Using Infrared Sensor for Large Area Canopy Total Temperature Measurements of Rice Plants

Abstract

Measuring the temperature of rice plant canopies is important for agronomy and crop-growth research. Commercial infrared thermometers are poorly suited for this task because they are unable to measure the temperature over a large area of rice canopy, and the emissivity measured is not specific to the rice plant canopy, resulting in large errors in measurement. By analyzing the infrared properties of rice plant canopies, an infrared optical system is used to develop an infrared sensor to measure the temperature of a large area of rice plant canopy. This study analyzes the principles of temperature measurement using infrared sensors and designs the optical and electrical systems for the sensor. The field of view (FOV) of the sensor is set to 53.2; consequentially, the sensor can measure the total temperature of a circular area with a diameter equal to the distance from the sensor to the rice canopy. Data analysis shows that the rice canopy emissivity is 0.9355; this value is inserted into the measurement model. This study analyzes the following variables with respect to rice canopy temperature measurement: 1) accuracy of the sensor versus a thermometer, 2) influence of different varieties of rice plants and 3) the influence of sensor distance from the canopy. Between 5 and 60 cm is determined to be the optimal measurement range. The results show that the methods proposed in this article can measure the temperature of large areas of rice canopy (when the measuring distance is set to 60 cm, the measuring area is 0.283 m2). This method has the advantage of real-time, highly sensitive, and non-contacted measurements.