Start Date | Start Time | End Date | End Time | Data Quality Metric |
---|---|---|---|---|
11/02/1994 | 1640 | 11/02/1994 | 1900 | Incorrect |
Subject: | SGP/EBBR/E8 - T/RH Check |
DataStreams: | sgp30ebbrE8.b1, sgp15ebbrE8.b1, sgp5ebbrE8.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: 1640, 1645, 1650, 1655, 1700, 1705, 1710, 1715, 1720, 1725, 1730, 1735, 1740, 1745, 1750, 1755, 1800, 1805, 1810, 1815, 1820, 1825, 1830, 1835 15 minute: 1645, 1700, 1715, 1730, 1745, 1800, 1815, 1830, 1845 30 minute: 1700, 1730, 1800, 1830, 1900 (EDITOR'S NOTE: The following analysis referrs 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: | sgp5ebbrE8.b1: more
sgp15ebbrE8.b1: more sgp30ebbrE8.b1: more |