INS Alignment Duration Reduction Using GNSS Heading

In some application, INS must be fully operational, i.e. must provide its full performance as soon as possible. For some fast patrol boat operational scenario, the ship must reach the fattest it can a rendezvous point in a GPS denied environment. So the initial settling time may be an important parameter. This paper propose to reduce it by inserting external GNSS heading. High-grade Inertial Navigation Systems (INS) need an alignment procedure before they are fully operational. Generally, the alignment procedure is divided into two steps: • During the first step, a coarse alignment estimates attitude with sub degree error and heading with few degrees error. • As soon as the attitude and heading errors can be linearized, a Kalman hybridization filter is initiated during the second step to complete the alignment process and achieve a heading performance of around 1 milliradian (mrad). During the first step, the heading is typically self-estimated by the INS or can come from a stored heading alignment. In this paper, we propose an architecture that utilizes GNSS heading information to reduce the duration of the coarse alignment process. During previous navigations, an algorithm is employed to determine the bore sighting angles between the vehicle and the two GNSS antennas. This information is then utilized during subsequent alignment procedures, where the GNSS heading data can be used to initialize the heading of the INS. This paper details the operational case of alignment duration reduction on a fast patrol boat proving that alignment duration can be reduced by a 30% factor.