Surface mapping and imaging using low power lasers

Preliminary results are given for a developmental imaging system which will use a triangulation principle for obtaining maps of underwater surfaces at close range (<2 m). For high resolution, triangulation is advantageous in comparison to time-of-flight or interferometric methods due to its simplicity and low cost. In operation, a low power semiconductor laser, operating in the red portion of the spectrum, is scanned across a region of space along two perpendicular axes. The scan is completed in 50 ms corresponding to a 20 Hz scan rate. Light reflected from surface points within the field-of-view (FOV) is detected and converted to relative position and intensity at each scan angle. The position information is used to compute the depth coordinate of the point of reflection from a knowledge of the system geometry. Initial results indicate that an angular resolution of 200 by 200 points minimum is achievable over a ±45 degree FOV while maintaining a depth resolution of 1 millimeter at a 1 m nominal range. The paper addresses system operation, design considerations, laboratory test results, and implementation of an adaptive algorithm for reduction of turbidity induced errors