MGD77 Data (Bathymetry, Geomagnetism, Gravity)
Header Record
Information relating to the survey navigation in general as well as observation equipment, observation method and data processing method are recorded in the header record.Header record is comprised of 80 bytes long records of 24 pieces.
Unused field is left blank , the letters are to fill in the left-justified.
Format rules of the header record:
- All decimal points are omitted.
- Beginning of zero and space is treated equally.
- Unknown or unused field is filled in a blank.
- All of revised and correction values (time zone correction, diurnal variation correction of geomagnetism, Eotvos correction of gravity) are added and used. (Ex. revised value of the time zone is the time to be added to time recorded in the data record in order to determine the GMT.
Header Record (No.1)
Field Data Type Item Name Explanation 01 Integer Record Type Setting Value "4" (header record) 02-09 Letter Measuring Identification Number Measuring ID number allocated by the survey institute or by US NGDC
Same as the survey ID number used in the data record10-14 Letter Format Acronym Setting Value "MGD77" 15-22 Integer Data Center File Number Measuring ID number provided by the data center 23-26 Unused Blank 27-31 Measuring Item Implementation Code Implementation status of each observation item in this measurement
(Cord in the field 27-31)
0 or blank: missing
1: Not measured
3: Measured but not recorded in this file
5: Measured and recorded in this file27/TD> Integer Bathymetry Example : Use of 12 kHz or 3.5 kHz 28 Integer Geomagnetism 29 Integer Gravity 30 Integer High Resolution Sonic Survey e.g. ： 3.5kHz 31 Integer High Output Sonic Survey e.g. : Large air gun 32-39 Integer Date of File Creation Last updated date of the data record (including century)
（YYYYMMDD）
Year: YYYY, Month: MM, Day: DD40-78 Letter Survey Institute Name of Survey Institute 79-80 Integer Record Serial Number Setting Value "01" Header Record (No.2)
Field Data Type Item Name Explanation 01-18 Letter Country name 19-39 Letter Name of platform 40 Integer Platform type cord 0: Missing
1: Vessel
2: Submersible boat
3: Aircraft
4: Buoy
5: Mobile ground station (automobile)
6: Fixed ground station
7: Towing device
8: Seabed setting device
9: Others, describe names in the field 41-4641-46 Letter Platform type name e.g. ： such as "SHIP", "PLANE", "SUB" 47-78 Letter Chief researcher Name of chief researcher 79-80 Integer Record serial number Setting Value "02" Header Record (No. 3)
Field Data Type Item Name Explanation 01-58 Letter Plan e.g. ： "SURVOPS 6-69", "INDOPAC, Leg 3" 59-78 Letter Financial resources Fund investor (Government agency, Research institute, etc.) 79-80 Integer Record serial number Setting Value "03" Header Record (No.4)
Field Data Type Item Name Explanation 01-08 Integer Departure date YYYYMMDD
Year: YYYY, Month: MM, Day: DD09-40 Letter Departure port Name of city, Country name 41-48 Integer Arrival date YYYYMMDD
Year: YYYY, Month: MM, Day: DD49-78 Letter Arrival port Name of city, Country name 79-80 Integer Record serial number Setting Value "04" Header Record (No.5)
Field Data Type Item Name Explanation 01-40 Letter Nautical equipment e.g. ： "SAT/LORAN A/SEXTANT" 41-78 Letter Positioning method e.g. ： "WGS84/PRIM - SATELLITE, SEC-LORAN A" 79-80 Integer Record serial number Setting Value "05" Header Record (No.6)
Field Data Type Item Name Explanation 01-40 Letter Echo sounder Inclusion of information such as frequency, beam width, "sweep speed" of recorder 41-78 Letter Record other than sounding data e.g. ： "MICROFILM", "ANALOG RECORDS" 79-80 Integer Record serial number Setting Value "06" Header Record (No.7)
Field Data Type Item Name Explanation 01-40 Letter Magnetometer e.g. ： "PROTON PRECESSION MAG-GEOMETRICS G-801" 41-78 Letter Record other than magnetometer data e.g. ： "ANALOG RECORDS" 79-80 Integer Record serial number Setting Value "07" Header Record (No.8)
