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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.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Improved Nominal Operating Cell Temperature (NOCT) test procedure

A procedure is developed to improve testing of Nominal Operating Cell Temperature (NOCT) as it applies to solar energy conversion modules. NOCT is a direct reflection of module thermal design and is closely related to the representative ambient temperature. It is also a key to array energy production and estimates of module lifetimes. Present NOCT test and evaluation procedures are inconsistent, producing significant scatter. Test refinements would specify a clear sky, the addition of 10% to the insolation level for ground reflection, the addition of a ground emission factor of 0.8 (at 30C ground temperature), an effective wind direction of 135 degrees from the North, and a module tilt of 30 degrees from the horizon.

Wen, L.↗
NASA NTRS1977

Determination of stack plume properties from satellite imagery

LANDSAT imagery data were analyzed to determine the quantitative properties of a stack plume emitted from a moderate-sized pulp mill. Overlapping, consecutive-day MSS data provided plume/no plume radiances upwelling from the area of interest. These values from both the plume and its shadow were used to evaluate plume radius, height, particle concentration and scattering function, and total particle loading. Imagery data from a 10 by 10 km region in the vicinity of the mill were normalized to correct for minor atmospheric, solar and viewing angle changes for the two observation days, and cloud shadow data were used to evaluate sky radiance. The effects of the Sun angle, surface reflectance, SNR and spatial resolution are treated in the paper.

Staylor, W. F.↗
NASA NTRS1983

Spectral radiance errors in remote sensing ground studies due to nearby objects

Attention is given to the error that can occur in all radiometric measurements owing to the presence of nearby objects. When a researcher positions himself on the side of a target point opposite the sun, his body gives rise to two erroneous effects. First, it blocks a portion of the incoming diffuse sky radiance to the target point, and second, it reflects incoming diffuse and direct solar irradiance and ground exitance onto the target point. It is noted that the same phenomenon occurs for any nearby object, whether it be a field truck, a building structure, or a row of trees. This error deriving from nearby objects is often not recognized by researchers or is considered insignificant with no knowledge of its magnitude. The approach taken here is to mathematically model the radiant transfers that take place between the global irradiance, panel, or scene and the object and to report the magnitude of this error for various solar zenith angles, wavelengths, size and distances of objects (steradian blockage), and spectral reflectances of the scene and object. The scene, object, and panel are assumed to be Lambertian, and the object is always located on the side of the target point opposite the sun.

Kimes, D. S.↗
NASA NTRS1987

Atmospheric optical depth effects on angular anisotropy of plant canopy reflectance

The effects of varying atmospheric aerosol optical depth on the bidirectional reflectance distribution of vegetation canopies is investigated. The reflectance distributions of two pasture grass canopies and one soya bean canopy under different sky irradiance distributions were measured, and the data were analyzed in the visible and IR spectral bands. It is observed that, for the pasture grass canopies, the change in reflectance is due to the percentage of shadowed area viewed by the sensor, and for the soya bean, the specular reflection effect and increased diffuse irradiance penetration into the canopy cause reflectance changes. It is detected that the reflectivity for the soya bean canopy on a hazy day is lower than on a clear day; however, the opposite change is observed for the pasture grass. It is also detected that the normalized difference vegetation index values differ under clear and hazy conditions for the same vegetation canopy conditions.

Deering, Donald W.↗
NASA NTRS1987

Regional and seasonal variations of surface reflectance from satellite observations at 0.6 micron

A global series of seasonal visible surface reflectance maps derived from NOAA-5 Scanning Radiometer observations is presented. Methods for isolating clear-sky observations from satellite data are evaluated and the magnitude of atmospheric effects (Rayleigh scattering and ozone absorption) are presented. A preliminary analysis of digital vegetation and soils data bases, which were analyzed in conjunction with the satellite observations, is discussed. Regional and global reflectance homogeneity of land-cover types, and snow brightening for types, are presented. Results demonstrate that the statistical approach for isolating clear-sky radiances used in this study obtains accurate enough values for each location to allow meaningful measurements of seasonal, spatial and ecosystem variations in surface reflectance.

