2.3 NOS Efforts 

 2.3.1 Tide Stations 



NOS's experiences witli water level measurements in polar regions liave been 

 only in the Arctic in Alaskan waters north of the Aleutians. There are presently 

 16 permanent National Water Level Observation Network (NWLON) stations 

 operating in Alaskan coastal waters (see Figure 3). Only one of them, Prudhoe 

 Bay, is located in Arctic waters, and it is presently operated on a seasonal basis 

 (July - September) although there are plans to make it a year-round station 

 starting this year. There have been approximately 1,100 short-term historical 

 stations established in Alaska, but only 20% of them were north of the Aleutians. 

 The majority of these stations were operated during the summer months, and 

 most utilized bottom-mounted, pressure-type gauges whereas a typical NOS 

 primary tide station (Figure 4) operated year-round would have an Analog to 

 Digital Recorder (ADR) gauge with a float inside a 12-inch stilling well and a 

 bubbler gauge as a back-up. 



In general, the combination of insufficient resources and the harsh Arctic 

 winter has prevented the establishment of any long-term, year-round NOS water 

 level stations to-date. The specific obstacles to establishing Arctic tide stations 

 with NOS's present water level measurement technology, whether it be the older 

 ADR or the newer Next Generation Water Level Measurement System 

 (NGWLMS), can be summarized as follows: 



• Lack of vertical support structures for stilling and protective wells; 



• Ice pack movement, shallow water depths, freezing wells; 



• Bench mark instability; and 



• Difficulty and cost of transportation, logistics, utilities, maintenance, etc. 

 due to the remoteness of the sites. 



Although the NGWLMS uses an air acoustic device as its primary water level 

 sensor, and therefore also requires a support structure, it can also take inputs 

 from pressure transducers or other underwater sensors and transmit the data via 

 the GOES satellite communication system so that system performance can be 

 monitored and users receive the data in near real-time (see Figure 5). A NGWLMS 

 unit with an acoustic water level sensor has been recently installed, however, in 



