Claire Samson

Imaging and tracking elements of the International Space Station using a 3D autosynchronized scanner

The Neptec Design Group has developed a new 3D auto-synchronized laser scanner for space applications, based on a principle from the National Research Council of Canada. In imaging mode, the Laser Camera System (LCS) raster scans objects and computes high-resolution 3D maps of their surface features. In centroid acquisition mode, the LCS determines the position of discrete target points on an object. The LCS was flight-tested on-board the space shuttle Discovery during mission STS-105 in August 2001. When the shuttle was docked on the International Space Station (ISS), the LCS was used to obtain four high-resolution 3D images of several station elements at ranges from 5 m to 40 m. A comparison of images taken during orbital day and night shows that the LCS is immune to the dynamic lighting conditions encountered on orbit. During the mission, the LCS also tracked a series of retro-reflective and Inconel targets affixed to the Multi-Purpose Lab Module (MPLM), when the module was stationary and moving. Analysis shows that the accuracy of the photosolutions derived from LCS centroid data is comparable to that of the Space Vision System (SVS), Neptecs product presently used by NASA for ISS assembly tasks.

Aeromagnetic surveying using a simulated unmanned aircraft system

Carleton University and Sander Geophysics are developing an unmanned aircraft system (UAS) for aeromagnetic surveying. As an early indication of the expected performance of the unmanned aircraft system, a simulated unmanned aircraft system (sUAS) was built. The simulated unmanned aircraft system is a T-shaped structure configured as a horizontal gradiometer with two cesium magnetometers spaced 4.67 m apart, which is the same sensor geometry as planned for the unmanned aircraft system. The simulated unmanned aircraft system is flown suspended beneath a helicopter. An 8.5 km 2 area in the Central Metasedimentary Belt of the Grenville Province, near Plevna, Ontario, Canada, was surveyed with the simulated unmanned aircraft system suspended 50 m above ground. The survey site was chosen on the basis of its complex geological structure. The total magnetic intensity (TMI) data recorded were compared to that obtained during a conventional fixed-wing survey and a ground survey. Transverse magneto-gradiometric data were also recorded by the simulated unmanned aircraft system. The simulated unmanned aircraft system total magnetic intensity data have a higher resolution than the conventional fixed-wing data and were found to have a similar resolution to that of the ground survey data. The advantages of surveying with the simulated unmanned aircraft system were: (1) the acquisition of a detailed data set free of gaps in coverage at a low altitude above the terrain and (2) substantial saving of time and effort. In the survey site, the 4.67 m simulated unmanned aircraft system gradiometer measured the transverse magnetic gradient reliably up to an altitude of 150 m above ground.

Surface roughness of rock faces through the curvature of triangulated meshes

In this paper, we examine three different measures of roughness based on a geometric property of surfaces known as curvature. These methods were demonstrated using an image of a large rock face made up of a smooth blocky limestone in contact with a rough friable dolostone. The point cloud analysed contained 10,334,288 points and was acquired at a distance of 3m from the rock face. The point cloud was first decimated using an epsilon-net and then meshed using the Poisson surface reconstruction method before the proposed measures of roughness were applied. The first measure of roughness is defined as the difference in curvature between a mesh and a smoothed version of the same mesh. The second measure of roughness is a voting system applied to each vertex which identifies the subset of vertices which represent rough regions within the mesh. The third measure of roughness uses a combination of spatial partitioning data structures and data clustering in order to define roughness for a region in the mesh. The spatial partitioning data structure allows for a hierarchy of roughness values which is related to the size of the region being considered. All of the proposed measures of roughness are visualised using colour-coded displays which allows for an intuitive interpretation. Mapping curvature highlights heavily fractured rock faces.Curvature-based roughness measures provide estimates of roughness in meshes.Colour-coding of mesh elements allows visualisation of rougher/smoother surfaces.

Designing and building an unmanned aircraft system for aeromagnetic surveying

Carleton University, in collaboration with Sander Geophysics Limited, has developed an original design for an unmanned aircraft system (UAS) for aeromagnetic surveying, the GeoSurv II. A UAS has the potential of collecting higher resolution data compared to conventional aircraft due to its lower altitude flight capability. A first prototype of the GeoSurv II has been built. It is an allcomposite modular aircraft of a twin-boom pusher configuration with a wing span of 4.88 m and a length of 4.27 m, and a maximum takeoff mass of 90 kg. This prototype will first be used for flight tests and later be instrumented with two Cesium magnetometers on the wingtips and a fluxgate magnetometer in the fuselage. Concurrently with the assembly of the prototype, a simulated UAS has been built. The simulated UAS is a modified magnetic bird towed beneath a helicopter. It features two magnetometers with the same separation distance as in the GeoSurv II design. A test survey was flown using the simulated UAS and the data acquired are compared with conventional regional aeromagnetic data collected using a fixed-wing aircraft.

Mode-converted volcanogenic massive sulphide ore lens reflections in vertical seismic profiles from Flin Flon, Manitoba, Canada

In October 2006, three-component zero-offset vertical seismic profile data were acquired from a deviated well in the Flin Flon mining camp in Manitoba, Canada, using a dynamite source. These vertical seismic profile data were processed to reveal reflections originating from the 85.5 Mt Flin Flon-Callinan-777 volcanogenic massive sulphide ore system. From drill records, mine plans, surficial maps, and seismic data, 3D voxel models of the local geology and known ore zones were built, which were then used in 3D finite-difference modelled simulations of the vertical seismic profile surveys. The number of geological units partitioning the model was incrementally increased to study the effects of the massive sulphide ore and the major rock units on the seismic response. The simulations and field data were jointly visualized, and reflections originating at some of the known ore zones were identified. These reflections were observed in each of the three components in both the real field and the forward modelled data and indicate a strong mode-converted component of the reflected wavefield.

