UNITED
ARAB EMIRATES
Clifford J. Mugnier,
C.P., C.M.S.
The contents of this column reflect the views of the
author, who is responsible for the facts and accuracy of the data presented
herein. The contents do not necessarily
reflect the official views or policies of the American Society for
Photogrammetry and Remote Sensing and/or the Louisiana State
University.
Originally settled in the Bronze
Age, the Umm an-Nars culture established itself near modern Abu Dhabi in the 3rd century B.C.,
and its influence extended to the interior of the Arabian
Peninsula as well as along the coast to Oman. Some later settlements by the Greeks have
been found, and in the Middle Ages most of the region
was part of the Kingdom
of Hormuz, which
controlled trade in the Arabian Gulf. The Portuguese arrived in 1498 and stayed
until 1633 until the British took control of the area. By 1820, the British had destroyed or
captured all Qawasim pirate ships and they imposed a General Treaty of Peace on
nine Arab sheikhdoms in the area and installed a garrison. The area was known as the Trucial Coast
until 1971. The seven emirates are Abu Dhabi (Abu Zaby), Ajman, Dubai
(Dubayy), Al Fujayrah, Ras al Khaymah, Sharjah (Ash Shariqah), and Umm al
Qaywayn. The United Arab Emirates cover an area
slightly smaller than the state of Maine. Much of the interior of the UAE is desert and
runs to the edge of the Empty Quarter of Saudi Arabia, the largest sand desert
in the world. The northern and eastern
sections are mountainous and green while the coastal areas are marked with salt
flats.
The first
major geodetic Datum of the Arabian Gulf area was established by W.E. Browne of
the Iraq Petroleum Company in 1927-1931 at the South End Base at station
Nahrwan (East of Baghdad) such that: Φo = 33° 19 10.87
North, Λo = +44° 43 25.54 East of
Greenwich, and the Clarke 1880 is the ellipsoid of reference where:
a = 6,378,300.782 m, and 1/f = 293.4663077. The Nahrwan Datum of 1929 is the most
prevalent coordinate system of the entire Arabian Gulf
area and is still found to this day.
The Sir
Bani Yas Island Datum of 1933 was established by the British Royal Navy in 1933
such that: Φo = 24° 16 44.83
North, Λo = 52° 37 17.63 East of
Greenwich, and the Clarke 1880 is the ellipsoid of reference.
The Ajman
Datum of 1946 origin is such that: Φo = 25° 23 50.19
North, Λo = 55° 26 43.95 East of Greenwich and is
referenced to the Helmert 1906 ellipsoid where a = 6,378,200 m,
and 1/f = 298.3. The first Grid was the WWII Trucial
Coast/Qatar Grid on the Cassini-Soldner projection. The Central
Meridian λo = +50° 45 41 E,
the False Northing Latitude of Origin (φFN) = 25° 22 56.5 N,
and both the False Eastings and False Northings are 100 km. Of course, the scale factor at origin by
definition is equal to unity.
In 1967,
the Directorate of Military Surveys recomputed the Mainland Trucial
Coast and Qatar
triangulations on the International ellipsoid,
European Datum 1950. Those
coordinates were then transformed into Nahrwan Datum 1929. The Trucial Coast Transverse Mercator Grids
became preferred to the old Cassini Grid.
The Central Meridian λo = +55° 00 E,
and the False Eastings have had values of 100 km and 1,200 km. The False Northings are 2,000 km as
measured from the Equator. The series
covered the entire UAE. Topographic
mapping was compiled in the 1960s by the British Directorate of Military
Surveys, and a 1:50,000 scale map series (K763) comprising 155 sheets was
completed in 1969.
Limited
1:50,000 mapping was produced in the early 1980s with the assistance of Syria, but
coverage of Dubai
was based on only 4 third order points in the south east corner of the
Emirate. A military Survey Department
was set up by the Emirates and new mapping was published between 1989 and 1991
as 138 orthophoto sheets on the Nahrwan Datum of 1929 with the UTM Grid. A new GPS network was initiated for Dubai in 1991 with a new
local Grid. The Dubai Local Transverse
Mercator (DLTM) Grid is referenced to the WGS 84 ellipsoid, the Central Meridian λo = +55° 20 E,
and the False Easting = 500 km.
The Northings are presumably measured from the Equator. Analysis of the old network indicated a
potential positional error of the old classical control of up to 9 meters
horizontal. The First order Geodetic GPS
Network of Dubai is composed of 62 monumented points with distances between
points ranging from 5 to 10 km. Of
particular interest is that Dubai
has completely abandoned the previous classical geodetic work extant in the
Emirate. Zero effort was (apparently)
made to relate the old to the new! I
personally do not agree with this philosophy because I prefer to relate
historical records to current and future work.
However, I suspect that this unfortunate tack may be chosen from
time-to-time for the sake of expediency.
Satellite positioning studies (by
others) in the United Arab Emirates derived a set of Datum shift parameters
from WGS72 Datum to Nahrwan Datum of 1929 where: ΔX = +225.4 m,
ΔY = +158.7 m, ΔZ = +378.9 m, based on
observations of 8 stations. I personally
would consider the tenths of a meter used in these parameters as very
optimistic. Interestingly, NIMA lists
the transformation from Nahrwan 1929 to WGS 84 as ΔX = -249 m,
ΔY = -156 m, ΔZ = -381 m, ±25 m, based on 2
stations observed in 1987.
Prof. Clifford
J. Mugnier (cjmce@LSU.edu)
Surveying, Geodesy, & Photogrammetry
LOUISIANA
STATE UNIVERSITY
2408 CEBA Building
Baton
Rouge, LA 70803
Voice & Facsimile: (225) 388-8536