Orbiting satellites often have two types of digital imaging sensors:
– Multispectral, i.e. different sensors for different colors (including IR), or different filters in front of the same sensor. Each individual band can be shown as a black-and-white image; multiple bands can each be assigned a color, and combined to form an RGB color image.
– Panchromatic, “meaning all the colors”, a single broad-spectrum sensor. This are usually displayed as a monochromatic image (i.e. black-and-white).
The panchromatic sensors usually have a higher spatial resolution than the multispectral. For example, on the Landsat 7 spacecraft, the 6 multispectral bands have a spatial resolution of roughly 30 meters (a seventh has 60 meters), while the panchromatic sensor has a resolution of about 15 meters. Here’s an example of an image created from three of the Landsat multispectral bands (data from the Global Land Cover Facility):