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Office of Coast Survey
Tidal Corrector Application
National Geodetic Survey
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Hydrographic Survey Support
The Hydrographic Planning Team (HPT) coordinates all of the hydrographic survey support activities conducted by the National
Ocean Service's Center for Operational Oceanographic Products and Services (CO-OPS).
Following assessment of requirements for water level data acquisition and datum determination, HPT provides input for hydrographic
and photogrammetric survey project instructions to ensure vertical control in accordance with National Ocean Service standards. Consultation is
provided to the Office of Coast Survey's Hydrographic Surveys Division (HSD) and to the National Geodetic Survey's Remote Sensing Division
(RSD) for both in-house and contract surveys.
Photogrammetry: Aerial photography is taken at mean high water and mean low water for boundary determination and shoreline mapping.
Hydrography: OCS conducts hydrographic surveys primarily with side scan and multibeam SONAR. SONAR (Sound Navigation and Ranging) uses sound waves to
find and identify objects in the water and to determine water depth. Most survey vessels are equipped with side scan and multibeam sonar systems; while
other vessels use single beam echo sounders. Some contractors employ LIDAR, which uses light to determine objects in the water and water depth.
Tidal Constituents and Residual Interpolation (TCARI)
TCARI is a method of computing water level correctors to reference hydrographic sounding to Chart Datum (MLLW) using tide gauges and/or
GPS-tracked Buoys. TCARI offers a procedure of "continuous" tidal zoning which improves upon discrete tidal zoning (see below). Also, TCARI can produce
a correction value for any sounding time and position within a survey area bounded by a local network of operating water level stations (shore or buoy).
Click here for more information on TCARI.
The image above shows the grid mesh for the Straits of Juan de Fuca and Puget Sound.
The image on the left shows a sample datum
interpolation across the survey area in the Straits of Juan de Fuca and Puget Sound.
|Discrete Tidal Zoning
HPT also develops discrete tidal zoning schemes. Discrete Tidal zoning is the extrapolation of and/or interpolation of tidal characteristics
from a known tide station(s) to a desired survey area using correctors in the form of time differences and range ratios.
Preliminary tidal zoning is for survey planning and for operations when the survey is in post-processing mode. Correctors are applied to
the control station of a NOAA tide prediction reference station.
Final tidal zoning correctors are applied to the observations during the survey period from appropriate subordinate and/or control stations
as specified in project instructions.
Requests for final approved tides result in the dissemination of approved time-series data, datum references, and tide note documentation to
HSD for final survey sheet processing.