The Mixing Zephyr Pages
Mixing Zephyr Program
Information from the CTD data logger is recorded every two
seconds and yields very complete but significantly large data
files. Ideally, the fish navigation is computed and recorded every
minute. Thus, navigation data for the towed package needs thus to be
extrapolated from the sixty second interval to the two second interval.
Unfortunately, several problems were encountered with the navigation
Tow Navigation Data Reduction:
Merging ACNAV with CTD Data
In order to remedy these problems merging of the navigation was
realized in two steps. The navigation was first filtered using
RADs graphical interface. Most bad fixes were thrown out of the data.
The filtered navigation was then used to extrapolate the fish position
at the times the CTD data was recorded at. The positions were linearly
interpolated in a table lookup fashion. The resulting grid positions
(x,ys) were then used to calculate the latitude and longitude of the
fish during the tows.
- Fliers / bad fixes: About five to ten percent (sometimes
more, depending on the position of the package with respect to the
transponder net used) of the navigation data contains erroneous fixes
for the fish position. These bad fixes are usually caused by bad travel
time information such as secondary echoes. This problem gets more acute
when the fish is far away from the transponder net.
- Baseline problem: Another pervasive problem occured every
time the fish crossed the baseline of the transponder net used. This
led the navigation to go erratic unless the code used (ACNAV) was
switched to compute the fish fixes out of another transponder pair.
Even in this case a gap usually remains in the navigation information.
- Distance from net: Several tows extended over the limits of
the transponder net used during Mixing Zephyrs Is deployement.
This led to lose navigation at the ends of these tows.
The following table summarizes the times in between which the
navigation data is available and where gaps existed for each
tow. It also lists the beginning and ending times of the unmerged and
merged CTD data. All the resulting merged data is shown in the next
Summary Table of Tow Navigation
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The Mixing Zephyr Pages
Maintained by Russ McDuff (firstname.lastname@example.org)
Copyright (©) 1995,1996 University of Washington; Copyright Notice
Content Last Modified 6/19/95
Page Last Built 8/4/96