1.0 INTRODUCTION 



Continuous sea level measurements have been made and recorded for more 

 than 100 years, but their importance has increased dramatically in the past few 

 years due to the great international interest for monitoring global levels in 

 anticipation of climate warming. Some scientists believe that the long term rise 

 of sea level is due to three processes: thermal expansion of the upper layers of 

 the ocean, the melting of glacial ice, and the addition of mass from the polar caps. 



Since the National Ocean Service (NOS) in the National Oceanic and Atmos- 

 pheric Administration (NOAA) is the primary agency for measuring and recording 

 water levels in the United States, it is being encouraged to increase the number 

 of permanent sea level measuring stations, especially in the polar regions where 

 the data are extremely sparse. 



Personnel from the Physical Oceanography Division (POD) and the Ocean 

 Systems Division (OSD) of the Office of Oceanography and Marine Assessment 

 (OOMA) held a meeting on March 29, 1 990 to discuss the status and requirements 

 of water level measurement in the polar regions with special emphasis on the 

 needs of NOAA's Climate and Global Change Program and the Global Sea Level 

 Observing System, known as GLOSS. It is called GLOSS because it measures 

 the global level of the sea surface, a smooth level after averaging out waves, tides 

 and meteorological events. GLOSS, co-ordinated by the Intergovernmental 

 Oceanographic Commission (IOC), provides high quality standardized data from 

 which valuable sea level products are prepared for international and regional 

 research programs as well as for practical national applications. 



This report is a follow-up to that March 1990 meeting and includes a survey 

 of the work that NOS and others are or have been doing in this area and also 

 assesses the state-of-the-art of the technology, the potential for future develop- 

 ment, and provides recommendations for near- and long-term projects. This 

 report can be used as a basis for planning, for future discussions within NOS and 

 NOAA and with other U.S. agencies, and also with other nations. 



2.0 PRESENT EFFORTS AND TECHNOLOGY 



2.1 Background 



The lack of U.S. sea level data in the polar regions is due to the lack of NOS 

 measurement stations in those areas. Most of the Alaskan stations are sited on 



