Sequoia LISST-HOLO, Руководство пользователя

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LISST-
HOLO User’s Guide
61
9 FAQs
What is a hologram? Fundamentally, holograms are 3-D images that have first been projected, and then stored on a 2-D
surface. In the type of holograms captured by the LISST-HOLO (so-called in-line holograms), a laser
beam is emitted and a small part of it is being scattered by the particles in the water. The part of the
laser beam that is not being scattered by particles interferes with the scattered light. This creates an
interference pattern - a hologram. The interference pattern is captured by a small digital camera.
Upon processing of the captured interference pattern (i.e. the hologram), it is possible to recover the
original image that created the hologram. Thus, the LISST-HOLO does NOT capture and store an
image of the suspended particles. It is the hologram of the particles that is stored. During data
processing, the image of the suspended particles is reconstructed from the hologram. Subsequently
standard image processing methods can then be applied to get information about particle shape,
size, area, etc.
Why can't the LISST-
HOLO be used when
the flow speed is more
than 0.5 m/s? It takes a few micro-seconds to capture the hologram using the digital camera. The image captured
by any digital camera is made up by a large number of pixels. If the particles in the water move more
than half a pixel during the time it takes to capture and store the hologram, it is impossible to process
the hologram and get reliable results. For the pixel size used in the LISST-HOLO, a flow speed of
more than 0.5 m/s will begin to blur the hologram. Consequently, if the LISST-HOLO is used on a
profiling platform, e.g. a CTD, the profiling speed must be 0.5 m/s or less. Likewise, if the LISST-
HOLO is deployed on a mooring or tripod, the current velocity around the instrument must be less
than 0.5 m/s.
Why should I connect
the LISST-HOLO to the
Internet? Connecting the LISST-HOLO to a local area network that is connected to the Internet has benefits.
The first benefit is that the instrument is accessible from different locations across the network.
Connecting the instrument to the Internet has other advantages such as checking for firmware
updates, syncing the time with international standards, and transmitting log files to Sequoia. It is not
necessary to have the instrument connected to a network or the Internet but it can be useful when
needed.
How do I connect the
LISST-HOLO to the
Internet? The LISST-HOLO comes configured with a pre-selected IP address, netmask, gateway, DNS 1, and
DNS 2. These settings will work with the provided wireless router but they will probably not work with
your existing local area network. Because the LISST-HOLO requires a static IP address an IP
address must be selected so as not to interfere with other computers on your network. It is highly
recommended that users work with their network administrators to determine the proper settings for
their network. The new value can be entered on the Tools page (see section 8.3). Be sure to double
check the values before pressing the Apply button on the Tools page. Once the Apply button is
clicked the IP address will change immediately and you will need to log into the new IP address
before LISST-HOLO communication can be re-established. If incorrect values are entered it is
possible to change them manually through serial port communication. Contact Sequoia for details of
this procedure.
Why does it take 2
minutes to process
one hologram? Processing (or reconstruction) of a hologram is a mathematically intensive task. Therefore a LISST-
HOLO hologram is split up into ROIs (Regions Of Interest), which are each processed separately.
This is in order to avoid memory problems during processing. Once the ROIs have been processed
they are merged into one image with particles and processed for size, area, shape, etc. The 2 minute
processing time per hologram is the maximum expected time on a standard 2.2GHz windows PC
with 4GB of memory. However, since the processing is fully automated, it is possible to process
holograms overnight or during weekends.
Is it possible to get
data in real-time from
the LISST-HOLO? No. It typically takes 2 minutes to reconstruct a hologram into an image that can be analyzed for
particle size, shape, area, etc.
Does the LISST-HOLO
support DHCP? No. The LISST-HOLO does not support DHCP (Dynamic Host Configuration Protocol).
What is the maximum
sample rate for the
LISST-HOLO? The maximum sample rate for the LISST-HOLO is 0.2 Hz (one hologram every 5 seconds).
Can I connect the
LISST-HOLO directly
to the Ethernet port on No. You must always connect via the supplied router or a local network. With the router, you can
connect wirelessly to your PC. If your PC does not have wireless capability you can plug the router
into your PC. However, in both circumstances the LISST-HOLO must be plugged into the router and