Tactical underwater navigation system (TUNS)

The problem of underwater navigation for an individual diver is particularly challenging. GPS navigation is unsuitable for most underwater operations and particularly covert operations use because the GPS RF signal is attenuated below usable levels as it penetrates the water column. Dead reckoning methods, which rely on magnetic compass and approximate distance measurements, are susceptible to magnetic interference, inaccurate distance estimates and current induced drift. Pure inertial navigation methods require expensive systems to meet mission accuracy objectives, due to mission lengths of several hours. Advances in the performance of MEMS inertial sensors, solid state compasses and the development of water based Doppler velocity sensors have enabled a positioning solution that meet USMC diver cost and performance goals. A technology development team organized by Honeywell has developed a self-contained prototype system that integrates a GPS receiver, an inertial measurement unit, a solid state magnetometer, a pressure sensor and a multi-axis Doppler velocity sensor that functions as a surface or underwater navigator and also enables the user to perform underwater surveying and mapping. The sensor integration approach was based on a Kalman filter aided strapdown navigator. Gyro and accelerometer information is processed by the strapdown navigation algorithms to produce navigation solution. An extended Kalman filter processes the GPS, magnetometer, Doppler Velocity Log (DVL), and depth sensor measurement to aid the navigation solution and update sensor error estimates. This paper presents an overview of the system hardware and software implementation as well as test results from ocean trials off the coast of Hawaii.