Notes

Outline

Radiation 11 May 99 Meteorological Satellite Analyst SSgt Dave Mayer

Scientific Principles

Electromagnetic Spectrum

Sources of Radiation The sun emits majority of UV, visible, near infrared photons The earth emits majority of longwave (thermal) infrared and microwave photons The atmosphere and clouds absorb and re-emit thermal IR photons

Slide 5

Radiation Properties Radiation can be Emitted Reflected (also called Scattering) Transmitted Absorbed All objects (air, clouds, aerosols, water, earth’s surface) play a part in the atmospheric radiative process

Earth’s Radiation Budget Visible -- Main source:  sun  Main sink:  absorption Thermal IR -- Main source:  earth / atmos. Main sink:  space

Atmospheric Transmissivity The atmosphere responds selectively to various photons of various wavelengths Sensors measure photons in particular wavelength bands (wavebands) to detect specific atmospheric processes

Commonly Used Wavebands Visible  .55 - .75 micrometers (microns) View earth and atmosphere during the day Visible and near IR  .55 - 1.5 microns View city lights at night, moonlight visible Thermal (far) IR  10.5 - 12.5 microns View temperature of the earth’s surface, ocean, atmosphere and clouds Microwave  13.5 - 85 GigaHertz (GHz) View convective structure of thunderstorms, observe ocean surface through cloud cover

Comparison of Wavebands Visible                                  Thermal Infrared

Slide 11

Comparison Continued Visible                 85GHz Microwave