Fourth Study Conference on BALTEX Scala Cinema Gudhjem

3. Image Calibration
The images required very accurate navigation data sets of
both Helipod and Tornado. Beside the measurement of
position and attitude it was necessary to make assumptions
about the internal algorithms that control the aperture stop of
the Tornado IR camera. So after recalculation of the images
horizontal shift, deformation, and non-uniform exposure, a
proper calibration of the image gray scale with the surface
temperature (Helipod measurements) became feasible (Fig.
5 and 6). A detailed description of these algorithms will be
published soon.
Fig. 5: Tornado image containing two Helipod flights.
Fig. 6: Same as Fig. 5, after the calibration. The color
scale covers temperatures between 19° C (forest) and
63° C (roofs).
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4. Results and Conclusions
Since the Tornado IR camera used analog technique
(chemical films) the spatial resolution is in the order of a
meter or (depending on aircraft's altitude) even better. The
first impressive result of the analysis of these
photographies is that the heterogeneity of the experimental
site was much stronger than assumed by the numerical
models used so far. Especially the influence of the water
content of different soil types is clearly visible. But even
in a uniformly planted field the temperature variations
were large due to the varying water content of the soil.
The measurements at several ground stations give the
opportunity for data quality control and cross-validation.
The deviation from ground-based measurements was
always smaller than 2 K. The temperature accuracy of the
calibrated images (in comparison with the Helipod data)
was better than 2 K in 95 % of all properly calibrated
images. Some images (marked with an 'I' in Fig. 7) show
systematic temperature bias due to a lack of absolute
temperature measurements.
Fig. 7: Calibrated temperature map of the LITFASS-
2003 experimental site.
Acknowledgments
We are deeply grateful to the 51st reconnaissance
squadron (AG 51) 'Immelmann' of the German Air Force
in Jagel. We are much obliged to the crew of the FJS
Helicopter Service in Damme (Germany). The Helipod
flights were funded by the German government (BMBF:
EVA-GRIPS within DEKLIM, grant no. 01-LD-0301
References
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