Tidal Datum

A base elevation from which elevations or depths are referred to

A vertical datum used to reckon heights or depths for marine applications

A water level datum used as a reference to any soundings on a particular survey

A datum to which depths on a chart are referred

A water level datum defined in terms of certain tide phases

The period over which water level datums derived through tidal observations are computed

The period used for tidal observations to obtain mean tidal values

The type of datum that has a local plane elevation and is used as a reference in the specific area where water-level observations were made

The datum generally used as a reference for land elevations

The datum used as a reference level in bathymetric soundings

The process that makes conversion between water level datums and geodetic vertical datums possible

A standard elevation defined by a particular tide phase and used as a reference to measure local water levels

The fixed points to which most tidal datums are referenced so they can be recovered easily when needed

The reference points used as a basis for tidal datums and surveying works

The highest tide which can be predicted to occur

The tide whose height may be exceeded because of meteorological conditions

The mean of the higher high-water height observed in each tidal day over the National Tidal Datum Epoch

The average of all daily tidal high-water heights observed over the National Tidal Datum Epoch

The datum that is the average height of the sea for all stages of the tide

The datum that is increasingly used as the base for general leveling operations

The datum used as the reference datum for depth measurement and defined as the mean of all low waters observed over long periods

The common chart datum that is the average of all heights of the lower of two low waters over long periods

The datum usually employed when a great deal of tidal range results from marked diurnal inequality

The lowest tide which can be predicted to occur

The datum sometimes used as a chart datum and representing the lowest tide that can be predicted to occur

The condition that can cause water to fall lower than the usual LAT height

The arithmetic mean of MHHW and MLLW

The arithmetic mean of MHW and MLW

The height difference between MHHW and MLLW

The height difference between MHW and MLW

One-half the average difference between the two high waters of each tidal day over the National Tidal Datum Epoch

The value obtained by subtracting MHW from MHHW

One-half the average difference between the two low waters of each tidal day over the National Tidal Datum Epoch

The value obtained by subtracting MLLW from MLW

The average interval in hours between the moon's transit over the Greenwich meridian and the following high water at a location

The average interval in hours between the moon's transit over the Greenwich meridian and the following low water at a location

The maximum height reached by a rising tide due to periodic tidal forces and meteorological, hydrologic, and oceanographic conditions

The minimum height reached by a falling tide due to periodic tidal forces and meteorological, hydrologic, and oceanographic conditions

A fixed base elevation established at a tide station and used as reference to all water-level measurements

The datum referenced to a primary benchmark at the station and held constant regardless of changes to the water-level gauge or tide staff

The official time segment over which tide observations are taken and reduced to obtain mean values

The length of the National Tidal Datum Epoch

The process of establishing the relationship between a geodetic datum and tidal datum by connecting the tidal benchmark to the national reference system

The process of connecting a tidal benchmark to nearby geodetic benchmarks with known geodetic elevations

The method of determining the geodetic elevation of a tidal benchmark by occupying the benchmark with a GPS receiver

The traditional method used to connect a tidal benchmark to nearby geodetic benchmarks

The satellite-based method used to determine the geodetic elevation of a tidal benchmark

The recommended number of known benchmarks to use when verifying the tidal-geodetic connection

The purpose of connecting to more than one known benchmark

The factor that prevents the elevation relationship between tidal and geodetic datums from simply being extrapolated from a single location

The tool mentioned for careful interpolation of tidal and geodetic relationships

The type of interpolation that must account for variations in tide level, bathymetry, topography, geoid variations, and vertical land movement

The application of tidal datum information concerned with safe clearance beneath ships in harbors

The engineering application concerned with designing structures in coastal regions

The application involving establishment of seaward boundaries for tax claim revenue purposes in the offshore oil industry

The application involving private-state boundary delineation because of coastline variations

The intersection of the local tidal datum plane with the beach topography or coast

The error in the tidal datum

The slope of the coastal topography

The error in the seaward boundary line

The relationship between tidal datum error, coastal slope, and seaward boundary-line error

The error in the seaward boundary line when the tidal datum error is 0.30 m and the beach slope is 5°

The direction in which the shoreline is displaced in the example when the tidal datum error is 30 cm and the beach slope is 5°

The hydrographic application involving the use of real-time water-level corrections

The positioning technology identified as an emerging trend for determining real-time water-level corrections

The correction method using RTK GPS to determine real-time water-level corrections

The height of the RTK GPS antenna above the reference ellipsoid

The raw depth obtained from the echosounder calibrated to the static waterline

The height of the RTK GPS antenna measured above the static waterline

The conventional tide correction

The RTK tide correction

The separation between the Chart Datum and the Reference Ellipsoid

The charted depth after applying the necessary corrections

The dynamic draft correction

The correction that accounts for the vessel's dynamic draft

The value of dynamic draft correction when the vessel is in a static state

The instrument used to obtain the antenna height above the reference ellipsoid in the RTK Tide technique

The instrument used to measure raw depth in the RTK Tide technique

The waterline used as the basis for the raw depth measurement when the echosounder is calibrated accordingly

The formula for RTK Tide correction

The formula for chart sounding using RTK Tide variables

The correction obtained from the RTK GPS antenna height, antenna height above static waterline, dynamic draft, and ellipsoid-to-chart-datum separation

The condition in which RTK Tide correction and conventional tide correction have the same value

The vessel condition in which heave, pitch, and roll are ignored in the RTK Tide illustration

The vessel motion effect caused by the relative movement of the ship's hull through the surrounding water that lowers the vessel closer to the seabed

The lowering of a vessel due to its movement through surrounding water

The combined lowering of the vessel due to squat and settlement

The variable that must be known to account for vessel squat and settlement in the RTK Tide technique

The condition in which the dynamic draft cannot be determined in the RTK Tide technique

The value assigned to dynamic draft when it cannot be determined

The correction that can still provide the correct sounding when dynamic draft is unknown according to the lesson illustration

The conventional method that may give a different chart sounding when dynamic draft is unknown

The primary purpose of tidal datums in hydrographic surveying

The main reason tidal datums are important in engineering designs

The main reason tidal datums are important in seaward boundary mapping

The main reason tidal datums are important in nautical charting