Solar hydrogen Lyman-alpha-profile spectrograph.
High resolution UV spectrograph with echelle, noting optical line-up for photographing H- Lyman alpha line at 1216 angstroms
SOLAR SPECTRUM↗
SEARCH · Engineering Papers
Results for “solar optics”
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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Solar radiation, phytoplankton pigments and the radiant heating of the equatorial Pacific warm pool
Recent optical, physical, and biological oceanographic observations are used to assess the magnitude and variability of the penetrating flux of solar radiation through the mixed layer of the warm water pool (WWP) of the western equatorial Pacific Ocean. Typical values for the penetrative solar flux at the climatological mean mixed layer depth for the WWP (30 m) are approx. 23 W/sq m and are a large fraction of the climatological mean net air-sea heat flux (approx. 40 W/sq m). The penetrating solar flux can vary significantly on synoptic timescales. Following a sustained westerly wind burst in situ solar fluxes were reduced in response to a near tripling of mixed layer phytoplankton pigment concentrations. This results in a reduction in the penetrative flux at depth (5.6 W/sq m at 30 m) and corresponds to a biogeochemically mediated increase in the mixed layer radiant heating rate of 0.13 C per month. These observations demonstrate a significant role of biogeochemical processes on WWP thermal climate. We speculate that this biogeochemically mediated feedback process may play an important role in enhancing the rate at which the WWP climate system returns to normal conditions following a westerly wind burst event.
Siegel, David A.↗
Bulk Photovoltaic Effect Driven by Collective Excitations in a Correlated Insulator
We investigate the bulk photovoltaic effect, which rectifies light into electric current, in a collective quantum state with correlation driven electronic ferroelectricity. We show via explicit real-time dynamical calculations that the effect of the applied electric field on the electronic order parameter leads to a strong enhancement of the bulk photovoltaic effect relative to the values obtained in a conventional insulator. The enhancements include both resonant enhancements at sub-band-gap frequencies, arising from excitation of optically active collective modes, and broadband enhancements arising from nonresonant deformations of the electronic order. The deformable electronic order parameter produces an injection current contribution to the bulk photovoltaic effect that is entirely absent in a rigid-band approximation to a time-reversal symmetric material. Furthermore, our findings establish that correlation effects can lead to the bulk photovoltaic effect and demonstrate that the collective behavior of ordered states can yield large nonlinear optical responses.
14 SOLAR ENERGY↗
Optical properties of thermal control coating contaminated by MMH/N2O4 5-pound thruster in a vacuum environment with solar simulation
Cat-a-lac Black, and S13G thermal control coatings were exposed to the exhaust of a thruster in a simulated space environment. Vacuum was maintained at less than 10 to the minus 5th power torr during thruster firing in the liquid helium cooled facility. The thruster was fired in a 50-millisecond pulse mode and the accumulated firing time was 224 seconds. Solar absorptance (alpha sub s) and thermal emittance (sigma) of the coatings were measured in-situ at intervals of 300 pulses. A calorimetric technique was used to measure alpha sub s and sigma. The tests, technique, and test results are presented. The Cat-a-lac Black coatings showed no change in alpha sub s or sigma. The S13G showed up to 25 percent increase in alpha sub s but no change in sigma.
Sommers, R. D.↗
Optical properties of thermal control coatings contaminated by MMH/N2O4 5-pound thruster in a vacuum environment with solar simulation.
Cat-a-lac Black and S13G thermal control coatings were exposed to the exhaust of a thrustor in a simulated space environment. Vacuum was maintained at less than 10 microtorr during thrustor firing in the liquid helium cooled facility. The thrustor was fired in a 50-millisecond pulse mode, and the accumulated firing time was 224 seconds. Solar absorptance and thermal emittance of the coatings were measured in-situ at intervals of 300 pulses, using a calorimetric technique. The Cat-a-lac Black coatings showed no change in solar absorptance or thermal emittance. The S13G showed up to 25% increase in solar absorptance but no change in thermal emittance.
