User:Marshallsumter/Radiation astronomy2/Transmissivity

Transmissivity is usually the ratio of the amount of energy transmitted over that received.

In the diagram on the right the absorption bands of water vapor, carbon dioxide, oxygen, and ozone are noted.

Theoretical transmissivity
Def. a "measure of the capacity of a material to transmit radiation (the ratio of the amounts of energy transmitted and received)" is called transmissivity.

Def. "the fraction of incident light, or other radiation, that passes through a substance" is called transmittance.

Def. "the property that light passes through it almost undisturbed" is called transparency.

Translucency
Def. the quality of "allowing light to pass through, but diffusing it" is called translucency.

Def. not "allowing light to pass through" is called opaque.

Stopping powers
At right, the figure shows the stopping power of aluminum metal single crystal for protons.

"Choosing materials with the largest stopping powers enables thinner detectors to be produced with resulting benefits in radiation tolerance (which is a bulk effect) and lower leakage currents. Alternatively, choosing smaller stopping powers will increase scattering efficiency, which is a requirement for polarimetry, or say, the upper detection plane of a double Compton telescope."

Muons
The image of muon radiography on the right is a measure (density) of the translucency of volcanic rock to muons.

Blues
"The light blue background is the dayglow emission (less than 1 kR) caused by the interaction between the photoelectrons generated by solar UV radiation and atmospheric molecules and atoms." This background occurs when imaging an Earth aurora from space using ultraviolet astronomy at the VUV wavelengths (135.6 ± 1.5 nm and 149.3 ± 1.5 nm).

"[P]referential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon".

Atmospheres
This figure shows the absorption bands in the Earth's atmosphere (middle panel) (when there are no clouds present: clouds average 60-65% cover and independently impact radiation transfer) and the effect that this has on both solar radiation and upgoing thermal radiation (top panel). Individual absorption spectrum for major greenhouse gases plus Rayleigh scattering are shown in the lower panel.

Both the Earth and the Sun emit electromagnetic radiation (e.g. light) that closely follows a blackbody spectrum, and which can be predicted based solely on their respective temperatures. For the Sun, these emissions peak in the visible region and correspond to a temperature of ~5500 K. Emissions from the Earth vary following variations in temperature across different locations and altitudes, but always peak in the infrared.

The position and number of absorption bands are determined by the chemical properties of the gases present. In the present atmosphere, water vapor is the most significant of these greenhouse gases, followed by carbon dioxide and various other minor greenhouse gases. In addition, Rayleigh scattering, the physical process that makes the sky blue, also disperses some incoming sunlight. Collectively these processes capture and redistribute 25-30% of the energy in direct sunlight passing through the atmosphere. By contrast, the greenhouse gases capture 70-85% of the energy in upgoing thermal radiation emitted from the Earth surface.

Water ices
"The right figure shows the absorption length as a function of depth. The bulk of the scientifically-useful optical sensors in AMANDA are embedded between 1500 and 1900 m beneath the surface."

"The optical properties of in situ ice beneath the south pole are measured by a combination of in situ N2 lasers, DC lamps, and YAG laser pulses from the surface. The properties vary with depth due to climatological variation such as ice ages. [...] The two properties that most strongly affect the reconstruction capabilities of AMANDA-II are absorption and scattering."

"The absorption strongly depends on wavelength. Notice [in the figure at right] that the absorption also depends on depth at wavelengths where the absorption coefficient is relatively small. For short wavelengths, the absorption coefficient is small and dust contributes significantly, which is responsible for the depth dependence. At 532nm, the absorption coefficient is large, and the value is largely determined by intrinsic properties of ice (i.e, the roll of dust is less obvious)."

"The [second figure at right] shows the average scattering coefficent (1/scattering_length) as a function of depth. Note that the effective scattering length, L_eff, is (approximately) the average length to isotropize the direction of all but 1/e of the photons. This important parameter for diffusion calculations is related to the geometric scattering length by L_eff=L_geo/(1-). The solid curve shows the coefficient of the scattering length for 400 nm light. Other colors behave differently due to the slight dependence of the scattering length on wavelength."

"At depths below 1400m, dust is responsible for light scattering in ice. The rapid rise in scattering at shallow depths (relative to the surface) is due to onset of air bubbles trapped in the ice. The dashed blue line shows the intrinsic scattering from dust in the region dominated by air bubbles."

The "maximum absorption length is slightly more than 100m at AMANDA-II depths, but the scattering length is only 20m for wavelengths that correspond to the longest absorption lengths."

Gaia spacecraft
The Gaia DR1, Gaia DR2 and Gaia EDR3/Gaia DR3 releases use different photometric systems. The spectral sensitivities of the detectors and the transmissivities of the filters as shown in the image for DR2 and other optical components determine pass bands and are recalibrated for each. Calibration of the readings is part of the research and it is to expected that subsequent catalogs will each use modified sensitivity curves, taking into account factors such as background brightness, aging of the sensors, radiation damage and pixel defects and thin ice deposits on the sensors and mirrors. The Gaia mission is self-calibrating and the later versions of the Gaia catalogs are increasingly being calibrated using the entire measurement data.