reradiated

Reradiated refers to energy that is emitted again by a body after it has absorbed or otherwise interacted with incoming radiation. In this sense, reradiation describes the re-emission of electromagnetic or acoustic energy and can involve changes in direction, spectrum, phase, or timing.

In optics and spectroscopy, reradiation covers scattering as well as processes where energy is absorbed and then re-emitted. Elastic scattering, such as Rayleigh scattering, leaves photon energy unchanged, while inelastic processes shift energy to different wavelengths. Fluorescence and phosphorescence are common examples where absorbed light is re-emitted at longer wavelengths after a short or long delay. Raman scattering involves characteristic shifts in frequency due to interactions with molecular vibrations.

In astronomy and atmospheric science, reradiation is central to radiative transfer. Dust, gas, and planetary atmospheres absorb incident radiation and reradiate energy, typically at infrared wavelengths. This reradiated emission influences thermal balance, climate, and observational signatures of celestial objects, and it underpins the greenhouse effect on planets.

In radio frequency and acoustics, objects and materials can reradiate energy when illuminated by an external field. The reradiated field contributes to scattering, reflection, or the apparent brightness and is relevant in imaging, radar, wireless communications, and acoustic sensing.

Reradiation is often analyzed through concepts such as absorption and emission coefficients, emissivity, and the spectral distribution of emitted energy. It is related to, but distinct from, mere reflection, as reradiation involves absorption processes that subsequently generate new emission.