A miniature integrated sensor for measuring reflectance, relative humidity, and temperature: A greenhouse example

Authors: Fletcher, Reginald; Fisher, Daniel

Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2018
Publication Date: 11/30/2018
Citation: Fletcher, R.S., Fisher, D.K. 2018. A miniature integrated sensor for measuring reflectance, relative humidity, and temperature: A greenhouse example. Agricultural Sciences. 9(11):1516-1527.

Interpretive Summary: There is a growing interest in using miniature multi-sensor technology to monitor plant, soil, and environmental conditions in greenhouses and in field settings. ARS Scientists at Stoneville, MS built a small multi-channel sensing system (approximately 3 x 3 inches) with the ability to measure visible and near infrared light reflectance, relative humidity, and temperature. They tested the system in a greenhouse by measuring light reflectance properties of plants and soilless media and the relative humidity and the temperature of the greenhouse environment. Reflectance, relative humidity, and temperature measurements collected with the miniature multi-sensor system was comparable to reflectance, relative humidity, and temperature data collected with expensive laboratory and greenhouse equipment. Advantages of using the sensor system are that the user has more control over when it collects data and has the ability to use open source and free software to customize scripts needed to control the sensor system for their projects. Overall, the proposed sensing system showed good potential as a tool to measure spectral response patterns of plant and potting mix material and environmental conditions relevant to greenhouse studies. The system was inexpensive to build; the total cost of its components was $123.

Technical Abstract: There is a growing interest in using miniature multi-sensor technology to monitor plant, soil, and environmental conditions in greenhouses and in field settings. The objectives of this study were to build a small multi-channel sensing system with ability to measure visible and near infrared light reflectance, relative humidity, and temperature, to test the light reflectance sensors for measuring spectral characteristics of plant leaves and soilless media, and to compare results of the relative humidity and temperature sensors to identical measurement obtained from a greenhouse sensor. The sensing system was built with off-the-shelf miniature multispectral spectrometers and relative humidity and temperature sensors. The spectrometers were sensitive to visible, red-edge, and near infrared light. The system was placed in a greenhouse setting and used to obtain relative reflectance measurements of plant leaves and soilless media and to record temperature and relative humidity conditions in the greenhouse. The spectrometer data obtained from plant leaf and soilless media were compatible with baseline spectral data collected with a hyperspectral spectroradiometer. The greenhouse was equipped with a relative humidity and temperature sensor. The relative humidity and temperature sensor measurements from our sensor system were strongly correlated with the relative humidity and temperature results obtained with the greenhouse sensors, and the mean relative humidity and temperature sensor values were similar for our system and the greenhouse system. Overall, the proposed sensor showed good potential as a tool to measure spectral response patterns of plant and potting mix material and environmental conditions relevant to greenhouse research. The system was inexpensive to build; the total cost of its components was $123.