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Bureau of Mineral Resources, Geology & Geophysics

BMR PlmU· 'A :'~'-.:' '. J' .... 'ACiUS (LE11IHI'-lG SECnON>'

NORTH EAST AUSTRALIA 3 BMR MARINE SURVEY 75

EXPLANATORY NOTES TO ACCOMPANY THE RELEASE OF NON-SEISMIC DATA

by

Gray Saunders

and

E. John Mowat

on contained in this report has been obtained by the Bureau of Mineral Resources. Geology and Geophysics as part of the policy lian Government to assist in the exploration and development of mineral resources. It may not be published in any form or used in ospectusor statement without the permission in writing of the DirE:ctor .

III ~ II UII ~ * R 9 1 100 0 1 *

Bureau of Mineral Resources, Geology and Geophysics

DIVISION OF MARINE GEOSCIENCES & PETROLEUM GEOLOGY

RECORD 1991/100

NORTH EAST AUSTRALIA 3 BMR MARINE SURVEY 75

EXPLANATORY NOTES TO ACCOMPANY THE RELEASE OF NON-SEISMIC DATA

by

Gray Saunders

and

E. John Mowat

~commonwealth of Australia, 1991

This work is copyright. Apart from any fair dealing for the purposes of study, research, criticism or review, as permitted under the Copyright Act, no part may be reproduced by any process without written permission. Inquiries should be directed to the Principal Information Officer, Bureau of Mineral Resources, Geology and Geophysics, GPO Box 378, Canberra, ACT, 2601.

ISSN 0811-062X ISBN 0 642 16947 0

CONTENTS

INTRODUCTION 2

DATA ACQUISITION SYSTEM 2

GEOPHYSICAL SYSTEMS & PERFORMANCE 5

DATA PROCESSING 8

DATA AVAILABILITY 19

FIGURES

FIGURE 1: Bathymetry traces before and after processing by program SALVG. · . . . .. 11

FIGURE 2: Satellite fix assessment plot prior to processing. . · . . . . . . 17

FIGURE 3: Satellite fix assessment plot post processing. · . . . . . 18

FIGURE 4: Track map of Rig Seismic Survey 75 . . 20

TABLES

TABLE 1: Acquisition channel allocations Survey 75 . . 3

TABLE 2: Percentage use of Navigation Systems 6

TABLE 3: Gravity tie data for Survey 75 7

TABLE 4: Processing channel allocations 8

TABLE 5: Sample satellite fix listing 14

TABLE 6: Final channel allocations . . . . . . . . . . . . .. 16

1

INTRODUCTION

The aims of BMR Marine Survey 75 were: to define the structural and sedimenta1ogica1 evolution of the Marion Plateau, in particular, to determine the timing and the extent of reef growth on the Plateau; to define the relations between the evolution of the Marion Plateau and the Great Barrier Reef; and to conduct site surveys in support of the Ocean Drilling Program proposals.

This report summarises the processing techniques applied to the non-seismic geophysical data gathered during North East Australia 3, BMR Marine Survey 75, which was conducted between the 4th of September and the 6th of October 1987, departing from Brisbane and finishing at Townsville. The survey was part of BMR Project No 121.11.

THE DATA ACQUISITION SYSTEM ( DAS )

The Data Acquisition System (DAS) was primarily responsible for the acquisition of Navigation, Bathymetry, Gravity and Magnetics data. The system was based on a Hewlett Packard 1000 F-Series computer fitted with 2 Mega bytes (Mb) of memory and used two 50Mb HP 7920 and two 20Mb HP 7906 disc drives for programs and short term data storage. Long term storage of data was via a HP7970E magnetic tape Unit. The computer operated under the H-P Real Time Executive (RTE-6/VMS) System which allowed data to be collected on a time sharing basis with other users.

The main program in the system, PROCO, controlled the operation of most of the other programs. The acquisition program ACQ which acquired time data, gravity and MXl107RS data through an RS-232C HP mUltiplexer interface, and magnetics, bathymetry and both the sonar doppler and gyro compass data through a BMR designed 16 channel digital multiplexer. After preliminary processing, plotting on stripchart recorders and listings on a variety of printers, the data were recorded on 9-track, 1600 bpi, phase-encoded magnetic tape in HP's 32-bit floating-point format.

