South African Journal of Geomatics最新文献

{"title":"Pseudorange multipath at Zomba geodynamics Continuously Operating Reference Station (CORS) in Malawi","authors":"Robert S.B. Galatiya Suya, M. Soko, Harvey Chilembwe, Arles C. Kapachika, Chikondi Mphamba","doi":"10.4314/sajg.v10i1.1","DOIUrl":"https://doi.org/10.4314/sajg.v10i1.1","url":null,"abstract":"Multipath effects are mostly regarded as a nuisance in Global Navigation Satellite System (GNSS) receiver measurements and it is of utmost relevance to expose the magnitude this error has on observations. The impact of multipath is characterized in the context of a given environment and application. In Malawi, Zomba geodynamics Continuously Operating Reference Station (CORS) is in a multipath prone environment. The GNSS observations for this station have been used in geodynamics studies in Malawi without an understanding of multipath affecting the positioning accuracy. Taking this as an advantage, this paper evaluated pseudorange multipath (MP) and signal noise ratio (SNR) on both L1 (MP1 and SNR1) and L2 (MP2 and SNR2) for the station. This was specifically addressed by computing the elevation mask with minimum and maximum multipath effects. In addition, the number of satellite vehicles (SVs) and their associated Geometric Dilution of Precision (GDOP) are also determined to define their relationship with respect to elevation angles. One week GNSS observations spanning a twenty-four hour interval for DOY 001 to DOY 007 in January 2018 were analysed in Translation Editing and Quality Check (TEQC) software at four (10º, 15º, 20º and 25º) cut-off angles. Results indicate high multipath effects for both MP1 and MP2 at 10º elevation mask among the four elevation masks. The least MP1 and MP2 multipath effects were detected at an elevation angle of 25º. In addition, MP1 multipath was worse than MP2 all the angles. Moreover, statistical results demonstrated an increase in both SNR1 and SNR2 with respect to elevation angle. For these days, L2 signal was more affected by noise than L1. Further to this, an assessment of SVs and GDOP for the CORS show that at least ten (10) satellites were observed in each day at 10º and 15º elevation cut-off. The number of satellites dropped to five (5) at the elevation angle of 25º resulting into a larger GDOP value of 4.5 (a decrease by about 38% from 1.7 at 10º and 15º elevation cut-off angles). Therefore, to increase both the number of satellites and precision, Zomba CORS may be upgraded to a multi-constellation CORS by including other navigation systems such as GLONASS, Galileo and BeiDou. While it is possible to reject GNSS satellite observations below the horizon, it is recommended that post-processing of GNSS data for Zomba geodynamics CORS be done at elevation masks above 15º. Considering that multipath repeats itself every sidereal day, it is thus recommended to model or remove multipath affecting Zomba geodynamics CORS. In addition, the study also recommends that trees very close to Zomba CORS antenna be removed to reduce signal scattering.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42554169","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":"A seasonal relationship between land surface temperature and normalized difference bareness index","authors":"S. Guha, H. Govil","doi":"10.4314/sajg.v10i2.12","DOIUrl":"https://doi.org/10.4314/sajg.v10i2.12","url":null,"abstract":"The present study analyzes the seasonal variability of the relationship between the land surface temperature (LST) and normalized difference bareness index (NDBaI) on different land use/land cover (LULC) in Raipur City, India by using sixty-five Landsat images of four seasons (pre-monsoon, monsoon, post-monsoon, and winter) of 1991-1992, 1995-1996, 1999-2000, 2004-2005, 2009-2010, 2014-2015, and 2018-2019. The results show that the post-monsoon season indicates the best correlation (0.59), followed by the monsoon (0.56), pre-monsoon (0.47), and winter (0.44) season. The water bodies reflect a strongly positive correlation in all the four seasons (0.65 in pre-monsoon, 0.51 in monsoon, 0.53 in post-monsoon, and 0.62 in winter). On green vegetation, this correlation is also strongly positive in monsoon (0.57), post-monsoon (0.62), and winter (0.55), whereas it is moderate positive in pre-monsoon (0.37) season. The built-up area and bare land build a moderate positive correlation in all the four seasons (0.35 in pre-monsoon, 0.43 in monsoon, 0.48 in post-monsoon, and 0.39 in winter). Among the four seasons, the post-monsoon season builds the best correlation for all LULC types, whereas the pre-monsoon season has the least correlation. This research work is beneficial for land use and environmental planning of any city under similar climatic conditions.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42618337","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":"Regional ionospheric total electron content over Africa from ground-based GNSS observations","authors":"M. Moses, J. D. Dodo, L. M. Ojigi, K. Lawal","doi":"10.4314/sajg.v10i1.2","DOIUrl":"https://doi.org/10.4314/sajg.v10i1.2","url":null,"abstract":"Due to the wide use of GNSS receivers both on satellites at low earth orbit and on the ground, continuous and long-time ionospheric data with increasing accuracy have been obtained and used to study variations in the Earth’s ionosphere. Daily data from 2010.001 to 2017.365 sampled at 30 seconds from 104 African Geodetic Reference Frame (AFREF) dual-frequency GNSS Continuously Operating Reference Stations receivers distributed across Africa, were used in this study. Single Layer Model which assumes that all free electrons are concentrated in a shell of infinitesimal thickness, provides determining ionospheric total electron content value. In this study, the SLM model was used to derive total electron content values. TEC values obtained from the AFREF GNSS CORS measurements were compared with the TEC values from the global ionosphere maps provided by the Centre for Orbit Determination in Europe (CODE). The comparison was achieved by means of time series and wavelet analyses, and also by considering various model validation metrics. Comparative results for TEC estimates from both datasets based on goodness of fit measures, time series and wavelet analyses show good agreement on a statistical basis (r = 0.948) within the limits of experimental observation.