Remotely sensed c3 and c4 grass species aboveground biomass variability in response to seasonal climate and topography

Seasonal climate and topography influence C3 and C4 grass species aboveground biomass (AGB). Climate change further threatens these grasses AGB, thereby compromising their ability to provide ecosystem goods and services. This emphasises the need to monitor their AGB for well-informed management. New-generation sensors, with improved resolution capabilities present an opportunity to explore C3 and C4 AGB. This study therefore investigated the response of remotely sensed C3 and C4 grasses AGB to seasonal climate and topography. Overall, the spatial and temporal responses of AGB due to seasonal climate and topography were observed across the study area

Optical remote sensing of aboveground forest biomass and carbon stocks in resource-constrained African environments.

Ph. D. University of KwaZulu-Natal, Pietermaritzburg 2015.No abstract available

Experimental Investigation of Forces Produced by Misaligned Steel Rollers

The International Space Station (ISS) Solar Alpha Rotary Joint (SARJ) uses a roller-based mechanism for positioning of the solar arrays. The forces and moments that develop at the roller interfaces are influenced by the design including the kinematic constraints and the lubrication condition. To help understand the SARJ operation, a set of dedicated experiments were completed using roller pairs. Of primary interest was to measure the axial force directed along the axis of rotation of the roller as a function of shaft misalignment. The conditions studied included dry and clean surfaces; one surface plated by a gold film, and greased surfaces. For the case of a bare 440C roller against a nitrided 15-5 roller without lubrication, the axial force can be as great as 0.4 times the normal load for a shaft angle of 0.5 deg. Such a magnitude of force on a roller in the SARJ mechanism would cause roller tipping and contact pressures much greater than anticipated by the designers. For the case of a bare 440C roller against a nitrided 15-5 roller with grease lubrication, the axial force does not exceed about 0.15 times the normal load even for the largest misalignment angles tested. Gold films provided good lubrication for the short duration testing reported herein. Grease lubrication limited the magnitude of the axial force to even smaller magnitudes than was achieved with the gold films. The experiments demonstrate the critical role of good lubrication for the SARJ mechanism

Understanding the influence of land cover change and landscape pattern change on evapotranspiration variations in Gwayi catchment of Zimbabwe

Understanding dynamics in hydrological processes helps toimprove water resource management. Climate and land coverchanges influence ecohydrological processes. This study soughtto assess the influence of climate, land cover and landscape struc-ture dynamics on actual evapotranspiration (ETa). To achieve this,the catchment parameter (w) was parameterised and the relation-ship between ETa and selected landscape metrics was deter-mined. The ratio of precipitation to potential evapotranspirationwas<1 and thewwas<2, suggesting that land cover changeswere more influential to ETa changes than climate variations.Given the loww(1<w<2), we conclude that the catchment hada low water retention capacity and was sensitive to land coverchanges

The enrolled pensioner scheme in Canada West, 1851-1858, with specific reference to the plan at Amherstburg.

Dept. of History, Philosophy, and Political Science. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1982 .D834. Source: Masters Abstracts International, Volume: 40-07, page: . Thesis (M.A.)--University of Windsor (Canada), 1982

ISS Solar Array Alpha Rotary Joint (SARJ) Bearing Failure and Recovery: Technical and Project Management Lessons Learned

The photovoltaic solar panels on the International Space Station (ISS) track the Sun through continuous rotating motion enabled by large bearings on the main truss called solar array alpha rotary joints (SARJs). In late 2007, shortly after installation, the starboard SARJ had become hard to turn and had to be shut down after exceeding drive current safety limits. The port SARJ, of the same design, had been working well for over 2 years. An exhaustive failure investigation ensued that included multiple extravehicular activities to collect information and samples for engineering forensics, detailed structural and thermal analyses, and a careful review of the build records. The ultimate root cause was determined to be kinematic design vulnerability coupled with inadequate lubrication, and manufacturing flaws; this was corroborated through ground tests, metallurgical studies, and modeling. A highly successful recovery plan was developed and implemented that included replacing worn and damaged components in orbit and applying space-compatible grease to improve lubrication. Beyond the technical aspects, however, lie several key programmatic lessons learned. These lessons, such as running ground tests to intentional failure to experimentally verify failure modes, are reviewed and discussed so they can be applied to future projects to avoid such problems

Influence of termites on the soil seed bank in an African savannah

In savannah ecosystems, termites drive key ecosystem processes, such as primary production through creation of patchiness in soil nutrients availability around their nests. In this study, we evaluated the role of termites in altering the soil seed bank size, an important ecosystem component that has often been overlooked in previous work. Data on above ground vegetation and soil seed bank samples were collected from four microhabitats, that is, the wooded mound, unwooded mound, tree sub‐ canopy and the open grassland matrix in a protected game reserve in south‐central Zimbabwe. The seedling emergence method was then used to identify species present in the soil samples. One‐way analysis of variance followed by Tukey's multiple comparison tests was executed to test for significant differences in plant species richness among the four microhabitats. The results indicate that plant species richness was high on wooded termite mound but did not differ between the unwooded and the sub‐canopy microhabitats

