PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
August 2014
713
government eventually drafted a democratic constitution and
held flawed presidential elections in 1996 and 2001. In 1998,
a rebellion broke out in northern Chad, which has sporadically
flared up despite several peace agreements between the
government and the insurgents. In 2005, new rebel groups
emerged in western Sudan and made probing attacks into
eastern Chad despite signing peace agreements in December
2006 and October 2007. In June 2005, President Idriss Deby
held a referendum successfully removing constitutional
term limits and won another controversial election in 2006.
Sporadic rebel campaigns continued throughout 2006 and
2007. The capital experienced a significant insurrection in
early 2008, but has had no significant rebel threats since then,
in part due to Chad’s 2010 rapprochement with Sudan, which
previously used Chadian rebels as proxies. Deby in 2011 was
reelected to his fourth term in an election that international
observers described as proceeding without incident. Power
remains in the hands of an ethnic minority. In January 2014,
Chad began a two year rotation on the UN Security Council”
(World Factbook, 2014)
.
Slightly more than three times the size of California, Chad is
bordered by Cameroon (1,094 km) (
PE&RS
, May 2007), Central
African Republic (1,197 km) (
PE&RS
, March 2012), Libya
(1,055 km) (
PE&RS
, June 2006), Niger (1,175 km) (
PE&RS
,
November 2011), Nigeria (87 km) (
PE&RS
, February 2009),
and Sudan (1,360 km). The terrain has broad arid plains in
the center of the country, desert in the north, mountains in
the northwest, and lowlands in the south. The lowest point is
Djourab (160 m), and the highest point is Emi Koussi (3,415 m)
(World Factbook, 2014)
.
“Trig lists were compiled by the French Equatorial Africa
(
Afrique Équatorial Française
, AEF) but these were of the
astros that the French used to position their 1:200,000 series.
The 12
th
Parallel Traverse ran through the country from near
N’Djamena to the Sudanese triangulation near Geneina in
Sudan. Temporary coordinates would have been computed on
the Sudan datum, Adindan. Upon completion of the traverse
fromDakar, the whole would have been computed on a common
datum, I don’t remember which but probably Adindan. Go to
Wikipedia for N’Djamena, scroll to Gallery. What does the
temporary radio station look like to you? Possibly an early
satellite tracking station. Observatory in the background.
Brand new military tires on the trailer axels. Back to AEF trig
lists. One station was located at Ft. Lamy in a “Tata.” Check
that in your French dictionary and you probably won’t find
anything reasonable. It is a fortified Sudanese encampment
(and also the central fort) where a chieftain lives with his
family, his herd,
etc
.”
(Personal Communication, John W.
Hager, 23 May 2014).
In regard to Mr. Hager’s comments, that’s a BC-4 satellite
station. The 12-inch focal length camera case is on the ground
next to the little observatory. (I have one of those BC-4 cameras
myself.) Since the BC-4 system had to be synchronized into a
network, that’s what the electronics hut was for. They worked
at 600 cycles per second. While I was stationed at Army Map
Service & TOPOCOM, I went over to NOAA in Rockville, MD
to see the system they had worked up for the program. It
was designed by Dr. Helmut Schmid, a German V-2 Rocket
Scientist that had originally designed the BC-4 cameras for
his missile tracking work at Aberdeen Proving Grounds. (Dr.
Duane C. Brown was his protégé.) I was introduced to Dr.
Schmid who was so impressed by a Corps of Engineers Captain
that he looked me up and down, grunted, and walked away!
The Adindan Datum origin is in the
Blue Nile
Province
of Sudan, and sometimes it is called the Blue Nile Datum.
Referenced to theClarke 1880 ellipsoidwhere:
a
=6,378,249.145
m,
1
/
f
= 293.465; the origin is at: Φ
o
= 22° 10′ 07.1098″ N, Λ
o
=
31° 29′ 21.6079″ E. According to
TR8350.2
, the transformation
parameters
from
Adindan Datum
to
WGS84 for Sudan are:
ΔX = –161 m ±25m, ΔY = –14 m ±25m, ΔZ = +205 m ±25m.
Based on observations at 14 stations in Sudan, there are no
parameters published specifically for Chad. Being a former
French Colony, the UTM Grid System is likely the only
operational
plane coordinate system ever used for Chad.
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 Center for GeoInformatics (C
4
G).
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