Abstract
Thermal infrared cameras provide unique
information on surface temperature that can benefit a range of
environmental, industrial and agricultural applications. However, the
use of uncooled thermal cameras for field and unmanned aerial vehicle
(UAV) based data collection is often hampered by vignette effects,
sensor drift, ambient temperature influences and measurement bias. Here,
we develop and apply an ambient temperature-dependent radiometric
calibration function that is evaluated against three thermal infrared
sensors (Apogee SI-11(Apogee Electronics, Santa Monica, CA, USA), FLIR
A655sc (FLIR Systems, Wilsonville, OR, USA), TeAx 640 (TeAx Technology,
Wilnsdorf, Germany)). Upon calibration, all systems demonstrated
significant improvement in measured surface temperatures when compared
against a temperature modulated black body target. The laboratory
calibration process used a series of calibrated resistance temperature
detectors to measure the temperature of a black body at different
ambient temperatures to derive calibration equations for the thermal
data acquired by the three sensors. As a point-collecting device, the
Apogee sensor was corrected for sensor bias and ambient temperature
influences. For the 2D thermal cameras, each pixel was calibrated
independently, with results showing that measurement bias and vignette
effects were greatly reduced for the FLIR A655sc (from a root mean
squared error (RMSE) of 6.219 to 0.815 degrees Celsius (℃)) and TeAx 640
(from an RMSE of 3.438 to 1.013 ℃) cameras. This relatively
straightforward approach for the radiometric calibration of infrared
thermal sensors can enable more accurate surface temperature retrievals
to support field and UAV-based data collection efforts.
Keywords
thermal infrared camera
calibration
vignetting
UAV
agricultural monitoring
Apogee SI-111
FLIR A655sc
TeAx 640
Tau 2
RPAS