Lambertian (true, flat) albedo
True or flat albedo is the diffuse reflectance coefficient, that is, the ratio of the luminous flux scattered by a flat surface element in all directions to the flux incident on this element.
In the case of illumination and observation normal to the surface, the true albedo is called normal .
The normal albedo of pure snow is ~0.9, of charcoal ~0.04.
Geometric albedo
Geometric optical albedo of the Moon is 0.12, of the Earth - 0.367.
Bond (spherical) albedo
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Synonyms:See what "Albedo" is in other dictionaries:
ALBEDO, the fraction of light or other radiation reflected from a surface. An ideal reflector has an albedo of 1; for real ones this number is less. Snow albedo ranges from 0.45 to 0.90; albedo of the Earth, from artificial satellites, ... ... Scientific and technical encyclopedic dictionary
- (Arabic). A term in photometry that shows how much light rays a given surface reflects. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. albedo (lat. albus light) a value characterizing... ... Dictionary of foreign words of the Russian language
ALBEDO- (Late Latin albedo, from Latin albus white), a value characterizing the relationship between the flux of solar radiation falling on various objects, soil or snow cover, and the amount of such radiation absorbed or reflected by them;... ... Ecological dictionary
- (from Late Latin albedo whiteness) a value characterizing the ability of a surface to reflect a flow of electromagnetic radiation or particles incident on it. Albedo is equal to the ratio of the reflected flux to the incident flux. An important characteristic in astronomy... ... Big Encyclopedic Dictionary
albedo- several albedo m. lat. albedo. white. 1906. Lexis. The inner white layer of citrus peel. Food industry Lex. Brokg.: albedo; SIS 1937: albe/pre... Historical Dictionary of Gallicisms of the Russian Language
albedo- Characteristics of the reflectivity of the body surface; is determined by the ratio of the luminous flux reflected (scattered) by this surface to the luminous flux incident on it [Terminological dictionary for construction in 12 languages... ... Technical Translator's Guide
albedo- The ratio of solar radiation reflected from the earth's surface to the intensity of radiation incident on it, expressed as a percentage or decimal fractions (the average albedo of the Earth is 33%, or 0.33). → Fig. 5 … Dictionary of Geography
- (from Late Lat. albedo whiteness), a value characterizing the ability of a surface to l.l. body to reflect (scatter) the radiation incident on it. There are true, or Lambertian, A., coinciding with the coefficient. diffuse (scattered) reflection, and... ... Physical encyclopedia
Noun, number of synonyms: 1 characteristic (9) Dictionary of synonyms ASIS. V.N. Trishin. 2013… Synonym dictionary
A value characterizing the reflectivity of any surface; expressed by the ratio of radiation reflected by the surface to solar radiation received on the surface (for black soil 0.15; sand 0.3 0.4; average A. Earth 0.39; Moon 0.07) ... ... Dictionary of business terms
When astronomers talk about the reflective properties of the surfaces of planets and moons, they often use the term albedo. However, by turning to reference books and encyclopedias for an explanation of this concept, we learn that there are many different types of albedo: true, apparent, normal, flat, monochromatic, spherical, and so on. There is something to be sad about. So let's try to understand this cycle of terms.
The word “albedo” itself comes from the Latin albedo - whiteness. In its most general form, this is the name given to the fraction of incident radiation reflected by a solid surface or scattered by a translucent body. Since the magnitude of the reflected radiation cannot exceed the magnitude of the incident radiation, this ratio, that is, the albedo, is always in the range from 0 to 1. The higher its value, the greater the proportion of incident light will be reflected.
The visibility of all non-self-luminous bodies is completely determined by their albedo, that is, their reflectivity. One might even say that we simply would not see non-self-luminous objects if they could not reflect light. Thanks to this property, we “by eye” determine the shape of the body, the nature of the material, its hardness and other characteristics. However, a skillfully selected albedo can hide an object from us - remember military camouflage or the Stealth stealth aircraft. When studying the bodies of the Solar System, measuring albedo helps to determine the nature of the material located on the surface of a celestial body, its structure and even chemical composition.
