Interesting article about calibrating sensors:
Effective Calibration of Low-Cost Soil Water Content Sensors
Heye Reemt Bogena * , Johan Alexander Huisman, Bernd Schilling, Ansgar Weuthen and Harry Vereecken Institute of Bio- and Geosciences, Agrosphere Institute (IBG-3), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany * Author to whom correspondence should be addressed.
Academic Editor: Gonzalo Pajares Martinsanz
Received: 27 November 2016 / Revised: 12 January 2017 / Accepted: 16 January 2017 / Published: 21 January 2017
Abstract Soil water content is a key variable for understanding and modelling ecohydrological processes. Low-cost electromagnetic sensors are increasingly being used to characterize the spatio-temporal dynamics of soil water content, despite the reduced accuracy of such sensors as compared to reference electromagnetic soil water content sensing methods such as time domain reflectometry. Here, we present an effective calibration method to improve the measurement accuracy of low-cost soil water content sensors taking the recently developed SMT100 sensor (Truebner GmbH, Neustadt, Germany) as an example. We calibrated the sensor output of more than 700 SMT100 sensors to permittivity using a standard procedure based on five reference media with a known apparent dielectric permittivity (1 < Ka < 34.8). Our results showed that a sensor-specific calibration improved the accuracy of the calibration compared to single “universal” calibration. The associated additional effort in calibrating each sensor individually is relaxed by a dedicated calibration setup that enables the calibration of large numbers of sensors in limited time while minimizing errors in the calibration process. View Full-Text
Keywords: soil water content; permittivity; calibration; sensor-to-sensor variability; SMT100 sensor
This article is available here: http://www.mdpi.com/1424-8220/17/1/208