Data were acquired and saved at a lO-second rate, regardless of the ship's speed and written to tape in 1 minute (6 record) blocks of 128 channels of data. The acquisition channels that were recorded are listed in Table 1.

2

TABLE 1: Acquisition channel allocations Survey 75

1 - RTE clock (survey & day number) 2 - GMT acquisition time from RTE clock (hours,mins,secs) 3 - Master clock time at acquisition (hours,mins,secs) 4 - Latitude - best estimate (radians) 5 - Longitude - best estimate (radians) 6 - Speed - best estimate (knots) 7 - Heading - best estimate (degrees) 8 - Magnetometer No.1 (nT) 9 - Magnetometer No.2 CnT)

10 - Bathymetry No.1 (metres) 11 - Bathymetry No.2 (metres) 12 - Magnavox sonar doppler - fore/aft (counts) 13 - Magnavox sonar doppler - port/starboard (counts) 14 - Raytheon sonar doppler - fore/aft (counts) 15 - Raytheon sonar doppler - port/starboard (counts) 16 - Paddle log (counts) 17 - Not use 18 - Heading No.1 Arma-Brown gyro-compass (degrees) 19 - Heading No.2 Robertson gyro-compass (degrees) 20 - Not used 21 - Miniranger range 1 (metres) 22 - Miniranger range 2 (metres) 23 - Miniranger range 3 (metres) 24 - Miniranger range 4 (metres) 25 - Hifix fine A (centi1anes) 26 - Hifix fine B (centi1anes) 27 Hifix fine C (centi1anes) 28 Hifix coarse A (centi1anes) 29 - Hifix coarse B (centi1anes) 30 - Hifix coarse C (centi1anes) 31 - Reserved for Multiplexed data 32 - Reserved for Multiplexed data 33 - Reserved for Multiplexed data 34 - Reserved for Multiplexed data 35 - Reserved for Multiplexed data 36 - Reserved for Multiplexed data 37 - Reserved for Multiplexed data 38 - Reserved for Muitiplexed data 39 - T-set North standard deviation (metres) 40 - T-set East standard deviation (metres) 41 - T-set satellite numbers 42 - T-Set time (GMT sees) 43 - T-Set Dilution of precision (dop) 44 - T-Set latitude (radians) 45 - T-Set longitude (radians) 46 - T-set height above Geoid (metres) 47 - T-Set speed (knots * 10) 48 - T-Set course (degrees * 10) 49 - T-Set frequency bias 50 - T-Set GMT (hours,mins,secs) 51 - Latitude calculated from Magnavox sonar-doppler (radians) 52 - Longitude calculated from Magnavox sonar-doppler (radians) 53 - Speed calculated from Magnavox sonar-doppler (knots)

3

54 - Course calculated from Magnavox sonar-doppler (degrees) 55 - Latitude calculated from Raytheon sonar-doppler (radians) 56 - Longitude calculated from Raytheon sonar-doppler (radians) 57 - Speed calculated from Raytheon sonar-doppler (knots) 58 - Course calculated from Raytheon sonar-doppler (degrees) 59 - Latitude calculated from spare log (radians) 60 - Longitude calculated from spare log (radians) 61 - Speed calculated from spare log (knots) 62 - Course calculated from spare log (degrees) 63 - Latitude calculated from Radio nav (radians) 64 - Longitude calculated from Radio nav (radians) 65 - Speed calculated from Radio nav (knots) 66 - Course calculated from Radio nav (degrees) 67 - GMT time from MXl107RS satnav (hours,mins,secs) 68 - Dead-reckoning time from MXll07RS (hours,mins,secs) 69 - Latitude from MXl107RS (radians) 70 - Longitude from MXl107RS (radians) 71 - Speed from MXl107RS (knots) 72 - Heading from MXl107RS (degrees) 73 - GMT from MXl142 satnav (hours,mins,secs) 74 - Dead-reckoning time from MXl142 (hours,min,secs) 75 - Latitude from MXl142 (radians) 76 - Longitude from MXl142 (radians) 77 - Speed from MXl142 (knots) 78 - Heading from MXl~42 (degrees) 79 - Gravity (rm s~c- * 0.1) 80 - ACX roll (ms- * 1000) 81 - ACY pitch (ms- 2 * 1000) 82 - Sea state 83 - Magnetic anomaly No.1 (nT) 84 - Magnetic anomaly No.2 (nT) 85 - Magnetic difference (nT) 86 - Shot time (hours,mins,secs) 87 - Shot point number 88 - Hifix A range 10 minute drift (centilanes) 89 Hifix B range 10 minute drift (centilanes) 90 - Hifix C range 10 minute drift (centilanes) 91 - Hifix A range cumulative drift (centilanes) 92 - Hifix B range cumulative drift (centilanes) 93 - Hifix C range cumulative drift (centilanes) 94 - 128 not used

4

THE GEOPHYSICAL SYSTEMS & PERFORMANCE

The following is a description of the systems used during the acquisition of Navigation, Bathymetry, Gravity and Magnetics data and the performance of these systems during Survey 75.

