Long-time-sequence automatic monitoring device and method for underwater target

The long-time-sequence automatic monitoring device comprises a hanging frame, a spherical monitoring assembly is arranged in the hanging frame, a cleaning assembly is arranged at the position, close to the upper portion of the spherical monitoring assembly, of the inner side of the hanging frame, the lower portion of the hanging frame is connected with a balance weight base, and the hanging frame comprises a supporting ring; a U-shaped frame is fixedly arranged on the lower portion of the supporting ring, an arc-shaped dragging block is arranged on the lower portion of the inner side of the U-shaped frame, the spherical monitoring assembly is arranged on the inner side of the U-shaped frame, the cleaning assembly comprises an annular frame, an arc face cover is arranged on the inner side of the annular frame, and penetrating holes allowing the two ends of the U-shaped frame to penetrate through are formed in the two sides of the top of the annular frame. According to the device, the surface of the spherical m