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63-411: Like all planets, Mars reflects a portion of the light it receives from the sun. The fraction of sunlight reflected is a quantity called albedo , which ranges from 0 for a body that reflects no sunlight to 1.0 for a body that reflects all sunlight. Different parts of a planet's surface (and atmosphere) have different albedo values depending on the chemical and physical nature of the surface. No topography

126-491: A big role in the heating and cooling effects of albedo, high insolation areas like the tropics will tend to show a more pronounced fluctuation in local temperature when local albedo changes. Arctic regions notably release more heat back into space than what they absorb, effectively cooling the Earth . This has been a concern since arctic ice and snow has been melting at higher rates due to higher temperatures, creating regions in

189-415: A body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects all incident radiation). Surface albedo is defined as the ratio of radiosity J e to the irradiance E e (flux per unit area) received by a surface. The proportion reflected is not only determined by properties of the surface itself, but also by

252-400: A climate trade-off: increased carbon uptake from afforestation results in reduced albedo . Initially, this reduction may lead to moderate global warming over a span of approximately 20 years, but it is expected to transition into significant cooling thereafter. Water reflects light very differently from typical terrestrial materials. The reflectivity of a water surface is calculated using

315-539: A consequence of land transformation" and can reduce surface temperature increases associated with climate change. Albedo is not directly dependent on the illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth's surface at that location (e.g. through melting of reflective ice). However, albedo and illumination both vary by latitude. Albedo

378-460: A dark surface is thought to be indicative of a primitive and heavily space weathered surface containing some organic compounds . The overall albedo of the Moon is measured to be around 0.14, but it is strongly directional and non- Lambertian , displaying also a strong opposition effect . Although such reflectance properties are different from those of any terrestrial terrains, they are typical of

441-461: A distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4. The average albedo of Earth is about 0.3. This is far higher than for the ocean primarily because of the contribution of clouds. Earth's surface albedo is regularly estimated via Earth observation satellite sensors such as NASA 's MODIS instruments on board

504-480: A given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual averages. Unless given for a specific wavelength (spectral albedo), albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is often given for the spectrum in which most solar energy reaches the surface (between 0.3 and 3 μm). This spectrum includes visible light (0.4–0.7 μm), which explains why surfaces with

567-748: A greater fraction of their foliage for direct interception of incoming radiation in the upper canopy. The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy. Studies by the Hadley Centre have investigated the relative (generally warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests. They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming. Research in 2023, drawing from 176 flux stations globally, revealed

630-555: A group of minerals that is very common in basalt. Spectra of the redder dark areas are consistent with mafic materials covered with thin alteration coatings. Thermal inertia measurement is a remote-sensing technique that allows scientists to distinguish fine-grained from coarse-grained areas on the Martian surface. Thermal inertia is a measure of how fast or slow something heats up or cools off. For example, metals have very low thermal inertia. An aluminum cookie sheet taken out of an oven

693-625: A knowledge of the intrinsic properties of the surface. Human activities (e.g., deforestation, farming, and urbanization) change the albedo of various areas around the globe. Human impacts to "the physical properties of the land surface can perturb the climate by altering the Earth’s radiative energy balance" even on a small scale or when undetected by satellites. Urbanization generally decreases albedo (commonly being 0.01–0.02 lower than adjacent croplands ), which contributes to global warming . Deliberately increasing albedo in urban areas can mitigate

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756-426: A low albedo appear dark (e.g., trees absorb most radiation), whereas surfaces with a high albedo appear bright (e.g., snow reflects most radiation). Ice–albedo feedback is a positive feedback climate process where a change in the area of ice caps , glaciers , and sea ice alters the albedo and surface temperature of a planet. Ice is very reflective, therefore it reflects far more solar energy back to space than

819-446: A low albedo because the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis . For this reason, the greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of deforestation ). In other words: The climate change mitigation effect of carbon sequestration by forests is partially counterbalanced in that reforestation can decrease

882-407: A major part of the astronomical field of photometry . For small and far objects that cannot be resolved by telescopes, much of what we know comes from the study of their albedos. For example, the absolute albedo can indicate the surface ice content of outer Solar System objects, the variation of albedo with phase angle gives information about regolith properties, whereas unusually high radar albedo

