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Dead Reckoning navigation for UAS

One of the biggest challenges facing any cutting-edge Attitude & Heading Reference System / Inertial Navigation System (AHRS/INS) is the ability to perform a mission in a degraded environment. Dead reckoning navigation for UAS  is the process of calculating one’s current position by using a previously determined one, and advancing it based upon known or estimated speeds (integrated) over elapsed time and course. Evidently each integration is subject to a cumulative error; the aim therefore is to reduce this error in order to increase precision.

An AHRS/INS uses a computer and a series of sensors, such as accelerometers, gyroscopes and occasionally magnetometers, which are used continuously to calculate: position, orientation and velocity of a navigation system or moving object without the need of external references, such as GNSS devices.

UAV Navigation-Grupo Oesía develops and manufactures high-end autopilots and as such is completely committed to products which are capable of precise and reliable navigation. Navigation in degraded environments (e.g. with no GNSS input) is a major objective. There follows a description of the test results achieved in this field. Significant advances in wind estimation (which is key to good dead reckoning performance) and in other fields have been made in the UAV Navigation-Grupo Oesía system which lead to greater navigation accuracy in degraded enviornments.

 

Flight control setup for Dead reckoning navigation for UAS 

The equipment used to produce the following results is the VECTOR, UAV Navigation-Grupo Oesía's cutting-edge autopilot. VECTOR features a highly advanced, high-end, MEMS-based AHRS/INS. It has been designed for system integration in avionics packages or other attitude sensing applications, and includes:

  • Attitude Heading & Reference System (AHRS)
  • Inertial Measurement Unit (IMU)
  • Inertial Navigation System (INS)
  • Air Data System (ADS)
  • GNSS (only for data comparison)

 

VECTOR has accumulated thousands of hours of flight time and has proven itself in a variety of highly dynamic environments, giving outstanding results.

Redundancy built into the software allows it to survive individual sensor failures while maintaining accurate estimates of attitude and position. Its high-performance MEMS-based IMU is calibrated and compensated over the full industrial temperature range.

In order to simulate a degraded scenario in these tests, the GNSS information was completely excluded, whilst all the other systems (see above) were functional.

 

Platform setup

In order to achieve the most realistic and representative results possible, the test was carried out in a fixed wing aircraft flying a precise Flight Plan (FP). The aircraft used is one of the fixed wing test platforms available in the UAV Navigation-Grupo Oesía fleet. The platform has a 2.5m wingspan and is equipped with a single piston, two-stroke gasoline engine.

The test platform is capable of carrying all the required flight measurement devices and is able to produce repeatable results, even in highly dynamic manoeuvres. The Flight Plans and tests performed are described below.

 

Procedure

The platform takes off from a known position and once the test altitude and location are achieved the GNSS is disabled (GNSS information is still recorded onboard, but it is not used for estimation). Two different manoeuvres are then performed which characterize the worst case dead reckoning scenarios: (1) circular hold, and (2) square pattern. Wind conditions for the tests were measured at the Ground Control Station as a constant 3m/s.

The following table explains the operations executed during the flight:

 

HOLD mode, circular pattern (300m radius). DEAD RECKONING

3 minutes

AUTO mode, square pattern (400x350m). DEAD RECKONING

2 minutes

 

Achieved results

The following charts show the navigation performance of the VECTOR under degraded conditions: actual position of the platform versus estimated position (derived from the integration performed by the INS).

Dead Reckoning

Figure 1. Real position vs Estimated position in Dead reckoning navigation for UAS. HOLD mode.

HOLD Mode.   The results (Figure 1 above) show that in a manoeuvre lasting 3 minutes a position drift of around 100m in total is accumulated, giving a Position Drift Rate of 33 m/min.

No GPS

Figure 2. Real position vs Estimated position in Dead Reckoning mode. HOLD mode.

Square Pattern.   The results (Figure 2 above) show that in a manoeuvre lasting 2 minutes a position drift of around 70m is accumulated, giving a Position Drift Rate of 35m/min.

