ARO88 HEADER FIELDS (Aeromagnetic Survey Data)

GEODAS Documentation Headers provide documentation for data files in the various GEODAS Data Exchange Formats.

Record Type

The Record type in GEODAS Headers is always set to 4, meaning Header Record.

Survey Identifier

Identifier supplied by the contributing organization, else given by NGDC in a manner which represents the survey data. It consists of 1 to 8 Uppercase Alphanumeric characters with - or / allowed.

Format Acronym

GEODAS covers several geophysical database types. Each database has a digital exchange format which includes both Survey Documentation (the Header) and data records. For aeromagnetic data:
ARO88 - Aeromagnetic Survey Header Format 1988


NGDC Number

A unique 8-character identifier assigned by NGDC to each survey in the database. The scheme for numbering is as follows:
The first 2 characters identify the source (for MGD77 or HYD93)
The first 4 characters identify the platform or project
The last 4 digits are assigned consecutively

ARO88 Parameters Surveyed

The geophysical parameters collected during this survey. The 5 codes for ARO88 Headers are as follows (in order in the field):
F - Total Field Magnetics
X - xyz Components
D - dhz Components
R - Residual Field Magnetics
O - Other (r = radiometrics)

File Creation Date

This is the date (YYYYMMDD) when the digital data records were last altered.

Source Organization

Institution, agency or other group which collected the data, or occasionally the group which contributed the data to NGDC.

Sequence Number

Each GEODAS Header is made up of 24 80-character records. The last 2 characters of each record is the sequence number, 01 through 24.

Country

The country which originally collected the survey data.

Platform Name

Name(s) of the ship, aircraft, etc. which collected the survey data.

Platform Type with Code

The Platform Type Code, followed by a plain language description, details the type of platform which collected the data:
0 - Unspecified
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 in platform type field

Chief Scientist(s) or Hydrographer(s)

The Chief Scientist or Hydrogapher is often the final source for information about the survey.

Project

The descriptive name for a survey or set of surveys, as given by the collecting organization. This may contain abbreviations and/or plain language descriptions.

Departure date

The starting date of this survey formatted as YYYYMMDD (Year,Month,Day).

Departure Port or Airport

Sarting place of survey, including city and country if known.

Arrival Date

The ending date of this survey formatted as YYYYMMDD (Year,Month,Day).

Arrival Port or Airport

Ending place of survey, including city and country if known

Flight Line Spacings

Flight line spacing and direction. (e.g. NW-SE 37 km.)

Airborne Magnetometer(s) Used

Type and model of magnetometer used. (e.g. Geometrics G801/3 Proton precession)

Aircraft Altitude

Altitude level the survey was conducted at. (e.g. 9000-11000 meters BAR)

Aircraft Velocity

Velocity survey was conducted at. (e.g. 120 knots)

Sampling Rate

The general rate the instrument sampled the data at. For bathymetry this is written as number of soundings per second (e.g. 1/second); for magnetics and gravity it is the instrument sampling rate in seconds.

Magnetics Sensor Tow Distance

The distance aft the platform in meters, at which the magnetics sensor was towed.

Magnetics Reference Field

Reference field used to determine residual magnetics value: (e.g. IGRF-85)

Total Aeromagnetic Observations

The total number of aeromagnetics data values in this file.

Magnetometer Sensitiviy

Instrument sensitivity. (e.g. .001 ntesla)

Data Parameter Format and Units Description

Describes the format of the data records in this file. Uses standardized names for each parameter followed by a Fortran edit descriptor:
LATITUDE(F9.5),LONGITUDE(F10.5),ALT-BAROMETRIC-FT(I5),TOTAL-MAG-FIELD-T(F6.1)

10 Degree Area Identifiers

These are a series of area identifiers based on a four-digit number which translates to a specific 10 degree by 10 degree area on the globe. MGD77 contains fields for up to 30 identifiers in Header Sequences 16 and 17. ARO88 has fields for up to 70 identifiers in Sequences 12 thru 16. The first field in the set is the number of identifiers for the survey. The identifiers themselves follow, the last being followed by 9999 unless all 30 or 70 fields are needed. The construction of the identifiers is as follows:

Quadrant - The first-digit identifies the quadrant of the world as follows:
Code Latitude Longitude
1 = North East
3 = South East
5 = South West
7 = North West

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

Survey Limits

The confines of the survey are represented by 4 values: top latitude, bottom latitude, left longitude, and right longitude. In the ARO88 Headers, these boundaries expand to the next whole degree.

Archival NGDC Tape Numbers

Internal NGDC tape numbers where data is archived.

Additional Documentation

Information about the survey not found in the Header fields, or where Header fields are inadequate.