Drone Technology

UAV Technology


The drones employed by INFOMAR are capable of mapping coastal and intertidal terrain with a high degree of vertical accuracy. This is essential as the aim is to merge these datasets, where possible, with the seabed bathymetry offshore to create a seamless map that crosses the boundary between land and ocean. Such a map would be vital for studies such as flood risk assessment and coastal erosion.


Whereas the offshore vessels utilise sonar technology, or acoustics, to map the depth of the seabed below sea level, the drones use a different method known as photogrammetry. Equipped with a high resolution digital SLR (Single Lens Reflex) camera, each drone takes a series of overlapping photographs of the ground while flying at a fixed altitude and in a series of parallel lines (similar to the parallel lines run by offshore survey vessels).


Photogrammetry is a method that has existed for a long time – it is essentially a way of measuring the distance to an object that appears in two or more photos taken from different angles (much like the human eye does all the time).  However, with the advent of powerful computing, it is possible now to take many overlapping pictures over an area of landscape and generate a 3D model of its surface. Through pattern recognition and advanced processing, computers can analyse each pixel in these photographs and generate accurate point clouds of real features.


Such methods are possible with even basic cameras and a household object such as a coffee cup, as long as one has the appropriate software to import the photos and carry out the computation. However, simply mapping an object’s shape is not enough – for INFOMAR’s purposes, we must map landscape features relative to a real coordinate reference frame, such as the WGS84 ellipsoid (this is the basic default reference frame for most GPS equipment). For most drones to achieve this, it is necessary to place “control points” at various points in the area to be surveyed – these are simply clear, physical markers, such as an “X” painted on flat material. Theses markers must be visible in the final photographs. Their coordinates in 3D space, with respect to the WGS84 ellipsoid, are accurately recorded prior to the survey using GPS equipment. These points serve as a form of ground truthing, making it possible to hang the 3D landscape model in real space with respect to other datasets such as the bathymetry.


Certain drones, such as the MD4-3000, contain direct georeferencing capability and so do not need ground control points – though they still remain a useful quality control measure in such cases.