Showing papers on "Sky published in 1982"

Skylight Polarization patterns and Animal Orientation

Abstract: 1.Although many invertebrate animals orient by means of ultraviolet sky-light polarization patterns, existing measurements of these patterns are inadequate for full analysis of the biologically relevant information available from the sky. To fill this gap we have used a precision scanning polarimeter to measure simultaneously the intensity, degree, and direction of vibration (E-vector orientation) of polarized light at 5° intervals over the sky. The resulting sky maps were constructed for u.v. (350 nm) and visible wavelengths (500 and 650 nm) under a variety of atmospheric conditions. 2.Our measurements confirmed that the patterns of radiance and degree of polarization of skylight are highly variable and hence unreliable as orientation cues; but patterns of E-vector orientation are relatively stable and predictable over most of the sky under all but very hazy or overcast conditions. 3.The observed E-vector patterns correspond more closely to predictions based on first order (Rayleigh) scattering at 650 and 500 nm than at 350 nm. This is true both in terms of absolute accuracy and the proportion of the sky with relatively ‘correct’ information. Yet most insects respond to polarization patterns only at u.v. wavelengths. This apparent paradox can perhaps be resolved by assuming that there is no great selective advantage for any particular wavelength when large areas of blue sky are visible, but that under special and difficult conditions ultraviolet has advantages over longer wavelengths. Measurements under partially cloud-covered sky, for instance, or under extensive vegetation, show that both spuriously polarized and unpolarized light resulting from reflexions present more troublesome interference at longer wavelengths than in the u.v. 4.The accuracy of orientation achieved by dancing honey bees appears to be greater than can readily be accounted for by assuming that they use a strictly geometrical or analytical processing system for their orientation to polarized light.

A model of thermal radiation from partly cloudy and overcast skies

Abstract: A mathematical model for predicting thermal radiation from partly cloudy and overcast skies was developed. The model uses previous clear sky equations for predicting full-spectrum sky emittance and 8–14 μm atmospheric window transmittance and then assumes that the cloud contribution to sky thermal radiation must be transmitted to the earth's surface through the atmospheric window. Unlike previous ‘cloud corrections,’ the cloud contribution is computed from surface vapor pressure and temperature, cloud amount, and elevation data, as recorded by National Weather Service observers. The average predicted increase due to 100% cloud cover was 18% for Phoenix in 1978 with a theoretical upper limit of about 40%. Comparisons were made between model predictions and measured values of sky radiation for a wide range of weather conditions. The agreement was excellent with an overall coefficient of determination for fit to a 1:1 line of 0.941 on an hourly basis and of 0.960 on a daily total basis.

Infrared radiative transfer through a regular array of cuboidal clouds

Abstract: Infrared radiative transfer through a regular array of cuboidal clouds is studied and the interaction of the sides of the clouds with each other and the ground is considered. The theory is developed for black clouds and is extended to scattering clouds using a variable azimuth two-stream approximation. It is shown that geometrical considerations often dominate over the microphysical aspects of radiative transfer through the clouds. For example, the difference in simulated 10 micron brightness temperature between black isothermal cubic clouds and cubic clouds of optical depth 10, is less than 2 deg for zenith angles less than 50 deg for all cloud fractions when viewed parallel to the array. The results show that serious errors are made in flux and cooling rate computations if broken clouds are modeled as planiform. Radiances computed by the usual practice of area-weighting cloudy and clear sky radiances are in error by 2 to 8 K in brightness temperature for cubic clouds over a wide range of cloud fractions and zenith angles. It is also shown that the lapse rate does not markedly affect the exiting radiances for cuboidal clouds of unit aspect ratio and optical depth 10.

A Study of the Incoming Longwave Atmospheric Radiation from a Clear Sky

Abstract: A band model for atmospheric absorption is used to calculate the incoming longwave atmospheric radiative flux for some typical clear sky conditions. The sky radiation is also measured using a specially-designed calorimetric apparatus over a wide range of ground-level atmospheric conditions. Good agreement is obtained between the measurement and the calculation using appropriate atmospheric conditions. Two simple equations are proposed for the prediction of seasonal values of sky radiation: one for summer-type conditions without a quasi-permanent temperature inversion, and one for winter-type conditions with a quasi-permanent temperature inversion. Spectral information of the atmospheric radiation is presented, and the spectral flux in the wavelength range 8–14 μm is computed for typical conditions.

An automatic all sky scanning radiometer

Abstract: A microcomputer controlled all sky scanning radiometer covering the short wave (0.3–3.0 μm) and long wave (3.0–80.0 μm) regions and using a pyroelectric detector has been constructed for continuous automatic measurement of sky radiance. Angular distributions of short, long, and total wave sky radiance are recorded and plotted at each solar hour angle from which irradiances of tilted surfaces are computer calculated. Measurement of the local earth surface radiance facilitates estimation of short wave earth surface albedo and net income of radiation to variously oriented black surfaces. Total scanning, computation, and plotting time for each hour angle observation is 8 min.

The moon illusion: I. How high is the sky?

Abstract: The most common explanations of the moon illusion assume that the moon is seen at a specific distance in the sky, which is perceived as a definite surface. A decrease in the apparent distance to the sky with increasing elevation presumably leads to a corresponding decrease in apparent size. In Experiment 1 observers (N = 24) gave magnitude estimates of the distance to the night sky at different elevations. The results did not support the flattened-dome hypothesis. In Experiment 2 observers (N = 20) gave magnitude estimates of the distance to the sky at points around a 360 degrees circle just above the horizon. The results were consistent with those of Experiment 1, and in addition, estimates were highly correlated with the physical distances of buildings at the horizon. In a third, control experiment, observers (N = 20) gave magnitude estimates of the distances of buildings at the horizon. A power function fit the relation between estimated and physical distance (exponent = 1.17) as well as the relation between estimates of the sky points above the buildings (Experiment 2) and estimates of building distances (exponent = .46). Taken together, the results disconfirm all theories that attribute the moon illusion to a "sky illusion" of the sort exemplified by the flattened-dome hypothesis.