We easily distinguish snow from asphalt because snow almost completely reflects light, while asphalt almost completely absorbs it. However, we can also easily distinguish snow from a sheet of polished aluminum, although both of them reflect light almost completely. This means that just knowing the fraction of reflected light is not enough to judge the nature of the material. Snow scatters light diffusely in all directions, while aluminum reflects specularly. To take into account these and other reflection features, several types of albedo are distinguished.
True (absolute) albedo coincides with the so-called diffuse reflection coefficient: this is the ratio of the flux scattered by a flat surface element in all directions to the flux incident on it.
To measure true albedo, laboratory conditions are required, because it is necessary to take into account the light scattered by the body in all directions. For “field” conditions it is more natural apparent albedo- the ratio of the brightness of a flat surface element illuminated by a parallel beam of rays to the brightness of an absolutely white surface located perpendicular to the rays and having a true albedo equal to unity.
If a surface is illuminated and observed at an angle of 90 degrees, its apparent albedo is called normal. The normal albedo of pure snow approaches 1.0, and that of charcoal is about 0.04.
Often used in astronomy geometric (flat) albedo- the ratio of the illumination on Earth created by the planet in full phase to the illumination that would be created by a flat absolutely white screen of the same size as the planet, placed in its place and located perpendicular to the line of sight and the sun's rays. Astronomers usually express the physical concept of “illumination” with the word “brilliance” and measure it in stellar magnitudes.
It is clear that the albedo value affects the brightness of celestial objects as much as their size and position in the solar system. For example, if the asteroids Ceres and Vesta were placed side by side, their brightness would be almost the same, although the diameter of Ceres is twice that of Vesta. The fact is that the surface of Ceres reflects light much worse: Vesta’s albedo is about 0.35, while Ceres’s is only 0.09.
The albedo value depends both on the properties of the surface and on the spectrum of the incident radiation. Therefore, albedo is measured separately for different spectral ranges (optical, ultraviolet, infrared, and so on) or even for individual wavelengths (monochromatic albedo). By studying the change in albedo with wavelength and comparing the resulting curves with the same curves for terrestrial minerals, soil samples and various rocks, some conclusions can be drawn about the composition and structure of the surface of planets and their satellites.
To calculate the energy balance of planets it is used spherical albedo (Bond albedo), introduced by American astronomer George Bond in 1861. This is the ratio of the flux of radiation reflected by the entire planet to the flux incident on it. In order to accurately calculate the spherical albedo, generally speaking, it is necessary to observe the planet at all possible phase angles (the Sun-planet-Earth angle). Previously, this was only possible for the inner planets and the Moon. With the advent of artificial satellites, astronomers were able to calculate the spherical albedo near the Earth, and interplanetary spacecraft made it possible to do this for the outer planets. The Bond albedo of the Earth is about 0.33, and the reflection of light from clouds plays a very important role in it. For the atmosphere-less Moon it is 0.12, and for Venus, covered with a thick cloudy atmosphere, it is 0.76.
Naturally, different parts of the surface of celestial bodies, having different structure, composition and origin, have different albedo. You can see this for yourself by at least looking at the Moon. The seas on its surface have an extremely low albedo, unlike, say, the ray structures of some craters. By the way, observing the ray structures, you will easily notice that their appearance greatly depends on the angle at which the Sun illuminates them. This occurs precisely due to a change in their albedo, which takes on a maximum value when the rays fall perpendicular to the surface of the Moon, where these formations are located.
And one more experiment. Look at the Moon through a telescope (or at any planet, preferably Mars or Jupiter) with various light filters. And you will see that, for example, in red rays the surface of the Moon looks slightly different than in blue rays. This suggests that radiation of different wavelengths is reflected from its surface in different ways.
But what specific albedo should be discussed in the examples described above, try to guess for yourself.
To understand the processes affecting the climate of our planet, let's remember some terms.
