIS, remote sensing, and the multi-criteria decision-making (AHP) approach, Ethiopia

ABSTRACT Solid waste management (SWM) in Ethiopian cities is a significant public health, economic, and environmental issue, with access to suitable disposal locations becoming challenging due to social, environmental, economic, and technical factors. This study aims to propose suitable landfill sites for Debrebirhan Town's solid waste disposal using an integrated survey mechanism, including geographical information system, remote sensing, and analytical hierarchy process (AHP), to address limiting factors. Economic, social, and environmental data were used for the suitable site selection. Satellite images were processed by ERDAS IMAGINE Software, and ArcGIS software was used to identify and map the potential landfill sites. The suitability map was produced by the combined effect of the weights of the criteria and the suitability of the factor maps. The result is summarized with four suitability levels labeled as highly suitable (23%), moderately suitable (51.75%), less suitable (0.25%), and unsuitable (25%). The most suitable landfill sites were found in three locations in the west, north-west, and north directions of Debrebirhan Town that fulfill the economic feasibility, environmental safety, and social acceptability requirements for solid waste disposal. The findings are relevant for governmental decision-making and policy framework implementation.