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Using Remote Sensing to Best Monitor Crops and Assess Damage

It is extremely important to keep a finger on the health of all crops. Knowing early on about an infestation can be the key to good productivity. Different factors such as lack of moisture, pests, weeds and fungi should be detected early so that the farmer can deal with the problem. Therefore, it is important that the farmer see images of a crop weekly, at least, and within two days of the image being acquired. This can be done trough remote sensing imagery.

Crops seldom grow evenly all over a field and therefore productivity might be lower in one area of the field compared to another. This may be because of differences in soil nutrition or other stresses. With remote sensing, the farmer can see these problem spots on a field and change the circumstances by, for example, adding fertilizer, herbicide or pesticide. This way, a farmer can improve productivity and decrease spending and environmental impact.

So many players in the industry sell, price and trade crops that have never even been to a field. These people need to know about a crop’s performance globally so that he or she can price and trade appropriately. Most of these tradesmen use services like a crop assessment index to see how a crop’s growth rates, or productivity, compares year to year. They may even use these products to assess a country’s agricultural performance.

Remote sensing may also be able to find areas that may have productivity problems in the future. Take the Ethiopian Famine in the 1980s, for example: it was cause by a drought that killed thousands of crops. When future problem areas are known, efforts to go to their aid can be planned.


Why Remote Sensing?

There are several ways that remote sensing monitors crops. Optical sensing (VIR) offers a particular advantage by showing infrared activity. With infrared, the sensor can better see the health, stress or damage of a crop. In addition to making the invisible visible, remote sensing can show an overview – giving a big-picture view of the land. Recently, farmers are able to use Remote sensing to see problems and communicate the necessary information to address those problems in a timely fashion. Remote sensing reports information about too little or too much moisture, insect or fungal infestations, and damages caused by weather. Remote sensing allows farmers to not only see the problems, but also how the solutions are working.

This picture shows the crop damage caused by a tornado in Winnipeg, Manitoba. A healthy crop would have a lot of chlorophyll (that which makes most plants green). A plant with a lot of chlorophyll would not reflect much light in the blue or red spectrum (because chlorophyll absorbs it), but instead reflect green and near-infrared light. If a crop is damaged or stressed, it would have less chlorophyll, and therefore change its internal structure. Less chlorophyll means less green reflection and internal damage means less near-infrared reflection. If a farmer can see these decreases in reflecting certain spectrums of light, he or she can use this information to detect cop stress early on. Comparing infrared light reflection to  red light reflection is a good ratio to examine the health of a crop.

This is why many have indexed crops. Take the normalized differential vegetation index (NDVI), for example. A healthy plant would rank high on the NDVI because it reflects much infrared light and little red light. One must study the seasonal changes and work hard to affect the NDVI. Irrigated crops versus non-irrigated crops demonstrate how well remote sensing can show a crop’s true health. Irrigated crops look green in a photo, and the rangeland looks darker. But in CIR (color infrared simulated image), healthy crops look bright red – showing that they are reflecting infrared light while rangeland vegetation is low in its reflectance.

It is even possible to understand the health of multiple kinds of crops in one field. If an area is healthy, it would look red on the CIR, but if it is not, it would look darker. The data can be geotagged, making it possible for a farmer with GPS equipment to quickly and easily find the problem spot.

Data Requirements

High-resolution and multispectral imagery are necessary for the detection and monitoring of a crop. It is essential that images acquired are quickly given to the farmer. If a farmer gets an images from two weeks previous, it is of no use to the farmer, who needs to attend to his or her crops in real time and mitigate damages. Images must be frequent and taken at specific times. With remote sensing, a farmer will still need to go out into the fields to attend to the crops, but now will know exactly what demands the most attention.

Canada and the World

Agriculturalists globally care about being efficient, and many nations outside of Canada require remote sensing of a crop’s health. However, most other nations work on a smaller scale. Fields in Asia and Europe are smaller and therefore necessitate higher-resolution but smaller areas to cover. Conversely, The U.S., Russia and Canada, for instance, have larger agricultural areas and have either developed or are developing systems of communicating information. Therefore, lower resolutions on a regional scale (1 kilometer, for example) would work. A lower resolution can be easier on a computer, requiring less memory and processing and therefore increasing efficiency and data storage.

As part of an international investigation, date palms have been suggested to be investigated in the Middle East to see if remote sensing can spot damage caused by the red palm weevil. This crop is one of the Arabian Peninsula’s most important. Dates are very popular in the region. A weevil infestation could destroy hundreds of millions of dollars worth of crop. Spectral analysis will be used to see how healthy the crops are. In a photo, infested spots would look yellow, but will show less near-infrared light reflectance and more red light reflectance on the CIR. There is a hope that remote sensing will help agriculturalists pinpoint infected areas and destroy the weevil while saving the crop. 

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