Navigation

The navigation data were collected by three distinct systems, Dead Reckoning, Global Positioning System (GPS) and Radio Navigation. Each system was utilised according to its availability and reliability at the time of selection.

Dead Reckoning Systems: The primary system consisted of a Magnavox MXl107RS dual channel short-count Transit satellite navigator with ship's speed from a Magnavox 6l0D dual-axis sonar-doppler and heading from an Arma-Brown SGB 1000 gyro-compass. A secondary system consisted of a Magnavox MXl142 single channel short-count Transit satellite navigator with ship's speed from a Raytheon DSN 450 sonar-doppler and heading from a Robertson gyro-compass.

GPS System: A Magnavox T-Set Global Positioning System (GPS) providing the user with the means to receive signals from orbiting GPS satellites. The signals provided orbital data from which the T-Set computed ship's position in geographical coordinates and continuously calculated speed and heading. A rubidium frequency standard was used as a frequency control throughout the survey enabling GPS system to navigate with two satellites when required.

Radio Navigation System: Consisted of a Decca Hifix Radio navigator working in hyperbolic mode using at any time a set of three Hifix ranges (channels) transmitted from stations located on the coast.

Performance Comments: Both satellite navigators performed reliably when Hifix and T-Set were not available. However the Magnavox sonar-doppler lost track whenever the 3.5kHz echo-sounder was in operation, so speed data from the Magnavox recorded at these times were recalculated. Note also that off the shelf sonar doppler speed is a speed relative to ocean currents at depth.

The T-Set data were accurate when there were three and four satellites available which was usually between 0800 and 1800 (GMT). As a general rule navigating on two satellites was considered inaccurate when T-Set first became available, however it was possible to navigate on two satellites for a very short period using altitude and clock aiding before T-Set went off. The reason for this was related to the frequency bias. When the T-Set first became available the frequency bias was still calibrated to the satellites used for navigation 8 to 12 hours previously. This meant the frequency bias was not applicable to the current set of satellites. However after navigating for 7 to 8 hours with the use of 3 and 4 satellites, navigating with 2 satellites was used on the basis that the frequency bias would already have been calibrated during the past 7 to 8 hours. When it became evident that

5

T-Set was becoming inaccurate it was switched off and Radio Navigation or Dead Reckoning were employed.

Radio Navigation performed poorly over distances greater than 350 kms from the transmitting stations, however over distances of 100, to 300 kms when the geometry of the intersec~ing lanes was good the Hifix system provided acceptable accuracy compared with positions from the Sat-Navs and T-Set.

Table 2: Percentage use of Navigation Systems during Survey 75.

System

Dead Reckoning T-set Hifix

Bathymetric Systems

% Use

52% 41%

7%

The bathymetry data were acquired using the 12kHz Raytheon Bathymetric System consisting of a Raytheon Power Transceiver used as the initial power output, and a 9-transducer array Receiver/Transmitter with a maximum output of 2000 Watts creating signals which, after returning from the sea bed, were picked up by the Raytheon Correlation Echo Processor (CESP-1), which checked for a valid echo by comparing an already coded output pulse in the CESP-l to the return signals. After they were accepted the signals were sent to the Precision Depth Digitiser (PDD-200C) where an analogue record was produced for the Universal Graphic Recorder (EPC). The PDD-200C also displayed its digital values in metres and sent the digital values, via a 16 Channel BMR multiplexer, to the computer. Finally the values were recorded on magnetic tape ready for processing.

In addition to digital depths and various alarm flags the system provided an automatic tracking facility that would provide useable bathymetric data even in marginal recording conditions.

While the ship was at geological sample sites the 3.SkHz Raytheon System was utilised because of its sub bottom penetration qualities.