945-413: A marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (the ice–albedo positive feedback ). In Switzerland, the citizens have been protecting their glaciers with large white tarpaulins to slow down the ice melt. These large white sheets are helping to reject the rays from the sun and defecting

1008-435: A net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate. Mid-to-high-latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming. Modeling that compares the effects of albedo differences between forests and grasslands suggests that expanding the land area of forests in temperate zones offers only

1071-423: A substantial increase in global warming. However, the link to climate change has not been explored to date and it is unclear whether or not this represents an ongoing trend. For land surfaces, it has been shown that the albedo at a particular solar zenith angle θ i can be approximated by the proportionate sum of two terms: with 1 − D {\displaystyle {1-D}} being

1134-480: A temporary mitigation benefit. In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily. Deciduous trees have an albedo value of about 0.15 to 0.18 whereas coniferous trees have a value of about 0.09 to 0.15. Variation in summer albedo across both forest types is associated with maximum rates of photosynthesis because plants with high growth capacity display

1197-425: A warm air mass ), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow–temperature feedback. However, because local weather is dynamic due to the change of seasons , eventually warm air masses and a more direct angle of sunlight (higher insolation ) cause melting. When the melted area reveals surfaces with lower albedo, such as grass, soil, or ocean,

1260-648: Is +0.2 W m , with a range +0.1 to +0.4 W m . Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo. In astronomy, the term albedo can be defined in several different ways, depending upon the application and the wavelength of electromagnetic radiation involved. The albedos of planets , satellites and minor planets such as asteroids can be used to infer much about their properties. The study of albedos, their dependence on wavelength, lighting angle ("phase angle"), and variation in time composes

1323-466: Is a technique that measures the amount of sunlight absorbed or reflected by the Martian surface at specific wavelengths. The spectra represent mixtures of spectra from individual minerals on the surface along with contributions from absorption lines in the solar spectrum and the Martian atmosphere. By separating out (“deconvolving”) each of these contributions, scientists can compare the resulting spectra to laboratory spectra of known minerals to determine

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1386-410: Is another prominent dark area that lies north of the main belt. Bright areas, excluding the polar caps and transient clouds, include Hellas , Tharsis , and Arabia Terra . The bright areas are now known to be locations where fine dust covers the surface. The dark markings represent areas that the wind has swept clean of dust, leaving behind a lag of dark, rocky material. The dark color is consistent with

1449-743: Is cool to the touch in less than a minute; while a ceramic plate (high thermal inertia) taken from the same oven takes much longer to cool off. Scientists can estimate the thermal inertia on the Martian surface by measuring variations in surface temperature with respect to time of day and fitting this data to numerical temperature models. The thermal inertia of a material is directly related to its thermal conductivity , density, and specific heat capacity . Rocky materials do not vary much in density and specific heat, so variations in thermal inertia are mainly due to variations in thermal conductivity. Solid rock surfaces, such as outcroppings, have high thermal conductivities and inertias. Dust and small granular material in

1512-507: Is generally to cool the planet; the indirect effect (the particles act as cloud condensation nuclei and thereby change cloud properties) is less certain. Another albedo-related effect on the climate is from black carbon particles. The size of this effect is difficult to quantify: the Intergovernmental Panel on Climate Change estimates that the global mean radiative forcing for black carbon aerosols from fossil fuels

1575-746: Is highest near the poles and lowest in the subtropics, with a local maximum in the tropics. The intensity of albedo temperature effects depends on the amount of albedo and the level of local insolation ( solar irradiance ); high albedo areas in the Arctic and Antarctic regions are cold due to low insolation, whereas areas such as the Sahara Desert , which also have a relatively high albedo, will be hotter due to high insolation. Tropical and sub-tropical rainforest areas have low albedo, and are much hotter than their temperate forest counterparts, which have lower insolation. Because insolation plays such

1638-475: Is indicative of high metal content in asteroids . Enceladus , a moon of Saturn, has one of the highest known optical albedos of any body in the Solar System, with an albedo of 0.99. Another notable high-albedo body is Eris , with an albedo of 0.96. Many small objects in the outer Solar System and asteroid belt have low albedos down to about 0.05. A typical comet nucleus has an albedo of 0.04. Such

