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Title: Oxford Tract Radiometer Comparison - 06/2019
Date:2019-06-18
Data File: OxfordRadComp_PAR_20190723.csv
OxfordRadComp_Rnet_20190619.csv
OxfordRadComp_RnetUD_20190723.csv
Refers to:990353, 990352, 021029, 990354, 041556, 990351, 140455, 010161, 030380, 10162, 161073, 030381, 16048

We set up a tower of radiometers at Oxford Tract (Oxford Street & Virginia). We borrowed a CNR4 4-band radiometer and a K&Z PQS1 PAR sensor from Ameriflux to serve as reference sensors. The Rnet and CNR4 sensors were installed facing south, over bare soil. The PAR sensors were installed on a platform facing north. All sensors were leveled and wired to a CR6 datalogger with an AM16/32B multiplexer and powered by a 12V deep-cycle battery. We later replaced the large battery with a sealed 9-cell battery and a small solar panel (both directly wired to the CR6. The datalogger scans every 10 seconds and records 1-minute averages. I calculated the 10-min averages to use for analysis here (calibrations factors calculated using 1-min and 10-min averages were similar according to our previous PAR calibration).

At 2019-06-25 10:00, Joe removed Rnet_3 sensor (sn 021029) and added a homemade Peltier chip sensor in that same channel.

15609071937413.png

 

Rnet sensor Factory calibration [µV/(µmol/m2·s)]

Field calibration (correct orientation) [µV/(µmol/m2·s)]

(% difference from factory calibration)

 Field calibration (upside down orientation)

[µV/(µmol/m2·s)]

(% difference from factory calibration)

 Recommendation
K&Z NR-LITE sn 990351 13.9 uV/(W/m2) 14.0 (+1%) 13.5 (-3%) Use field calibration (correct orientation)
K&Z NR-LITE sn 990352 14.2 uV/(W/m2) 13.7 (-4%)

14.8 (+4%)

 Use field calibration (correct orientation)
K&Z NR-LITE sn 990353

12.3 uV/(W/m2)

 12.0 (-2%) 12.8 (+4%) Use field calibration (correct orientation)
K&Z NR-LITE sn 990354 12.9 uV/(W/m2) 12.7 (-2%) 15.4 (+20%) Large calibration change when upside down compared to correct orientation; more testing needed
K&Z NR-LITE sn 021029 14.1 uV/(W/m2) 13.1 (-7%) n/a (removed from field) Use field calibration (correct orientation)
K&Z NR-LITE sn 041556 14.2 uV/(W/m2) 12.8 (-10%) 14.3 (+1%) Large calibration change when upside down compared to correct orientation; more testing needed

 

PAR sensor

 Factory calibration [µV/(µmol/m2·s)]

Lab calibration [µV/(µmol/m2·s)]

(% difference from factory calibration)

Field calibration [µV/(µmol/m2·s)]

(% difference from factory calibration)

 Recommendation
K&Z PQS1 sn 161073 (reference) 4.78 n/a n/a n/a
K&Z PQS1 sn 140455 8.15 8.47 (+4%) 8.30 (+2%) Use field calibration
K&Z PAR-LITE sn 010161 5.27 5.16 (-2%) 5.32 (+1%) Use field calibration
K&Z PAR-LITE sn 10162 5.27 5.56 (+6%) 5.76 (+9%) Use field calibration
K&Z PAR-LITE sn 030380 5.31 2.91 (-45%) 5.26 (-1%) Use field calibration
K&Z PAR-LITE sn 030381 5.32 5.30 (+0%) 5.43 (+2%) Use field calibration

 

Figure 1. Reference 4-band radiometer and calculated Rnet.

Figure 2. Rnet sensors with reference Rnet calculated from reference sensor.

Regression Data

Residuals

Figure 3. Linear regression between reference Rnet and 6 Rnet sensors.

Figure 4. Upside-down Rnet sensors with reference Rnet calculated from reference sensor.

Regression Data

Residuals

Figure 5. Linear regression between reference Rnet and 6 upside-down Rnet sensors.

Figure 6. PAR data.

Regression Data

Residuals

Figure 7. Linear regression between reference PAR and 5 PAR sensors.