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41298394","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":"Obituary David Warton (Dave) Kirby","authors":"Francis Ulman Naude","doi":"10.4314/sajg.v10i1.7","DOIUrl":"https://doi.org/10.4314/sajg.v10i1.7","url":null,"abstract":"Obituary compiled by Frank Naude from input by the Kirby family and friends.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41313660","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":"The status of aerial photogrammetry in South Africa: a transition to digital imagery system","authors":"L. Ngcofe, Bulelwa Semoli","doi":"10.4314/sajg.v11i1.3","DOIUrl":"https://doi.org/10.4314/sajg.v11i1.3","url":null,"abstract":"The digital image camera technology has revolutionized the aerial imagery capture throughout the world. It has provided high spatial and spectral resolution together with superior efficiency and reliability compared to the traditional analogue aerial imagery method. In so doing, this has provided great accuracy in various photogrammetric applications. The South African survey and mapping organisation currently known as Chief Directorate: National Geospatial Information (CD: NGI) has been capturing aerial photography dating back as early as the 1930s. However, from 2008 CD: NGI embraced a transition to digital aerial imagery capture at 50cm Ground Sample Distance (GSD) (from 2008 to 2016) and 25cm GSD (as from 2017 till date). This has resulted to 1370 digital aerial imagery already captured (this number will continue to change as there are jobs that are still being flown which are yet to be recorded). The continuous enhancement of digital camera technology opens for more possibilities of national aerial imagery capture at even greater spatial resolution such as 10cm GSD in the foreseeable future.However, the continuous digital imagery capture has not been without challenges such as the current global Covid-19 pandemic which has resulted in budget reprioritization, the organisation’s technical knowledge transfer from one generation to another together with the determination of the CD: NGI requirement for digital imagery specifications. The organisation values stakeholders’ engagement to ensure relevance, completeness and consistency on the data produced. This is possible through collaboration and partnership between State institutions, the private sector, research, and tertiary institutions through sharing of resources.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48810865","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":"Urban land use land cover mapping in tropical savannah using Landsat-8 derived normalized difference vegetation index (NDVI) threshold","authors":"M. Idrees, D. Omar, A. Babalola, Hussein. A. Ahmadu, Abdulganiyu Abdu Yusuf, Falilat O. Lawal","doi":"10.4314/sajg.v11i1.8","DOIUrl":"https://doi.org/10.4314/sajg.v11i1.8","url":null,"abstract":"Generation of land use/land cover map at different spatial scales using satellite remote sensing data has been in practice as far back as early 1970s. Since then, research focus has been on the development of classification steps and improving the quality of the resulting maps. In recent times, the demand for detailed high accuracy land-use and land-cover (LULC) data has been on the increase due to the growing complexity of earth processes, while, at the same time, processing step is becoming more complex. This paper explores Landsat 8 derived normalized difference vegetation index (NDVI) threshold for the purpose of simplifying land cover classification process. NDVI images of January, May and December, 2018, representing dry, wet and harmattan seasons were generated. Thereafter, NDVI values corresponding to the location of a set of training data representing the target urban land covers (water, built-up area, soil, grassland and shrub) were extracted. Using the statistics of the extracted values, NDVI threshold for the respective land cover type were determined for the classification process. Finally, the classification accuracy was evaluated using the unbiased matrix coefficient technique which produced overall accuracy of 71.3%, 46.4% and 75.6% at 95% confidence limit for the months of January, May and December of the year review respectively. The result has shown that NDVI threshold is a simple and practical alternative to obtain LULC map at a reasonable time with a few data.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42402780","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":"Small dams: determining the minimum waterbody surface area that can be successfully detected using Sentinel-1 SAR imagery","authors":"M. von Fintel, J. Kemp","doi":"10.4314/sajg.v11i2.9","DOIUrl":"https://doi.org/10.4314/sajg.v11i2.9","url":null,"abstract":"Water is a scarce resource in South Africa, and approximately 62% of the water used in South Africa is for irrigation. This water is stored in many small dams scattered across the country. If not managed correctly, they could have a negative effect on catchment areas and on the availability of water. As such, there is a need for a new monitoring and management system to be developed. This study determined the minimum surface area that would be required for a waterbody to be detected on Sentinel-1 Synthetic Aperture Radar imagery. A Random Forest classifier was used to detect waterbodies on a Sentinel-1 image calculated from a time series of imagery taken over a period of three months. Steep incidence angles outperformed shallow incidence angles, with the classification having an overall accuracy of 80%. Detection rates were almost 90% for waterbodies of one hectare and greater, with no false positives, and a 10% false negative rate. These findings provide the foundation for developing a detection and monitoring system, which would allow for the better management of water resources in South Africa.