South African Journal of Geomatics最新文献

{"title":"Comparison of GRACE Gravity Anomaly Solutions for Terrestrial Water Storage Variability in Arid and Semi-arid Botswana","authors":"Mooketsi Segobye, Loago K. Motlogelwa, B. Nkwae, Y. Ouma, Lopang Maphale, Bagadzi M. Manisa","doi":"10.4314/sajg.v12i1.4","DOIUrl":"https://doi.org/10.4314/sajg.v12i1.4","url":null,"abstract":"Explorations of the differences between Gravity Recovery and Climate Experiment (GRACE) solutions in local regions and basins are fundamental in determining their suitability and applicability in these environments. Because of the different mathematical inversions used by the respective processing centers, individual solutions exhibit discrepancies in terms of mass increase or loss, which makes it difficult for users to select the best model for studying terrestrial water storage anomalies (TWSAs). This study compares TWSA trends, as derived from different GRACE solutions over the arid and semi-arid Botswana (2002-2019), where both storage and flux from CSR, JPL, GFZ, TUGRAZ, AIUB, and COST-G[1] were compared. The results show that the six solutions are fairly correlated with the least correlation of R=0.829 between JPL and AIUB, and a maximum of R=0.921 between CSR and TUGRAZ at a 95% confidence level. The TWSA analyses for 2002-2019 indicate that TWS is increasing in Botswana, with the least linear trend of +0.11cm/yr detected from the TUGRAZ inversion model, and the highest linear trend at +0.43cm/year from the COST-G model. On comparing TWS with rainfall, all the solutions presented the same spatio-temporal trends as the rainfall patterns, indicating that the GRACE solutions exhibit the same responses with respect to the received rainfall.  Over the 18 years investigated, the long-term rainfall trend was found to decrease, which was only detected by the TUGRAZ model in terms of the recorded equivalent water height (EWH) of -0.008cm/yr from the monthly trend observations. Overall, the AIUB inversion solution gave a better result as its signal was found to be the same as the rainfall signal. \u0000  \u0000[1] CSR = Center for Space Research;  JPL = Jet Propulsion Laboratory; GFZ = the German Research Center for Geosciences; TUGRAZ = Graz University of Techology; AIUB = the Astronomical Institute of the University of Bern; COST-G = the International Combination Service for Time-Variable Gravity Fields","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48301827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hartebeesthoek Radio Astronomy Observatory (HartRAO) antenna axis offset determined by geodetic VLBI analysis and ground survey","authors":"M. Nickola, H. Krásná, L. Combrinck, Jan Boehm, A. de Witt","doi":"10.4314/sajg.v12i1.7","DOIUrl":"https://doi.org/10.4314/sajg.v12i1.7","url":null,"abstract":"In the Very Long Baseline Interferometry (VLBI) space geodetic technique, various station-specific error sources corrupt the observable VLBI delay. An antenna axis offset (AO) model is applied in the VLBI data analysis for antennas with non-intersecting rotational axes, such as the 26-m and 15-m antennas for the Hartebeesthoek Radio Astronomy Observatory (HartRAO). The a priori AO values recommended by the International VLBI Service for Geodesy and Astrometry (IVS) for use in geodetic VLBI data analysis are taken, where possible, from values measured in ground surveys. The a priori AO values used for the HartRAO antennas in geodetic VLBI analysis have been identified as possible sources of error. The a priori AO value of 6695.3 mm for the 26-m antenna originates from a 2003 co-locational ground survey, conducted before a major bearing repair in 2008, which could have changed the AO. The a priori AO value of 1495.0 mm for the 15-m antenna was determined in 2007 in only a preliminary GPS survey. In this study, the respective AO values of the HartRAO 26-m and 15-m antennas were estimated from a VLBI analysis using the Vienna VLBI and Satellite Software (VieVS) and compared with measurements from co-locational ground surveys. It was found that the VLBI estimated values do not agree within the formal margins of error with the ground survey values, in that they differ by up to eight millimetres (8 mm) for the 26-m antenna and up to five millimetres (5 mm) for the 15-m antenna. As the ground survey values are considered to be more accurate than the VLBI estimated values, a further investigation of the site-specific error sources that may be contaminating the accuracy of VLBI results is required.