Field Data Type Item Name Explanation 01-40 Letter Gravimeter e.g.： "L and R S-26" 41-78 Letter Record other than gravity data e.g. ： "MICROFILM", "ANALOG RECORDS" 79-80 Integer Record serial number Setting Value "08" Header Record (No.9)
Field Data Type Item Name Explanation 01-40 Letter Sonic survey instrument Including the information of sound source, frequency band, number of frequency (e.g. "1700 cu. in., AIRGUN, 8-62 Hz, 36 CHANNELS") 41-78 Letter Form of sonic survey record e.g. such as "DIGITAL", "MICROFILM", "NEGATIVES" 79-80 Integer Record serial number Setting Value "09" Header Record (No.10)
Field Data Type Item Name Explanation 01 Letter Format type Setting Value "A" : means the inclusion of Integer type, Floating-point type, Letter (Alphanumeric) type 02-75 Letter Format description Description of data section format in FORTRAN type
Set as follows :"(I1,A8,I3,I4,3I2,F5.3,F8.5,F9.5,I1,F6.4,F6.1,I2,I1,3F6.1,I1,F5.1,F6.0,F7.1,":
(Follow the next record)76-78 Unused Blank 79-80 Integer Record serial number Setting Value "10" Header Record (No.11)
Field Data Type Item Name Explanation 01-19 Letter Format description Continuance of the previous record.. Set as follows :
"F6.1,F5.1,A5,A6,I1)"20-40 Unused Blank 41-43 Integer Latitude of the uppermost end of the survey waters Unit is degree* 44-46 Integer Latitude of the lowermost end of the survey waters Unit is degree* 47-50 Integer 測Longitude of the leftmost end of the survey waters Unit is degree* 51-54 Integer Longitude of the rightmost end of the survey waters Unit is degree* 55-78 Unused Blank 79-80 Integer Record serial number Setting Value "11" Header Record (No.12)
Field Data Type Item Name Explanation 01-03 Real Number Bathymetry value recording interval Unit is in minutes, to 1/10 place
Recording interval to the data record (e.g.: for 5 minutes interval, the setting value is "050".04-15 Letter Bathymetry value measuring interval alue that depends on the sounder (e.g. : "1/SECOND" 16-20 Real Number assumed underwater sound velocity Unit is in m/sec, to 1/10 place
Historically, this velocity in the US is 800 fathoms/sec = 1463.0 m/sec but this is corrected to 1500.0 m/sec in some recorders.
(e.g. : for 1463.0 m/sec, the setting value is "14630"21-22 Integer Bathymetry datum level code 00: Non-correction (Sea surface)
01: Lowest Low-water Level
02: Average Low-water Level
03: Lowest Low-water level
04: Mean lower low-water spring
05: Indian spring low water
06: Mean low-water spring
07: Mean water level
08: Mean low water level
09: Equator low water level spring
10: Regression lower low-water level
11: Lowest Astronomical Tide
88: Others ? Specify with additional documents (Header record No.19～No.24)23-78 Letter Interpolation In case the interpolation value is used for the Bathymetry value with the data record, describe the interpolation method used in the calculation of its value (e.g. : "5-MINUTE INTERVALS AND PEAKS AND TROUGHS") 79-80 Integer Record serial number Setting Value "12" Header Record (No.13)
Field Data Type Item Name Explanation 01-03 Real Number Recording interval of magnetic force value Unit is in minutes, to 1/10 place
Recording interval to the data record04-05 Integer Measuring interval of magnetic force value Unit is in seconds
Value that depends on the magnetometer (e.g. : for 3 seconds interval, the Setting Value is "03")06-09 Integer Towing distance of magnetic force sensor Unit is in meters
Distance to the magnetic sensor from the positioning point10-14 Real Number Magnetic sensor depth Unit is in meters, to 1/10 place
Estimated depth of magnetic force sensor15-17 Integer Horizontal interval of magnetic sensor Unit is in meters
Describe when two sensors are used18-19 Integer Standard magnetic field code Cords of standard magnetic field used for determining the magnetic abnormal value :
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
14: IGRF-95