Finite-difference time-domain modelling of through-the-Earth radio signal propagation

This research seeks to extend the knowledge of how a very low frequency (VLF) through-the-Earth (TTE) radio signal behaves as it propagates underground, by calculating and visualizing the strength of the electric and magnetic fields for an arbitrary geology through numeric modelling. To achieve this objective, a new software tool has been developed using the finite-difference time-domain method. This technique is particularly well suited to visualizing the distribution of electromagnetic fields in an arbitrary geology. The frequency range of TTE radio (400-9000Hz) and geometrical scales involved (1m resolution for domains a few hundred metres in size) involves processing a grid composed of millions of cells for thousands of time steps, which is computationally expensive. Graphics processing unit acceleration was used to reduce execution time from days and weeks, to minutes and hours. Results from the new modelling tool were compared to three cases for which an analytic solution is known. Two more case studies were done featuring complex geologic environments relevant to TTE communications that cannot be solved analytically. There was good agreement between numeric and analytic results. Deviations were likely caused by numeric artifacts from the model boundaries; however, in a TTE application in field conditions, the uncertainty in the conductivity of the various geologic formations will greatly outweigh these small numeric errors. HighlightsSoftware to simulate through-the-Earth radio signal propagation has been developed.Finite-difference time-domain method is used to directly generate a time series.A graphics processing unit was used to parallelize and accelerate computations.Model results were validated against three analytic solutions.Two complex geologic environments that are not solvable analytically were modelled.

Magnetic and magneto-gradiometric surveying using a simulated unmanned aircraft system

Carleton University and Sander Geophysics are developing an unmanned aircraft system (UAS) for aeromagnetic surveying. As an early indication of the performance to expect from the UAS, a simulated UAS (sUAS) was built. The sUAS is a T-shaped structure suspended beneath a helicopter which has the same magnetometers and sensor geometry as planned for the UAS. A test survey was conducted using the simulated UAS and the total magnetic intensity (TMI) data recorded were compared to that obtained during a conventional regional fixed-wing survey and a ground survey. Transverse magneto-gradiometric data were also recorded by the sUAS.

Characterization of waste density and settlement via microgravity

Optimizing the utilization of landfill space and production of biogas, which can be used as an energy source, is dependent on understanding the compaction and stabilization of waste over time. Maximum compaction minimizes the landfill footprint; however, it might not provide the optimal environmental conditions for bacteria development and waste stabilization. This paper reports on a research project which pilots the use of repeated microgravity surveys to map changes in waste density of waste over time in a bioreactor landfill. Over the duration of 3 years, several microgravity surveys will be conducted on a new cell at a bioreactor landfill in Sainte- Sophie, Quebec, Canada, as it is gradually filled with waste up to a height of 25 m. The paper presents a comparison of gravity data acquired in June 2010 (waste height ≈5.5 m) and April 2011(waste height ≈13 m).

Automation of the SLUTH method: a novel approach to airborne magnetic data interpretation

A useful property of the anomalous magnetic field T associated with some simple geological bodies is that the field is homogeneous with respect to horizontal distance and height. Its horizontal and vertical derivatives are also homogeneous fields so the angle ratio θ of the lateral gradient over the vertical gradient is constant along rays emanating outward from a single point that represents the body location. Hence drawing these raypaths, which connect the same θ values at different upward continued heights along a profile, can be used to identify the location and depth of the source. This is the basis for the source location using the total-field homogeneity (SLUTH) method. A six-step procedure is proposed to automate the SLUTH method, allowing large amounts of data to be interpreted quickly and easily. Furthermore, the rate of decay of the field along these raypaths provides a means to estimate the type of body that is the cause of the anomaly. Once the type of body is known, a quantity related to the susceptibility can be estimated. An analysis of the results in the case when there is interaction between two proximal magnetic sheets shows a distortion when the bodies are within 600 m of each other. A similar distortion is seen when analysing field data from Timmins, Ontario, Canada, which consists of many other magnetic body models such as contacts and thin sheets. Adding noise to synthetic data shows that the estimates we obtain for the source parameters are robust for the typical noise levels seen in survey data. Because a lot of information about the characteristics of the causative geologic body can be determined using the method, it is a challenge to summarize the results on a single map. Our approach is to use different shaped symbols for each type of body, with the size of the symbol being proportional to the susceptibility-thickness and the shade indicative of the error in estimating the position. Data from Chibougamau, Quebec, Canada are used to illustrate these display techniques.

Tessellation of Ground-Based LIDAR Data for ICP Registration

A technique to improve the positional accuracy of mobile ground-based LIDAR systems is proposed. Terrapointpsilas TITAN(TM) system scans the same objects at different times, so by aligning scans, any drift over time can be estimated. This paper describes a simple way of tessellating the scanned data into segments based on the vehiclepsilas path. Principal Components Analysis is then used to estimate how well pairs of segments will align when registered with an Iterative Closest Point algorithm. The results show that this analysis does indeed find segments which are likely to register well. Finally a more formal method to analyze the results is proposed, to better determine the quality of the registration so that it can be used to improve the position estimate for the LIDAR system.