Design and operation of an imaging sensor for detecting vegetation

There is a need to sense vegetation from ground‐based vehicles so that plants can be treated in a selective way, thus saving on crop treatment measures. This paper introduces a sensor for detecting vegetation under natural illumination that uses three filters, red, green, and near infra‐red (NIR), with a monochrome charge couple device (CCD) camera. The sensor design and the data handling are based on the physics of illumination, reflection from the vegetation, transmission through the filters, and interception at the CCD. In order to model the spectral characteristics of the daylight in the NIR, we extend an existing standard using a black body model. We derive suitable filters, develop a methodology for balancing the sensitivity of each channel, and collect image data for a range of illumination conditions and two crop types. We present results showing that the sensor behaves as we predict. We also show that clusters form in a measurement space consisting of the red and NIR chromaticities in accordance with their expected position and shape. Presentation in this space gives a good separation of the vegetation and nonvegetation clusters, which will be suitable for physically based classification methods to be developed in future work. © 2000 John Wiley & Sons, Inc. Int J Imaging Syst Technol 11, 144–151, 2000