The Group discussed the five technical conclusions of the Committee's draft 

 report and made the following recommendations: 



• "It is recommended that all gauges used to monitor mean sea-level must 

 have a local network of bench marks (6 to 1 0) that are resurveyed by 

 accurate levelling or GPS at least once per year and that information on 

 this local bench mark control should be collected by the Permanent 

 Service for Mean Sea Level (PSMSL). 



• Using the accuracy of differential GPS stated in the report (1 cm in 1000 

 km) and the positions of the lERS (VLBI/SLR), it is possible to identify 

 those GLOSS gauges that can be fixed to within 1 cm radially with 

 respect to the I EPS stations. It is recommended that the GLOSS gauges 

 within this range and with, for example, (a) 20 years mean sea-level data 

 and (b) 60 years mean sea-level data be identified and priority be given 

 to geocentric location of these gauges. 



• It is recommended that GLOSS gauges that have 60 years mean 

 sea-level data, and where no lERS station is within 1000 km, should be 

 identified as priority locations for either permanent VLBI/SLR stations or 

 for mobile VLBI/SLR measurements. 



• It is recommended that present lERS stations with no suitable GLOSS 

 gauges within 1000 km should be identified and consideration should 

 be given to installing suitable tide gauges within this range. 



• It is recommended that the PSMSL would be a suitable center to collect, • 

 archive and distribute the geodetic information for each TGBM and that 

 the PSMSL should consult the lERS Directing Board with regard to the 

 information defining the geodetic reference frame that needs to be 

 stored." 



2.6.3 Workshop on Sea Lev el Measurements in Antarctica 



This meeting was held in Leningrad, USSR in May 28-31, 1990. The par- 

 ticipants at this workshop reported the following specific problems facing in- 

 stallers of reliable tide gauges in the Antarctic region: 



• Ice scouring on the near-shore sea bed; 



• the destruction of support structures by sea ice; 



• the logistics of gauge maintenance; 



• the lack of ice free locations and/or the unknown spurious effects 

 encountered when using a gauge with a heated stilling well; 



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