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48884779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessment of Land Use Efficiencies of Ghanaian Cities: Case Study of Sekondi-Takoradi Metropolis","authors":"M. S. Aduah, S. Mantey","doi":"10.4314/sajg.v12i1.6","DOIUrl":"https://doi.org/10.4314/sajg.v12i1.6","url":null,"abstract":"Urban land use efficiency is a key indicator of the resilience of a city and its sustainability. However, in Africa and Ghana, information on land use efficiency in cities is lacking. There is little to no understanding as to how urban development is affecting the lives of people, the economy and the environment. In this study, geospatial techniques were used to estimate urban land use efficiency (LUE), the changes in the built-up area per capita and urban sprawl speed (SS) for the Sekondi-Takoradi Metropolitan area. Multi-temporal land use maps and population data were used for this purpose. The results indicate that generally land use efficiency in the city has improved since 2002, from a value of 0.67 between 2002 and 2008 to 0.88 between 2008 and 2016, and that it deteriorated slightly above one (1) between 2016 and 2021. The city has also become more built up over the period, with the rate of sprawling  also declining. However, the study shows that land in the city that was either agricultural land or grassland has been converted to built-up land use/land cover, which is indeed a challenge for urban agriculture. The results of this study can be used by city authorities as a guide to urban development.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47171330","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluation of EGM96 and EGM08 based on GPS/Levelling Heights in Egypt","authors":"Khaled Mahmoud Abdel Aziz, Karim Samir Rashwan, Nasr Saba","doi":"10.4314/sajg.v12i1.3","DOIUrl":"https://doi.org/10.4314/sajg.v12i1.3","url":null,"abstract":"The heights determined by  Global Positioning System (GPS) refer to the ellipsoid called the World Geodetic System 1984 (WGS84).  Global Geopotential Models (GGMs) that are available on GNSS commercial software are generally used to transform  ellipsoidal heights to orthometric heights. In this study, the geoid heights of GPS/Levelling were computed to evaluate the accuracy of the geoid heights obtained from two GGMs, namely, the Earth Gravitational Model 96 (EGM96) and the Earth Gravitational Model 08 (EGM08). Seventeen (17) GPS/Levelling stations of the High Accuracy Reference Network (HARN) over Egypt were used for this purpose. The standard deviations for the differences between the geoid heights obtained through GPS/Levelling and those obtained from EGM96 and EGM08 were determined as  ± 1.212 m and ± 0.543 m, respectively. This research confirms that the geoid heights obtained from EGM08 are closer to the geoid heights determined using GPS/Levelling over Egypt.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45584066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mapping of human displacement by Boko Haram in Nigeria from 2009 to 2021","authors":"Olusola Gabriel Omogunloye, Nnamdi Samson Iyasele, Olufemi Ayoade Olunlade, O. Abiodun, Tosin J. Salami, Abiodun O. Alabi","doi":"10.4314/sajg.v12i1.5","DOIUrl":"https://doi.org/10.4314/sajg.v12i1.5","url":null,"abstract":"Insurgencies by Boko Haram, a terrorist group operating in the north-west African states,   have negatively impacted the sense of national security in Nigeria. The activities of the sect have assumed political dimensions in that they have evaded all the possible technical and military solutions that have been implemented. The humanitarian crisis caused by incessant attacks by  Boko Haram sects has led to a growth in the population of internally displaced persons and the associated camps accommodating them. This research examined the activities of the Boko Haram sect and how they relate to internally displaced persons, as well as to the challenges faced by the latter from 2009 to 2021. The data used comprise data from the Armed Conflict and Location Event Data Database (ACLED), from the National Emergency Management Agency (NEMA), and geospatial data from Diva-GIS. The method that was applied for this purpose incorporated the use of GIS techniques for mapping the activities of the sect from 2009 to 2021: Microsoft Excel was used for the purposes of data refinement and analysis; while ArcGIS was used for the mapping of the camps of internally displaced persons, as well as for the hotspot and directional analyses in this particular context.. The findings of this research study show that Borno state experiences a 77% frequency of insurgency attacks,  followed by Yobe state with 11%. Over the years under study, 2015 is the year recording the highest number of fatalities in Nigeria, with Adamawa recording the highest number of fatalities in a state in spite of it being the least of all the states susceptible to terrorism. Borno, the most terrorized of the states, hosts the largest number of IDP camps but the challenges that these state experiences are relatively limited.