Measurements

Starting in June 1994 weather data has been collected in the wet sedge experimental plots (block 1) at the Arctic Tundra LTER site at Toolik Lake. Air temperature and relative humidity (3 meters) and soil temperatures at surface, 10 and 25 cm depths are measured on the following treatment plots:

• Control
• Nitrogen alone
• Phosphorus alone
• Nitrogen plus phosphorus
• Greenhouse.

Air temperature and relative humidity are measured every minute and averaged every hour while soil temperatures are measured every 3 minutes and averaged every 4 hours. The shade and greenhouses covers are only installed June thru August.

Sensor and Equipment Description

Following are brief descriptions of the sensors used. Company addresses follow the list.

• Data Logger - Campbell Scientific CR10 Multiplexer - Campbell Scientific AM416 Panel temperature - Campbell Scientific 10TCRT Air temperature/ RH - Campbell Scientific 207; Humidity sensor replaced every 2-3 years. Replaced with CS500 Aug 1999
• Soil Thermocouples - Custom made using Omega Engineering, Copper-Constantan wire. Range -200 to 350 °C. Limits of error: Standard wire 1.0°C or 0.75% above 0°C and 1.0°C or 1.5% below 0°C. Special wire 0.5°C or 0.4%.
• Campbell Scientific, Inc. 81 W. 1800 N. Logan, Utah 84321-1784 (435)750-1739  Omega Engineering, Inc. P.O. Box 4047 Stamford, CT 06907-0047 (800)826-6342

Calculations

• DAYS: JULIAN + (HOUR/2400)
• VAPOR PRESS: If Air Temp > 0 then (RH /100) * 6.1121 * exp(17.368 * AIR TEMP /(238.88 + AIR TEMP )) If Air Temp < 0 then (RH /100) * 6.1121 * exp(17.966 * AIR TEMP/(238.88 + AIR TEMP )) From Buck 1981. Reference Citations: Buck, A.L. 1981 New equations for computing vapor pressure and enhancement factor. Journal of Applied Meteorology 20:1527-1532

Notes and comments

• Shade and greenhouses are not covered year round. They are covered early June and uncovered mid-August. The sensors are up year round.
• During the winter of 1994-1995 a program error caused the data from 20Aug94 to 28Mar95 to be lost. Data was also lost during winter 1995-1996.
• 1996 – Relative humidity is low, never reaching above 90%. Data were not corrected. RH sensor replace summer 1996.
• 1999 18Aug Changed out the 207 temp/RH sensor replacing with a CS500. Since the CS500 only goes to -39 C the 207 is used to measure the temperatures below -40C and as a backup. Note that the 207 measurement error below -40 C is large. See Campbell's manual on the 207/107. The 207 was discontinued since the RH senor is no longer available.
• 2001 Added a subroutine to calculate the reference and air 107 temperature probes using a Steinhart-Hart equation: The voltage of a 107 probe is converted to resistance then converted to both Kelvin and Celsius using 1/T= A + B ln Rs + C(lnRs)^3 where T = Kelvin and A,B and C are constants derived from the temperature vs resistance data of the Fenwell thermistors. Rs is the measured resistance. This will improve the accuracy of temperatures below -30C.
• 2002 The control relative humidity sensor stopped working. Not sure why.
• 2003 The data logger stopped collecting data from Feb through May. The temperature and RH sensors failed from May to August due to a faulty splice in the cable. The 3 meter temperature was not replaced until June 2004
• 2004 The 3 meter temperature/RH probe replace June with the same model - CS500
• 2011 Lost power from 4Aug to 6Aug caused by a corroded battery wire.
• 2012 Replace 207 with a 107 Thermistor. The old 207 cable was cracking. The 107 is in the same shield as the CS500.
• 21Mar2014  Changed soil output to every hour with reads every 120 sec.  Seeing if this will give smoother temperature values. Jim L
• 2015May added panel temperature average to output.  Trying to see if this is causing jumpy soil temps.  Jim L
• May2015 Corrected the coefficients on the Steinhart equation.  The thermistor is a newer one (Belatherm 100k6A). Jim L
• Aug 2015 Redid the subroutine for calculating the Steinhart Hart equation based on the Campbells Scientific's 109 manual. Using a half bridge to read the 107 See notes in Sub 3   Changed the soil to 3 hour averages. Jim L
• Aug 2019 Changed logger to a CR23XPB.  It now uses the PakBus radio Network and will have room for more soil temperature probes.  Jim L