Abstract: Flood monitoring based on network dome camera has become one of the hot spots in water conservancy construction. In order to monitor the flow rate, water level and flow rate in multi-field-of-view, the camera needs to rotate, zoom in and out the focal length. Because of the defects of the camera transmission, the preset point can't be reset accurately when the multi-field-of-view is switched, resulting in the gap error. It creates a large deviation in analyzing water level and flow rate from single image. In this paper, a method of gap error correction for water level measurement is proposed. Firstly, the water level ruler of the preset point is precisely calibrated, and the parameters of the water level equation are obtained. And two correction points with obvious features are selected on the image. Then, The image coordinates of the correction points in the instantaneous field-of-view are linear corrected to the preset field-of-view. Finally, water level in the instantaneous field-of-view is calculated by using the water level equation of the preset point. Through field test, the maximum gap error in different instantaneous field-of-view is 8 pix, and the water level error is 5cm. But the water level error is about 5mm by paper's method. It is shown that the paper's method can greatly reduce gap error in water level measurement.

Key words: flood monitoring, gap error, linear correction, water level equation, water level accuracy