Start Date | Start Time | End Date | End Time | Data Quality Metric |
---|---|---|---|---|
10/22/1996 | 1730 | 02/05/1997 | 1400 | Suspect |
Subject: | SGP/TWR/C1 - RH Probe affected by tower damage |
DataStreams: | sgp1440twr25mC1.a0, sgp30twr25mC1.a1, sgp30twr60mC1.a1, sgp1twr60mC1.a0, sgp1440twr60mC1.a0, sgp1twr25mC1.a0 |
Description: | On Feb. 3 and 4 the SGP CART 60 m tower western elevator was repaired. This included the replacement of cables on the 60 m carriage and connectors on the 25 m carriage. Although damaged, the 60 m carriage cable had been temporarily repaired by Site Operations several months ago, with apparent success. However, evidence since then suggests that the repair was not totally successful. Tests since then suggest that the low return for the RH sensor may have been floating, or at least the connection was poor. At the same time, the 25 m carriage connectors and tower receptacles were bent in planes perpendicular to each other, apparently resulting in the same condition as existed for the 60 m carriage. The damage was partially the result of improper routing of the cables on the 60 m carriage by the tower installer and partially the result of improper parking of the carriages (damaging the 25 m carriage connectors and receptacles). The cables were reoriented and the connectors and receptacles replaced by the tower installer on 3-4 Feb 97. Because of the damage to the 25 m carriage connectors, the 25 m carriage was left off of the tower and no correct data was collected from the 25 m level from 22 Oct 97 at 1730 GMT until 4 Feb 97 at 1400 GMT. Only the 60 m level reported useful data during this period. During this period a slope of 1.107 was applied in the datalogger programming before the 60 m RH value was output to the logger memory. Calibrations of the probe by Vaisala last month show that the logger slope was appropriate for the sensor behavior at RH less than 85%. Calibration of sensors SN 109 and 231 by Vaisala showed the outputs to be several percent low near 0% RH and nearly correct at 100%. The calibrations by the original manufacturer caused the outputs to be outside the specifications for the bottom 3/4 of the sensors' range. Vaisala adjusted the slope and offset for both sensors. In use at 60 m on the tower, the RH probe slope changed above 85% RH, becoming larger with increasing RH. At saturation the 60 m sensor RH value was being reported as 110.7% to 111.0% (in other words the slope in the logger of 1.107 X 100%). Apparently, at higher voltages the poor low side connection was less of a factor in the voltage output by the probe. Comparison with sonde data for RH above 85% yields the correction in the next paragraph. Therefore, my recommendation for the period listed above is to use the 60 m RH data as is for RH less than 85%. Reported RH above 85% can be roughly corrected with the following: actual RH = 36 + 0.577 X (60 m reported RH) . Vapor pressure can then be recalculated by the user from the correct RH values and the temperature. On Feb. 4 and 5, I conducted a number of tests on the carriages and RH probes (SN 231 at 25 m, SN 109 at 60 m), then replaced the RH probes with the probes recently (SN 234 at 25 m, SN 226 at 60 m) calibrated by Vaisala. One minute 60 m T and RH data is extremely consistent with the data from the sonde at 60 m height since 5 Feb 1997. In fact, the comparisons have never been better, reflecting the problem with obtaining correct calibrations from the original manufacturer (even before the tower was damaged), and the problems created by the damage on the tower. The problems resulting from damage to the tower carriage cables and connectors began around June 1995 (although the 60 m AC cable and 25 m receptacles had been damaged at least twice previously). I made a number of corrections to the RH data between June 1995 and when the tower was repaired this past February. 25 and 60 m T and RH data since the tower repairs and the Feb. 5, 1997 replacement of the RH probes are very consistent with the sonde data. The only significant difference between the 60 m RH probe and the sonde RH probe occurs when the surface to 60 m RH gradient is large; this is expected since the RH probe on the sonde cannot respond to large changes in gradient quickly enough to produce the same measurement as the 60 m tower RH probe. I will continue to compare the sonde, SMOS, and tower sensors for data quality purposes, as I have routinely for the past year. |
Suggestions: | |
Measurements: | sgp1twr25mC1.a0: more
sgp30twr25mC1.a1: more sgp1twr60mC1.a0: more sgp1440twr60mC1.a0: more sgp1440twr25mC1.a0: more sgp30twr60mC1.a1: more |