MONTSERRAT

positions



Subject: Exact locations in Montserrat

Richard Herd of MVO very promptly supplied the following answer to the
question about the exact location of the GPS and EDM points used by MVO. 

Date: Tue, 1 Apr 1997 11:12:20 -0400
Subject: from Richard Herd

.... the exact locations of our GPS / EDM pins.  Here is a list of them. 
They are in Latitude and Longitude projected onto the WGS 1984 ellipsoid. 
Heights are relative to this ellipsoid.  To obtain heights relative to sea
level add about 40m.  Lat and Long are degrees, minutes, seconds.

Site	                    Lat(N)	    Long(W)  Height (in metres)
Brodericks	        16  41  56.29	62  11  59.65	146.96
Castle Peak reflector	16  42  32.88	62  10  32.15	666.74
Chances reflector	16  42  28.65	62  10  52.86	816.84
Chances Peak	        16  42  33.04	62  10  51.22	875.83
Dagenham	        16  42  56.71	62  12  38.76	84.72
FT3              	16  42  50.72	62  10  44.66	758.31
Farrells	        16  43  13.79	62  10  48.46	495.69
Galways (M37)	        16  41  44.81	62  11  15.55	311.33
Galways (Obs)	        16  42  6.99	62  10  51.89	544.31
Harris (M18)	        16  44  28.96	62  10  4.01	245.73
Hermitage	        16  43  17.52	62  10  11.19	438.64
Long Ground	        16  43  29.02	62  9  30.49	201.82
Lookout Yard	        16  47  23.13	62  11  17.24	132.83
Lower Amersham	        16  42  18.62	62  12  24.83	108.77
M27	                16  44  59.52	62  13  44.95	37.35
Ogarras (EDM)	        16  40  48.96	62  11  14.24	-9.98
Ogarras (M46)	        16  40  39.81	62  11  18.34	-27.19
Perches	                16  42  32.07	62  9  52.87	749.41
Roches Yard	        16  42  14.25	62  9  11.70	313.04
St Georges (M25)	16  43  21.77	62  12  29.79	317.78
Tar River	        16  43  12.77	62  9  39.89	255.52
Upper Amersham	        16  42  35.29	62  11  39.77	317.37
Whites	                16  43  52.52	62  9  34.39	143.36
Windy Hill	        16  44  32.23	62  11  26.28	374.36

The occupations we make are usually:
BIGNET - M18, Whites, Tar River, Dagenham, M46
EASTNET - M18, Whites, Tar River, Farrells, Windy Hill
WESTNET - Dagenham, Lower Amersham, Upper Amersham, Galways, M46
NORTHNET - M18, Dagenham, M27, Lookout Yard
CLOSENET - M18, FT3, Hermitage, Chances Peak, Perches

Individual stations may be substituted or dropped depending on activity of
the volcano and weather conditions.  Long Ground is quite often substituted
for the Tar River site if there is a threat to personnel and equipment from
pyroclastic flows.  At the moment flows are travelling down the White River
region from Galways wall, making the M46 and M37 sites very dangerous.

The technique used is differential GPS where two stations are run
simultaneously.  One station is held fixed and the position of the second
calculated relative to that.  In our processing, M18 has been chosen as the
fixed station.  For the networks above we use rapid-static GPS where one
station is run as a base for a few hours, while the equipment is moved
between the other stations (i.e. roving station).  The roving station
occupies the point for about 15 minutes allowing derivation of the point
position to a few mm.  The last station occupied by the roving station
becomes the new base and is left running whilst the equipment at the base
station is moved around the other sites.  In this manner all possible lines
between the stations are measured.  Long occupation GPS experiments (around
20 hours) are also run to give a very good fix on a single point and an
assessment of measurement errors.  This is usually done for the high, more
dangerous sites (FT3, Hermitage, Chances Peak and Perches).

EDM measurements are made in a series of triangles and loose lines to
reflectors:
Northern Triangle - Instrument at Windy Hill and St. Georges Hill; target
at Farrells.
Western Triangle - Instrument at Lower Amersham; targets at Dagenham, Upper
Amersham and Chances Peak Steps.
Southern - Instrument at Ogarras EDM and M37; permanent target at Chances
Peak EDM, temporary target at M37.
Eastern Triangle - Instrument at Whites, Long Ground and Tar River;
permanent target on Castle Peak.  This triangle has been dropped because
Castle Peak has been engulfed by the lava dome.

Hope this is of some use.  Let me know if more details are needed. 
...
Regards - Richard Herd, MVO

Montserrat Volcano Observatory

. . . The Electronic Evergreen, courtesy of GEM Radio Network
END

first version: August 8, 1997; file:/~ehem/car/islands/MTS_latlong.html;


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