Showing papers on "Zenith published in 1974"
TL;DR: In "Stratospheric ozone depletion and solar ultraviolet radiation on Earth" by P. Cutchis (5 Apr., p. 13), the legend to Fig. 5 was inadvertently omitted by the printer.
Abstract: In "Stratospheric ozone depletion and solar ultraviolet radiation on Earth" by P. Cutchis (5 Apr., p. 13), the legend to Fig. 5 was inadvertently omitted by the printer. The legend should read "Fig. 5. Direct solar UV irradiance and scattered UV irradiance on a horizontal surface at sea level for solar zenith angles θ of 0°, 30°, 60°, and 75° and 0.341 atm-cm of total ozone [data from (10)]."
121 citations
TL;DR: In this article, a review of ground-based and rocket techniques that are presently being used to determine electron density profiles in the ionospheric D region is presented, including time and height resolution, accuracy estimates, preferred height ranges, and problems encountered.
Abstract: This paper reviews the ground-based and rocket techniques that are presently being used to determine electron density profiles in the ionospheric D region. Ground-based techniques include VLF, LF, and MF sounding; differential absorption and differential phase measurements using partial reflections; wave interaction; and incoherent scatter. Rocket techniques include differential absorption and Faraday rotation in association with high-resolution dc probes calibrated by means of the radio measurements. The characteristics of the aforementioned techniques are presented, including time and height resolution, accuracy estimates, preferred height ranges, and problems encountered. Electron density profiles obtained with these techniques are presented for comparable solar zenith angles and undisturbed solar and geophysical conditions.
63 citations
01 Apr 1974
TL;DR: In this article, the effect of solar zenith angle, atmospheric conditions, windspeed, spectral region, and direction of view on the sensitivity to small changes in chlorophyll concentration was studied.
Abstract: : The apparent spectral signal available to a remote sensor flying over ocean waters is studied. Report considers the effect of solar zenith angle, atmospheric conditions, windspeed, spectral region, and direction of view on the sensitivity to small changes in chlorophyll concentration. A method of synthesizing the inherent spectral radiance signature of the ocean surface is developed and new measurements of the downwelling spectral irradiance at the ocean surface and the radiance of the zenith sky are presented. Also studied are reflectance characteristics of the ocean surface when wind-generated whitecaps, foam, and spray are present.
54 citations
TL;DR: In this article, a three-dimensional study of atmospheric gamma rays with energy greater than 30 MeV has been carried out, using a 15 cm by 15 cm digitized wire grid spark chamber.
Abstract: A three-dimensional study of atmospheric gamma rays with energy greater than 30 MeV has been carried out. A knowledge of these atmospheric secondaries has significant applications to the study of cosmic gamma rays. For detectors carried on balloons, atmospherically produced gamma rays are the major source of background. For satellite detectors, atmospheric secondaries provide a calibration source. Experimental results were obtained from four balloon flights from Palestine, Texas, with a 15 cm by 15 cm digitized wire grid spark chamber. The energy spectrum for downward-moving gamma rays steepens with increasing atmospheric depth. Near the top of the atmosphere, the spectrum steepens with increasing zenith angle. A new model of atmospheric secondary production has calculated the depth, the energy, and the zenith angle dependence of gamma rays above 30 MeV, using a comprehensive three-dimensional Monte Carlo model of the nucleon-meson-electromagnetic cascade.
39 citations
TL;DR: The results of a survey already published have been used to construct contour maps and ruled surface diagrams of the brightness temperature at 29·9 MHz near the galactic plane between I = 225° and 30°.