1701-517: Is modified by feedbacks: increased by "self-reinforcing" or "positive" feedbacks and reduced by "balancing" or "negative" feedbacks . The main reinforcing feedbacks are the water-vapour feedback , the ice–albedo feedback , and the net effect of clouds. When an area's albedo changes due to snowfall, a snow–temperature feedback results. A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling. In principle, if no outside temperature change affects this area (e.g.,

1764-539: Is the astronomical albedo, D {\displaystyle D} is the diameter in kilometers, and H {\displaystyle H} is the absolute magnitude. Syria Planum Syria Planum is a broad plateau on surface of Mars , forming part of Tharsis region. It is located at the summit of the Tharsis bulge, and was the center of volcanic and tectonic activity in Martian history from

1827-483: Is visible on Mars from Earth-based telescopes. The bright areas and dark markings on pre-spaceflight-era maps of Mars are all albedo features. (See Classical albedo features on Mars .) They have little relation to topography. Dark markings are most distinct in a broad belt from 0° to 40° S latitude. However, the most prominent dark marking, Syrtis Major Planum , is in the northern hemisphere, outside this belt. The classical albedo feature Mare Acidalium ( Acidalia Planitia )

1890-501: The Fresnel equations . At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally specular manner (not diffusely ). The glint of light off water is a commonplace effect of this. At small angles of incident light, waviness results in reduced reflectivity because of the steepness of the reflectivity-vs.-incident-angle curve and a locally increased average incident angle. Although

1953-586: The Terra and Aqua satellites, and the CERES instrument on the Suomi NPP and JPSS . As the amount of reflected radiation is only measured for a single direction by satellite, not all directions, a mathematical model is used to translate a sample set of satellite reflectance measurements into estimates of directional-hemispherical reflectance and bi-hemispherical reflectance (e.g., ). These calculations are based on

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2016-447: The bidirectional reflectance distribution function (BRDF), which describes how the reflectance of a given surface depends on the view angle of the observer and the solar angle. BDRF can facilitate translations of observations of reflectance into albedo. Earth's average surface temperature due to its albedo and the greenhouse effect is currently about 15 °C (59 °F). If Earth were frozen entirely (and hence be more reflective),

2079-503: The contrails of heavy commercial airliner traffic. A study following the burning of the Kuwaiti oil fields during Iraqi occupation showed that temperatures under the burning oil fires were as much as 10 °C (18 °F) colder than temperatures several miles away under clear skies. Aerosols (very fine particles/droplets in the atmosphere) have both direct and indirect effects on Earth's radiative balance. The direct (albedo) effect

2142-467: The regolith surfaces of airless Solar System bodies. Two common optical albedos that are used in astronomy are the (V-band) geometric albedo (measuring brightness when illumination comes from directly behind the observer) and the Bond albedo (measuring total proportion of electromagnetic energy reflected). Their values can differ significantly, which is a common source of confusion. In detailed studies,

2205-574: The urban heat island effect. An estimate in 2022 found that on a global scale, "an albedo increase of 0.1 in worldwide urban areas would result in a cooling effect that is equivalent to absorbing ~44 Gt of CO 2 emissions." Intentionally enhancing the albedo of the Earth's surface, along with its daytime thermal emittance , has been proposed as a solar radiation management strategy to mitigate energy crises and global warming known as passive daytime radiative cooling (PDRC). Efforts toward widespread implementation of PDRCs may focus on maximizing

2268-404: The Martian surface. Mars is an inviting target for Earth-based radar investigations because of its relative proximity to Earth and its favorable orbital and rotational characteristics that allow good coverage over wide areas of the planet's surface. Radar echoes from Mars were first obtained in the early 1960s, and the technique has been vital in finding safe terrain for Mars landers. Dispersion of

2331-642: The albedo effect of the colour of external clothing. Albedo can affect the electrical energy output of solar photovoltaic devices . For example, the effects of a spectrally responsive albedo are illustrated by the differences between the spectrally weighted albedo of solar photovoltaic technology based on hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si)-based compared to traditional spectral-integrated albedo predictions. Research showed impacts of over 10% for vertically (90°) mounted systems, but such effects were substantially lower for systems with lower surface tilts. Spectral albedo strongly affects

