Je Osborn

Schooling affects the feeding success of Australian salmon (Arripis trutta) when preying on mysid swarms (Paramesopodopsis rufa)

When feeding on mysid swarms (Paramesopodopsis rufa), juvenile Australian salmon (Arripis trutta) had higher rates of successful attacks when foraging in a group of six fish (55% total advances) than when foraging alone (39% total advances). Six schooling fish had lower approach rates than solitary fish (25% and 37% of total advances, respectively). This result indicated that schooling fish were better at reducing the confusion effect of swarming prey, resulting in more efficient feeding. In larger areas, schools achieved higher rates of successful attacks (19 prey/fish in the large tank, compared with 11 prey/fish in the smaller tank). There was no influence on the feeding success of individual fish when changes were made to the number of prey presented to each fish. Nearest neighbour distances were smallest in the absence of prey, and increased with the introduction of prey and again in an attack sequence. Six fish schooled more cohesively than three fish, indicating increased benefits of schooling in larger groups that contribute to advanced vigilance and foraging techniques.

Drag force and surface roughness measurements on freshwater biofouled surfaces

The detrimental effect of biofilms on skin friction for near wall flows is well known. The diatom genera Gomphonema and Tabellaria dominated the biofilm mat in the freshwater open channels of the Tarraleah Hydropower Scheme in Tasmania, Australia. A multi-faceted approach was adopted to investigate the drag penalty for biofouled 1.0 m × 0.6 m test plates which incorporated species identification, drag measurement in a recirculating water tunnel and surface characterisation using close-range photogrammetry. Increases in total drag coefficient of up to 99% were measured over clean surface values for biofouled test plates incubated under flow conditions in a hydropower canal. The effective roughness of the biofouled surfaces was found to be larger than the physical roughness; the additional energy dissipation was caused in part by the vibration of the biofilms in three-dimensions under flow conditions. The data indicate that there was a roughly linear relationship between the maximum peak-to-valley height of a biofilm and the total drag coefficient.

Mapping ear canal movement using area-based surface matching

Movement of the external ear canal, associated with jaw motion, relative to the concha region of the pinna has been studied. Pairs of open-jaw and closed-jaw impressions were taken of 14 ears from 10 subjects. Three-dimensional coordinate data were obtained from the concha and the anterior surface of the canal using a reflex microscope. Proprietary area-based matching software was used to evaluate distortion of the two surfaces between the two jaw positions. The canal data from each pair were placed into the same coordinate system with their respective concha regions aligned. Difference maps of the canal data were used to demonstrate the amount of anterior-posterior (A-P), superior-inferior (S-I), and medial-lateral (M-L) movement, relative to the concha, that occurred between the open- and closed-jaw impressions. The concha regions did not undergo significant deformation. The canal regions underwent varying amounts of deformation with all canals conforming within an rms of 136 microm across the entire surface. The majority of canals underwent significant movement relative to the concha. M-L movement ranged from +2.0 to -3.8 mm; eight canals moved laterally, five moved medially, and two showed no movement. S-I movement ranged from +3.7 to -2.7 mm; nine canals moved inferiorly, two moved superiorly, and three showed no movement. A-P movement ranged between +7.5 and -8.5 mm, with five canals moving anteriorly, three posteriorly, and four in a mixed fashion. This study has shown the variability of canal movement relative to the concha and does not support previous reports that suggest that the ear canal only widens with jaw opening.

Characterizing the roughness of freshwater biofilms using a photogrammetric methodology.

The physical roughness of a surface changes when freshwater biofilms colonize and grow on it and this has significant implications for surfaces enclosing water conveying systems such as pipelines and canals. Plates with surfaces initially artificially roughened with varying grit size were deployed in an open channel system and biofilms were allowed to grow on the exposed surface. The plates were retrieved at intervals in time and their surfaces mapped using close range photogrammetry. For a fine grit surface (0.5–4 mm particles), diatom-dominated biofilms initially grew between the roughness elements; they subsequently developed as a mat to create a physically smoother outer surface than the underlying rough surface. For a coarse grit surface (2–4 mm), biofilms colonized faster; in one instance, larger clumps of biofilm were observed as transverse ripples across the plate.

Alternatives to LiDAR-derived canopy height models for softwood plantations: a review and example using photogrammetry

ABSTRACT Airborne LiDAR data is now commonly acquired by the Australian plantation sector in order to generate accurate digital terrain models and canopy height models at high spatial resolution for resource assessment estimates. However, these airborne surveys are relatively expensive and there is a desire to identify more affordable options for collecting or updating this information. This review presents alternative approaches to deriving canopy height models, including the use of stereo optical imagery from satellites, manned and unmanned airborne platforms, and the use of synthetic aperture radar. In addition, we illustrate the potential of airborne photogrammetry with multi-view dense point matching to produce an accurate, hybrid photo-LiDAR canopy height model at high spatial resolution along a transect covering stands of several softwood tree species.

