1. is radiated by atomic particles at the
source (the Sun),
2. propagates through the vacuum of
space at the speed of light,
3. interacts with the Earth's
atmosphere,
4. interacts with the Earth's surface,
5. interacts with the Earth's atmosphere
once again, and
6. finally reaches the remote sensor
where it interacts with various optical
systems, filters, emulsions, or
detectors.