Tides and water level requirements for NOS hydrographic surveys

The Center for Operational Oceanographic Products and Services (CO-OPS) of the National Ocean Service (NOS) contributes to the NOAA Nautical Charting Program by establishing requirements for, and providing the critical water level data necessary to produce accurate depth measurements. CO-OPS efforts involve six main functional areas: 1) tide and water level requirement pla nning; 2) preliminary tidal zoning development; 3) water level station inst allation, operation and removal; 4) data quality control, processing, and t abulation; 5) tidal datum computation and tidal datum recovery; and 6) gene ration of water level reducers and final tidal zoning. For each functional area, CO-OPS maintains appropriate specifications and standard operating pr ocedures under the umbrella of an overall Data Quality Assurance Plan (DQAP ). The objective of this effort is to provide the tide and water level corr ection information necessary to reduce soundings to Chart Datum. The goal i s to provide water level correction information that meets current error bu dgets for correctors to soundings. The total uncertainty in the water level corrections are derived from three main sources: 1) errors in the actual m easurement of water level, 2) uncertainties in the computation of tidal dat ums based on short period observations and in the datum recovery process at historical locations; and 3) uncertainties in the application of tidal zon ing within the survey area. CO-OPS plans tide and water level requirements by balancing these uncertainties to provide the most effective combination of water level observations and zoning that meets allowable error budgets.