SEARCH · Engineering Papers

Results for “Sunlight”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,099 records · Page 61

All sources NASA NTRS DOE OSTI

NASA NTRS1988

Stratospheric column NO2 measurements from three Antarctic sites

The significance of stratospheric odd-nitrogen compounds in Antarctic ozone depletion studies has prompted an increase in Antarctic activities. Although several species are being studied, work has concentrated on the acquisition of NO2 data. Ground-based measurements of stratospheric column NO2 have been made at Arrival Heights, Antarctica, since spring 1982, with some gaps in the data base. Additional data has been acquired since February 1986 at Pole Station and Halley Bay, thus providing a chain of stations across the continent. The technique used is that of absorption spectroscopy in several wavelength regions, although here only those measurements are reported in the 430 to 450 nm region where strongly structured absorption been determined experimentally. However, theory features due to NO2 are identified in scattered sunlight in the zenith sky. Operation of a moon-tracking system at Arrival Heights has provided some additional data during the polar night. Previous analyses have shown that the NO2 column observed from the ground is strongly influenced by the season, and by the location of the site with respect to that of the polar vortex. The column amount correlates strongly with stratospheric temperature at about 70 mbar. The present data set further illustrates these features, and demonstrates both the strengths and qualifications apparent in the technique.

Keys, J. G.↗

NASA NTRS1988

An integral sunshade for optical reception antennas

Optical reception antennas (telescopes) must be capable of receiving communications even when the deep-space laser source is located within a small angle of the Sun. Direst sunlight must not be allowed to shine on the primary reflector of an optical reception antenna, because too much light would be scattered into the signal detectors. A conventional sunshade that does not obstruct the antenna aperture would have to be about five times longer than its diameter in order to receive optical communications at a solar elongation of 12 degrees without interference. Such a long sunshade could not be accommodated within the dome of any existing large-aperture astronomical facility, and providing a new dome large enough would be prohibitively expensive. It is also desirable to reduce the amount of energy a space-based large-aperture optical reception facility would expend orienting a structure with such a sizable moment of inertia. Since a large aperture optical reception antenna will probably have a hexagonally segmented primary reflector, a sunshade consisting of hexagonal tubes can be mounted in alignment with the segmentation without producing any additional geometric obstruction. An analysis of the duration and recurrence of solar-conjunction communications outages (caused when a deep-space probe near an outer planet appears to be closer to the Sun than a given minimum solar elongation), and the design equations for the integral sunshade are appended.

Kerr, E. L.↗

NASA NTRS1988

Shutters and slats for the integral sunshade of an optical reception antenna

Optical reception antennas used at a small Sun-Earth-probe angle (small solar elongation E) require sunshading to prevent intolerable scattering of light from the surface of the primary mirror. An integral sunshade consisting of hexagonal tubes aligned with the segmentation of a large mirror was proposed for use down to E = 12 degrees. For smaller angles, asterisk-shaped vanes inserted into the length of the hexagonal tubes would allow operation down to about 6 degrees with a fixed obscuration of 3.6 percent. Two alternative methods are investigated to extend the usefulness of the integral sunshade to smaller angles by adding either variable-area shutters to block the tube corners that admit off-axis sunlight or by inserting slats (partial vanes) down the full length of some tubes. Slats are effective for most operations down to 6 degrees, and obscure only 1.2 percent. For E between 10.75 and 12 degrees, shutters cause even less obscuration.

Kerr, E. L.↗

NASA NTRS1988

Effects of global atmospheric perturbations on forest ecosystems: Predictions of seasonal and cumulative effects

The physical effects of certain large events, such as giant impacts, explosive volcanism, or combined nuclear explosions, have the potential of inducing global catastrophes in our terrestrial environment. Such highly energetic events can inject substantial quantities of material into the atmosphere. In turn, this changes the amount of sunlight reaching the Earth's surface and modifies atmospheric temperatures to produce a wide range of global effects. One consequence is the introduction of serious stresses in both plants and animals throughout the Earth's biosphere. For example, recent studies predict that forest lands, crop lands, and range lands would suffer specific physical and biological degradations if major physical and chemical disruptions occurred in our atmosphere. Forests, which cover over 4 times 10 to the 9th power hectares (4 times 10 to the 7th power sq km) of our planet, or about 3 times the area now cultivated for crops, are critical to many processes in the biosphere. Forests contribute heavily to the production of atmospheric oxygen, supply the major volume of biomass, and provide a significant percentage of plant and animal habitats.