Sommers, R. D.↗
A note on the acceleration phase of high-energy particles in the solar flare on 7 July, 1966.
The acceleration phase of solar cosmic rays and relativistic electrons is studied on the basis of the observational data available on the optical, radio, X-ray, and particle events associated with the solar flare that occurred on July 7, 1966. The generating process of hydromagnetic shock waves which excited the type-II radio burst detected at a frequency below about 100 MHz is also discussed. The results of the study suggest that no secondary acceleration process after the explosive phase can contribute much to the generation of high energy particles. The ejection of solar cosmic rays and relativistic electrons seems to be related to the expansion of the magnetic bulge which can trap accelerated electrons from the triggering region of solar flares.
Sakurai, K.↗
Optical Design of the RAISE Sounding Rocket Instrument
The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) is a recently selected sounding rocket program to investigate the dynamics and heating of the outer solar atmosphere on time scales as short as looms. Its optical design represents the first in a new class of two-reflection W / E W imaging spectrometers with Toroidal Varied-Line Space (TVLS) gratings. Due to the remarkable imaging properties of such gratings, RAISE will measure spectra simultaneously over four different wavelength bands (1205-1243 & 1524-1559 A in first order, 602.5-621.5 & 762.0-779.5 A in second), with an unprecedented combination of spatial, spectral, and temporal resolutions. These spectral regions include many bright, well-resolved lines covering the temperature range from the low chromosphere up to the 2 MK Fe XI1 corona. The RAISE optical design features an extremely fast beam (f/7.0) and a minimum number of reflections, which together allow enough throughput to provide high quality spectral data even at its very short exposure times. Moreover, by operating with high magnification (x4.25), the RAISE spectrometer can most effectively utilize the full length and width available in the sounding rocket payload. First launch of this exciting new instrument is scheduled for 2006 June 21.
Thomas, Roger J.↗
MODIS Aqua Optical Throughput Degradation Impact on Relative Spectral Response and Calibration on Ocean Color Products
Since Moderate Resolution Imaging Spectroradiometer Aqua's launch in 2002, the radiometric system gains of the reflective solar bands have been degrading, indicating changes in the systems optical throughput. To estimate the optical throughput degradation, the electronic gain changes were estimated and removed from the measured system gain. The derived optical throughput degradation shows a rate that is much faster in the shorter wavelengths than the longer wavelengths. The wavelength-dependent optical throughput degradation modulated the relative spectral response (RSR) of the bands. In addition, the optical degradation is also scan angle-dependent due to large changes in response versus the scan angle over time. We estimated the modulated RSR as a function of time and scan angles and its impacts on sensor radiometric calibration for the ocean science. Our results show that the calibration bias could be up to 1.8 % for band 8 (412 nm) due to its larger out-of-band response. For the other ocean bands, the calibration biases are much smaller with magnitudes at least one order smaller.
Lee, Shihyan↗
Measurement of the X-ray emission of the solar atmosphere during a period of low activity
A large-area high-sensitivity X-ray spectrometer has been constructed and used to measure the 1.8- to 5.3-A X-ray emission of the sun under quiescent conditions. The instrument utilizes Bragg reflection from mosaic graphite crystals. The data indicate that the X-ray emission can best be accounted for by a multitemperature model of the solar atmosphere in which both the overall corona and active regions contribute to the X-ray spectrum. Theoretical calculations of the X-ray flux of a hot, optically thin plasma have been used to estimate the solar conditions at the time when the measurements were made.
