Research on the application of ultra-small scale color IR Aerial Photography in investigation of renewable natural resources and environment
Spatial Resolution
Generally, the following formula is accepted for spatial resolution:
G = Rf / H
Where G----ground resolution (pair of line per meter)
H----flight height (m)
f-----focal length of the camera lens (mm)
R---overall resolution of lens and film system (pair of line per milli metr)
Now, the commercially applied advanced aerial cameras can have a spatial resolution as high as up to 150 pairs of line mm (e.g. RMK, MSK 4etc.). Color IR film also develops in the direction
of high resolution (its resolution is higher than 100 pairs of line/mm). As a consequence, the overall resolution of the lens/film system can be higher than 100 pairs of line/mm. In addition, color IR air photography possesses a good capability to penetrate fog, and the elimination of scattered blue light improves film contrast, and the difference of reflectance of vegetation of scattered blue light improves film contrast, and the difference of reflectance of vegetation in phographic IR section is usually larger, The higher contrast ratio leads to better spatial resolution.
Therefore, color IR airphotos (especially film) have quite high spatial resolution.
In somewhere, Hebei Province, the RC-10 aerial camera with f=88mm was used to take the color IR photographs of scale 1:1300000. Suppose the overall resolution of the system to be 100 pairs of line per mm, the deduced ground spatial resolution of the airphotos would be
G = Rf / H = (100 x 88)
/ 11434.8 = 0.7692 (pairs of lines per m)
Theoretically, the minimum object width that could be distinguished on the photos is 0.65 meter.
It is known through measurement on the enlarged ultra-small scale color IR air photos and through comparison with ground measurement, that the measurement on the photos has a relative error of only 3.2% and the spatial resolution exceeds one meter. These results coincide with theoretical calculation.
The shape, size shadow and the relative of objects could be interpretated on the enlarged images of ultra-small scale color IR aerial photos through stereoscopic instrument (e.g. and analytical plotter,) thus three-dimensions spatial information could be obtained, which could be called the three-dimensions spatial resolution. Such property of the photographs is of important elements in forest inventory. This is extremely interesting in the field of forestry remote sensing, since they have seen a new way of forest resources inventory that is highly effective and of low cost.
Examples of measuring some isolated trees indicated that the accuracy of three dimensional measuration of ultra-small scale color IR aerial photos might be rather high, and the relative error could be less than 5%. The extra-small scale color IR aerial photos that a possess a good three-dimensional resolution greatly strengthen its characteristics of interpretability and measuration, and spead a wide prospect for its application
The Integrated Resolution
The spectral resolution and spatial resolution of remote sensing images are inseparable, and to comprehensively analyse them would help image interpretation.
According to the researches of J.a. Howard and D.C.Schwaar, maize ridge of about 0.7m ground width colud be identified by its integrated effect of the color IR aerial photos of the scale 1:120000, this could be called integrated resolution.
Discussion on application technology of ultra-small scale color IR aerial photos
- Correction and Enlargement
It is commonly accepted in the field of aerial survey that the air photos corrected and linearly enlarged to 7 times are feasible. However, the following practice is surprising and satisfactory.
Although the used film possesses a resolution of only 60 linepairs per millimeter, and the ultrasmall scall color IR aerial photos were corrected and linearly enlarged by 25 times into the color images of the scale 1:50000, various objects still possess sufficient clearness and chromatic saturation, that is , a rather good resolution, and they are quite suitable for interpretation, mapping and measurement of high precision (measured with x10, x20 measuration magnifier).
- Interpretation and Measurement by analytical
Plotter (Planicomp)
Cof
the analytical plotting system (Planicomp) of models C110, C120, P2 of
OPTON CORP. of FRD as example, it has a viewing system with fixed or
zoom lens that results in changeable magnification rate (x7.5-30, zoom
lens). The ultra-small scale color IR aerial photos could be directly
interpretated or stereoscopically measured under the viewing system of
high man\gnification rate (the maximum reaches 30), and thus the
application cost is greatly reduce, with a high working efficiency.
