TRITON sensor calibration methods

Wind speed sensors:

The number of propeller rotation is checked with a digital counter given by a motor (Young, model 18801) at 500 rpm (corresponding to the wind speed of 2.45m/s), 1000 (4.9), 3000 (14.7), 5000 (24.5), 7000 (34.3), and 9000 (44.1). Propeller torque for starting rotation is checked in laboratory with a torque meter to keep within the manufacture-recommended value of 2.6 gm ・ cm.

Wind direction sensors:

They are calibrated by checking the output from an encoder in the ASIMET wind sensor module with an encoder reader (Digital, model AD2A), and adjusted to zero degree before deployment if necessary. After the encoder check, directions from ASIMET wind sensor modules are checked in an outfield calibration table before and after deployment, and the vane and the compass are checked at every 90-degree in a clockwise direction and a counterclockwise one.

Air temperature sensors:

They are calibrated using a CTD calibration bath with a reference sensor (SBE-3plus). The calibration factors are derived at 1, 7, 12, 17, 22, 27 and 32 degree-C.

Relative humidity sensors:

They are calibrated at 14 levels from 28.1 %RH to 94.8 %RH using a humidity chamber (Thunder Scientific, Benchtop Two-Pressure Humidity Genarator, model 2500 with humidity generator EM25). The humidity from the chamber is calibrated to make traceable with HYGRO M4-RH/D-2-XR once a year by the Japan Quality Assurance Organization.

Shortwave radiometers:

They are calibrated using an artificial sun chamber (Ishikawa Trading Co., Ltd, model XC-500A with a 500W xenon lamp) in the range from 50 W/m^2 to 1350 W/m^2 by changing the distance between the lamp and a radiometer. Reference radiometer (Epply pyranometer, model PSP) is calibrated to make traceable once a year by the Japan Meteorological Agency.

Optical rain gages:

The output signals being in the allowable range response to the electric test signal inputs are just checked using a manufacture-provided tool. The real water is not used for the calibration.


They are calibrated using a digital pressure controller (Rusuka Instrument Corporation, model 7010) in the range from 880 hPa to 1025 hPa.

The calibration factors of the wind speed and direction sensors, air temperature and humidity sensors, shortwave radiometers and barometers will be rewritten before deployment when the error exceeds the following value, respectively:

+-0.3m/s (wind speed)

+-0.2 degree (wind direction)

+-0.1 degree-C (air temperature)

+-3 %RH (humidity)

+-2 % (shortwave)

+-0.02 % (barometric pressure)