The aim of the project is to develop a solution to provide centimetre accuracy to an unmanned aerial vehicle or manned aircraft for the purpose of conducting surveys and exploration and the best possible accuracy. Inherently GNSS under the best conditions can consistently provide an accuracy of approximately 10cm, while this is fantastic, some applications do need an increased accuracy. Previously this has been achieved predominantly by use of differential GPS base stations and ground control points. Traditionally the differential GPS data would be applied to GPS data obtain from surveying or exploration after the mission has been completed, making this an onerous task for the parties involved in processing the data obtained by surveying or exploration.

How Dronetech aims to solve this problem

The first problem that will be solved is the fact that previous aircraft, be it unmanned or manned have not been capable of centimetre accuracy in real-time. This is the primary matter that will be addressed, the further benefits are products of the accuracy being captured in real-time.

The presented solutions will also mitigate the need for ground infrastructure to be established before missions are flown, there may well be more permanent ground infrastructure in place to achieve the goal but dynamic infrastructure will be eliminated

Differential GPS calculations need normally to be applied after the fact. The proposed methods here will apply the differential GPS corrections to the aircraft from a base station, resulting in the obtained GPS data by the air aft already being corrected and at centimetre accuracy, therefore that is no post processing required to correct GPS, saving man many hours or intensive labour.

Deliverable under this project

This project involves performing a technical feasibility study into the development of a centimetre accuracy platform for aircraft:

  • Delivering a GNSS solution for centimetre accuracy.
  • Delivering a platform that may be installed on an aircraft, manned or unmanned.

Problems with positioning systems to date

Inherently GNSS under the best conditions can consistently provide an accuracy of approximately 10cm, while this is fantastic, some applications do need an increased accuracy. Previously this has been achieved predominantly by use of differential GPS base stations and ground control points. Traditionally the differential GPS data would be applied to GPS data obtain from surveying or exploration after the mission has been completed, making this an onerous task for the parties involved in processing the data obtained by surveying or exploration.

How Dronetech will solve these problems

The first problem that will be solved is the fact that previous aircraft, be it unmanned or manned have not been capable of centimetre accuracy in real-time. This is the primary matter that will be addressed, the further benefits are products of the accuracy being captured in real-time.

The presented solutions will also mitigate the need for ground infrastructure to be established before missions are flown, there may well be more permanent ground infrastructure in place to achieve the goal, but dynamic infrastructure will be eliminated

Differential GPS calculations need normally to be applied after the fact. The proposed methods here will apply the differential GPS corrections to the aircraft from a base station, resulting in the obtained GPS data by the air aft already being corrected and at centimetre accuracy, therefore that is no post processing required to correct GPS, saving man many hours or intensive labour.

In addition to pure GNSS positioning Gyrotek will also develop a GNSS platform capable of centimetre accuracy as well as an inertial reference system, the benefit of this would be that the inertial reference system will be able to deliver an assortment of data to the autopilot and survey and exploration equipment which would aid in improving the accuracy of the final deliverable product.

The other alternative is to use the ago of tried and tested concept of triangulation from three or more radio frequency towers.

Differential GPS with RTK

RTK is a recent development, real time kinematics. What makes this so ground-breaking is that in the past differential GPS data would have been applied to obtained data post flight to correct the apparent GPS to result in accurate data. By virtue of the sentence being long the process is onerous and complicated. With RTK the differential GPS corrections are communicated with the GNSS receiver on board the aircraft in real-time, correcting the GPS data and ensuring that GPS data output is correct from the receiver to the exploration equipment mitigating the needs for all the onerous work after the exploration has been completed.

RTK is a technique that uses carrier-based ranging and provides ranges (and therefore positions) that are orders of magnitude more precise than those available through code-based positioning. RTK techniques are complicated. The basic concept is to reduce and remove errors common to a base station and aircraft pair.     

The calculated ranges still include errors from such sources as satellite clock and ephemerides, and ionospheric and tropospheric delays. To eliminate these errors and to take advantage of the precision of carrier-based measurements, RTK performance requires measurements to be transmitted from the base station to the aircraft station.

A complicated process called “ambiguity resolution” is needed to determine the number of whole cycles. Despite being a complex process, high precision GNSS receivers can resolve the ambiguities almost instantaneously.

The aircraft station determines its position using algorithms that incorporate ambiguity resolution and differential correction. Like DGNSS, the position accuracy achievable by the rover depends on, among other things, its distance from the base station (referred to as the “baseline”) and the accuracy of the differential corrections. Corrections are as accurate as the known location of the base station and the quality of the base station’s satellite observations. Site selection is important for minimizing environmental effects such as interference and multipath, as is the quality of the base station and rover receivers and antennas.

This system is quite simple, it has a GNSS receiver on board the aircraft with a base station that is setup on the ground. This system is able to guarantee an accuracy of 1cm at 1km from the base station, this then increases by 1mm for every km that the aircraft moves from the base station. Survey operations will need to remain within a 10km radius from the base station to ensure maximum accuracy.

Differential GPS with RTK and Inertial Reference System

This option has the same benefit as the GPS with RTK only with the added benefit or delivering telemetry to exploration and surveillance sensors

The GPS-aided inertial navigation system is new generation of fully-integrated, combined GPS, GLONASS, GALILEO, QZSS, BEIDOU and L-Band navigation and high performance strapdown system, that determines position, velocity and absolute orientation (Heading, Pitch and Roll) for any device on which it is mounted. Horizontal and Vertical Position, Velocity and Orientation are determined with high accuracy for both motionless and dynamic applications. The INS utilizes advanced single and dual antenna GNSS receiver, barometer, 3-axes each of calibrated in full operational temperature range precision Fluxgate magnetometers, Accelerometers and Gyroscopes to provide accurate Position, Velocity, Heading, Pitch and Roll of the device under measure. The on-board sensor includes a fusion filter, state of the art navigation and guidance algorithms and calibration software.

Triangulation of Fixed Base Stations by Radio Frequency

The simplest way to describe this technique would be by virtue of a diagram as below.

How we would achieve this is by placing a radio receiver at each receiver location as above. The UAV has an interrogator on board that on an independent frequency “pings” the receivers as 10 millisecond intervals, a basic formula is run on board the UAV by the interrogator unit to reference the position relative to the know positions provided by the base station that have been placed and positions recorded by the ground support team.

It is evident that this system requires a little more effort than the previous suggested systems, so the questions would be, why go to this amount of effort. The answer is really consistency and accuracy.

This system being under the complete control of Dronetech is not susceptible to:

  • Intentional signal degradation by government.
  • Solar influences on GPS signal travelling thousands of km’s from satellites.
  • GPS signal jamming.
  • Infrastructure of any other, person, government or company.

Some of the benefits of this system:

  • More calculations can be conducted by the interrogator due to the radio frequency signal only have to travel a total distance of a few kilometres as opposed to traveling approximately 40 000 kilometres to make once round trip, or measurement. This results in a higher frequency of calculations and therefore increases accuracy.
  • Due to the shorter round trip, the influence of environmental factors will be considerably less than that of a GPS system.
  • The system has proprietary frequency bands minimizing interference and clutter.

Deliverables

This project involves performing a technical feasibility study into the development of a centimetre accuracy positioning system:

  • Describing the science behind the concept and technical feasibility study.
  • Design of hardware and software.
  • Development of a prototype.
  • Testing of a prototype.

Summary

Dronetech will provide and investigate the feasibility of developing a centimetre accuracy positioning system which will increase the accuracy of position measurements by an order of magnitude and enable unmanned and small manned aircraft to obtained centimetre position accuracy.