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  Wind Speed and Direction
  Temperature and Relative Humidity
  Water Temperature
  Shortwave Radiation
  Longwave Radiation

  Lake Tahoe Site Sensors

Wind speed and direction
The Met One cup and vane and the RM Young propeller and vane units operate on similar principles. For speed, the cups or the propeller rotate a shaft. The data logger counts the number of shaft rotations over a period of time and calculates the wind speed. For direction, the vane is mounted on a vertical shaft which turns a potentiometer (a variable resistor). The resistance of the potentiometer is proportional to direction. The data logger measures the resistance by applying a fixed voltage, and then converts the result to wind direction.

The Vaisala/Handar sonic wind unit uses the speed of sound to measure wind speed and direction. There are three sensor arms, each with a sound transmitter and a microphone. The three sensors form an equilateral triangle, with two of the sensors aligned north-south, while the third is to the east. The unit transmits a sound signal both ways between each pair of sensors, and measures the time it takes for the sound to travel from one to the other. Since the sound will travel faster downwind than upwind, the unit uses the measured travel times to calculate both wind speed and direction.

Temperature and relative humidity
The Campbell Scientific (Vaisala) HMP45C unit uses a platinum resistance thermometer (PRT) and Vaisala’s Humicap® 180 capacitive relative humidity sensor.

The RM Young 42372VC uses a platinum resistance temperature detector (RTD) for temperature and a Vaisala Intercap® interchangeable capacitive humidity sensor.

Water temperature
The Campbell Scientific 107 temperature sensor uses a thermistor with a half-bridge circuit to measure temperature. A thermistor is a resistor whose resistance varies with temperature. The datalogger applies a fixed voltage and measures the output voltage, which is converted to temperature.

Shortwave radiation
The Kipp and Zonen CM21, and the two CM3 shortwave sensors which are part of the K+Z CNR1 net radiometer, measure solar radiation with wavelengths between 0.3 and 2.8 microns (micrometers), which includes the visible light spectrum.

Longwave radiation
The Eppley PIR, and the two CG3 longwave sensors which are part of the K+Z CNR1 net radiometer, measure infrared (thermal) radiation, with wavelengths between approximately 5 and 50 microns.

The TE525 rain gauge uses a tipping bucket to measure precipitation. A funnel collects rain or snow over a fixed area and directs it to the center of the unit. Inside the unit is an arm with a small container on each end. One or the other of the containers is always underneath the funnel. When the container fills with a calibrated amount of water, its weight causes the arm to tip, spilling the water and moving the opposite container into position. The data logger counts the number of tips and calculates the amount of rainfall. In the TE525, each 0.254 millimeters (0.01) inch of rain causes the arm to tip.

Lake Tahoe Site Sensors
-- More sensor details at the Sensors link under Online Guide of the REMOTE site or click here.

Parameter Manufacturer Model Description Locations Link
Wind speed and direction Met One Instruments 034A/B Cup and vane USCG, Tahoe Vista, Sunnyside, Rubicon, Timber Cove, Cave Rock Link
Vaisala/Handar 425AH Sonic USCG Link
RM Young 5106 MA Propeller and vane TDR1, TDR2 Link
RM Young 32500 Electronic compass TDR1, TDR2 Link
Air temperature and relative humidity Campbell Scientific (Vaisala) HMP45C   USCG, Tahoe Vista, Timber Cove, Cave Rock, TDR2 Link
Campbell Scientific (Vaisala) CS500   Sunnyside Link
RM Young 41372VC   TDR1 Link
Water temperature Campbell Scientific 107 Thermistor USCG, Tahoe Vista, Sunnyside, Rubicon, Timber Cove, TDR1, TDR2 Link
Shortwave radiation Kipp and Zonen CM21   USCG Link
Kipp and Zonen CNR1 Shortwave and longwave net radiometer USCG Link
Longwave radiation Eppley PIR Precision infrared radiometer USCG Link
Kipp and Zonen CNR1 Shortwave and longwave net radiometer USCG Link
Barometric pressure Campbell Scientific (Vaisala) CS105   USCG, Cave Rock Link
Precipitation Campbell Scientific (Texas Electronics) TE525 Tipping bucket gauge USCG, Tahoe Vista, Sunnyside, Cave Rock Link