Performance Comments: The quality of the performance was a function of sea-state and sometimes water depth. In rough seas and depths of between 1000m to SOOOm the analogue and digital records were mostly poor. In medium seas the records were acceptable and in a smooth to low swell the records were good. The 3.5kHz system performed well at all the geological sampling sites during the survey.

Magnetics:

The magnetics data were obtained using a Geometries G80l Marine Proton-Precession Magnetometer which measured the total intensity of the earth's magnetic field at a 10 second sampling rate. Operating on the

6

principles of nuclear magnetic resonance, the precession frequency of about 2000 Hertz was converted to Binary Code Decimal (BCD) format, displayed as Nano-Teslas on the Geometrics unit and sent to the computer via a 16 channel BMR Multiplexer, and finally recorded on magnetic tape.

Performance comments: The magnetometer was utilised for a period of 11.5 days and with the exception of one occasion when the magnetometer head filled with water, it performed satisfactorily over this period.

Gravity

The Gravity data were recorded from a Bodenseewerk Geosystem (KSS-3l) marine gravity meter. The gravity sensing element is mounted on a gyro-stabilised table as near as possible to the ship's centre of pitch and roll. The control and processing electronics are housed within the stabilised platform and in the following equipment modules: the Bodenseewerk Power Supply (PS-3l) module, the Platform Electronics (KE-3l) module, the System Controller (ZE-3l) module and the Sensor Electronics (GE-30) module.

Every 10 seconds gravity data were sent to the DAS via an RS-232C link, after being converted to a digital value by the ZE-3l System Controller, and then recorded on magnetic tape.

In order to determine the drift of the KSS-3l gravity meter during the survey a gravity tie was performed in Brisbane before commencing the survey and in Townsville at the completion of the survey. The gravity tie information is provided in Table 3.

TABLE 3: Gravitx tie information for SurveX 75.

Place Date Time (GMT) KSS-3l Corrected(pms-2)

Brisbane 04.09.87 2345 -1245.45 9803967.5 Townsville 06.10.87 0110 -1783.09 9804005.0

Gravity meter drift:- Brisbane to Townsville 37.5 (pms-2)

Performance Comments: Although the KSS-3l has the ability to interface with the navigation system enabling the use of speed and heading to account for the effect of sea state and turns on the gravity data, due to a supplier software problem the KSS-3l was not provided with any navigation data from the DAS. These corrections were made during Phase 2 of the data processing. The KSS-31 was operated for the entire survey without any problems and provided satisfactory gravity data.

-7

DATA PROCESSING

The non-seismic geophysical data were processed on a Hewlett Packard HP 1000 F-Series computer utilising similar hardware and the same operating system as the DAS. The processing was applied in two phases, as follows:

Phase 1:

Phase 1 processing was primarily concerned with the filtering, cleaning and salvaging of the data. A number of programs were run in sequence to bring the data to a form where it could be used for Phase 2 of the processing. A description of the programs used in Phase 1 is in the following steps.

FCOPY: The main function of this program was the transcription of the data from the field tapes to disc and the concatenation into a number of working files normally 7 days long each. The program listed any time-, jumps that may have occured ego a negativ~ jump or jumps caused by the DAS crashing during acquisition or a port call.

FIXTM: By running this program any time jumps reported in FCOPY were either automatically or manually corrected with a time correction file and the acquisition channels were swapped to the required processing channels ie. from 1 minute (6 record) blocks of 128 channels of data to 1-minute (6 record) blocks of 64 channels of data. Also any single end of files were removed from the data until a double EOF was encountered. Table 4 is an example of the processing channels created by FIXTM.

TABLE 4: Processing channel allocations Survey 75.

1 - Clock (survey & day number) 2 - GMT acquisition time from computer clock (hours,mins,secs) 3 - Master clock time at acquisition (hours,mins,secs) 4 - Latitude - best estimate (radians) 5 - Longitude - best estimate (radians) 6 - Heading - best estimate (degrees) 7 - Speed - best estimate (knots) 8 - Bathymetry No.1 (metres) 9 - Bathymetry No.2 (metres)

