Surveying land and water (and in between)
John Oswald and Associates, LLC (JOA), offers core surveying support for large hydrographic, lidar and shoreline mapping projects. JOA specialties include tide/water level station installation, tidal datum determination, tidal zoning, GPS surveying, and GPS base station installation.
Tidal Datums
The members of JOA have received specialized training by NOAA/NOS/Center for Operational Oceanographic Products and Services (COOPS) in tidal tabulation and datum computations. JOA has developed a detailed knowledge of tidal datum determination and water boundaries in diverse tidal regimes and marine environments.
Tidal Zoning
Zoning tides from control tide stations plays a critical part in maintaining the accuracies required on large hydrographic, bathymetric and shoreline mapping projects. JOA has become efficient at verifying zoning schemes through empirical observations with short term tide gauge installations. Most recently, JOA has analyzed PPK GPS heights of hydrographic survey boats (corrected by an IMU for pitch and roll) to determine tidal characteristics throughout project areas.
Water Level Correctors
JOA has developed web services and in house software to increase the accuracy and efficiency of tide data processing, allowing JOA to deliver tide corrections quickly. Tide data is automatically downloaded from remote stations every hour by the JOA server and displayed on the JOA website for immediate quality review. Erik Oppegard has designed, tested and implemented software with a polynomial curve fitting algorithm, which smoothes raw tide data and extracts high and low waters automatically.
GPS Tides
JOA has also taken the initiative to develop and test the feasibility and accuracy of kinematic GPS for measuring water level heights relative to the ellipsoid. JOA has performed experiments with this technology every year since 2003. Of particular interest, JOA measured the extreme tides in the Knik Arm of Cook Inlet using GPS receivers on three separate cata-rafts.
GPS Surveying for Vertical Datums
JOA has extensive experience performing high accuracy static GPS surveys to meet the stringent standards of NGS-58 for 2cm ellipsoid height accuracy and can accurately and efficiently process and adjust this GPS data using a variety of software packages including Trimble Total Control, Trimble Geomatics Office and NGS software Page-NT and Adjust. JOA has successfully submitted GPS surveying projects to NGS for Bluebooking and provides benchmark descriptions to NGS in wddproc format.