What are multispectral cameras and what are they used for?

A multispectral camera captures not only the three colour channels of visible light, but also several narrow, clearly separated wavelength ranges – typically green, red, red edge and near-infrared. Each channel is recorded as a separate greyscale image and later combined computationally.

Why this shows more than a conventional camera

Healthy plants strongly reflect near-infrared light and weakly reflect red light – stressed plants gradually reverse this relationship. To the human eye, the crop still appears green, whereas the difference is clearly measurable in the infrared channel. Vegetation indices are calculated from the ratio of the channels, the best-known being NDVI. The result is a map showing where problems occur in the crop – often days or weeks before they become visible.

Typical applications

• Agriculture: crop development, fertiliser requirements, irrigation, delineating damaged areas, site-specific application.
• Forestry: stand vitality, drought stress, detecting infestations at an early stage.
• Environmental monitoring and renaturation: documenting vegetation development over several years.
• Soil science: visualising differences in moisture and composition.

Do not confuse it with thermal imaging

A thermal imaging camera measures emitted temperature in the long-wave infrared range. A multispectral camera measures reflected light in several bands. Two different physical quantities, two different questions – and two different sensors.

What you need to consider when using them

Multispectral data is only comparable when the recording conditions are comparable as well. This is why these systems include a light sensor mounted on the top of the drone and a calibration panel that is captured before and after the flight. Without calibration, you cannot meaningfully compare one day's map with another's – and comparing data over time is usually the main purpose.

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