Abstract: The results of a survey already published have been used to construct contour maps and ruled surface diagrams of the brightness temperature at 29·9 MHz near the galactic plane between I = 225° and 30°. The angular resolution was 0°· 8 at the zenith, and the range of zenith angles involved was ± 30°. Restoration of the background was achieved with the aid of a low resolution filled-aperture survey carried out by others. The brightness temperature scale was calibrated absolutely. The optical depth of the Galaxy in directions within 40° of latitude from the centre has been estimated by a method which relies only on the shapes of brightness temperature profiles and not on absolute temperature calibrations. If an electron temperature is assumed, r.m.s. electron densities can be deduced. The average value of the disc emissivity at 29·9 MHz and the value of its spectral index have been calculated from brightness temperature profiles observed at a number of different frequencies, calibrations being required for these purposes. About 29 discrete absorption regions have been observed and identified with optically observed HII regions, and the fact that these are all nearer than 4 kpc permits a choice between kinematic distances in two cases. The Carina nebula and RCW 108 lend themselves to the measurement of local emissivities, and values of these together with their implications have already been published. A number of previously unlisted nonthermal sources have been observed, many of which are objects of low surface brightness and probably are supernova remnants.
25 citations
TL;DR: In this article, the possibility of experiments with cosmic neutrinos of energy E > 3 × 1017 eV was discussed and the upper bound of neutrino-nucleon cross-section σ < 93 × 10−30 cm2 was obtained from the zenith angular distribution of extensive air showers under some particular astrophysical assumptions.
24 citations
TL;DR: It is proposed that the method will be valuable for the interpretation of measurements made by instruments on spin-stabilized spacecraft on planetary missions, since in these cases the required angular coverage is obtained automatically for most trajectories.
Abstract: The principles of remote sounding of vertical temperature profiles in planetary atmospheres containing cloud layers are presented for an approach that uses measurements at different angles to the local vertical to eliminate the unknown cloud effects. A numerical example for a model of the earth's atmosphere shows that soundings separated by 40 deg in zenith angle permit the recovery of the temperature profile with an error that is not significantly greater than that obtained in the clear atmosphere case, and without serious horizontal smear. It is proposed that the method will be valuable for the interpretation of measurements made by instruments on spin-stabilized spacecraft on planetary missions, since in these cases the required angular coverage is obtained automatically for most trajectories.
17 citations
TL;DR: In this article, the spectral distribution of the radiation is measured using a Michelson interferometer with an optical path difference of ± 10 cm, using a 77°K reference blackbody.
16 citations
TL;DR: The results strongly support the colourpattern hypothesis, which postulates that bees perceive the polarization pattern in the sky as a colour pattern, and that certain aspects of this colour pattern are used as a beacon for compass orientation.
Abstract: 1. The directions of waggling dances of bees, trained for a feeding place in a given direction, are recorded on a horizontal comb. The comb is covered by a white tent with a central circular opening towards the zenith. 2. The orientation of the dances is seriously disturbed under spectral filters, absorbing UV. The orientation of the dances is much less disturbed under greyfilters, which decrease the level of stimulation of all types of receptors. These results show that the polarization perception is based on the integration of the contributions of at least two different types of receptors. 3. By selective blocking of polarized light in certain areas of the sky by means of polaroidfilter configurations (Fig. 3c), the importance of spatial differences in the stimulation ratio between the blue and UV receptors is shown. The blue receptor contribution appeared to be predominant in the solar vertical, whereas the contribution of the UV receptors is predominant in a celestial band perpendicular to the solar vertical in the zenith. 4. The colour pattern, which according to the colourpattern hypothesis (VAN DER GLAS, 1975), bees would perceive as a result of the polarization of the skylight, is simulated by an artificial colourpattern, i.e. a configuration of colour filter segments (Fig. 8, 10 and 12) in the colours bluegreen and purple, combined with a depolarizer for the incident skylight. The "stable" dances (see methods) under this colourpattern are orientated in the predicted directions. Control experiments with greyfilter contrasts in a similar configuration, in which the stable dances of the bees are mainly desorientated, proved that the colours in the pattern are essential. It seems that the direction of the bluegreen segments is used by the bees as a beacon for the menotactic orientation in the dances. 5. If half of the field of view around the zenith of the normal free sky is screened, the orientation is better when the dividing-line of the free half-moon shaped field of view is perpendicular to the solar vertical than when this dividing-line is directed along the solar vertical. With similar apertures for artificial colourpatterns (Fig. 16), the same effects are observed. Consequently the differences in orientation behaviour in both cases is due to differences in screening of essential features of the colour pattern. Suggestions for possible senso-neural integration of the information of fields of ommatidia are given. 6. The results strongly support the colourpattern hypothesis, which postulates that bees perceive the polarization pattern in the sky as a colour pattern, and that certain aspects of this colour pattern are used as a beacon for compass orientation.