10 - Magnetometer No.1 (nT) 11 Magnetometer No.2 (nT) 12 - Magnetic gradient (nT/m) 13 - Gravity (pms-2 * 0.1) 14 - Pitch acceleration (ms- 2) 15 - Roll acceleration (ms- 2) 16 - Magnavox sonar doppler - fore/aft (knots) 17 - Magnavox sonar doppler - port/starboard (knots) 18 - Raytheon sonar doppler - fore/aft (knots) 19 - Raytheon sonar doppler - port/starboard (knots) 20 - Paddle Log (knots) 21 - T-set Latitude (radians) 22 - T-Set longitude (radians) 23 - Arma-Brown gyro-compass (degrees)

8

24 - Robertson gyro-compass (degrees) 25 - Miniranger range 1 (metres) 26 - Miniranger range 2 (metres) 27 - Not used 28 - Not used 29 - Not used 30 - Hifix (fine) A (centi1anes) 31 - Hifix (fine) B (centi1anes) 32 - Hifix (fine) C (centilanes) 33 - Hifix (coarse) A (centi1anes) not used 34 - Hifix (coarse) B (centi1anes) not used 35 - Hifix (coarse) C (centilanes) not used 36 - T-Set height above geoid (metres) 37 - T-Set speed (knots) 38 - T-set eourse (degrees) 39 - T-Set frequency bias 40 - Latitude calc. from Magnavox sonar-doppler + Arma-Brown (radians) 41 - Longitude calc. from Magnavox sonar-doppler + Arma-Brown (radians) 42 - Speed calc. from Magnavox sonar-doppler (knots) 43 - Course calc. from Magnavox sonar-doppler + Arma-Brown (degrees) 44 - Latitude calc. from Raytheon sonar-doppler + Robertson (radians) 45 - Longitude calc. from Raytheon sonar-doppler + Robertson (radians) 46 - Speed calc. from Raytheon sonar-doppler (knots) 47 - Course calc. from Raytheon sonar-doppler + Robertson (degrees) 48 - Latitude calc. from spare log (radians) 49 - Longitude calc. from spare log (radians) 50 - Speed calc. from spare log (knots) . 51 - Course calc. from spare log (degrees) 52 - Latitude calc. from Radio nav (radians) 53 - Longitude calc. from Radio nav (radians) 54 - Speed calc. from Radio nav (knots) 55 - Course calc. from Radio nav (degrees) 56 - Latitude from MX1107RS (radians) 57 - Longitude from MXl107RS (radians) 58 - Speed from MX1107RS (knots) 59 - Course from MX1107RS (degrees) 60 - Latitude from MXl142 (radians) 61 - Longitude from MXl142 (radians) 62 - Speed from MXl142 (knots) 63 - Course from MXl142 (degrees) 64 - Not used

VARPL: All the raw data channels to be processed in Phase 1 were plotted as strip records on a Zeta-8 Plotter and used to determine what editing was required and as a guide for the setting of filter parameters.

FTAPE: This program was used for a variety of tasks:

(1) Removal of hardware/software flags in'bathymetric data using a routine in FTAPE called RAYWD. The Raytheon echo-sounder system provides, in addition to digital bathymetry, 'flags' indicating that the echo-sounder has lost track or that the digitiser gate is searching for an echo. These flags were removed as appropriate. Flagged values were replaced by the number 1.0 x 1010, to indicate absent data.

9

(2) Using the DLETE option in FTAPE, large blocks of irretrievable data in selected channels were deleted.

(3) Bad magnetic values were detected by the routine BADMG and replaced with unknowns ie, (1.0 x 1010).

(4) By the use of the routine FILL data gaps of up to 120 seconds were automatically interpolated across in the processing channels where it was necessary.

GMUL2: All the ship's velocity data from.the Magnavox and Raytheon Sonar Dopplers and paddle-log were converted from counts recorded during the acquisition to knots for the processing.

The gravity data during the acquisition were multiplied by a value of 100 bef02e being recorded on tape. These data were converted back to 10 x umsec- by dividing by 100 which was done using an option in GMUL2.

EDATA: This program was utilised for the manual editing of problem areas in the data that could not be filtered or automatically edited.

SALVG: (Water depth recovery): The problem with bathymetry recovey was to fill in all the gaps left after the Raytheon hardware/software flags were removed and to discriminate against the bad bathymetric values that still remained.

