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DIGITAL IMAGE ENHANCEMENT OF NOISY SCANNER IMAGERY 
by 
Manfred EHLERS and Peter LOHMANN 
Institut für Photogrammetrie und Ingenieurvermessun- 
gen der Universität Hannover, Nienburger Straße 1, 
3000 Hannover 1, F.R.Germany 
ABSTRACT 
Digital filtering of thermal scanner imagery prior to the use of atmospheric correc- 
tion yields an increase in accuracy of temperature allocation. For this purpose a 
special digital filter-method for scanner imagery is developed and compared with 
common methods. This filter-method allows a quantitative evaluation even of images 
with a very low signal-to-noise-ratio. 
INTRODUCTION 
The special research unit SFB 149 at Hanover University (speaker: G.Konecy) is work- 
ing in the field of monitoring coastal areas by means of remote sensing. For mapping 
of the discharge of power stations the quantitative evaluation of thermal Mes 
Scanner data has been proved (KONECNY 1979). Interpretation of raw data is distorted 
by interior (instrumental) and exterior (atmospheric) influences (EHLERS and LOHMANN 
1982). In the following the correction of both is demonstrated using the thermal 
recording of a flight (altitude: 1600 m) with Bendix M2S scanner above the Jade 
estuary (12. August 1976). 
Accuracy of the results can be checked by using 27 in-situ boat measurements of 
water temperature. Processing of the image data was performed with the SFB image 
processing facilities MOBI and DIVAH (MOBI 1982, DIVAH 1982). 
ATMOSPHERIC CORRECTIONS 
The measured radiation temperature at flight level H is distorted by the absorption 
and emission of the intervening atmosphere.Besides this one has to take into account 
that the earth has a lower absorptivity than an ideal black body. Therefore one part 
of the atmospheric radiation is reflected into the recording system. 
The recorded temperatures are additively distorted by interior distortions like for 
instance miscalibration of the instrument. 
To assure an accuracy in recording of t 0.2 K the black bodies have to be stabi- 
lized within * 0.1 K. Therefore a careful calibration of the scanner is necessary. 
Using thermal control points and interpolation techniques it is possible to achieve 
an absolute accuracy of t 0.2 K (LOHMANN 1980). This method requires high logistic 
efforts. These efforts can be reduced by using atmospheric corrections. 
Correction of absorption and emission of the atmosphere 
The radiance L measured by a scanner at hight H at the apparent surface temperature 
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consists of the radiance of the surface and the intervening atmosphere (LORENZ 1973). 
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