Abstract: As an important part of hydrometry, river discharge monitoring plays an irreplaceable role in water resources management and scheduling, flood prevention and disaster reduction. Spatio-temporal image velocimetry (STIV) has the advantages of simple principle, high real-time and security. However, the measurement method also has certain limitations, such as the flow and velocity is small, and the tracing is not obvious, the spatio-temporal image can not produce an effective texture structure, which greatly affects the detection of main direction of the texture, thereby affecting the accuracy of the algorithm. In order to solve the above problems, in this paper, combination of inter-frame difference and the local Fourier maximum angle analysis is proposed, which uses the inter-frame difference method to calculate the pixel difference between two consecutive frames of images, captures and identifies the minor changes of the river, and superimposes the kinematic saliency map with the original video to generate spatio-temporal image (STI), and uses the method of local Fourier maximum angle analysis to calculate the main direction of the texture of the spatio-temporal image, which improves the robustness and accuracy of the spatio-temporal image velocimetry algorithm. In this paper, the results are calculated by using the video filmed in the river compared with the measurement results of the propeller current meter, which show that in the case of small velocity and river discharge and insufficient tracer, the accuracy of this paper's method in the calculation of the average velocity and river discharge has been significantly improved, the stability and real-time performance of the velocity measurement is good.

Key words: spatio-temporal image velocimetry, frame difference method, texture primary orientation, local Fourier maximum angle analysis method