Altimeter for precise terrain following to enable drone flight at low and constant AGL

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Integrated Systems
April 15, 2021

True Terrain Following mode enables the drone to fly at low and constant AGL altitudes (starting from 0.5m) without the need to import a precise Digital Elevation Model (DEM) height map into UgCS.

Radar Altimeter for UAS

Adding a Radar rangefinder to a drone enables it to precisely follow the terrain during the flight, based on the data received from the altimeter.

In True Terrain Following mode, the drone flies at low and constant AGL altitudes (starting from 0.5m) without the need to import precise Digital Elevation Model (DEM) height-map into UgCS.

How It Works

The integrated system that enables the drone to fly in True Terrain Following (TTF Data Sheet) consists of:

  • UAV
  • DJI M300 RTK
  • DJI M600/M600 Pro (incl.RTK)
  • DJI M210/M210 v2 (incl.RTK)
  • DJI A3 (custom built)
  • Pixhawk with ArduCopter
  • Radar/laser Altimeter
  • Altimeter (radar or laser)
  • Onboard computer UgCS SkyHub
    Data-sheet »»»
    User Manual »»»

One of the main components of the integrated system, enabling efficient survey planning is UgCS - flight planning software providing tools for easy creation and calculation of flight paths, and interpretation of acquired data in a user-friendly manner.

Flying low. Accurately so

Magnetometers and Ground Penetrating Radars (GPR) have an extremely useful ability — they can see below the ground. For this very reason, they are widely used in mining, engineering, construction, and many other industries – even in archaeology. As usual, where the surface of the terrain is too dangerous (or fragile) for humans to walk on, sensor-carrying drones come into play. But there is one problem with this: how can you fly drones at a precise height – a very, very precise height?

Too little, too much
Usually, digital elevation model (DEM) data that represents the surface of the terrain is used for such purposes. However, this kind of data is not available for many remote areas, and when it is, it is often not sufficiently accurate. For example, one of the best available commercial DEM data (WorldDEM) has a vertical precision of three metres. If for your mission the sensor needs to be two or even one metres above ground level, this data is simply of no use.

LiDARs seemingly offer a solution. They can create extremely accurate terrain maps by providing a precision level of up to one centimetre. As good as this sounds, for a drone mission planning this means a lot of time wasted because in this case missions have to be based on too many waypoints (we’re talking hundreds and hundreds). As the waypoints need to be loaded onto the DJI drone in batches of no more than 99 at a time, following a LiDAR-mapped area of terrain precisely would involve flying over the area time and time again. And that’s without mentioning the drain on the batteries.

Measuring on the go
Why not use actual terrain information instead of relying on sub-optimal pre-existing data? That was the game-changing thinking behind a new integration solution brought onto the market by SPH Engineering, which provides unmanned systems integration services and software development.

By adding a proprietary onboard computer UgCS SkyHub and a radar altimeter to the drone carrying a Magnetometer or GPR (the feature is currently available for DJI M300 RTK, DJI M600/M600 Pro, and M210/M210 v2 drones and can also be used with custom drones based on DJI A3 autopilot) SPH Engineering makes it possible to follow the terrain accurately without crowding the mission with too many waypoints and thus making it inefficient.

First, the radar altimeter gathers an uninterrupted data flow by measuring the distance to the surface of the terrain. Second, the onboard computer adjusts the drone flight height accordingly. As it uses actual data, rather than pre-existing information, this mode is called True Terrain Following.

True terrain-following with one click
All of this, combined with a special add-on of SPH Engineering’s UgCS software, allows for hassle-free drone mission planning with immaculate flight height precision. True Terrain Following mode requires no more than two waypoints on each survey line, thus sparing you from unnecessary interruptions to missions. The operator just needs to set the desired flight height and speed and activate the True Terrain Following mode. The rest of the work will be done automatically.

In addition to mining, engineering, and archaeology, this new solution is useful in situations where Magnetometers and GPRs are not used, but flying over objects or following the surface at a particular height is required for other reasons. This could include spraying plants in agriculture and many other situations where accuracy is a priority.

Case Studies

GPR+UAV+Laser altimeter integrated system for archaeological investigation of Inca ruins

The system integrates a Ground Penetrating Radar (GPR) and a drone equipped with a laser altimeter, allowing the drone to fly in the True Terrain Following mode. The golden rule for GPR surveys is: to fly as slow and low as possible. The adding of the laser altimeter enables the drone to fly in the True Terrain Following mode without requiring Digital Elevation Model (DEM) data to guarantee the delivery of accurate survey results.

GPR-Integrated system with laser altimeter for true terrain following

By adding a proprietary onboard computer UgCS SkyHub and a laser altimeter to the drone carrying a GPR SPH Engineering makes it possible to follow the terrain accurately without crowding the mission with too many waypoints and thus making it inefficient.

Ground penetrating radar flying at 60cm AGL

DJI M600 drone equipped with Zond-12e Drone 500A ground penetrating radar (GPR). The adding of the onboard computer UgCS SkyHub and a laser altimeter to this integrated system enables the drone to fly on 60cm altitude in the True Terrain Following mode - the drone adjusts itself according to sensor's data to keep at an exact altitude above ground level.

UgCS for flight planning and control

One of the main components of the integrated system, enabling efficient survey planning is UgCS - flight planning software providing tools for easy creation and calculation of flight paths, and interpretation of acquired data in a user-friendly manner.

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