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49304936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An Experiment in Determining the High-water Mark","authors":"J. Whittal, K. Mackie","doi":"10.4314/sajg.v12i1.1","DOIUrl":"https://doi.org/10.4314/sajg.v12i1.1","url":null,"abstract":"As a boundary of the seashore, the high-water mark (HWM) is relevant to the public, the State, and other rights holders in the coastal zone. Unlike most fixed property boundaries that are surveyed and beaconed, the HWM is subject to dynamic natural coastal processes and moves over time. Its location is difficult to determine, and the precision of this determination is unknown. This paper reports on an experiment to measure the precision (variability/repeatability) of the location of the HWM at a variety of sites near Cape Town, by volunteer participants. Four sites were chosen along stable (non-mobile) shores along the open, high energy oceanic shores south of Cape Town on the Cape Peninsula. One of these sites exhibits large variation in coastal terrain and type – at this site three sets of measurements were undertaken, bringing the total number of experimental sites to six. Surveying was undertaken in the South African national control survey system using network real-time kinematic global navigation satellite systems (GNSS). \u0000This experiment shows that the professional land surveyors located the HWM to ±1,6m, coastal engineers to ±4,1m, and the group of ‘others’ to ±4,2m. The professional land surveyors determined the height of the HWM to ±0,4m over all sites, compared to ±0,7m for all participants. The HWM is likely to be about 4 - 5m above the lowest astronomic tide. However, the line is not a contour – it is affected by weather and local variations in the coastline such as slope and seashore composition. The averaged heights of the HWM at each of the sites for all participants showed a range of 1,3m. Since the boundaries of the seashore cannot be determined with precision, property, cadastral and environmental law needs to continue to respect the nature of this environment and the limitations of locating the HWM.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":"1 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41438917","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Exploring the spatial variation of the effect of Covid-19 on property market activity in Kampala District","authors":"Davis Ssemwanga, R. Ssengendo, Lilian Oryema, Ivan Bamweyana","doi":"10.4314/sajg.v12i1.2","DOIUrl":"https://doi.org/10.4314/sajg.v12i1.2","url":null,"abstract":"The real estate sector in Uganda has been substantially impacted by the onset of COVID-19 in this country. Studies conducted worldwide have indicated that, pandemics affect property market activities differently. Additionally, the effect of pandemics on property market activity varies from one place to another. Studies conducted in Uganda, however, have not captured how the effect of COVID-19 on property market activities varies from one place to another. This study therefore explored the spatial variability of the effect of COVID-19 on property market activities in Kampala district, Uganda. The study took advantage of the spatial statistical analytical models advocated by GIS (Getis-Ord Gi*, OLS, GWPR) and a unique dataset of property transactions registered by the Ministry of Lands, Housing and Urban Development (MLHUD) during the outbreak of the deadly disease. Whereas the study observed high volumes of property transactions registered in the residential outskirts of the city, low volumes were observed in the Central Business District (CBD) and the low-income areas of the eastern and western parts of the district. On the other hand, the local model approach of GWPR exposed the substantial effects of COVID-19 on property market activities that varied from -39% to 10%. It was further established that COVID-19 generated negative effects in areas with low and high prices of land per acre, to the extent of increasing as the prices dropped or increased. On the contrary, a positive effect was realized in the residential outskirts of the city where prices of land per acre were moderate. Work from home, land parcel size as well as the composition of the population, proved to be the main drivers of the changes in property market transactions (activity). The findings of the study underpin the earlier postulations of various researchers that pandemics affect property market activity. However, the effects of the pandemics vary from one pandemic to another and from one place to another.