Unmanned Systems Technology 023 I Milrem Multiscope I Wireless charging I Logistics insight I InterGeo, CUAV London & USA show reports I VideoRay Defender I OS Engines GR400U-FI I Ultrabeam Hydrographic Ultra-2 I IMUs

direction and magnitude of the external field. They are among the easiest types of MEMS magnetometers to fabricate, and are therefore suited to lower-cost IMUs and AHRSs. In addition to providing Magnetic North references for headings, magnetometer data can also be incorporated into sensor fusion algorithms alongside GNSS to provide more accurate estimates for position and orientation. The alternative to using a magnetometer for heading references is to install a dual-antenna GNSS, which can provide headings without being affected by magnetic fields. While GNSS signals can be lost in urban or forested environments (or be inaccessible for UUVs), advances in IMUs (or ‘INSs’ when combined with a processor and GNSS) enabling high update rates and calibrations against short-term drift compensate increasingly well using ‘dead reckoning’ between GNSS outages. Conclusion As the number of IMUs installed in each unmanned system increases, advances in MEMS and FOG technology – and fusions with payload sensors, pitot tubes and new satellite constellations – will drive a growing specialisation of inertial sensors. This will better enable systems integrators to find IMUs for most applications and with minimal calibration. Acknowledgements The author would like to thank Samantha Samuelli of Trimble, Andy Hughes of Silicon Sensing, Anton Barabashov of Inertial Labs, Alexis Guinamard of SBG Systems, Romain Pare of Advanced Navigation, Sean McCormack of KVH, Arnout Koelewijn of XSens, Jakub Maslikowski of VectorNav, Eric Yates of Gladiator Technologies, Andy Williams of Systron Donner Inertial, Aviram Feingold of Physical Logic, Yves Paturel of iXblue, and David Pinta and Miguel Ángel de Frutos of UAV Navigation for their help with researching this article.