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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
should be a bit conservative in our mission flight altitude
planning by flying lower in hopes that a finer pixel will offset a
reduction in relief exaggeration.
The DMC's greater radiometric depth of 12 bits vs. the usual
scanned imagery's 8 bits does not appear to improve the
matching process. In preliminary tests we have confirmed this
by resampling DMC imagery from 12 bits down to 8 bits and
running auto-matching. More investigation is necessary in this
area.
As for the generation of pan-sharpened colour orthophotos, the
processing sometimes creates false-colour artefacts that must be
carefully compensated for in each set of imagery. In some
cases, the final product shows “bleed-over” effects because it is
not possible to correctly assign, for example, the correct R, G,
B, and NIR values for a 0.3m pan pixel from a 1.4m colour/CIR
pixel. As long as one doesn’t magnify the imagery too much,
the effect is usually not noticeable, but it is there. Fortunately, if
one were using the DMC imagery in the context of a
multispectral classification process, one would probably be
quite satisfied just to work with the raw colour/CIR coarse/not-
pan-sharpened imagery. Also, if one is using the pan-sharpened
imagery just to do visual interpretation and if one doesn't
zoom-in too much, the quality of the colour/CIR imagery is
quite adequate and still looks markedly superior to scanned
film.
5. CONCLUSION
In this paper the design of the Digital Mapping Camera (DMC)
has been introduced in some detail. The data flow of DMC
image acquisition and georeferencing is presented. The
technical data of some DMC projects flown at various flying
heights over different terrain types to produce different output
products are given. As shown in Table 2, all results met the
mapping accuracy requirements.
Overall, the DMC offers much better quality in spatial
resolution for panchromatic imagery, and its multiband
resolution is adequate for real-world colour/CIR multispectral
analysis application. The DMC's FMC capability gives it more
latitude in terms of lighting conditions (cirrus overcast, poor
contrast surfaces, poor reflecting surfaces, and time of year and
day [if shadow length specs are relaxed]), superior potential
capital utilization efficiency can be achieved if it is placed on a
faster platform, and, most importantly, the DMC's accuracy is
sufficient to support 3-D mapping to any map accuracy
standard.
Automatic image matching software needs to be modified to
take advantage of the higher dynamic band of DMC imagery.
More investigation is needed to analyze 12-bit vs. 8-bit imagery
as well as the impact of the DMC's reduced B/H ratio on overall
height accuracy when collected DTMs are used in support of
contour mapping.
6. ACKNOWLEDGEMENTS
This paper has been prepared with the use of several DMC
blocks provided by 3001, Inc. We used some of these blocks for
accuracy analysis as well as for georeferencing comparing
direct and indirect sensor orientation. We acknowledge the
401
help of Gregory Horwell of 3001 who has provided us with
valuable analysis of several DMC practical projects.
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