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

Apogee SI-111 Standard View

The SI-111 has a 22 degree half angle field of view. The sensor has tinned leads for connecting to a datalogger. Applications include measuring the temperatures of road surfaces, plant canopies, and soil, snow and water surfaces.

If you are using any SI-100 series sensor with Campbell Scientific Dataloggers, please view the three notices from Campbell Scientific and Apogee to the right.

Measures surface temperature rapidly.
Calibrated target temperature range from -30 to 65°C.
Uncertainty of 0.2°C (95% confidence)
8-14 µm germanium atmospheric window

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°
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.

Radiation shield included
Multiple field of view (FOV) options
Rugged and lightweight

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.


Approximate Sensitivity: 60 µV per C
Output from Thermistor: 0 to 2500 mV (typical, depends on input voltage)
Input Voltage Requirement: 2500 mV excitation (typical, other voltages can be used)
Calibration Uncertainty (-20 to 65°C): 0.2°C, when target and detector temperature are within 20°C
Calibration Uncertainty (-40 to 80°C): 0.5°C, when target and detector temperature are different by more than 20°C
Measurement Repeatability: < 0.05°C
Stability (Long-term Drift): less than 2 % change in slope per year when germanium filter is maintained in a clean condition
Response Time: 0.2 s
Field of View: 22° half angle
Spectral Range: 8 to 14 µm; atmospheric window
Operating Environment: -55 to 80°C, 0 to 100% relative humidity (non-condensing)
Dimensions: 2.3 cm diameter and 6.0 cm length
Mass: 190 g (with 5m of lead wire)
Cable: 5m of four conductor, shielded, twisted-pair wire. Additional cable available in multiples of 5m. Santoprene rubber jacket (high water resistance, high UV stability, flexibility in cold conditions). Pigtail lead wires.
Warranty: 4 years

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.

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.


  • AA-100: Protective Carrying Case
    Protective carrying case designed to transport and store Apogee meters, sensors, and accessories.
  • Infrared Radiometer/Frost Detector Mounting Bracket
    The AM-210 mounting bracket is designed to orient sensors at varying angles to satisfy all applications. The bracket can be mounted to a mast or pipe with an outer diameter of 1.3 to 2.1 inches, while the sensor bracket will accommodate sensors with an outer diameter of 1.0 to 1.5 inches (e.g. SI-100 series and SF-110).