tools positioned on satellites. To understand how these tools
operate the first thing that must be understood is what the instruments
are actually measuring.
Electromagnetic SpectrumAll objects at a temperature greater than absolute zero emit, absorb, and reflect electormagnetic energy. This energy, measured in photons travels in the form of waves at a variety of wavelengths. The complete array of wavelengths is known as the electromagnetic spectrum which is brocken down into regions that are defined by specific wavelenghts.
As this energy travels through the Earth's atmosphere some is reflected and some is absorbed and reemitted. By measuring the energy reaching a satellite one can characterize the features producing the reponse recorded by the sensor.
Radiation Laws - having some problems making images of equationsKirchhoff's Law states that for all blackbodies at the same temperature, the ratio of emitted radiation to absorbed radiation is the same. Emissivity is then calculated as the ratio of the emittatnce of an object and the emittance of a blackbody at the same temperature.
Stefan-Boltzmann Law states that the energy per unit area that a blackbody emits increases as the temperature of the blackbody increases. Total emitted radiation is calculated by:
Lastly, Wien's Displacement Law describes the relationship between the wavelength of emitted radiation and the temperature of the object. This law shows that as the temperature of an object increases the wavelength of maximum emittance increaeses.
Interactions with the Earth's AtmosphereAll electromagnetic radiation must travel through the Earth's atmosphere and along the way several things can happen to the radiation that alter the radiation in some way either by redirection or a change in energy level. The further away a sensor is from it's target, the the larger the atmospheric effects are upon the radiation.
Particles that are small relative to the wavelength of incoming radiation create rayleigh scattering. Rayleigh scattering is wave length dependant, favoring short wavelengths, ansd is responsible for our sky appearing blue.
Mie scattering is produced by particles having diameter approzimately equal to the wavelength of the imcoming radiation. Mie scattering is typically created by dust, smoke, haze and water droplets in the lower atmosphere.
Atmospheric Windows and Useful Wavelengths
Different Types of Sensors/Satellites(?)Polar orbiting