15: IGRF-00
88: Others, describe the contents in the field 20-3120-31 Letter Model name of standard magnetic field e.g. ： "IGRF-85" 32-78 Letter Calculation value of magnetic abnormal value Description of method used for the calculation of magnetic abnormal value (e.g. : "LINEAR INTERP. in 60-mile SQUARE") 79-80 Integer Record serial number Setting Value "13" Header Record (No.14)
Field Data Type Item Name Explanation 01-03 Real Number Recording interval of gravity value Unit is in minutes, to 1/10 place
Recording interval to data record04-05 Integer Measuring interval of gravity value Unit is in seconds
Value that depends on the gravity meter and set it to "00" if it is continuously measured06 Integer Regular gravity calculating formula code 1: Heiskanen 1924
2: International 1930
3: IAG System 1967
4: IAG System 1980
8: Others, describes the contents in the field 07-2307-23 Letter Name of regular gravity calculating formula e.g. ： such as "INTERNATIONAL '30", "IAG SYSTEM (1967)" 24 Integer Reference system code 1: Local system、Describes the contents in the field 25-40
2: Potsdam system
3: System IGSN 71
9: Others, describes the contents in the field 25-4025-40 Letter Description of reference system e.g. ：such as "POTSDAM SYSTEM","SYSTEM IGSN 71" 41-78 Letter Correction applicable method escription related to the correction of drift and bias, etc. (e.g. : "+0.075 MGAL PER DAY") 79-80 Integer Record serial number Setting Value "14" Header Record (No.15)
Field Data Type Item Name Explanation 01-07 Real Number Gravity value of departure point Value above sea level Unit is in milligals to 1/10 place 08-40 Letter Description of departure point Name and number of departure point 41-47 Real Number Gravity value of arrival point Value above sea level Unit is in milligals to 1/10 place 48-78 Letter Description of arrival point Name and number of arrival point 79-80 Integer Record serial number Setting Value "15" Header Record (No.16)
Field Data Type Item Name Explanation 01-02 Integer 1Number of 10 degrees gridded areas* Measuring areas is included. Number of 10 degrees gridded areas (list is described below)
In addition, cord "9999" is not put in the number. （Refer to Appendix A）03 Unused Blank 04-78 Integer 10 degrees gridded areas* Measuring areas is included. List of 10 degrees gridded areas code (expressed with 4 digits). Comma delimited (Refer to Appendix A）
Cord "9999" follows the last 10 degrees gridded areas cord.79-80 Integer Record serial number Setting Value "16" Header Record (No.17)
Field Data Type Item Name Explanation 01-75 Integer 10 degrees gridded areas* List of 10 degrees gridded areas code. Continuance of the previous record. 76-78 Unused Blank 79-80 Integer Record serial number Setting Value "17" ヘッダーレコード（No. 18 ～ No. 24）
Field Data Type Item Name Explanation 01-78 Letter Additional descriptive items Describe the information which is not included in the header record 79-80 Integer Record serial number "24" from "18" *Field 41-54 of the record No.11 (latitude/longitude of measurement range) and Field 1-78 of the record No.16～No.17 (number and list of 10 degree gridded areas code) may be filled with a blank at the time of file creation. Data center calculates these values for the determination from the latitude and longitude of the data included in the MGD77 file.
Data Record
Location, Bathymetry, total magnetic force, gravity and sonic survey information at the observation time are described in the data record.Format Rule of Data Record:
- All decimal points are omitted.
- Leading zeros and spaces are treated as an equality.
- Unknown or unused field is filled in "9".
- All of revised and correction values (time zone correction, diurnal variation correction of geomagnetism, Eotvos correction of gravity) are added and used. (Ex. revised value of the time zone is the time to be added to time recorded in the data record in order to determine the GMT.