 

The Visual Navigation System, VNS01 Empowering Dead reckoning navigation for UAS

To address the challenges of Dead reckoning navigation for UAS, UAV Navigation-Grupo Oesía has designed the Visual Navigation System (VNS01) that delivers accurate navigational information, ensuring the success of missions even in scenarios where GNSS signals are unavailable, unreliable or compromised.

Specifically developed to address such challenges, the VNS01 offers a critical solution for a wide range of operations, significantly enhancing the capabilities of NATO Category I and II Unmanned Aerial Systems (UAS) operating in GNSS-denied environments.

By enabling precise positioning and autonomy, this innovative system greatly improves UAS operations in demanding and hostile surroundings, ultimately amplifying mission effectiveness and overall situational awareness for the operator.

At the core of the VNS01 there is an onboard camera that captures images throughout the flight, allowing for the creation of an internal map that can be used when GNSS signals are absent. This map plays a vital role in correcting accumulated navigational drift during dead reckoning. Leveraging a combination of visual odometry and pattern recognition techniques, the VNS01 seamlessly integrates with other onboard sensors, providing the Flight Control Computer (FCC) with precise positioning data even in the absence of GNSS signals.

The Visual Navigation System (VNS01) ensures enhanced mission success by providing accurate positioning and autonomy in environments where GNSS signals are unavailable. Even when operating in areas without pre-existing maps and relying only on visual odometry, the VNS01 maintains an exceptionally low drift rate of approximately 10 meters per minute, guaranteeing reliable navigation throughout.

 

TYPICAL DEAD-RECKONING DRIFT FIGURES 
Standard AHRS-INS (3rd party)  100 m/min
UAV Navigation-Grupo Oesía POLAR AD-AHRS < 35 m/min
Visual Odometry < 10 m/min
Pattern Recognition Pattern Recognition

 

Square Pattern performed using Visual Navigation. Data Acquision on the right.

 

UAV Navigation-Grupo Oesía GNSS-Denied Navigation Kit

The GNSS-Denied Navigation Kit is specifically designed to thrive in GNSS-denied environments, offering unparalleled navigation capabilities in challenging scenarios. It combines the precision and reliability of UAV Navigation-Grupo Oesía's Attitude and Heading Reference System (AHRS), the POLAR-300, with the state-of-the-art Visual Navigation System, the VNS01. This powerful integration ensures unmatched dead reckoning navigation capabilities with minimal drift, setting new standards for precision and stability in challenging scenarios. Immune to external disruptions, this kit represents the future of autonomous navigation. With GNSS signals increasingly under threat from both unintentional and intentional interference, the shortcomings of traditional navigational systems are evident.

Find out more about our GNSS-Denied Navigation Kit.

 

Conclusion

The performed tests have demonstrated that the UAV Navigation-Grupo Oesía system excels in extracting optimal results from MEMS-based sensor technology and, therefore, executing operations using inertial navigation. However, it is important to acknowledge that outcomes may vary across different platforms, influenced by factors such as wind conditions, platform performance and the autopilot installation quality to minimize vibration.

For this reason, the Visual Navigation System (VNS01) developed by UAV Navigation-Grupo Oesía has been specifically designed to provide accurate navigational information, reducing the accumulated drift from the inertial sensors and ensuring mission success even when GNSS signals are compromised.

For this reason, the Visual Navigation System (VNS01) and the GNSS-Denied Navigation Kit developed by UAV Navigation-Grupo Oesía have been specifically designed to provide accurate navigational information, reducing the accumulated drift from the inertial sensors and ensuring mission success even when GNSS signals are compromised.

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About

UAV Navigation is a privately-owned company that has specialized in the design of flight control solutions for Unmanned Aerial Vehicles (UAVs) since 2004. It is used by a variety of Tier 1 aerospace manufacturers in a wide range of UAV - also known as Remotely Piloted Aircraft Systems (RPAS) or 'drones'. These include high-performance tactical unmanned planes, aerial targets, mini-UAVs and helicopters.