2394-536: The albedo of surfaces from very low to high values, so long as a thermal emittance of at least 90% can be achieved. The tens of thousands of hectares of greenhouses in Almería, Spain form a large expanse of whitened plastic roofs. A 2008 study found that this anthropogenic change lowered the local surface area temperature of the high-albedo area, although changes were localized. A follow-up study found that "CO2-eq. emissions associated to changes in surface albedo are

2457-544: The albedo to 0.9. Cloud albedo has substantial influence over atmospheric temperatures. Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8. "On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth." Albedo and climate in some areas are affected by artificial clouds, such as those created by

2520-429: The arctic that are notably darker (being water or ground which is darker color) and reflects less heat back into space. This feedback loop results in a reduced albedo effect. Albedo affects climate by determining how much radiation a planet absorbs. The uneven heating of Earth from albedo variations between land, ice, or ocean surfaces can drive weather . The response of the climate system to an initial forcing

2583-611: The average temperature of the planet would drop below −40 °C (−40 °F). If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about 0 °C (32 °F). In contrast, if the entire Earth was covered by water – a so-called ocean planet – the average temperature on the planet would rise to almost 27 °C (81 °F). In 2021, scientists reported that Earth dimmed by ~0.5% over two decades (1998–2017) as measured by earthshine using modern photometric techniques. This may have both been co-caused by climate change as well as

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2646-433: The composition of surface materials. The bright areas are reddish- ochre in color, and the dark areas appear dark gray. A third type of area, intermediate in color and albedo, is also present and thought to represent regions containing a mixture of the material from the bright and dark areas. The dark gray areas can be further subdivided into those that are more reddish and those less reddish in hue. Reflectance spectroscopy

2709-478: The directional reflectance properties of astronomical bodies are often expressed in terms of the five Hapke parameters which semi-empirically describe the variation of albedo with phase angle , including a characterization of the opposition effect of regolith surfaces. One of these five parameters is yet another type of albedo called the single-scattering albedo . It is used to define scattering of electromagnetic waves on small particles. It depends on properties of

2772-408: The effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating. Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow. Over Antarctica snow albedo averages a little more than 0.8. If

2835-526: The effects of small errors in the measurement of albedo, can lead to large errors in energy estimates. Because of this, in order to reduce the error of energy estimates, it is important to measure the albedo of snow-covered areas through remote sensing techniques rather than applying a single value for albedo over broad regions. Albedo works on a smaller scale, too. In sunlight, dark clothes absorb more heat and light-coloured clothes reflect it better, thus allowing some control over body temperature by exploiting

2898-465: The heat. Although this method is very expensive, it has been shown to work, reducing snow and ice melt by 60%. Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water. Sea water absorbs more solar radiation than would the same surface covered with reflective snow. When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above,

2961-512: The landing site. Other areas show high levels of roughness in radar that are not discernible in images taken from orbit. The average surface abundance of centimeter- to meter-scale rocks is much greater on Mars than the other terrestrial planets. Tharsis and Elysium, in particular, show a high degree of small-scale surface roughness associated with volcanoes. This extremely rough terrain is suggestive of young, ʻaʻā lava flows. A 200-km-long band of low to zero radar albedo ("stealth" region) cuts across

3024-497: The material ( refractive index ), the size of the particle, and the wavelength of the incoming radiation. An important relationship between an object's astronomical (geometric) albedo, absolute magnitude and diameter is given by: A = ( 1329 × 10 − H / 5 D ) 2 , {\displaystyle A=\left({\frac {1329\times 10^{-H/5}}{D}}\right)^{2},} where A {\displaystyle A}

3087-419: The other types of land area or open water. Ice–albedo feedback plays an important role in global climate change . Albedo is an important concept in climate science . Any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body . When seen from

3150-563: The performance of bifacial solar cells where rear surface performance gains of over 20% have been observed for c-Si cells installed above healthy vegetation. An analysis on the bias due to the specular reflectivity of 22 commonly occurring surface materials (both human-made and natural) provided effective albedo values for simulating the performance of seven photovoltaic materials mounted on three common photovoltaic system topologies: industrial (solar farms), commercial flat rooftops and residential pitched-roof applications. Forests generally have

3213-472: The polar layered deposits are composed of almost pure ice, with no more than 10% dust by volume and that fretted valleys in Deuteronilus Mensae contain thick glaciers covered by a mantle of rocky debris. Albedo Albedo ( / æ l ˈ b iː d oʊ / al- BEE -doh ; from Latin albedo  'whiteness') is the fraction of sunlight that is diffusely reflected by

