ABSTRACT
We all use our natural senses to observe and explore the environment in which we live. Certain of these — smell, taste and, more often than not, touch — permit us to assess environmental qualities directly, through our neurophysical responses to the gases, liquids and solids with which we have immediate contact. The others — sight and hearing — can make us aware of more distant features through the patterns of energy propagations associated with them. Feeling, e.g. manifested through the sensitivity of skin to heat, also enables us to assess some characteristics of distant phenomena. These last three appreciations of the behaviour of energy sources some distance from ourselves are natural forms of remote sensing.
