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September 2020
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
ce Islands Colony in 1916. Independence was granted to the
Gilbert, Phoenix and Line Islands in 1979 as the Republic of
Kiribati. The Ellice Islands had previously seceded, in 1975,
as the Republic of Tuvalu. The International Date Line pass-
es through Kiribati, but the Government of Kiribati has (le-
gitimately) legislated that the Line and Phoenix Islands will
observe the same date as the Gilbert Islands.
S
urvey
H
istory
The Royal Navy carried out hydrographic surveys, based on
astro fixes, from the early nineteenth century onward. Little
survey and mapping work was done by the British colonial
authorities before WW2. Japanese military occupation of the
Gilbert Islands in 1941 lead to extensive aerial photography
and mapping by the US armed forces, who drove out the ene-
my in fierce fighting. Post-WW2: Aerial photography: Gilbert
Islands RNZAF 1962/63; USN 1964; Fiji Lands, Mines and
Survey Department 1968/69. The 1968/69 cover was used sub-
sequently by the Directorate of Overseas Surveys (DOS) for
mapping. Line Islands RAF 1950s. Phoenix Islands RNZAF
1962/63. All Kiribati, 1984/85, by the Royal Australian Sur-
vey Corps, as part of Operation Anon, one of the Australian
Army’s Pacific Doppler campaigns.
S
urvey
DOS control surveys 1967-73, by Tellurometer traversing,
covered all the islands in the Gilbert group, with each atoll
on its own astro datum and local Transverse Mercator grid.
International Spheroid (DOS’s default spheroid for the Pacif-
ic) was used. Christmas Island was surveyed by the RNZN,
British Military Survey and contract staff between 1941 and
the 1960s, and by the Kiribati Survey Department in 1979/80.
DOS then brought those surveys together, computing on
Christmas Island 1967 Astro Datum, International Spheroid,
Kiritimati Local [TM] Grid. The first modern survey work in
the Phoenix and Line Islands was the precise Doppler cam-
paign of 1984/85. Mapping: DOS produced 1:25,000 (a few
sheets were done at 1:12,500 & 1:10,000), photomap series
of all the islands between 1972 and 1996. The larger atolls,
Tarawa and Kiritimati (Christmas Island), were also mapped
at 1:50 000 on single sheets. Generally two editions were pro-
duced, one showing the local TM grid, and the other (for mil-
itary use) UTM grid. Early editions of the Christmas Island
sheet showed UTM Grid only. Southern Tarawa was mapped
at 1:2500 and 1:1250.” All of these classical Datums are refer-
enced to the International 1924 ellipsoid where a = 6,378,388
m, and
1
/
f
= 297.
Starting with specifics for the Gilbert Islands Group, for the
Abaiang Datum of 1962, the Datum origin is at the first-or-
der station Flagstaff of Government Station, also called HMS
Cook Astro “H” where Φ
o
= 01° 49´ 25.029˝ N and Λ
o
= 173°
01´ 25.830˝ East of Greenwich. According to a British Admi-
ralty Report of Survey file, “The Government flagstaff on a
coral rock plinth in the centre of the Government Station –
Taburao.” The local grid is based on the Transverse Mercator
projection with the central meridian,
l
o
= 172º 55´ E, the False
Easting = 20 km, and the False Northing = zero. The Scale
Factor at Origin is unity (m
o
= 1.0). From Abaiang Datum of
1962 to WGS 84 Datum, the converted Doppler solution is ∆X
= +254.8 m, Y = –322.4 m, and ∆Z = –270.0 m. The Operation
ANON 1984-85 solution is ∆X = +254.3 m, ∆Y = –323.4 m, and
∆Z = –275.6 m. For the Abemama Datum of 1944, the Datum
origin is at Signal Station, southwestern tip of Steve Island
(Station ‘Flag’), where Φ
o
= 00° 27´ 36˝ N and Λ
o
= 173° 49´ 11˝
East of Greenwich. For the Abemama Datum of 1959, the Da-
tum origin is at Cook Astro Point where Φ
o
= 00° 24´ 19.02˝ N,
Λ
o
= 173° 55´ 36.57˝ East of Greenwich, and H
o
= 2.14 m.
The local grid is based on the Transverse Mercator projection
with the central meridian,
l
o = 173º 51´ E, the False Easting
= 20 km, and the False Northing = 100 km. The Scale Fac-
tor at Origin is unity (m
o
= 1.0). From Abemama Datum of
1959 to WGS 84 Datum, the converted Doppler solution is ∆X
= +289.4 m, ∆Y = +656.2 m, and ∆Z = +303.4 m. Note that the
UTM coordinates of local traverses depend on the position of
Observation Spot that was connected by traverse to C where
j
o
= 00° 24´ 29.02˝ N and
l
o
= 173° 55´ 36.57˝ E.
For the Arorae Datum of 1965, the Datum origin is at Aro-
rae Astro Observation Spot where Φ
o
= 02° 38´ 36.7˝ S and Λ
o
= 176° 49´ 33.3˝ East of Greenwich. The local grid is based on
the Transverse Mercator projection with the central meridi-
an,
l
o
= 176º 49´ E, the False Easting = 10 km, and the False
Northing = 500 km. The Scale Factor at Origin is unity (m
o
= 1.0). From Arorae Datum of 1965 to WGS 84 Datum, the
converted Doppler solution is ∆X = +221.4 m, ∆Y = –34.4 m,
and ∆Z = –21.6 m.
For the Beru Datum of 1970, the Datum origin is at third-or-
der station BRZ 10 where Φ
o
= 01° 19´ 29.9632˝ S, Λ
o
= 175°
59´ 16.9134˝ East of Greenwich, and H
o
= 1.73 m. The local
grid is based on the Transverse Mercator projection with the
central meridian,
l
o
= 175º 59´ E, the False Easting = 10 km,
and the False Northing = 300 km. The Scale Factor at Ori-
gin is unity (m
o
= 1.0). From Beru Datum of 1970 to WGS 84
Datum, the converted Doppler solution is ∆X = +179.9 m, ∆Y
= –595.3 m, and ∆Z = +6.96 m. The Operation ANON 1984-85
solution is ∆X = +181.3 m, ∆Y = –585.6 m, and ∆Z = –7.2 m.
For the Butaritari Datum of 1965, the Datum origin is at
third-order station BTZ 26 where Φ
o
= 03° 15´ 40.629˝ N, Λ
o
= 172° 41´ 45.8381˝ East of Greenwich, and H
o
= 1.87 m. The
local grid is based on the Transverse Mercator projection with
the central meridian,
l
o
= 172º 50´ E, the False Easting = 20
km, and the False Northing = zero. The Scale Factor at Origin
is unity (m
o
= 1.0). From Butaritari Datum of 1965 to WGS 84
Datum, the converted Doppler solution is ∆X = +253.8 m, ∆Y
= +6.1 m, and ∆Z = +528.2 m. The Operation ANON 1984-85
solution is: ∆X = +254.2 m, ∆Y = +3.2 m, ∆Z = +544.2 m.
For the Kuria Datum of 1962, the Datum origin is at HMS
Cook Astro, Kuria 1962 where Φ
o
= 00° 13´ 00.4˝ N and Λ
o
=
173° 23´ 06.8˝ East of Greenwich. The local Kuria and Arana-