Greenhouse effect– this is an increase in the temperature of the lower layers of the atmosphere compared to the temperature of the planet’s thermal radiation. The essence of the phenomenon is that the surface of the planet absorbs solar radiation, mainly in the visible range and, when heated, radiates it back into space, but in the infrared range. A significant portion of the Earth's infrared radiation is absorbed by the atmosphere and partially re-emitted to the Earth. This effect of mutual radiative heat exchange in the lower layers of the atmosphere is called the greenhouse effect. The greenhouse effect is a natural element of the Earth's heat balance. Without the greenhouse effect, the average surface temperature of the planet would be -19°C instead of the actual +14°C. Over the past few decades, various national and international organizations have advocated the hypothesis that human activity is leading to an increase in the greenhouse effect, and therefore to additional heating of the atmosphere. At the same time, there are alternative points of view, for example, linking temperature changes in the Earth’s atmosphere with natural cycles of solar activity.(1)
The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (2013-2014) states that there is more than a 95% probability that human influence has been the dominant cause of warming observed since the mid-20th century. The consistency of observed and estimated changes across the entire climate system indicates that observed climate changes are caused primarily by increases in atmospheric concentrations of greenhouse gases resulting from human activities.
Current climate change in Russia as a whole should be characterized as continuing warming at a rate more than two and a half times the average rate of global warming.(2)
Diffuse reflection- this is the reflection of a light flux incident on a surface, in which the reflection occurs at an angle different from the incident one. Reflection becomes diffuse if surface irregularities are on the order of the wavelength (or exceed it) and are randomly located. (3)
Albedo of the Earth(A.Z.) - The percentage of solar radiation emitted by the globe (together with the atmosphere) back into the world space, to solar radiation received at the boundary of the atmosphere. The return of solar radiation by the Earth consists of reflection from the earth's surface, scattering of direct radiation by the atmosphere into space (backscattering) and reflection from the upper surface of clouds. A. 3. in the visible part of the spectrum (visual) - about 40%. For the integral flux of solar radiation, the integral (energy) A. 3. is about 35%. In the absence of clouds, visual A. 3. would be about 15%. (4)
Spectral range of electromagnetic radiation from the Sun- extends from radio waves to x-rays. However, its maximum intensity occurs in the visible (yellow-green) part of the spectrum. At the boundary of the earth's atmosphere, the ultraviolet part of the solar spectrum is 5%, the visible part is 52% and the infrared part is 43%; at the surface of the Earth the ultraviolet part is 1%, the visible part is 40% and the infrared part of the solar spectrum is 59%. (5)
Solar constant- the total power of solar radiation passing through a single area, oriented perpendicular to the flow, at a distance of one astronomical unit from the Sun outside the earth's atmosphere. According to extra-atmospheric measurements, the solar constant is 1367 W/m².(3)
Earth's surface area– 510,072,000 km2.
- Main part.
Changes in the modern climate (toward warming) are called global warming.
The simplest mechanism of global warming is as follows.
Solar radiation entering the atmosphere of our planet, on average, is reflected by 35%, which is the integral albedo of the Earth. Most of the remainder is absorbed by the surface, which heats up. The rest is absorbed by plants through the process of photosynthesis.
The heated surface of the Earth begins to radiate in the infrared range, but this radiation does not go into space, but is retained by greenhouse gases. We will not consider types of greenhouse gases. The more greenhouse gases there are, the more heat they radiate back to the Earth, and the higher, accordingly, the average temperature of the Earth's surface becomes.
The Paris Agreement, an agreement under the United Nations Framework Convention on Climate Change, addresses the need to “keep global average temperature rise “well below” 2°C and “make efforts” to limit temperature rise to 1.5°C.” But apart from reducing greenhouse gas emissions, it does not contain an algorithm for solving this problem.
Considering that the United States withdrew from this agreement on June 1, 2017, a new international project is needed. And Russia can offer it.
The main advantage of the new agreement should be a clear and effective mechanism for mitigating the impact of greenhouse gases on the Earth's climate.