Wolff, R. S.↗
An Initial Analysis of the Pixel-Level Uncertainties in Global MODIS Cloud Optical Thickness and Effective Particle Size Retrievals
Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals of cloud optical thickness and effective particle radius employ well-known solar reflectance techniques using pre-calculated reflectance look-up tables. We evaluate the quantitative uncertainty in simultaneous retrievals of cloud optical thickness and particle size for this type of algorithm. The technique uses sensitivity calculations derived from the reflectance look-up tables, coupled with estimates for the effect of various error terms on the uncertainty in inferring the actual cloud-top reflectance. The error terms include the effects of instrument calibration, surface spectral albedo, and atmospheric corrections on both water and ice cloud retrievals. Because particle shapes in ice clouds are highly variable, the effect of particle shape is analyzed separately with a more approximate method. Results will deal exclusively with pixel-level uncertainties associated with plane-parallel clouds; real-world radiative departures from a plane-parallel model are an additional consideration. While we demonstrate the uncertainty technique with operational 1 km MODIS retrievals from the Terra and Aqua satellite platforms, the technique is applicable to any reflectance-based satellite- or air-borne sensor retrieval using similar spectral channels.
Platnick, S.↗
A Strategy to Assess Aerosol Direct Radiative Forcing of Climate Using Satellite Radiation Measurements
Atmospheric aerosols have a complex internal chemical composition and optical properties. Therefore it is difficult to model their impact on redistribution and absorption of solar radiation, and the consequent impact on atmospheric dynamics and climate. The use in climate models of isolated aerosol parameters retrieved from satellite data (e.g. optical thickness) may result in inconsistent calculations, if the model assumptions differ from these of the satellite retrieval schemes. Here we suggest a strategy to assess the direct impact of aerosol on the radiation budget at the top and bottom of the atmosphere using satellite and ground based measurements of the spectral solar radiation scattered by the aerosol. This method ensures consistent use of the satellite data and increases its accuracy. For Kaufman and Tanre: Strategy for aerosol direct forcing anthropogenic aerosol in the fine mode (e.g. biomass burning smoke and urban pollution) consistent use of satellite derived optical thickness can yield the aerosol impact on the spectral solar flux with accuracy an order of magnitude better than the optical thickness itself. For example, a simulated monthly average smoke optical thickness of 0.5 at 0.55 microns (forcing of 40-50 W/sq m) derived with an error of 20%, while the forcing can be measured directly with an error of only 0-2 W/sq m. Another example, the effect of large dust particles on reflection of solar flux can be derived three times better than retrievals of optical thickness. Since aerosol impacts not only the top of the atmosphere but also the surface irradiation, a combination of satellite and ground based measurements of the spectral flux, can be the most direct mechanism to evaluate the aerosol effect on climate and assimilate it in climate models. The strategy is applied to measurements from SCAR-B and the Tarfox experiments. In SCAR-B aircraft spectral data are used to derive the 24 hour radiative forcing of smoke at the top of the atmosphere of (Delta)F(sub 24hr)/(Delta)tau = - 25 +/- 5 W/sq m. Ground based data give forcing at the surface of (Delta)F(sub 24hr)/(Delta)taur = -80 +/- 5 W/sq m. In TARFOX a mixture of maritime and regional pollution aerosol resulted in a varied forcing at the top of the atmosphere, (Delta)F(sub 24hr)/(Delta)tau, between -26 W/sq 2 and -50 W/sq m depending on mixture of coarse and accumulation modes, for Angstrom exponents of 1.0 and 0.2 respectively.
Kaufman, Yoram J.↗
MODIS Retrievals of Cloud Optical Thickness and Particle Radius
The Moderate Resolution Imaging Spectroradiometer (MODIS) provides an unprecedented opportunity for global cloud studies with 36 spectral bands from the visible through the infrared, and spatial resolution from 250 m to 1 km at nadir. In particular, all solar window bands useful for simultaneous retrievals of cloud optical thickness and particle size (0.67, 0.86, 1.2, 1.6, 2.1, and 3.7 micron bands) are now available on a single satellite instrument/platform for the first time. An operational algorithm for the retrieval of these optical and cloud physical properties (including water path) have been developed for both liquid and ice phase clouds. The product is archived into two categories: pixel-level retrievals at 1 km spatial resolution (referred to as a Level-2 product) and global gridded statistics (Level-3 product). An overview of the MODIS cloud retrieval algorithm and early level-2 and -3 results will be presented. A number of MODIS cloud validation activities are being planned, including the recent Southern Africa Regional Science Initiative 2000 (SAFARI-2000) dry season campaign conducted in August/September 2000. The later part of the experiment concentrated on MODIS validation in the Namibian stratocumulus regime off the southwest coast of Africa. Early retrieval results from this regime will be discussed.
