Apogee Surface Temperature Sensors

Infrared radiometers in a range of models for measuring the temperature of vegetation or other surfaces

Measurement of surface temperature is a crucial component of energy transfer. Accurate measurement of the leaf-to-air temperature gradient is essential to the determination of the transpiration rate and stomatal conductance in both single leaves and plant canopies. This gradient is often less than 1oC, which means that leaf temperature should be measured to within 0.2oC.

To achieve this accuracy, the Apogee Instruments precision Infrared Radiometers measure two temperatures. The primary thermocouple is used to measure the sensor body temperature. The output follows fundamental physics of the Stefan-Boltzmann Law allowing for a version of the S-B equation to correct for the effect of sensor body temperature.



  • Most accurate infrared radiometer on the market
  • Measures surface temperature rapidly
  • Uncertainty of 0.2°C (95% confidence)
  • 8-14 m germanium atmospheric window
  • Radiation shield included
  • Multiple field of view (FOV) options
  • Calibrated target temperature range from -30 to 65°C
  • Rugged and lightweight
  • Four year warranty
  • Output - Models with analogue or digital (SDI-12) output
  • Water resistant, designed for continuous outdoor use



  • SI-111: Field of view 22° half angle, analogue output
  • SI-121: Field of view 18° half angle, analogue output
  • SI-131: Field of view 14° half angle, analogue output
  • SI-1H1: Field of view 32° horizontal, 13° vertical, analogue output
  • SI-411: Field of view 22° half angle, SDI-12 output
  • SI-421: Field of view 18° half angle, SDI-12 output
  • SI-431: Field of view 14° half angle, SDI-12 output
  • SI-4H1: Field of view 32° horizontal, 13° vertical, SDI-12 output


About the manufacturer

Apogee manufacture a specialised range of sensors for biophysical studies including light sensors, oxygen and surface temperature (IR) sensors.

All Apogee products are covered by an industry-leading four-year warranty against failure due to defects in materials and workmanship.


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Infrared Meter Specifications

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Infrared Sensor - Analogue - Specifications

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Infrared Sensor - Digital - Specifications

File Size 1.02MB   Filename infrared-sensor-sdi12-specs.pdf   Download