How to perform a Viewshed Analysis for BVLOS operations

Understanding the environment around you while operating a drone is crucial, including the geographical landscape. Whether you're flying within Visual Line of Sight (VLOS) or beyond it (BVLOS), ensuring a clear visual line of sight, either to the pilot or between the drone and its dock is a vital step for safe operations.

That's where viewshed analysis comes in.

What is a viewshed analysis?

A viewshed analysis is a geographical technique used in geographic information systems (GIS) to determine the visibility or "viewshed" from a specific location. It calculates the areas visible from a given vantage point (called the observation point), often taking into account factors such as terrain, surface obstructions, and the height of the observation point and target reference.

The process typically involves creating a digital surface model (DSM) or digital terrain model (DTM) of the area, which represents the area in a grid of elevation values. Then, the GIS software analyses which areas are visible from the observer's location based line of sight obstruction by terrain features (such as hills, ridges and valleys) or other structures (like trees and buildings), depending on what information is included in the supplied elevation model.

Why is a viewshed analysis important?

For BVLOS operations, it is suitable to have a high understanding of the 3D environment you wish to operate within, and how this environment may impact the installation location of drone-in-a-box infrastructure, such as HubX or HubT.

For standard operations, it is important to maintain visual line of sight to the drone at all times. Understanding the 3D environment around the operating area is important to ensure the observation location is appropriate for the operation.

How to conduct a viewshed analysis?

Setting up the software

1. Download and install QGIS
2. Loading in your elevation model
1. Navigate through Layer → Add Layer → Add Raster Layer (Ctrl + Shift + R)
2. Paste or navigate the source to the file directory.
3. Click Add and then close the import window.
3. Open the Processing Toolbox
1. Navigate through View → Panels and turn on the Processing Toolbox (if not on by default).
2. Observe it on the right hand side of the screen.

Conducting the viewshed analysis

1. In the search bar of the Processing Toolbox, search for Viewshed
2. Double-click on the processing tool GRASS → Raster → r.viewshed
3. Set the viewshed parameters
1. Elevation = the elevation model layer you have imported
2. Coordinate identifying the viewing position = the proposed HubX install location
1. Use the three dots on the left hand side to then click on the map to select the location)
3. Viewing angle above the ground = the height above the ground that the observation is to be made. For a HubX with DJI Dock 2, this is around 2.00m. The units for this value are the ones used in the elevation model (typically meters, but best to confirm).
4. Offset for target elevation above the ground = the height above any point on the elevation model we want to verify is visible. If this is zero, we would be trying to see the ground level from the observation point. We can use this to check different AGL flight altitudes in the viewshed instead by inserting the AGl flight altitude in (same units as for above).
5. Maximum visibility radius (default -1 = infinity) = exactly as it suggests. We could put in here the maximum rated signal off the specification sheet if our BVLOS site was large enough that it would be relevant. Leave as -1 otherwise.
6. Refraction coefficient = a term for the amount that light bends in air. If there was a value for this that represents radio waves propagating in air, we would use that. But it isn’t as simple as that, so leave it as default (we don’t consider curvature as per the Advanced Parameters).
7. Amount of memory to use in MB = computer resourcing. Leave as default as this typically isn't resource intensive processing.
8. Under Advanced Parameters
1. Enable Output format is invisible = 0, visible = 1. This will provide us with a binary yes or no result for the viewshed, rather than the angle-mode it is by default.
2. Leave all others unticked.
9. Click Run.

Reviewing the results

In the examples above, the viewshed was conducted several times at different altitudes of the target. This is to simulate the areas that a point Xm above the ground surface can be observed from the observation point, meaning for the variable flight altitude levels, where would the Dock have line of sight to the aircraft.

• At 10m there is considerable coverage at either end of the property, with a large section through the lowest valley returning no line of sight coverage.
• At 20m there is filling in of the coverage zones all across the property, with the lowest valley still providing minimal line of sight coverage.
• At 30m there is significant coverage across the entire property, with only a few small sections with no line of sight coverage.
• At 40m the entire property is guaranteed to maintain line of sight between the Dock and Aircraft.

Real-world testing indicated we could fly as low as 15-20m above the troublesome valley section, particularly the area at the south of the property that according to the viewshed analysis requires around 40m to maintain line of sight.

This indicates line of sight is a great baseline to understand the minimum coverage you could expect for any given installation location, but that the drone has the ability to propagate signal over hillsides and other changes in the terrain to an appreciable degree that should be reasonably considered during the installation process.

If you are interested in learning more or starting your BVLOS journey, reach out to us via 1800 119 111 or by using the form below.