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CORRECTIONS TO ECHO SOUNDINGS (HYDRO)

Overview of Tides and Tides Support for Hydrographic Surveying Naval Oceanographic Office IHMEP May 01, 2012. CORRECTIONS TO ECHO SOUNDINGS (HYDRO). Tides and Water Level Requirements For Hydrographic Surveys. FUNCTIONAL AREAS. NOS Responsibility.

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CORRECTIONS TO ECHO SOUNDINGS (HYDRO)

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  1. Overview of Tides and Tides Support for Hydrographic Surveying Naval Oceanographic Office IHMEPMay 01, 2012

  2. CORRECTIONS TO ECHO SOUNDINGS (HYDRO)

  3. Tides and Water Level Requirements For Hydrographic Surveys FUNCTIONAL AREAS NOS Responsibility 1. Tide and Water Level Requirement Planning 2. Preliminary Tidal Zoning Development 3a. Control Water Level Station Operation NOS or Contractor Responsibility 3b. Supplemental Water Level Station Installation, Operation and removal 4. Data Quality Control, Processing and Tabulation 5. Tidal Datum Computation and Tidal Datum Recovery 6. Generation of Water Level Reducers and Final Tidal Zoning

  4. WATER LEVEL MEASUREMENTSUPPORT TO HYDROGRAPHIC SURVEY OPERATIONS • Project Planning • Requirements, Desired Accuracies • Budget, Timeframe (In-survey processing, post-processing) • Station Locations, Configuration and Installation Timeframe • Operations • Station O&M • Data Collection, QC, Processing • Leveling, Bench Mark Network, Geodetic Datum Connections • Tidal Datum Computation • Final Tidal Zoning

  5. Request for Tide Planning Determination of the Survey Boundaries and Time Frame

  6. NOAA ERROR BUDGET FOR WATER LEVELS • THE WATER LEVEL REDUCER CAN BE THE MOST SIGNIFICANT CORRECTOR TO THE SOUNDINGS • THE COMPONENT OF THE TOTAL ERROR BUDGET DUE TO APPLICATION OF THE WATER LEVEL REDUCERS CAN ALSO BE QUITE SIGNIFICANT • THE ALLOWABLE CONTRIBUTION OF THE ERROR FOR TIDES AND WATER LEVELS TO THE TOTAL SURVEY ERROR BUDGET FALLS BETWEEN 0.20 METERS AND 0.45 METER (95% CONFIDENCE LEVEL) DEPENDING UPON COMPLEXITY OF THE TIDAL REGIME AND THE SURVEY AREA. • THE ERROR BUDGET NEEDS TO BE ESTIMATED IN ADVANCE IN THE PLANNING STAGES SO THAT THE POTENTIAL ERROR IN WATER LEVELS CAN BE APPROPRIATELY BALANCED AGAINST ALL OTHER SURVEY ERRORS IN THE PROJECT DESIGN

  7. ERROR BUDGET CONSIDERATIONS FOR WATER LEVELS (NOAA Specs.) THE ALLOWABLE CONTRIBUTION OF THE ERROR FOR TIDES AND WATER LEVELS TO THE TOTAL SURVEY HAS THREE MAJOR COMPONENTS: • THE MEASUREMENT/PROCESSING ERROR IN COLLECTION OF GAUGE/SENSOR DATA AND THE PROCESSING OF THE DATA. • THE ERROR IN COMPUTATION OF TIDAL DATUMS FOR THE ADJUSTMENT TO A 19-YEAR NATIONAL TIDAL DATUM EPOCH (NDTE) FROM SHORT-TERM STATIONS • THE ERROR IN THE APPLICATION OF TIDAL OR WATER LEVEL ZONING

  8. 1. Tide and Water Level Requirement Planning

  9. Tide and Water Level Requirement Planning2. Preliminary Tidal Zoning

  10. 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 RATIOSPRELIMINARY TIDAL ZONING IS FOR SURVEY PLANNING AND FOR OPERATIONS WHEN THE SYRVEY IS IN POSTPROCESSING 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 OR(AND) CONTROL STATIONS AS SPECIFIED IN THE PROJECT INSTRUCTIONSTHE GEOGRAPHIC STRUCTURE OF THE DISCRETE TIDE ZONING IS LARGELY BASED ON THE LOCATION OF THE ESIMATED CO-TIDAL LINES. THIS STRUCTURE CHANGES ONLY WHEN NEW INFORMATION IS OBTAINED FROM NEW SUBORDINATE STATIONS THAT IMPROVES THE ACCURACY AND RESOLUTION OF THE EXISTING ZONING Discrete Tidal Zoning

  11. 3a. Control Water Level Station Operation

  12. 3a. Control Water Level Station Operation • The control station must be in operation during the entire survey • period if used for direct control. • Must be in operation for the entire time period a subordinate station • is in operation for datum determination of the subordinate and for • gap filling if necessary • Control stations are usually operated by other groups than the • survey parties or field teams. The operational leads of the parties • or teams must ensure operation of the control stations by linking to • the data sources and maintaining communication with the control • station operating unit. • Program planning must include designating alternate control station • scenarios.

  13. 3b. Subordinate Water Level Station Installation, Operation and removal

  14. 3b. Subordinate Water Level Station Installation, Operation and removal • If possible, subordinate stations should be established prior • to the survey operations: • - to operate for a minimum one-month to determine • a tidal (Chart Datum) datum at new locations, • - to operate several days prior to the survey to ensure • operation of the tide gauge relative to an existing tidal datum • at historical locations • Must be in operation for duration of survey or for specified tide • zones in the project instructions – operation must be monitored • by the field parties • Should have a backup plan if the gauge goes down

  15. 4. Data Quality Control and Processing

  16. 4. Processing and Tabulation Must fill gaps in record using documented and acceptable use of curve fitting (for small gaps) backup gauge data, data from nearby stations, or predicted tides

  17. 5. Tidal Datum Computation and Tidal Datum Recovery LAT Must have simultaneous data from both subordinate and control tide stations

  18. 6. Generation of Water Level Reducers and Final Tidal Zoning

  19. 6. Generation of Water Level Reducers and Final Tidal Zoning • Water level reducers are time series of observed or final “zoned” • data corrected to the appropriate tide station observations • for the time period of the soundings and are relative to Chart Datum. • In post-processing mode, the reducers and final zoning must await • final level close-outs, data processing, datum determination, and • generation of final tide reducers after the survey period is over. • For an In-Survey processing mode, data are being collected from • the control and/or subordinate stations routinely or in near-real time • and applied relative to Chart Datum shortly after sounding collection • if the tide station has a verified Chart Datum prior to the survey. • In this mode, the zoning must be well established “final” zoning • that would not expect to change with new measurements. • Final Quality assurance must be done on all data and meta-data • records regardless of the operational mode.

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