Browsing by Author "Odera, Patroba Achola"

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    Open Access
    Estimation of Above Ground Biomass in Forests Using Alos Palsar Data in Kericho and Aberdare Ranges
    (Scientific Research, 2017-03-20) Maina, Eunice Wamuyu; Odera, Patroba Achola; Kinyanjui, Mwangi Jame
    Above Ground Biomass is one of the six pools identified in the inventory of forest resources and estimation of greenhouse gas emissions and sinks from the forestry sector. The pool varies by management practices in different agroecological or agro-climatic zones in forests. The quantification of above ground biomass (AGB) hence carbon sequestration in forests has been very difficult due to the immense costs required. This research was done to estimate AGB using ALOS PALSAR L band data (HH, HV polarisation) acquired in 2009 in relation with ground measurements data in Kericho and Aberdares ranges in Kenya. Tree data information was obtained from ground measurement of DBH and tree heights in 100 circular plots of 15 m radius, by use of random sampling technique. ALOS PALSAR image is advantageous for its active microwave sensor using L-band frequency to achieve cloud free imageries, and the ability of long wavelength cross-polarization to estimate AGB accurately for tropical forests. The variations result between Natural and plantation forest for measured and estimated biomass in Kericho HV band regression value was 0.880 and HH band was 0.520. In Aberdare ranges HV regression value of 0.708 and HH band regression value of 0.511 for measured and estimated biomass respectively. The variations can be explained by the influence of different management regimes induced human disturbances, forest stand age, density, species composition, and trees diameter distribution. However, further research is required to investigate how strong these factors affect relationship between AGB and Alos Palsar backscatters.
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    Open Access
    Estimation of Tree Height and Forest Biomass Using Airborne LiDAR Data: A Case Study of Londiani Forest Block in the Mau Complex, Kenya
    (Commercial, 2017-04-27) Mutwiri, Faith Kagwiria; Odera, Patroba Achola; Kinyanjui, Mwangi James
    Tactical decisions on natural resource management require accurate and up to date spatial information for sustainable forest management. Remote sensing devices by the use of multispectral data obtained from satellites or airborne sensors, allow substantial data acquisition that reduce cost of data collection and satisfy demands for continuous precise data. Forest height and Diameter at Breast Height (DBH) are crucial variables to predict volume and biomass. Traditional methods for estimation of tree heights and biomass are time consuming and labour intensive making it difficult for countries to carry out periodic National forest inventories to support forest management and REDD+ activities. This study assessed the applicability of LiDAR data in estimating tree height and biomass in a variety of forest conditions in Londiani Forest Block. The target forests were natural forest, plantation forests and other scattered forests analysed in a variety of topographic conditions. LiDAR data were collected by an aircraft flying at an elevation of 1550 m. The LIDAR pulses hitting the forest were used to estimate the forest height and the density of the vegetation, which implied biomass. LiDAR data were collected in 78 sampling plots of 15 m radius. The LiDAR data were ground truthed to compare its accuracy for above ground biomass (AGB) and height estimation. The correlation coefficients for heights between LiDAR and field data were 0.92 for the pooled data, 0.79 in natural forest, 0.95 in plantation forest and 0.92 in other scattered forest. AGB estimated from LiDAR and ground truthed data had a correlation coefficient of 0.86 for the pooled data, 0.78 in natural forest, 0.84 in plantation forest and 0.51 in other scattered forests. This implied 62%, 84%and 89% accuracy of AGB estimation in natural forests, other scattered forests and plantation forests respectively. The even aged conditions of plantation forests might have resulted to better estimates of height and AGB as compared to uneven aged natural forests and scattered forests. The results imply the reliability of using Airborne LIDAR scanning in forest biomass estimates in Kenya and are an option for supporting a National Forest Monitoring System for REDD+.
