FruitLook 2021 March: How does satellite data work?

Satellites can help us gain more information on our crop than is visible to the eye. Calculations made with multiple light spectrums can show us vegetation properties and teach us about the state of crops. But what is the light spectrum?

Light spectrum:

The light which our eyes – our “remote sensors” – can detect is part of the visible spectrum. It is important to recognize how small the visible portion is relative to the rest of the spectrum. There is a lot of radiation around us that is “invisible” to our eyes but can be detected by other remote sensing instruments and used to our advantage. The visible wavelengths cover a range from approximately 0.4 to 0.7 µm. The longest visible wavelength is red and the shortest is violet.

The electromagnetic spectrum ranges from the shorter wavelengths (including gamma and x-rays) to the longer wavelengths (including microwaves and broadcast radio waves). There are several regions of the electromagnetic spectrum which are useful for remote sensing. For most purposes, the ultraviolet or UV portion of the spectrum has the shortest wavelengths which are practical for remote sensing. This radiation is just beyond the violet portion of the visible wavelengths, hence its name. Some Earth surface materials, primarily rocks and minerals, fluoresce or emit visible light when illuminated by UV radiation.

 

Satellites:

There are more than 2.500 satellites currently in space providing us services on earth, around 450 of them are used for earth observation. The others are there for communication, research, GPS service, etc. Those satellites carry different equipment and focus on different parts of the earth surface. For FruitLook Sentinel-2 and Landsat 8 are among the satellites used on a weekly basis. They provide us with large images in different spectra which we can calculate with, an import aspect is the reflectance of crops that we can capture.

Reflectance:

Near-infrared (NIR) and red reflectance (RED) are used widely to indicate the health of vegetation. Red reflectance is absorbed by chlorophyll for photosynthesis and the structure of plant cells reflects near-infrared. A healthy plant will absorb therefore more red reflectance and reflect more near-infrared.

What about water?

The Actual Evapotranspiration (ETact):  refers to all water “used” in transpiration and evaporation from the surface. The models used in FruitLook revolve around solving the surface energy balance, or simply put: determining how the energy from the sun that reaches the earth is used in different processes.  This includes warming the air and soil and driving transpiration and evaporation. These same processes can be measured in the field via energy flux measurements.  Results from the past years showed that the ETact from FruitLook compares well to the one independently measured in the field, for a range of land uses.

We hope to have given you some more information on what is happening behind the scenes of FruitLook. If you want to know more, just let us know! You can reach us on email and find us on FacebookLinkedIn and for tutorials on YouTube. This Thursday we will have webinars ready for you in Afrikaans with information on how to use FruitLook, check the webinar that is best for you!

Part 1/3  – Getting Started: This is for beginners who have never been on FruitLook before and would like some help to register fields for the first time. This part is starting at 09:00. Click on the link for more information and to register.

Part 2/3 – Introduction to FruitLook: For those who already have an account and fields ordered, you can join from here onwards. In this part, the data components and website functionalities will be explained, as well as how the data is produced. This webinar session will start at 10:00. Click on the link for more information and to register.

Part 3/3 – Website functionality and data analysis: For the users already well accustomed to this tool, you can choose to only join at this part, at 11:00. Please click on the link to find out what we will be presenting in this part and to register for it.

Have a fruitful week!

The FruitLook Team