Reflected radiation

EMITTED RADIATION AND REFLECTED RADIATION CONCRETE ASPECTS 

We have already looked at the central topics in regard to centi-millimetric waves we now need only clarify some ideas on the near and middle infrared, which is now being exploited intensively. 

The reflectivity power (of solar energy) decreases as the wavelength increases, until the radiation emitted by the object is dominant. The point of intersection where emitted radiation is greater than reflected radiation 

We can see immediately that the highest values and sharpest contrasts are found at wavelengths under 3 m, with the exception of the basalts. On the other hand, size 

Beyond this (longer wavelengths), the contrasts are less sharp, the absolute values are smaller, and intersections between curves can cause some confusion in interpretation. 

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When the applied magnetic field is swept to bring the sample into resonance, MW power is absorbed by the sample. This changes the matching of the cavity to the waveguide and some power is now reflected and passes via the circulator to the detector. This reflected radiation is thus the EPR signal. 

For opaque materials, the reflectance p is the complement of the absorptance. The directional distribution of the reflected radiation depends on the material, its degree of roughness or grain size, and, if a metal, its state of oxidation. Polished surfaces of homogeneous materials reflect speciilarly. In contrast, the intensity of the radiation reflected from a perfectly diffuse, or Lambert, surface is independent of direction. The directional distribution of reflectance of many oxidized metals, refractoiy materials, and natural products approximates that of a perfectly diffuse reflector. A better model, adequate for many calculational purposes, is achieved by assuming that the total reflectance p is the sum of diffuse and specular components p i and p. ... 

FIGURE 11.31 Radiaiion fluxes at the buildirtg facade the solar radiation components (direct or beam, diffuse, and reflected radiation from the ground or other buildings) and the components of the radiation back from the building facade (reflected solar and thermal infrared radiation from the building envelope). 

Reflectance A measure of the extent to which a surface is capable of reflecting radiation, defined as the ratio of the intensity of reflected radiant flux to the intensity of the incident flux. 

Abstrahlung,/. reflection radiation. Abstrebekraft, /. centrifugal force. Abstreicheisen, n. scraper skimmer, abstreichen, jj.i, wipe or scrape off skim strike out deduct. 

Since radiation arriving at a black surface is completely absorbed, no problems arise from multiple reflections. Radiation is emitted from a diffuse surface in all directions and therefore only a proportion of the radiation leaving a surface arrives at any other given surface. This proportion depends on the relative geometry of the surfaces and this may be taken into account by the view factor, shape factor or configuration F, which is normally written as F, for radiation arriving at surface j from surface i. In this way, F,y, which is, of course, completely independent of the surface temperature, is the fraction of radiation leaving i which is directly intercepted by j. 

Fig. 17-1 The global climate system, (a) Energy fluxes, including incoming solar radiation, reflected radiation, emitted longwave radiation (from an effective altitude of ca. 6 km), and atmospheric and oceanic heat flux toward the polar regions, (b) The atmospheric circulation corresponding to part (a). Refer back to Fig. 7-4 and associated text for a discussion of the general circulation.

It is fortunate, however, that there are small amounts of other gases in the atmosphere, notably carbon dioxide and water vapour. Both these gases absorb strongly in the infrared region of the reflected radiation, keeping the heat... 

IR absorption spectroscopy follows the principles of classical absorption spectrocopy. A sample is irradiated with electromagnetic radiation and the transmitted or reflected radiation is (spectrally) analysed. In IR spectroscopy, the wavelengths used are in the pm-range. 

The beam of the radiation passing through the studied object interact with the material that induces a certain scattering pattern of the reflected radiation detectable by the radiation sensors. This scattering is caused by the... 

Black bodies emit and reflect radiation at all wavelengths with equal efficiency. 

Since the earth has temperature, it emits radiant energy called thermal radiation or planetary infrared radiation. Measurements by satellites show an average radiant emission from the earth of about 240 watts per square meter. This is equivalent to the radiation that a black body would emit if its temperature is at -19°C (-3°F). This is also the same energy rate as the solar constant averaged over the earth s surface minus the 30% reflected radiation. This shows that the amount of radiation emitted by the earth is closely balanced by the amount of solar energy absorbed and since the earth is in this state of balance, its temperature will change relatively slowly from year to year. 

The assumption that the difference between the incident and the transmitted radiation is a measure of the radiation absorbed by the analyte is not completely true because this may not be the only reason why the incident radiation does not appear in the transmitted form. A certain amount of radiation will be reflected from the surface of the sample holder, usually a glass or plastic cell, or absorbed by the material of which the cell is composed. The sample may also be dissolved in a solvent which itself may also absorb or reflect radiation ... 

In some situations measurement of the reflected, rather than the transmitted, radiation may be made to assess the amount of radiation that has been absorbed by the sample. There are two main ways by which radiation might be reflected. Specular reflection is similar to the reflection by a mirror and, for quantitative work, the angles of the incident and the reflected radiation are important. Diffuse reflection is from within the layers of the material and the reflected light is disbursed over a range of 180°. This type of reflection is measured in the thin films used in dry chemistry systems. The term reflectance density is often used, which is defined in a manner comparable to absorbance the logarithm of the ratio of incident to reflected light. 

The components of the instrument are similar to absorptiometry but their relative positions are changed in order to catch the reflected radiation. In most of these instruments, rather than incorporating a monochromator, a light-emitting diode (LED) of a specific wavelength is used to produce the incident radiation. 

Spectra of solid samples are usually recorded in the units of reflectance (R) or percent reflectance (%/ ), which is analogous to percent transmittance in that reflectance equals the ratio of the reflected radiation to the incident radiation. With diffuse reflectance, the reflected signal is attenuated by two phenomena absorption (coefficient k) and scattering (coefficient s). Lollowing the Kubelka-Munk theory, these two coefficients are related to the reflectance of an infinitely thick sample, by... 

The light available to a molecule in air for absorption and photodissociation includes both direct and scattered and reflected radiation coming from all directions as described earlier and depicted in Fig. 3.16. The term actinic flux or spherically integrated actinic flux, denoted by F( A), is used to describe the total intensity of this light and is the quantity of interest in calculating kp. 

A branched or furcated expiotron may be variously configured to increase the light from-blast separation efficiency and to optimize the coupling of the reflected radiation with the irradiable target T. Fig 2 shows the "Y Configuration Expiotron. Both "T ... 

UV reflectors also reflect radiation energy in the visible and infrared (IR) energy spectral regions at least as efficiently as in the UV region. This is undesirable in such cases where the substrate or the piece being irradiated is heat sensitive. To overcome this, the surface of the reflector is coated with... 

B. Dimensional Stability Boroscope Miniaturized T.V. Microscope Radiation Reflectance or Diffraction Photocell (visible) X-ray diffraction U.V. reflectance spectroscope y-Ray back-scatter Scintillation read out Infrared reflectance Radiation emission Infrared scan Profilometer... 

Surface cracks migration products roughness accumulation of degradation products oxidizer concentration owing to moisture localized dewetting All surface and sub-surface changes that effect reflected radiation density Subjective observations traveling mechanisms required... 

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