OBS Survey 2003 Western Norway

Gravitymeter basereadings

University of Bergen (UiB)
Dept. of Earth Science (IFG)
Allé gt. 41, N-5007 Bergen, Norway
Tel: (+47) 5558 3600 Fax: (+47) 5558 3660
December 1, 2004 (OM)


The project had participants from these institutions:

The survey was conducted from May 20 to June 30, 2003, onboard University of Bergen research vessel RV Håkon Mosby.

Pictures can be found here ...


Content

  1. Data, log files, format descriptions
  2. Instrumentation
  3. Notes

 

1. Data, log files, format descriptions

1.1 Data and log files

1
Line id.
2
Log sheet (scanned)
3
Nav data
Datum, UTM Zone
 4
Survey Computer
files:
a) OBS positions
b) Shot event log files
c) Grav/mag data, 10 sec log interval 
5
Shot event time stamp files Note 1)
[GPS time=UTC+13s]
6
Gravitymeter
Data files
SORTED BY JULIAN DATE
7
Mini-streamer data
From LinAcq recording system
Note 2)
8
Cheif obs.
9
Notes
A,B ./line-AB/log-sheet/ WGS84
Zone 31
./line-AB/EIVA ./line-AB/shot-timestamp/ ./gravity-data Not used OM  
C ./line-C/log-sheet/ ED50
Zone 31
./line-C/EIVA/ ./line-C/shot-timestamp/ ./gravity-data ./line-C/linacq/ OM LinAcq screen capture
D ./line-D/log-sheet/ ED50
Zone 31
./line-D/EIVA/ ./line-D/shot-timestamp/ ./gravity-data ./line-D/linacq/ OM LinAcq data just for recording of air gun pressure; note error in EIVA serial string capture.
F ./line-F/log-sheet/ ED50
Zone 32
./line-F/EIVA/ ./line-F/shot-timestamp/ ./gravity-data ./line-F/linacq/ OM  
H ./line-H/log-sheet/ ED50
Zone 32
./line-H/EIVA/ ./line-H/shot-timestamp/ ./gravity-data ./line-H/linacq/ OM  
J ./line-J/log-sheet/ ED50
Zone 32
./line-J/EIVA/ ./line-J/shot-timestamp/ ./gravity-data ./line-J/linacq/ OM
  1. LinAcq files. No. 1 and 3 has ±1.25V range. No. 2 has ±2.5V range (should be scaled).
  2. GUNCO data collected. See format description.
I ./line-I/log-sheet/ ED50
Zone 32
./line-I/EIVA/ ./line-I/shot-timestamp/ ./gravity-data Not used OM Survey computer (EIVA) time 23 seconds behind GPS- should be 13. This affects all timestamps in EIVA data log files.
G ./line-G/log-sheet/ ED50
Zone xx
./line-G/EIVA/ ./line-G/shot-timestamp/ ./gravity-data ./line-G/linacq/ EG  No data yet.
K ./line-K/log-sheet/ ED50
Zone xx
./line-K/EIVA/ ./line-K/shot-timestamp/ ./gravity-data ./line-K/linacq/ EG  No data yet.
L ./line-L/log-sheet/ ED50
Zone xx
./line-L/EIVA/ ./line-L/shot-timestamp/ ./gravity-data ./line-L/linacq/ EG  No data yet.

Table 1: Data, log files

Note 1:
During the survey, GPS time was ahead of UTC time by 13 seconds. The decision to introduce a leap second in UTC is the responsibility of the International Earth Rotation Service (IERS).
Note 2:
Data in Seismic Unix format. This is modified SEG-Y, refer to description on this web page: http://www2.geo.uib.no/seismic-unix/
Data recorded in little-endian form. To read these files on big-endian machines first use the SUSWAPBYTES command in Seismic Unix, ref.: http://www.cwp.mines.edu/sututor/node47.html
Airgun pressure recorded in some files; the SUT trace header field was used for this purpose. The SURANGE command (also part of Seismic Unix) will show if the SUT field is in use.
 

 

 

1.2 Format description Survey Computer (EIVA) log files:

Shot (= Event) files; format example:

 004105 20:19:49 0711074.16 07809167.80 01.00 160.0 00969.12 -06.23 141.600 Filtered 2490.80 52816.00 12683.04 

 Field no.  Example Parameter Notes
1 004105 Shot (event) number  
2 20:19:49 Time  Survey computer time not accurate - could differ by more then 10 seconds from UTC.
3 0711074.16 UTM Easting  Refered to antenna position in mast.
4  07809167.80  UTM Northing  Refered to antenna position in mast.
5 01.00 Standard deviation  
6 160.0  Gyro compass reading   
7 00969.12 DAL  = Distance along line [m]
8 -06.23 DOL  = Distance off line [m]
9 141.600 KP  = Kilometer post
10 Filtered    (check)
11 2490.80 Depth  From EK500 Echo Sounder
12 52816.00 Magnetometer  (Length of mag tow fish cable - check!)
13 12683.04 Gravitymeter  (check - filtered, raw??)