The most interesting way to reduce the impact of greenhouse gases on the climate may be to increase the average albedo of the Earth.
Let's take a closer look at it.
In Russia there are about 625,000 km of roads covered with asphalt, in China and the USA - a total of an order of magnitude more.
Even if we assume that all roads in Russia are single-lane and category 4 (which in itself is absurd), then the minimum width will be 3 m (according to SNiP 2.07.01-89). The road area will be 1875 km2. Or 1,875,000,000 m2.
The solar constant outside the atmosphere, as we remember, is 1.37 kW/m2.
To simplify, let’s take the middle band, where solar energy at the surface of the earth (averaged value for the year) will be approximately 0.5 kW/m2.
We get that the power of solar radiation falls on the roads of the Russian Federation is 937,500,000 Watts.
Now divide this number by 2. Because. The earth is spinning. That turns out to be 468,750,000 watts.
The average integral albedo of asphalt is 20%.
By adding pigment or broken glass, the visible albedo of asphalt can be increased by up to 40%. The pigment must spectrally match the emission range of our star. Those. have yellow-green colors. But, at the same time, it should not worsen the physical characteristics of asphalt concrete and be as cheap and easy to synthesize as possible.
With the gradual replacement of old asphalt concrete with a new one, in the process of natural wear and tear of the first one, the total increase in reflected radiation power will be 469 MW x 0.4 (visible part of the solar spectrum) x 0.2 (difference between the old and new albedo) 37.5 MW.
We do not take the infrared component of the spectrum into account, because it will be absorbed by greenhouse gases.
In the whole world, this value will be more than 500 MW. This is 0.00039% of the total incoming radiation power to the Earth. And to eliminate the greenhouse effect, it is necessary to reflect the power 3 orders of magnitude more.
The situation on the planet will also be worsened by the melting of glaciers, because... their albedo is very high.
| Surface | Characteristic | Albedo, % |
| Soils | ||
| black soil | dry, flat surface freshly plowed, damp | |
| loamy | dry wet | |
| sandy | yellowish whitish river sand | 34 – 40 |
| Vegetation cover | ||
| rye, wheat at full ripeness | 22 – 25 | |
| floodplain meadow with lush green grass | 21 – 25 | |
| dry grass | ||
| forest | spruce | 9 – 12 |
| pine | 13 – 15 | |
| birch | 14 – 17 | |
| Snow cover | ||
| snow | dry fresh wet clean fine-grained wet soaked in water, gray | 85 – 95 55 – 63 40 – 60 29 – 48 |
| ice | river bluish-green | 35 – 40 |
| sea milky blue color. | ||
| water surface | ||
| at the height of the Sun 0.1° 0.5° 10° 20° 30° 40° 50° 60-90° | 89,6 58,6 35,0 13,6 6,2 3,5 2,5 2,2 – 2,1 |
The predominant part of the direct radiation reflected by the earth's surface and the upper surface of the clouds goes beyond the atmosphere into outer space. About one third of the scattered radiation also escapes into outer space. The ratio of all the reflected and absent-minded solar radiation to the total amount of solar radiation entering the atmosphere is called planetary albedo of the Earth. The planetary albedo of the Earth is estimated at 35–40%. The main part of it is the reflection of solar radiation by clouds.
