DEMs: A True Underdog

Digital Elevation Models (DEMs) produced from satellite data aren’t as well-known as other elevation products generated from more traditional platforms such as fixed-wing aircraft. Hence, satellite-generated DEMs are unfairly dismissed despite their excellent value for money and high suitability for many industrial applications. If this were a playground, these DEMs would be picked last :( — a true underdog

Though DEMs provide a very similar insight compared to the more familiar aerial LiDAR survey, the perception of its complexity and the lack of general understanding means that it’s an underutilized technology. We’re here to shed some light on that.

An example of a DEM. Credit: Cornell University

An example of a DEM. Credit: Cornell University

Satellite imagery generated from orbital instruments varies in resolution from tens of metres down to tens of centimetres and at each resolution a large range of spectral wavelengths are also available. These images are typically orthorectified (aka orthoimages or orthophotos) and provide immense value on their own, but at the end of the day it’s just a 2-dimensional image. It’s the next level of products(referred to as value-added products) that provides even more insight and value to those who know how to use them. An example of such a value-added product is, yup, you guessed it, a DEM, which is a generalized term that includes Digital Terrain Models (DTMs) and Digital Surface Models (DSMs).

What exactly is a DEM?

In a nutshell, DEMs are a digital 3D representation of a terrain’s surface created from elevation data. This information provides value to a number of industries, including mining, oil and gas, and forestry, where the terrain profile and topography have an immediate impact on the operations and activities, and ultimately their bottom-line.

It is possible to acquire the information a DEM provides through more traditional manual surveying or custom aerial surveys, but often times this proves to be very time consuming and limits the area that can be covered. On the other hand, DEMs from satellite data can be a cost effective and efficient option, due to the variety of sensors and methodologies to generate such models are readily available and proven for mapping applications. Who doesn’t like to save time and money?

How are DEMs created and used?

DEMs can be created through a few different ways, but satellite technology best achieves this through 3 methods:

  • 2 passes over an area with a synthetic aperture radar (SAR) instrument (e.g. RADARSAT, TerraSAR-X);

  • Single pass over an area with a synthetic aperture radar (SAR) instrument with dual antennas (e.g. SRTM, ASTER);

  • Stereoscopic pairs of optical satellite imagery captured at 2 different angles of an area (e.g. Pleiades, WorldView-2/3).

Pleiades satellites. Credit: Blueline Publishing

Pleiades satellites. Credit: Blueline Publishing

The quality of a DEM is measured by how accurate the elevation is at each pixel and the topographic feature it represents(which makes sense!).

Common uses for DEMs include:

  • Extracting terrain parameters for geomorphology for exploration activities

  • Calculation of stockpile volume

  • Relief maps

  • Base mapping

  • Surface analysis

DEM data contain the elevation of the terrain over a specific area, at a fixed grid interval (tens of metres) over a set surface area. In order to create a DEM, it requires the combination of pre-existing elevation data as well as contour data or ground control points (GCPs). This external data improves the accuracy of a DEM from tens of metres to just a few metres horizontally and vertically — SCORE!

DEMs win on quality

Several factors influence the quality of DEMs such as: terrain roughness, sampling density, grid resolution or pixel size, and vertical resolution, to name a few. The quality of information provided by an accurate DEM allows for anybody, from the ground crew to the office staff to have the data needed to develop strategies to meet specific objectives, prior to crews being deployed into the field — you wouldn’t start an off-roading adventure without a map and an idea of the terrain you would be traversing, would you?!

The level of preparedness directly translates to cost efficiencies of personnel and related capital expenditures (again with the cost savings… AND having happy, well-prepared staff). There is an ever-increasing demand for DEM information use in the mineral exploration and mining industries, and ever-present pressure from multiple industries to develop models of higher spatial resolution, higher accuracy, and better overall reliability anywhere in the world.

A sample 3D model made from a DEM. Credit: University of Utrecht

A sample 3D model made from a DEM. Credit: University of Utrecht

DEMs win on cost

Mining activities can take place in fairly remote regions of the world, with many mining companies typically relying on aerial surveys (LiDAR) to capture the information they require about the terrain. However, weather conditions and aircraft availability can substantially impact the project timelines. Even seeking permission to fly aerial photographic surveys can be problematic, often resulting in losses in the tens or even hundreds of thousands of dollars. In such cases, space-based methodologies can be vital because they can provide medium-high resolution data over large areas at reasonable costs (few thousand dollars, comparatively) and at different times of the year (unlike aerial surveys, which are limited to the dates in which they were undertaken). The information acquired from a satellite can create an accurate, up-to-date DEM able to meet the needs of a mining company without having to rely on a LiDAR survey.

In summary, DEMs can provide high accuracy topographic data of your site in a timely fashion, at a low cost and with little effort on your part — just imagine what you can do with all that spare time and money!

(Here’s a great excerpt and video explaining more about what DEMs are all about)

And now you know.

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