[Acoustics] Delay in GPS data processing

[Tracy Vermeyen]

Hi Francois,

I have seen this problem too!  Can you send me a brief explanation on how you determined the 1 -15 sec delay intervals?  I have run a few crude tests where I disconnect the GPS from the serial cable and note the ENS # and then checked to see when WINRIVER reports NO DATA.  It usually is delayed by 1 or maybe 2 ensembles.

Here is my information for you.

Computer used - Dell Latitude, C640 running XP
communication ports (USB, PCMCIA, etc.), ADCP on COM1 (computer serial port), GPS and Depth Sounder on a 2-port Quatech PCMCIA serial port card.
GPS receiver, Garmin GPSMAP 76CS, and Trimble RTK 5800 series
Output frequencies, ADCP @ 9600baud, GPS @ 4800 baud
Type of modem radio link - The Trimble 5800 has a radio link that we was updating at 1 Hz, otherwise, no radio link.

Cheers, Tracy
>>> Rainville,François [CIS-WSB] <Francois.Rainville at ec.gc.ca> 04/03/06 12:53PM >>>
Hello all!

We have observed that GPS data is sometimes delayed and lagging with respect to the ADCP data collected.  This can be observed as a strange path that does not correspond well to the shape obtained by bottom track but which in fact corresponds to events (velocities) of moments before. This delay is sometimes quite small (by 1 second) and sometimes bigger (up to 15 s).  We have not yet been able to determine any trend in the type of computer and communication systems causing this to happen.  But this is definitly a problem we would like to resolve.

- Did any of you also witness such problems while using GPS?

- If so, can you provide a brief description of the type of computer used, communication ports (USB, PCMCIA, etc.), GPS receiver, output frequencies, type of modem radio link if any used?



Many thanks for helping us with this issue!

Francois Rainville
Water Survey of Canada
Environment Canada
373 Sussex Drive, Ottawa, Ontario;  K1A 0H3
Phone: 613-992-1673;  Fax: 613-992-4288


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