Design and implementation of an inshore hydrographic surveying system
Computers are no widely used in hydrographic surveys to take advantage of their ability to provide navigation function and data processing capabilities. The design parameters that play an important role when we try to create an automatic data acquisition and processing systems are the accuracy with which sea bottom is represented, the reliability, the compatibility with existing hardware, the man/machine interaction, the modularity and the cost of the system. In order to optimize the design parameters, an automatic data acquisition and processing system was built around the Apple IIe personal computer. The algorithms required to meet the design objectives have been implemented in larger systems. These systems are downs scaled to a system that will serve the needs of near shore hydrography. Different systems of lines, used to sample the depth, are compared: straight parallel lines, lines of position of electronic positioning systems, circles and radial lines (“star” mode). In order to filter the position data simple getting techniques are compared with Least Squares and Kalman Filters. In order to filter the depth data depth filtering techniques are examined. The results indicate that the Apple IIe with commercially available peripherals and standard software, offers great promise of replacing larger and more expensive hydrographic data acquisition and navigation controllers. Straight parallel lines give efficient coverage of the survey area only if they can be modified on-line. The “star” mode is the best shoal examination pattern with respect to track keeping ability. The memory and computational speed constraints of personal computers require the use of simple linear filters to filter the position data. Visual comparison of digital depths with analog depths is an efficient depth filtering technique.