Effect of landcover/land-use changes on water availability in and around Ruti Dam in Nyazvidzi catchment, Zimbabwe

The aim of this study was to quantify the upstream land-use and landcover changes and assess their effect on Ruti Dam levels and water availability in Nyazvidzi catchment. Remote-sensing techniques, hydrologic modelling and statistical inference were applied. Spatial landcover dynamics were derived from Landsat satellite data for the years 1984, 1990, 1993, 1996, 2003, 2008, and 2013 using the maximum likelihood classification technique. Results showed that forests and shrubs decreased by 36% between 1984 and 2013 whilst cultivated areas increased by 13% over the same period. The HEC-HMS rainfall-runoff model was used to simulate steamflow for the Nyazvidzi catchment, Zimbabwe. For the calibration period (2000–2001), a satisfactory Nash–Sutcliffe efficiency (NSE) model peformance of 0.71 and relative volume error (RVE) of 10% were obtained. Model validation (1995—1997) gave a NSE of 0.61 and RVE of 12%. We applied the Mann-Kendall trend test to assess for monotonic trends in runoff over the study period and the results showed that there were significant decreases in observed runoff at Station E140 (monthly time scale) and at Stations E62 and E140 (seasonal time scale). Results showed that the wet season (Nov–Feb) had higher mean water balance values with an excess runoff of 8.12 mm/month. The dry season (April— Sept) had lower mean water balance values, with the lowest at 0.04 mm/month. Strong positive relationships (r2) between dam levels and land-use changes were obtained as follows: bare (0.95), cultivation (0.76) and forests (0.98). The relationship between runoff generated and land-use changes was found to be relatively weaker (0.54 for forests, 0.51 for bare and 0.14 for cultivation). Findings of this study underscore the relevance of applying hydrological models, remote sensing and statistical inference in quantifying and detecting environmental changes, as well as how they affect the availability and the quality of water resources in space and time

Use of remotely sensed derived metrics to assess wetland vegetation responses to climate variability-induced drought at the Soetendalsvlei wetland system in the Heuningnes Catchment, Western Cape province, South Africa

Wetland vegetation plays an important role in the environmental functioning of wetlands through the provision of ecosystem services, such as food and critical habitat for organisms that live in or near water resources. The ecosystem services provided by wetland vegetation are facing several pressures due to the impacts of drought. Drought can induce significant declines in overall plant productivity and even lead to high rates of plant mortality. Therefore, assessing vegetation response to a drought is important for wetland assessment. In this study, the subtle changes in vegetation distribution were used as a proxy to examine and quantify the extent of drought impacts on the Soetendalsvlei wetland within the Heuningnes Catchment, South Africa. First, the vegetation health information was extracted by calculating the Normalized Difference Vegetation Index (NDVI) during the wet and dry seasons for the period between 2014 and 2018. The derived NDVI results were further statistically linked to the corresponding rainfall and evapotranspiration observed during the study period. An analysis of NDVI results revealed that gradual vegetation health change occurred across the study area. The highest derived NDVI (0.5) for wetland vegetation was observed during 2014, but progressively declined over the years. Change in vegetation health indicated a significant (r = 0.8–0.92) and positive correlation to the amount of rainfall received over the same period, whereas with evapotranspiration the relationships showed an opposite trend (r = −0.7 to −0.5). The results of this study highlight the importance of integrating remotely sensed data and climate variability information in assessing wetland vegetation seasonal and long-term variations. Such information can help in decision-making on the conservation of wetlands and effective monitoring of wetland ecosystems

A new modified spatial approach for monitoring non-perennial river water availability using remote sensing in the Tankwa Karoo, Western Cape, South Africa

Non-perennial rivers (N-PRs) make up two thirds of all rivers in South Africa, yet many are ungauged. Traditionally, it has been assumed that when a flow is recorded, there is water throughout that river. These assumptions have led to incorrect estimations of available water resources. This work thus aimed at developing a new spatially explicit framework, for monitoring river water availability in a N-PR system. The Tankwa River in South Africa was used for testing this approach. The length of the river reach with water was determined using the Sentinel-1 and Sentinel-2 data derived indices. Image thresholding was applied to Sentinel-1, and the normalised difference water index (NDWI) to Sentinel-2. Sentinel-2 yielded an overall accuracy (OA) of 85%, whereas Sentinel-1 yielded an OA of 38%. The analysed reach of the Tankwa River had an actual length of 9 244 m. Based on the performance of Sentinel-2 data, further analysis was undertaken using Sentinel images acquired during the months of February, May and July of 2016. The results indicated that the lengths of the reaches of inundated Tankwa River were 2 809 m, 3 202 m and 2 890 m, respectively. Overall, the findings of this study show that an estimated length of a river inundated by water can be determined using new-generation Sentinel data and these results provide new insights on the dynamics of N-PRs – a previously challenging task with broadband multispectral satellite datasets