Browsing by Author "De Cauwer, Vera"

Now showing 1 - 7 of 7
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    The future Okavango project: SP05 - Impacts of altered land use practises on the plant related ESF&S. TFO fieldwork report 2010 - 2012 for task 6 of SP05: Timber provision of Burkea Woodlands
    (2013) De Cauwer, Vera
    This short field work report gives an overview of the forest inventory work done during the first two years of The Future Okavango (TFO) project, a project implemented till 2015 and funded by the German Ministry of Education and Research. TFO aims to integrate ecosystem functions and services into an ecological and economic approach to sustainable land management at a regional scale. Forest assessments are part of subproject 5 of TFO, which focuses on the vegetation in the Okavango basin of Angola, Namibia and Botswana. Objectives include : (1) qualitative and quantitative assessment and valuation of the plant based ecosystem functions and services, (2) a functional analysis of important aspects of the multiple interdependence between ecosystem compartments and drivers of change, (3) the study of the projection of current trends with regard to possible scenarios and their cumulative consequences, (4) the study of the potential for regional improvement given by the spatiotemporal composition and patterns of different land use options with the involved trade-offs and synergies.
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    Manual for working with MODIS images in SeaDAS 6.2.
    (2013) De Cauwer, Vera
    This manual was written for the students of the School of Natural Resources and Tourism, NUST during the pilot project “Assessing potential to produce final Ocean Colour maps of Namibia’s marine environment”, which is supported by the BCLME Programme and the NUST. The manual is written for students working with the SeaDAS software on the Linux computer of the Department of Land Management (operating system is Fedora Core 10) or the version of SeaDAS which can be installed in Windows through a virtual application Vmware player (seadasva). The images used are MODIS Aqua provided by NASA (HDF version 4 format).
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    Mapping of the BCLME shoreline, shallow water & marine habitats: Physical mapping project.
    (Benguela Environment Fisheries Interaction & Training Programme (BENEFIT), Benguela Current Large Marine Ecosystem (BCLME) Programme, 2007) De Cauwer, Vera
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    Optical remote sensing in support of eutrophication monitoring in the southern North Sea.
    (European Association of Remote Sensing Laboratories (EARSeL)., 2004) De Cauwer, Vera; Ruddick, Kevin; Park, Young-Je; Nechad, Bouchra; Kyramarios, Michael
    Spring mean and maximum chlorophyll a (chl a) concentrations are main factors to determine the eutrophication status of the Belgian waters as agreed within OSPAR in 2002. Other important assessment parameters to measure the degree of nutrient enrichment - the amounts of inorganic phosphate and nitrogen in winter - appeared to be above thresholds for most measurements performed in the period 1974-2002. As the standard in situ monitoring programme does not give a clear picture of the temporal and spatial distribution of chl a, it is logical to complement these measurements with optical remote sensing. However, chlorophyll concentrations derived from sensors such as SeaWiFS are unreliable in the Case 2 waters of this region because of high particulate and dissolved yellow substance absorption. Another important limitation of ocean colour sensors is the amount of useful images due to cloud cover. The combination of data from different ocean colour sensors in order to enable a better temporal coverage might be hampered by the different chlorophyll retrieval algorithms used. This study compares different global chl a algorithms (MODIS, SeaWiFS, MERIS) as well as a turbid water algorithm for the Southern North Sea. This is done by running the different algorithms on in situ reflectance spectra collected at 107 stations in the period 2001-2002 over the Southern North Sea and comparing them with in situ chl a concentrations, as well as by running the algorithms on a MERIS image of the 29th of July 2002. Based on this validation the accuracy of these products and their suitability for eutrophication monitoring in the Southern North Sea are assessed.
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    Potential, realised, future distribution and environmental suitability for pterocarpus angolensis DC in southern Africa.
    (ScienceDirect, 2014) De Cauwer, Vera; Muys, Bart; Revermann, Rasmus; Trabucco, Antonio
    The deciduous tree species Pterocarpus angolensis occurs in the dry woodlands of southern Africa and grows under a broad range of environmental conditions. It is threatened by overharvesting due to its valuable timber (Blood wood, Kiaat) and by land use changes. Information on the most suitable environmental conditions for the species is often old and anecdotal, while available data on its occurrence refer to range extent and not to distribution. Species distribution models (SDM) could provide more accurate information on distribution and environmental requirements and thereby assist sustainable management of this tree species. Maxent models were developed to estimate the potential, realised and future distribution of P. angolensis and to identify detailed environmental requirements. Occurrences data of the species were sourced from herbaria and other published sources; environmental data from global GIS databases. Relevant environmental predictors were selected through a jack-knife test of the first model runs. The addition of information on competing species, fires and deforestation was tested to determine realised distribution. Model quality was evaluated with an independent presence-absence dataset. The model was projected with two different climate change scenarios to study their effect on the distribution by 2080. Results show that a potential distribution map can be obtained with good discrimination of the presence of the species (AUC 0.83) and fairly good calibration (correlation coefficient 0.61). Range extent and environmental requirements are more detailed than those described in literature. The distribution of the species is mainly influenced by the amount of summer rainfall, by the minimum temperature in winter and by temperature seasonality. Potential and realised distributions are very similar, with Madagascar as major exception where the species can grow but does not occur. Adding the fire history of the last 13 years or the distribution maps of potentially competing species as predictor variables did not improve the distribution model. It did illustrate that P.angolensis is mainly found in areas with annual fire frequency below 45% and that only a few of the tested species show signs of competition. Using a forest cover map improved the realised distribution slightly (Kappa coefficient 0.64). Climate change can decrease the species range considerably, especially in the west, threatening species existence in Namibia and Botswana. On the other hand, the species’ occurrence is predicted to increase in Zambia.
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    Seaborne measurements of near infrared water-leaving reflectance: The similarity spectrum for turbid waters.
    (American Society of Luminology and Oceanography, 2006) Ruddick, Kevin; De Cauwer, Vera; Park, Young-Je; Moore, Gerald
    Theory and seaborne measurements are presented for the near infrared (NIR: 700–900 nm) water-leaving reflectance in turbid waters. According to theory, the shape of the NIR spectrum is determined largely by pure water absorption and is thus almost invariant. A ‘‘similarity’’ NIR reflectance spectrum is defined by normalization at 780 nm. This spectrum is calculated from seaborne reflectance measurements and is compared with that derived from laboratory water absorption measurements. Factors influencing the shape of the similarity spectrum are analyzed theoretically and by radiative transfer simulations. These simulations show that the similarity spectrum is valid for waters ranging from moderately turbid (e.g., water-leaving reflectance at 780 nm of order 1024 or total suspended matter concentration of order 0.3 g m23) to extremely turbid (e.g., reflectance at 780 nm of order 1021 or total suspended matter of order 200 g m23). Measurement uncertainties are analyzed, and the air-sea interface correction is shown to be critical for low reflectances. Applications of the NIR similarity spectrum to atmospheric correction of ocean color data and to the quality control of seaborne, airborne, and spaceborne reflectance measurements in turbid waters are outlined.