2.5 - Bidirectional reflection

So far we have seen that the visual perception of colour is related to the differential absorption/reflection of radiation by an object in the different regions of the electromagnetic spectrum. But why do we perceive different intensities of light? What physical explanation is behind the creation of patterns of lightness and darkness?

To answer to this question we must consider the different ways an object may reflect light. This is primarily a function of the object surface’s roughness.

Exercise: According to this, objects are classified as (Please select the proper figure corresponding to each definition):

The Sun Glint effect mentioned in the exercise can be seen in next figure taken with MSG-1:

Figure 2.11 - Midday sun glint over the Kongo river (in black) MSG-1, 24 March 2004, 09:00 UTC, Channel 3.9 μm
(Image taken from http://oiswww.eumetsat.org/WEBOPS/msg_interpretation/PowerPoints/Channels/Channel_IR39.ppt, accessed in 2010)