DQRID : D020628.14
Start DateStart TimeEnd DateEnd Time Data Quality Metric
11/14/1994182011/14/19942000Incorrect
more
Subject:
SGP/EBBR/E9 - T/RH Check
DataStreams:sgp5ebbrE9.b1, sgp30ebbrE9.b1, sgp15ebbrE9.b1
Description:
During the month of November 1994, site operations personnel conducted
field comparisons of the temperature and relative humidity sensors in the
EBBRs and the HMI31 portable T/RH meter (with the removable probe).  As is
reflected in the home signal output, the automatic exchange mechanism was
disabled in order to conduct the checks.

Measurements were taken every 5 minutes, for a half hour each in the
aspirated radiation shields (the HMI31 was inserted into the EBBR aspirated
radiation shield to provide the same aspiration as the EBBR sensors
received).  Measurements of aspirator flow were also recorded.  This
information was provided to the mentor.  The mentor then compared the field
checks with the data recorded by the EBBRs.

The periods of data and data fields that are incorrect because of the checks
are listed below.  Times are those at which the data are reported.


Data Fields

5 minute:  tair_top, tair_bot, thum_top, thum_bot, hum_top, hum_bot,
           vp_top, vp_bot
15 minute: rr_thum_r, rr_thum_l, mv_hum_r, mv_hum_l, tair_r, tair_l
30 minute: tair_top, tair_bot, thum_top, thum_bot, hum_top, hum_bot,
           vp_top, vp_bot, bowen, e, h


5 minute:  1820, 1825, 1830, 1835, 1840, 1845, 1850, 1855, 1900,
           1905, 1910, 1915, 1920, 1925, 1930, 1935, 1940, 1945
15 minute: 1830, 1845, 1900, 1915, 1930, 1945
30 minute: 1830, 1900, 1930, 2000


(EDITOR'S NOTE:  The following analysis refers to all EBBRs installed in Nov 1994)

Results of the T/RH comparisons:
The combined accuracy of the HMI31 and EBBR temperature sensors
(thermocouples or PRTDs) is +/- 0.4 degrees C.  The combined accuracy of the
HMI31 and EBBR RH sensors is +/- 4% for RH less than 80%, and +/- 6% for RH
greater than 80%.  The combined accuracy for each pair of EBBR sensors of
the same type is essentially the same as the quantities stated above.

All of the pairs of EBBR sensors show differences that fall within the
stated combined accuracies.  Although this sounds wonderful, a few of the
differences are close to the combined accuracy, which, because of the small
differences in temperature being measured (normally smaller than the
magnitude of the combined accuracy) could lead to some incorrect estimation
of sensible and latent heat flux.  However, unless there would be substantial
differences of calibration slope of two sensors in a pair, the switching of
height of the sensors every 15 minutes by the automatic exchange mechanism
will remove the offset between the sensors.

The comparisons between the EBBR sensors and the HMI31 T/RH meter showed
much larger differences.  The range of differences were: -2.4 to 0.0 degrees
for the thermocouples, -2.1 to 0.1 degrees for the RH probe PRTDs, and -6.6 to
6.7 percent for the RH sensors.  Six Thermocouples indicated differences from
the HMI31 greater than the combined accuracy.  Seven PRTDs indicated
differences from the HMI31 greater than the combined accuracy.  Four RH
sensors indicated differences from the HMI31 greater than the combined
accuracy.  The temperature differences (for both thermocouples and PRTDs)
were nearly all of one sign; the HMI31 indicated the greater temperature,
which may suggest a bias in the HMI31 temperature measurement, even though
a dozen differences of +/- 0.2 degrees were measured.  Four differences of
zero and only one positive difference (out of 40) were measured.  Thirteen of
the 20 RH differences were positive (HMI31 indicating the lower
RH), with the differences near the level of the combined accuracies being
approximately 50% positive and 50% negative.  It does not appear that the
HMI31 has a RH bias.

Plots of EBBR sensor/HMI31 differences as a function of time from the
installation of the individual sensors (a range of 10 to 30 months in the
field) shows no obvious pattern of sensor drift with time.  This is encouraging.
Suggestions: 
Measurements:sgp30ebbrE9.b1:
  • temp_air_bottom
  • temp_air_top
  • rh_bottom_fraction
  • vapor_pressure_bottom
  • temp_trh_bottom
  • vapor_pressure_top
  • temp_trh_top
  • latent_heat_flux
  • rh_top_fraction
  • bowen_ratio
  • sensible_heat_flux
more
sgp15ebbrE9.b1:
  • temp_air_left
  • rh_left_mv
  • temp_trh_right_rr
  • temp_air_right
  • rh_right_mv
  • temp_trh_left_rr
more
sgp5ebbrE9.b1:
  • rh_bottom_fraction
  • temp_air_bottom
  • temp_trh_bottom
  • vapor_pressure_top
  • temp_trh_top
  • temp_air_top
  • rh_top_fraction
  • vapor_pressure_bottom
more

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