Light sensor with modulated radiant polychromatic source

Abstract

An apparatus is described for assessing plant chlorophyll content remotely sensed by the invention thereby allowing selective monitoring or treatment of individual plants. In one preferred embodiment, a polychromatic emitter provides light beams substantially in the red edge portion of a plant's reflectance spectrum. This light beam illuminates a surface area on the plant, which may be bare ground or plants. The beam of light may be focused, collimated or non-focused. A detector array, usually composed of an array of spectrally sensitive detectors, detects portions of this polychromatic light beam reflected by the surface area and provides a signal indicative of the change in chlorophyll status by determining the wavelength of the red edge inflection point REIP. In another preferred embodiment of the invention, an array of sequentially pulsed monochromatic emitters provides light beams having wavelengths substantially along the red edge portion of a plant's reflectance spectrum. These light beams illuminate a surface area on the plant, which may be bare ground or plants. The beams of light may be focused, collimated or non-focused. A photodetector detects the light reflected by the surface area and provides a signal indicative of the change in chlorophyll status by determining the wavelength of the red edge inflection point REIP. In both embodiments, a controller analyzes the resulting REIP wavelength and responds by activating a device to take some action with respect to the plant or stores the analyzed signal with corresponding DGPS position in the controller's memory for later analysis.

Description

[0001] This invention is a continuation in part to U.S. patent application Ser. No. 10 / 703,256BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention relates to a structure and a method for determining changes in the chlorophyll status of a plant via remote sensing of the plant's reflectance spectrum spanning from approximately 650 nm to 800 nm. [0004] 2. Description of Related Art [0005] In order to manage our natural resources in an efficient and cost-effective manner, producers and turf professionals need a way in which to measure and assess the health and performance of their landscapes. For example, the need to know when and how much fertilizer (nitrogen) and other nutrients to apply to a plant to elicit the appropriate growth response is primarily guess work to the producer. Because nitrogen is required by the plant in the greatest quantities and because nitrogen is rather mobile in soils, producers have practiced a one time application of nitrogen t...

AI Technical Summary

Benefits of technology

[0009] The new sensor of the present invention overcomes the time-of-day and fair weather limitations of passive technologies by incorporating its own radiant source and by rejecting the influence of ambient light on the measured canopy reflectance. Unlike passive sensor technology, this sensor will be able to operate under completely dark or full sun conditions. Additionally, the new sensor apparatus is an improvement both in performance and cost over competing active-sensor technologies commercially available.

[0010] As discussed above, the invention presented here will be advantageous in a number of commercial applications. For site-specific agricultural applications, the developed sensor would allow the producer to reduce the amount of nitrogen fertilizer applied to a crop or facilitate spoon-feeding the crop during the growing season, thus having the potential for lowering production costs and enhancing environmental quality. Also, by being able to determine the appropriate fertilizer needs of the crop at any given location in the field, the producer can apply only the fertilizer needed to prevent yield loss or degradation of product quality (i.e., protein content in wheat and barley or sugar content in sugar beets). Subsequently, decreased fertilizer rates will substantially lower nitrogen runoff and leaching losses, which will improve the health of our watersheds, waterways, lakes, and oceans. In addition, data produced by the sensor may be used to produce relative yield maps for forecasting crop production. As for turf grass applications, the sensor technology would allow turf managers to map changes occurring on turf landscapes or for monitoring the status of turf quality.

[0011] In accordance with the present invention, structures and methods are provided for assessing plant status using the chlorophyll status changes and / or biomass properties of the plant remotely sensed, in the red-edge portion of the vegetative reflectance spectrum (˜650 nm to ˜800 nm), thereby allowing selective monitoring or treatment of individual plants.

[0012] When incorporated into variable rate applicator and / or sprayers systems, the present invention significantly reduces the use of fertilizers by precisely applying agricultural products to individual plants to be treated or eliminated. Moreover, the present invention is operable under a wide variety of conditions including cloudy conditions, bright sunlight, artificial illumination, or even total darkness. The advantage to the producer is that field operations do not have to be timed to daytime sunlight hours for operation.

Problems solved by technology

However, over application of nitrogen on agricultural and commercial landscapes has resulted in the contamination of ground and surface waters.

Nitrate contamination is increasing both in area and concentration, particularly beneath landscapes dominated by corn production.

For example, early research by Resource21™ determined that during the optimal fly over times between 10 a.m. and 11 a.m. for satellite imaging, cloud cover had adverse affects on visibility.

Also, spatial resolution for satellite imagery is poor (Landsat, 20 meter and panchromatic, 10 meter).

Similar problems plague aerial photographic methods as well.

Both techniques, however, suffer from the need for extensive data processing (performed by third party providers at high cost and long lead time) and geo-referencing issues.

Even with spectroradiometric methods using sunlight as the ambient light source, cloud cover and time of day (8 a.m. to 8 p.m.) demands limit the mainstream acceptance of the technology for addressing the nitrogen rate over-loading problem.

In certain crops or plant varieties, nutrient deficiencies constitute only part of the management problem.

In particular, the basic problem of determining or monitoring plant status with respect to stress whether it stems from nutrient, water, pest, disease, or otherwise is of primary concern.

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