Diffuse interstellar clouds associated with dark clouds.

Abstract: Measurements of CH emission at 9 cm toward the bright stars ..cap alpha.. Cam and kappa Cas and from dark clouds near the stars reveal an association between diffuse clouds and dark clouds. Here the term diffuse clouds refers to clouds seen in optical absorption; the term dark clouds refers to opaque regions on the Palomar Sky Survey observed through radio techniques. The radio emission toward ..cap alpha.. Cam, and possible emission twoard kappa Cas, occurs at the same velocity as the optical CH absorption. The column densities derived from both techniques are similar. A dark cloud near each star also shows emission at the velocity of absorption The column density of CH is larger in the dark cloud. From these data, it is concluded that for most lines of sight, diffuse clouds are the outer, relatively transparent portions of dark clouds.

Analysis of ocean color spectra (II): Effect of reflected sky light

Abstract: A method for evaluating the radiance due to sky light reflected by the sea surface and radiance emerging from the sea is described. The calculation is made as a function of the sun altitude, sky condition and sea state for varying optical properties of sea water. As a result of the contribution of reflected sky light, the shape of the spectral distribution for radiance just below the surface is considerably distorted above the surface, especially when chlorophyll concentrations are high. Special attention is paid to the ratio of radiance emerging from the sea to total upwelling radiance at the wavelength of 670 nrn. The variation in the ratio with wind-speed is small and the ratio decreases with increase in the atomospheric turbidity factor.

Galactic and zodiacal light surface brightness measurements with the Atmosphere Explorer Satellites.

Abstract: Galactic and zodiacal light surface maps are presented at 7320, 6300, 5577, 5200, and 4278 A. These were prepared from measurements made with the Visible Airglow Experiment on board the Atmosphere Explorer-C, -D, and -E satellites.

Far-ultraviolet studies. VI - Further limits on diffuse galactic light scattered at large angles by dust

Abstract: The Apollo 17 wide-field far-ultraviolet spectrometer was used to scan six large bands of the sky during trans-earth coast. After accounting for internal scattered light and the light expected from stars in the field of view, no significant residual flux remains. This imposes important constraints on the scattering properties of the interstellar dust grains: either the grains are extremely strongly forward scattering, or the albedo of the grains is low. The absence of a scattered light signal from dusty, moderate galactic latitude regions of the sky indicates that the high galactic latitude flux reported by Henry et al. (1977) and by Anderson et al. (1979) does not represent starlight backscattered by dust.

Snow‐sky and water‐sky luminance at an arctic station

Abstract: Luminance measurements of water-sky and snow-sky were carried out at Ny-Alesund, Svalbard. The luminance of a well-developed water-sky is found to be about 40% of that of the adjacent snow-sky. Once the‘luminance level’of a comparatively pure snow-sky is reached, there is only a very slight further luminance increase towards zenith. This is in good agreement with FRITZ’theory as well as with the light conditions experienced during‘white-out’situations. By measuring the angular elevation of the border between water-sky and snow-sky and the height of the cloud base, good estimates are obtained of the distance to the corresponding border on the ground between snow surface and open water.

A catalog of red stars near l1454.

Abstract: In view of their potential interest as individual objects of study, a catalog is presented of stars noted by the Duerr and Craine (1982) study of the nature of the dark cloud L1454 to have V-I magnitudes greater than about 2.5. Finding charts are given for these 156 stars, with attention to the individual quadrants of the region studied. The original star counts had been made with Near Infrared Photographic Sky Survey data.

Automated star counts in the dark cloud L 1454

Abstract: The Near Infrared Photographic Sky Survey (NIPSS) is a data base with broad potential not only for optical identification of point infrared sources, but also for a variety of studies related to the distribution of red stars. It has been suggested that these applications could be greatly aided by digitization of the data base, for which a feasibility study is under way. As a part of this study a NIPSS visual and near-infrared photographic pair, encompassing the dark cloud L 1454, was digitized. Star counts in this region suggest the existence of two clouds along the line of sight and allowed the distances, extinctions, and masses of the clouds to be estimated. In addition, maps of the region as a function of the redness of the constituent stars were generated. These, when compared to the extinction maps, allow a discussion of the star-formation properties of the region.

Near Infrared Observations of Galactic WN Stars

Abstract: The observations reported here have been obtained with the ESO Reticon system attached to the Boller and Chivens spectrograph at the 3.6 m telescope. The reciprocal dispersion was 228 A mm−1 with a useful spectral range extending from 5800 A to 11000 A. The slit was 200 pm wide which corresponds to 1.4 arcsec on the sky and to about 33.5 μm(∿ 7.6 A) in the plane of the detector. Sky substraction was performed by means of observations at 93 arcsec. East and West of the object. The correction for atmospheric extinction was based on a mean extinction curve of La Silla (Tug, 1977). As a consequence the strongest atmospheric bands are still present on the final spectra. The data were also corrected for the instrument sensitivity response by using calibrated stars selected from Breger’s catalog (1976). As these reference data are from filter photometry, they are not well suited to the resolution of our spectra, at least in some regions. This problem can be significant, as clearly illustrated by Johnson (1980).