We have initiated an errata system we call E77, to efficiently report errors found in historic mgd77 cruises without overwriting original mgd77 files. E77 tables are carefully reviewed before being publicly released, although, with more than 5,000 cruises reviewed, we make no guarantee ensuring complete improvement. We encourage scientists to contribute to this effort by submitting their reviewed E77 tables along with data or plots aiding in their reviews.
E77 errata tables are generated, after review,handled by the Generic Mapping Tools supplemental 'mgd77' package. Adding E77 format support to your data processing tools will link your code with the mgd77 tools.
E77 Error output is divided into (1) a header containing information globally applicable to the cruise and (2) individual error records summarizing all errors encountered in each cruise record.
E77 Header|
Information reported as E77 header information pertains to an entire cruise, such as NGDC and survey institution identification codes, cruise examination time, two-way travel time corrector information, data precision warnings, as well as regression statistics from global grid comparisons and anomaly recalculations.
# Cruise 08010001 ID 71042601 MGD77 FILE VERSION: 19840223 N_RECS: 8359
After careful consideration, the data reviewer chooses to either 'E' and 'W' (error/warning) flags distinguish between errors that are correctible using E77 and those that are not (i.e., integer precision). For posterity, data reviewers provide names and processing comments. |
E77 Data Records
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Individual error records have strict format. Included is the NGDC id followed by a time or distance column, record number, a formatted error code string, and finally a verbose description of errors detected in the record. Three error classes are encoded into the error code string with different alphabetic characters representing unique error types. See below for a description of the following error code. If the reviewer does not approve E77 data record correction flags, boundaries may be adjusted in mgd77sniffer, or disagreeable error records may be removed.
# Errata: Data
Error Record Format [cruise id] [time/distance] [record number] [error code string (NAV-VAL-GRAD)] [description] Error Class Descriptions NAV (navigation): 0 - fine A - time out of range B - time decreasing C - excessive speed D - above sea level E - lat undefined F - lon undefined VAL (value): 0 - fine K - twt invalid L - depth invalid O - mtf1 invalid etc. GRAD (gradient): 0 - fine K - d[twt] excessive L - d[depth] excessive O - d[mtf1] excessive etc. The NAV error class has unique cases while the VAL and GRAD classes are described by alphabetic characters for each of the 24 numeric fields in MGD77 format order. MGD77 bit-pattern w/ E77 alpha characters |-------------------------------------------------|----------| | X W V U T S R Q P O N M L K J I H G F E D C B A | E77 Code | | - - - - - - - - - - - - - - - - - - - - - - - - | - - - - -| | n f e g m d m m m m b b d t p l l m h d m y t d | F I | | q a o o s i s a t t t c e w t o a i o a o e z r | i D | | c a t b d u e g f f c c p t c n t n u y n a t | e | | s r n 2 1 t r t r | l | | s h h | d | | - - - - - - - - - - - - - - - - - - - - - - - - | - - - - -| | 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 | Bit place| | - G C G C C - G G G - - G G - - - T T T T T - - | Bit type | |-------------------------------------------------|----------| Bit types: (G)eophysical, (C)orrection, (T)ime |
Step 3:
The data reviewer finally toggles the "Errata table verification status" from 'N' to 'Y' to indicate thorough review of all recommended corrections.
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Maintained by Michael Hamilton ○ Last modified: December 07 2021.