Over-water distance surveying instrument for oceanographic engineering surveying and mapping

The invention belongs to the technical field of ocean engineering, and discloses an on-water distance surveying instrument for ocean engineering surveying and mapping, which comprises a main floating plate and an echo detector, a cavity is arranged in the main floating plate, a vertical shaft is arranged in the cavity, two annular limiting blocks are arranged on the vertical shaft, a square block is arranged on the vertical shaft between the two annular limiting blocks, and the echo detector is arranged on the square block. The four corners of the square block are symmetrically connected with L-shaped rods, the L-shaped rods are connected with auxiliary floating plates, an air cylinder is arranged at the bottom of one auxiliary floating plate, the two ends of the air cylinder are fixedly connected with the bottoms of the opposite-angle auxiliary floating plates respectively, an equipment box is arranged at the top of the main floating plate, and a first swing correcting assembly and a second swing correcting