Papers by Frank Shillington
Presentation given at the 15th GHRSST science meeting (XV), Cape Town, South Africa, June 2 - 6, ... more Presentation given at the 15th GHRSST science meeting (XV), Cape Town, South Africa, June 2 - 6, 2014.
Proceedings of OceanObs'09: Sustained Ocean Observations and Information for Society, 2010
The last few years have witnessed the foundation and development of a new discipline, coastal alt... more The last few years have witnessed the foundation and development of a new discipline, coastal altimetry, and the coalescence of an active community of researchers who are now enthusiastically developing the topic. In the present community white paper, we summarize the technical challenges that satellite altimetry faces in the coastal zone, and the research that is currently being carried out to overcome those challenges. We introduce the new coastal altimetry data that are becoming available, and describe how we can calibrate/validate those data. Then we show several of the possible applications of coastal altimetry and conclude by looking at the future of the discipline, and at how we can build capacity in coastal altimetry.
Elem Sci Anth
Over the past three decades, marine resource management has shifted conceptually from top-down se... more Over the past three decades, marine resource management has shifted conceptually from top-down sectoral approaches towards the more systems-oriented multi-stakeholder frameworks of integrated coastal management and ecosystem-based conservation. However, the successful implementation of such frameworks is commonly hindered by a lack of cross-disciplinary knowledge transfer, especially between natural and social sciences. This review represents a holistic synthesis of three decades of change in the oceanography, biology and human dimension of False Bay, South Africa. The productivity of marine life in this bay and its close vicinity to the steadily growing metropolis of Cape Town have led to its socio-economic significance throughout history. Considerable research has highlighted shifts driven by climate change, human population growth, serial overfishing, and coastal development. Upwelling-inducing winds have increased in the region, leading to cooling and likely to nutrient enrichme...
African Journal of Marine Science
The accuracy of the Content should not be relied upon and should be independently verified with p... more The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden.
Eprint Arxiv Physics 9909023, Sep 13, 1999
Examples of heavy mineral placer deposits are presented in which wave reflection, refraction, dif... more Examples of heavy mineral placer deposits are presented in which wave reflection, refraction, diffraction and resonance would appear to have played a major concentrating role. Their geometry is compared with the computer generated patterns predicted for the reflection, refraction and diffraction of surface waves moving over fairly simple, idealised bathymetries. Much of this work is founded on the idea that similar sediments document equivalent (or once equivalent) flow-tractional environments. Most of the examples could be satisfactorily explained in this fashion. It may therefore be possible to ignore the exact physics of the boundary layer, longshore and tidal return currents etc. at the scale on which these examples occur, leaving the way open for the qualitative use of results obtained using the likes of the mild slope wave equation. A "Monte Carlo" approach based on wave induced tractions should therefore succeed in elucidating presently known heavy mineral placer deposits and, consequently, in predicting other deposits which remain as yet undiscovered.
An examination of tidal records from stations on the south coast of southern Africa revealed a Ts... more An examination of tidal records from stations on the south coast of southern Africa revealed a Tsunami like disturbance on 11 May 1981. The phenomenon is manifest as a long period wave propagating from west to east abruptly and having a maximum crest to trough elevation of 50 cm. Microbarograph records of air pressure fluctuations revealed a small amplitude, short period atmosphric pulse which propagated above the south coast with an average speed of 17 m/s. The disturbance in the sea, first identified as a Tsunami, are explained in terms of coastal trapped edge waves, generated by unusual, short period, air pressure oscillations. The event of 11 May 1981 is unusual in that the oscillations measured at the tide gauge locations were rather large and showed distinct starting times. This allowed the generation area to be identified together with a reasonable explanation of the dynamics of the waves. Further atmospheric pulses were identified on barograph records, and more cases of coastally trapped waves are discussed.
South African Journal of Science, 1990
South African Journal of Marine Science
ABSTRACT
Progress in Oceanography, 2003
Satellite remote sensing has revolutionized modern oceanography, providing frequent synoptic-scal... more Satellite remote sensing has revolutionized modern oceanography, providing frequent synoptic-scale information that can be used to deduce ocean processes. However, it is often difficult to extract interpretable patterns from satellite images, as data sets are large and often non-linear. In this methodological paper, we describe the self-organizing map (SOM), a type of artificial neural network adept at pattern identification. The ability of the SOM to extract patterns from a variety of satellite data, including scatterometer and thermal imagery, is illustrated by example. We characterize inter-annual, seasonal and event-scale variability by using the SOM and relate the output to auxillary variables by using a number of techniques that enhance interpretation. Practical recommendations for the fruitful application of SOMs are given. Although the SOM has only rarely been used in oceanography previously, it is a promising applied mathematical tool for pattern extraction from many types of data, especially large and complex satellite data sets.
