Petrobar-2007 / SVALEX-2007 - GRAVITYMETER REPORT

Introduction

An attempt is made to establish two gravity stations in Longyearbyen - one at Bykaia, and the other close to Gamlekaia (Nor-Cargo). The difference between the offical gravity station at Longyearbyen airport, and these two new stations, has been measured on several occations. Refer to SVALEX-2005 gravity report for description of these two new stations.

The station at Longyearbyen airport is in the terminal building. A new terminal will be opened October 2007. The old building is said to be kept intact.

Gravitymeter position within ship

Fig.1: Gravitymeter location in RV "Håkon Mosby"

In the photos below one can easily see the welding joints between decks. If distance from wharf to sea surface is not given (due to port congestion, the ship moved from wharf to wharf and it happened that it was not time to perform these measurements) one can estimate position of gravitymeter onboard, and position of the land gravitymeter on wharf.

August 5, 2007: Start of survey

The gravitymeter was loaded onto the ship Sat. August 4. Power to land gravitymeter switched on. The marine gravitymeter switched on Sunday 5 August. Due to port congestion, the ship had to stay in Adventfjorden. It was not possible to obtain still/base reading before the survey started. It was decided to carry on as planned, and use later base readings/gravity ties to extrapolate drift in gravitymeter readings.

18 August, 2007: Base reading, Bykaia

The ship did not stay here for long. There was a queue of ships waiting in line.

Location: Bykaia:

Wharf to sea: 2.62 m

Still readings: See gravitymeter log files (the ship was about to move). Day of year = 230.

Fig. 2: 18 Aug 2007, base reading, Bykaia, Longyearbyen

Land gravtymeter beside ship

   Time
   UTC   Reading
   ----------------------
   13:13 6434.350
   13:15 6434.351
   13:17 6434.348

New location: Bykaia "gravity station"

Fig. 3: Basereading, 18 Aug 2007, Bykaia "gravity station."

   Time
   UTC   Reading
   ----------------------
   13:25 6434.785
   13:29 6434.760
   13:31 6434.780

Still readings: See gravitymeter log files (the ship was about to move). Day of year = 230.

20 August, 2007: Base reading, Kullkaia

Wharf to sea: 2.9 m

Still reading gravitymeter, start

   232:07:22:40 14634.1 14634.2 .0 -9 .0

Land gravitymeter, start

Land gravitymeter:

   Time
   UTC  Reading
   ----------------------
   7:31 6435.135
   7:34 6435.128
   7:37 6435.140

Land gravitymeter readings, position as shown:

Fig. 4: Basereading 20 Aug 2007, Kullkaia, Longyearbyen

Fig. 5: Base reading 20 Aug 2007, Kullkaia, Longyearbyen

Fig. 6: Base reading 20 Aug 2007, Kullkaia, Longyearbyen

New location: Longyearbyen airport, gravity station

Land gravitymeter:

   Time
   UTC  Reading
   ----------------------
   8:14 6432.600
   8:15 6432.602
   8:17 6432.600
   8:18 6432.600

Fig. 7: Base reading 20 Aug 2007, Longyearbyen Airport

Fig. 8: Base reading 20 Aug 2007, Longyearbyen Airport

Location: Back to Kullkaia, same place

---

Land gravtymeter:

   Time
   UTC  Reading
   ----------------------
   8:34 6435.135
   8:36 6435.142
   8:38 6435.138

Location: Bykaia, in order to establish new "gravity station"

Land gravitymeter:

   Time
   UTC  Reading
   ----------------------
   9:00 6434.708
   9:03 6434.710
   9:05 6434.712

Refer to similar readings in 2005.

Fig. 9: Base reading 20 Aug 2007, Bykaia, Longyearbyen

Fig. 10: Base reading 20 Aug 2007, Bykaia, Longyearbyen

Location: Nor-Cargo, in order to establish new "gravity station"

Land gravitymeter:

   Time
   UTC  Reading
   ----------------------
   9:13 6435.145
   9:16 6435.150
   9:18 6435.151

Refer to similar readings in 2005.

Fig. 11: Base reading 20 Aug 2007, Gamlekaia (Nor-Cargo), Longyearbyen

Still reading gravitymeter, end

   232:09:45:30 14634.1 14634.2 .0 -2.0 .0

23 August, 2007: Base reading, Gamlekaia (Nor-Cargo)

Still reading gravitymeter, start

   235:07:20:00 14633.1 14633.1 .0 10 -.1

Land gravitymeter, start

   Time [UTC] Reading
   ----------------------
   7:25       6434.100
   7:28       6434.090
   7:30       6434.095

Location:

Fig. 12: Base reading 23 Aug 2007, Gamlekaia (Nor-Cargo), Longyearbyen

Fig. 13: Base reading 23 Aug 2007, Gamlekaia (Nor-Cargo), Longyearbyen

Fig. 14: Base reading 23 Aug 2007, Gamlekaia (Nor-Cargo), Longyearbyen

Land gravitymeter readings "reference position Nor-Cargo"

Land gravitymeter:

   Time [UTC] Reading
   ----------------------
   7:35       6435.116
   7:37       6435.110
   7:39       6435.105

Still reading gravitymeter

    235:07:42:00 14633.0 14633.0 .0 10 .2

31 August 2007: Base reading, Bykaia

Distance wharf-sea: 3,90 m

Still reading, start

   243:08:18:00  14632.7  14632.7  .0  7.  .1

Land gravitymeter, start

   Time [UTC] Reading
   ----------------------
   8:30       6434.230
   8:33       6434.223
   8:35       6434.225

Fig. 15: Base reading 31 Aug 2007, Bykaia, Longyearbyen

Fig. 16: Base reading 31 Aug 2007, Bykaia, Longyearbyen

Location: Bykaia "gravity station"

   Time [UTC] Reading
   ----------------------
   8:56       6434.620
   8:58       6434.618
   9:00       6434.620

Location: Longyearbyen airport

   Time [UTC] Reading
   ----------------------
   9:17       6432.535
   9:19       6432.532
   9:21       6432.531

Location: Bykaia "gravity station"

   Time [UTC] Reading
   ----------------------
   9:32       6434.620
   9:34       6434.622
   9:36       6434.622

Location: Beside ship, Bykaia

   Time [UTC] Reading
   ----------------------
   9:42       6434.230
   9:44       6434.235
   9:46       6434.235

Distance wharf-sea: 3.65 m

Still reading, end

   243:09:54:50  14632.7  14632.7  .0  10.0  -.1

Longyearbyen gravity station

Calibration table, land gravitymeter