Gašper Derganc (2009) Computer reading of rainfall graphs. EngD thesis.
Abstract
An algorithm aimed at automatic detection and digitalisation of the rainfall signal recorded by float based rain gauges on paper strip charts is presented. The algorithm consists of several steps that gradually lead to the desired goal. The rainfall signal is extracted from the digital image of the strip chart. By cooperation of moving average method and curve edge following method the rainfall curve is detected and uniquely determined - in each image column there is one single point representing the rainfall curve plotline. From the curve plotline high resolution rainfall time series is obtained. Beside image analysis techniques in the design of the algorithm, the mechanical features of the recording instrument have been taken into consideration. The availability of high resolution rainfall time series is required in many applications, including rainfall classifcation, analysis of extreme rainfall events, calibration of raifall-runoff models, weather prediction models and many research projects. The algorithm has been tesed on 58 pluviograph strip chart images. The comparison between the data obtained by the proposed algorithm and the official data from the Environmental Agency of the Republic of Slovenia shows that the algorithm usually accurately detects the rainfall curve and consequently an accurate rainfall time series is obtained. Since it is not always 100% reliable it should be used as a component of a system that would enable the inspection of the detected curve and when required it should also enable interactive changing of the parts needing correction.
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