Table 2.6
Dependence of quantity TO n depending on the latitude and time of year
| Latitude | Months | |||||||
| III | IV | V | VI | VII | VIII | IX | X | |
| 0.77 | 0.76 | 0.75 | 0.75 | 0.75 | 0.76 | 0.76 | 0.78 | |
| 0.77 | 0.76 | 0.76 | 0.75 | 0.75 | 0.76 | 0.76 | 0.78 | |
| 0.77 | 0.76 | 0.76 | 0.75 | 0.75 | 0.76 | 0.77 | 0.79 | |
| 0.78 | 0.76 | 0.76 | 0.76 | 0.76 | 0.76 | 0.77 | 0.79 | |
| 0.78 | 0.76 | 0.76 | 0.76 | 0.76 | 0.76 | 0.77 | 0.79 | |
| 0.78 | 0.77 | 0.76 | 0.76 | 0.76 | 0.77 | 0.78 | 0.80 | |
| 0.79 | 0.77 | 0.76 | 0.76 | 0.76 | 0.77 | 0.78 | 0.80 | |
| 0.79 | 0.77 | 0.77 | 0.76 | 0.76 | 0.77 | 0.78 | 0.81 | |
| 0.80 | 0.77 | 0.77 | 0.76 | 0.76 | 0.77 | 0.79 | 0.82 | |
| 0.80 | 0.78 | 0.77 | 0.77 | 0.77 | 0.78 | 0.79 | 0.83 | |
| 0.81 | 0.78 | 0.77 | 0.77 | 0.77 | 0.78 | 0.80 | 0.83 | |
| 0.82 | 0.78 | 0.78 | 0.77 | 0.77 | 0.78 | 0.80 | 0.84 | |
| 0.82 | 0.79 | 0.78 | 0.77 | 0.77 | 0.78 | 0.81 | 0.85 | |
| 0.83 | 0.79 | 0.78 | 0.77 | 0.77 | 0.79 | 0.82 | 0.86 |
Table 2.7
Dependence of quantity TO b+c depending on latitude and time of year
(according to A.P. Braslavsky and Z.A. Vikulina)
| Latitude | Months | |||||||
| III | IV | V | VI | VII | VIII | IX | X | |
| 0.46 | 0.42 | 0.38 | 0.37 | 0.38 | 0.40 | 0.44 | 0.49 | |
| 0.47 | 0.42 | 0.39 | 0.38 | 0.39 | 0.41 | 0.45 | 0.50 | |
| 0.48 | 0.43 | 0.40 | 0.39 | 0.40 | 0.42 | 0.46 | 0.51 | |
| 0.49 | 0.44 | 0.41 | 0.39 | 0.40 | 0.43 | 0.47 | 0.52 | |
| 0.50 | 0.45 | 0.41 | 0.40 | 0.41 | 0.43 | 0.48 | 0.53 | |
| 0.51 | 0.46 | 0.42 | 0.41 | 0.42 | 0.44 | 0.49 | 0.54 | |
| 0.52 | 0.47 | 0.43 | 0.42 | 0.43 | 0.45 | 0.50 | 0.54 | |
| 0.52 | 0.47 | 0.44 | 0.43 | 0.43 | 0.46 | 0.51 | 0.55 | |
| 0.53 | 0.48 | 0.45 | 0.44 | 0.44 | 0.47 | 0.51 | 0.56 | |
| 0.54 | 0.49 | 0.46 | 0.45 | 0.45 | 0.48 | 0.52 | 0.57 | |
| 0.55 | 0.50 | 0.47 | 0.46 | 0.46 | 0.48 | 0.53 | 0.58 | |
| 0.56 | 0.51 | 0.48 | 0.46 | 0.47 | 0.49 | 0.54 | 0.59 | |
| 0.57 | 0.52 | 0.48 | 0.47 | 0.47 | 0.50 | 0.55 | 0.60 | |
| 0.58 | 0.53 | 0.49 | 0.48 | 0.48 | 0.51 | 0.56 | 0.60 |
Falling on the earth's surface, the total radiation is mostly absorbed in the upper, thin layer of soil or water and turns into heat, and is partially reflected. The amount of reflection of solar radiation by the earth's surface depends on the nature of this surface. The ratio of the amount of reflected radiation to the total amount of radiation incident on a given surface is called the surface albedo. This ratio is expressed as a percentage.
So, from the total flux of total radiation Isinh+i, part of it (Isinh + i)A is reflected from the earth's surface, where A is the surface albedo. The rest of the total radiation (Isinh + i) (1- A) is absorbed by the earth's surface and goes to heat the upper layers of soil and water. This part is called absorbed radiation.
