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7612
Intersection of Azimuth and Elevation Axes
None
25-Meter VLBA

N 41° 46' 17.12930"
W 91° 34' 26.89110"
255.730 meters
222.302 meters
ATSC / 15-DEC-97
IERS ITRF94 (1993)
NGVD 1929

ATSC

None

(4007-S)
NORTH LIBERTY 1987 (NGS)
VLBA RM 1
VLBA RM 2
VLBA RM 3

(4007-S)
NORTH LIBERTY 1987 (NGS)

The mark for Station 7617 is a point represented by the perpendicular intersection of a plane through the elevation axis with the azimuth axis of the NRAO VLBA (Very Long Base Array) antenna. The point is not accessible and cannot be occupied. No survey disk or mark designates the point. It should be noted that the antenna elevation axis is offset by 3.133 meters (7 feet) from the azimuth axis.

Reference Mark 1 is a punchmark in the rounded top of a 0.014 meter diameter stainless steel rod set 0.10 meters below ground. (NOTE: the punchmark is not set exactly on the top center of the rod, but approximately 1 to 2 mm toward the northeast. The rod is set in concrete in the center of a 0.15 meter diameter PVC pipe which is encased in a 0.5 x 0.6 meter concrete monument. The monument is covered with 0.18 meters of soil to the top of an aluminum logo cover attached to the top of the PVC pipe. The logo cover is stamped "7617 RM1". The monument is located 10.16 meters north of the NRAO site north fence corner and 8.65 meters south of the NRAO north property corner (iron pipe). It is set at a distance of 71.6 meters and at a geodetic azimuth of 346.1 degrees from Station 7617.

Reference Mark 2 is a punchmark in the rounded top of a 0.014 meter diameter stainless steel rod set 0.07 meters below ground. The rod is set in concrete in the center of a 0.15 meter diameter PVC pipe which is encased in a 0.34 meter diameter concrete monument. The monument is covered with 0.05 meters of soil to the top of an aluminum logo cover attached to the top of the PVC pipe. The logo cover is stamped "7617 RM2". The monument is located 11.02 meters northeast of the NRAO site east fence corner and 17.48 meters northeast of the NRAO east property corner (iron pipe). It is set at a distance of 42.1 meters and at a geodetic azimuth of 73.2 degrees from Station 7617.

Reference mark 3 is a standard NASA-GSFC brass disk. The disk is counter-sunk 0.015 to 0.020 meters and epoxied into a 0.37 x 0.67 meter section exposed lava outcropping. The disk is stamped "7617 RM3". The lava outcrop is located at the northeast base of a long sloping ridge line consisting of jagged broken lava rocks. it is set 27.08 meters south of the NRAO site south fence corner and 1.48 meters southwest of the NRAO south property corner (iron pipe). It is located at a distance of 53.4 meters and at a geodetic azimuth of 182.9 degrees from Station 7617.

One additional survey monument is set inside the fenceline of the NRAO site. It was designated "VLBA BM". The station mark is a 0.050 meter diameter brass disk set flush in the center of a 1.00 meter diameter concrete monument. The monument slopes up from ground level to 0.04 meters above the ground at the brass disk. The disk is unstamped. It is located 38.5 meters southeast of the centerline of the NRAO site entrance road/gate. 2.28 meters southeast of fence pole #12 as counted from the entrance gate southeast fence pole and 1.12 meters north of fence pole #13. It is set 0.87 meters northeast of the fenceline.

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Comments:

4007
0.455 Meter Diameter Stainless Steel Plate
North Liberty-VLBA GPS STATION MARK-
JPL 4007-S 1992
GPS

N 41° 46' 17.72780"
W 91° 34' 29.61034"
240.490 meters
206.970 meters
BFEC / 18-DEC-92
ITRF-89
NGVD 1929

ATSC

None

NORTH LIBERTY 1987 (NGS)

NORTH LIBERTY 1987 (NGS)

"JPL 4007 S 1992" is a 0.455 meter diameter stainless steel plate set flush in the center of a 0.610 meter diameter concrete monolith that projects 0.465 meters above the ground. The steel plate is engraved "NORTH LIBERTY - VLBA GPS STATION MARK JPL 4007 S 1992 NASA FLINN SITE NORTH AMERICAN HIGH PRECISION FIDUCIAL NETWORK BLEWITT AND CLARK SPACE - GEODETIC PIONEERS JPL/GSFC COLLABORATION". It is set approximately 26 meters southwest of the northwest corner of the chain link fence that surrounds the vlba site; and 12.98 meters west of the western most fenceline. It is located 65.6 meters at a geodetic azimuth of 286 degrees from SGP Station 7612.

"NORTH LIBERTY" is a standard brass National Geodetic Survey horizontal control disk set flush in the center of a 0.310 meter diameter concrete monument that is flush with the ground. The disk is stamped "NORTH LIBERTY 1987". It is set 25.02 meters at a magnetic azimuth of 5 (five) degrees from the northwest corner of the chain link fence. it is located 78.3 meters at a geodetic azimuth of 328 degrees from SGP Station 7612.

"NORTH LIBERTY NO 1" is a standard brass National Geodetic Survey reference mark disk set flush in the center of a 0.26 meter diameter concrete monument that is flush with the ground. The disk is stamped "NORTH LIBERTY NO 1 1987". It is located at a geodetic azimuth of 7 (seven) degrees and a distance of 15.1 meters from monument "NORTH LIBERTY 1987".

"NORTH LIBERTY NO 2" is a standard brass National Geodetic Survey reference mark disk set flush in the center of a 0.26 meter diameter concrete monument that is flush with the ground. the Disk is stamped "NORTH LIBERTY NO 2 1987". It is located at a geodetic azimuth of 127 degrees a distance of 15.2 meters from monument "NORTH LIBERTY 1987".

"NORTH LIBERTY NO 3" is a standard brass National Geodetic Survey reference mark disk set flush in the center of a 0.26 meter diameter concrete monument that is flush with the ground. The disk is stamped "NORTH LIBERTY NO 3 1987". It is located at a geodetic azimuth of 247 degrees a distance of 15.3 meters from monument "NORTH LIBERTY 1987".