Multispectral sensors collect information across the entire electromagnetic spectrum

Multispectral sensors collect information across the entire electromagnetic spectrum, using multiple bandwidths, which allows the spectrum to be split into distinct regions.
 
Near-infrared orthomosaic generated from UAS-acquired multispectral imagery showing Algal bloom areas accumulating near the shores of Milford Lake in Kansas (top). 

Near-infrared image of an area in North Dakota’s Theodore Roosevelt National collected with a multispectral sensor mounted on a UAS (bottom).

Most commercially available UAS-compatible multispectral sensors can collect the visible and near-infrared (VNIR) wavelengths in individual bands which provides one of the best imagery sources for land surface classification and vegetation monitoring. UAS-collected multispectral imagery with bands in the visible red and near-infrared (NIR) range can be used to generate Normalized Difference Vegetation Index (NDVI) maps. NDVI calculations create a standardized index utilizing the amount of red light compared to NIR light reflected from a plant. Within this range, red indicates areas with high NIR reflectance, associated with healthy plants, and blue shades indicate lower NIR reflectivity and possibly less healthy vegetation.