8
ERDC/CRREL TR-02-10
and the reported accuracy is approximately 0.11 m s1. Wind direction was meas-
ured with a model 024a Met-One wind direction sensor. The accuracy, as reported
by the manufacturer, is within 5. The wind direction sensors are calibrated
annually by obtaining the full-scale return of the resistor and scaling this to the
desired 360 output. Additionally, the heading of the wind direction sensors are
checked periodically each year by pointing the vane at four compass points.
Radiation instruments are annually installed in the spring, usually during
April, and are taken down in the fall, typically early September. Since rime ice,
nocturnal frost, snowfall, and freezing precipitation can obscure the sensors in
these instruments, values reported during periods of below-freezing air tempera-
ture must be used cautiously. The following radiation components were meas-
ured: incoming and reflected short-wave radiation, atmospheric and terrestrial
long-wave radiation, and net radiation. Radiometer calibrations were checked
locally each year by comparison to the output of an instrument of known preci-
sion. All radiometers are frequently sent to independent laboratories for recondi-
tioning and recalibration.
Incident short-wave radiation was measured using an Eppley model PSP pre-
cision spectral pyranometer. This instrument has a reported spectral range of
0.2852.800 m and a reported accuracy of 1% in the range of values encoun-
tered. The cosine response of this instrument is 1% between 0 and 70 and
3% between 70 and 80 zenith angle. Eppley model PIR precision infrared
pyrgeometers were used to measure long-wave radiation, both terrestrial and
atmospheric. The spectral range of this type of instrument is 450 m, and the
accuracy reported as 1% between 0 and 700 W m2. Net radiation was measured
with Q-7.1 sensors manufactured by Radiation and Energy Systems. The spectral
range of this type of instrument is 0.2560 m, and the accuracy is not reported.
Air temperature and relative humidity were measured throughout the year
with a Campbell Scientific HMP35C or HMP45C. The accuracy of the air tem-
perature is within 0.45 across the measurement range. The accuracy of the rela-
tive humidity sensor is reported to be within 3% at worst case. Warm-season
rainfall precipitation is measured with a TE525 tipping bucket rain gage manu-
factured by Texas Electronics. The rain gage is calibrated to record 0.01 in. of
rain per tip. In the low-intensity rain events typically observed (less than 1 in./hr)
the accuracy is reported at 1%. No precipitation measurements were taken dur-
ing the cold season.
This report only considers a small subset of the data that were collected as
part of this ongoing effort (Kane et al. 2000). The complete data archive can be
found at the National Snow and Ice Data Center in Boulder, Colorado
(http://nsidc.org/data/arcss015.html).
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