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Enabling better global research outcomes in soil, plant & environmental monitoring.

Apogee SI-100 Series Infrared Radiometers

Apogee Instruments Infrared Radiometers (IRRs) measure surface temperature by converting thermal energy radiated from any surface in its field of view (FOV) to an electrical signal with a response time less than 1 second.

Applications include measuring the temperatures of road surfaces, plant canopies, and soil, snow and water 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 transpiration rate and stomatal conductance in both single leaves and plant canopies.

Available Field of View options:

  • Model SI-111 FOV = 22.0°
  • Model SI-121 FOV = 18.0°
  • Model SI-131 FOV = 14.0°
  • Model SI-1H1 FOV = Horizontal 32.0°, Vertical 13.0°

Radiation shield included.

Field of View (FOV) is reported as the half-angle of the apex of the cone formed by the target (cone base) and the detector (cone apex). The target is a circle from which 98% of the radiation being viewed by the detector is being emitted.

The 8-14 µm window of the SI models corresponds to the atmospheric window. This minimises the effects of water bands below 8 µm and above 14 µm.

Each IRR carries an impressive uncertainty of 0.2°C at 95% confidence to ensure accurate measurements. The resilient 8 – 14 µm germanium window corresponds to the atmospheric window in order to minimise the effects of water bands below 8µm and above 14µm.

The radiation shield, included free of charge with every IRR, insulates the sensor from rapid temperature changes, thus reducing noisy measurements. Multiple field-of-view (FOV) options range from half angles of 14, 18, and 22 degrees, for circular apertures, to 13 and 32 degrees for the vertical and horizontal half angles, respectively, of the horizontal aperture.

The large range of calibrated target temperature, from -30 to 65°C, allows you to make accurate terrestrial measurements when the sensor body temperature is within 20°C of the target temperature. The durable clear anodised aluminium housing makes your sensor strong and lightweight, capable of withstanding extreme weather conditions

Analogue Output:
SI-111 60 µV per °C
SI-121 40 µV per °C
SI-131 20 µV per °C
SI-1H1 40 µV per °C
Input Voltage Requirement: 2500 mV thermistor excitation (typical, other voltages can be used)
Analogue Output from Thermistor: 0 to 2500 mV (typical, depends on input voltage)
Calibration Uncertainty (-20 to 65°C, when target and detector ΔT are < 20°C):
SI-111 0.2°C
SI-121 0.2°C
SI-131 0.3°C
SI-1H1 0.2°C
Calibration Uncertainty (-40 to 80°C, when target and detector ΔT are > 20°C):
SI-111 0.5°C
SI-121 0.5°C
SI-131 0.6°C
SI-1H1 0.5°C
Measurement Repeatability: Less than 0.05°C
Long-term Drift: Less than 2% change in slope per year when germanium filter is maintained
Field of View (half-angle):
SI-111 22°
SI-121 18°
SI-131 14°
SI-1H1 32° horizontal; 13° vertical
Response Time: 0.6s, time for detector signal to reach 95% following a step change
Spectral Range: 8 to 14µm; atmospheric window
Operating Environment: -55 to 80°C; 0 to 100% relative humidity (non-condensing)
Dimensions: 23mm diameter, 60mm length
Mass: 190g (with 5m of lead wire)
Warranty: 4 years against defects in materials and workmanship