Matthews, Elaine↗
NASA NTRS1999

Dust Optical Properties derived from Sun/Sky Measurements and Satellite Data

We derive the optical properties of dust originating from the Sahara and nearby regions using a combination of ground based and satellite measurements. The AErosol ROBotic NETwork (AERONET) sun/sky radiances from Cap Verde and Sede Boker are used together with Landsat TM data over Senegal and the Atlantic Ocean. The data introduce a cascade of increasing complexity of dust optical properties: The sky aureole radiance is sensitive mainly to the dust size distribution; the TM data over the ocean at 150 deg scattering angle are also sensitive to the spectral refractive index from 470 to 2,210 nm. The TM data over the land measure the balance between the dust scattering and absorption of light reflected by the bright surface, thus very sensitive to dust spectral absorption. Sky radiance at scattering angle of 120 deg, add sensitivity to the dust nonsphericity. Preliminary results, indicative of the ambient dust in the entire atmospheric column, show that dust is less absorbing and with smaller nonspherical properties than anticipated from in situ measurements. Dust is dominated by particles with effective radius of 2 to 2.5 micron, refractive index for wavelengths less then 1 micron of 1.53-0.001i and nonsphericity that increases the phase function at 120 deg above that of spheres by 1.8 and 1.7 at 673 nm down to 1.2 and 1.3 for 1020 nm for Cap Verde and Sede Boker respectively. No significant nonsphericity effect is noticed for scattering angle of 150 deg. This agrees with a mixture of 30% and 45% respectively of Mishchenko et al (JGR, 102, 1997: plate 5 on page 16,841) "polydisperse equiprobable shape mixture of prolate and oblate spheroids with aspect ratios ranging from 1.4 to 2.21, with the rest being spherical particles.

Kaufman, Yoram J.↗
NASA NTRS1971

Effects of skylight polarization, cloudiness, and view angle on the detection of oil on water.

Three passive radiometric techniques, which use the contrast of sunlight reflected and backscattered from oil and water in specific wavelength regions, have potential application for remote sensing of oil spills. These techniques consist of measuring (1) total radiance, (2) the polarization components (normal and parallel) of radiance, and (3) the difference between the normal and parallel components. In this paper, the best view directions for these techniques are evaluated, conclusions are drawn as to the most promising technique, and explanations are developed to describe why previous total-radiance measurements yielded highest contrast between oil and water under overcast skies. The technique based on measurement of only the normal polorization component appears to be the most promising. The differential technique should be further investigated because of its potential to reduce the component of backscattered light from below the surface of the water. Measurements should be made about 45 deg nadir view angle in the direction opposite the sun. Overcast sky conditions provide a higher intensity of skylight relative to clear sky conditions and a lower intensity of backscatter within the water relative to surface reflectance. These factors result in higher contrast between oil and water under overcast skies.

Millard, J. P.↗
NASA NTRS1987

Cloud cover over the equatorial eastern Pacific derived from July 1983 International Satellite Cloud Climatology Project data using a hybrid bispectral threshold method

A set of visible and IR data obtained with GOES from July 17-31, 1983 is analyzed using a modified version of the hybrid bispectral threshold method developed by Minnis and Harrison (1984). This methodology can be divided into a set of procedures or optional techniques to determine the proper contaminate clear-sky temperature or IR threshold. The various optional techniques are described; the options are: standard, low-temperature limit, high-reflectance limit, low-reflectance limit, coldest pixel and thermal adjustment limit, IR-only low-cloud temperature limit, IR clear-sky limit, and IR overcast limit. Variations in the cloud parameters and the characteristics and diurnal cycles of trade cumulus and stratocumulus clouds over the eastern equatorial Pacific are examined. It is noted that the new method produces substantial changes in about one third of the cloud amount retrieval; and low cloud retrievals are affected most by the new constraints.

Minnis, Patrick↗
NASA NTRS1994

Statistics and topology of the COBE differential microwave radiometer first-year sky maps

We use statistical and topological quantities to test the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR) first-year sky maps against the hypothesis that the observed temperature fluctuations reflect Gaussian initial density perturbations with random phases. Recent papers discuss specific quantities as discriminators between Gaussian and non-Gaussian behavior, but the treatment of instrumental noise on the data is largely ignored. The presence of noise in the data biases many statistical quantities in a manner dependent on both the noise properties and the unknown cosmic microwave background temperature field. Appropriate weighting schemes can minimize this effect, but it cannot be completely eliminated. Analytic expressions are presented for these biases, and Monte Carlo simulations are used to assess the best strategy for determining cosmologically interesting information from noisy data. The genus is a robust discriminator that can be used to estimate the power-law quadrupole-normalized amplitude, Q(sub rms-PS), independently of the two-point correlation function. The genus of the DMR data is consistent with Gaussian initial fluctuations with Q(sub rms-PS) = (15.7 +/- 2.2) - (6.6 +/- 0.3)(n - 1) micro-K, where n is the power-law index. Fitting the rms temperature variations at various smoothing angles gives Q(sub rms-PS) = 13.2 +/- 2.5 micro-K and n = 1.7(sup (+0.3) sub (-0.6)). While consistent with Gaussian fluctuations, the first year data are only sufficient to rule out strongly non-Gaussian distributions of fluctuations.