9 citations
TL;DR: In this article, an infrared radiometer has been developed for measurement of water vapor content in the stratosphere using a Golay cell as detector, and the instrument has been flown on balloons to a maximum altitude of 27 km.
Abstract: An infrared radiometer has been developed for measurement of water vapor content in the stratosphere. The instrument observes atmospheric emission in the strong water vapor rotational lines beyond 40-μm wavelength and at two zenith angles of 45° and 70°. The method automatically compensates for instrumental gain change. A Golay cell is used as detector, and the instrument has been flown on balloons to a maximum altitude of 27 km. Results obtained so far over Australia indicate a dry lower stratosphere with water vapor values in the 1–3 ppm range and a mean value of 2.1 ppm at 20 km, but on one occasion a wet layer (∼6 ppm) was observed near 20-km altitude.
9 citations
TL;DR: The atmospheric attenuation at 1.3 and 0.87 mm was measured above Mount Hamilton, California in the period December 5 to December 9, 1973 as discussed by the authors, and the total beamwidth of the 120" Lick Observatory telescope used in the Coude configuration was measured to be 3' at 3.3 mm.
Abstract: The atmospheric attenuation at 1.3 and 0.87 mm was measured above Mount Hamilton, California in the period December 5 to December 9, 1973. The measured value of the zenith attenuation varied from 1 to 5 dB at 1.3 mm over this five-day period, and was 2.5 dB at 0.87 mm on December 9, 1973. The total beamwidth of the 120" Lick Observatory telescope used in the Coude configuration was measured to be 3' at 1.3 mm.
TL;DR: All the features of the spectra can be identified with known constituents of the atmosphere and the comparison with a theoretical emission calculation using a tropical atmospheric model was satisfactory except for the H(2)O that showed a smaller concentration than was assumed in the model at these altitudes.
Abstract: Atmospheric emission spectra in the 700–2800-cm−1 region have been measured from an aircraft at 9.45–11.89-km altitudes. All measurements were made viewing at the zenith at a spectral resolution of 2 cm−1. The measurements were obtained using interferometer spectrometers, and the atmospheric radiation was modulated with a liquid nitrogen cooled chopper that eliminated the thermal emission of the spectrometers from the measured spectra. Essentially all the features of the spectra can be identified with known constituents of the atmosphere. The comparison with a theoretical emission calculation using a tropical atmospheric model was satisfactory except for the H2O that showed a smaller concentration by a factor of 5 than was assumed in the model at these altitudes.
TL;DR: In this article, an analysis of the atmospheric attenuation data for the microwave region has been made and some rather simple expressions for computing the attenuation as a function of zenith angle are developed with an accuracy suitable for satellite antenna footprint calculations.
Abstract: In an earlier paper by the authors1 it was mentioned that atmospheric attenuation effects could be included by assuming that the attenuation is directly proportional to number of air masses. While this assumption is valid for the optical region, it is not true in the microwave region (1 to 40 GHz). For a clear atmosphere, the two constituents which absorb microwaves are oxygen and water vapor. An analysis of the atmospheric attenuation data for the microwave region has been made and some rather simple expressions for computing the attenuation as a function of zenith angle are developed with an accuracy suitable for satellite antenna footprint calculations.
TL;DR: The absolute integral sea-level spectra of single muons at zenith angles θ=45 °W and 60 °W have been estimated by means of a range spectrograph near the geomagnetic equator (12 °N) in the muon momentum range (0.4÷3) GeV/c.
Abstract: The absolute integral sea-level spectra of single muons at zenith angles θ=45 °W and 60 °W have been estimated by means of a range spectrograph near the geomagnetic equator (12 °N) in the muon momentum range (0.4÷3) GeV/c. The measured spectra after corrections, when compared to our vertical integral spectrum, follow the cosine lawI(θ)=I(0) cosnθ. The average value ofn=1.85±0.10 is in accordance with the results of Sreekantanet al., Judge and Nash, and Crookes and Rastin. The experimental spectra agree well with the theoretical spectra calculated after Barrettet al.
