DIARY # 12
SPARKLING LAKE
RAFT PLANNING
The Sparkling Lake Raft, with its numerous
air and water sensors, Campbell Scientific CR21X data logger,
batteries, and solar panel, and cell phone/modem arrangement was
pulled out of the water in late June and its decks retreated so
it can stand another winter in the water.
While out, several discussions took place over
when and how we should install the wireless system on it.
While both Tim Kratz and his chief technical
assistant Tim Meinke would have liked us to do the installation
on the raft while it was out of the water, it could not be done
until the data flow issues from the Data Logger on the Raft -
currently using a Campbell specially wired modem, Cell Phone,
and programming code in the compiled Data Logger which responds
to a Cell Phone call from a computer running PC208W 3.0 software
- are all changed and modified to enable a totally different kind
of access to the data, which currently is done from the Limnology
Center in Madison, and only for troubleshooting purposes and intermittently
from Trout Lake Center itself.
In other words, putting the radio, antenna,
solar panel, battery, and connector cables on the raft is the
easy part. The hard part is to redesign the data flow hardware
and software, routing, their ultimate repository in remote data
bases, and thinking through to what extent the frequency and nature
of data capture should change, given the new 24/7 accessibility
of the data to the outside from the center of the lake, rather
than the limited once-a-day cell phone access and data capture
have to be resolved before anything more than test installations
can be made. This data capture work once the wireless system is
in place, has to be planned and programmed by the LTER staff.
It is beyond the scope of our Wireless Project, for it is integral
to use of the system for the biological data collection scheme
of the researchers and PI.
However, there were still plenty of practical
questions on just how to fit the new gear on the small raft, already
jammed with equipment. So we met around the raft several times
to ponder the pros and cons of different physical placements,
taking into account that, while the raft is on the lake, it has
to be visited and someone has to be able to stand on it and do
work. With little standing room space.
In order not to risk loss of data from failed
rechargeable batteries that are drug down by the added current
drain by radios, I decided we needed to entail a totally separate
power system for the radio, until such time as we have measured
actual battery power usage, and efficiency of the solar panels
when left through the winter (snow and ice) on the raft.
The Solar Panel is the largest and most awkward
item. We selected a Siemans SM46, 13 by 42.6 inch, 45 watt self
regulating panel. It must not only be in the open on the raft,
but must be tilted toward the sun, and have sufficient angle to
let snow slide off. The picture above, Tim Kratz on the left,
pondering, shows a technical assistant showing one possible placement
of the panel. Another placement is shown below, with Margo, student
assistant, in the background.
It was finally decided to put it at an angle
on a plywood cover that can lift up, hinged, when work is done
in the weatherproof box holding the data logger beneath it.
Then there will have to be a separate smaller
weatherproof box, with our Marine battery inside, and probably
the Freewave DRG115W radio - even though the radio can be directly
in the weather. There was some discussion of the placement of
the Yagi 915Mhz omni antenna up on the mast, so that it does not
interfere with the accurate wind measurement operations of the
anemometers on the mast. (The same question influenced the placement
of the large flat panel solar panel). Fortunately the strength
of signal that we observed using a hand held 5 db gain antenna
the other side of the lake insured we could use an Omni antenna,
and not a directional Yagi, which in turn would force Trout Lake
to anchor the raft to maintain a fixed orientation, with no more
than 15 degrees of drift off center. As long as the vertical,
thin mast antenna 'stands off' a few inches from the main mast,
there should be no problem.
As an alternative to simply going for an installation
on the raft first, with all the variables which have to be dealt
with, and some confidence that the entire end to end wireless
system will work reliably from the start, we decided to set up
a shore-based duplicate of the battery, solar power, radio, data
logger link, and network link and let it operate for a few weeks
at least, before totally swapping out the prover cell phone system
with it.
When a wireless system is being attached to
a newly deployed data logger system, it can all be designed at
once, deployed, and the bugs worked out. But when a data collection
system has been operating for 10 years, a total change in method
needs to be taken step by cautious step.
Wireless is wonderful - but a lot of other
things have to change when it replaces a different system.
The raft was launched Friday morning onto Sparkling
Lake, with the original cell phone system in place.
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