A portable instrument can generate video images indicative of physiological stress in plants. The instrument exploits the known relationships among physiological stress in plants, loss of chlorophyll, and changes in spectral reflectance. The instrument acquires multispectral video images of a scene that contains plants, digitizes the images, and processes the image data to generate a new image that maps chlorophyll loss in the scene.
The instrument (see figure) is based partly on the instruments described in the two preceding articles, "Spectral Reflectometer for Quantifying Stress in Plants" (SSC-00050) and "Portable Multispectral Telescope" (SSC-00048). It includes a multispectral telescope similar to the one described in the second-mentioned preceding article, with three spectral channels. Two of the channels would contain narrow-band optical filters centered at wavelengths of 700 and 840 nm, respectively. The third channel is left unfiltered to obtain a panchromatic video image. The images in all three channels are collected by identical video cameras, the outputs of which are processed. As explained in the noted prior article about the multispectral telescope, the three video images are inherently coregistered; this is an important advantage in that it eliminates the need for additional registration steps in processing of image data.
A set of image data is acquired with the telescope aimed at the plants of interest, while two reference detectors, one with identical 700-nm filters and one with identical 840-nm filters, are exposed to incident solar radiance. The ratio of the 700-nm image with the 700-nm reference and the ratio of the 840-nm image with the 840-nm reference are being computed as the images are scanned. Then the outputs are ratioed 700-840 nm to create the final output. This ratio is the desired quantity indicative of the amount of chlorophyll lost by the plant part(s) imaged in the pixel. This ratio is used to control local brightness levels in a synthetic image to indicate local contents of chlorophyll. The synthetic chlorophyll image could, if desired, be overlaid on the panchromatic image.
This work was done by Bruce A. Spiering and Gregory A. Carter of Stennis Space Center.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Stennis Space Center; (228) 688-1929
Refer to SSC-00049