NavList:

Irv,

thanks for bringing this to our attention.  I cannot address whether or not it should be SOA or SOG, but have forwarded that portion over to the Sailwx webmaster for review.

You were correct in that the ship erroneously jumped from Eastern to Western hemispheres on 10/29 - 18UTC observation.

here is their raw observation in standard WMO FM-13 code.  Looking at the third group past the call sign, you see that they encoded a "5" instead of a "3" for quadrant of the globe (51314 should have been 31314). You can refer to page 2-9 of the linked Observing handbook No 1 to see the coding rules.

If you look at the 22244 group in the same 18UTC observation, the 3 hourly average ships course was coded as a 4 (southerly) with a 3 hourly ships speed average also a 4 (16 to 20 knots). (refer to page 2-75 in the Handbook No. 1)

In the VOS program, we ask the ships to use SOG values to determine their 3 hrly speed average as well as their true wind from apparent.


Most ships in the US VOS program use our AMVER/SEAS electronic logbook to encode their observation.  SEAS has a QC check to catch inadvertent typos from E to W or N to S entries.  This particular ship prefers to use the TURBO Electronic Software from the Netherlands VOS program and I have just verified with them that Turbo also has this QC check in place.  For more detailed information regarding the Turbo QC checks please see the link below.

As this ship submits their observations via email & our communication servers only hold a few days worth of submission, we cannot see the ships initial input to verify that they submitted a Typo or if our system (which is just a pass through type) did something to "tweak" this one individual observation.

.Hope this helps,

Luke

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Robert .

Hi Irv,

I'm not the best person to answer questions about SOA (speed of advance) (or speed over ground calculations), but offer the following information in case it is useful:

This website describes in general terms how the international Voluntary Observing Ship (VOS) programme works:
     http://www.bom.gov.au/jcomm/vos/vos.html
including data elements generally reported by the various types of VOS, and that "Ship's observations are made at the standard synoptic hours of 0000, 0600, 1200 and 1800 UTC and are sent to a meteorological service as soon as they are made, either by radio telephony to a coast radio station, by telex over radio, or by INMARSAT-C."

My understanding is that SOA (or nautical miles run) data are not transmitted from the ships in the real-time (GTS) ship messages, in which case those quantities as displayed by Sailwx must be calculated elsewhere (perhaps by Sailwx by comparing successive individual marine reports). Individual GTS ship reports include reported latitude, longitude, time, and ship's course information, and there can certainly be errors in those elements, due to a original reporting problems or other downstream factors.

Responding to your original question 3), the above referenced webpage also describes how: "The quality of VOS reports is monitored by several major meteorological centres, primarily the Met Office, United Kingdom. Results of this monitoring are compiled and distributed at monthly and six-monthly intervals to PMOs, who are expected to take follow-up actions to correct deficiencies."  Probably many erroneous data will be detected after original receipt at national meteorological centers through their QC measures and removed/flagged in the database (or possibly corrected) e.g. for weather forecasting applications. I think the quality of observations may vary considerably depending on the shipboard equipment (e.g., electronic logbooks can result in improved data quality).

Robert Luke (cc'd), NOAA's VOS Program Manager, may be able to comment further on some of your questions. (Also, Luke I believe has been in touch with the Sailwx firm.) So I have attached your two previous messages relating to the Amsterdam's positions etc. for Luke's information.

Hope this helps. Regards,  -Scott


On 11/18/09 11:14 AM, Irv Haworth wrote:

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___________________________________

Scott Woodruff, NOAA/ESRL (PSD3)

325 Broadway; Boulder, CO 80305 USA

phone: +1 303-497-6747 (fax: -6181)

Scott.D.Woodruff@noaa.gov

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