ATTITUDE DETERMINATION WITH ASHTECH 3-D DIRECTION FINDING SYSTEM

The Ashtech 3-dimensional Direction Finding system (3DF) utilizes carrier phase measurements from the Global Positioning System (GPS) to provide real-time attitude information along with highly accurate position and velocity. The 3DF system includes a 24-channel receiver and four microstrip antennae. The receiver's 24 channels are configured in four six-channel banks. Each bank is connected to a separate antenna. Attitude is the angular orientation of a body with respect to some reference. This orientation is determined using the GPS signals and knowledge of the precise relative antenna positions. Mounting at least three antennae on a rigid platform and determining the relative positions provides three-dimensional attitude information. The Ashtech 3DF system uses four antennae for rapid determination of differential phase ambiguities and for continuation of position and attitude information even when satellite visibility is low. Potential applications of the 3DF system include land, marine, and airborne navigation. Specific issues that arise in these applications are discussed in detail. Test results of the 3DF in several environments will also be presented.