Navigation-aiding Using a 94GHz Radar for Helicopter Operations

J. McKitterick, T. Case, M. Elgersma

Abstract:	Inertial devices for navigation are used almost universally, but require additional input to correct for the inevitable drift that occurs. Currently, the most common aiding source is GPS, and this provides impressive capabilities over a wide range of applications. However, GPS is easily jammed and suffers from multipath and other ills. To overcome these problems, an alternative source of aiding for the inertial device is needed. This paper describes the use of Honeywell’s innovative 94 GHz radar as an alternative aiding sensor, particularly useful for helicopter operations. The choice of a radar as an aiding sensor has a number of attractive features. The Honeywell 94 GHz radar is much less affected than optical sensors by weather or dust, has a range capability suitable for high-speed helicopter flight (greater than 2 km), and is relatively small and light-weight (less than 20 pounds). Moreover, the Honeywell radar is interferometric, so that in addition to the superior range resolution (as low as 0.22 m), the angular resolution can be as small as 2 mrad, depending on the target. The design of the antenna also maximizes the radar’s abilities for navigation-aiding, with a large 4 degree beamwidth in elevation (the interferometric axis) and a smaller 0.35 degree beamwidth in azimuth. This allows coverage of a large area in a single azimuth sweep, providing a large amount of data in a very short time. This paper describes how the Honeywell radar can be used for navigation-aiding. Because the radar is interferometric and has very good range resolution, the volume associated with any detection is quite small. This makes it possible to create a good 3D map of the ground out to a range of 2 km or more. We can then compare this map to pre-existing data such as DTED to develop corrections in the six navigational degrees of freedom. This method works very well for correcting errors in roll, pitch, and especially altitude; for altitude, the results can have a precision of less than 0.1 m. However, this method is not suitable in many terrains for determining any errors in latitude, longitude, or heading, since corrections in those degrees of freedom requires variations in terrain that may not exist. The Honeywell radar, in addition to being interferometric, also has a very good signal-to-noise ratio. This enables the creation of two-dimensional intensity maps that provide an impressive image capability, approaching the quality of SAR images. In these images, field edges, power transmission lines, and other features in the landscape are clearly seen. These images can be aligned to satellite photographs of the area to obtain corrections to latitude, longitude, and heading. Our results show that alignment between the satellite images and the radar data can easily be maintained to within 4 meters over a several minute flight, when the two-dimensional intensity map is created with a 4-meter pixel size. These two methods, combined with the capabilities of the Honeywell 94 GHz radar, allow us to correct navigation errors in all six degrees of freedom. While a complete navigation system incorporating feedback from the radar into the Kalman filter will still require much development, these first steps show how powerful a good radar sensor can be in providing navigation aiding.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2562 - 2568
Cite this article:	McKitterick, J., Case, T., Elgersma, M., "Navigation-aiding Using a 94GHz Radar for Helicopter Operations," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 2562-2568.
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