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Crop canopy sensing with GreenSeeker

Crop canopy sensing technology has been increasingly used in precision agriculture. Imagine that if farmers are able to know the crop’s growth status just by scanning leaves, then the field management will be much more convenient and accurate. Since I am interested in precision agriculture technology, the canopy sensing is really attractive to me. And in my summer internship, I get the chance to experience this fascinating technology.


The canopy sensing technology I use is called GreenSeeker®. It is an active sensing device which contains a light emitter and a receiver. The emitter emits certain wavelengths of light towards the crop canopy, and the receiver measures the light that is reflected by leaves. By comparing the intensity of different wavelengths in reflection, the GreenSeeker can calculate the extent of canopy absorbance of light, which can be use as an indicator of crop growth status. In my case, the normalized difference vegetation index (NDVI) is calculated by the relative absorbance of near-infrared and visible light. High NDVI value (close to 1) indicates vigorous growth, while low NDVI value (close to 0) suggests that the crop is in stress.


To gather the NDVI data at different crop growth stage, field scanning was conducted for many times during my intern. I carried the GreenSeeker and held the sensor above the canopy, walked through the field with my finger pressed on the trigger that controlled the emission of light. The track of my walk was captured by the GPS and was shown on the PDA attached to the GreenSeeker, so I also needed to notice the screen to make sure that I walked in relatively straight line. The sensor emitted one pulse of light per second, so the final results were lines of data points across the field.


Each data point carried lots of information include speed, direction, GPS location, calculated NDVI value, etc. With the GIS software (ArcGIS), we got a scanning map that showed the distribution of NDVI values in the scanned area. The difference in NDVI value indicated the uneven growth status of crops in the field. Such uneven pattern could be explained by the spatial variability of nutrients content in soil, for example, the nitrogen was abundant in some area but deficient in other parts of the field. Then according to different levels of need for nutrients, farmers can adopt variable rate application of fertilizer to maximize the nutrient use efficiency. In this way, farmers could save fertilizer from plants that already had enough nutrients supply from the soil, and thus reduce nutrient losses caused by excessive application.

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