AEROcontrol is IGI's GPS/IMU system for the precise determination of position and attitude of an airborne sensor. This can be the position of the projection center and the angles omega, phi, kappa of the aerial camera system or an airborne laser scanner.

The AEROcontrol system consists of a fibre-optic gyro based Inertial Measurement Unit (IMU-IId) and a computer with an integrated 12-channel L1/L2 GPS receiver.

AEROcontrol can be operated either as a stand alone system or via IGI's CCNS guidance and management system for aerial survey flight missions. The CCNS and AEROcontrol together form a fully integrated system.

Installation material for the IMU, including a mechanical adapter plate, are available for the Wild/Leica RC10, RC20 / RC30, the Zeiss Jena LMK, LMK-1000, LMK-2000, and the Zeiss Oberkochen RMK-TOP aerial camera systems. AEROcontrol is successfully operated with different digital cameras and laserscanner systems.

Image showing from left to right: Inertial Measurement Unit (IMU-IId), Airborne Computer Unit (CAE) with integrated 12-channel L1/L2 GPS receiver and L1/L2 GPS antenna.

Depending on GPS constellation and distance from GPS Base/Monitor Station, a positioning accuracy better than 0.1m RMS and attitude accuracy of 0.01 deg RMS for heading and of 0.004 deg RMS for roll and pitch is is available in post-processing.

This accuracy is sufficient for direct georeferencing for many tasks. For large scale photogrammetric projects where a higher accuracy is required, the use of AEROcontrol results as additional information for an aerial triangulation (Integrated Sensor Orientation) leads to large savings in GCPs and processing time.

The airborne computer of the AEROcontrol system is used for data recording of:

• IMU-IId raw data, i.e. angular and acceleration increments
  (64 Hz, 128 Hz or 256 Hz)
• GPS raw data, positions and velocities (1Hz or 2Hz).

Real-time platform calculations allow to use this information as navigational input for IGI's CCNS.

All collected raw data (IMU and GPS) are stored on the AEROcontrol Misson Card for post flight processing.

The system approximately records 11MB (64Hz), 18MB (128Hz) or 32MB (256Hz) of data per hour giving a maximum mission time of at least 14 hours with available 256 MB PC-Cards.

For the precise position determination of the airborne sensor, the position of the phase center of the aircraft (a/c) GPS antenna has to be transformed to the sensor position. The lever arm between the GPS antenna and the sensor can be determined during the system installation.

Because of a/c movements in flight, this lever arm has to be corrected for the actual attitude.

• If the camera is rigidly mounted to the a/c's frame, the lever arm remains constant during sensor operation. In this case, the projection center is calculated directly from the constant lever arm and the GPS/IMU information. No additional measurements are needed.

In this case this movement has to be taken into account for the lever arm correction. This can be done by using the attitude information of the stabilized mount.

If the IMU is installed together with the aerial sensor system, the body frame of the IMU does not exactly match with the sensor frame. For the calculation of the actual sensor attitude, the angles between both frames have to be determined by a flight over a calibration field (boresight alignment). Using these mounting angles, the IMU angles (heading, pitch, roll) are transformed to the real sensor attitude (kappa, phi, omega) for photogrammetric operation, e.g. orthophoto mapping.