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e Guidance to the mission area
e Approach to pre-planned imaging lines
e High-precision guidance on the imaging lines.
Orientation is being improved by the implementation of
moving map displays, based on standard pixel maps.
Displacements from the planned flight line are displayed
and corrective actions suggested to the pilot (figure 7). The
displayed flight path is calculated using an abstract model
of the aircraft characteristics and the dependent parameters
such as aircraft speed over ground and wind drift.
Independent of the operator’s display the pilot can select
his own display configuration and representation of the
screen. No longer do both the pilot and the operator have
the same display. Acting as a client the pilot can indeed Figure 7. Navigation systems example screen
control the complete sensor system from his interface in the
case of operation by a one-person crew.
8.3 Sensor Control
The sensor control module interfaces the specialised image data acquisition hardware. Parameters either set by the
operator or defined by the flight plan are transferred to the hardware and status information read back. Through
modelling the hardware and related aspects, the ADS40 is encapsulated and represented in abstract form to the flight
management system.
84 Flight and Error Data Log
During the flight a wide range of different data is stored in order to allow precise evaluation. The flight track together
with start and stop locations of imaging sequences together with the individual sensor parameter settings can be
retrieved after the flight. Additional entries in the log provide exact servicing and error analysis functionality, a feature
that eases and optimises the maintenance of the ADS40.
8.5 Test and Service Facility
The test and service facility is mainly used by trained service personnel or specially trained operators. It assists the
servicing process and deeply analyses the complete sensor system with all its subsystems. As a result turnaround times
and maintenance intervals can be improved and optimised, allowing the service technician to locate and replace faulty
parts directly or update internal software with the latest releases.
9 ATTITUDE AND POSITION MEASUREMENT SYSTEM
In order to reconstruct high-resolution images from line scanner data, the orientation data of each line has to be
determined. This can be done by using observations from image matching techniques only, as provided in modern
aerotriangulation packages. But computational effort for this indirect method is so large that direct observations from
attitude and position sensors are seen as the means of reducing processing time: the indirect method is time consuming,
whereas the direct method is capital intensive. The decision was made to find an optimal trade-off by including direct
measurements from GPS and IMU sensors of only a certain accuracy into the triangulation. Attitude and position
measurements, therefore, are provided by an integrated GPS/inertial Position and Orientation System (POS) that has
been designed specifically by Applanix Corporation to meet the unique requirements of the ADS40. The advantages
are:
© data processing time to rectify line scanner data is reduced significantly
* price/performance ratio of medium priced IMU sensors is likely to improve over time.
The tight integration (figure 8) with the focal plane of a digital line sensor has great potential for further reduction of
ground processing.
The system comprises four main components: an inertial measurement unit (IMU), a POS computer system, a high
performance L1/L2 GPS receiver and a post-processing software package for optimal carrier-phase DGPS/inertial
Processing.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part Bl. Amsterdam 2000. 263
