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NASA NTRS1971

Analytic cross sections for 1 1S, to 1 1S to 2 1S, 1 1S to 2 1P transitions in helium by electron impact

The 1 1s yields 1 1s elastic and 1 1s yields 2 1s and 1 1s yields 2 excitation cross sections of Helium atoms by collision with a charged particle are obtained as analytic functions of incident velocity. The first order time dependent scattering theory is used. Numerical values of electron -He cross sections are obtained for incident energies in the range 30 eV to 800 eV and compared with earlier Born approximation calculations and with available experimental data. It is found that at 100 eV and above, the present results are in good agreement with the experimental results. They are also closer to the experimental results than the corresponding Born calculations.

Sukumar, C. V.↗

NASA NTRS1979

Venus - Preliminary topographic and surface imaging results from the Pioneer Orbiter

Three large Venus surface features, identified previously in images obtained from earth-based radar observations, are shown by the Pioneer Venus radar mapper to be elevated 5 to 10 km above the surrounding terrain. Two of these features, one bright and the other dark, lie adjacent to each other astride the 65 N parallel between longitudes 310 E and 10 E. The combined region forms a huge tectonically uplifted plateau, surmounted by radar-bright ridges that may have either a volcanic or tectonic origin. The third feature, located at 30 N, 283 E, is radar-bright and may consist of volcanic material extruded along a fault zone. A first radar-scattering image, compiled from data obtained by the mapper in its imaging mode, shows a region north of the equator; several circular depressions seen in this area may result from meteoritic impact.

Pettengill, G. H.↗

NASA NTRS1990

Elastic scattering of e- and e+ from Rb and Cd

Differential cross section results are calculated for the elastic scattering of electrons and positrons from the ground state of Rb and Cd atoms. An optical model potential approach is used for the calculation. Results are compared with the available electron impact experimental results.

Pangantiwar, A. W.↗

NASA NTRS1993

Electric field measurements in the vicinity of noctilucent clouds and PMSE

We report mesospheric electronic field structure in the vicinity of noctilucent clouds (NLC) and polar mesospheric summer echoes (PMSEs) measured on the DECIMALS-B rocket payload launched during the international rocket-radar campaign NLC-91 from Esrange, Sweden on August 10, 1991. Unusually large vertical E- fields, E(sub Z), about 100-300 mV/m on ascent and greater than 1 V/m on descent were detected at 82.5-84.5 km. The region of the large E(sub Z) was clearly limited by the NLC layer on the bottom and by the distinctly separated PMSE layer on the top. A narrow negative peak in the E(sub Z) height profile observed on ascent in the lower part of the NLC layer was apparently caused by the interaction of the field mill with impacting NLC particles possibly carrying negative charge. If the impact signature is due to single particles, their size is estimated to at least 0.5 microns and their concentration about 10(exp -4)/cu cm locally. Based on the light-scattering properties of NLC such massive particles can only be a minor part of the NLC population.

Zadorozhny, Alexander M.↗

NASA NTRS2006

ROCK AND SOIL PHYSICAL PROPERTIES AT THE MER GUSEV CRATER AND MERIDIANI PLANUM LANDING SITES

Following the successful landings of both Mars Exploration Rover (MER) vehicles at Gusev Crater and Meridiani Planum, respectively, their Athena suite of instruments is being used to study the geologic history of these two very different landing sites on Mars that had been selected on the basis of showing different types of evidence for aqueous processes in the planet s past. Utilizing the on-board instruments as well as the rovers mobility system, a wide range of physical properties investigations is carried out as well - the subject of this abstract - that provide additional information on the geology and processes at the sites. Results of the mission in general as well as of the physical properties studies thus far greatly exceed expectations in that observations and measurements by both vehicles show a rich variety in materials and processes: the Gusev site in the vicinity of the lander is remarkably flat and generally devoid of large rocks along traverses up to the time of this writing (approx.Sol 50) and suggestive of a deflated surface with generally only thin veneers of bright dust while exhibiting evidence of a widespread occurrence of a crust from cemented fines that has been observed to fail in the form of blocky clods when disturbed by vehicle rolling action; numerous small and shallow depressions - presumably created by impacts - are observed at the site which are infilled with bright, fine-grained material that likewise appears indurated and which was studied by a trenching experiment; small ripple bedforms are scattered across the site and were characterized in terms of particle size distributions. At the Meridiani site, studies so far - up to approx.Sol 33 - have focussed on soils and the rock outcrop encountered within the approx.20 m diameter crater that the spacecraft came to rest in: from a physical properties point of view, a mantle of dark, well-sorted, apparently basaltic sand with small to moderate cohesion has been of interest - and has been studied by a trenching experiment - as well as a fine-grained unit underlying the mantle at least locally within the crater. Rock grindings were accomplished successfully at both sites at the time of this writing, suggesting different strengths of the two targets (the basaltic rock nicknamed Adirondack at Gusev and the Meridiani rock outcrop) in addition to enabling compositional measurements below the original rock surfaces.

