The amount of energy that vegetation reflects is related to the internal structure of the plant, and the amount of moisture in the plant. A surface like astro-turf, which is coloured green, will appear dark in the near infrared, because it doesn't have the internal structure of living vegetation. Another feature to notice is that clear water reflects visible light only, so it will appear dark in infrared images.

The image on the left is of wavelengths in the near infra red only, while the one on the right is a combination of red, near infra red and middle infra red wavelengths, in false colours. The combination of these three makes the image easier to interpret. The dark areas in these images signify water.
In the image to the right, the darker shades of green signify coniferous forest, while brighter greens signify leafy forest or meadow. Areas that appear pink are either areas of wood felling, or cultivated land.
The image is from the Landsat satellite, and is taken in August over South-Eastern Norway.

Since the human eye can only perceive radiation within a limited interval of the electromagnetic spectrum, instruments for remote sensing outside the visible wavelengths actually represent an extension of our visual field. They give us access to additional information about the physical reality surrounding us.

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