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49519740","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":"Analysing the changes in the bathymetry of Saldanha Bay between the years 1977 and 2021","authors":"L. Du Toit, Ivan Henrico, J. Bezuidenhout, B. Mtshawu","doi":"10.4314/sajg.v11i2.11","DOIUrl":"https://doi.org/10.4314/sajg.v11i2.11","url":null,"abstract":"The construction of the Saldanha Port has been the reason for the major changes in the bathymetry and sediment dynamics observed in Saldanha Bay in the last decades. In this paper, newly acquired soundings from the National Hydrographer were used to analyse the changes between 1977 and 2021 - over a 44-year period - in the bathymetry of Saldanha Bay. The Ordinary Kriging (OK) interpolation method, available through the Geostatistical Wizard in ArcGIS Pro, was used for creating surface models to conduct comparisons with the bathymetry of Saldanha Bay. The results indicate a general increase in depth since 1977 of between 0.395 and 3.203 m, and an average increase in depth within the Big Bay of 1.799 m. Between 1977 and 2021, a total volume loss of 49 364 560.0 m3 in sediment was calculated - an indication of how the sedimentation process in Saldanha Bay has changed subsequent to the construction of the harbour.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47191673","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":"Geospatial assessment of land suitability for oil palm (Elaeis guineensis Jacq.) growing in Northern Uganda.","authors":"Anjo Abraham, Ivan Bamweyana","doi":"10.4314/sajg.v11i2.10","DOIUrl":"https://doi.org/10.4314/sajg.v11i2.10","url":null,"abstract":"Under the second phase of the National Oil Palm Project, the Government of Uganda plans to extend the oil palm project to Northern Uganda. According to the Final Project Design Report (2017) of the National Oil Palm Project, and based on the rainfall, soil and temperature of the region, areas in Northern Uganda have already been mapped for the project. However, no detailed information on the degree of suitability of the areas has been provided. In this research, other parameters such as land cover, elevation and slope were identified through the literature review. Furthermore, on the basis of the reclassify tool in ArcMap 10.8, the data were then reclassified into four classes, namely, highly suitable (S1), moderately suitable (S2), marginally suitable (S3) and unsuitable (N.) With the aid of the Analytical Hierarchical Process (AHP), pairwise comparison matrices were constructed and the weight of each parameter was computed. The suitability map obtained from a weighted linear combination identified 38.18%, 35.54%, 21.41% and 4.87% of the land area as highly suitable, moderately suitable, marginally suitable and unsuitable, respectively. A geospatial assessment of the suitability of the land for oil palm growing was carried out. It was based on only the soil types, but excluded the chemical properties of the soil. Therefore, further research on the chemical properties of the soils at suitable sites should be carried out. In-depth research should be carried out While considering social and economic factors among the criteria to determine the willingness and financial capability of the people to venture into oil palm growing as a source of income, Oil Palm Uganda Limited should conduct in-depth research into this issue.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43628824","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":"Geospatial assessment of land use/cover, rainfall, and flood incidents in Eti–Osa, Lagos, Nigeria","authors":"Toka Sunday Onajomo","doi":"10.4314/sajg.v11i2.3","DOIUrl":"https://doi.org/10.4314/sajg.v11i2.3","url":null,"abstract":"Flooding in Lagos State has been on the rise in the past two decades, especially in the Eti-Osa area of the state. This is largely due to the increased volume of rainfall associated with climate variability and sea level rise. Flooding incidents have led to loss of lives and properties. The objective of this study is to examine the dynamics of flood occurrences in the Eti-Osa area of Lagos metropolis. Rainfall data for the area covering a period of 30 years (1990 to 2019) were obtained from the Nigerian Meteorological Agency (NiMET) in Lagos, and analyzed using the basic descriptive statistical technique. The purpose was to evaluate rainfall characteristics that were influencing flooding events in the area. Furthermore, remotely sensed multi-date Landsat imageries of 1990, 1997, 2001, 2012, and 2017 were obtained, and analyzed to determine how land use and land cover characteristics have changed and have been affected by flooding over the study period. The data were subjected to digital image processing and supervised classification was carried out on the images of the various dates. Results showed that flooding became prevalent as more areas became built up and as vegetated areas declined. Also, flooding events appeared to be responsive to the climatic extremes. Moreover, poor drainage, increased population number s, and non-compliance to building and current environmental regulations were key factors that exacerbated the increased prevalence of flooding in the area. The study recommended that flood control policies, including land-use planning for the area, need to be pursued urgently.","PeriodicalId":43854,"journal":{"name":"South African Journal of Geomatics","volume":null,"pages":null},"PeriodicalIF":0.5,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43843790","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}