01 Apr 1974
TL;DR: In this article, the results of a statistical investigation of the variation of E-region critical frequency f0E with solar activity, solar zenith angle and season, are synthesized to obtain a describing function of f 0E in terms of geographic latitude, solar zero angle and 10°7 cm solar radio-noise flux, for the design of ionospheric transmission paths.
Abstract: The results of a statistical investigation of the variation of E-region critical frequency f0E with solar activity, solar zenith angle and season, are synthesised to obtain a describing function of f0E in terms of geographic latitude, solar zenith angle and 10°7 cm solar radio-noise flux, for the design of ionospheric transmission paths. The reliability of the f0E expression is assessed by comparing predicted and observed values at various stations, and the standard error of estimate is determined.
26 Mar 1974
TL;DR: In this article, the asymptotic directions and cut-off rigidities for Palestine, Dallas, amd Midland, Texas were calculated as a function of various zenith and azimuth angles.
Abstract: Using the trajectory-tracing technique, the asymptotic directions and cut-off rigidities for Palestine, Dallas, amd Midland,Texas were calculated as a function of various zenith and azimuth angles. Continuation of the trajectory-tracing process below the Stormer cutoff allows an evaluation of the reentrant albedo; the invariant latitude of the guiding center of the trajectory at the albedo origin is seen to be the same as the invariant latitude of the guiding center of the particle trajectory at the specified zenith and azimuth angle of the detection point. Tables of asymptotic directions, cutoff rigidities, and the location of the reentrant albedo for each of these locations are given. Summaries of cutoff rigidity calculations as a function of zenith and azimuth directions for some miscellaneous locations are also included. (GRA)
TL;DR: The absolute sea level differential cosmic muon spectra at zenith angles 45 degrees and 60 degrees in the western azimuth have been determined near the geomagnetic equator (at 12 degrees N) by using the range spectrograph in the momentum interval 0.5-3 GeV/c as discussed by the authors.
Abstract: The absolute sea level differential cosmic muon spectra at zenith angles 45 degrees and 60 degrees in the western azimuth have been determined near the geomagnetic equator (at 12 degrees N) by using the range spectrograph in the momentum interval 0.5-3 GeV/c. The experimental muon spectra after corrections agree well with the spectra, calculated after Jabs theory for the same location, above muon momentum 1.8 GeV/c. The results have been compared with others obtained at higher latitudes. It is found that the variation of differential muon intensity with 1g sec theta ( theta is the zenith angle of the spectrograph axis) diminishes slowly with the increase of muon momentum from 1 to 3 GeV/c. The variation of the cosine exponent in the expression I( theta )=I(0) cosn theta agrees with that calculated after Jabs. The present spectra after latitude corrections for 55 degrees N agree well with that magnetic spectrograph result of Allkofer and Andresen for the same latitude at 45 degrees W and with that of Judge and Nash for 60 degrees W.
26 Mar 1974
TL;DR: In this paper, the asymptotic directions and cut-off rigidities for Palestine, Dallas, and Midland, Texas were calculated as a function of various zenith and azimuth angles.
Abstract: : Using the trajectory-tracing technique, the asymptotic directions and cut-off rigidities for Palestine, Dallas, and Midland, Texas were calculated as a function of various zenith and azimuth angles. Continuation of the trajectory-tracing process below the Stormer cutoff allows an evaluation of the reentrant albedo showing that the invariant latitude of the guiding center of the trajectory at the albedo origin is the same as the invariant latitude of the guiding center of the particle trajectory at the specified zenith and azimuth angle of the detection point. Tables of asymptotic directions, cutoff rigidities, and the location of the reentrant albedo for each of these locations are given. Summaries of cutoff rigidity calculations as a function of zenith and azimuth directions for some miscellaneous locations are also included.
TL;DR: In this paper, the mesospheric electron density values derived from multifrequency radio wave absorption data for a low-latitude station with the ionization production rates of O2+ and NO+ under different conditions of solar zenith angles and solar activity levels were compared.