| Field | Data Type | Item Name | Explanation |
|---|---|---|---|
| 001 | Integer | Record type | Setting Value "5" (Data Record) |
| Letter | ID number | Measuring ID number allocated by the survey institute or the same center at the time of re-submission of the data to the US NGDC Same as the survey ID number used in the data record |
|
| 010-012 | Integer | Revised value of time zone | Values to be added to correct the time of the field 13-27 in GMT. Unit is in hours In the case where the GMT is used for the time of the field 13-27, the value in this column becomes zero. Normally, values between "-13" and "+12" |
| 013-016 | Integer | Year | Observation year includes century (e.g. 1972) |
| 017-018 | Integer | Month | Observation month (e.g. 1May is "05") |
| 019-020 | Integer | Day | Observation day |
| 021-022 | Integer | Time | Observation hour (00-23) |
| 023-027 | Real Number | Minute x 1000 | Observation minute (e.g. for 3.1 minute, the setting value is "03100") |
| 028-035 | Real Number | Latitude x 100000 | + : North latitude, - : South latitude, Unit is in degrees Between "-9000000" (-90.00000°) and "9000000" (90.00000°) |
| 036-044 | Real Number | Longitude x 100000 | + : East Longitude, - : Wets longitude, Unit is in degrees Between "-18000000" (-180.00000°）and "18000000" (180.00000°) |
| 045 | Integer | Positioning type code | Type of latitude/longitude 1: Station 3: Interpolation point 9: Interpolation point |
| 046-051 | Real Number | Reciprocating time of bathymetry - sonic wave | Unit is in seconds to 1/10000 place |
| 052-057 | Real Number | Bathymetry - corrected bathymetry | Unit is in meters to 1/10place |
| 058-059 | Integer | Bathymetry corrected cord | Describe the procedure used for the correction of sonic velocity in bathymetry. 01-55 : Matthews' zone (#1-#55 59: Matthews' zone (number is unknown) 60: S. Kuwahara Formula 61: Wilson Formula 62: Del Grosso Formula 63: Carter's Tables 88: Others (describe in the additional description items of the header record No.18～No.24) 97: Use 1500m/s 98: Procedure is unknown 99: Missing |
| 060 | Integer | Sounding type cord | Type of bathymetry 1: Actual value 3: Interpolation value ? method is described in the header recoed-2 9: Missing |
| 061-066 | Real Number | Total magnetic force value (No. 1 sensor) | Unit is in nanoteslas (nT) (=gamma) to 1/10 place For the first or front sensor. Also used in the case of a single sensor. |
| 067-072 | Real Number | Total magnetic force value (No. 2 sensor) | Unit is in nanoteslas (nT) (=gamma) to 1/10 place For the second or rear sensor. |
| 073-078 | Real Number | magnetic abnormal value | Unit is in nanoteslas (nT) (=gamma) to 1/10 place Standard magnetism used is described in the header record No.13 |
| 079 | Integer | Sensor used for calculation of magnetic abnormal value | 1: First or front sensor 2: Second or rear sensor. 9: Missing |
| 080-084 | Real Number | Diurnal variation corrective value of geomagnetism. | Unit is in nanoteslas (nT) (=gamma) to 1/10 place If this field is satisfied with "9" (e.g. "+9999"), it is assumed that total magnetic force value and magnetic abnormal value were not corrected. |
| 085-090 | Real Number | Depth/altitude of magnetic sensor | Unit is in: meters +: below the sea level -: above the sea level |
| 091-097 | Real Number | Actual value of gravity | Unit is in milligals to 1/10 place |
| 098-103 | Real Number | Eotvos corrective value | Unit is in milligals to 1/10 place E = 7.5 V cosφ sinα + 0.0042 V*V |
| 104-108 | Real Number | Free air abnormal value | Unit is in milligals to 1/10 place Free air abnormal value = Gravity Value (actual value) - Gravity Value (theoretical value) |
| 109-113 | Letter | Sonic survey ? measuring line number | Used for checking of sonic survey data |
| 114-119 | Letter | Sonic survey ?shot point number | |
| 120 | Integer | Positioning accuracy cord | 5: Judged that observer is suspicious 6: Judged that the data center is suspicious 9: No problems |
Appendix A 10 Degrees Gridded Area Cord
10 degrees gridded area cord is comprised of four digits of numbers about 10 degrees square grid to be surrounded by latitude and longitude lines divisible by 10 degrees.- Quadran
- The first digit indicates the quadrant divided by surface to be made in the standard meridian and the 180-degree meridian and the surface of equator.
Ist digit = Quadrant number (Qc Code)
Qc Code Latitude Longitude 1 North Lat. East Long. 3 South Lat. East Long. 5 South Lat. West Long. 7 North Lat. West Long.
- 10 Degrees Grid
- The following 3digits numbers indicate the area of 10 degrees square.
2nd digit = Number of the tens place with the lower latitude (degree) among the meridian which surrounds the areaExamples:
3rd digit = Number of the hundreds place with the smaller longitude (degree) among the parallel which surrounds the area
4th digit = Number of the tens place with the smaller longitude (degree) among the parallel which surrounds the area
Qc, Lat., Long., Long.: 10 degrees grid area code
Qc Lat. Long. Long. (1) 37°48' S, 4°13' E 3 3 0 0 (2) 21.6°S, 14.3°W 5 2 0 1 (3) 34°28' N, 143°27' W 7 3 1 4 (4) 75°N, 43°E 1 7 0 4