Mapping a non-carious cervical lesion using stereoimagery and dental casts incorporating optical texture

OBJECTIVES Recent advances in digital photogrammetry have enabled a new approach to high resolution mapping of tooth surfaces. The aim of this study was to assess the accuracy and the precision of a new system using automatic digital stereo-photogrammetry combined with an experimental casting material and to measure tooth surface loss in a non-carious cervical lesion. METHODS A test object and tooth replicas incorporating optical texture obtained at baseline, one and 2 years were imaged with a pre-calibrated stereocamera. The stereoimagery was then processed with digital photogrammetric software to automatically generate digital surface models. Test object models were analysed for accuracy and precision and tooth surface models were aligned with point cloud analysis software and tooth surface loss determined. RESULTS Replicas were mapped to an accuracy of (6+/-13)microm. The sensitivity of change detection on tooth replicas was 40 microm with change ranging from 40 to 70 microm per annum in a discrete part of the lesion. CONCLUSIONS In the case examined, the change detection data were of sufficient accuracy and resolution to draw meaningful conclusions about the spatial distribution and quantum of tooth hard tissue loss. The results of this investigation suggest that annual change detection studies will provide a clearer picture of the pattern of tooth surface loss and, in combination with other analytical techniques, a more detailed explanation of the natural history of these lesions.

Novel 3D geometry and models of the lower regions of large trees for use in carbon accounting of primary forests

The largest uncertainty in human’s contribution to climate change from land use is the fate of carbon that was below ground in pre-modified forests. We produced high-resolution 3D models of the rarely measured zone near the base of large, mature trees by using photogrammetry. The models led to equations linking the easy-to-measure trunk diameter and ground slope to attributes such as tree buttress shape, humus mound, wood and hollow area, and root volume. The equations can be used for carbon accounting. The 3D models are irreplaceable, being for increasingly rare, large trees, and may be useful to other scientific endeavours.

Evaluating the robustness of point clouds from small format aerial photography over a Pinus radiata plantation

ABSTRACT Extensive research and operational trials over the past 20 years have led to the operational implementation of airborne laser scanning (ALS)-based forest inventory becoming increasingly common. More recently, digital aerial photography (AP), processed using Structure from Motion Multiview Stereopsis (SfM-MVS) photogrammetry, is emerging as an alternative to ALS. Aerial photography may provide some advantages compared with ALS, including lower deployment and data collection costs, easier access to a variety of platforms and sensors, and the opportunity for forest managers to capture and process the data in-house. This study presents an analysis of point-cloud data derived from airborne small format digital AP, and a comparison with ALS data for a Pinus radiata plantation located in north-east Tasmania. The AP was processed using commercially available photogrammetric software and three different processing strategies. The influence of processing strategy, terrain slope, canopy occlusion, canopy cover, photo-overlap and camera location are investigated in order to characterise the point clouds generated using these methods, and to assess the robustness of the photogrammetric solution to these variables. Our analysis provides strong evidence of the robustness of small format AP-based point clouds in this type of forest: characteristics of the dense point cloud are shown to be largely robust to different photogrammetric processing strategies. Observations regarding the influence of terrain slope, photo-overlap, canopy occlusions, canopy cover and camera location can be used to optimise flight planning and photo-acquisition.

Comparing yield estimates derived from LiDAR and aerial photogrammetric point-cloud data with cut-to-length harvester data in a Pinus radiata plantation in Tasmania

ABSTRACT Accurate mapping of timber resources in commercial forestry is essential to support planning and management operations of forest growers. Over the last two decades, Light Detection and Ranging (LiDAR) systems have been successfully deployed for the collection of point-cloud data for accurate modelling of forest attributes that are traditionally obtained from plot-based inventory. In recent years, studies conducted in North America and Scandinavia have shown that three-dimensional point clouds derived from digital aerial photogrammetric (AP) data can be used to model forest attributes with a level of accuracy similar to traditional LiDAR-based approaches. A comparative analysis of the performance of the two point-cloud technologies has never been attempted in Australian plantations. In this study, we compared the performance of LiDAR-based and AP-based point clouds for estimating total recoverable volume in a Pinus radiata plantation at Springfield in north-eastern Tasmania, using volume data collected by harvesting machines as a reference. Our results showed that AP point clouds can be used for mapping total recoverable volume in P. radiata plantations with levels of accuracy that are comparable to LiDAR-based estimates. Plot-level relative root mean squared error (RMSE%) values were 23.85% for LiDAR and ranged from 22.07% to 27.10% for the three AP dense point-cloud settings evaluated. At the stand level, RMSE% decreased to 9.86% and 8.91% for LiDAR and AP, respectively. Both LiDAR-based and AP-based modelled volumes showed a close agreement with volumes measured using harvester head data, demonstrating the potential of AP technology for the management and planning of forestry operations in softwood plantations.