Abstract: Attempts have been made to compare the mesospheric electron density values derived from multifrequency radio wave absorption data for a low-latitude station with the ionization production rates of O2+ and NO+ under different conditions of solar zenith angles and solar activity levels. For both 80 km and 90 km the relation q ∝ N is found to be a better approximation than the simple recombination type of relation q ∝ N2. In addition, the situation at 80 km appears to be more complicated and indicates the possibility of a lower NO density than that implied in the observation by Meira (1971).
TL;DR: In this article, a large incoherent scatter radar system has been proposed as the principal element in a binational center for studies of the upper atmosphere, which is designed to yield a sensitivity comparable to the best now available and yet provide a latitude coverage of the F region of ±13°.
Abstract: A new large incoherent scatter radar system has been proposed as the principal element in a binational center for studies of the upper atmosphere The radar has been designed to yield a sensitivity comparable to the best now available and yet provide a latitude coverage of the F region of ±13°
The radar shall comprise a 100-m diameter parabolic reflector antenna that can be tilted in the magnetic meridian plane by ±85° from the zenith This antenna will be coupled to a UHF pulse transmitter with a peak power of 10 Mw, and will serve for both transmitting and receiving Two auxiliary fully steerable antennas will be located northeast and northwest of the main antenna and will also receive the signals This will enable the velocity of the ion drift to be studied, permitting measurements of neutral winds, electric fields, and fluxes of ions into or from the magnetosphere The auxiliary antennas will form 10 coplanar pencil beams, so that these drift measurements may be made at 10 heights simultaneously
The paper describes how the above concept was developed and the work of selecting a site for the radar By locating the main station near L = 4, and the auxiliary stations about 550 km distant, it will be possible to measure the electric fields in the F region over the range 3 ≤ L ≤ 8 to an accuracy of ±2 mv m−1 Thus, the radar should be able to map the electric fields produced by substorms at auroral and subauroral latitudes In addition, the properties of the ionosphere and many parameters of the atmosphere will be determined over the altitude range 100 to 1000 km
TL;DR: In this article, an extreme ultraviolet telescope system was flown on an Aerobee 170 rocket from the White Sands Missile Range on Oct. 22, 1971, and measurements of extreme ultraviolet radiation from the night sky were made with a set of Parylene, aluminum and tin filters behind a grazing incidence concentrator.
Abstract: An extreme ultraviolet telescope system was flown on an Aerobee 170 rocket from the White Sands Missile Range on Oct. 22, 1971. Measurements of extreme ultraviolet radiation from the night sky were made with a set of Parylene, aluminum, and tin filters behind a grazing incidence concentrator. If the aluminum and tin filter data are interpreted as being due to only the He I 584-A and He II 304-A lines, the nightglow flux at 25 deg zenith angle and 270 deg azimuth angle at 180-km altitude was I(584) = 4.4 plus or minus 1.9 R and I(304) = 1.3 plus or minus 0.5 R.
TL;DR: In this paper, the probability distribution of atmospheric emission noise from the zenith at 110 GHz has been measured by a radiometer at Slough, UK, and derived attenuations in the vertical direction exceed 13 and 6 dB for 0·5 and 5% of the time, respectively.
Abstract: The probability distribution of atmospheric emission noise from the zenith at 110 GHz has been measured by a radiometer at Slough, UK. The derived attenuations in the vertical direction exceed 13 and 6 dB for 0·5 and 5% of the time, respectively.
TL;DR: The ability of a 3.3-mm radiometer to produce thermal images with a 10 arc-minutes resolution on a real-time display has been proved in this paper.
TL;DR: In this article, the variability of the refraction from one measurement to the next is found to depend upon the zenith angle and season and to be mainly due to ionospheric disturbances whose presence is not usually revealed by measurements of the F2 critical frequency.
