Terrain or site analysis using aerial video – looking at pictures taken from the air and getting information about a site – has come full circle, from simple to complex, and back to simple. I’ll tell you how in the following, and why that’s good for forensic investigation. Including – for certain in the future – a first-in-Atlantic-Canada aerial video.
It’s simple terrain analysis when the aerial video or photograph is taken near the ground – a few 10s of feet high. The resolution and detail are good and anyone can look at the video and get evidence and data from it. No special skills and software are needed. Forensic experts like that: Reliable, precise evidence easily got and understood by everyone, including the client.
It’s complex when aerial photographs are taken from high in the sky – 1000s of feet. The resolution and detail are not so so good and special skills are needed. For example, skill in photogrammetry in the past as well as today, and also knowing how to use different software.
(Photogrammetry is the science of making reliable measurements between objects with the use of photographs and especially aerial photographs (as in land surveying and mapping).
(Terrain is a geographic area or piece of land. It can also mean the physical features of a tract of land. Also, a stretch of land, especially with regard to its physical features)
The simple terrain analysis today might be more correctly thought of as site analysis. Site analysis is the type of analysis done on small, compact sites where most personal injury accidents, structural failures and problems occur rather than on large tracts of land – for example, the site of the accident, or the building or crane collapse.
Traditionally in terrain analysis, you look at the ground surface of quite large tracts of land as captured in aerial photographs. You identify the physical features characterizing the surface, assess how the features relate to one another, then assess how the individual features and their relationships are relevant to your interest in the terrain.
For example, you might want to construct a road in an unmapped area. The location and nature of features like hills, valleys, steep slopes, streams, forest, flora, existing structures and the underlying foundation soils are all relevant to what you want to do in the area.
Why not just go for a walk in the area and see for yourself? That is done to some extent and is called ground proofing - confirming that the features you’ve identified in the aerial photographs are what they seem to be. But for large, unmapped areas it’s not practical, maybe not safe either.
I worked for an Australian firm that selected preliminary routes for roads in Indonesian jungle by terrain analysis. I’ve worked in jungle. I learned after leaving one site that a man was taken by a crocodile in a mangrove swamp and eaten.
In the simple beginning of terrain analysis – the late 1800s – aerial cameras were taken aloft on balloons and kites and photographed the ground from quite low down. As cameras improved this gave good detail from a different angle – above the site rather than at ground level. In a sense, you saw your site in 3D – from the front, the side and above. As good as it was, the area covered was limited.
Time passed and during WW 1 then more so in WW 2, cameras were taken aloft in reconnaissance planes, and understandably flew quite high and out of range of enemy guns. Extensive areas were photographed this way and features of interest identified in the aerial photographs by the user. Terrain analysis started to get complex.
More time passed and large areas of land were photographed this way and topographic maps made of the areas using photogrammetry. All of Canada has been mapped from planes flying 1000s of feet in the air.
I’ve used these aerial photographs for years in my engineering work. The planes flew at about 6,000 feet. The detail was okay but not great, but better than not having a 3D aerial view of a site.
Various remote sensing methods were developed and increased the accuracy. Photogrammetry continued to develop and LiDar also came along.
(Lidar (light detection and ranging) is a remote-sensing technique that uses laser light to densely measure the surface of the earth, producing highly accurate x, y, z measurements of a point on the ground. In a sense, the location of the front, side and top of many closely spaced points on the earth – like the points defining the edge of a bog. Lidar is emerging as a cost-effective alternative to traditional surveying techniques such as photogrammetry)
I used Lidar to investigate the cause of the foundation failure of a house and swimming pool in Cape Breton. A Lidar map accurately showed the location of the edge of a bog and the probable location of compressible fill soil placed on a small area of the bog near the edge. The foundations were constructed on the weak, compressible fill and bog and over time settled and subsided a lot – I remember 6.0 inches at one location. It was an easy analysis and conclusion as to cause.
Still more time passed and in recent years simple drones fitted with video cameras came along – like motorized kites and balloons from the late 1800s -, and the cameras were much better too. We got back to simple terrain/site analysis and the potential for taking forensic engineering investigation to another level is good.
Most recently for me, staging how an engineering failure might occur and photographing the scene from a drone fitted with a video camera. I’m also looking forward to flying low and capturing the reenactment of a slip, trip and fall accident on video. I’m certain it’ll be a first-in-Atlantic-Canada.
In hindsight, I wish now I had flown and got aerial video of the reenactment of a power tool accident that I investigated. I got good video from the ground and the case was resolved, but aerial video of the reenactment would’ve been nice. Next time.
I hope you’ve got an idea of site analysis and agree that simple is good. Forensic experts certainly like it: Reliable, precise evidence, simply and easily got, easily analysed, understood by everyone, and explained jargon-free. Not very high tech – simple low flying drones fitted with video cameras – but good and reliable. You’ve got to agree.
It’s good like getting your hands dirty and mud on your boots tramping around on site on any occasion, including during ground proofing of the analysis of aerial video taken from low flying drones. (Ref. 1)
Also good like if you can measure it you can manage it. (Refs 2 and 3) The measurements you can get from a screen-grab off aerial video are almost as good as those from a boots-on-the-ground land survey of a site. The land surveyor in me knows this.
Simple is good, and it’s good to have come full circle and to be back where we started, in a sense, in the late 1800s.
- An expert’s “dirty hands and muddy boots”. Posted December 20, 2013
- “If you can measure it you can manage it” – and do thorough forensic engineering, and cost effective civil litigation. Posted June 18, 2015
- If you can measure it you can manage it, even if it’s a real mess like a car or truck accident. Posted June 23, 2016