AFREF First Computation: Processing and Analysis of GNSS Data

1

The meeting of the Committee on Development Information, Science and Technology (CODIST)

By Elias Lewi

Institute of Geophysics Space Science and Astronomy (IGSSA)Addis Ababa University (AAU)

ETHIOPIA

May 2, 2011

Economic Commission for AfricaAddis Ababa, Ethiopia

The internal Structure of IGSSA

IGSSA Director Advisory Board

•Director office

•Academic commission•Registrar

Personnel FinanceAudit

General service

PurchasingStore

Administration

Seismology, Earthquake

& Geotechnic

al Engineering

Geomatics Geodesy &

Gravimetery

Applied Geophysic

s

Space Sciences

Atmospheric &

Oceanic Sciences

Departments (5)

Instrumentation

Centre

Computational Centre

Centres (2)

Remote Observatories of Departments

Top Left: The Inauguration of the Geophysical Observatory November 1957 by H.I.M. Haile Selasie I

BottomLeft:

Lidge Kassa W/Mariam, 1st president of AAU signing guest book

Shown on the left is Prof. Pierr Gouin, 1st director of the Geophysical Observatory

Top right: IGSSA’s old building

Some of the geodetic work in the Geophysical Observatory

GPS survey in the Dobi Graben, 1992 GC

A Geodemeter Network by the Observatory (1969 GC)

The late Ato Alemu Mamo during a Geodimeter survey in 1990 GC.

Compared to the demand the present day continuously measuring GNSS stations in Ethiopia are negligible

These 16 GPS stations and possible future additional stations will play pivotal role in: 1)In the realization of the African Reference Frame (AFREF)2)numerous infrastructure work related to development

3)diverse fields such as: Research in geodesyResearch in Space

scienceResearch in atmospheric

scienceEarth rotationair- and auto-navigationGeodynamicGeographyDefence etc.

GNSS data from the 12 stations run by IGSSA is available in the internet to the international scientific community and even better to national organizations

International GNSS Stations (IGS) network

The station ADIS, at IGSSA, is one of IGS stations in Africa and it will play pivotal role in the definition of the African Reference Frame (AFREF)

ADIS

ADIS Station at IGSSA

http://igscb.jpl.nasa.gov/network/site/adis.html

It is not only one of the rare station in Africa, but also one of the few that can broadcast data live. The data is available to all, in the internet after a 4 second latency period.

Available Ntrip Real-Time GNSS Streams

Results from the GNSS stations in Ethiopia already proved that the stations can be used as high quality reference stations not only nationally but regionally and internationally.

Dr. Addisu Hunegnaw during the Airborne gravity survey.

Consortium of international and national Institutions participated in the survey are

•University of Edinburgh•Danish Space Centre•IGSSA•Ethiopian Mapping Agency•Ethiopian Ministry of Defence•Ethiopian Geological Survey

IGSSA and the airborne gravity survey of Ethiopia

The aircraft used for the survey was from Abyssinia flight, which is an Ethiopian private company

The computational facilities at the computational center of IGSSA

Computational server “Tekle” with 128 processors

Air-conditioning system

Data Server “Kagnew” with 20 TB memories

Computational server “Tatek” with 24 processors

A modern, multi-purpose computational facility and Lecture room at IGSSA

• The main Objective of AFREF is the establishment,

maintenance and enhancement of a three dimensional

African geodetic reference frame.

• The data that emanates from different geodetic stations

should be properly archived, analysed and made accessible

for geodetic and non-geodetic applications

• Necessary to use receiver and software independent

formats.

• Therefore the main aim of the data analysis centres should

be to provide well monitored products with sufficient

accuracy to the end-user, without interruption in receiver

and software independent format.

Goals and Objectives

• It should also target the easy transformation and integration of

the AFREF to other international reference frame

• To accommodate this objective it is necessary to develop

appropriate standards and encourage continent wide data

analysis center to adhere to this standard and conventions.

• On the other hand, these standards should be accommodative

enough to allow the usage of different receivers and software.

Goals and Objectives cont.

• The expected products from the analysis center among others

are:

 

The three dimensional coordinates of reference stations

with the associated accuracies. Here the vertical

coordinate will be a geometric, height until the

development of a common orthometric height system in

Africa.

The velocity field of the different stations, with the

associated accuracies. These might need to wait for some

few years to get enough data from some stations.

The determination of a common geoid, at a later stage.

Goals and Objectives cont.

•The responsibility of these centers is to receive and process

primarily, but not limited, GNSS data from the data centers to

produce high accuracy coordinates and velocities (other

products might be included in the future).

•It is not expected from each processing center to provide all

possible products, i.e., a center may focus on particular

objectives of the AFREF.

Scope of activity

• Different centres, based on the availability of software, might use different internationally accepted processing software such as GAMIT, BERNESE or GIPSY

• Data should be acquired using Receiver INdependent Exchange (RINEX) format from AFREF data centres

• Daily solutions should be computed at each data analysis centre in a daily basis

• Specific daily products should be exported to compute the final weekly solution

• Products should be updated each week for weekly solutions

• Final product should be submitted to a selected evaluation and consolidation centre in the continent using SINEX (Software INdependent EXchange) format, to produce a unique AFREF solution. In the future as the computational capacity of many member nations are strengthened, final products might be released from different regional centres

Proposed processing Scheme

Model of processing GNSS data(AFREF Data Analysis Center)

(Adopted from EUREF Local Analysis Center)

•The proposed geodetic datum is ITRF 2005

•Ambiguities should be resolved using QIF strategy

•Elevation cut-off should be set to 50

•Ocean loading using FES2004

•Based on the availability, a minimum of 18 selected common

sites should be fixed for all data processing centres

Proposed major processing criteria

The AFREF stirring committee calls for expression of interest from any African Institution to serve as a data Analysis Center independently or in collaboration with any other international Institution working in the area. Certain non-African organizations that might already be working in the continent with the same or similar aim can also express their interest in collaboration with an African Institution. Call for participation is currently open, though not limited, for a GNSS data analysis to a broad range of organizations. The scope of expression to participate in the AFREF data analysis center may encompass any degree of support that can be made available by the applicant institution.  It is expected that the institutions that express their interest are ready to adhere to the major guideline for a data analysis center, to assure the quality of the products and their consistency and homogeneity with the ITRF.

Call for expression of interest

20

Thank You