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jal targets. The first 
ie second application 
ors. In both cases the 
€ structural dynamic 
duced vibration. A 
comparison between 
targets were tracked 
nd offline processing 
the photogrammetric 
visualisations of the 
iper will describe the 
> geometry and image 
| to track the target 
IGHT VEHICLES 
etric monitoring of 
f the membrane and 
icle. These 250 mm 
ges of research and 
role in military 
vell as the subject of 
s and materials. The 
pment is primarily in 
Defense Advanced 
develop micro aerial 
inches and a speed of 
's of wings are under 
tions have generally 
insparent  monofilm 
hite/epoxy spars or 
is that it will be an 
a sensor and radio 
) be a vision system 
red bands, however 
diation counters or 
ly. The vehicles will 
return intelligence 
ved advantages of the 
detected, relatively 
capable of providing 
accurate and valuable information from redundant sources. 
Micro-flight vehicles also have civilian applications to search 
and rescue or fire fighting operations, for example. 
Previous research on micro-flight vehicles has concentrated on 
fixed wing designs with testing carried out in wind tunnels 
(Waszak et al, 2001). Both qualitative (flow visualisation) and 
quantitative (target tracking from a single, high frame rate 
camera) videometric techniques have been used to characterise 
the deformation of the membrane surfaces under wind load and 
at different angles of attack (Waszak et al, 2001). The new 
concept under development at Langley is a flapping wing type 
vehicle with a self-contained power source, avoiding the noise 
or exhaust trail associated with conventional propulsion 
systems. The flapping of the wings is generated by a simple, 
low speed electric motor with an off-centre counterweight to 
induce flapping indirectly. 
The measurement task for the micro-flight vehicle prototype 
was to characterise the motion of the wing surfaces at different 
flapping frequencies and to compare two membranes of 
differing thickness. The set-up to capture imagery is shown in 
figure 1. The wings and flap motor are mounted vertically on 
an optical table, opposite two Hitachi monochrome CCD 
cameras, also mounted vertically. The configuration was later 
changed to a horizontal mounting of the cameras to improve the 
sensitivity of the tracking. The Hitachi cameras generate RS- 
170 analog video output with a resolution of 752 by 480 pixels, 
captured in this case by dual Epix frame grabber cards. The 
cameras were locked together using a master-slave link through 
external synchronisation from one camera to the other. Ring 
lights were used to illuminate the retro-targets, placed both on 
the fixture, to provide a fixed reference, and on the spars of the 
wings, to determine the shape of the wings. Retro-targets were 
not placed on the membrane sections as the material is very 
delicate and because the spars control the overall shape of the 
surface. 
The camera set-up was calibrated using the small 3D target 
array seen lying on the optical table in figure 1. This fixture 
was moved around within the field of view of the cameras to 
simulate a  multi-exposure, convergent photogrammetric 
network. The network for the simultaneous calibration of the 
two cameras comprised 44 targets and 40 full frame exposures. 
The relative precision of the network was 1:32,000, 
corresponding to a mean coordinate precision of several 
micrometres for the targets. The camera calibration and the 
relative orientation of the two cameras were derived from the 
network. This technique uses post-processing of the camera 
station data to determine the base vectors and relative rotations 
of the two or more cameras, and has been used successfully for 
underwater stereo-video (Harvey and Shortis, 1996) and wind 
tunnel testing (Shortis and Snow, 1997) applications. 
Fields, rather than frames, were captured during the 
measurement process to increase the sample rate to 60Hz. The 
calibration data sets for the cameras were converted from 
frames, captured during the calibration process, to fields, 
captured during the measurement process, using the known 
relationship between frames and odd/even fields (Shortis and 
Snow, 1995). The use of fields, rather than frames, halves the 
vertical resolution of the exposures. However the aspect ratio of 
the object allowed the CCD sensors to be aligned with the 
horizontal axes parallel to the general direction of motion 
-9] — 
    
  
Figure 1. Initial experimental set-up for the calibration and 
measurement of the wing surfaces of the micro-flight vehicle. 
within the images, thereby minimising any loss in system 
sensitivity. 
Left and right images were captured as a sequence of individual 
images in TIFF format, and correlated using VITC time code 
generator input, as shown on the two images in figure 2. A 
number of sequences were captured at different wing flap 
  
Figure 2. Left (top) and right images of the wing surfaces 
of the micro-flight vehicle.