Regional Albedo Research Articles

Anthropogenic increase of winter surface albedo

Summary The range of surface albedo in winter increased fourfold after densely forested swamps in Orange County, New York were turned into farmland, making the local microclimate considerably more sensitive to the presence and duration of snow cover. Today, the peaty onion fields when dry have an albedo of 0.08 when snowfree and 0.79 when covered with fresh snow. Before clearance in the late 18th century, the albedo of the swamps ranged from approximately 0.10 when snowfree to 0.28 when snow covered. Prior to the arrival of white settlers, the regional surface albedo, as modeled over a large portion of southeastern New York, ranged from 0.12 when snowfree to 0.31 when snow covered. It ranged from 0.15 (snow-free) to 0.59 (snow covered) when deforestation peaked in the late 19th century. Present values are 0.14 and 0.47, respectively. As a result of these changes in albedo, we estimate that approximately the same amount of solar radiation was absorbed in the naturally vegetated New York region in a snowy winter (with the ground snow covered 75% of the time) as in a snow-dry winter in the late 19th century (with a 10% duration of snow). Deforestation elsewhere in the middle latitudes has had qualitatively similar effects.

“Dust” streaks on Mars

Global mapping and photometry of selected areas on Mars are used to investigate the nature of bright and dark wind streaks that extend from topographic obstacles. Occurrence of both bright and dark streaks is strongly latitude dependent and is only weakly correlated with surface properties such as albedo and thermal inertia. Data on the colors, albedos, and phase behavior of streaks are consistent with models of bright streaks as mosaics of plains material and brighter, redder dust. Less than 20% of the ground need be covered by the optically thick dust in the brightest parts of the streaks; the amount of dust in optically thick layers could be as little as 10 −3 g/cm 2. Dark streaks can be interpreted as erosional windows in a patchy dust cover. Our model of dust deposition in optically thick patches is sedimentologically different from scenarios involving the deposition of ubiquitous, optically thin layers. It has the advantage that large amounts of dust can be deposited without affecting regional albedos.

High resolution planetary albedos—values and variability

The spectral variability of high-resolution planetary albedo is shown to be a useful tool in surface-type analysis. The possibility of using comparison between planetary albedos in selected wavelength regions for cirrus cloud identification has been investigated. The results of an analysis of digital data streams from the polar orbiter satellite, TIROS-N, in three wavelength regions. Channel 1 (0.55–0.90 μm), Channel 2 (0.725–1.10 μm), and Channel 3 (3.55–3.93 μm) are described. These preliminary findings suggest that a spectral relationship exists for high-resolution planetary albedos in clear sky situations which permits surface type/cover discrimination. However the variability of planetary albedo in regions of cirrus cloud cover appears to be a strong function of the underlying surface or cloud type particularly when the cirrus cloud is tenous and/or it overlies highly reflective surfaces or clouds.

Arid land monitoring using Landsat albedo difference images

The Landsat albedo, or percentage of incoming radiation reflected from the ground in the wavelength range of 0.5 μm to 1.1 μm, is calculated from an equation using the Landsat digital brightness values and solar irradiance values, and correcting for atmospheric scattering, multispectral scanner calibration, and sun angle. The albedo calculated for each pixel is used to create an albedo image, whose grey scale is proportional to the albedo. Differencing sequential registered images and mapping selected values of the difference is used to create quantitative maps of increased or decreased albedo values of the terrain. All maps and other output products are in black and white rather than color, thus making the method quite economical. Decreases of albedo in arid regions may indicate improvement of land quality; increases may indicate degradation. Tests of the albedo difference mapping method in the Desert Experimental Range in southwestern Utah (a cold desert with little long-term terrain change) for a four-year period show that mapped changes can be correlated with erosion from flash floods, increased or decreased soil moisture, and increases or decreases in the density of desert vegetation, both perennial shrubs and annual plants. All terrain changes identified in this test were related to variations in precipitation. Although further tests of this method in hot deserts showing severe “desertification” are needed, the method is nevertheless recommended for experimental use in monitoring terrain change in other arid and semiarid regions of the world.

Moderate resolution thermal mapping of Mars: The channel terrain around the Chryse Basin

Moderate resolution (∼30 km) thermal inertia estimates have been made for several regions in the northern hemisphere of Mars. Examples of these maps are presented here for the region 0°–45°N, 0°–90°W. The thermal inertia of Kasei Vallis is found to be significantly higher than that of the surrounding terrain. The assumption of a uniform grain size surface gives maximum diameters of 1.0 mm inside and 0.05 mm outside Kasei Vallis for the surface materials. High inertia regions are well correlated with low albedo (A ∼ 0.14) regions. Three large channels in the Oxia Palus quandrangle also have high inertia floors. There is some indication that the thermal inertia increases toward the mouth of one of these channels. The Chryse and Acidalia basins have uniform high inertia surfaces with no decrease in inertia as distance increases from the major channels. There are numerous craters in the region which have high inertia‐low albedo features on the crater floor. This correlation has been observed for many other craters on Mars, both from Mariner 9 and Viking data. A possible explanation is the accumulation of coarsegrained, windblown material within the craters. Average grain sizes of these materials range from 0.5 to 1.1 mm, corresponding to medium to coarse sand. The Viking 1 landing site is located in the lowest inertia region within the area studied which met the latitude and elevation capabilities of that vehicle.

