Satellite Imagery-A Valuable Aid to Farmers in Spotting Vegetation Changes in their Fields
|Harel Greenblatt* email@example.com, Ministry of Agriculture and Rural Development|
|February 1, 2021|
In the course of the last few decades, satellite imagery has become a valuable tool in providing information in many domains. One of its many uses is in agriculture. The purpose of this short article is to give a summary of its development and to explain its use and value to farmers.
Today, many companies offer methods to provide access to vegetation indices like NDVI among others, of which NDVI (Normalized Difference Vegetation Index) is one of the most commonly used: it is often quoted in the literature on many research projects. The NDVI was developed after the launching of the Landsat1 satellite in 1973 and has been used since then as a tool to identify and quantify areas with vegetation. During the past few years, the mechanization and technology department in the extension services at the Ministry of Agriculture in Israel has developed a number of websites which allow anyone to get information without any payment whatsoever and with no need to register.
Until the information that is today made available through the use of NDVI, farmers were unable to see variance in their fields without being physically present. Today, it is easy for a farmer to spot the areas with robust vegetation and those where growth is poor and be able to plan a tour of the problematic areas only.
The websites are very friendly and easily accessible worldwide. All that a user needs to do is focus on his area and change the date. The layer will then automatically update.
These websites are based on Sentinel 2 satellites which have a 5- day revisit and a spatial resolution of10 meters which gives 10 pixels in a dunam (or 100 pixels in a hectare). Due to the size of the pixel, these websites are considered the most suitable for field crops, row crops and other crops which are not grown under cover. In each of the websites, there is a slider that enables the user to move easily between images, making it easier to see patterns of growth. Today, although other satellites are available, some with better temporal and spatial resolution, for NDVI monitoring, the Sentinel 2 is still considered the best because access to the data is free and easily obtained.
The main disadvantage with the use of these satellite-based websites is the effect of clouds and shadows. A user may need to wait until the skies are clear. Problems with clouds and shadows can easily be spotted by switching to the "natural color" layer.
The image below shows how easy it is to see if there are clouds.
The best practical illustration of the usefulness of these websites has come from farmers. Here are two examples.
In the second picture, we see the image of the two beds through the eyes, as it were, of a drone.
Finally, in the third picture, we see the view of the two beds from a satellite.
The three images almost speak for themselves, making clear the connection between NDVI and the state of the actual vegetation in the field.
The author would be happy to give advice or to deal with queries:
*Harel Greenblatt, firstname.lastname@example.org
Mechanization and Technology Instructor, Extension Service.