RS fundamentals are physics and knowledge engineering.
Physics is about hypothesis generation and testing by performing measurements.
Knowledge engineering is about translating application domain questions or hypotheses to likelihoods given prior knowledge and RS measurements.
In optical RS the quantum nature of light is fundamental. Sensors allow the estimation of number of photons captured in a sensor volume by measuring the charge generated in the charge wells of typical charge coupled devices. In the spectral analysis of emitted or reflected photons, the estimation of matter- and geometry specific absorptance provides most information about matter and processes.
In the thermal infrared part of the photon energy spectrum, emitted photons represent the local outgoing radiant energy. With proper modelling of emittance it is possible to estimate the temperature of the optical boundary layer.