17 



could vary substantially year-to-year with temperature, etc. Considering 

 two or more tide gages, the noise may be correlated in space and time 

 positively, negatively, with an arbitrary phase or uncorrelated. The more 

 widely separated the gages, the greater the likelihood that the noise will 

 be uncorrelated. Thus, there are advantages to averaging many records 

 along a coast, possibly with an appropriate coastal length weighting 

 factor. Finally, the best estimate of eustatic sea level (and thus 

 eustatic sea level rise) and one which yields the most understanding as to 

 the stability of the results is a progressive averaging in which larger and 

 larger data bases are averaged, i.e., 



IK 



.E, '?i(t)wi 



rilK (t) = ^ (2.3) 



1 Wi 



i=l 



where Wj^ is a distance weighting factor and IK is the total number of gages 

 along a selected coastal segment, perhaps a continent. The worldwide 

 estimate of eustatic sea level, r?g(t) could then be obtained by averaging 

 over all available coastal segments 



IKTOTAL _ 



\ (^^ = IKfifAL J^ "ikC^) ^2.4) 



IK — 1 



Other ways of extracting meaningful information relating to 

 post-glacial rebound could include averaging first over longitude for 

 certain increments of latitude. 



2.4 RESEARCH NEEDS 



In general, improvements in our understanding of eustatic sea level 

 change can come about through use of the existing data base or development 

 of new data. Extraction of more meaningful results from the existing data 

 base will require either more powerful analysis procedures or an improved 

 understanding and application of the physics of relative sea level change, 



