Gavin Docherty Unmanned Aerial System (UAS) technology is gaining traction in the Australian survey, mining, agriculture and civil construction industries, with different types of UAS available for various applications.
Fixed wing or rotary?
There are two main types of UAV available that are suitable for surveying work. The first is a fixed wing model, such as the SIRIUS by MAVinci.
These compact, lightweight units are built for one-man survey operation, with a 1.6 metre wingspan and weighing only 2.7 kilograms. They are ideal for aerial mapping and terrain modelling larger areas, including mine sites and stockpiles, and undertaking topographic surveys.
The second style of UAV is a rotary blade, or propeller-based system. Unlike the fixed wing models, these mini-copters are able to fly in every direction, horizontally and vertically, as well as hover in a fixed position. This makes them the perfect instrument for detailed inspection work or surveying hard-to-reach areas such as pipelines, bridges, power lines and rail tracks.
The Aibox X6 by Aibotix is one such system, with its unique hexagonal shape that includes six propellers, with a high-resolution camera underneath the blades that can rotate to film both vertically and horizontally.
Setting up for an aerial survey using an UAS begins with route planning via the desktop software that comes included with the system. To do this, you will need to program in a take-off and landing area (based on current/forecast wind and weather conditions), and outline the area you wish to map. Once satisfied with your route, you then load this onto the UAV and go through the checklists provided with your kit to make sure all components are functional, that you have adequate battery power, and so on. The launch process for each UAV will be different based on the specific model you are using.
The SIRIUS has the simplest launch technique available, as you simply stand in your desired takeoff location, with the nose of the plane pointed into the wind, and throw the UAV into the air!
To launch the Aibot X6 multi-copter, you have a choice of manual take-off using the included tablet PC, or alternatively an automatic option.
Once airborne, both the SIRIUS and Aibot X6 will then fly your pre-planned route automatically, taking images at a rate of one image per second at 85% overlap (for a high-accuracy, 2 cm result). Users can then track the progress of the UAV via their tablet PC controller, with real-time status updates on position, GPS signal, radio link status and battery power. In addition, the user of either the SIRIUS or Aibot is able to take manual control at any time. Manual controls are useful for detailed inspection work using the Aibot, as the user is able to manoeuvre the UAV close to specific objects, while the built-in distance control will prevent any collisions.
There is also the option of real-time viewing with the Aibot, using either a ground station or video display goggles, giving the user a first-person view as though they were holding the camera.
Although manual controls are generally not required when mapping larger areas with a UAV like the SIRIUS, it is useful to have the option of landing manually in order to avoid any unforeseen obstacles. SIRIUS also features an ‘autopilot assist’ mode, that provides simple ‘up, down, left, right’ control over the UAV while stabilising the aircraft automatically.
Operating conditions and safety features
One of the great advantages of aerial surveying via UAS is the ability to complete a flight despite dense cloud cover, wind and even rain. As manned aircraft are required to fly higher, they are often cancelled due to inclement weather, whereas a UAS will still be able to fly. The SIRIUS has the ability to fly in winds up to 50 km/hr, with gusts up to 65 km/hr, while the Aibot X6 can fly in 43 km/hr winds. A typical cruising height for generating high-accuracy (<2 cm) orthophotos and terrain maps with 85% overlap is 400 feet, or 120 metres.
The UAV are capable of flying much higher than this, however, accuracy decreases the higher you fly and at 500 feet you may enter controlled air space. Both systems come with a number of safety features that enable the UAV to land safely, even if they fly out of range or lose battery power. SIRIUS utilises two wireless radio links with a range of up to 40 km line of sight and an additional manual RC transmitter link with a range of 3 km to minimise the risk of losing radio connectivity. However, if the UAV does lose all radio links, it will still complete the flight as all route information is stored onboard the system. Other safety features of the SIRIUS include:
- If battery power is lost during flight, the autopilot assist feature will still control the UAV’s descent and enable it to land safely.
- A ‘return home’ function that the user can activate at any time during a flight – this will direct the SIRIUS to return to the ground station
- In the event of no GPS signal, the UAV will circle in the air until signal is regained
The Aibot X6 also features a ‘return home’ function that enables the user to safely return the Aibot to the controller at any time during the flight. The Aibot’s unique design also protects it from any damage during a flight, as with six propellers the UAV will remain airborne even if one or two of the propellers fail.
Training and qualifications required
Position Partners requires all customers who purchase a UAS to complete mandatory training before taking delivery of their system. The training covers route planning, safe handling of the UAV, troubleshooting and practical guidelines for safe flying. Australia’s Civil Aviation Safety Authority (CASA) requires the chief controller of a UAV system to have passed the theory, but not the practical, component of a Private Pilot Licence. For more information about qualifications and guidelines published by CASA, visit its website www.casa.gov.au.
Post-processing and achieved accuracies
Once the UAV has successfully landed in the programmed area, the next task is to transfer the images from the UAV memory card to a PC for post processing. Although the flight time for the SIRIUS and Aibot X6 is 40 minutes and 30 minutes respectively, the area you can cover with a UAV depends upon the accuracy required for the finished product. To achieve greater accuracy there must be an increase in overlap of the images, and therefore multiple flights may be required if high accuracy is required over a large area. As an example, SIRIUS accuracy specifications are based on Ground Sampling Distance (GSD), which stands for the area represented by each pixel in a digital photo. The area covered and accuracy achieved during a single 40-minute flight ranges from 55 hectares at 2 cm GSD (with 75-85% overlap of images), to 670 hectares at 10 cm GSD (with 10% overlap of images).
Although the physical area covered in these examples was larger, these figures show the area captured at full 3D quality.
UAS aerial mapping can achieve significant cost savings over traditional survey methods and manned flyovers. Users are able to survey large areas with a one-man survey crew and have the flexibility to fly under cloud and despite wind and rain, avoiding costly time delays associated with manned flyovers. For users who only require the occasional aerial survey, there is the option to outsource the process – from flight planning through to post processed results – to a UAS service provider. Increasingly, survey companies are broadening the scope of their services to include new technology such as mobile vehicle mapping and UAS surveying, making it an ideal option for those wanting to test the water or who are not ready to invest in owning their own system.
How will UAS benefit the Australian survey industry?
UAS mapping presents a viable alternative to costly and unreliable manned aerial surveys, giving the user greater control over what they map, when they map it and the accuracies they wish to achieve from a flight. While the technology will not replace traditional land-based surveying methods, UAS can add another dimension to a surveyor’s tool kit and for some applications, such as stockpile volume measurements, provide a safer solution that removes survey crews from operating near heavy machinery and on hazardous terrain.
These systems also offer an easily deployable and cost-effective solution for mapping and monitoring large areas quickly and efficiently, with a high level of accuracy. Propeller-based systems such as the Aibot X6 also enable detailed inspections of difficult to reach areas. UAS technology is unquestionably a part of Australia’s surveying future. As we learn more about the huge range of applications it can be used for and become more efficient with processing the vast amount of data UAS products are capable of capturing, we will realise its full potential.