Intercalibration method for underwater three-dimensional mapping laser line scan systems

I present a method to calibrate absolutely a new family of underwater bathymetric laser scanner systems that use a single target range. Depth is calculated by triangulation among the source, the receiver, and the instantaneous position of a single spot produced by a highly collimated laser beam scanned across the target. For calibration, the refractive index of seawater is used to modulate the triangulation parameters rather than use of different target ranges to calibrate for extended range operation. Exploitation of a unique triangulation configuration allows the receiver characteristics to be ignored initially so that the scanner parameters can be determined. This allows the accurate positioning of the laser spot so that the receiver, in turn, can be calibrated. This intercalibration method provides high-resolution parameterization of the source-receiver characteristics and their geometric layout within the system so that an absolute bathymetric calibration can be realized in situ. In addition, a theoretical model derived to develop the methodology can be used to characterize and optimize future designs.