Most of the charts available to recreational boaters and fishermen (including the electronic ones) are simply reproductions of bathymetric data collected by the U.S. Coast and Geodetic Survey Department (now part of the National Oceanographic & Atmospheric Administration, NOAA), as far back as the 1950's and ‘60's. Due to the limitations of surveying equipment available at the time, the data is often sketchy and doesn't adequately address areas frequented by recreational boaters, or is outdated due to natural and man-made changes in the sea floor. Recent hurricanes alone have created enormous problems in local waterways, including storm debris and shifting bottom configurations; all of which present obstacles to recreational boaters.

Limited government funding and an emphasis on mapping areas of high commercial and military importance has constrained government production and publication of more updated charts for the recreational user. Further, given the breadth of the task and the cost of equipment and software to collect new geographic information, there are few, if any, private sector initiatives to collect and publish up-to-date chart information for recreational use. The need for and desire to have better charted data of water depths is echoed by boating organizations, marine supply chandleries and many boaters.

With the growing availability of relatively-affordable, sophisticated equipment and computer software, it is now more economically feasible to collect bathymetric and position data necessary for the production of boating charts. Hydro Engineering & Mapping, Inc. (Hydro EMI) uses Real Time Kinematic Global Positioning System (RTK GPS) electronics to collect and correct three-dimensional position data from orbiting satellites. The RTK GPS system is comprised of two GPS units, a base and a rover. The base station is fixed at a point of known elevation and location. The elevation at the base station is referenced to a local mean lower low tidal datum. The base continuously computes and transmits three-dimensional position corrections to the rover unit which is mounted on the mapping boat.

When combined with depth soundings from an on-board echo sounder, the data stream is fed to an on-board computer where it is processed by a sophisticated marine surveying software package known as HYPAK. As the base station is correcting both the horizontal and vertical positions of the rover unit, vertical errors due to the influence of tides and swells on the measured depth are significantly corrected. To obtain the best corrections, the base station is positioned in close proximity to the area being mapped. Since three-dimensional positions and water depth are collected once each second, the potential effect of other errors are minimized by averaging the huge amount of data collected in the contouring process. To see a pictorial presentation of this process click here.

Completed data sets are efficiently scanned to identify and remove obviously inconsistent data points that occasionally result from propeller turbulence and dislodged bottom sediment. HYPAK’s triangular irregular network (TIN) terrain modeling feature is then utilized to process the position and depth information into depth contours (lines of equal depth) referenced to mean lower low water. The depth contours are typically shown on a geo-referenced aerial photograph background. Depths are indicated in feet and positions are referenced to the 1984 World Geodetic System (WGS 84) which is the same datum used by the GPS satellites. A typical boating chart can be seen by clicking here or going to our online store.