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32 I n these days of global satellite networks, it may seem that inertial navigation is an old-school technology, but the need to know the exact location of an unmanned system has never been more important, and inertial measurement technology is an essential element in the system’s design, no matter which realm it operates in. Driverless cars for example need reliable data that is accurate to the nearest centimetre, while UAVs need data in all three dimensions, and at sea the height of the waves becomes a vital data point. All these different requirements are driving innovation in both the sensors and the software of the latest inertial measurement units (IMUs). IMUs can also be used in payloads such as cameras or Lidar laser mapping systems to provide a separate source of location data. That allows the payload to be separate from the craft’s navigation system, making installation easier by requiring fewer connections between the navigation system and the payload. It also allows the payload to have a higher accuracy for the positioning data from the craft, for example for surveying in environments where data accurate to the centimetre or even the millimetre may be needed and satellite navigation isn’t good enough. An IMU consists of several elements, and is based around an accelerometer for measuring acceleration and a gyroscope for measuring rotation to provide position data relative to a known point. Other elements such as a magnetometer, to measure the local magnetic field, and temperature and pressure sensors – and even an altimeter – can also be added to boost the accuracy of the data coming out of the device. An inertial measurement system (IMS) meanwhile adds in satellite navigation elements such as receivers for the GPS, Galileo or GLONASS systems. The GNSS data can feed either into the IMU, creating an IMS, or directly into a craft’s navigation system. That means there are many different specifications for an IMU depending on the application, which gives opportunities Prime position December/January 2017 | Unmanned Systems Technology Inertial measurement units are proving key to unmanned system navigation. Nick Flaherty looks at the latest innovations in the technology