Tides are measured using a submerged pressure type gauge secured in a heavy concrete mooring at Casey.
Tidal records are retrieved from the gauge using an inductive loop lowered through a hole in the ice hence the gauge has been undisturbed since it was deployed.
Documentation dated 2001-03-07
Casey Submerged Tide Gauge
The gauge used at Casey was designed in 1991/2 by Platypus Engineering, Hobart, Tasmania.
It was intended to be submerged in about 7 metres of water in a purpose made concrete mooring in the shape of a truncated pyramid.
The gauge measures pressure using a Paroscientific Digiquartz Pressure Transducer with a full scale pressure of 30 psi absolute. The accuracy of the transducer is 1 in 10,000 of full scale over the calibrated temperature.
The overall accuracy of the system is better than +/- 3 mm for a known water density.
Data is retrieved from the gauges by lowering a coil assembly on the end of a cable over a projecting knob on the top of the gauge and by use of an interface unit, a serial connection can be established to the gauge. Time setting and data retrieval can be then achieved.
One of these of these gauges was deployed at Casey in early 1992 in a mooring in Geoffrey Bay.
The mooring was apparently moved by sea ice and was later found, but the gauge is missing.
A new mooring, one which was originally made for Harry Burton for use in one of the Vestfold Hills lakes, was taken by ship to Casey and was placed in Geoffrey Bay using a collection of 200 litre fuel drum to float the mooring into position.
A new gauge was deployed in March 1996.
The gauge was lowered into position with the holding grab wired closed to check that the device fitted in the mooring. The gauge became jammed so was left in situ with the grab preventing access to downloading. In April that year Roger Handsworth attached weights to the floating ropes of the grab to sink them out of the way of the freezing surface water.
Divers located the mooring and gauge in late 1997 and 22 months of tidal records were retrieved.
The gauge was restarted to clear the memory and allow another two years of data to be collected without any problems from a small software bug.
Conversion of raw data to tidal records is done as detailed in document DATAFORMAT1.DOC .
Levelling
In December 1997 a set of water level observations were made by the station leader. These observations have been sent to National Tidal Facility, Flinders University, SA to derive a value for mean sea level.
Documentation dated 2008-10-17
There is one submerged bottom mounted gauge at Casey. (TG02)
The wharf based tide gauge installation at Casey has been upgraded with 2 Campbell Scientific CR1000 dataloggers.
One logger (Main) receives signals from two wharf installed submerged Paroscientific Digiquartz pressure sensors and a barometer. The other logger (Backup) receives signals from only the two submerged sensors.
Pressures are recorded in hPa, temperatures from the Digiquartz sensors in degrees C and temperatures from thermistors in the water column in unscaled A/D values.
The two submerged pressure sensors are separated vertically by 2.007 metre.
The backup logger streams 30 second average pressure values from both submerged sensors.
The main datalogger records 3 pressure and 6 temperatures and controls the water heaters.