To accomplish this, a file was first created of manually digitised water depths at selected tie points usually at inflexion points in the water bottom. SALVG read this file in conjunction with the raw unprocessed data file, using the 12Khz data (channel 9) ,producing a processed data file of water depths (channel 57). SALVG performed a straight line interpolation between adjacent tie points and compared ~he interpolated depth with the 10-second digital depth. If the difference was less than a user-specified threshold, ·the digital depth was accepted and was used to replace the previous depth. If the difference was greater than the threshold, the 10-second digital depth was replaced by the interpolated depth.

In this way, the program tracked along the acceptable water depths, providing the threshold was small enough to reject bad data and large enough to accept the good data. In the case of the digital data being totally unacceptable, as during poor sea conditions, the threshold was set to a very small number (0.01 m) and the process became one of simple linear interpolation between adjacent tie points derived from each change in gradient. In practice, the interval between manually digitised tie points varied from several hours in the case of good digital 10-second data, to several minutes in the case of poor 10-second data or a very rugged seabed.

The success of this process, which is routinely applied to all Rig Seismic bathymetric data, can be seen in the following 'before and after ' plots of Figure 1.

10

FIGURE 1: Bathymetric traces before (lower) and after (upper) processingby program SALGV.

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Vertical scale: 20cm/1000m Horizontal scale: 45mm/hour.

11

FDATA: This program used a median non-linear filter to remove noisespikes in the navigation and the geophysidal data. Such a filter isessential for magnetic data, which is susceptible to spikes arising fromeither poor tuning of the magnetometer or from electrical interference.A filter threshold of 7.0 nT was used with a filter window length of 13samples for magnetic data. A threshold of 1 knot with a window length of13 samples was used for the velocity data.

EDATA: This is a utility program used for the manual editing of problemareas that are not able to be filtered or automatically edited.

MUFF: This program was used to anti-alias filter certain data channelsprior to resampling to 60-seconds for Phase 2 processing. Magnetics,gravity, incremental latitude/longitudes and velocities were filtered. ASING function was used for the magnetic and gravity data with a filterperiod of 180 seconds. The filter was extended to the third zero crossingof the abscissa each side of the filtered point. For the velocities,latitude and longitudes a filter period of 60 seconds was used.

DELTA: This program read in the smoothed velocity data outputfrom program MUFF and used the heading data from the Arma-Brown andRobertson gyro-compasses to compute incremental (delta) latitude andlongitudes every 10 seconds. This effectively created two dead-reckoningsystems.

INTEG: Re-integrated the filtered incremental latitude and longitudeoutput from DELTA over a specified time interval of 60 seconds. Theseincremental distances were now ready to be used in Phase 2 of theprocessing to compute the Dead-Reckoning vector over each satellite fixinterval.

VARPL/EDATA: All the processing channels were plotted on a Zeta-8plotter using VARPL and if required, program EDATA was used to correct anyremaining data problems.

RESAM: As the final stage in Phase 1 processing this program resampled the10 second data to 1 minute data to be used in Phase 2 by outputting every6th sample to an output file.

The program also reblocked the data from 64 channels in 1 minuteblocks of 10 second data (64x6), to 64 channels in 10 minute blocks of 1minute data (64x10) making the data ready for Phase 2 of the processingsequence.

Phase 2:

Phase 2 of data processing involved the processing of navigation datato produce an accurate set of latitudes and longitudes as a final productto tie seismic and other geophysical data. To achieve this result thefollowing programs were used.

CONCT: The data output from RESAM were concatenated to a single 1-minutedata file.

12

SATFX: Satellite data from the field tapes were stripped out usingthis program and two ASCII files were created, one for the MX1107RSdata and the other for the MX1142 data.

M0742: Magnavox MX1142 satellite fixes and the Magnavox MX1107RSsatellite fixes were merged together to create one file using thisprogram.

RESAF: This program re-formatted the satellite fix files created by .M0742 so that it could be read by the next steps in the satelliteprocessing and adjusted each fix to the nearest whole minute using theship's speed and heading at the time of the fix. The program also listedwhen the T-Set data were available, the computed T-set position and thedifference in kilometres between the two navigation systems.

FIXES: This program produced a listing of the re-formatted satellitefixes produced by RESAF and the accompanying data acquired at the time ofthe fixes. Table 5 is an example of that information.

TABLE 5 :Listing of satellite fix parameters produced by program FIXES.

* Sample survey only.

- "-- ._.

fIX F1l 11 liE LA' LOIIG SlSlEP. SAl OK ELE'I C01JH! nER IH.O~ [IHQR n! SLT ~tM C~D~

1 U.32:' .0<>121":0 20 S4.8H 152 ~5.318 1 H::' 2~O 1 31 3! 3 5£ .~6 16: 0 0

2 711.327.003_00 20 54.642 152 ~5.564 \107 48C 1 2Q 28 3 511 .11 4'1 0 0 3 n. n'. 020.1":00 205'1.013 '~1 57.'211'i' \107 '.HO II 3_ 35 3 SU 1.35 14'1 0 0 S

-16.327 .1j31M~ 21 ~7.nf. !~3 .074 I'O? 500 II 8 21 1- SE 4.34 159 0 0 "2

5 H.3:!:'.045100 21 37.10S 153 3.3" 1107 110 1 29 30 3 ~E. 5.37 150 ? 0

b 76.:!27 .()~O70~ 21 4L~~3 153 _.051 1I07 sr.1\ H 84 . 32 e SE. .13 ql 0 0 2 7 7c.~~7 .OblSO~ 22 .~~~ 1 ~7

"~ 7.0~Q 11~' 11~ ~ 31 31 :3 SI! .17 110 0 0 8 ?6.32:'.O~540'l 22 ~ • :3'12 153 7.684 n07 '2~() ~ s:! 27 '2 S! .02 2~7 0 0 '1 n.3::7.~7170'l 2~ 1l.'192 153 e.'1:!b "07 2~1) Y l' ~~ b HE .11 IS ~ 0

~~ :t.~:!?~~~O!'~ ~~ 25.~:~ 153 n.()~~ ~~~7 '2~~ ~ , ~ 2' :\ 5'l • ~ 2 ::~I 0 ~

'! 7t..!":!: .~'?OW: ~~ ~1 ~,g; 153 13.'t~Q n07 2'1') 1 6' 3~ :\ !llJ .10 150 0 0

Column headings as follows:

FIX - satellite fix number within file.

Ce'JR':E

174.0 1&9.8 "3.7 173.1 171.7 1:'~ .1 1;>~.l

16!5.e I bt..O ".,.., ~ I ..... ,

, 10.a

FIX TIME - computed time of fix in format SS.DDD.HXMMSS, where SS is the

LAT,LONG

SYSTEM SAT OK ELEV COUNT ITER GEOM ERROR DIR SLT,SLN CODE COURSE,SPEED

survey number (75), DDD is the Julian day number in 1987, and HHMMSS is the GMT time.

- Latitude and Longitude of fix in Degrees and Decimal Minutes.

- Magnavox 1107 or 1142, or dummy via (DFIX). - sata1lite number. - accepted (Y) or rejected (N) on-board. - maximum elevation of satellite (degrees). - number of doppler counts received. - number of iterations required to compute fix. - geometry of pass. - amount of shipboard update (n.miles). - direction of shipboard update (degrees). - standard deviation of latitude & longitude (metres). - error code if fix not accepted by sat nav. - vessel's course and speed at time of fix.

14

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•

SAT12: At this stage of Phase 2 processing, most of the satellite navigation processing takes place. The quality assessment of the satellite fixes was done and those of poor quality were deleted and the incremental latitudes and longitudes produced in Phase 1 were tied to the good satellite fixes. To achieve this, several passes of the program SAT12 were required as each round of satellite fix assessments was done. During each pass a number of routines were used:

Pass 1

a. SATEL: - read in the file of satellite fixes and stored them in memory. Any fix intervals with dubious speeds (too low or too high) were flagged in the output listing. Any intervals that were very short «15 minutes) or very long (>120 minutes) were also flagged.

b. DRNAV: - used the incremental latitude/longitudes stored in the Phase 1 file and the satellite fix information to compute the DR path (or DR vector) for each satellite fix. This was saved as an ASCII parameter file.

c. CALNV: - read the DR file created by DRNAV and computed the ratio of the average DR velocity to the velocity computed from successive satellite fixes. This was done for each DR system used, and the results were listed.

d. CALPL: - Produced a line printer plot of the velocity ratios for each satellite fix interval.

Pass 2

a. CFACT: - used the DR file and a user-created calibration factor interval file to compute velocity calibration factors for each DR system.

b. APROX: - used the calibration factors computed in CFACT and the DR file to produce an approximately calibrated DR file.

c. ASSES: - used the approximately calibrated DR file created by APPROX to produce a line printer plot of the current and summed error vectors between satellite fixes. The plot was produced at a 10-minute sample interval.

The basis of satellite processing was that option 'ASSES' takes the summed latitude and longitude error vectors at each fix (ie. a running sum of the DR position to satellite fix position vectors at the time of each fix) and used a piece-wise cubic polynomial curve-fitting function (the Akima spline) to compute error vectors at all times between satellite fixes. It was assumed that the ensuing smooth variation of the error vector was due to ocean currents or winds. Poor quality fixes would produce unrealistic or possibly large and variable ocean currents. At each round of assessment (and usually at least three rounds were required for each file) the satellite fixes were checked wherever the summed error and current vectors suggested a problem. Fixes of poor quality were deleted for the next program run. The effect of this process can be seen

15

in the example in Figures 2 and 3.

SAT3: Used the final file of satellite fixes and the DR data to produce final positions for each DR system. This program again used the Akima spline to compute the assumed currents acting at all times between satellite fixes and applied those currents to the DR data to compute positions.

FINAV: As the final program in navigation processing, FINAV performed the following:

a. Computed final I-minute positions based on a 'mix' of DR, GPS and Hifix navigation systems according to a weighting parameter file specified by the user.

b. Converted the KSS-3l gravity value (which is relative to an arbitrary datum) to absolute gravity and applied a drift correction for the gravity meter.

c. Computed the Eotvos correction and added it to the absolute gravity to produce final gravity.

VARPL/EDATA/FIXTM/MUFF: Phase 2 positions, water depths, magnetic, and gravity data were plotted and edited where necessary as a final check. Data were then re-blocked using program FIXTM to 8 channels by 60 records per block (I-hour blocks). Final channel allocations are shown in Table 6. Gravity spikes were finally edited at turns using EDATA and filtered of sea noise using MUFF with a filter of IS-minute period.

TABLE 6. Final channel allocations

Channel number

I 2 3 4 5 6 7 8

Contents

Time (SS.DDD) Time (.HHMMSS) Latitude (radians) Longitude (radians) Water depth (metres) Gravity (pms-2) Total magnetic field (nT) Not used

Figures 2 & 3 (following pages) show satellite fix assessment plots for a part of Survey 75. 10-minute times (DD.HHMM) are along the bottom of the plot. Satellite fixes are indicated by the vertical row of dashes (eg. at 251.1010).

16

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DATA AVAILABILITY

Digital Data

a. Navigation^ M-75N0001T

b. Navigation, Gravity, Magnetics and Bathymetry^M-75N0002T

9-track, 1600 bpi, Phase Encoded ASCII records,80 characters per record, 10xl-minute records per block.

Inquires concerning the purchase of data should be addressedto:

Marketing Manager,Division of Marine Geosciences & Petroleum Geology,Bureau of Mineral Resources,GPO Box 378,Canberra, ACT 2601, Australia.

Maps

a. Track Maps^ Sheet No.^Product No.

1:1000000 Sheet Name

Townsville SE 55^ 1^M-75M0001PSE 56^ - 2^M-75M0002PClermont SF 55^ 3^M-75M0003PRockhampton SF 56^ 4^M-75M0004FBrisbane SG 56^ 5^M-75M0005P

b. Profile Maps

Bathymetric Profiles^1 to 3^M-75M0006PFree-Air Anomaly Profiles^1 to 3^M-75M0007PResidual Magnetic Anomaly Profiles^1 of 2^M-75M0008P

c. Post Maps

Bathymetric Values^ 1 to 3^M-75M0009PObserved Gravity Values^1 to 3^M-75M0010PObserved Magnetic Values^1 to 2^M-75M0011PObserved Magnetic Anomaly Values^1 to 2^M-75M0012P

NORTHEAST

145'00' 14G'OO'

11'00'

+

+

+

+

AUSTRALIAN NATIOHAL SPHEROID

UNlVERSAl ttERCILTOR _SPHERE'

WITH HATUIIAL SCAlE CORRECT

AT LATITUDE 0 00

14S'00'

+

+

+

AUSTRALIA 3 EDITION OF 1989/10/24

152'00' 15"'00' 155'00'

1,'00'

.. '

+ + 18'00'

+

+ +

+ +

+ + +

075.248.0600

NORTHEAST AUSTRALIA 3

SURVEY 7S (S07SFD)

Figure 4: Track map of BMR Marine Survey 75.

20