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41443334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Post-conflict land administration in Edendale N Wirewall project","authors":"M. Barry","doi":"10.4314/sajg.v8i1.4","DOIUrl":"https://doi.org/10.4314/sajg.v8i1.4","url":null,"abstract":"The Edendale N Wirewall case is instructive for land tenure administration, project management and group tenure schemes in post-conflict land tenure administration and housing project management. The Greater Edendale Area experienced major localised conflict in the lead up to the end of apartheid. The Edendale N Wirewall project is a problematic state subsidised housing project. Innovations in development techniques and land tenure models are necessary in times of far reaching change. However, innovations should be justified by robust empirical evidence if failure might have a significant impact on the intended beneficiaries. Corruption, maladministration, patronage and inefficiencies can be expected in post-conflict land administration and project governance as new politicians come into power, the state is fragile and personnel changes and power shifts occur in the civil service. Fixing major problems in housing projects arising out of poor project management and poor project governance can result in costly remedial action and tenure insecurity in the decades following project completion. If the situation allows it, external expert checks on land administration operations management and far more frequent and independent project audits, on-site inspections and audit surveys may mitigate some of these challenges.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42108169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Assessing the impact of variations in atmospheric water vapour content over Nigeria from GNSS measurements","authors":"O. A. Isioye, L. Combrinck, J. Botai, M. Moses","doi":"10.4314/sajg.v8i1.3","DOIUrl":"https://doi.org/10.4314/sajg.v8i1.3","url":null,"abstract":"This study analyses the meteorological impact of the variability of precipitable water vapour (PWV) retrieved from ground-based global navigation satellite system (GNSS) stations over Nigeria from 2013 to 2014; these measurements represent the foremost probe of GNSS PWV distribution and variability over Nigeria. In this study, GNSS PWV daily estimates were grouped into monthly and seasonal averages; the variations in the monthly and seasonal estimates of GNSS PWV were characterized and correlated with different weather events that are regarded as good climate change indicators. The results revealed that the spatiotemporal changes in PWV content are largely subjugated by the effects of latitude, topographical features, the seasons and the continental air masses. Our study shows that there is a very strong seasonal interplay among the GNSS PWV, relative humidity, rainfall and cloud estimates. In addition, GNSS PWV and total electron content (TEC) estimates show an opposite relationship; the semi-diurnal relationship between GNSS PWV and TEC is stronger than the seasonal relationship. The seasonal relation among GNSS PWV, temperature and wind speed appears weak, while very strong interplay exists among the GNSS PWV, sun spot number and total solar radiation estimates. Our results confirm that GNSS PWV is a good pointer for weather forecasting/monitoring and fit for climate monitoring if available on a longer time scale. Finally, we recommend the densification of the GNSS network in Nigeria, as this will enable 3D profiling of PWV, thereby providing more information on GNSS PWV time series, which is needed for long-term climatology.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43707319","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analysis of GNSS baseline solutions in Ghana","authors":"Osman Mohammed Abukari1, Akwasi Acheampong, C. Fosu","doi":"10.4314/sajg.v8i1.1","DOIUrl":"https://doi.org/10.4314/sajg.v8i1.1","url":null,"abstract":"Accuracy is highly desired in all geodetic and mapping projects. Global Navigation Satellite Systems (GNSS) has many positioning capabilities which can produce the desired accuracies needed for establishing Ground Control Points (GCPs). However accuracy of positioning results from GNSS survey routines are influenced by session duration and baseline length. This study is targeted at determining optimum observation times for specific baseline lengths for GCP fixing and densification in Ghana. The study used four ground stations in Accra, Kumasi, Assin-Fosu and Sunyani. Each station was occupied for a total of four hours on three different days and the data were later split into various time segments to obtain different data sets. Using the Kumasi station as base, each of the baselines was processed three times for each of 3-day 4-hour observation sessions and the mean results accepted as the ‘true’ position values. Repeatability tests were carried out on the computed baselines and the ratios ranged between 1:1,141,100 and 1:4,918,000. All comparisons were based on the true position values. Root Mean Square Error (RMSE) and accuracies were computed from the differences. A plot of the RMSE against time showed that accuracy of positions continued to improve but after 50 minutes of observation there was no significant improvement in the accuracy of measured baselines. This study therefore set 50 minutes as the optimum duration for GNSS baselines up to 195km when using geodetic grade GNSS receivers in differential mode to establish GCPs.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47129173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}