Apogee Infrared Radiometers

SI-1xx, SI-4xx, MI-1xx
Surface Temperature

For measurement of surface temperature.

Now available with SDI-12 output option.

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 Infra Red 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.


  • Field of View - 4 options:
    • Standard SI-111: 22oC half angle
    • Narrow SI-121: 18oC half angle
    • Ultra-narrow SI-131: 14oC half angle
    • Horizontal SI-1H1: 32oC horizontal, 13o C vertical
  • Power Supply Requirements: 2.5V Excitation
  • Accuracy:
    • -10 to 65°C = ± 0.20oC
    • -40 to 70°C = ± 0.50oC
  • Output - 2 options:
    • Analogue - Datalogger Channels required: 1 x Differential Voltage (Target Surface) & 1 x Single Ended Voltage (Sensor Body)
    • Digital - Datalogger Channels required: 1 x Digital (SDI-12)
  • Operating Environment: -55 to 80°C; 0 to 100% RH (non-condensing); Water resistant, designed for continuous outdoor use
  • Response Time: Less than 1 second to changes in target temperature
  • Wavelength Range: 8 to 14 µm



Carry Case The AA-100 carry case is an optional accessory for protecting meters in the field
Mounting Bracket

The AM-210 is designed to mount on a pole and orient sensors at varying angles to satisfy all applications.

Replacement Shield

The AI-100 improves the performance of Apogee infrared radiometer sensors in applications where there is a significant solar load on the sensor housing. This shield is included on all new infrared sensors and is offered as an accessory for customers wishing to retro-fit previously purchased infrared sensors.

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

File Size 1.08MB   Filename infrared-meter-specs.pdf   Download

Infrared sensor specifications - Analogue

File Size 1.04MB   Filename infrared-sensor-specs.pdf   Download

Infrared sensor specifications - SDI12

File Size 1.04MB   Filename infrared-sensor-sdi12-specs.pdf   Download