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Navigation systems aboard D-CALM

Post-processing of navigation data to provide aircraft track

Post-processing of navigation data to provide aircraft track

Precise navigation is of prime importance for remote sensing projects, with most users requiring an end product that can readily be overlaid on existing map and image data. Indeed, the IDS (Integrated Data System) has been developed to integrate the image data with the navigation and attitude data to provide fully geo-referenced digital data without the use of ground control points (Level 3a in NASA HDF product standard). For this reason, D-CALM is currently fitted with two stand-alone systems which record a unique combination of "at sensor" and "aircraft frame" navigation and attitude. These measurements are based on INS (Inertial Navigation System) and high rate GPS (Global Positioning System) data, and are used in real-time displays of image data as well as post-processing image data, and to drive an integrated pilots display providing flight guidance. Read about the evolution of the navigation systems below.

The Applanix PosAV system

The Applanix PosAV system

The Applanix system

The Applanixexternal link POS AV is a hardware and software system specifically designed for direct georeferencing of airborne sensor data. Supported by Applanix' industry expertise and technological innovation, POS AV is engineered for aerial cameras, scanning lasers, imaging sensors, synthetic aperture radar, and LIDAR technology.

The IPAS20 system

Leica Geosystems has been a pioneer in integrating direct IMU georeferencing systems into airborne sensors. The Leica IPAS20external link standalone system delivers direct georeferencing for a wide range of airborne sensors such as imaging, LIDAR, synthetic aperture radar (SAR), thermal and Hyperspectral systems. IPAS20 is equipped with the latest GPS/GLONASS technology and a plug and play IMU interface.The ARSF uses two IPAS systems for the LiDAR and Eagle/Hawk/Thermal navigation data.

The IPAS20 Control Unit

The IPAS20 Control Unit

Historical development of ARSF navigation systems

The ATM original mechanical gyro was disconnected and replaced by the Litef LCR-92 Attitude and Heading Reference System (AHRF). This fibre-optic gyro system provides 64Hz attitude information on pitch/roll angles and magnetic heading. The aircraft frame attitude was measured by 4 GPS antennae arranged on a cruciform fashion on the fuselage and wings of the then Piper Navajo. An Ashtech receiver with 4 GPS receivers board was adopted for this task.

In 2000 the Ashtech 3DF GPS was upgraded to the Javad AT-4 20Hz dual channels (L1 and L2) GPS attitude and position reference system which synchronises the GPS information with scan line acquisition time from both the ATM scan-head and the casi-2 system.

The Litef gyro was superseded in 2002 by the improvement of the AT-4 working in stand-alone mode providing a kinematic attitude and position solutions at 20Hz.

In 2003, the ARSF acquired an Applanix POS-AV System integrating a "strap down" Litton IMU gyro providing attitude measurements at 200 Hz and a GPS receiver. Accurate attitude and position measurements are obtained in the post-processing phase of the navigation data. The quality of the solution depends upon the availability of a local GPS base station (Differential GPS), located within 30 km of the survey site. The final integration of high accurate kinematic measurements and high rate attitude angles (roll, pitch and yaw) provide adequate solution for the per-scan geo-referenced imagery.