Towards Real‐Time Geodemographics: Clustering Algorithm Performance for Large Multidimensional Spatial Databases

Geodemographic classifications provide discrete indicators of the social, economic and demographic characteristics of people living within small geographic areas. They have hitherto been regarded as products, which are the final “best” outcome that can be achieved using available data and algorithms. However, reduction in computational cost, increased network bandwidths and increasingly accessible spatial data infrastructures have together created the potential for the creation of classifications in near real time within distributed online environments. Yet paramount to the creation of truly real time geodemographic classifications is the ability for software to process and efficiency cluster large multidimensional spatial databases within a timescale that is consistent with online user interaction. To this end, this article evaluates the computational efficiency of a number of clustering algorithms with a view to creating geodemographic classifications “on the fly” at a range of different geographic scales.     

Improving the computational efficiency of the ambiguity function algorithm

Techniques are described in this paper for improving the Ambiguity Function Method (AFM) for differential GPS positioning using phase observations, (a) that take advantage of optimal dual-frequency observable combinations to improve thereliability of the AFM, and (b) that significantly shorten the computation time necessary for the AFM. The procedure can be used for kinematic positioning applications if a Kalman filter predicted position is accurate enough as an initial position for the suggested AFM searching procedure, or pseudokinematic mode using say a triple-difference solution as an initial position for static positioning if the baseline length is short (typically <5km).     

Verification and mitigation of the power-induced measurement errors for airport pseudolites in LAAS

Certain GPS receivers exhibit a power-induced measurement error when the input signal power exceeds a certain threshold that is a function of the receiver architecture. The characterization of this error is important in the case of airport pseudolites (APLs) due to receiver saturation at ranges close to the transmission antenna. This paper details an effort using laboratory test to characterize the power-induced measurement error in NovAtel Millennium and Beeline receivers that are widely used for APL development. The results from the laboratory tests show that this effect can lead to errors as large as 3 m on pseudorange measurement for the dynamic range typical for APLs. The carrier-phase error however is seen to be limited to 5 cm. On the verification and characterization of the error, a cost-effective mitigation technique for LAAS is proposed. A solution for the ground subsystem is sought by employing power-control measures to limit the amount of APL power that LGF GPS/APL receivers are exposed to. In order to keep the integration cost low, the solution for the airborne subsystem does not involve hardware modifications or additions, but rather relies on the transition to a differential carrier-phase positioning algorithm prior to the onset of the power-induced error along the approach path. The proposed architecture was flight-tested to verify successful mitigation of the power-induced error on both the ground and air, and the results from these tests are presented in the paper.     

PERFORMANCE ANALYSIS OF INTEGRATED GPS/GLONASS CARRIER PHASE-BASED POSITIONING

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Re-mapping regulatory space: The new governance of Australian dairying

Despite questions currently raised about the future of neoliberalism, it remains embedded within Australian agricultural policy and practice. This paper explores the strengths and limitations of mechanisms contributing to neoliberalism’s survival through a close examination of the restructuring of Australian agricultural production and governance processes under the influence of both globalising impulses and adherence to neoliberal strategies. We trace the changes in governance flowing from the dismantling of regulatory structures in the Australian dairy industry, and the creation of new forms of governance that have both facilitated this transition and dealt with its adverse, often unintended, consequences. The changing governance of Australian dairying is analysed through the lens of three arenas of governance: state, industry and place. Drought has played an important part in re-spacialising dairying and re-shaping the balance between farmers and industry, demonstrating the contingency at play in emerging governance structures. This study of processes of change within the highly export-oriented dairy sector of Australia focuses attention on resistance and on some of the messy actualities of the interplay between state, place and industry - and nature - in neoliberal agri-food governance.     

Book reviews

Marine decapod Crustacea of southern Australia: a guide to identification. By Gary C. B. Poore. Published in 2004 by CSIRO Publishing, P.O. Box 1139, Collingwood, VIC 3066, Australia. 608 p., hardcover. ISBN: 0–643–06906–2. Price: AU$180.00 (orders: publishing.sales@csiro.au).

Marine mammals: fisheries, tourism and management issues. Edited by Nicholas J. Gales, Mark A. Hindell and Roger Kirkwood. Published in 2003 by CSIRO Publishing, P.O. Box 1139, Collingwood, VIC 3066, Australia. 446 p., hardcover. ISBN: 0–643–06953–4. Price: AU$116 (orders: publishing.sales@csiro.au).

Freshwater fishes of north‐eastern Australia. By Brad Pusey, Mark Kennard, and Angela Arthington. Published in 2004 by CSIRO Publishing, P.O. Box 1139, Collingwood, VIC 3066, Australia. 700 p., hardcover. ISBN: 0–643–06966–6. Price: au$89.00 (orders: publishing.sales@csiro.au).     

Improved ocean-geoid resolution from retracked ERS-1 satellite altimeter waveforms

The ocean geoid can be inferred from the topography of the mean sea surface. Satellite altimeters transmit radar pulses and determine the return traveltime to measure sea-surface height. The ERS-1 altimeter stacks 51 consecutive radar reflections on board the satellite to a single waveform. Tracking the time shift of the waveform gives an estimate of the distance to the sea surface. We retrack the ERS-1 radar traveltimes using a model that is focused on the leading edge of the waveforms. While earlier methods regarded adjacent waveforms as independent statistical events, we invert a whole sequence of waveforms simultaneously for a spline geoid solution. Smoothness is controlled by spectral constraints on the spline coefficients. Our geoid solutions have an average spectral density equal to the expected power spectrum of the true geoid. The coherence of repeat track solutions indicates a spatial resolution of 31  km, as compared to 41  km resolution for the ERS-1 Ocean Product. While the resolution of the latter deteriorates to 47  km for wave heights above 2  m, our geoid solution maintains its resolution of 31  km for rough sea. Retracking altimeter waveform data and constraining the solution by a spectral model leads to a realistic geoid solution with significantly improved along-track resolution.     

Employment and Socio-spatial Relations in Australia's Cultural Economy

This paper examines the significance and contribution of Australian 'creative' industry activities in light of recent debates on the emergence of the 'cultural economy of cities'. First, census employment data and business location counts are used to illustrate patterns of metropolitan primacy and concentration in the cultural industries both across states and in Sydney. Second, the specificities of the locations of cultural production, and the links between cultural industry activities and wider urban-regional change are explored in more detail. A set of observations of urban-regional change is used to demonstrate how the notion of 'cultural economy' should include complex interactions between the material activities of consumers and producers, and the discursive worlds of image makers and place marketers. Urban renewal, housing market pressures and intra-regional migration all mediate Australian experiences of the 'cultural economy'. Such interactions, in addition to key quantitative data on employment and business activity, suggest important policy considerations.