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    Municipal solid-waste collection and disposal management using geospatial techniques in Maseru City, Lesotho
    (2022) Moremi, Makhosi; Odera, Patroba Achola
    The use of geospatial techniques plays a crucial role in solid waste management. Collection and transportation of solid waste must be done in an efficient manner to avoid negative environmental impacts. At the time of study, there are no collection and routing system in Maseru City, leading to haphazard collection and disposal of Municipal Solid Waste (MSW). The aims of the study are: (i) To get an understanding and address the challenges faced by relevant stakeholders in solid waste management for Maseru City, (ii) To minimize adverse environmental impacts due to unscientific location of a disposal site and (iii) To minimize transportation costs and time during collection. The objectives of this study are summarized in the following: assess the current solid waste management, model suitable disposal/dump sites, determine MSW collection points and develop an optimal route for MSW collection and disposal in Maseru City. To assess the current solid waste management, 130 households, 73 community waste pickers, 15 Maseru City Council (MCC) management staff and 3 drivers were interviewed, and relevant data collected. Both primary and secondary data collection methods were used. Primary data collection methods included interviews, questionnaires and observations and creating feature classes in a geo database. Secondary data collection was done from relevant government repositories, digitization, and internet web sites. Simple random, area, cluster, and convenience sampling techniques were applied. Geographical Information Systems (GIS) and Remote sensing techniques were used to carry out suitability and network analysis, and location of MSW collection points. The study found out that the dump site (Ts'osane) was used by MCC and was not suitably located, hence more suitable alternative dump sites have been proposed. However, Ts'osane dump site was adopted in the analysis as it is the one used by MCC at the time of study. The researcher also found out that there were no designated MSW collection points and optimal routes, and that solid waste collection was done by both MCC and CBOs. In this regard, 334 collection points have been determined based on population and generated solid waste per Constituency and were randomly located in the study area. However, due to the policy that within 25m from the road no development could take place, only collection points which fell v within 25m from the road were selected and used in the routing analysis. One truck was used in the analysis, although more trucks could be used as it was at the time of study. For future research, there is a need to research on policy so that criteria for locating solid waste disposal and location of collection points is explicitly specified in the law to be able to conduct scientific analyses. A multi modal network analysis that would include all the vehicles used by MCC and the CBOs to develop a comprehensive network analysis that would also include necessary attributes such as road names, type, class, and length is needed.
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    Open Access
    On the development of a digital elevation model over South Africa using ground and satellite data
    (2022) Malindi, Mihlali; Odera, Patroba Achola
    A digital elevation model (DEM) represents the bare land surface of the Earth. DEMs are used in a wide range of applications, including geological studies, geomorphology, water resources and hydrology, evaluation of natural hazards, and vegetation surveys. In recent years, DEMs have increasingly been used in geographic information systems (GIS), mainly due to the availability of free satellite-based DEMs, some with global coverage. The satellite-based DEMs over South Africa provide topographic surface representation but are associated with errors, and in recent decades there have been significant efforts to improve accuracy. In South Africa, the ground levelling (trigonometrical beacon) data is more capable of representing the terrain heights accurately. However, the data points are farther apart, which makes it difficult for accurate continuous terrain representation. In this research, contributions are made towards the development of an accurate digital elevation model from ground and satellite data over South Africa. This is achieved by preparing satellite-based DEMs (AW3D30, SRTM, ASTER, TanDEM-X, and MERIT), assessing the quality of the satellite-based DEMs, selecting candidate DEMs for fusion, modelling candidate DEM errors, and fusing DEMs. The aerial-based DEM from LiDAR is also applied in the assessment of the quality of satellite-based DEMs, although this was only possible in selected areas due to a lack of LiDAR data covering the whole of South Africa. Following removal of outliers from each DEM, a different number of ground levelling data is used in the assessment of the DEMs (26364, 25728, 23773, 25967 and 24485) ground levelling points for AW3D30, SRTM, ASTER, TanDEM-X and MERIT, respectively. The vertical quality assessment results indicate that the standard deviations of the differences between ground levelling and DEMs heights are ±5.09, ±7.03, ±9.20, ±4.99 and ±8.36 m for AW3D30, SRTM, ASTER, TanDEM-X and MERIT, respectively. In general, the vertical accuracies of the satellite-based DEMs are relatively lower in higher areas than in low areas. The results of height differences between satellite-based and LiDAR DEMs heights in different geomorphological ranges indicate that the AW3D30 and TanDEM-X are better candidate DEMs for generating a new DEM over South Africa. Applying a combination of linear regression, multiple regression, and adaptive terrain-dependent methods to these DEMs, their vertical accuracies improved. The standard deviations of the differences between ground levelling and the improved DEMs at 8,657 points over South Africa decreased from ±5.745 to ±4.995 m for AW3D30 and ±5.073 to ±4.582 m for TanDEM-X. A fused DEM was developed from improved AW3D30 and TanDEM-X DEMs using a combination of different fusion methods (linear combination, weighted averaging, and simple averaging) over South Africa. The fused DEM was assessed using 8,657 ground levelling points over South Africa. The standard deviation of the height differences between ground levelling and the fused DEM is ±4.290 m, indicating the superiority of the fused DEM over all the satellite-based DEMs used in this study. The fused DEM can be applied in areas with a slope less than 20° where an accuracy of less than 4.3 m is achievable. In the steepest areas, it can still achieve better vertical accuracies compared to other satellite-based DEMs tested.