Abstract: About 2000 measurements of source positions obtained at 80 MHz with the Culgoora radioheliograph near the peak of the solar activity cycle in 1968-71 have been used to determine the regular ionospheric lefraction. Diurnal, seasonal and zenith-angle dependencies of the refraction are deduced and found to be qualitatively consistent with the known gradients in peak electron density. The variability of the refraction from one measurement to the next is found to depend upon the zenith angle and season and to be mainly due to ionospheric disturbances whose presence is not usually revealed by measurements of the F2 critical frequency. A quantitative comparison of the measured values of angular refraction with the F2 critical frequency and its north-south and east-west gradients demonstrates the validity of the theoretical expressions for regular refraction developed by Komesaroff (1960) and yields a value of 190± 12 km for the equivalent thickness of the nocturnal ionosphere. A comparison of the present measurement of the thickness parameter with measurements of the same quantity made during the minimum of solar activity shows that the shape of the F2 layer is not dependent on the solar activity cycle and hence is not a sensitive measure of the gas temperature.
01 Aug 1974
TL;DR: In this article, a general expression for the F layer electron density profile as a function of latitude and longitude for that part of the earth which is in direct sunlight including dawn and dusk was derived.
Abstract: A general expression is derived for the F layer electron density profile as a function of latitude and longitude for that part of the earth which is in direct sunlight including dawn and dusk. Furthermore, the derived model is extended to encompass the night-time ionosphere. The expressions allow determination by standard means of the range correction for arbitrary ray path directions. It is also shown that the naive application of the Chapman ionospheric model entails range correction errors which for low elevation angles (less than 20 deg) and large solar zenith angles (40 deg) cannot be tolerated. Numerical calculations are displayed showing the dependence of the range correction on the pertinent parameters.
01 Jun 1974
TL;DR: In this paper, the authors presented daytime atmospheric optical data collected with airborne instruments during a field expedition in southern Illinois in the summer of 1971, including the natural irradiance upon horizontal plane surfaces, scalar irradiances, total volume scattering coefficients, atmospheric beam transmittances, path radiances, directional path reflectances, and directional terrain reflectances.
Abstract: : This report presents daytime atmospheric optical data collected chiefly with airborne instruments during a field expedition in southern Illinois in the summer of 1971. Results from four flights and selected ground-based data are presented. The data include the natural irradiance upon horizontal plane surfaces, scalar irradiances, total volume scattering coefficients, atmospheric beam transmittances, path radiances, directional path reflectances, and directional terrain reflectances. Data for sunlight conditions were derived for downward-looking paths of sight inclined at six zenith angles (95, 100, 105, 120, 150, and 180 degrees) from maximum altitudes of 3000 to 5100 meters above ground level and lower in three spectral regions, as follows: two narrow band optical filters with mean wavelengths of 478 and 664 nanometers; and one broad band sensitivity representing the photopic response with a mean wavelength of 557 nanometers.
TL;DR: In this article, the termination for the solar flare effect on the ionosphere at VLF reflecting heights occurred between solar zenith angles 84° and 87°, considerably less than the sunset Zenith angle of 94° for this height.
TL;DR: In this article, a summary has been made of all the available data on the charge ratio of cosmic-ray muons at energies above 50 GeV and the data have been combined into zenith-angle bins and average values have been plotted for mean angles of approximately 0°, 60° and 80°.
Abstract: A summary has been made of all the available data on the charge ratio of cosmic-ray muons at energies above 50 GeV The data have been combined into zenith-angle bins and average values have been plotted for mean angles of approximately 0°, 60° and 80° Following the method outlined by MacKeown and Wolfendale an approximate analysis has been made to determine limits on the ratio of kaons to pions (K/π) and K+/K− for energetic secondaries produced in the interactions of primary particles in the energy range (500÷10000) GeV It is shown that there is no evidence for a dramatic change in these quantities over the next decade of energy above that available at the Intersecting Storage Ring experiment at CERN
TL;DR: The variation of atmospheric refraction between the zenith distances 65° and 90° has been observed using a simple achromatic camera as discussed by the authors, and a new formula was proposed to give the angle of refraction more accurately at large distances than the familiar tangent ξ formula.
Abstract: The variation of atmospheric refraction between the zenith distances 65° and 90° has been observed using a simple achromatic camera A new formula gives the angle of refraction more accurately at large zenith distances than the familiar tangent ξ formula The techniques used for camera calibration are also presented