Satellite altimeters have become an important tool for the study of global and regional mean sea level change, offering near global coverage and unprecedented accuracy. Issues of calibration and validation remain central to their ability to determine estimates of change at accuracies of better than 0.5 mm/yr.This Thesis provides an absolute calibration of the TOPEX/Poseidon (T/P) and Jason-1 satellite altimeters, undertaken in Bass Strait, Australia. The research provides a contribution to the international calibration effort, with the Bass Strait site situated as the only one of its kind in the Southern Hemisphere. A unique in situ absolute calibration methodology is presented, reliant on the episodic deployment of GPS equipped buoys at an offshore comparison point. In contrast to other calibration studies, data from the GPS buoys are used to solve for the absolute datum of an offshore oceanographic array (incorporating a pressure sensor, temperature and salinity recorders and a current meter array). Combined with data from a coastal tide gauge and a regional GPS network, the methodology enables the cycle-by-cycle computation of absolute bias, without the necessity of estimating a marine geoid. Emphasis within this Thesis is given to the design and development of the GPS equipped buoys, in addition to the standardisation requirements of the geodetic analysis. The GPS buoy design is applied to both the altimeter calibration problem, in addition to a near shore application involving the calibration of tide gauges in the Antarctic and Sub-Antarctic.The attention to standardisation ensures comparable estimates of in situ and altimeter sea surface height. Differences at the 9 mm level for the pole tide displacement and plus or minus 5 mm for the solid Earth tide displacement are revealed when using the GAMIT GPS analysis suite.The implications of non-standardisation are further illustrated with the presentation of time series analysis from various continuous GPS datasets. Absolute bias and 1-sigma uncertainties from a formal error budget are 0 plus or minus 14 mm for T/P and +152 plus or minus 13 mm for Jason-1 (for the GDR POE orbits, computed over the calibration phase, 18 Jan 2002 14 Aug 2002). Results over the duration of the T/P mission confirm a dependence on the choice of Sea State Bias (SSB), with the overall mean absolute bias not statistically different from zero. Extending the comparison period between Jason-1 cycles 1 to 101 (18 Jan 2002 06 Oct 2004) reduces the Jason-1 mean absolute bias by approximately 10 mm and reveals a significant slope of -7.6 plus or minus 5.6 mm per year.Whilst the cause for the significant absolute bias remains unexplained, the source of the drift appears attributable to the microwave radiometer, observed to be measuring drier over time (-5.9 plus or minus 2.1 mm/yr). Drift of the POE orbit relative to the JPL GPS orbit is shown to account for the remaining trend observed at the Bass Strait site.After considering geographically correlated errors, absolute bias results show excellent agreement with other international calibration studies.These results aid in understanding the performance of both the T/P and Jason-1 altimeters, further underscoring calibration and cross calibration of altimeters as essential for the study of low frequency oceanographic processes, including regional and global mean sea level change.The inference of geographically correlated orbit errors, and the significant unexplained Jason-1 absolute bias emphasises the need for maintaining globally distributed verification sites and makes it clear that further work is required to improve our understanding of the Jason-1 instrument and its algorithm behaviour.

Continental shelf waters are subject to the greatest impact by humans. If marine ecosystems are to be efficiently managed and protected from the adverse effects of human activities, then identification of the types of marine habitats and the communities they contain is required. Research cruise data and existing data were collected at three diverse study sites on polar, temperate and tropical continental shelves within Australia's Exclusive Economic Zone (EEZ). This project conducted a multi-disciplinary analysis of satellite imagery, multibeam sonar, seismic profiles, oceanographic data, underwater video, and the results of sediment sampling. A Geographic Information System (GIS) was utilised to model the spatial boundaries of the physical and biological datasets. Spatial and multivariate statistical analyses were conducted on the GIS models and datasets to explore the relationships between abiotic and biotic patterns. GIS was used to map the spatial distribution of benthic habitats at each study site within a hierarchical context. The East Antarctic continental shelf has had few studies examining the macrobenthos structure or relating biological communities to the abiotic environment. On the George V Shelf, GIS was used to map the geomorphology, surficial sediment and near-seabed water mass boundaries. A study of underwater photographs and the results of biological sampling provided information to infer the dominant trophic structure of benthic communities within geomorphic features. A hierarchical method of benthic habitat mapping was applied to the Geomorphic Unit and Biotope levels at the local (10s of km) scale. The study revealed that mud content, iceberg scour, and oceanic currents are the likely dominant abiotic factors in the broad-scale distribution of macrofauna on the George V Shelf. To better understand the relationships between the geology of the seabed and associated biological communities, a multibeam sonar survey was conducted over New Zealand Star Bank, eastern Bass Strait, Australia. Through spatial and multivariate analyses of surficial sediment composition and underwater video, the biological assemblage patterns were related to the variation in geomorphology and substrate. A hierarchical method of benthic habitat mapping was applied to the Secondary Biotope and Biological Facies levels at the site (<10 km) scale. The major differences which control the distribution of biological communities in the New Zealand Star Bank area appear to be related to variations in substrate. To help answer the question whether geophysical data from habitats can be used to predict the occurrence of benthic biodiversity, a multibeam sonar survey was conducted in the northern Great Barrier Reef - Gulf of Papua region. Multivariate statistical analyses were applied to the biological and physical datasets to determine patterns in the distribution of megabenthos, and the relationship with abiotic variables. A hierarchical method of benthic habitat mapping was applied to the Secondary Biotope and Biological Facies levels at the site (<10 km) scale. The combination of substrate type, sedimentary dynamics and physical processes related to nearseabed currents appear to be a dominant control on the benthic communities in the northern Great Barrier Reef - Gulf of Papua region. Benthic habitat mapping plays a vital part in understanding marine ecosystems and the processes which influence the spatial distribution of benthos. The results of this research have made significant in-roads in the development of a framework for ecosystem-based management of the study areas, the contribution to the ongoing bioregionalisation of Australia, and through an examination of the use of geophysical proxies for the occurrence of biological assemblages, which are fundamental to the establishment of Marine Protected Areas.