Ming, Douglas W.↗

NASA NTRS2021

Impacts of Varying Concentrations of Cloud Condensation Nuclei On Deep Convective Cloud Updrafts – A Multimodel Assessment

This study presents results from a model intercomparison project, focusing on the range of responses in deep convective cloud updrafts to varying cloud condensation nuclei (CCN) concentrations amongst seven, state-of-the-art, cloud-resolving models. Simulations of scattered convective clouds near Houston, Texas are conducted, after being initialized with both relatively low and high CCN concentrations. Deep convective updrafts are identified, and trends in the updraft intensity and frequency are assessed. The factors contributing to the vertical velocity tendencies are examined to identify the physical processes associated with the CCN-induced, updraft changes. The models show several consistent trends. In general, the changes between the High- CCN and Low-CCN simulations in updraft magnitudes throughout the depth of the troposphere are within 15% for all of the models. All models produce stronger (~+5-15%) mean updrafts from ~4–7 km above ground level (AGL) in the High-CCN simulations, followed by a waning response up to ~8 km AGL in most of the models. Thermal buoyancy was more sensitive than condensate loading to varying CCN concentrations in most of the models and more impactful in the mean updraft responses. However, there are also differences between the models. The change in the amount of deep convective updrafts varies significantly. Furthermore, approximately half the models demonstrate neutral-to-weaker (~-5-0%) updrafts above ~8 km AGL, while the other models show stronger (~+10%) updrafts in the High-CCN simulations. The combination of the CCN-induced impacts on the buoyancy and vertical perturbation pressure gradient terms better explains these middle- and upper-tropospheric updraft trends than the buoyancy terms alone.

deep convective cloud updrafts↗

NASA NTRS1990

Cirrus radiative characteristics and the radiative impact of small particles

An understanding of the way radiation interacts with clouds is vital for understanding the sensitivity of the earth's climate to both natural and anthropogenic changes in the atmosphere. Cirrus clouds are thought to be an important modulator of climate sensitivity. The feedback effect of cirrus on climate can be positive or negative depending upon the microphysics and scattering properties of the cloud. These properties of cirrus clouds are not well understood partly because of their thin tenuous nature and partly because of their microphysical properties. The high altitude and cold temperatures within these clouds along with their transparency greatly increase the difficulty in which accurate measurements can be obtained and interpreted both by aircraft and remote sensing. Therefore, the understanding of the interaction of radiation in cirrus clouds is crucial to determining the ways in which these clouds interact with climate forcings. The sensitivity of the radiative budgets of cirrus cloudiness to their microphysical composition and the environments in which they occur is examined. Especially important is the impact of small particles on the radiative properties of cirrus. Remote sensing estimates of the effective crystal size of cirrus and in situ measurements show large differences up to 100 microns. Thus it becomes important to identify the sources of these differences. For this reason, simulations of actual FIRE cases are compared with the in situ radiative observations and inferences are made concerning the cause of the discrepancies.

Stackhouse, Paul W., Jr.↗

NASA NTRS1980

Electron impact cross sections for v = 0-1 vibrational excitation in CO at electron energies of 3 to 100 eV

The paper discusses the measurements of normalized, absolute differential cross-sections for electron-impact vibrational transition in CO. Integral and momentum-transfer cross-sections were obtained from these differential results; incident electron energies were in the 3 to 100 eV range, and the scattering angles were 10 to 135 deg. A comparison of these results with measurements made with pure vibrationally elastic cross-sections in N2, and with the data based on a two-potential theory for electron scattering from diatomic molecules showed that the present CO cross-sections are similar to those in N2. This indicates that the long-range effect of the small CO dipole moment is negligible in promoting vibrational excitation; moreover, a significant peak in the integral and momentum-transfer cross-sections is observed at 20 eV. Finally, the low-energy integral cross-sections are compared with a recent set of swarm data for vibrational excitation.

