The Ethiopian Reference System and the future direction

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The Ethiopian Reference System and the future
direction
First meeting of the committee on Development
Information, Science and Technology (CODIST)
Economic Commission for Africa Addis Ababa,
Ethiopia
April 28, 2009
By Elias Lewi (Institute of Geophysics Space
Science and Astronomy, AAU) Roger Hipkin and
Addisu Hunegnaw (University of Edinburgh) M.
Becker and S. Leinen ( Darmstadt University of
Technology) Eric Calais and Laura Benati (Purdue
University) Belete Terfe ( Ethiopian Mapping
Agency)
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IGSSA
Computational centre
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Major research activities in the depatement of
Geomatics, Geodesy and gravimetery at IGSSA
The June 17, 2006 Seismo-Tectonic event in Afar,
as interpreated from INSAR data
The gravity survey to study the active divergent
boundary in the Afar region
A study on the water mass balance of the Nile
Basin using time varying Gravity signal from
GRACE Satellite
Study of large structures in East Africa from
Global Gravimeteric models
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Research activities in earth rotation area
Top left Maximum Linear correlation of filtered
SSTA with filtered LOD data at each longitude and
the time lag (?) at which this maxima are
occurring.
Top right and right Result of the coherence
analysis (a) Maximum squared coherence and the
frequency band at which it occurs (b) The
comparison of the time lag obtained from the
coherence analysis and correlation analysis.
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The Reference stations for previous Geodetic
datums

• The Ethiopian 1936 datum was established by the
  Italinas at the west end of Metahara Base.
• Presumed reference ellipsoid was the
  International reference frame of 1924
• Vertical datum is beleved to be based of the tide
  gauge measurements at Massawa
• The next was the 1958 Blue Nile geodetic network
  funded by Ethiopian and US governments

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The Blue Nile Triangulation Points of 1958

• Geodetic work was carried out by by the US
  departemnt of commerece for cost and geodetic
  survey
• The origin of the 1958 geodetic network was the
  Sudanese stations 245 and 246 that were derived
  from the stations at southeren Egypt near Abu
  Simble, south of Lake Nasser, at Station Adindan.
• Reference ellipsoid is Clarke 1880 (modified)
• Adindan is the name of the reference station
  (origin) not a reference datum.
• Tide gauge measurement at Alexanderia and Asab
  were used as the base for the vertical reference

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New concept to Upgrade the Ethiopian Vertical
Reference System
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How can we derive Height from gravity?
Geopotential number defines height
Different systems use different definitions of
gravity to convert cP to metres (Helmert
Orthometric Heights, Dynamic Heights, Normal
Heights)
Classically cP is found by levelling
combined with a national levelling-datum constant
Wo WLD
The new system will compute WP from GPS derived
coordinates h,f,l using a locally refined Earth
gravity model and the datum potential defined by
Wo Uo where Uo is defined by the constants of
GRS80/WGM84.
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The airborne gravity survey of Ethiopia Here
shown as gravity disturbances corrected for the
gravity effect of topography derived from the
Shuttle Radar Topography Mission (SRTM) using the
hedgehog algorithm.
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The unrefined airborne gravity were included in
EGM08. Early tests using the EGM08 gravity model
already gives a local standard deviation in
levelled v gravimetric heights of 10 cm and
identifies regional datum values. The new
Ethiopian Vertical Reference System Gravity Model
will be available in the summer and should give
orthometric type heights to a few
centimetres. Heights will be available on the
globally absolute datum at an isolated point
without intermediate heigh or reference to tide
gauges. Within a decade we plan to have an
airborne gravity system operating out of Ethiopia
for general use within Africa to help set up
equivalent vertical reference systems in other
countries
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The free air anomaly from Airborne gravity
survey GOAAU, EMA, GSE, UE, DGC
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Present day continuous GPS station in Ethiopia
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The Preconstruction work for the IGS station ADIS
Pre-construction study of the masking angle from
different features in the surrounding
The construction design
The geological model of the subsurface as
interpreted from Vertical Electrical sounding
(VES) measurements with the help of borehole data
for parameterization in the vicinity.
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The construction of the IGS station ADIS
0.7 meters soil and 1.30m basalt is removed for
the foundation The base of the monument is
anchored to a basalt bedrock at 2 meters depth,
using iron bars, by drilling 0.30m in the basalt
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Available Ntrip Real-Time GNSS Streams
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Assessment of data quality from two station using
GAMIT software
Daily solution for the station ADIS (left) and
DAMY (right) aligned to ITRF2005, using MALI,
YIBL, BAHR, RAMO and NKLG
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Thank You