on them and to survey to it; and also hard to maintain their stability on the ocean 

 bottom. If the entire instrument package is underwater, proper operation is a 

 continual verification problem. If the data recorder is land-based, the cabling is 

 extremely difficult to protect, particularly at the shore/sea interface. Bottom- 

 mounted pressure gauges have been installed several times by the State of 

 Alaska and it's contractors with limited success. 



Short-term data requirements, mostly for hydrographic or photogrammetric 

 operations, are met simply by conducting measurements during the ice-free 

 summer months. Standard bubbler pressure gages are used as they are 

 relatively easily transported and installed in remote and/or rugged areas. In 

 situations where staff installations are difficult or subject to constant destruction 

 from storms, several alternative methods are available. Sometimes a rod is driven 

 into the ocean bottom in a shallow area. The high point of the rod is connected 

 by survey levels to the bench mark net, and a staff is held on the high point for 

 staff readings during an observation. The equivalent of a staff reading may also 

 be made by leveling from a bench mark to the waters edge, if sea conditions are 

 calm enough. These methods are dependent upon reasonably sheltered loca- 

 tions, however. 



2.4 Canadian Efforts 



With the discovery of oil and gas in the Canadian Arctic and subsequent 

 decisions to transport these products to southern markets by sea, the Canadian 

 Hydrographic Service (CHS) increased its involvement in collecting arctic tidal 

 measurements. Initially, the emphasis was directed towards collecting short-term 

 tidal records in order to obtain a general knowledge about tidal propagation 

 through the complex archipelago in the Canadian Arctic. The method used to 

 collect these data consisted of deploying self-recording pressure gauges on the 

 sea bed and recovering the gauges after a specified elapsed time. The data 

 collected from these short-term deployments were generally not corrected for 

 atmospheric pressure variations and were not tied to bench marks. 



In 1985, the CHS developed a permanent gauging system with limited 

 application in the Arctic. This gauge used a conventional gas-purge system to 

 measure sea levels. The system is connected to a brass orifice which is located 

 in a protective housing attached to a wharf face. Data collected by the gauge is 



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