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We design an event recognition-analysis system that can automatically detectsolar type III radio burst and can mine information of the burst from thedynamic spectra observed by Nancay Decameter Array (NDA). We investigate thefrequency drift rate of type III bursts and the speed of electron beamsresponsible for the generation of the bursts. Several computer vision methodsare used in this automatic analysis system. The Hough transform is performed torecognize the line segment associated with type III bursts in the dynamicspectra. A modified active contour model is used to track the backbone of theburst and estimate the frequency drift rate at different frequency channels. Werun this system on the NDA data from 2012 to 2017, and give a statisticalsurvey of the event number distribution, the starting and stopping frequenciesof bursts, the frequency dependence of the drift rate, and the exciter speedusing three corona density models. The median value of the average frequencydrift rates is about 6.94MHz/s for 1389 simple well-isolated type III burstsdetected in the frequency range 10--80 MHz of NDA observation. The frequencydrift rate changes with frequency as $df/dt = -0.0672 f^{1.23}$ from aleast-squares fitting. The average exciter speed is about 0.2c based thedensity models. We do not find any significant dependence of the drift rate andthe exciter speed on the solar activity cycle.

A type III radio burst automatic analysis system and statistic results for a half solar-cycle with the Nan\c{c}ay Decameter Array data