OBJECTIVES OF AFREF - United Nations Economic Commission for

Call for Participation
The Processing of AFREF GNSS Data
United Nations Economic Commission for Africa
R Wonnacott
Addis Ababa
2 May 2011
• Executive Summary
• Summary of Call for Participation
• Details of Areas of Participation
• Background to AFREF
• References
• Fundamental point of departure for projects, services or
products requiring geo-spatial information is a uniform & reliable
co-ordinate reference frame.
• Over 50 countries in Africa each with their own geodetic
reference system and frame and some with 2 or more systems.
• Although there are many areas of conflict there are also areas
where peace has been restored and require a lot of development.
• It is known that many private commercial enterprises are setting
up their own reference frames particularly in the oil and mining
• AFREF is, therefore, an African initiative to unify the geodetic
reference frames of Africa based on the ITRF through a network
of GNSS base stations at a spacing such users will be at most
within ~1000 km of a base station.
International Endorsement
• UN ECA CODIST (Committee on Development Information,
Science & Technology)
– Have adopted the Windhoek Declaration
– Created a Working Group to deal specifically with AFREF
• UN OOSA (UN Office for Outer Space Affairs)
– Have recognized the importance of AFREF for variety of applications
– Supported travel for some AFREF activities
• IAG (International Association of Geodesy)
– Have created structures to co-ordinate the project and provide
technical assistance and expertise
• IGS (International GNSS Service)
– Has strong commitment to support AFREF
Objectives of AFREF 1
– To determine a continental reference system for
Africa consistent and homogeneous with the global
reference frame of the ITRF as a basis for national 3-d
reference networks.
– To realize a unified vertical datum and to support
efforts to establish a precise African geoid.
– To establish continuous, permanent GNSS base
stations at a spacing such that the users will be
within 1000km of a base station and that data is freely
available to all nations.
Objectives of AFREF 2
– To determine the relationship between the existing
national reference frames and the ITRF to preserve
legacy information based on existing frames.
– To provide a sustainable development environment
for technology transfer so that these activities will
enhance the national networks and other
– Assist in establishing in-country expertise for
implementation , operation, processing and analysis
of modern geodetic techniques, primarily GNSS.
Progress to Date 1
• The AFREF Operational Data Centre (ODC) is currently archiving
on a daily or near daily basis data from nearly 62 permanent GNSS
base stations at average of 31 stations daily ( as at mid-April 2011).
• Data is freely and openly available to all users.
• Project reached the stage where a computation of all available
stations can be carried out.
• National Mapping Organizations will be able to use results plus
available GNSS data from ODC to compute National Reference
Frames based on ITRF.
Progress to Date 2
Active stations
being archived
at the AFREF
Data Center
(February 2011)
Progress to Date 3
Number of activities underway to install permanent
base stations or move towards ITRF:
South Africa
Progress to Date 4
As agreed at CODIST I (April 2009), an Operational Data
Centre has been established.
www.afrefdata.org or ftp.afrefdata.org
– Data from 62 (mid-April 2011) continuous stations brought
together from number of data centres into one place. Data
centres include:
Plus data from 3 stations being directly downloaded from
Progress to Date 5
Number of stations listed for which no data available - it is
known that these stations are operating but data not available.
Number of campaign stations listed hence only periodic data
available .
Areas of Participation 1
Processing and analysis of data from the network of GNSS
base stations to produce a continental reference frame:
Computation of network of fiducial stations based on well
established stations with long term reliability and publically
available data;
An initial processing will provide set of co-ordinates for use at
National level - frozen in time;
In addition will provide ongoing processing to maintain
network and provide set of velocity vectors and to make
allowance for the addition of new stations;
Processing to be done using IAG guidelines.
Areas of Participation 2
Computation of national networks based on the continental
reference frame:
Major objective project is conversion of National geodetic
networks to AFREF and hence ITRF;
NMOs will have to occupy number of strategically placed
points whose co-ordinates are well established in the National
frame using GNSS;
Processing could either be as series as campaign or using
permanent stations to convert / transform current frame to
Respondents will have to set out proposed strategy.
Areas of Participation 3
Training and capacity building of geodesists and surveyors in
NMOs and Universities
Respondents to CfP will be required to address the
Describe the form of training whether for individuals or
components of NMOs;
In case of individual training, will training lead to some form
of qualification?;
What level of sponsorship will be offered, if any? ;
Proposal must describe level of expertise required to
undertake training; and
Any other details not covered in the above.
Call for Participation includes a section on the background
to AFREF which will not be covered in this presentation.
Commitment to project to be at least 5 years to create an
environment for sustainable environment.
Proposals to be evaluated by panel of independent experts.
The CfP also covers multi-disciplinary aspects of AFREF
such as collaborations with;
- Africa Array - seismology
- Africa Monsoon Multi-disciplinary Array-GPS (AMMA-GPS) –
- Scintillation Network Decision Aid (SCINDA) – space weather
- Dates for submission of CfP proposals still to be finalized.
Inter-disciplinary Collaboration
Thank you
Global Context 1
Global distribution of four space based positioning techniques
available for realization of International Terrestrial Reference
Frame (ITRF)
+ GPS Only ; + DORIS only; + SLR Only; + VLBI Only
4 Techniques;
3 Techniques;
2 Techniques
Global Context 1
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