The Mars opposition effect at 20°N. latitude and 20°W. longitude

Low phase angle observations in the Chryse-Acidalia region have been obtained the Viking Orbiter 1 spacecraft under clearer atmospheric conditions than reported earlier. A variety of surface features were recorded, e.g., crater streaks, dark and bright patches. Several findings for this scene include: an abrupt brightness increase (10%) was found at phase angles less than 3°, an effect dependent on surface albedo and possibly particle distribution; a slight weakening of reflectance surge with decreasing wavelengths; a larger opposition effect for features of high albedo was recorded; and a greater reddening with increase phase angle took place for low albedo regions. Both reflectance and contrast values are provided at three wavelengths as a function of phase angle from 0.15 to 20°.

On the nature of the blue and ultraviolet absorption in the Jovian atmosphere

Spatially resolved reflectivities from 3000 to 6600 Å of three positions from the center to the limb of the Jovian Equator, North Equatorial Belt, and North Tropical Zone are analyzed to determine the vertical distribution and wavelength dependence of various sources of blue and uv absorption. Six different models of the distribution of absorbing dust particles are examined. In each model, the variation of dust optical depth and cloud single-scattering albedo are determined. Only those models having dust above the upper NH 3 cloud layer will fit the data. The high altitude dust distribution is approximately uniform over the three regions examined. The contrast in reflectivity of the belts and zones may be modeled by a different cloud single-scattering albedo in the different regions.

Global color variations on the Martian surface

Surface materials exposed throughout the equatorial region of Mars have been classified and mapped on the basis of spectral reflectance properties determined by the Viking II Orbiter vidicon cameras. Frames acquired at each of three wavelengths (0.45 ± 0.03 μm, 0.53 ± 0.05 μm, and 0.59 ± 0.05 μm) during the approach of Viking Orbiter II in Martian summer ( L s = 105°) were mosaicked by computer. The mosaics cover latitudes 30°N to 63°S for 360° of longitude and have resolutions between 10 and 20 km per line pair. Image processing included Mercator transformation and removal of an average Martian photometric function to produce albedo maps at three wavelengths. The classical dark region between the equator and ∼30°S in the Martian highlands is composed of two units: (i) and ancient unit consisting of topographic highs (ridges, crater rims, and rugged plateaus riddled with small dendritic channels) which is among the reddest on the planet (0.59/0.45 μ m ⋍ 3) ; and (ii) intermediate age, smooth, intercrater volcanic plains displaying numerous mare ridges which are among the least red on Mars (0.59/0.45 μ m ⋍ 2) . The relatively young shield volcanoes are, like the oldest unit, dark and very red. Two probable eolian deposits are recognized in the intermediate and high albedo regions. The stratigraphically lower unit is intermediate in both color (0.59/ 0.45 μ m ⋍ 2.5) and albedo. The upper unit has the highest albedo, is very red (0.59/0.45 μ m ⋍ 3) , and is apparently the major constituent of the annual dust storms as its areal extent changes from year to year. The south polar ice cap and condensate clouds dominate the southernmost part of the mosaics.

The Optical Properties of Ice and Snow in the Arctic Basin

AbstractMeasurements of light transmission and reflection were carried out on first-year sea ice near Point Barrow, Alaska, and on multi-year ice near Fletcher’s Ice Island in the Beaufort Sea (lat. 84° N., long. 77°W.). Spectral albedos (400-1 000 nm) and extinction coefficients (400-800 nm) were determined for melt ponds, snow, and various types of bare ice. Albedos were largest in the 400-600 nm range, decreasing toward longer wavelengths at a rate which appeared to be related to the liquid-water content of the near-surface layers. Extinction coefficients remained nearly constant between 400 and 550 nm, but increased rapidly above 600 nm. At 500 nm, albedos ranged from 0.25 over mature melt ponds to 0.93 over dense dry snow, while the corresponding extinction coefficients ranged from 0.6 to 16 m-1. Intensity profiles taken in the upper 50 cm of the ice indicated that the extinction coefficient at a particular wavelength was nearly constant with depth below 15 cm, although the bulk extinction coefficient decreased with depth because of the strong attenuation in the red. Near the surface it was found that multi-year ice absorbed slightly more energy than did first-year blue ice, but at depths below 10 cm the flux divergence in the first-year ice was three to four times larger than that in the multi-year ice. A simple procedure is described for estimating light transmission and absorption within the ice under clear or cloudy skies from total flux measurements at the surface. Methods by which satellite data could be used to estimate regional albedos, melt-pond fraction, and lead area are also presented.

The Optical Properties of Ice and Snow in the Arctic Basin

AbstractMeasurements of light transmission and reflection were carried out on first-year sea ice near Point Barrow, Alaska, and on multi-year ice near Fletcher’s Ice Island in the Beaufort Sea (lat. 84° N., long. 77°W.). Spectral albedos (400-1 000 nm) and extinction coefficients (400-800 nm) were determined for melt ponds, snow, and various types of bare ice. Albedos were largest in the 400-600 nm range, decreasing toward longer wavelengths at a rate which appeared to be related to the liquid-water content of the near-surface layers. Extinction coefficients remained nearly constant between 400 and 550 nm, but increased rapidly above 600 nm. At 500 nm, albedos ranged from 0.25 over mature melt ponds to 0.93 over dense dry snow, while the corresponding extinction coefficients ranged from 0.6 to 16 m-1. Intensity profiles taken in the upper 50 cm of the ice indicated that the extinction coefficient at a particular wavelength was nearly constant with depth below 15 cm, although the bulk extinction coefficient decreased with depth because of the strong attenuation in the red. Near the surface it was found that multi-year ice absorbed slightly more energy than did first-year blue ice, but at depths below 10 cm the flux divergence in the first-year ice was three to four times larger than that in the multi-year ice. A simple procedure is described for estimating light transmission and absorption within the ice under clear or cloudy skies from total flux measurements at the surface. Methods by which satellite data could be used to estimate regional albedos, melt-pond fraction, and lead area are also presented.