ENVIRONMENT
power and data cables. Instead,
each station is self-contained
wind direction and changing ex-
perimental needs). The instru-
(powered bybatteries and solar
panels) and connected to the
ments require only minimum maintenance, are stable over periods of
weeks, and are easy to calibrate.
center by two-way telemetry.
The greater extent of the sensor
The nature of the dispersing
cloud affects instrument requirements. The cold gas condensesessentially all the water vaporin the
air close to the pond, forming a
thick fog (see front cover) that
poses problems not only for optical
array imposes severe burdens on
the instruments and the measurement stations. Both are light and
‘portable (so that they can be towermounted and easily moved to accommodate shifts in the mean
400
T
]
:
|
|
|
300 -—
7
1
instruments but also for sensors
that rely upon the chemical or thermodynamic properties of the gas.
Hence, each type of instrument
must be specifically adapted to
function properly within a cold,
dense fog.
Because of turbulence, hydrocarbon concentrations within the
gas cloud fluctuate significantly
even over time intervals as short as
0.2 s. Turbulence andits effect on
7
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1
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1
T
O
4
200 -—
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¢ 100 ;~-
8
0
04s
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+
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+ 4
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© 100-—
—
© Gas sensor station
2007—-
A Anemometer station
T
.
O Turbulencestation
S00; COM3 code calculation
400
800
1
l
600
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|
400
J
200
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200
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400
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7000
Distance —m
Pig. ©
Far-field dispersion arrayfor 40-m’spill tests
at China Lake, with calculated concentration
contours for a 40-m7/minspill rate. Gas sensors, anemometers, and thermocouplesare at elevations of I, 3,
and &m above the ground. Each of the instrument stations
is self-contained (powered by batteries and solarcells) and
connected to a central data-processing trailer by two-way
telemetry. Each of the stations is portable so that the array
can be rearranged in responseto shifis in the average wind
direction or changes in experimental conditions.
35