Human eyes see the reflected energy from objects in three channels: red, green and blue. We don’t have the luxury of seeing ultraviolet and infrared radiations on our own.
This can be done with multispectral and hyperspectral sensors.
Visible (red, green and blue), infrared and ultraviolet are descriptive regions in the electromagnetic spectrum.
We made up these regions for our own purpose – to conveniently classify them. Each region is categorized based on its frequency (v) /wavelength (λ):
- Visible light for humans: 380 nm to 700 nm
- Infrared: 700 nm to 1mm
- Ultraviolet: 10 nm to 380 nm
The main difference between multispectral and hyperspectral is the number of bands and how narrow the bands are.
1. Multispectral imagery generally refers to 3 to 10 bands that are represented in pixels. Each band is acquired using a remote sensing radiometer.
Multispectral Example: 5 wide bands (Image not drawn to scale)
2. Hyperspectral imagery consists of much narrower bands (10-20 nm). A hyperspectral image could have hundreds of thousands of bands. This uses an imaging spectrometer.
Hyperspectral Example: Imagine hundreds of narrow bands (Image not drawn to scale)
Multispectral vs Hyperspectral
Having a higher level of spectral detail in hyperspectral images gives better capability to see the unseen.
For example, hyperspectral remote sensing can distiguish between 3 minerals because of its high spectral resolution.
It also adds a level of complexity: 200 narrow bands can be difficult to work with at times.
Hyperspectral and multispectral images have many real world applications. For example, hyperspectral imagery has been used to map invasive species and help in mineral exploration.
There are hundreds more applications in the fields of agriculture, ecology, oil and gas, oceanography and atmospheric studies where multispectral and hyperspectral remote sensing are being used to better understand the world we live in.
Case Study : Agriculture
This vital sector is always pleased to integrate new solutions built to improve the efficiency and results of collections. Being exposed to numerous stress factors, it is necessary to spot as soon as possible a lack of water or nutriments and the presence of parasites or other wild animals for example.
Thanks to a UAV equipped with an hyperspectral camera, this troubling factors can be spot early while already occurring but not being visible yet with the naked eye. The camera covers the entire field by scanning it. The disturbed areas will reflect certain wavelengths while the rest of the field won’t.
This precious and quickly obtained information allows to define precisely the area in need of an intervention. Therefore, the resources are used where they are needed and this management guarantee successful collection with cost-efficient surgical operations.