| Pseudolite Research
APL
Flight Experiments
Two
experimental flight campaigns were carried out at the airport of Braunschweig.
An IntegriNautics IN 500 P-code APL was used. APL signals were amplified.
Configuration and control of the APL took place by means of the IN 500 software
running on a Windows laptop. Transmission of the APL signals was realized
by a dB Systems MLA antenna. MLA means Multipath Limiting Antenna which provides
a sharp signal power attenuation for low elevations in order to mitigate
signal reflections at buildings, etc. The DGPS (and DAPL) reference station
was located about 750 m away from the APL on plane grasslands. Reference
and rover site were equipped with NovAtel ProPak_II receivers including an
APL firmware. A Dornier Do 128 aircraft served as rover. The following images
show a selection of hard- and software deployed during the experiments.
IN 500
APL with amplifier and laptop
APL
Tx antenna and control station
Test aircraft
Do 128
Reference station environment
The first
flight campaign was mainly to establish a well-performing test environment.
This comprised the optimal choice and best locations for the hardware components
as well as the optimal settings of the software. The second campaign was
to carry out numerous approaches to determine the position accuracy with
and without APL as well as with and without applied APL error model. The
processed solutions are carrier-smoothed code solution according to the RTCA
(Radio Technical Commission for Aviation) standard. The processed results
show that a further improvement in accuracy is possible when applying the
error model. By means of the error model during the approaches an average
accuracy of 2 - 5 decimeter in the height component depending on the distance
to the airport was reached using differential carrier-smoothed code solutions.
A remarkable importance of the APL was detected when limiting the number
of available satellites to the minumum number of four. In this case the APL
solution leads to accuracies in the height component of about 5 decimeter.
More important, in comparison with the solution without AOL the accuracy
improves by more than factor two.
Accuracy
of height component - all satellites processed
Accuracy
of height component - only the four satellites of heighest elevation
processed
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