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    Towards a geoid consistent vertical datum in South Africa
    (2021) Mphuthi, Matthews Siphiwe; Odera, Patroba Achola
    Traditionally, vertical datums have been realised through mean sea level (MSL) data, at one or more tide gauge station(s), followed by a precise levelling procedure to establish a network of benchmarks. Most countries around the world are still using mean sea level based vertical datums, and South Africa is not an exception. However, these vertical datums suffer from a myriad of problems such as; numerous errors from the levelling networks and tide gauge sea level measurements, high cost of maintenance and upgrade, instability due to high MSL variability, inconsistency with data acquired by satellite and space-based measurement instruments and techniques, just to mention a few. Therefore there is a need to establish a geoid-based vertical datum to mitigate the limitations of mean sea level based vertical datum and to open further frontiers in geodesy, geophysics and geodynamics research, and related applications. Establishment of a national geoid-based vertical geodetic datum requires critical studies on the existing national height system(s) and related distortions, appropriate height system and related reference surface, offset between a local height datum and the intended reference surface, among others. The world is moving towards global unification of vertical datums to modernise the vertical positioning technique, an international height reference system (IHRS) would provide a globally unified height reference system. The horizontal positioning is already realised on the international terrestrial reference frame (ITRF) with high precision, and a similar approach for the realisation of a new vertical datum for South Africa is required. This study carries out analysis on the following aspects over South Africa: comparison between spheroidal, orthometric and normal height systems; accuracy of levelling network; vertical datum offset in relation to geoid, quasigeoid and the IHRS. It concludes by providing a unique framework for establishing a geoid-based vertical datum in South Africa. A numerical investigation of the correlation between the South African spheroidal, orthometric and normal height systems is conducted. It is determined that the spheroidal orthometric height system is more correlated with the normal height system (~ 21.3 cm on average) than the orthometric height system (~ 40.7 cm on average). A further numerical assessment was conducted to determine the magnitude of misclosures and the empirical value for the first order levelling network on the levelling loops. It was determined that majority of the levelling loops fall within the acceptable empirical value for the first order levelling network (c = 0.003). However, only one levelling loop does not fall within the acceptable range of misclosure for the first order levelling network, with a misclosure from spirit levelling measurement of −10.2 cm while the estimated acceptable misclosure is 9.7 cm. The vertical datum offset between the South African local vertical datum and global vertical datum was achieved by estimating the vertical datum offset and the geopotential values on the four fundamental benchmarks. A single-point-based geodetic boundary value problem (GBVP) approach was used following Molodensky's theory for estimating the height anomalies from the disturbing potential using Bruns's formula. The gravity potential at each tide gauge benchmark (TGBM) in South Africa deviates from the potential of the global reference surface by 0.585, −2.023, −2.597 and 2.105 m!s"! for Cape Town, Port Elizabeth, East London and Durban tide gauge benchmarks, respectively. The corresponding vertical datum offset between the international height reference system and the four fundamental benchmarks over South Africa are 5.973, −20.647, −26.518 , and 21.496 cm for Cape Town, Port Elizabeth, East London and Durban tide gauge benchmarks, respectively. The datum offsets between the land levelling datum (LLD) and the global vertical datum has been estimated, for the first time over South Africa, in this study. A preliminary geoid-based vertical datum in relation to the IHRS for South Africa was determined and evaluated using 138 GPS/levelling data points distributed over the country. However, since it would be difficult to identify exactly which data points are associated with a particular TGBM, the TGBM in Cape Town was held fixed for this analysis. During this analysis, the spheroidal orthometric height was unified to the IHRS (5#$%&#), an existing bias between the 5#$%&# and the local quasigeoid is estimated to be approximately 15.8 cm on average. An adequate data coverage is required to improve the quality of the determined vertical datum offset for the South African vertical datum in relation to the global vertical datum. It is proposed in this study that a normal height system should be adopted for South Africa, with the relevant reference surface being quasigeoid model. Some considerations to be taken during the implementation and adoption of a consistent geoid-based vertical datum in South Africa are discussed.