Smoot, G. F.↗
NASA NTRS1997

Correlation of S-Band Weather Radar Reflectivity and ACTS Propagation Data in Florida

Previous work has shown that Ka-band attenuation due to rainfall and corresponding S-band reflectivity are highly correlated. This paper reports on work whose goal is to determine the feasibility of estimation and, by extension, prediction of one parameter from the other using the Florida ACTS propagation terminal (APT) and the nearby WSR-88D S-band Doppler weather radar facility operated by the National Weather Service. This work is distinguished from previous efforts in this area by (1) the use of a single-polarized radar, preventing estimation of the drop size distribution (e.g., with dual polarization) and (2) the fact that the radar and APT sites are not co-located. Our approach consists of locating the radar volume elements along the satellite slant path and then, from measured reflectivity, estimating the specific attenuation for each associated path segment. The sum of these contributions yields an estimation of the millimeter-wave attenuation on the space-ground link. Seven days of data from both systems are analyzed using this procedure. The results indicate that definite correlation of S-band reflectivity and Ka-band attenuation exists even under the restriciton of this experiment. Based on these results, it appears possible to estimate Ka-band attenuation using widely available operational weather radar data. Conversely, it may be possible to augment current radar reflectivity data and coverage with low-cost attenuation or sky temperature data to improve the estimation of rain rates.

Wolfe, Eric E.↗
NASA NTRS2002

Technical Report Series on Global Modeling and Data Assimilation: A Coupled Ocean-Atmosphere Radiative Model for Global Ocean Biogeochemical Models - Volume 22

An ocean-atmosphere radiative model (OARM) evaluates irradiance availability and quality in the water column to support phytoplankton growth and drive ocean thermodynamics. An atmospheric component incorporates spectral and directional effects of clear and cloudy skies as a function of atmospheric optical constituents, and spectral reflectance across the air-sea interface. An oceanic component evaluates the propagation of spectral and directional irradiance through the water column as a function of water, five phytoplankton groups, and chromophoric dissolved organic matter. It tracks the direct and diffuse streams from the atmospheric component, and a third stream, upwelling diffuse irradiance. The atmospheric component of OARM was compared to data sources at the ocean surface with a coefficient of determination (r2) of 0.97 and a root mean square of 12.1%.

Gregg, Watson W.↗
NASA NTRS2004

Final Report for the Advanced Camera for Surveys (ACS)

ACS was launched aboard the Space Shuttle Columbia just before dawn on March 1, 2002. At the time of liftoff, the Hubble Space Telescope (HST) was reflecting the early morning sun as it moved across the sky. After successfully docking with HST, several components were replaced. One of the components was the Advanced Camera for Surveys built by Ball Aerospace & Technologies Corp. (BATC) in Boulder, Colorado. Over the life of the HST contract at BATC, hundreds of employees had the pleasure of working on the concept, design, fabrication, assembly, and test of ACS. Those employees thank NASA - Goddard Space Flight Center and the science team at Johns Hopkins University (JHU) for the opportunity to participate in building a great science instrument for HST.

Source record↗
NASA NTRS1984

Stratocumulus cloud field reflected fluxes - The effect of cloud shape

The reflected fluxes of stratocumulus cloud fields are calculated as a function of sky cover aspect ratio and cloud shape. In order to obtain a better fit with general circulation models (GCMs), cloud liquid water volume values were kept invariant relative to cloud shape. On the basis of the required accuracy of the Earth Radiation Budget Experiment (ERBE), an order of magnitude value of 10 W per sq m was used to estimate the difference between plane-parallel and broken cloudiness reflected fluxes. An empirical relationship for effective cloud cover at a solar zenith angle of 60 deg is derived. The relationship allows for the accurate computation of broken cloud field reflected fluxes using plane-parallel calculations. It is predicted that more accurate estimates of broken cloud field radiative properties may be possible in the future.

Welch, R. M.↗
NASA NTRS2017

What is the Uncertainty in MODIS Aerosol Optical Depth in the Vicinity of Clouds?

MODIS dark-target (DT) algorithm retrieves aerosol optical depth (AOD) using a Look Up Table (LUT) approach. Global comparison of AOD (Collection 6 ) with ground-based sun photometer gives an Estimated Error (EE) of +/-(0.04 + 10%) over ocean. However, EE does not represent per-retrieval uncertainty. For retrievals that are biased high compared to AERONET, here we aim to closely examine the contribution of biases due to presence of clouds and per-pixel retrieval uncertainty. We have characterized AOD uncertainty at 550 nm, due to standard deviation of reflectance in 10 km retrieval region, uncertainty related to gas (H2O, O3) absorption, surface albedo, and aerosol models. The uncertainty in retrieved AOD seems to lie within the estimated over ocean error envelope of +/-(0.03+10%). Regions between broken clouds tend to have higher uncertainty. Compared to C6 AOD, a retrieval omitting observations in the vicinity of clouds (< or = 1 km) is biased by about +/- 0.05. For homogeneous aerosol distribution, clear sky retrievals show near zero bias. Close look at per-pixel reflectance histograms suggests retrieval possibility using median reflectance values.

