Dr.Christopher W. Hughes
CCMS Proudman Oceanographic Laboratory
Bidston Observatory
L43 7RA, U.K.

                     IAPSO Endorsement of GLOUP Activity

Dear Dr Le Provost,

I am writing to draw your attention to recent efforts at Bidston to
assemble a global ocean bottom pressure database. GLOUP stands for Global
Undersea Pressure, and its purpose is to provide easy access to the
historical database of in-situ ocean bottom pressure measurements.
There are currently 179 records available, of which 71 are short (< 100
days) and shallow (< 200 m), and 49 are long (> 100 days, mostly about a
year, some 2 years, one 4 years) and deep (> 1000 m).  These are mostly
in the Atlantic Ocean and the Atlantic sector of the Southern Ocean and
can currently be accessed on the World Wide Web from

http://www.pol.ac.uk/psmslh/gloup/gloup.html

For over 60 years, the Permanent Service for Mean Sea Level (PSMSL) at
Bidston Observatory, operating under the auspices of the International
Council of Scientific Unions (ICSU), has collected sea level records,
analysed them, and distributed them to the scientific community. One of
its tasks is to compile the IAPSO pelagic tidal constants dataset. The
British Oceanographic Data Centre (BODC) at Bidston is currently the
WOCE "delayed mode" sea level Data Archiving Centre (DAC), and has a
responsibility to WOCE for Bottom Pressure data collection.  The data
described above consists largely of the UK ACCLAIM project data from
the Southern Ocean, plus data from the British Oceanographic Data
Centre archives.

The immediate reason for compiling these data in a more accessible database is
the approval for launch of a satellite mission (GRACE) which promises
to be able to measure fluctuations in ocean bottom pressure by the
gravitational influence of the associated changes in the distribution of
atmospheric and oceanic mass.  This is a new form of technology whose
limitations are not yet understood.  Interpretation of GRACE results
will be strongly dependent on the information from in-situ bottom pressure
measurements and on the ability to model high frequency (periods less than
2 months) bottom pressure variations.

An international meeting on ocean bottom pressure and GRACE was
recently held in London, at which results were presented by several
modellers, and compared with data from the earliest version of the
GLOUP database.  The value of the in situ data was clear, and promises
of more historical data to add to the database were obtained from a
number of attendees.

In view of the international interest in bottom pressure data, I
would like to request you, as the President of the IAPSO Commission on
Mean Sea Level and Tides (CMSLT) which is the body to which the PSMSL
reports, to enable the formal IAPSO endorsement of GLOUP at the IAPSO/IUGG
Conference in Birmingham in July as an IAPSO activity managed within the
PSMSL at Bidston, as the IAPSO pelagic tidal constants set is managed at 
resent. IAPSO endorsement will be very valuable in establishing GLOUP as
the official repository for ocean bottom pressure data, and making these
data easily accessible. The endorsement of such an activity will also be
sought from the IOC/GLOSS Group of Experts at their Sixth Meeting in Toulouse
in May. Long-term stability and quality control of the database will be
assured by the close links between GLOUP/PSMSL, IOC/GLOSS, and with the
British Oceanographic Data Centre.  


Yours sincerely,

                  Dr C W Hughes

Christopher W. Hughes
Proudman Oceanographic Laboratory, Bidston Observatory, Birkenhead, 
Merseyside L43 7RA, U.K.    Tel: +44-151-653 8633     Fax: 653 6269
URL: http://www.pol.ac.uk                     email: cwh@ccms.ac.uk