SCICEX: Archerfish 1997 Navigation description

Approximately one minute sampled ship's position, water depth, heading, velocity and ship's depth information for the SCICEX-97 cruise are available via anonymous ftp or the web from Lamont-Doherty. The text file (Archerfish.nav) contains 42746 lines of data covering the complete cruise on the USS Archerfish.

The one minute data file (gzipped) is available by anonymous FTP . This gzipped file is about 881 kilobytes and will expand to approximately 2.8 megabytes.

The data in this file are sampled ship's information acquired through the Submarine Data Recording System (SDRS) which were continuously logged as binary day files on the Data Acquisition and Quality Control System (DAQCS). After declassification of the underway data from SCICEX-97, the binary files were decoded to extract one second samples of the Ship's information. These data were decimated to create the file Archerfish.nav.

The DAQCS performed well during the cruise, there are no data gaps in the navigation data from the entry into the data box on julian (day of the year) day 246 until the termination of data logging on julian day 275. The position data presented here is the output of the Ship's Intertial Navigation System (SINS) corrected with correction parameters found in the SINS printer output, also captured via the SDRS. The ship was navigated with the corrected SINS output. Small tears in the correction parameters associated with occasional GPS fixes suggest that the SINS performed well during SCICEX-97. Computation of cross-over errors will permit evaluation of this assumption.

The data are sampled at about a 60 second interval. The file contains the first sample with a water depth for each one minute interval. Where there is no water depth given, the first available sample after the minute is taken. Typically the time between samples ranges between 55 and 66 seconds.

Two short segments of position information were hand edited from the navigation file. Positions received from SINS between 97+247:12:01:01 and 97+247:12:23:01 and from 97+261:01:37:02 until 97+261:01:53:01 were spurious. On julian day 247 the apparent error may have been caused by the sub crossing from 0 to 360 longitude (-180 to 180). On julian day 261 the apparent inconsistancy in position may have been caused by an update of the SINS.


Know your time source. As explained below, the times presented here are derived from the SDRS clock. This clock was synchronized to GMT prior to departure from Groton, but drifted during the cruise. How this clock relates to other, independently acquired time tags is not known. If you are attempting to relate various independently acquired observations (sail-mounted CTD, water sampling events, bathymetry) be aware that synchronization at better than a few minutes may not be possible. /H3> Data format example:

      -1-                 -2-             -3-            -4-    -5-      -6-     -7-
97+246:01:29:47.000	26.40358	84.008947	3965.61	355.45	27.66	135.18
97+246:01:30:09.000	26.42715	84.013884	3966.02	355.86	27.70	133.94
97+246:01:31:04.000	26.41425	84.016647	3966.47	355.69	27.70	134.58
97+246:01:32:10.000	26.41184	84.020240	3969.96	355.76	27.70	133.86
97+246:01:33:05.000	26.40673	84.026007	3969.91	355.66	27.70	134.91
97+246:01:34:00.000	26.39117	84.028221	3966.51	355.41	27.70	135.17
97+246:01:35:06.000	26.41499	84.031829	3966.43	3.61	27.58	133.99
97+246:01:36:01.000	26.41251	84.036778	3966.55	5.76	27.46	133.92
97+246:01:37:07.000	26.43247	84.040680	0.00	5.64	27.46	134.68
97+246:01:38:02.000	26.42233	84.043493	3966.61	5.53	27.46	134.90


1) Submarine Data Recording System time tag; yy+ddd:hh:mm:ss.000 ddd is the Julian day. Time is nominally GMT, but differs by an unknown amount from other time sources that may have been used for sampling.

2) Longitude (0-360) in decimal degrees.

3) Latitude in decimal degrees.

4) Full water depth (depth below keel + ship's depth) in meters (0.0 is no data).

5) Ship's heading (0-360).

6) Ship's speed in km/h.

7) Ship's depth in meters.

Anonymous FTP;

Connect via ftp to Log in as anonymous and follow the directions. Once you are connected, cd to /home/ftp/pub/scicex and take the file Archerfish.nav (2.8 Mbytes) or Archerfish.nav.gz (0.9 Mbytes; zipped using gzip; uncompress with gunzip).

via the Web;

Connect to the SCICEX website ( and follow the links for the Archerfish cruise.

If you have any questions please contact
Bernie Coakley

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