In broad terms, aerial surveying is a method of collecting information by using aerial photography or remote sensing technology using other bands of the electromagnetic spectrum, such as infrared, gamma, or ultraviolet. Other important concepts used in aerial photography are stereoscopic coverage, fiducial marks, focal length, roll and frame numbers, flight lines and index maps.
Although both maps and aerial photos represent a ‘bird’s eye’ view of the earth, aerial photographs are not maps. Maps are orthogonal representations of the earth’s surface, while aerial photos display a high degree of radial distortion. However, by using GIS in conjunction with aerial surveying, this distortion can be corrected for.
BASIC CONCEPTS OF AERIAL SURVEYING
To understand some of the terminology used in aerial surveying, the Natural Resources Canada website provides a very helpful summary of the concepts and fundamentals. Below is an excerpt from that site:
“Focal length: the distance from the middle of the camera lens to the focal plane (i.e. the film). As focal length increases, image distortion decreases. The focal length is precisely measured when the camera is calibrated.
Fiducial marks: small registration marks exposed on the edges of a photograph. The distances between fiducial marks are precisely measured when a camera is calibrated, and this information is used by cartographers when compiling a topographic map.”
3D Model of an open cut pit defined by LiDAR
A geometrically rectified aerial photograph can provide very accurate three dimensional terrain surface measurements. The relative positions of features and objects can be determined precisely. However, because of exposure and developing parameters, it is difficult to record unique, reproducible terrain spectral signatures. Electronic systems such as an optical/mechanical scanner or a thermal or microwave radiometer have the capability of recording detected electromagnetic energies with high levels of reproducibility. However, with state-of-the-art equipment, it is still difficult to maintain precise geometric fidelity of spectral data during computational analyses. Consequently, remote sensor data analyses have evolved into the two major categories of image interpretation and mensuration by human operators and spectral data analysis by computer.
Imagery can be obtained from cameras, scanners, or microwave devices. Photography, however, is the only directly recorded form of spectral information. Imagery from scanner or microwave systems is exposed as the result of the conversion of signal voltages into light intensities. Thus, even though such imagery is in fact a photographic record, variations in film density do not necessarily represent variations in visible or near-visible energy reflectance. Thermal infrared images record variations in apparent terrain surface temperature, whereas, microwave images record variations in microwave energy reflections or emissions.
Image analysis may consist of qualitative interpretation, film density or color mapping, or spatial mensuration. The interpretation of imagery is accomplished with the identification of discrete objects or features, or with a detailed description and mapping of regional natural and/or man-made phenomena. Such interpretations are usually based upon identification keys, visual recognition of characteristic patterns, or a deductive reasoning process representing the total experience of the interpreter.
The Natural Resources Canada website defines the terms used in aerial surveying however, technical library’s such as SME’s OneMine offer lots of detailed examples of the use of digital mapping in the mining industry. For the latest information on the use of unmanned aerial vehicles used for digital mapping, check out the Aerial Surveying UAV article from the International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences.
AERIAL SURVEYING USES IN MINING
Aerial surveying and mapping technologies have been used for over 40 years to assist mining companies through all phases of a mine’s life, including exploration, resource evaluation, feasibility, mine design, development, operations and site rehabilitation.
For much of this 40 year period, the most appropriate ‘fit for purpose’ aerial survey methodology for mining has been based around aerial photography and photogrammetry. The success and popularity of this method is dependent on the skill, experience, knowledge and delivery speed of the aerial survey company, ground support from mine site survey staff and some reasonably good weather.
The spatial data acquired from this methodology includes digital terrain models, feature coded mine vector mapping, orthorectified georeferenced imagery, topographic mapping, contours and pictorial imagery.
For active mining operations, aerial mapping is a vital tool to detect mine surface deformations, and to monitor changes in pit depths, waste dump height and levels of tailing dumps.
In exploration, aerial surveying has become a go-to for all exploration companies as it simplifies and speeds up the exploration process. The availability of multi-spectral, radar, and IR imaging, in variety of combinations allowed geologists to evaluate regions in much more detail than ever. In addition, the multiple flyovers allow a prospect to be viewed in different light during different seasons. This has greatly reduced the cost of regional exploration by precluding the need for repeated trips to a locale to reassess.
Pegmatite deposits are just one example of the advantages of using aerial surveying – pegmatites can often be located within granite bodies due to differential vegetation growth and erosion patterns which are prominent in aerial photos. The most elementary operation of remote sensing in mineral exploration is using aerial photographs to identify topographic surface features which may imply the subsurface geology. Such telling surface features as differential erosion, outcropping rock, drainage patterns, and folds/faults can be identified. These features can be compared to other potential targets in the region when looking for similar deposits. Faults, fractures, and contacts often provide a conduit or depositional environment for hydrothermal or magmatic fluids in regions of known mineralization, and thus make excellent targets for further investigation.
Other examples of how spatial data delivered by digital mapping is designed to support a diverse range of mining activities are:
- Exploration and resource evaluation
- Design and construction of mine plant and infrastructure
- Determination of ore body, pit and void volumes for mine planning
- Periodic determination of pit, bench, pre-strip and spoil surface volumes for auditing payments to earthworks contractors
- Periodic determination of stockpile volumes for inventory and accounting purposes
- Environmental planning, monitoring and reporting for the mining operation and the neighboring region
The importance of aerial surveying to the mining industry cannot be overstated. Aerial surveying has changed the overall way mining operations are conducted and revolutionized exploration.
Source: http://technology.infomine.com/reviews/aerialsurveying/welcome.asp?view=full
By: Maurie Phifer
