1. Climate Reference Network Temperature Measurements C. Bruce Baker, NCDC, Tilden P. Meyers, ATDD Mark E. Hall, ATDD, Richard R. Heim, Jr., NCDC

2. One of the Primary goals for the CRN is to Provide the Highest Quality Temperature Measurements to Detect Climate Change Most studies have addressed the errors in the measurement of temperature for non-ventilated shields Most Networks have used non-ventilated shields due to power constraints

3. Each temperature sensor will be individually calibrated using a traceable standard The standard is a NIST traceable Platinum Resistence Thermometer (PRT) The accuracy of the PRT is0.03 0 C Over the range Of -60 0 C to +60 0 C The CRN requirement is an accuracy of 0.3 0 C Over the range of -50 0 C to +50 0 C and0.6 0 C For -50 0 C to -60 0 C and +50 0 C to +60 0 C

4. Preliminary results indicate that a third order polynomial provides the best fit to the temperature sensors as compared to the standard The CRN uses a thermistor

5. The accuracy of the temperature sensors is being determined by a Hart Scientific Low Temperature Bath

6. A primary requirement for the CRN was adequate power to aspirate the temperature sensors and redundant measurements of temperature A study was conducted on a roof top in the summer for various shield designs

7. For this experiment data were sampled every 2 sec and averaged every 5 minutes The measured 5 minute average temperature from each aspirated shield was differenced with the 5 minute average temperature from the unaspirated shield Only data where the windspeed was less than 1 m/s were analyzed Temperature gradients between the surface and 1.5 m reached 25 0 C

8. The Functional Precision of the Temperature Sensors and shield was determined by using a total of 8 sensors, 4 in two Metone aspirated shields where the comparability is defined as: C =C = 0.1 0 C For all Combination of differences for the eight temperature sensors And was determined to be:

9. To evaluate the potential bias between the intake manifold and temperature sensor location fine wire thermocouples were placed at the air intake and thermistor location Mean absolute difference between the two thermocouples: 0.06 0 C Mean absolute difference between the thermocouple inside the shield and the CRN thermistors: 0.04 0 C Further substantiates that the aspirated shield introduces temperature biases that are no more than 0.1 0 C and are probably less than that

10. We can see that there is a significant difference in the measured temperature difference for the Metone (black), R. M Young (red), and Teledyne Geotech (blue)

11. It is apparent that the Metone shield provides the best estimate of temperature for solar radiation regimes between 400 W/m**2 and 1000 W/m**2 This shield will be used in the initial deployment of CRN stations but there will be an ongoing research effort to determine how well these shields and sensors perform over time and examine new technology in the measurement of temperature that potentially could be integrated into the CRN network

12. In the initial phase all of the CRN stations will be compared for system biases prior to deployment

13. Presently there are Two CRN stations deployed, one at the North Carolina Arboretum

14. And one at the North Carolina State Horticultural Center