No description available.

No description available.

No description available.

Marine phytoplankton produce the vast majority of primary production in the world’s oceans and sustain virtually all marine ecosystems. Despite this importance, it is currently unclear how global marine phytoplankton concentrations have been changing over the available oceanographic record, and what the causes and consequences of any such changes may be. In this thesis I use observational datasets, statistical modeling, theory, and experiments, to estimate how the global standing stock of marine phytoplankton (referenced by chlorophyll) has changed over the past century, and what the causes and consequences of any changes may be. I inter-calibrated shipboard measurements of upper ocean chlorophyll, transparency, and colour to generate a publicly-available global chlorophyll database spanning from 1890 to 2010. Generalized additive models and multi-model inference were used to estimate the magnitude and nature of changes over the available record, and to explore the effects of multiple oceanographic and climatic variables on these changes. Finally, I worked collaboratively to design and run a mesocosm experiment to test the mechanisms by which rising ocean temperatures influence phytoplankton and plankton community structure. I observed declining trends in upper ocean chlorophyll concentrations at local, regional, and global scales over the past century. Increasing trends were observed closer to coastlines, and were possibly related to increased land-based nutrient deposition there. I also observed inter-annual to multi-decadal fluctuations overlying the longterm trends, which were partly related to climate variability. Sea surface temperature was a consistently strong driver of observed chlorophyll trends. Strong negative effects of rising ocean temperatures on chlorophyll concentration were observed at mid, and low latitudes, and positive effects were observed at high latitudes. The overall effect of increasing temperature on chlorophyll was negative, yet the mesocosm experiment revealed that the primary mechanisms explaining this effect depend on the nature of the ecosystem. Under nutrient limitation, the physically-mediated effects (stratification) of increasing SST were dominant, while under nutrient saturation, the biologically-mediated effects (trophic) were dominant. This thesis provides new evidence that sustained declines in marine phytoplankton over the past century have occurred across multiple spatial scales and that rising ocean temperatures have contributed to this trend. The possible implications of this sustained decline are wide-ranging, with likely impacts on climate, geochemical cycling, fisheries, and ecosystem structure.

Continuously-operating networks of GPS receivers (CGPS) are not capable of determining the characteristics of crustal deformation at the fine temporal or spatial scales required. Four ???temporal densification schemes??? and two 'spatial densification schemes' to augment the CGPS networks have been developed and tested. The four ???temporal densification schemes??? are based on the high rate Real-Time Kinematic (RTK) GPS technique, GPS multipath effects, Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR). The 'serial scheme' based on using GPS as a seismometer has been proposed. Simulated seismic signals have been extracted from the very noisy high rate RTK-GPS results using an adaptive filter based on the least-mean-square algorithm. They are in very good agreement with those of the collocated seismometers. This scheme can improve the CGPS temporal resolution to 0.1 second. The 'retro-active scheme' takes advantage of the fact that the GPS multipath disturbance is repeated between consecutive days. It can therefore provide a means of correcting multipath errors in the observation data themselves. A reduction of the standard deviations of the pseudo-range and carrier phase multipath time series to about one fourth and one half the original values respectively, has been demonstrated. The 'all-GPS parallel scheme' uses the multipath effects as a signal to monitor the antenna environment. Models relating the changes of multipath and antenna environment have been derived. The 'cross-technique parallel scheme' integrates the collocated CGPS, VLBI and SLR results, taking advantage of the decorrelation among their biases and errors. Crustal displacement signature has been extracted as a common-mode signal using data from two stations: Matera in Italy and Wettzell in Germany. Two 'spatial densification schemes' which can verify with each other have been developed and tested. The 'soft' scheme integrates CGPS with radar interferometry (InSAR). The Double Interpolation and Double Prediction (DIDP) approach combines the strengths of the high temporal resolution of CGPS and the high spatial resolution possible with the InSAR technique. This scheme can improve the spatial resolution to about 25m. The 'hard' scheme requires the deployment of single-frequency receivers to in-fill the present CGPS arrays. Alternatively some receivers may be installed at some geophysically strategic sites outside existing CGPS arrays. The former has been tested within Japan's GEONET, while the latter has been tested using a five-station array.

