The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
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suspended take-off and landing and without the need of a 
runway, unmanned airship would be the second choice, but a 
field of no shorter than three fuselage lengths is needed. A 
stadium within the city, a square or even a lawn can all serve as 
the landing fields, yet it hardly needs a landing field when 
flying outside the city. 
For unmanned fixed-wing aircrafts, there are restrictions on the 
airfield, the runway of which should be even and flat, have at 
least ten fuselage lengths and two wingspan widths. In addition, 
adequate headroom is also required. According to Guangzhou 
flight test, such technologies as catapult take-off, hit net 
recovery, water surface take-off and landing or a combination 
of both must be developed for an unmanned fixed-wing aircraft 
to better suit the flight in well-developed water networks and 
vegetation-intensive areas, which ensure that the unmanned 
fixed-wing aircraft can take off anywhere and at anytime. 
Under the conditions of no pixel compensation device, the 
maximum flying speed of a low-altitude unmanned aircraft will 
be restricted. Take the test in Zhumadian city for example, the 
provisions of pixel displacement is 8 = 1/3 pixel, i.e., viz. . 
Meanwhile, the exposure time is set at t = ^ ^ ^Os , relative 
altitude at ^ = 236m , an( j altitude difference at ^ = , 
focus at /-12mm , w hj c h the maximum permitted speed 
can be calculated at w ~ 84km / h Therefore, it is particularly 
important to improve the range capability of an aircraft in 
speed- limited circumstances. The cruise duration of an 
unmanned helicopter, an unmanned fixed-wing and an 
unmanned airship used in the tests reported this paper is 2.5 h, 
2h and 2h respectively, all of which needs further improvement. 
6. CONCLUSION 
Through comprehensive analysis and summary of the 
experiment on aerial photogrammetry of unmanned helicopters, 
unmanned fixed-wing aircraft and unmanned airship, following 
conclusions can be drawn: 
1. In regard to professional photogrammetry, all three systems 
of unmanned aircraft low-altitude aerial photogrammetry meet 
the requirements of small regional large-scale aerial 
photogrammetry. 
2. Taking security, cost, efficiency into account, development 
of unmanned fixed-wing aircraft and unmanned airship should 
be given priority. Perfecting unmanned airship technology, 
solving the problem of flying in urban areas and improving the 
unmanned fixed-wing technology all help to realize highly 
efficient and secure flight in areas outside the city. 
3. The development of low-altitude photogrammetry system of 
unmanned civil aircraft should be combined with professional 
application, matching the system's performance with 
professional requirements so as to avoid the waste of resources 
caused by the simplified civil use of high-performance military 
aircraft. 
Following proposals are made to further improve the 
technology in low-altitude unmanned aircraft aerial 
photographic system: 
1. Three-axis stabilized platform technology, the key problem 
in low-altitude unmanned aircraft aerial photogrammetry 
system, needs further improvement. 
2. The study of double-engine and double-generator unmanned 
fixed-wing aircraft helps to further improve the reliability and 
range capability of unmanned fixed-wing aircraft. 
3. Payload swath is not only closely related with altimetric 
measurement accuracy, but is also an efficient way to improve 
the operating performance. At present, in the circumstances of 
limited single pixel CCD, the study of optical synthetic aperture 
camera is necessary. 
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