Subject: [IGSMAIL-1592] Summary and Recommendations, Sea Level Workshop Pasadena '97
From: Ruth Neilan
Date: Thu, 1 May 1997 16:41:26 PDT

******************************************************************************
IGS Electronic Mail      Thu May  1 16:41:26 PDT 1997      Message Number 1592
******************************************************************************

Author: Ruth Neilan
Subject: Summary and Recommendations, Sea Level Workshop Pasadena '97

Subject: Summary and Recommendations, Sea Level Workshop Pasadena '97

Dear colleagues,

The recent workshop on "Methods for Monitoring Sea Level:  GPS and Tide
Gauge Benchmark Monitoring, GPS Altimeter Calibration" was held at JPL on
March 17 and 18, 1997. The Sea Level workshop was specifically organized to
review the status in measuring changes in sea level as the third in a
sequence of workshops over the past ten years. The first was held at Woods
Hole Oceanographic Institution, USA in 1988 and the second at the Institute
of Oceanographic Sciences, Surrey, UK (1993). These first two workshops
resulted in the 'Carter Reports'. It was the summary recommendations from
the Surrey Workshop that was the catalyst for the organization of this
workshop as a joint meeting between the GPS and Sea Level communities. The
workshop was convened jointly by the Permanent Service for Mean Sea Level
(PSMSL) and the International GPS Service (IGS).

March '97 IGS Analysis Center Workshop
----------------------------------------------------
The Sea Level workshop was preceded by an IGS Analysis workshop held March
12 - 14, and the plan to gain balanced GPS representation at the Sea level
workshop was realized with participants from the IGS/GPS community. A
concise summary of the IGS workshop was distributed by Gerhard Beutler,
Chair of the IGS Governing Board, in IGS Mail Message #1569, dated
Wednesday, March 26 (available at http://igscb.jpl.nasa.gov under IGS Mail
Messages). A number of the items discussed at the IGS workshop are of
direct interest to participants in the Sea Level workshop, such as the site
specific issues, GPS station combination solutions, and tropospheric
studies with GPS. (The summary will be also be appended to the Sea Level
workshop report)

Sea Level Workshop Objectives
----------------------------------------------------
The summary recommendations and requirements  from the '93 Surrey Workshop
targeted using the structure of the IGS and GPS to measure and understand
the  position and velocities of global tide gauge stations within the ITRF,
with emphasis on the vertical velocities and accuracies at selected global
locations. The '97 Pasadena workshop focused on how the techniques of GPS
and tide gauges, can be applied to:

    1) studying the long term changes in sea level through understanding
the deformation  of the solid earth, particularly the vertical motions, and
how this affects the observations  of the tide gauge records and;

    2) measuring  the drift of the altimeter instruments for sea surface
height determination  on missions like TOPEX/Poseidon, and several planned
follow-on missions such as JASON, GFO, etc.

     3) organizing those people and agencies involved in making such
measurements, facilitating cooperation and soliciting sponsorship.

5th IOC GLOSS GE
----------------------------------------------------
On March 19- 21, following the Sea Level workshop, the Fifth Session of the
Intergovernmental Oceanographic Commission (IOC) Group of Experts on the
Global Sea Level Observing System (GLOSS) was held at JPL, hosted locally
by the IGS Central Bureau. The agenda for this meeting included review and
sanctioning of the recommendations set forth by the Sea Level Workshop and
further formulation of GLOSS recommendations that will guide the national
oceanographic agencies through the IOC of UNESCO. Once the GLOSS report is
finalized, these recommendations will be included as a reference appendix
to the forthcoming workshop proceedings.

==============================================================================
Summary Recommendations of the "Workshop on Methods for Monitoring Sea Level"
==============================================================================

1)	FOR THE PURPOSE OF MONITORING AND UNDERSTANDING LONG TERM CHANGES
IN SEA LEVEL, including the contribution of land motion to these changes,
this group recommends that:

	Science Working group(s) be formed that interface with the IGS or
are components of the IGS, at the Associate Analysis Center level (such as
the Regional Network Analysis Centers RNACC), following all conventions
established by the IGS Densification Project.  (See this report for
details.)

2)	FOR THE PURPOSE OF MONITORING THE DRIFT OF SATELLITE ALTIMETERS it
is recommended that:

	Approximately 10 additional stations be incorporated into the IGS
Global Analysis and Data Flow.

IN ORDER TO REALIZE THE ABOVE OBJECTIVES, it is further recommended  that:

3) 	The IGS, in cooperation with the International Earth Rotation
Service (IERS), produce vertical velocity estimates to be updated annually
in addition to a height time series derived from GPS, expressed in the
International Terrestrial Reference Frame (ITRF).

4)	A working group on the free exchange of data be formed that
includes representation from the GPS and Sea Level communities, for the
purpose of establishing necessary data links.

5)	That science working groups that are established to address these
developments ensure their representation under the umbrella of
International Association for the Physical Sciences of the Ocean (IAPSO)
and the International Association of Geodesy (IAG), including IGS, IERS,
IAG Subcommission on Sea Level and Ice Sheets and the IAPSO Commission on
Mean Sea Level and Tides.

6)	A Technical Working Group be constituted to set up recommended
standards and specifications for operating GPS at Tide Gauge sites, in
collaboration with the IGS working group on "Site Specifications and
Network Operations".

This Working Group will consider, document and make recommendations on the
following types of tide gauge and site specific information:
  - making measurements for precise ties (e.g., between the GPS, the tide

    gauge, the tide gauge benchmarks, the local reference networks, etc.),
  - data handling of the survey tie information,
  - site stability aspects,
  - monumentation techniques,
  - collocation philosophy and observing methods (continuous measurement
    rationale),
  - absolute gravity measurements for complementary information on vertical
    coastal movements and mass redistribution,
  - environmental parameters, meteorological sensors, ancillary
measurements,
    etc.

==============================================================================

Message Summary
-------------------------

Submissions to the workshop proceedings are due to the session chairs and
to the IGS CB by May 30. Proceeding should be available midsummer. For
further information, contact [email-masked].

We would like to thank all attendees for their active participation and
efforts to formulate the next steps in these activities. Many thanks also
are due the session chairs for their interest and dedication to organizing
a successful workshop: Trevor Baker, Geoff Blewitt, Mark Merrifield, Gary
Mitchum, Steve Nerem, Carey Noll, Mike Watkins and Suzanna Zerbini.
Finally, for the local organization details, thanks to Priscilla Van Scoy
for her efforts in managing the logistics so very smoothly.

Sincere regards,

Ruth Neilan                                Phil Woodworth
IGS                                        PSMSL

===================================================================
Philip Woodworth
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              Internet mail: [email-masked]
===================================================================

============================================================================
Ruth E. Neilan                    Telephone:   (818)-354-8330
IGS Central Bureau                FAX:         (818)-393-6686
Jet Propulsion Laboratory         E-mail (IGS):      [email-masked]
MS 238-540                        E-mail (personal): [email-masked]
4800 Oak Grove Drive
Pasadena, CA 91109

World Wide Web:  http://igscb.jpl.nasa.gov/
============================================================================

[Mailed From: "Ruth E. Neilan" <[email-masked]>]