The albedo of the soil surface is generally in the range of 10-30%; in the case of wet chernozem it decreases to 5%, and in the case of dry light sand it can increase to 40%. As soil moisture increases, albedo decreases. The albedo of vegetation cover - forests, meadows, fields - is within 10-25%. For freshly fallen snow, the albedo is 80-90%, for long-standing snow - about 50% and lower. The albedo of a smooth water surface for direct radiation varies from a few percent at high sun to 70% at low sun; it also depends on excitement. For scattered radiation, the albedo of water surfaces is 5--10%. On average, the albedo of the surface of the world's oceans is 5-20%. Albedo of the upper surface of clouds - from several percent to 70-80% depending on the type and thickness of cloud cover; on average it is 50-60%. The given numbers refer to the reflection of solar radiation, not only visible, but throughout its entire spectrum. In addition, photometric means measure the albedo only for visible radiation, which, of course, may differ slightly in value from the albedo for the entire radiation flux.
The predominant part of the radiation reflected by the earth's surface and the upper surface of the clouds goes beyond the atmosphere into outer space. Part of the scattered radiation, about one third of it, also escapes into outer space. The ratio of this reflected and scattered solar radiation escaping into space to the total amount of solar radiation entering the atmosphere is called the planetary albedo of the Earth or simply the albedo of the Earth.
Earth's planetary albedo is estimated at 35-40%; it appears to be closer to 35%. The main part of the Earth's planetary albedo is the reflection of solar radiation by clouds.
Phenomena associated with radiation scattering
The blue color of the sky is the color of the air itself, due to the scattering of the sun's rays in it. With height, as the air density decreases, i.e., the number of scattering particles, the color of the sky becomes darker and turns into deep blue, and in the stratosphere into black-violet.
The more cloudy impurities in the air that are larger in size than air molecules, the greater the proportion of long-wave rays in the spectrum of solar radiation and the more whitish the color of the sky becomes. Scattering changes the color of direct sunlight. The solar disk appears yellower the closer it is to the horizon, that is, the longer the path of rays through the atmosphere and the greater the scattering.
The scattering of solar radiation in the atmosphere causes diffused light during the daytime. In the absence of an atmosphere on Earth, there would be light only where direct sunlight or solar rays reflected by the earth's surface and objects on it would fall.
After sunset in the evening, darkness does not come immediately. The sky, especially in that part of the horizon where the sun has set, remains light and sends scattered radiation to the earth's surface with gradually decreasing intensity - twilight. The reason for this is the illumination of high layers of the atmosphere by the sun below the horizon.
The so-called astronomical twilight continue in the evening until the sun sets 18° below the horizon; by this point it is so dark that the faintest stars are visible. Morning twilight begins from the moment when the sun has the same position under the horizon. The first part of the evening or the last part of the morning astronomical twilight, when the sun is below the horizon at least 8°, is called civil twilight.
The duration of astronomical twilight varies depending on latitude and time of year. In mid-latitudes it is from one and a half to two hours, in the tropics less, at the equator a little longer than one hour.
In high latitudes in summer, the sun may not fall below the horizon at all or may sink very shallowly. If the sun drops below the horizon by less than 18°, then complete darkness does not occur at all and the evening twilight merges with the morning one. This phenomenon is called white nights.
Twilight is accompanied by beautiful, sometimes very spectacular changes in the color of the sky towards the sun. These changes begin before sunset or continue after sunrise. They have a fairly natural character and are called dawn. The characteristic colors of dawn are purple and yellow; but the intensity and variety of color shades of dawn vary widely depending on the content of aerosol impurities in the air. The tones of illumination of clouds at dusk are also varied.
In the part of the sky opposite the sun, phenomena are observed anti-dawn, also with a change in color tones, with a predominance of purple and purple-violet. After sunset, the shadow of the Earth appears in this part of the sky: a grayish-blue segment growing in height and to the sides.
The phenomena of dawn are explained by the scattering of light by the smallest particles of atmospheric aerosols and the diffraction of light by larger particles.