Platnick, S.↗
Characterizing Heliostats at a Commercial Scale With Non-Intrusive Optics
The NIO methodologies objective is to precisely measure 3 sources of heliostat optical error quickly and automatically, without interfering with plant operations. This presentation will discuss in further depth what this means as well as review the solution.
commercial scale heliostats↗
Parameterization of cloud transmittance for expeditious assessment and forecasting of all-sky DNI
Radiative transfer models require vast computing resources to solve cloud transmittance and reflectance from the radiative transfer equation. As a result, models offering precise simulation in operations often acquire individual cloud transmittance or reflectance from a lookup table precomputed for practicable scenarios. To further expedite the computation of global horizontal irradiance and to reduce the storage requirements, the Fast All-sky Radiation Model for Solar applications (FARMS) parameterized the lookup table using elementary functions with specified coefficients. This study extends FARMS direct normal irradiance (DNI) computation by utilizing hyperbolic tangent functions and various polynomial functions to parameterize the cloud transmittance for scattered solar radiation in the circumsolar region. The parameterization is implemented in FARMS with DNI (FARMS-DNI) and accounts for the circumsolar radiation when assessing or forecasting DNI. The evaluation, with long-term observations at the National Renewable Energy Laboratory's, Solar Radiation Research Laboratory, and the Atmospheric Radiation Measurement, Southern Great Plains, Central Facility, shows that the parameterized DNIs are virtually identical with those computed by coupling FARMS-DNI to a lookup table of cloud transmittance. This parameterization has diverse applications in radiative transfer models and numerical weather prediction models used to assess or forecast direct solar radiation.
14 SOLAR ENERGY↗
Spectral irradiance measurements, section V
Optical characteristics and spectral irradiance of three solar simulation lamps
SOLAR SIMULATION↗
FEP covers for silicon solar cells
Fluorinated ethylene propylene covers for silicon solar cells, describing processing parameters effects on optical and electrical characteristics
Forestieri, A. F.↗
Degree and plane of polarization of multiple scattered light. 1: Homogeneous cloud layers
The degree of polarization and the direction of the plane of polarization are calculated by a Monte Carlo method for homogeneous layers. Two solar zenith angles and a range of optical thicknesses up to 10 are considered. The results are compared with calculations for single scattered photons. For a given pair of incident and scattered directions, there are only two possible values for the direction of the plane of polarization differing by 90 deg for single scattering from spherical aerosols. The choice between these two values depends only on the sign of the element M(-) in the first row and second column of the scattering matrix in the I, Q, U, V representation. In most cases there is little change in the direction of the plane of polarization when multiple scattering is taken into account, so that this quantity can usually be predicted from a very simple trigonometric relationship to good accuracy. Measurements of the direction of the plane of polarization at appropriately chosen angles provides information about the size distribution of the scattering centers.
Kattawar, G. W.↗
A study of two flares on 8 July 1968 in the light of their ionospheric effects.
Detailed study of the observed ionospheric effects of the X-ray flare on July 8, 1968, which was of considerable importance both from the ionospheric and solar physics point of view. The associated optical flare was of importance 3B. The ionospheric effects were examined in order to derive a suitable physical model of flare-induced ionization below 100 km, and hence to estimate the spectral characteristics of the ionizing radiations from the observed SID s. The electron loss coefficients below 70 km height calculated from the formula developed in the analysis are in agreement with available data.
Sengupta, P. R.↗