Integration of Inertial Measurements with GNSS: NovAtel SPAN Architecture

摘要

As a GNSS system manufacturer, NovAtel is in a unique position to integrate external sensors such as inertial measurement units (IMU) in order to extend and enhance the usefulness of satellite navigation systems For operational situations where navigation by GNSS only is either degraded or impossible, augmentation through the use of external sensors provides users with the required position and attitude solution accuracy and reliability. Several companies have integrated GNSS with IMU data to generate a combined solution in the past. However, with the SPAN Technology developed by NovAtel, the combination of GNSS + INS is unique because the system is based on the NovAtel OEM4 GNSS technology for a GNSS centric design. Rather than considering the IMU to be aided by GNSS, the GNSS is enhanced by the IMU. By exploiting the company's GNSS system expertise, the integration of inertial measurements is done with a much tighter coupling because of access to the GNSS receiver core. Through the tight coupling of the inertial data with GNSS core functionality such as satellite tracking, RTK carrier phase positioning, and clock modeling, the system provides a full 3-dimensional position, velocity and attitude solution with virtually continuous availability. This paper will discuss NovAtel's approach to INS/GNSS system architecture. Currently, the SPAN system supports two tactical grade IMUs: the Honeywell HG1700 AG58 and AG62. Recently work has been undertaken to evaluate the iMAR ilMU-FSAS within the SPAN system The ilMU-FSAS is a tactical grade IMU as well, manufactured in Germany and subject to German export licensing. Results of the initial evaluation of the ilMU-FSAS integration are presented herein. Tests were completed to assess the position, velocity, and attitude accuracy. Data was collected under clear GNSS conditions and controlled GNSS outages were applied. Errors after 10. 30 and 60 second GNSS outages are presented.