Geophysical Data Processing Programs and
Program Descriptions

• ATS1 -- Calculated current velocities between fixes from integrated ship's velocities and fix positions. This program was the first step in the processing of gravity acquisition data to SEAG1 or SEAG2 format.

ATS1 processed acquired gravity data in AQU1 format and navigation in FIXSE format. By integration of the velocities recorded in AQU1 format over the interval between fixes obtained from the FIXSE navigation data, ATS1 would compute the north and east velocities required to make the computed ship's position equal to the fix position. These velocities are known as the "current velocities" and are output along with fix times and fix positions in the NAVC7 format data. The NAVC7 data output from ATS1 are recombined with the AQU1 data and input to program ATS3 for final gravity processing.

• ATS3 -- Computed the free-air gravity anomaly, plus the Bouguer anomaly if corrected depth was available from the input data. A continuous fix stream is computed using the ship's velocity information and navigational corrections from the NAVC7 data output from program ATS1. The current velocities, provided by the NAVC7 records output from ATS1, are prorated on the basis of time and are used in the Eotvos calculation. Current velocities were not prorated for the position calculation. The velocities may be corrected for a consistent heading or speed error, and gravity may be corrected for systematic drift. Data are output in SEAG2 format.
• DTOB -- Merged break-slope bathymetry records in SEDEP format with navigation data in SEAG1, SEAG2 or FIXSE format and output MBATR format data.

Program DTOB processed SEDEP records and computed a position speed, heading and cumulative distance along the ship's track for each point by merging the data with SEAG or FIXSE navigation. Data were output in MBATR format data.

• ESORT -- Separated the output file of the aquisition program, EXEC, into files containing the component record types: gravity, one-minute automatically acquired bathymetry, and messages from the acquisition program itself. The desired geophysical data were then output in AQU1 format.
  The EXEC program was the data collection program integrated with the acquisiton hardware and responsible for logging of the digital data to magnetic tape. As previously mentioned, the EXEC program would also log system messages along with the valid data. In preparation of processing the data, these messages had to be sorted and removed from the actual data.

• EZTD -- Produces SEDEP formatted data from EASYD or SEDEP format input. If the Matthews' table correction numbers are given, then the program will also compute corrected water depths.
  To apply a Matthews' Table corrections, the data processor was required to create via some editor an editting table. Each record in this table included a start date and time and end date and time along with the selected Matthews' Table correction the processor selected to be applied for that time frame. Since EZTD based it's Matthews' Table correction on date and time, errors in the input record date field (e.g., duplicate records, invalid or out of sequence dates) needed to be corrected first. Program EZTD allowed the processor to detect these errors.

The editting table created by the processor could contain one record for the entire cruise, or several records spanning different portions of a cruise. Unfortunately, when a Matthews' Table correction was applied, it was most often one value applied over the entire cruise, and therefore the computed corrected depth values should be considered suspect.

• MANGS -- Took the observed magnetics value from either AQMAG , AQU1 , EASYM or SEAG and the ships's navigation data from either FIXSE or SEAG as the program data inputs. The selected input data were merged and the magnetic anomaly was computed. The magnetic anomaly was computed by calculating the regional field values at the four corners of a one-degree square containing the data point, interpolating the regional field value at the data point and subtracting this value from the observed (total) magnetic field. Data were output in the CALCM format.
• FCHK -- Checked FIXSE format data for errors. The input file was checked for unreasonable dates, latitudes, longitudes, K79 or K80-indicators or descriptors. The program computed the time difference and average speed from one fix to another and compares them to a maximum value specified at run time. Errors were listed on the processor's selected output device which could be either their working terminal or a print device. Additionally, the processor may select to list the input record, computed speed, time difference and heading.
• MRGDS -- Merged time-series depth data in SEDEP format with SEAG format gravity data and calculated a Bouguer anomaly. Output data was in SEAG format.
  Each SEAG gravity record processed was bracketed by time by two depth records. The depth and Matthews' Table correction from the SEDEP record were linearly interpolated to the time of the gravity record. The Bouguer anomaly is calculated unless there is a null free-air anomaly or a time-gap in the depth records. In thoses cases, the SEAG data are output with depths of zero and null value (9990) for Bouguer.

Return to R/V FAY data home page