Since its introduction in the early 1980????s, the Global Positioning System (GPS) has become an important tool for high-precision surveying and geodetic applications. Carrier phase measurements are the key to achieving high accuracy positioning results. This research addresses one of the most challenging aspects in the GPS data processing algorithm, especially for precise GPS static positioning, namely the definition of a realistic stochastic model. Major contributions of this research are: (a) A comparison of the two data quality indicators, which are widely used to assist in the definition of the stochastic model for GPS observations, has been carried out. Based on the results obtained from a series of tests, both the satellite elevation angle and the signal-to-noise ratio information do not always reflect the reality. (b) A simplified MINQUE procedure for the estimation of the variance-covariance components of GPS observations has been proposed. The proposed procedure has been shown to produce similar results to those from the standard MINQUE procedure. However, the computational load and time are significantly reduced, and in addition the effect of a changing number of satellites on the computations is effectively dealt with. (c) An iterative stochastic modelling procedure has been developed in which all error features in the GPS observations are taken into account. Experimental results show that by applying the proposed procedure, both the certainty and the accuracy of the positioning results are improved. In addition, the quality of ambiguity resolution can be more realistically evaluated. (d) A segmented stochastic modelling procedure has been developed to effectively deal with long observation period data sets, and to reduce the computational load. This procedure will also take into account the temporal correlations in the GPS measurements. Test results obtained from both simulated and real data sets indicate that the proposed procedure can improve the accuracy of the positioning results to the millimetre level. (e) A novel approach to GPS analysis based on a combination of the wavelet decomposition technique and the simplified MINQUE procedure has been proposed. With this new approach, the certainty of ambiguity resolution and the accuracy of the positioning results are improved.

Bibliography: p. 297-304. / xxix, 304 p. : ill., col. maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Uses a widely accepted stochastic model of scintillation activity to investigate the effects of scintillations on GPS receivers and systems. / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 2001?

Over the last century, increases in anthropogenic greenhouse gases and global temperature in the atmosphere has drawn our attention to changes in extra tropical cyclones which influence daily weather patterns in the mid and high latitudes and redistribute energy, momentum and moisture across the globe. This study is aimed at examining changes in extra tropical cyclones: observed over the past two decades using the NCEP-DOE reanalysis II data (NCEP2); and simulated in the CSIRO Mark2 atmosphere-ocean coupled general circulation model (GCM) with increasingCO2. Furthermore, we attempt to explore the physical mechanisms driving such changes by modelling idealised experiments with the Melbourne University atmospheric GCM. The Melbourne University cyclone finding and tracking scheme is utilised to detect and track cyclones observed in NCEP2 and simulated in the two models. / The study demonstrates significant changes in Southern Hemisphere (SH) cyclone features from 1979-2000. SH cyclones have decreased in their number at the surface but increased at the 500 hPa level. On the other hand, SH cyclone physical features such as intensity, radius and depth have significantly increased over the two decades at the mean sea level and 500 hPa level. Moreover, cyclones became vertically better organized in both hemispheres, and particularly in the SH. The changes in the characteristics of Northern Hemisphere (NH) cyclones were statistically less significant than their SH counterparts in the period of 1979-2000. / Results from the coupled climate model simulation with enhanced CO2 suggest general reductions in cyclone frequency and intensity throughout the troposphere between the surface and500 hPa level but increases in cyclone radius and organization of vertical structure. These changes are persistent throughout the entire transient run with increasing CO2 and during a 100 year stabilisation period. It is found in the CSIRO simulation with enhanced CO2 that the geographical changes of cyclone features are similar in both hemispheres and between the surface and 500 hPa level. Furthermore, we conclude that some observed changes in extra tropical cyclone features seem to follow the patterns of simulated changes with increasing CO2 from 1xCO2 to 2xCO2 particularly in the SH. / Modelling latitudinal temperature gradient at different levels of the troposphere has revealed that the warming over the tropics at the upper troposphere causes cyclone frequency and depth to increase in the high latitudes but decrease in the mid latitudes. By contrast, the warming over the high latitudes at the lower troposphere results in decreases in the cyclone features in the high latitudes but increases in them in the mid latitudes. Therefore, the warming over the tropics seems to play an important role in the changes in SH summer cyclone frequency and depth appearing in the simulation with enhanced CO2, whereas the warming over both tropics and high latitudes affects the changes in SH winter cyclone features. In the NH, the change in latitudinal temperature gradient seems less influential in the changes of cyclone features than it does in the SH.

Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 2001? / Bibliography: p. 297-304.

Thesis (Ph. D.)--University of New South Wales, 2000. / Also available online.