Description:
Small-area population densities and counts were estimated for Australian census collection districts (CDs), using Landsat TM imagery. A number of mathematical and statistical refinements to previously reported methods were explored. The robustness of these techniques as a practical methodology for population estimation was investigated and evaluated using a primary image for model development and training, and a second image for validation. Correlations of up to 0.92 in the training set and up to 0.86 in the validation set were obtained between census and remote sensing estimates of CD population density, with median proportional errors of 17.4% and 18.4%, respectively. Total urban populations were estimated with errors of + 1% and - 3%, respectively. These results indicate a moderate level of accuracy and a substantial degree of robustness. Accuracy was greatest in suburban areas of intermediate population density. There was a general tendency towards attenuation in all models tested, with high densities being under-estimated and low densities being over-estimated. It is concluded that the level of accuracy obtainable with this methodology is limited by heterogeneity within the individual CDs, particularly large rural CDs, and that further improvements are in principle unlikely using the aggregated approach. An alternative statistical approach is foreshadowed.
Description:
There is a fundamental spatial mismatch in the data available for modeling human population from satellite imagery. Spectral reflectances are available for each pixel of an image, but ground reference population data are available only for larger zones. The general response has been to build models for the average population density of the zones, utilizing spatially aggregated spectral data. This approach has limitations, both for the modeling process and for the utilization of the resulting spatially aggregated population estimates. A pixel-based alternative is described. Pixels of a Landsat TM image were classified as residential or non-residential using standard techniques. Initial reference populations were assigned by uniformly distributing the population of each zone across its residential pixels. An expectation-maximization (EM) algorithm was used to iteratively regress pixel population on spectral indicators and re-estimate pixel populations. Predictive validity was tested by applying the fitted regression equation to a second image. The pixel-based model produced population estimates of comparable accuracy to those resulting from a much more complex zone-based modeling procedure. The pixel-based procedure was also more robust and more amenable to refinement, particularly at the extremes of population density. The relative error in the estimated total urban population of both primary and secondary study areas was less than 1 percent. Median relative error in the population of individual zones was 16 percent in the primary study area (14 percent for urban zones) and 21 percent in the secondary study area (17 percent for urban zones).
Description:
The task of dragging sheep into position for shearing has been reported by shearers as the most physically demanding and one of the highest injury risk aspects of shearing, particularly with regard to back injury. This study aimed to identify which of the currently used drag paths induced the lowest energy consumption and risk of injury. The drag path with the lowest work economy (oxygen cost per sheep dragged per minute) and highest injury risk is used by left-handed shearers who are shearing from a workstation which is designed for right-handed shearers. Importantly, there were no significant differences in the work economy of the two drag paths which were used most frequently and which involved the lowest injury risk. These data have been used in advocating the adoption of simple shearing shed design solutions to assist in the control of injury risk and energy expenditure in the wool industry.
Description:
Variation in the song of the male Common Blackbird was investigated within and between two locations in western Victoria. Each of 400 phrases (100 phrases per male) was characterised by 61 measurements relating to 13 aspects of each phrase. Principal component and stepwise discriminant analyses were undertaken on these measurements. Classification of blackbird song for location and individuality was based on timing within the phrase of the loudest elements. Evidence was found for within-phrase variability, with the greatest variation in the middle of the phrase. Within- and between-site comparison found that blackbird song exhibited both individual and site-specific characteristics consistent with earlier suggestions of phrase sharing within local populations. The study demonstrated that an objective statistical approach to song analysis was able to disciminate between individual birds from different locations.
Description:
Variation in the song of the male Common Blackbird was investigated within and between two locations in western Victoria. Each of 400 phrases (100 phrases per male) was characterised by 61 measurements relating to 13 aspects of each phrase. Principal component and stepwise discriminant analyses were undertaken on these measurements. Classification of blackbird song for location and individuality was based on timing within the phrase of the loudest elements. Evidence was found for within-phrase variability, with the greatest variation in the middle of the phrase. Within- and between-site comparison found that blackbird song exhibited both individual and site-specific characteristics consistent with earlier suggestions of phrase sharing within local populations. The study demonstrated that an objective statistical approach to song analysis was able to disciminate between individual birds from different locations.