Table 2. Shot (event) file format description.


Logging of depth, gravity- and magnetometer data every 10 seconds; format example:

 06:21:59 23.05.2003; 553674.1175;6744618.7726; 060°49.995410'; 003°59.234563'; 326.2000; 12008.8500; 50667.0000 

Field no. Example Parameter Notes
1 06:21:59 Time  Survey computer time not accurate - could differ by more then 10 seconds from UTC. 
2 23.05.2003 Date  
3 553674.1175 UTM Easting  Refered to position of crane used to deploy the OBS.
4 6744618.7726 UTM Northing  Refered to position of crane used to deploy the OBS.
5  060°49.995410'  Latitude  
6 003°59.234563' Longitude  
7 326.2000 Depth  From EK500 Echo Sounder
8 12008.8500 Gravity  (check - filtered, raw??)
9 50667.0000  Magnetometer   (Length of mag tow fish cable - check!)

Table 3. 10 second interval log file format description.

Logging of OBS deployment positions

=================== Event 00001 Wednesday, June 11, 2003 07:47:27 MANUAL ===================
Message: OBS72
Cycle at 0.740 Gyro 320.35 Roll 0.00 Pitch 0.00 Heave 0.00 SOG 0.08 COG 63.78
LOP  Code System                Measurement   Converted    Error    Wgt
--------------------------------------------------------------------------------
 0      1 GPS1 (NMEA): Seapath   558940.057   558940.081   0.152   1.00
 1      1 GPS1 (NMEA): Seapath  7640272.663  7640272.614  -7.836   1.00
 2      1 GPS2 (NMEA): Trimble   558933.681   558933.768   0.918   1.00
 3      1 GPS2 (NMEA): Trimble  7640292.477  7640293.055   2.864   1.00
 4      1 Gyro: User Defined g      320.350      318.984 315.637   0.00
Position        Easting     Northing   Height    S.td   Data
---------------------------------------------------------------------------------
1        :   558940.410  7640277.937     0.00    5.36
Filtered :   558939.738  7640277.812     0.00   -1.00    - 
Kran     :   558937.809  7640273.477     0.00    0.00    -
EK500    :   558934.193  7640279.616    -1.00    0.12   D 2995.50   B  1.00 
input 1: :   559071.664  7640127.033     0.00    0.72   D 56013.00  B  0.00
input 2: :   558940.410  7640277.937     0.00    0.39   D 12534.17  B  0.00

 Some navigation related abbreviations: LOP = line of position, SOG = speed over ground, COG = course over ground.

The LOP's listed (0..4) are the positioning devices used in UTM coordinate calculation. Data from each unit has a certain weight (Wgt) in the calculation. 

The OBS is deployed from a crane; it's position is given in the "Kran" line.

EK500 is depth data, input 1 is magnetometer data (not valid as it is not in operation during OBS deployment) and input 2 is gravitymeter data (should be discarded, like mag data).

 

2. Instrumentation

2.1 Block diagram


Fig. 1. OBS-2003 Survey Instrumentation block diagram.

2.2 Airgun source layout, signature, spectrum

Click on image below to download pdf version.

Fig 2: Airgun source layout, signature, spectrum. Click to download pdf version. Software used: NUCLEUS, by PGS.

 

3. Notes

3.1 ASHTECH GPS, used for timestamp of GUNCO FTB.

Ashtech GPS had to be reconfigured at start of survey. Use the Ashtech Evaluate program - there are two directories, "evaluate1" that holds unzipped main file, ready to be installed, and "Ashtech Evaluate" that is copied from already installed version (the latter may or may not work if it is just copied to a new PC).  

Send these commands to the GPS (a modified version of this config file):

Command  Description
$PASHS,RST Reset with default settings
$PASHS,SYS,MIX Set receiver in mixed GPS/GLONASS mode
$PASHS,PEM,5 Set elevation mask to 5 degrees
$PASHS,NME,RMC,C,ON Send NMEA message RMC on port C
$PASHS,NME,PER,1.0 Set NMEA "send message interval" to 1 Hz
$PASHS,PHE,F Set event marker signal to falling edge
$PASHS,PPS,01.00,+000.0000,F Set 1PPS trigger edge to falling edge
$PASHS,NME,TTT,B,ON Output Event marker message on port B
$PASHS,TSC,GPS Output Event marker time in GPS-system-time
$PASHS,SAV,Y Save settings in battery backed-up memory

If this GPS should fail: Use the GUNSTAMP system (ask Trond S.).

 

3.2 TeraTerm terminal program - for setup of OBS

This terminal program permits 600 bits/second datarate, this is not common in other terminal programs. It's here.

 

3.3 Status web page with ship position, 24h track line, OBS positions and weather information




Fig. 2. Web page showing ship's position, 24h track line, OBS positions and data from Aanderaa Weather Station (click to enlarge).

The map showing ship's position and past 24 hour trackline is updated every minute. The weather station graphs are updated every 10 min. The web page itself is refreshed every 30 sec. More information on this software: