**THE MARINE GEOPHYSICAL DATA EXCHANGE FORMAT - \"MGD77\"**

**(Bathymetry, Magnetics, and Gravity)**

> NATIONAL GEOPHYSICAL DATA CENTER
>
> NATIONAL ENVIRONMENTAL SATELLITE, DATA, AND INFORMATION SERVICE
>
> NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
>
> U.S. DEPARTMENT OF COMMERCE
>
> KEY TO GEOPHYSICAL RECORDS DOCUMENTATION NO. 10 (REVISED)
>
> COMPILED BY THE MGD77 TASK GROUP
>
> Allen M. Hittelman, Chairman
>
> Robert C. Groman
>
> Richard T. Haworth
>
> Troy L. Holcombe
>
> Graig McHendrie
>
> Stuart M. Smith
>
> National Geophysical Data Center
>
> Boulder, Colorado
>
> September 1977
>
> December 1981 (Revised by Dan Metzger)
>
> February 1989 (Revised by Dan Metzger)
>
> January 1993 (Revised by Dan Metzger)
>
> October 1995 (Revised by Dan Metzger)
>
> August 1998 (Revised by Dan Metzger)

### Table Of Contents

> INTRODUCTION\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.....I
>
> GENERAL
> DESCRIPTION\...\...\...\...\...\...\...\...\...\...\...\...\...II
>
> THE HEADER
> RECORD\...\...\...\...\...\...\...\...\...\...\...\...\....III
>
> THE DATA
> RECORD\...\...\...\...\...\...\...\...\...\...\...\...\...\....IV
>
> 10-DEGREE IDENTIFIER CODE\...\...\...\...\...\...\...\....APPENDIX A
>
> NGDC CONTACTS\...\...\...\...\...\...\...\...\...\...\...\....APPENDIX
> B

I. INTRODUCTION

In January of 1977, a group of 24 geophysical data

managers from academia, government, industry and foreign

countries participated in a workshop at the National

Geophysical Data Center (NGDC) in Boulder, Colorado. The

\"Workshop for Marine Geophysical Data Formats\" established

the basic outline of a new format for the exchange of

digital underway geophysics data. A six member task force

was formed to work with NGDC in implementing the decisions

of the workshop into the new format. By the end of 1977 the

\"MGD77\" format was being disseminated by NGDC as its

standard exchange format.

The \"MGD77\" format has experienced much success over

the past 15 years. It has been sanctioned by the Intergov-

ernmental Oceanographic Commission (IOC) as an accepted

standard for international data exchange, and it has been

translated into French, Japanese, and Russian. Most con-

tributors of data to NGDC now send transfer data over the

internet in the \"MGD77\" format.

This newest revision makes the MGD77 format \"Year 2000

Compliant\", ensuring it\'s success into 21st Century.

II\. GENERAL DESCRIPTION

The digital format presented, and referred to as

\"MGD77\", is an exchange format for marine geophysical data

(bathymetry, magnetics, and gravity) It is intended to be

used for the transmission of data to and from a data center

and may be useful for the exchange of data to and from a

data center and may be useful for the exchange of data

between marine institutions. Data is to be exchanged in

files, one file per survey operation. Generally each survey

operation is a port-to-port operation of a survey vessel,

but in some cases several port-to-port operations of the

same vessel are combined in single survey operation,

especially if this is the manner of organizing the data at

the contributing institution. Data may be exchanged on via

the Internet or on various mass storage devices such as 8mm

or 9 track tapes, removable disks. The National Geophysical

Data Center uses CD-ROM disks as its chief method of distribution

of these data.

Data Exchange

1\. For exchange of MGD77 data via mass storage files on

magnetic or optical media participants shall establish type

and format of the media to be exchanged.

2\. Each survey operation shall be contained in one file

with Header and Data Records, or in 2 files, one Header

file and one Data Record file. If the media is too small

to contain one survey the data may be continued on a second

media.

3\. Each survey operation shall have one MGD77 Header

consisting of 24 80-character logical records.

4\. The MGD77 data records are sequentially and chronologically

organized until the end of the file. The data records are 120

logical characters.

5\. A survey is defined as all observations that conveniently

constitute a survey operation (e.g., a port-to-port survey or

in some cases several surveys). A survey file(s) ideally

should not span two media.

6\. For sequential files, the MGD77 Header shall consist of

24 sequential records of 80 logical characters each separated

by an end-of-record character(s) and, if the data records are

in the same file, the Header shall be at the beginning of the

file. The MGD77 Data Records shall be 120 logical characters

each.

7\. 9 Track tapes should be recorded as ASCI 1600 or 6250 BPI.

The tape structure consists of physical records of 1920

characters each, a header followed by data records, separated

by inter-record gaps (IRG) and organized into files. The files

are separated by end-of-file (EOF) marks (sometimes called

tape marks).

III\. THE HEADER RECORD

The purpose of the Header Record is to document both

the content and structure of the geophysical data contained

within subsequent data records. In general, documentation

that is constant throughout the survey will be in the Header

Record, while documentation that is variable will be in the

Data Records.

For sequential files, the MGD77 Header consists of 24

80-character sequential records. For 9 track magnetic tapes

the MGD77 Header is a physical record (block) consisting of

1,920 characters. In both cases the data records follow

immediately with no intervening end-of-file marks.

The Header Record contains fields which are both fixed

and freely formatted. All field lengths within the Header

that have not been coded with information should be blank-

filled, and all plain language statements should be left-

justified. The Header consists of a \"sequence\" of twenty-

four 80-character images. The field lengths within the

Header Records are designed to allow one to read the

information (from magnetic tapes) as a series of 120-

character logical records \-- the same logical record length

as the data records.

To help the marine geophysical community prepare this

documentation, a coding pad is available free of charge from

the National Geophysical Data Center.

Format Conventions for the Header Record:

1\. All decimal points are implied.

2\. Leading zeros and blanks are equivalent.

3\. Unknown or unused fields are to be blank filled.

4\. All \"corrections\", such as time zone, diurnal magnetics,

and Eotvos, are understood to be added (e.g., time-zone

correction is the number of hours which must be added

to the recorded time to determine GMT).

\*\*\* CHANGES SINCE LAST REVISION \*\*\*

Several changes in the MGD77 Header were required in order to

make the format \"Year 2000 Compliant\" (Y2K Compliant):

SEQUENCE DESCRIPTOR CHANGE

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_-

01 RECORD TYPE Change from \"1\" to \"4\"

01 FILE CREATION DATE Change to include century

From 6 digits (col 32-37)

to 8 digits (col 32-39)

01 SOURCE INSTITUTION Change from 41 chars (col 38-78)

to 39 chars (col 40-78)

04 SURVEY DEPARTURE DATE Change to include century

From 6 digits (col 1-6)

to 8 digits (col 1-8)

04 PORT OF DEPARTURE Change from 34 chars (col 7-40)

to 32 chars (col 9-40)

04 SURVEY ARRIVAL DATE Change to include century

From 6 digits (col 41-46)

to 8 digits (col 41-48)

04 PORT OF ARRIVAL Change from 32 chars (col 47-78)

to 30 chars (col 49-78)

The following is a detailed description of the Header Record.

Fields can be of type integer, real or character. Fields that

represent whole numbers are integers Fields that contain a

decimal component are real, and fields that are alphanumeric

are character.

Character Field

Nos. Length Type Description

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Sequence No. 1

1 1 int RECORD TYPE - Set to \"4\" (Header)

***nncc*IDENT2**

2-9 8 char SURVEY IDENTIFIER

***nncc*CRUISE** Identifier supplied by the contributing

organization, else given by NGDC in

a manner which represents the data.

Identical to that in data record.

10-14 5 char FORMAT ACRONYM - Set to\"MGD77\"

***nncc*ACRNYM**

15-22 8 int DATA CENTER FILE NUMBER

***nncc*DCFNUM** Survey identifier bestowed by the data

***nncc*HDNUM1** center. First 2 chars indicate the

***nncc*HDNUM2** source, first 4 indicate platform.

***nncc*DANUM**

27-31 5 int PARAMETERS SURVEYED CODE

Status of geophysical parameters for

this survey.

COLUMN PARAMETER SURVEYED

***nncc*BATHCD/*nncc*BATHX** 27 bathymetry (e.g., 12

kHz or 3.5 kHz used

for bathymetry)

***nncc*MAGCD/*nncc*MAGX** 28 magnetics

***nncc*GRAVCD/*nncc*GRAVX** 29 gravity

***nncc*HRSSCD/*nncc*HRSSX** 30 high-resolution seismics

(e.g., 3.5 kHz)

***nncc*DPSSCD/*nncc*DPSSX** 31 deep penetration seismics

(e.g., large airgun)

CODE - (for columns 27-31)

0 or blank - unspecified

1 - Parameter NOT surveyed

3 - Parameter surveyed,

not contained in file

5 - Parameter surveyed,

contained in file

32-39 8 int FILE CREATION DATE (YYYYMMDD)

***nncc*DATE2** Date data records were last

altered (including century).

40-78 39 char SOURCE INSTITUTION

***nncc*INST** Organization which collected the

data. Include contributor if different

from collector.

79-80 2 int SEQUENCE NUMBER - Set to \"01\"

***nncc*SEQ1**

Sequence No. 2

1-18 18 char COUNTRY

***nncc*CNTRY**

19-39 21 char PLATFORM NAME

***nncc*PLTFRM**

40 1 int PLATFORM TYPE CODE

***nncc*PLTCD** 0 - Unspecified

***nncc*PLTX** 1 - Surface ship

2 - Submersible ship

3 - Aircraft

4 - Buoy

5 - Mobile land

6 - Fixed land

7 - Deep tow

8 - Anchored seafloor instrument

9 - Other, specify

41-46 6 char PLATFORM TYPE

***nncc*PLTTP** (e.g., \"SHIP\",\"PLANE\", \"SUB\", etc.)

47-78 32 char CHIEF SCIENTIST(S)

***nncc*SCI**

79-80 2 int SEQUENCE NUMBER - Set to \"02\"

***nncc*SEQ2**

Sequence No. 3

1-58 58 char PROJECT

***nncc*PROJ** (e.g., \"SURVOPS 6-69\",

\"INDOPAC, Leg3\")

59-78 20 char FUNDING

***nncc*FUND** (i.e. agency or institution)

79-80 2 int SEQUENCE NUMBER - Set to \"03\"

***nncc*SEQ3**

Sequence No. 4

1-8 8 int SURVEY DEPARTURE DATE (YYYYMMDD)

***nncc*DPDT**

9-40 32 char PORT OF DEPARTURE

***nncc*DPPRT** (i.e. city, country)

41-48 8 int SURVEY ARRIVAL DATE (YYYYMMDD)

***nncc*ARDT**

49-78 30 char PORT OF ARRIVAL

***nncc*ARPRT** (i.e. city, country)

79-80 2 int SEQUENCE NUMBER - Set to \"04\"

***nncc*SEQ4**

Sequence No. 5

1-40 40 char NAVIGATION INSTRUMENTATION

***nncc*NAVIN** (e.g. \"SAT/LORAN A/SEXTANT\")

41-78 38 char GEODETIC DATUM/POSITION

***nncc*NAVMTH** DETERMINATION METHOD

(e.g. \"WGS84/PRIM - SATELLITE,

SEC-LORAN A\")

79-80 2 int SEQUENCE NUMBER - Set to \"05\"

***nncc*SEQ5**

Sequence No. 6

1-40 40 char BATHYMETRY INSTRUMENTATION

***nncc*BATHIN** Include information such as

frequency, beam width, and sweep

speed of recorder.

41-78 38 char ADDITIONAL FORMS OF BATHYMETRIC DATA

***nncc*BATHDA** (e.g., \"MICROFILM\",

\"ANALOG RECORDS\")

79-80 2 int SEQUENCE NUMBER - Set to \"06\"

***nncc*SEQ6**

Sequence No. 7

1-40 40 char MAGNETICS INSTRUMENTATION

***nncc*MAGIN** (e.g., \"PROTON PRECESSION

MAG-GEOMETRICS G-801\")

41-78 38 char ADDITIONAL FORMS OF MAGNETICS DATA

***nncc*MAGDA** (e.g., \"PUNCH TAPE\",

\"ANALOG RECORDS\")

79-80 2 int SEQUENCE NUMBER - Set to \"07\"

***nncc*SEQ7**

Sequence No. 8

1-40 40 char GRAVITY INSTRUMENTATION

***nncc*GRAVIN** (e.g., \"L and R S-26\")

41-78 38 char ADDITIONAL FORMS OF GRAVITY DATA

***nncc*GRAVDA** (e.g., \"MICROFILM\", \"ANALOG

RECORDS\")

79-80 2 int SEQUENCE NUMBER - Set to \"08\"

***nncc*SEQ8**

Sequence No. 9

1-40 40 char SEISMIC INSTRUMENTATION

***nncc*SEISIN** Include the size of the sound

source, the recording frequency

filters, and the number of

channels (e.g., \"1700 cu. in.,

AIRGUN, 8-62 Hz, 36 CHANNELS\")

41-78 38 char FORMATS OF SEISMIC DATA

***nncc*SEISDA** (e.g., \"DIGITAL\", \"MICROFILM\",

\"NEGATIVES\", etc.)

79-80 2 int SEQUENCE NUMBER - Set to \"09\"

***nncc*SEQ9**

Sequence No. 10

1 1 char FORMAT TYPE

***nncc*FORMAT** Set to \"A\", which means format

contains integers, floating points,

and alphanumerics

2-75 74 char FORMAT DESCRIPTION

***nncc*FRTRN1** This is one method of reading

***nncc*FILL1** (not writing) the data in FORTRAN.

Set to the following:

\"(I1,A8,F5.2,4I2,F5.3,F8.5,F9.5,I1,F6.4,

F6.1,I2,I1,3F6.1,I1,F5.1,F6.0,F7.1,\"

(NOTE: continued in sequence no. 11)

79-80 2 int SEQUENCE NUMBER - Set to \"10\"

***nncc*SEQ10**

Sequence No. 11

1-17 17 char FORMAT DESCRIPTION

***nncc*FRTRN2** Continued, set to following:

***nncc*FILL2** \"F6.1,F5.1,A5,A6,I1)\"

41-43 3 int TOPMOST LATITUDE OF SURVEY \*\*

***nncc*LATTOP** (to next whole degree)

44-46 3 int BOTTOMMOST LATITUDE

***nncc*LATBOT**

47-50 4 int LEFTMOST LONGITUDE

***nncc*LONGLT**

51-54 4 int RIGHTMOST LONGITUDE

***nncc*LONGRT**

***nncc*FILL3**

79-80 2 int SEQUENCE NUMBER - Set to \"11\"

***nncc*SEQ11**

Sequence No. 12

1-3 3 real GENERAL DIGITIZING RATE OF

***nncc*DIGRT1** BATHYMETRY

In tenths of minutes.

The rate which is present within

the data records (e.g., if values were

coded every 5 minutes, set to \"050\")

4-15 12 char GENERAL SAMPLING RATE OF

***nncc*SMPRT1** BATHYMETRY

This rate is instrumentation dependent

(e.g., \"1/SECOND\")

16-20 5 real ASSUMED SOUND VELOCITY

***nncc*SNDVEL** In tenths of meters per second.

Historically, in the U.S., this

speed has been 800 fathoms/sec,

which equals 1463.0 meters/sec.;

however, some recorders have a

calibration of 1500 meters/sec

(e.g., \"14630\")

21-22 2 int BATHYMETRIC DATUM CODE -

***nncc*BATHDM** 00 - No correction applied (sea level)

***nncc*BATHDMX** 01 - Lowest normal low water

02 - Mean lower low water

03 - Lowest low water

04 - Mean lower low water spring

05 - Indian spring low water

06 - Mean low water spring

07 - Mean sea level

08 - Mean low water

09 - Equatorial spring low water

10 - Tropic lower low water

11 - Lowest astronomical tide

88 - Other, specify in

additional documentation

23-78 56 char INTERPOLATION SCHEME

***nncc*INTRPL** This field allows for a description

of the interpolation scheme used,

should some of the data records contain

interpolated values (e.g., \"5-MINUTE

INTERVALS AND PEAKS AND TROUGHS\").

79-80 2 int SEQUENCE NUMBER - Set to \"12\"

***nncc*SEQ12**

Sequence No. 13

1-3 3 real GENERAL DIGITIZING RATE OF

***nncc*DIGRT2** MAGNETICS

In tenths of minutes.

The rate which is present

within the data records.

4-5 2 int GENERAL SAMPLING RATE OF

***nncc*SMPRT2** MAGNETICS

In seconds.

This rate isinstrumentation dependent

(e.g., if the pulse rate is every 3 sec,

set to \"03\")

6-9 4 int MAGNETIC SENSOR TOW DISTANCE

***nncc*SENDST** In meters.

The distance from the navigation

reference to the leading sensor.

10-14 5 real SENSOR DEPTH

***nncc*SENDTH** In tenths of meters.

This is the estimated depth of the

lead magnetic sensor.

15-17 3 int HORIZONTAL SENSOR SEPARATION

***nncc*SENSEP** In meters.

If two sensors are used.

18-19 2 int REFERENCE FIELD CODE - This is the

***nncc*REFCD** reference field used to determine

the residual magnetics:

00 - Unused

01 - AWC 70

02 - AWC 75

03 - IGRF-65

04 - IGRF-75

05 - GSFC-1266

06 - GSFC (POGO) 0674

07 - UK 75

08 - POGO 0368

09 - POGO 1068

10 - POGO 0869

11 - IGRF-80

12 - IGRF-85

13 - IGRF-90

88 - Other, specify

20-31 12 char REFERENCE FIELD

***nncc*REFFLD** (e.g., \"IGRF-85\")

32-78 47 char METHOD OF APPLYING RESIDUAL FIELD

***nncc*RESFLD** The procedure used in applying

this reduction to the data

(e.g., \"LINEAR INTERP. in

60-mile SQUARE\")

79-80 2 int SEQUENCE NUMBER - Set to \"13\"

***nncc*SEQ13**

Sequence No. 14

1-3 3 real GENERAL DIGITIZING RATE OF GRAVITY

***nncc*DIGRT3** In tenths of minutes.

The rate present within the data records

4-5 2 int GENERAL SAMPLING RATE OF GRAVITY

***nncc*SMPRT3** In seconds.

This rate is instrumentation dependent.

If recordingis continuous, set to \"00\"

6 1 int THEORETICAL GRAVITY FORMULA CODE

***nncc*TGFMCD** 1 - Heiskanen 1924

2 - International 1930

3 - IAG System 1967

4 - IAG System 1980

8 - Other, specify

7-23 17 char THEORETICAL GRAVITY FORMULA

***nncc*TGFM** (e.g., \"INTERNATIONAL \'30\", \"IAG

SYSTEM (1967)\", etc.)

24 1 int REFERENCE SYSTEM CODE

***nncc*RFSYCD** Identifies the reference field:

1 - Local system, specify

2 - Potsdam system

3 - System IGSN 71

9 - Other, specify

25-40 16 char REFERENCE SYSTEM

***nncc*RFSY** (e.g., \"POTSDAM SYSTEM\",

\"SYSTEM IGSN 71\", etc.)

41-78 38 char CORRECTIONS APPLIED

***nncc*CORRCT** Drift, tare and bias corrections

applied. (e.g., \"+0.075 MGAL PER DAY\")

79-80 2 int SEQUENCE NUMBER - Set to \"14\"

***nncc*SEQ14**

Sequence No. 15

1-7 7 real DEPARTURE BASE STATION GRAVITY

***nncc*DGRVBS** In tenths of milligals.

At sea level (Network value preferred.)

8-40 33 char DEPARTURE BASE STATION DESCRIPTION

***nncc*DGRVDS** Indicates name and number of station

41-47 7 real ARRIVAL BASE STATION GRAVITY

***nncc*AGRVBS** In tenths of milligals.

At sea level (Network value preferred.)

48-78 31 char ARRIVAL BASE STATION DESCRIPTION

***nncc*AGRVDS** Indicates name and number of station

79-80 2 int SEQUENCE NUMBER - Set to \"15\"

***nncc*SEQ15**

Sequence No. 16

1-2 2 int NUMBER OF 10-DEGREE IDENTIFIERS \*\*

***nncc*AREAID** This is the number of 4-digit

***nncc*FILL4** 10-degree identifiers, excluding

the \"9999\" flag, which will

follow this field. (see APPENDIX B)

4-78 75 int 10-DEGREE IDENTIFIERS - This is a

***nncc*AEREAF1** series of 4-digit codes,separated by

commas, which identify the 10-degree

squares through which the survey

collected data (see APPENDIX B).

Code \"9999\" after last identifier.

79-80 2 int SEQUENCE NUMBER - Set to \"16\"

***nncc*SEQ16**

Sequence No. 17

1-75 75 int 10-DEGREE IDENTIFIERS

***nncc*AREAF2** Continued

79-80 2 int SEQUENCE NUMBER - Set to \"17\"

***nncc*SEQ17**

Sequence Nos. 18-24

1-78 78 char ADDITIONAL DOCUMENTATION

***nncc*ADD18... *Nncc*ADD24** information concerning this survey

not contained in header fields.

79-80 2 int SEQUENCE NUMBER (\"18\" thru \"24\")

***nncc*SEQ18... *nncc*SEQ24**

\_\_\_\_\_\_\_\_\_\_\_\_\_\_

\*\* Fields 41-54 in sequence Number 11 and Fields 1-78 in

sequence numbers 16 and 17 may be blank filled by the

contributing institution. The data center can determine

these numbers by a computer search of the latitudes and

longitudes within the MGD77 file.

IV\. THE DATA RECORD

The data record presents underway marine geophysical

data in a correlative manner. Geophysical data (bathymetry,

magnetics, and gravity) and seismic identification (shot-point

identification) are presented with a corresponding time and

position. Documentation that is variable throughout the

survey also is included within each data record. If primary

navigation exists at a juncture where no geophysical data

are present, this record should be included with the data

parameter fields left unused (9s filled).

The logical record length is 120 characters and the

blocking factor is 16 logical records per physical record

(i.e., 1,920 characters).

\*\*\* CHANGES SINCE LAST REVISION \*\*\*

Several changes in the MGD77 Record were required in order to

make the format \"Year 2000 Compliant\" (Y2K Compliant):

DESCRIPTOR CHANGE

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_-

DATA-RECORD TYPE Change from \"3\" to \"5\"

(col 1)

TIME ZONE CORRECTION Change from hundredths of hours to hours

From 5 digits (col 10-14)

to 3 digits (col 10-12)

YEAR Change to include century

From 2 digits (col 15-16)

to 4 digits (col 13-16)

Format Conventions:

1\. All decimal points are implied.

2\. Leading zeros and blanks are equivalent.

3\. Unknown or unused fields are to be filled with 9s

(DO NOT BLANK FILL).

4\. All \"corrections\", such as time zone, diurnal

magnetics, and Eotvos, are understood to be added

(e.g., time-zone correction is the number of hours

which must be added to the recorded time to

determine GMT).

Length

Character of Fortran

Nos. Field code Description

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

1 1 int DATA RECORD TYPE

***nncc*IDENT** Set to \"5\" for data record.

2-9 8 char SURVEY IDENTIFIER

***nncc*CRUISE** Identifier supplied by the contributing

organization, else given by NGDC in

a manner which represents the data.

Identical to that in header record.

10-12 3 int TIME-ZONE CORRECTION

***nncc*TZ** Corrects time (in characters 13-27)

to GMT when added: equals zero when

time is GMT. Timezone normally falls

between -13 and +12 inclusively.

13-16 4 int YEAR

***nncc*DATE** including century (e.g. 1972)

17-18 2 int MONTH

(e.g. May is represented as 05)

19-20 2 int DAY

Day of month

21-22 2 int HOUR

***nncc*TIME** Hour of day

23-27 5 real MINUTES X 1000

28-35 8 real LATITUDE X 100000

\+ = North; - = South

Between -9000000 and 9000000

36-44 9 real LONGITUDE X 100000

\+ = East; - = West

Between -18000000 and 18000000

45 1 int POSITION TYPE CODE

***nncc*PSTN** Indicates how lat/lon was obtained:

***nncc*PSTNX** 1 = Observed fix

3 = Interpolated

9 = Unspecified

46-51 6 real BATHYMETRY, 2- WAY TRAVELTIME

***nncc*BTRVL** In ten-thousandths of seconds.

Corrected for transducer depth and

other such corrections, especially in

shallow water

52-57 6 real BATHYMETRY, CORRECTED DEPTH

***nncc*BDPTH** In tenths of meters.

58-59 2 int BATHYMETRIC CORRECTION CODE

***nncc*BCORCD** This code details the procedure

***nncc*BCORX** used for determining the sound

velocity correction to depth:

01-55 Matthews\' Zones with zone

59 Matthews\' Zones, no zone

60 S. Kuwahara Formula

61 Wilson Formula

62 Del Grosso Formula

63 Carter\'s Tables

88 Other (see Add. Doc.)

99 Unspecified

60 1 int BATHYMETRIC TYPE CODE

***nncc*TYPCD** Indicates how the data record\'s

***nncc*BTYPX** bathymetric value was obtained:

1 = Observed

3 = Interpolated (Header Seq. 12)

9 = Unspecified

61-66 6 real MAGNETICS TOTAL FIELD, 1ST SENSOR

***nncc*MTOT1** In tenths of nanoteslas (gammas).

For leading sensor. Use this field

for single sensor.

67-72 6 real MAGNETICS TOTAL FIELD, 2ND SENSOR

***nncc*MTOT2** In tenths of nanoteslas (gammas).

For trailing sensor.

73-78 6 real MAGNETICS RESIDUAL FIELD

***nncc*MRES** In tenths of nanoteslas (gammas).

The reference field used is in

Header Seq. 13.

79 1 int SENSOR FOR RESIDUAL FIELD

***nncc*MRESS** 1 = 1st or leading sensor

***nncc*MRESX** 2 = 2nd or trailing sensor

9 = Unspecified

80-84 5 real MAGNETICS DIURNAL CORRECTION -

***nncc*MDI** In tenths of nanoteslas (gammas).

(In nanoteslas) if 9-filled

(i.e., set to \"+9999\"), total

and residual fields are assumed

to be uncorrected; if used,

total and residuals are assumed

to have been already corrected.

85-90 6 F6.0 DEPTH OR ALTITUDE OF MAGNETICS SENSOR

***nncc*MDPTH** In meters.

\+ = Below sealevel

\- = Above sealevel

91-97 7 real OBSERVED GRAVITY

***nncc*GOBS** In tenths of milligals.

Corrected for Eotvos, drift, and

tares

98-103 6 real EOTVOS CORRECTION

***nncc*GEOTV** In tenths of milligals.

E = 7.5 V cos phi sin alpha +

0.0042 V\*V

104-108 5 real FREE-AIR ANOMALY

***nncc*GFAIR** In tenths of milligals.

Free-air Anomaly = G(observed) -

G(theoretical)

109-113 5 char SEISMIC LINE NUMBER

***nncc*SLINE** Used for cross referencing with

seismic data.

114-119 6 char SEISMIC SHOT-POINT NUMBER

***nncc*SSHOT**

120 1 int QUALITY CODE FOR NAVIGATION -

***nncc*QC** 5 - Suspected, by the

***nncc*QCX** originating institution

6 - Suspected, by the data

center

9 - No identifiable problem

found

(NOTE - Institution will most

frequently 9-fill this field;

however, should they wish to

code a \"5\", the data center will

not contradict. The data

center\'s quality control

program, which performs (among

other checks) a vectorial

analysis of the navigation, is

available in a printout form

upon request.)

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APPENDIX B 10-DEGREE-SQUARE IDENTIFIER CODE

A 10-degree-square area can be easily identified by

constructing a four-digit number. The components of this

number, in order of their construction are described as

follows:

Quadrant - A one-digit number identifies the quadrant of the

world with the following significance to each digit:

1st digit = Quadrant number

Qc Code Latitude Longitude

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1 North East

3 South East

5 South West

7 North West

10-Degree Square - The next three digits identify a unique

10-degree square; thus, the significant digits consist of:

2nd digit = Tens digit of degrees latitude

3rd digit = Hundreds digit of degrees longitude

4th digit = Tens digit of degrees longitude

10-DEGREE SQ IDENT. CODE

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EXAMPLES: Qc Lat Long Long

\(i\) 37 degrees 48\'S, 4 degrees 13\'E 3 3 0 0

\(ii\) 21.6 degrees S, 14.3 degrees W 5 2 0 1

\(iii\) 34 degrees 28\'N, 143 degrees 27\'W 7 3 1 4

\(iv\) 75 degrees N, 43 degrees E 1 7 0 4

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APPENDIX B NGDC CONTACTS

Dan Metzger: (303) 497-6542 dmetzger@ngdc.noaa.gov

or

John Campagnoli : (303) 497-3158 jcampagnoli@ngdc.noaa.gov

National Geophysical Data Center

NOAA, E/GC3

325 Broadway

Boulder, CO 80303-3328

TELEX 592811 NOAA MASC BDR

FAX (303) 497-6513

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