Tinus, R. W.↗

NASA NTRS1988

Darkness after the K-T impact: Effects of soot

Dust from the K-T impact apparently settled from the atmosphere in less than 6 months, restoring sunlight to minimum photosynthesis levels in about 4 months. However, the discovery of a global soot component in the boundary clay makes it necessary to reconsider the problem, as soot particles not only are smaller (0.1 vs. about 0.5 micrometer) and thus settle more slowly, but also are better light absorbers (optical depth of 13 mg soot cm(-2) about 1800; and are more resistant to rainout. Still, the darkness cannot have lasted very much longer than 6 months, else no larger animals would have survived. Perhaps the soot coagulated with the rock dust and fell out with it. Evidence on this point may be sought at a relatively undisturbed K-T boundary site, such as Woodside Creek, N.Z. There the boundary clay and lowermost Tertiary strata are finely laminated and show large chemical and isotopic differences on a millimeter scale, apparently representing a detailed time sequence. Researchers studied a 3 m section across the boundary at this site, analyzing the principal forms of carbon (soot, elemental C, kerogen, and carbonate) as well as 33 elements. Correlations among the elements were sought. Apparently soot came early and coagulated with the ejecta, staying with them for the primary fallout and in the next 5 cm, but then parting company, perhaps due to size sorting.

Wolbach, Wendy S.↗

NASA NTRS1989

Local intensity adaptive image coding

The objective of preprocessing for machine vision is to extract intrinsic target properties. The most important properties ordinarily are structure and reflectance. Illumination in space, however, is a significant problem as the extreme range of light intensity, stretching from deep shadow to highly reflective surfaces in direct sunlight, impairs the effectiveness of standard approaches to machine vision. To overcome this critical constraint, an image coding scheme is being investigated which combines local intensity adaptivity, image enhancement, and data compression. It is very effective under the highly variant illumination that can exist within a single frame or field of view, and it is very robust to noise at low illuminations. Some of the theory and salient features of the coding scheme are reviewed. Its performance is characterized in a simulated space application, the research and development activities are described.

Huck, Friedrich O.↗

NASA NTRS1988

The GONG Data Reduction and Analysis System

Each of the six GONG observing stations will produce three, 16-bit, 256X256 images of the Sun every 60 sec of sunlight. These data will be transferred from the observing sites to the GONG Data Management and Analysis Center (DMAC), in Tucson, on high-density tapes at a combined rate of over 1 gibabyte per day. The contemporaneous processing of these data will produce several standard data products and will require a sustained throughput in excess of 7 megaflops. Peak rates may exceed 50 megaflops. Archives will accumulate at the rate of approximately 1 terabyte per year, reaching nearly 3 terabytes in 3 yr of observing. Researchers will access the data products with a machine-independent GONG Reduction and Analysis Software Package (GRASP). Based on the Image Reduction and Analysis Facility, this package will include database facilities and helioseismic analysis tools. Users may access the data as visitors in Tucson, or may access DMAC remotely through networks, or may process subsets of the data at their local institutions using GRASP or other systems of their choice. Elements of the system will reach the prototype stage by the end of 1988. Full operation is expected in 1992 when data acquisition begins.

Pintar, James A.↗

NASA NTRS1988

Agriculture Multiband Experiment Radiometer

Agriculture Multiband Experiment Radiometer (Amber) was designed and built in 1979 to 1980 and deployed in 1981. Amber was designed to simultaneously measure sunlight reflected from vegetation in 15 optical bands. In 1982, program interest shifted from ground truth to satellite image reduction and Amber was retired. Early in 1987, the project scientists concluded that Amber, because of its 15 simple and independent optical systems, would be ideally suited to study polarized light. Changes were made to add polarimeter capability to the instrument. The changes are listed and briefly discussed.

