Understanding the difference between multispectral, hyperspectral, and SAR

April 28, 2022

Multispectral and hyperspectral satellites

A sensor’s spatial resolution, or how fine the pixels on the ground will be, is inversely related to its spectral resolution or how well it can discriminate between spectral bands. Because of this, satellites that record data along multiple spectral bands (hyperspectral) do not have the same spatial resolution as satellites that record data along larger bands of the light spectrum (multispectral).

This means that multispectral satellites can only capture data along 5-10 bands of the spectrum, most often all three primary colours and a few blocks in the infrared. Multispectral satellites orbit in a sun-synchronous, Low-Earth Orbit.

On the other hand, a hyperspectral satellite can detect thousands of different bands within the light spectrum. This can be extremely helpful in detecting certain minerals or objects if you are familiar with their spectral properties. It follows a sun-synchronous, Low Earth Orbit.


Synthetic Aperture Radar satellites (SAR)

It is important to note that synthetic aperture radar (SAR) satellites do not need sunlight to illuminate their images, unlike multispectral and hyperspectral satellites. A SAR image is created by sending successive radio waves to illuminate a target scene and receiving and recording the echoes of each pulse. However, the emitters of SAR satellites are powered by the sun, requiring a lot of recharge time between data collection.

In SAR satellites, images of objects, such as landscapes, are created in two or three dimensions. In radar, an image’s resolution is determined by the size of the aperture. In SAR, a larger antenna aperture is simulated by mounting the sensor on a moving satellite. By synthetically increasing the antenna size, the distance travelled in the time required to reflect radio waves increases the image’s resolution.

To learn more about these applications, read our Ultimate Satellite Imagery Guide.

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