Patadia, Falguni↗
NASA NTRS1977

Significance of vegetation in interpreting thermal radiation from a terrestrial surface

The regions between crop rows are modeled as infinitely long diffuse cavities. Geometrical view factors are calculated, accounting for reflected radiation emanating internal to the cavity and from the background sky. A 'cavity' emissivity dependent on local geometry is defined to allow for correcting apparent temperatures to true temperatures. The total emissivity appropriate for correcting aircraft thermal data is then calculated by averaging all emissivity components to account for soil, crop, and background. It is shown that even for the lowest crop and vegetation emissivities, if the crop height-to-spacing ratio is greater than unity, the composite emissivity is greatly increased, giving rise to a decreased error in remotely sensed temperature data.

Sutherland, R. A.↗
NASA NTRS1976

CTRANS: A Monte Carlo program for radiative transfer in plane parallel atmospheres with imbedded finite clouds: Development, testing and user's guide

The program called CTRANS is described which was designed to perform radiative transfer computations in an atmosphere with horizontal inhomogeneities (clouds). Since the atmosphere-ground system was to be richly detailed, the Monte Carlo method was employed. This means that results are obtained through direct modeling of the physical process of radiative transport. The effects of atmopheric or ground albedo pattern detail are essentially built up from their impact upon the transport of individual photons. The CTRANS program actually tracks the photons backwards through the atmosphere, initiating them at a receiver and following them backwards along their path to the Sun. The pattern of incident photons generated through backwards tracking automatically reflects the importance to the receiver of each region of the sky. Further, through backwards tracking, the impact of the finite field of view of the receiver and variations in its response over the field of view can be directly simulated.

Source record↗
NASA NTRS1987

Computation of diffuse sky irradiance from multidirectional radiance measurements

Accurate determination of the diffuse solar spectral irradiance directly above the land surface is important in characterizing the reflectance properties of these surfaces, especially vegetation canopies. This determination is also needed to infer the net radiation budget of the earth-atmosphere system above these surfaces. An algorithm is developed here for the computation of hemispheric diffuse irradiance using the measurements from an instrument called PARABOLA, which rapidly measures upwelling and downwelling radiances in three selected wavelength bands. The validity of the algorithm is established from simulations. The standard reference data set of diffuse radiances of Dave (1978), obtained by solving the radiative transfer equation numerically for realistic atmospheric models, is used to simulate PARABOLA radiances. Hemispheric diffuse irradiance is estimated from a subset of simulated radiances by using the algorithm described. The algorithm is validated by comparing the estimated diffuse irradiance with the true diffuse irradiance of the standard data set. The validations include sensitivity studies for two wavelength bands (visible, 0.65-0.67 micron; near infrared, 0.81-0.84 micron), different atmospheric conditions, solar elevations, and surface reflectances. In most cases the hemispheric diffuse irradiance computed from simulated PARABOLA radiances and the true irradiance obtained from radiative transfer calculations agree within 1-2 percent. This technique can be applied to other sampling instruments designed to estimate hemispheric diffuse sky irradiance.

Ahmad, Suraiya P.↗
NASA NTRS2000

The HOLO Series: Critical Ground-Based Demonstrations of Holographic Scanning Lidars

Results of two lidar measurement campaigns are presented, HOLO-1 (Utah, March 1999) and HOLO-2 (New Hampshire, June 1999). These tests demonstrate the ability of lidars utilizing holographic optical elements (HOEs) to determine tropospheric wind velocity and direction at cloud altitude. Several instruments were employed. HOLO-1 used the 1,064 mm transmission-HOE lidar (HARLIE, Goddard Space Flight Center), a zenith-staring 532 nm lidar (AROL-2, Utah State University), and a wide-field video camera (SkyCam) for imagery of clouds overhead. HOLO-2 included these instruments plus the 532 nm reflection-HOE lidar (PHASERS, St. Anselm College). HARLIE and PHASERS scan the sky at constant cone angles of 45 deg. and 42 deg. from normal, respectively. The progress of clouds and entire cloud fields across the sky is tracked by the repetitive conical scans of the HOE lidars. AROL-2 provides the attitude information enabling the SkyCam cloud images to be analyzed for independent data on cloud motion. Data from the HOE lidars are reduced by means of correlations, visualization by animation techniques, and kinematic diagrams of cloud feature motion. Excellent agreement is observed between the HOE lidar results and those obtained with video imagery and lidar ranging.

Wilkerson, Thomas D.↗