Design of a Distance-Compensated Infrared Thermometer for Canopy Temperature Monitoring

Infrared (IR) thermometry is essential for non-contact surface temperature monitoring in precision agriculture, but conventional single-pixel devices exhibit distance-dependent measurement errors that hinder field deployment. Most existing solutions require either fixed-geometry installations, post-processing corrections, or expensive thermal imaging systems with computational overhead. This paper presents the design, development, and evaluation of an IR thermometer measurement system that implements a lightweight signal processing algorithm for distance compensation. The instrumentation module integrates the thermometer's temperature signal with ultrasonic distance measurements and employs a distance-bias lookup table (LUT) calibrated at regulated setpoints. Real-time signal conditioning through bilinear interpolation generates corrected temperature outputs. Under controlled reference-target conditions, system evaluation across 5-200 cm shows that uncompensated errors reach approximately -5 °C at 200 cm, whereas the proposed signal processing reduces the distance-dependent residual RMSE to below 0.20 °C over the tested range. The instrument also preserves short-term repeatability, with standard deviations between 0.08 °C and 0.12 °C across stand-off distances from 20 to 200 cm. By delivering distance-invariant measurements through external signal processing, the system is designed to support flexible, height-independent deployment of single-pixel IR thermometry for precision agriculture applications such as canopy temperature monitoring. A preliminary field measurement on a live tree canopy under one overcast condition provides initial evidence that the distance-dependent drift can be reduced outdoors, with the compensated output remaining within 0.7 °C of an external handheld reference across the 5-200 cm range; comprehensive multi-condition field validation remains necessary in future work.