Introduction
Recent conflicts have exposed the vulnerability of Global Navigation Satellite Systems (GNSS) to electronic warfare, highlighting the importance of Inertial Navigation Systems (INS) for applications that demand Assured Position, Navigation and Timing (APNT). Mobile radar systems, especially those used in defence, depend on INS in situations where GNSS signals are disrupted or unavailable.
Vehicle-mounted mobile radar systems, in particular, need an INS because they constantly move and change orientation, making it crucial to maintain precise and continuous heading data for tracking accuracy. Over time, drift errors from the INS can accumulate, leading to significantly reduced pointing accuracy and tracking efficiency. In environments where GNSS signals are disrupted or jammed, vehicle movements can exacerbate and compound these errors.
Understanding Radar and Inertial Navigation
Radar, an acronym for Radio Detection and Ranging, is a technology that uses radio waves to determine the distance, velocity and often the physical nature of objects in its vicinity. There are two main types of radar systems:
360-degree radar: Also known as imaging radar, this type continuously rotates to scan its entire surroundings, providing comprehensive data on the range and density of detected objects. However, its need to complete a full 360-degree rotation may result in delays in detecting fast-moving targets until the radar returns to the same position.
Static radar: Unlike 360-degree radar, static radar maintains a fixed field of view and does not rotate. To achieve a full surveillance coverage similar to that of a 360-degree radar, multiple static radars are typically arranged within an array. These setups provide full coverage in different directions without the need for any single unit to rotate.
Both 360-degree and static radars have their unique advantages and both can be mounted on vehicles to form a mobile radar system. This allows for rapid deployment and repositioning, which helps keep their location hidden when they are not active as well as maintain a tracking lock on targets by moving to a more ideal location. Such mobility demands advanced navigation and stabilisation technologies, namely Inertial Navigation Systems (INS).
Critical to both radar systems, an INS tracks the position, orientation and velocity of moving objects using motion sensors such as accelerometers and gyroscopes. They can operate independently of external references like GNSS, making them exceptionally reliable in scenarios where GNSS signals are compromised by jamming, spoofing or multipath errors.
Mobile Radars for Defence
Mobile radar systems are indispensable and crucial in defence, providing critical capabilities such as battlefield surveillance, target tracking, asset guidance and threat detection. However, in hostile environments where GNSS is degraded, these systems would be unable to operate without a robust, accurate INS to control the radar’s orientation and maintain correct alignment.
As offensive drone threats grow, mobile radars are increasingly being used in counter-drone systems, where they are crucial for fast and accurate drone detection and tracking. This capability is needed in order to deploy effective countermeasures to protect personnel, infrastructure and critical assets.
How Radar Integrates with INS
Integrating a mobile radar system with an INS involves precise calculations and calibrations. One key process is determining the heading through the gyrocompassing capability of a high-performance FOG-based INS (fibre-optic gyroscope). This involves a two-step process:
The first step, coarse alignment, allows the gyrocompass to estimate true north within about two minutes. This step is then followed by fine alignment, where the system refines the heading accuracy to as precise as 0.01 degrees (depending on latitude), typically taking about ten minutes. Both the rapid determination of north and the precision of these alignments are crucial in defence scenarios.
In most modern mobile radar setups, the INS is mounted directly onto the vehicle frame, known as a strap-down INS. In this setup, the INS can continuously monitor the vehicle’s position and orientation, providing real-time data to the radar to maintain ponting accuracy. Without these updates, any changes in position or orientation could significantly compromise the accuracy of target tracking and the overall reliability of the radar system.
Further improvements can be made by incorporating an additional INS within the radar assembly and connecting it to the stabilisation system. This setup typically involves a gimbal to ensure the radar’s reference frame remains stable despite vehicle movements. A gimballed INS allows the control system to more precisely control the radar, further improving its overall performance in diverse operating conditions.
The High Stakes of INS Accuracy
To understand the impact of INS accuracy on mobile radar operations, consider two contrasting scenarios involving a mobile radar system on an armoured unit navigating a mountainous region to scout for enemy drones. As the vehicle moves over the rugged terrain, it will be subject to vibration and shifts in orientation, introducing azimuth and inclination errors into the radar system, affecting its pointing angles.
In the first scenario, the armoured unit has an unreliable INS, which struggles to accurately recalibrate for the radar’s heading and orientation caused by the vehicle’s movement. Without effective correction, these azimuth and inclination errors accumulate, resulting in poor tracking, and the reported location of the object being tracked will be inaccurate. As a result, the radar displays false readings, showing “ghost” drone locations where drones appear in incorrect positions, or in some cases, the drone may not be detected at all.
Consequently, any countermeasures initiated based on these inaccurate readings could fail to locate the actual target, while also revealing the radar’s location.
In the second scenario, the armoured unit is equipped with a high-performance INS, capable of quickly recalibrating the radar’s changing heading and orientation as the vehicle moves through challenging terrain. This advanced INS maintains true north accuracy and minimises azimuth and inclination errors, ensuring the precise tracking and display of drone positions. This then allows operators to effectively coordinate successfully countermeasures.
These two hypothetical scenarios highlight the critical need for high-quality INS technology in defence operations, showing how an advanced INS can enhance accuracy and reliability in contrast to an inadequate system that can lead to mission failures.
Benefits Beyond GNSS Redundancy
The primary advantage of integrating an INS into mobile radars is its ability to provide accurate position and orientation data, especially valuable in areas where GNSS is degraded or in densely populated urban areas prone to multipath errors. However, the benefits of INS extend beyond this:
Real-time data
Integrating INS with mobile radar systems equips them to deliver near-instantaneous updates on the position, velocity and orientation of incoming and nearby objects. This capability is vital for tactical decision-making, especially in defence scenarios where swift deployment of countermeasures can be the difference between success or failure. Whether mounted on fixed assets, vehicles or ships, the speed at which radars can detect threats is crucial.
Superior radar stabilisation
While strap-down INS units perform reliably, integrating a gimballed INS into radar systems brings an additional advantage – superior stabilisation. Equipped with high-performance gyroscopes, gimballed INS systems excel at maintaining precise radar pointing in dynamic environments, ensuring both accurate and effective target tracking.
Countering electronic warfare
As electronic warfare technologies proliferate, the integration of a high-performance INS into mobile radar solutions becomes increasingly important. When GNSS spoofing and jamming occurs, an INS can maintain accurate vehicle positioning and radar orientation, safeguarding its operational effectiveness.
In conclusion, integrating high-performance INS solutions into mobile radar systems is essential for modern defence operations where APNT is needed. With superior stabilisation, real-time updates and resilience against electronic warfare, INS ensures radars have the data they need for precise pointing, target tracking and effective countermeasures.
