Sequoia LISST-SL, Руководство по эксплуатации

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LISST-SL V2.1
User’s Guide
14
27-30
New and Factory backgrounds
27-30
Did I get a good
Background?
The quality of the background, we repeat, is everything
for a successful data run
. Please follow these steps
carefully.
Press the View Rings button on the screen again. This
will open a new screen showing a regular update of the
background about once every 2 seconds. A good
background can only be obtained if the rings view is
steady, with minimal or no change. If there are bubbles or
particles in the water, the rings display will show
variability. This is NOT a good situation to capture a
background file. If you see variability, remove bubbles
from the system, and remove particles (attach a filter to
the intake). Then repeat.
When the view rings display
updates with minimal variability, you are ready to
capture a background
. [A future version of this firmware
will guide you to automatically accept or reject a
background.] Press Cancel to go back to the Main Menu.
Again choose Calibrate. On the Clean Water Calibration
screen, DO NOT check the View Rings button (bottom
left). Press the Collect Background button.
A screen, Get Clean Water Background will open. Press
UPDATE button to capture an updated background. After
averaging 20 samples (roughly 25 seconds), the display
will show your new background data, and the factory
values (red line). Ideally, the two should be very similar.
Also displayed at the top of frame are two variables Lp
and Lref. We explain their meaning shortly. You may
save the new background file by pressing the SAVE
button at bottom right of the frame. The file will be saved
and you will see the Main Menu appear. If you list all the
files on your TCB, you will
not see this new file. However,
when you download files with the windows software on
your PC, this file, beginning with the letter Z will be
visible. This file will be used to subtract background light
scattering from the sediment in the next step.
Understanding the Background File: When you update
the background file, the display shows a set of blue bars,
which is the current (NEW) background scattering on the
rings of the detector. The red line is the factory value.
Over time, due to sand-blasting of windows or simply due
to fouling, your background will be higher than factory.
We explain how to interpret it in Appendix D.
For now, note also the two variables Lp and Lref, with
their factory values. These are displayed next to the top
right of the chart. Lp refers to the laser power (in digital
counts only), transmitted through water and through the
small hole at center of the ring detector. Lref is the laser
emitted power. In clean water, the ratio Lp/Lref should be