Biomedical Engineering Reference
In-Depth Information
200
150
100
50
0
-50
-100
-150
Uncalibrated Heading
Calibrated Heading
-200
0
20
40
60
80
100
120
140
160
180
Azimuth (deg)
FIGURE 9.7
The dotted line shows the response of the calibrated sensor to angular displacement. The solid line is the
output of an uncalibrated sensor in which polarization-filter angles were assumed to be separated by 60°.
are shown in
Figure 9.6
b. Heading errors in
excess of 20°, shown in
Figure 9.7
(solid line),
occur. After calibration of the filter geometry, the
problem is resolved and the signal is usable for
navigation, as shown in
Figure 9.7
(dotted line).
Determination of
F
i
revealed that polarization
filters were separated by 55° and 62° with respect
to the first sensor channel filter orientation.
Figure 9.9
. As predicted, the polarization-compass
output produced a discontinuity several times
during the flight as the solution passed through
180°. There were minor differences between the
two measures. The absence of any correction for
attitude probably contributed to the most devia-
tion between the magnetic and north-aligned
polarization heading.
9.4 OCELLI ATTITUDE
REFERENCE
9.3.2 Flight Test
The remotely piloted aircraft shown in
Figure 9.8
was instrumented with the calibrated polar-
imeter being tested and an inertial/magnetic
attitude and heading reference system that pro-
vided an independent measure of heading. The
flight was run early in the morning when the
sun was low to minimize the probability that
direct sunlight might saturate the sensor.
The output of the polarization heading solu-
tion and the compass bearing is shown in
Dragonflies are an ancient airborne predator
with clearly recognizable ancestors found in fos-
sil records from the carboniferous era 300 mil-
lion years ago
[26]
. Since that time, their basic
structure has changed little
[27]
. As hovering
animals, they are extremely reliant on vision for
flight control. Although dragonflies have com-
pound eyes with high visual acuity relative to
other species
[28]
, it appears that stabilization of