Jones, W. H.↗

NASA NTRS1988

Solar maximum mission fine pointing sun sensor dawn and dusk errors flight data and model analysis

SMM flight system control errors occurring at spacecraft dawn and dusk are analyzed. The errors are associated with the fine pointing sun sensor (FPSS), which is a primary component of the SMM attitude control system. It is shown that the source of the FPSS dawn/dusk distortion is the incomplete masking of sunlight reflected off the earth by the optical baffle covering the FPSS sensor heads onboard the SMM during periods of orbit dawn and dusk. For the most part, the modeled behavior of the FPSS under dawn and dusk lighting conditions matches the observed behavior in the SMM flight data.

Kulp, D. R.↗

NASA NTRS1988

Stratospheric NO2 over Antarctica as measured by the Solar Mesosphere Explorer during austral spring, 1986

This paper presents the results of polar NO2 measurements carried out by the SME satellite during the fall and spring of 1985 and 1986 and compares the results with observations at the north pole and the results of model calculations. During the austral spring, a polar low was observed in stratospheric NO2 densities measured between 24 and 40 km, consistent with the predictions of standard photochemical theory. The geographic extent of the area of low NO2 densities was found to decrease as the hours of sunlight increased, in marked contrast to the behavior of the Antarctic ozone hole during the same period. A comparison of measurements with model calculations for NO2 imply that much of the odd nitrogen is converted to HNO3 during the polar night. Data also suggest no evidence that changes in high-altitude odd nitrogen are influencing the ozone below, or that the 'ozone hole' penetrates above 24 km to affect odd nitrogen there.

Thomas, Ronald J.↗

NASA NTRS1988

Moorable spectroradiometers in the BIOWATT experiment

A new oceanographic instrument, the MER-2020, has been developed for the long term measurement of bio-optical properties. This instrument is a self-contained reflectance spectroradiometer with 40 megabytes of internal data storage and battery power permitting deployments for as long as 6 months. It can serve as the control and recording center for a variety of other sensors including fluorometers, transmissometers, temperature and conductivity probes. Instruments of this type were deployed at depths to 70 meters on a 5000 meter mooring during the BIOWATT experiment between February and November 1987. Measurements of the spectral diffuse attenuation coefficient and of the remote sensed reflectance from the ten month period in 1987 in the Northern Sargasso Sea are presented. In addition, the temperature, pressure, package orientation and sunlight stimulated natural fluorescence of phytoplankton are discussed. This instrument will be a key part of in situ optical calibration for future remote color sensors, and presently permits direct measurement of long term optical variability, important in visibility and communication problems.

Booth, C. R.↗

NASA NTRS1989

An exploratory 5-micron spectrum of Uranus

The intensity peak at 4.8 microns characterizing the spectrum observed for the disk of Uranus near 5 microns, in June 1987, exhibits steep declines at shorter and longer wavelength. An exploratory discussion is presented of various models in view of these data; it is noted that some component of the radiation must originate near the 140 K atmospheric irrespective of the radiation's origin in sunlight or thermal emission; physical considerations dictate that it be at least partly thermal in origin. One model consistent with the data requires the presence of a cloud top at the 8-bar level.

Orton, Glenn S.↗

NASA NTRS1989

Impact of heterogeneous reactions on stratospheric chemistry of the Arctic

The possible depletion of ozone due to heterogeneous reactions occurring in Arctic polar stratospheric clouds (PSCs) is fundamentally different from the Antarctic situation. PSCs in the Arctic are relatively short-lived and occur over limited regions of the Arctic stratosphere. The Arctic situation is examined using a model which calculates photochemical processes as a function of longitude in air circulating with fixed velocity around the pole at fixed pressure level and latitude. The model allows sunlight to vary diurnally and PSCs to occur in specified subregions of the domain. Measurements of chemical species including HCl, ClO, NO2 and HNO3 downwind from a PSC should show obvious changes compared to measurements in air unaffected by clouds. These species concentrations are found to be sensitive to sticking coefficients, cloud characteristics including particle number density and surface area, and to the PSC exposure time.

