Apogee SI-421 Посібник користувача - Сторінка 4

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Apogee SI-421 Посібник користувача
INTRODUCTION
All objects with a temperature above absolute zero emit electromagnetic radiation. The wavelengths and intensity of radiation
emitted are related to the temperature of the object. Terrestrial surfaces (e.g., soil, plant canopies, water, snow) emit radiation
in the mid infrared portion of the electromagnetic spectrum (approximately 4-50 µm).
Infrared radiometers are sensors that measure infrared radiation, which is used to determine surface temperature without
touching the surface (when using sensors that must be in contact with the surface, it can be difficult to maintain thermal
equilibrium without altering surface temperature). Infrared radiometers are often called infrared thermometers because
temperature is the desired quantity, even though the sensors detect radiation.
Typical applications of infrared radiometers include plant canopy temperature measurement for use in plant water status
estimation, road surface temperature measurement for determination of icing conditions, and terrestrial surface (soil,
vegetation, water, snow) temperature measurement in energy balance studies.
Apogee Instruments SI series infrared radiometers consist of a thermopile detector, germanium filter, precision thermistor (for
detector reference temperature measurement), and signal processing circuitry mounted in an anodized aluminum housing, and
a cable to connect the sensor to a measurement device. All radiometers also come with a radiation shield designed to minimize
absorbed solar radiation, but still allowing natural ventilation. The radiation shield insulates the radiometer from rapid
temperature changes and keeps the temperature of the radiometer closer to the target temperature. Sensors are potted solid
with no internal air space and are designed for continuous temperature measurement of terrestrial surfaces in indoor and
outdoor environments. SI-400 series sensors output a digital signal using SDI-12 protocol version 1.3.