Introduction

TIGAsA was initiated by the Hartebeesthoek Radio Astronomy Observatory (HartRAO) in response to the "Call for Participation" letter from the IGS, which solicited participation by agencies in the functions and objectives of TIGA. HartRAO was already in the process of installing GPS equipment at tide gauges and saw TIGA as an essential project to address the problem of analysing vertical motions at tide gauges on a global scale.

A meeting was subsequently organised and held (27 July 2001) at Environmentek (CSIR), Stellenbosch with possible participants. This meeting culminated in TIGAsA, the southern Africa component of TIGA.
 

Objectives

The objectives of TIGAsA have been identified within the framework of the objectives of TIGA, but have a regional approach.
 

1. Establish, maintain and expand a regional continuous GPS @ Tide Gauge network,  which will form part of the TIGA global CGPS @ TG network.

•      Install GPS stations at selected, existing tide gauges.

•      Apply IGS network operation standards.

•      Establish more continuously operating GPS stations

     Establish links between the CGPS@TG network and HartRAO's  SLR, VLBI, IGS
     and  GFZ's superconducting gravimeter (at Sutherland) stations to facilitate
     vertical motion determination.

     Contribute towards the development of minimum technical standards of
     the global tide gauge system to be included in the Pilot Study, e.g., sensor
     types, the nature of the levelling program, and metadata documentation.
 

2. Function as a TIGA Associate Analysis Centre (TAAC)

    TIGAsA will process GPS @ TG data on a routine basis to evaluate vertical
     motion rates. These evaluations will not be done in isolation, but will
     incorporate SLR and VLBI as well as absolute gravity obervations and solutions.

    We will in particular, attempt to explore and assess the potential of GPS to reduce the
    gravity signal caused by vertical movement, leading to a cleaner and better understood
    gravity signal at the GFZ Geophysical Observatory at Sutherland, in collaboration
    with GFZ. This will allow improvement of the IGS station SUTH vertical component.
    SUTH will be an important regional control point in determining vertical motion at
    the GPS @ TG network.
 

3. Function as a TIGA Data Centre

     TIGAsA will function as a regional TIGA Data Centre and will fulfill three functions:
 

•       Store GPS data
•       Store Metadata (e.g. levelling data, photos, maps and sketches).
•       Establish links to Tide Gauge Data Centres for easy and convenient data access.