Understanding the difference between multispectral, hyperspectral, and SAR

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Multispectral and hyperspectral satellites

There is an inverse correlation between a sensor’s spectral resolution, or how well it can discriminate between spectral bands, and sensor’s spatial resolution, or how fine the pixels on the ground will be. Which is why satellites which records data along a large number of spectral bands (hyperspectral) do not offer the same type of spatial resolution as satellites which record data along much larger bands of the light spectrum (multispectral).

 

As a result, very high resolution multispectral satellites only capture data along 5-10 bands of the spectrum, most often all three primary colours, and a few blocks in the infrared portion. Multispectral satellites follow a sun-synchronous, Low Earth Orbit.

 

Hyperspectral satellites, on the other hand can detect thousands of different bands within the light spectrum. Which is extremely helpful to detect certain minerals or objects if you are familiar with their spectral properties. Hyperspectral satellites follow a sun-synchronous, Low Earth Orbit.

 

Synthetic Aperture Radar satellites (SAR)

Contrary to multispectral and hyperspectral satellites, Synthetic-aperture radar (SAR) satellites do not require sunlight to illuminate the scenes they capture. To create a SAR image, successive pulses of radio waves are transmitted to "illuminate" a target scene, and the echo of each pulse is received and recorded. However, SAR satellites do require sun as their emitters are solar-powered. SAR satellites requires large recharge time between each data capture. 

SAR satellites are used to create two- or three-dimensional images of objects, such as landscapes. With radars, the size of the aperture determines the resolution of the image. With SAR, a larger antenna aperture is simulated by simply mounting the sensor on a moving satellite. The distance travelled in the time necessary for the radio waves to be reflected back to the antenna synthetically increases the size of the antenna, thus providing high resolution imagery.

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