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3276-416: The presence of mafic rocks, such as basalt . The albedo of a surface usually varies with the wavelength of light hitting it. Mars reflects little light at the blue end of the spectrum but much at red and higher wavelengths. This is why Mars has the familiar reddish-orange color to the naked eye. But detailed observations reveal a subtle range of colors on Mars' surface. Color variations provide clues to

3339-413: The probable identity and abundance of individual minerals on the surface. Using this technique, scientists have long known that the bright ochre areas probably contain abundant ferric iron (Fe) oxides typical of weathered iron-bearing materials (e.g., rust ). Spectra of the dark areas are consistent with the presence of ferrous iron (Fe) in mafic minerals and show absorption bands suggestive of pyroxene ,

3402-415: The proportion of direct radiation from a given solar angle, and D {\displaystyle {D}} being the proportion of diffuse illumination, the actual albedo α {\displaystyle {\alpha }} (also called blue-sky albedo) can then be given as: This formula is important because it allows the albedo to be calculated for any given illumination conditions from

3465-500: The reflection of sunlight (albedo). In the case of evergreen forests with seasonal snow cover, albedo reduction may be significant enough for deforestation to cause a net cooling effect. Trees also impact climate in extremely complicated ways through evapotranspiration . The water vapor causes cooling on the land surface, causes heating where it condenses, acts as strong greenhouse gas, and can increase albedo when it condenses into clouds. Scientists generally treat evapotranspiration as

3528-408: The reflectivity of water is very low at low and medium angles of incident light, it becomes very high at high angles of incident light such as those that occur on the illuminated side of Earth near the terminator (early morning, late afternoon, and near the poles). However, as mentioned above, waviness causes an appreciable reduction. Because light specularly reflected from water does not usually reach

3591-575: The regolith have low thermal inertias because the void spaces between grains restrict thermal conductivity to the contact point between grains. Thermal inertia values for most of the Martian surface are inversely related to albedo. Thus, high albedo areas have low thermal inertias indicating surfaces that are covered with dust and other fine granular material. The dark gray, low albedo surfaces have high thermal inertias more typical of consolidated rock. However, thermal inertia values are not high enough to indicate widespread outcroppings are common on Mars. Even

3654-587: The returned radar echoes from Mars shows that a lot of variation exists in surface roughness and slope across the planet's surface. Wide areas of the planet, particularly in Syria and Sinai Plana, are relatively smooth and flat. Meridiani Planum, the landing site of the Mars Exploration Rover Opportunity , is one of the flattest and smoothest (at decimeter-scale) locations ever investigated by radar—a fact borne out by surface images at

3717-588: The rockier areas appear to be mixed with a significant amount of loose material. Data from the Infrared Thermal Mapping (IRTM) experiment on the Viking orbiters identified areas of high thermal inertia throughout the interior of Valles Marineris and the chaotic terrain, suggesting that these areas contain a relatively large number of blocks and boulders. Radar studies provide a wealth of data on elevations, slopes, textures, and material properties of

3780-636: The snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases. The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts. As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback. Both positive feedback loops have long been recognized as important for global warming . Cryoconite , powdery windblown dust containing soot, sometimes reduces albedo on glaciers and ice sheets. The dynamical nature of albedo in response to positive feedback, together with

3843-675: The southwest Tharsis. The region corresponds to the location of the Medusa Fossae Formation, which consists of thick layers of unconsolidated materials, perhaps volcanic ash or loess . Ground-penetrating radar instruments on the Mars Express orbiter ( MARSIS ) and the Mars Reconnaissance Orbiter ( SHARAD ) are currently providing stunning echo-return data on subsurface materials and structures to depths of up to 5 km. Results have shown that

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3906-514: The spectral and angular distribution of solar radiation reaching the Earth's surface. These factors vary with atmospheric composition, geographic location, and time (see position of the Sun ). While directional-hemispherical reflectance factor is calculated for a single angle of incidence (i.e., for a given position of the Sun), albedo is the directional integration of reflectance over all solar angles in

3969-410: The viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light. Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces which reflect, adding up their reflectivities. Fresh 'black' ice exhibits Fresnel reflection. Snow on top of this sea ice increases

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