[Acoustics] Reported GPS problems

[David S. Mueller]

I recently spent a day in the field trying to track down a problem several
people had reported to me. The problem manifests itself as an extreme delay
in GPS data used in WinRiver (up to 110 sec old). This causes the beginning
of transects to go in the wrong direction (based on GPS) and not following
bottom track at all. It can also result in short DMG. The discharges are
obviously wrong.

After testing on two computers (one Win98 and on XP Pro) and using three
different serial ports (internal, new Socket card, Keyspan 4-port USB RS-232
adapter) I reached the conclusion that there is an incompatibility between
the new Socket cards and WinRiver.

By splitting the data coming from the GPS unit and monitoring it with a
second computer, it was clear that the GPS unit (Ag132) was providing
correct data but that the data were being buffered in the computer running
WinRiver. The problem grows between transects. It appears that between
transects when you are not recording data the GPS data gets buffered and
when you start another transect the buffer is not flushed and you start
using old GPS data. This occurred using 5 Hz update rate and 9600 baud rate.
However, it only occurred when the GPS was fed through the Socket card. The
problem was minimized (delay of about 2 seconds) going to a higher baud rate
19.2K. This problem occurred on both computers and only occurred when the
GPS data was fed into the Socket card. Reversing the ADCP and GPS ports
appeared to fix the problem, as did using the Keyspan.

I also tried an earlier version of WinRiver but that did not eliminate the
problem.

I would like to know if those of you who have experienced this problem are
using a newer Socket card and if so, does the problem go away by switching
ports are using a different external serial interface adapter.

The new Socket cards have a bar code on the back with the numbers:
8510-00073 J
I do not have the version number of the driver used.

I am aware of other software with incompatibilities with the new Socket
cards and expect that card is the cause of many of the GPS issues that have
appeared in the last 6 months.

Thanks for your help.

David S. Mueller
U.S. Geological Survey
Office of Surface Water
9818 Bluegrass Parkway
Louisville, KY 40299

dmueller at usgs.gov

Voice: 502-493-1935
Fax: 502-493-1909
Mobile:502-558-5907