Douglass, Anne R.↗

NASA NTRS1989

Calculation of solar attenuation coefficient using ACCOS V along a critical scattering path

An appraisal of the optical properties of the AVHRR is made for a proposed orbital trajectory which results in an unexpected solar stray-light path; i.e., bypassing the external scan mirror and Cassegrain telescope and proceeding directly to the inner conical baffle. This stray-light path is directed onto an internal beamsplitter which, in turn, is directly observed by the detectors. Stray-light analysis, as a goal, seeks to remove or minimize the influence of such critical scattering paths. The AVHRR path is evaluated using a standard optical ray-tracing program, ACCOS V. To determine the expected sensor degradation, a calculation of the expected attenuation coefficient of scattered sunlight in the AVHRR sensor is estimated based on this important critical scattering path.

Ames, Alan J.↗

NASA NTRS1989

Ionospheric dynamo theory for production of far ultraviolet emissions on Uranus

A model is presented to explain diffuse FUV emissions from the outer planets, specifically Uranus, in excess of those diffuse emissions that are currently explainable by scattering of sunlight and/or excitation by photoelectrons. These electroglow emissions in H Ly-alpha and H2 bands, which occur in the sunlit hemisphere slightly above the homopause, appear to require particle excitation in the 10- to 50-eV range. An in situ mechanism for accelerating photoelectrons (and ions is proposed, involving neutral wind dynamo generation of field-aligned currents analogous to what occurs in the earth's equatorial E and F regions. Sufficiently strong field-aligned currents are found in the model calculation for Uranus to produce a potential drop of about 100 eV or greater between the F peak and homopause, concentrated at lower altitudes, and capable in principle of accelerating photoelectrons (and ions) to the 10- to 50-eV energies required to explain the observed emissions. The fact that the excitation and ionization cross sections are larger than elastic scattering cross sections in an H2 atmosphere at these energies makes in situ acceleration feasible for the production of UV on the outer planets.

Hudson, M. K.↗

NASA NTRS1989

Triton - Do we see to the surface?

The quantity and physical state of methane and nitrogen in the atmosphere of Neptune's satellite Triton and on the surface are evaluated by means of new telescopic data and laboratory measurements of these volatiles. Methane ice is seen in some spectral regions, indicating that the atmosphere is sufficiently transparent to permit sunlight penetration to the surface. Some of the molecular nitrogen absorption occurs in the atmosphere, though some must occur in condensed nitrogen (liquid or solid) on Triton's surface, or in a thin cloud of condensed nitrogen. The Voyager spacecraft cameras should see the surface of Triton.

Cruikshank, D. P.↗

NASA NTRS1989

The thermal structure of Titan's atmosphere

The present radiative-convective model of the Titan atmosphere thermal structure obtains the solar and IR radiation in a series of spectral intervals with vertical resolution. Haze properties have been determined with a microphysics model encompassing a minimum of free parameters. It is determined that gas and haze opacity alone, using temperatures established by Voyager observations, yields a model that is within a few percent of the radiative convective balance throughout the Titan atmosphere. Model calculations of the surface temperature are generally colder than the observed value by 5-10 K; better agreement is obtained through adjustment of the model parameters. Sunlight absorption by stratospheric haze and pressure-induced gas opacity in the IR are the most important thermal structure-controlling factors.

Mckay, Christopher P.↗

NASA NTRS1988

A review of test results on parabolic dish solar thermal power modules with dish-mounted Rankine engines and for production of process steam

This paper presents results of development testing of various solar thermal parabolic dish modules and assemblies. Most of the tests were at modules and assemblies that used a dish-mounted, organic Rankine cycle turbine for production of electric power. Some tests were also run on equipment for production of process steam or for production of electricity using dish-mounted reciprocating steam engines. These tests indicate that early modules achieve efficiencies of about 18 percent in converting sunlight to electricity (excluding the inverter but including parasitics). A number of malfunctions occurred. The performance measurements, as well as the malfunctions and other operating experience, provided information that should be of value in developing systems with improved performance and reduced maintenance.

Jaffe, Leonard D.↗