The ability to have a UAV follow terrain at a specified height, during the execution of a planned flight isn’t something new.   Enterprise type drones have been offering this functionality for a while.

By having a constant flight capture height, a consistent Ground Sampling Distance (GSD) is theoretically possible, thereby assisting in maintaining accuracy across the survey area.

In open cut mines, maintaining a similar GSD is important.  Consider flying over an open pit at a  one altitude; the deepest part of the pit would have the highest GSD, and as a consequence, the poorest quality imagery.

Terrain following, also referred to as terrain awareness, is administered via flight controller software and is associated with some form of underlying Digital Surface Model (DSM). 

How the DSM is sourced differs dependent upon what flight control product you utilise. The DSM in some flight  control software must be sourced and loaded independently, whilst in other products, it’s integrated and you cant choose.

From auditing data sets and extensive experience in reviewing process workflows, we recommend Pilots thoroughly research the capabilities of their flight controller software before applying it to open cut mining surveys.  In short, when considering terrain awareness as a method to achieve consistency in the GSD ensure you test the DSM being applied to the flight plan before you buy and most definitely before you fly.

Properly research the capabilities of your flight controller software before assigning it to surveying open cut mines. Doing so forms part of your quality management system.

One flight control software product we reviewed utilises DSM’s that are outdated when applied to many open cut mining operations. The application utilises SRTM data as the DSM source in its terrain awareness functionality. 

These landform model express a surface shape prior to the development of many operational mines. Let’s be clear the supplier of the flight planning software states this imitation when describing this functionality.  They refer to the risk of stale data coverage in areas. 

How do you know if your flight control software accessed “stale” data? Realistically this should be picked up at the planning stage when the flight is designed.

Plotting a single traverse line across the site should provide a cross sectional view of the topographic profile. If it doesn’t match what you know to be current then the surface is likely outdated.

If your pilot understands what they are capturing and how the flight planning works they should recognise the potential issue immediately prior to capture.

With proper planning you shouldn’t being viewing a processed model and then recognize the drone increased in height as it flew over the pit and did not decrease in height as expected. 

Reliance on public domain source data such as SRTM to control terrain awareness  may result in an outdated surface, bearing no relationship to the present landform of existing pits or dumps on a site location. In some modified terrains you risk crashing a drone if it navigates into an unmapped feature such as high overburden dumps.

To get around this potential problem firstly understand you controller software’s capabilities. Preferably, choose a flight controller program that enables you to upload a DSM of your choice. Consider sourcing and filtering a recent terrain model that has been previously surveyed, creating a flight control DSM that is current.  Alternatively, fly to bench windows (we will discuss how to do this in a future post).

If relying on 3rd party DSM to maintain a terrain awareness capability, then test it first.  Find out if service providers utilise your previous surveys to update their terrain awareness data library. 

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