The reductions of soundings. Tidal observations are to be carried out for the full period when a ship is deployed to the survey area.
For predicting tidal characteristics & updating ANTT Observations. Obs should be carried out over at least 32days using a precise gauge.
6 uses of Tide Staff & Gauge info & data
Definition of Coastlines
Flood & Storm Warnings
Mean Sea Level
Criteria when considering a suitable site for a Tide Staff
Stability of site
Stability of structure
Stability of water column
Proximity to benchmarks
Proximity to power/phones
Ease of access
Minimum exposure to Tidal Ranges
Minimum exposure to tidal stream/current
Minimun exposer to waves
Minimum marine growth
Protection from vandalism
Avoid restricted entrances
4 Types of Tide Gauges
1. Floatation Types
2. Acoustic Types
3. Pressure Types - Electronic Types
Floats upon the surface & heights are determined by RTK & wave action is removed through low pass filters.
The water level is measured by sending an acoustic pulse down a small pipe within the environmental tube.
Gas (Bubbler gauge) Open/Closed: gas, usually nitrogen, is emitted from a submerged tube at a constant rate. Fluctuations in the hydrostatic pressure due to changes in the tidal height modify the emission rate of reading.
The changes in pressure are detected by a sensor immersed in the water and converted by an electrical signal.
In these systems the sensor may be a crystal transducer, stain gauge or other transducer.
Measure the change in sea level by monitoring the time-of-flight if a radar pulse from the sensor to the sea surface and back to the unit.
4 Main Tidal Records
Summary of Checks on Automatic Tide Gauge - F_03_05_AA217185