Tides are measured using a submerged pressure type gauge secured in a heavy concrete mooring in Horseshoe Harbour at Mawson.
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.
Document dated 2001-03-26
Mawson Submerged Tide Gauge
The gauge used at Mawson 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 range.
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.
The first of these gauges were first deployed Mawson in early 1992 in a a mooring in Horseshoe Harbour. The gauge was found to have some communications problems and was removed in May 1992. Tidal records from 6/3/92 to present have been retrieved from it.
A new gauge was deployed at Mawson in March 1993.
Data has been retrieved from these gauges irregularly since then. The records are complete since deployment except for a few days in late 1995. The loss was caused by a fault in the software which allows directory entries to overwrites data when the directory memory has been filled.
The first gauge used at Mawson in 1992 was refitted with a higher pressure transducer and was later deployed at Heard Island in Atlas Cove.
Conversion of raw data to tidal records is done as detailed in document DATAFORMAT1.DOC .
As the current gauge is expected to require a new battery soon, a new mooring has been placed close to the original and a new gauge has been deployed.
Several attempts have been made at precise levelling of the gauge.
The first was in the Summer of 1995/6. Roger Handsworth, Tom Gordon and Natasha Adams physically measured the level of the top of the gauge in its mooring and derived a reading when a known column of water was over the gauge.
The next attempt was in the Summer of 1996/7 when Roger Handsworth and Paul Delaney made timed water level measurements close to the gauge and the tide gauge benchmark. From this work, and from tidal records, a value for MSL for Mawson was derived.
In the summer of 1995/6 two possible sites for a permanent Aquatrak type tide gauge were identified.
As neither of these sites were approved, a survey in the Summer of 1996/7 identified two more suitable sites. One of these, the site at the base of East arm, near the Variometer Building, was approved and a bore hole was drilled to exit about 6 metres below MSL. A power cable was run from the variometer building to provide two phase 240V power to the site.
A heated borehole liner containing an Aquatrak wave guide and a Druck pressure transducer was inserted into the bore hole. Two datalogger will be added to the installation in 2001 to complete the installation.
A radio modem will be used to link the dataloggers to the AAD network.
Documentation dated 2008-10-21
A new submerged gauge, TG41, was deployed at Mawson on 2008-03-03.
Submerged Tide gauge TG20 was removed on 2008-08-26.
There is a useful overlap of data between the gauges of about 104 days.
The dataloggers used in the shored based tide gauge installation have been replaced with Campbell Scientific CR1000 dataloggers.
The aquatrak shore based gauge at Mawson has not been operating since March 2008.
The shore base pressure gauge is still operating.