South African Journal of Science
ABSTRACT
Progress in Oceanography, 2015
Progress in Oceanography, 2003
Estimation of primary production over large areas of the ocean requires information on the shape ... more Estimation of primary production over large areas of the ocean requires information on the shape of phytoplankton profiles. In this study we develop a generic quantitative approach to describe the continuous variation of profile shape within a region. We illustrate this approach by application to the dynamic southern Benguela upwelling system. First, we describe profile shape by fitting a four-parameter shifted Gaussian model. We then use a model-building approach to relate each parameter to a suite of environmental variables that are either known for each point of the ocean in time and space (depth of the water column, season, and area) or are easily obtained from remote sensing (sea surface temperature and surface chlorophyll a). As these variables are highly correlated and non-linearly related to profile shape, we use generalised additive models to visualise the non-linear relationships between each parameter and all environmental variables simultaneously. These relationships are then parameterised using generalised linear models to obtain a predictive equation for each profile parameter. Relationships identified made intuitive sense in terms of the evolution of phytoplankton blooms in upwelling systems. We found strong predictive relationships for the depth of maximum chlorophyll (r 2 = 0.70) and the total chlorophyll in the peak (r 2 = 0.74), the two most important parameters for estimating primary production. Predictive relationships were weaker for the width of the peak (r 2 = 0.21) and the background chlorophyll (r 2 = 0.15). The predictive equations identified can be applied on a pixel-by-pixel basis to concurrent sea surface temperature and ocean colour images to estimate profile shape, and can be imbedded within local algorithms to provide regional primary production estimates. This approach can easily be applied to other biogeochemical provinces.
Large Marine Ecosystems, 2006
Optics express, Jan 5, 2007
The effective cell size is expected to be one of the principal causes of variability in the inher... more The effective cell size is expected to be one of the principal causes of variability in the inherent optical properties (IOPs) of a phytoplankton population. However, establishing simple size descriptors is complicated by the typically complex particle size distributions of natural phytoplankton assemblages. This study compares the use of measured and equivalent particle size distributions on the modeled IOPs of a wide range of natural phytoplankton assemblages. It demonstrates that several equivalent size distributions, using simple parameterizations of complex size distributions based on the effective radius or diameter, are capable of modeling phytoplankton IOPs with sufficient accuracy for further use in marine bio-optical models. The results offered here are expected to be of use in bio-optical studies of phytoplankton dynamics e.g. harmful algal bloom oriented inverse reflectance models.
Capacity building in remote sensing is an important component of GOOS-Africa. This includes train... more Capacity building in remote sensing is an important component of GOOS-Africa. This includes training future scientists and environmental managers in the use of satellite data. With this in mind, the UNESCO-Bilko programme, supported by Intergovernmental Oceanographic Commission (IOC) of UNESCO, and the European Space Agency is developing teaching material for use in distance learning and through workshops and courses across
Progress in Oceanography, 2009
Equilibrium dynamics of the Benguela system is investigated using the holistic nature of the spat... more Equilibrium dynamics of the Benguela system is investigated using the holistic nature of the spatially and temporally cohesive output of a numerical model. The Regional Ocean Modeling System (ROMS) is used to simulate the Benguela system in its entirety. It successfully simulates the cool coastal upwelling regime and its division into seven distinctly separate cells, as well as the large-scale offshore regime and the respective seasonal fluctuations. It does however, present a cool bias at the coast due to an underestimation of the coastal wind drop-off as well as a warm bias offshore in the southern Benguela due to the overestimation of Agulhas Current input. The Benguela can be divided into northern and southern regimes, based on dynamic as well as topographic differences. Topographically, the division between the northern and southern regimes coincides with an abrupt narrowing of the continental shelf toward the north at 28°S. The large-scale depth-integrated flow to the north of this feature is weak but distinctly poleward, while to the south the flow regime is governed by the meandering nature of the equatorward Benguela Current and is the pathway for eddies that originate at the Agulhas retroflection. The poleward flowing regime of the northern Benguela is tied to the Sverdrup relation, which links meridional transport with wind stress curl. The Lüderitz upwelling cell at 27°S experiences the most vigorous upwelling throughout the year and, as a result, offshore volume fluxes in this region are extremely large. This upwelling cell divides the northern and southern Benguela coastal upwelling systems into separate regimes, based on the fact that their seasonal signals are out of phase. The offshore gradient of eddy kinetic energy (EKE) is generally strong in the Benguela system and exceptionally so in the southern Benguela due to vigorous mesoscale activity offshore of the shelf-edge, originating from the Agulhas retroflection area. The juxtaposition between the steep offshore EKE gradients in the south and much weaker offshore gradients of EKE in the northern Benguela has different implications for cross-shore exchanges.
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Papers by Frank Shillington