Chutjian, A.↗

NASA NTRS1983

Theory of time-dependent intense-field collisional resonance fluorescence

The time-dependent theory of Courtens and Szoke (1977) is generalized using the approach of Burnett et al. (1982) to derive time-dependent spectral intensities of resonance fluorescence from atoms driven by a pulsed laser in the presence of collisions. These results are valid both for laser detunings inside and outside the usual impact region of the spectrum, including Zeeman degeneracy effects. This theory is applied to a simple but important example (J = 0 to J = 1) to obtain quantitative predictions for the observable scattered-light spectrum which can be directly compared with recent experiments.

Kleiber, P. D.↗

NASA NTRS1984

Transport effects due to particle erosion mechanisms

Various processes can erode the surfaces of planetary ring particles. Recent estimates for Saturn's rings suggest that a centimeter-thick surface layer could be eroded from an isolated ring particle in less than 1000 yr by meteoroid impacts alone. The atoms, molecules, and chips ejected from ring particles by erosion will arc across the rings along elliptical orbits. For moderate ring optical depths, ejecta will be absorbed or inelastically scattered upon reintersecting the ring plane. Continuous exchange of ejecta between different ring regions can lead to net radial transport of mass and angular momentum, to changes in particle sizes, and to the buildup of chip regoliths several centimeters deep on the surfaces of ring particles. Because most of the erosional ejecta are not lost but merely exchanged over short distances, the net erosion rate of the surfaces of these ring particles will be much less than that estimated for an isolated particle. Numerical solutions for time-dependent ballistic transport under various assumptions suggest pile-up and spillover effects especially near regions of preexisting high optical depth contrast, such as the inner edges of A and B rings. Global redistribution could be significant over billions of years. Other features in planetary ring systems may be influenced by ballistic transport.

Durisen, R. H.↗

NASA NTRS1992

Effect of magnetic helicity upon rectilinear propagation of charged particles in random magnetic fields

When charged particles spiral along a large constant magnetic field, their trajectories are scattered by any random field components that are superposed on the guiding field. If the random field configuration embodies helicity, the scattering is asymmetrical with respect to a plane perpendicular to the guiding field, for particles moving into the forward hemisphere are scattered at different rates from those moving into the backward hemisphere. This asymmetry gives rise to new terms in the transport equations that describe propagation of charged particles. Helicity has virtually no impact on qualitative features of the diffusive mode of propagation. However, characteristic velocities of the coherent modes that appear after a highly anisotropic injection exhibit an asymmetry related to helicity. Explicit formulas, which embody the effects of helicity, are given for the anisotropies, the coefficient diffusion, and the coherent velocities. Predictions derived from these expressions are in good agreement with Monte Carlo simulations of particle transport, but the simulations reveal certain phenomena whose explanation calls for further analytical work.

Earl, James A.↗

NASA NTRS2001

Overview of ACE-Asia Spring 2001 Investigations on Aerosol Radiative Effects and Related Aerosol Properties

A primary, ACE-Asia objective was to quantify the interactions between aerosols and radiation in the Asia-Pacific region. Toward this end, radiometric and related aerosol measurements were made from ocean, land, air and space platforms. Models that predict aerosol fields guided the measurements and are helping integrate and interpret results. Companion overview's survey these measurement and modeling components. Here we illustrate how these components were combined to determine aerosol radiative. impacts and their relation to aerosol properties. Because clouds can obscure or change aerosol direct radiative effects, aircraft and ship sorties to measure these effects depended on predicting and finding cloud-free areas and times with interesting aerosols present. Pre-experiment satellite cloud climatologies, pre-flight aerosol and cloud forecasts, and in-flight guidance from satellite imagery all helped achieve this. Assessments of aerosol regional radiative impacts benefit from the spatiotemporal coverage of satellites, provided satellite-retrieved aerosol properties are accurate. Therefore, ACE-Asia included satellite retrieval tests, as part of many comparisons to judge the consistency (closure) among, diverse measurements. Early results include: (1) Solar spectrally resolved and broadband irradiances and optical depth measurements from the C-130 aircraft and at Kosan, Korea yielded aerosol radiative forcing efficiencies, permitting comparisons between efficiencies of ACE-Asia and INDOEX aerosols, and between dust and "pollution" aerosols. Detailed results will be presented in separate papers. (2) Based on measurements of wavelength dependent aerosol optical depth (AOD) and single scattering albedo the estimated 24-h a average aerosol radiative forcing efficiency at the surface for photosynthetically active radiation (400 - 700 nm) in Yulin, China is approx. 30 W sq m per AOD(500 nm). (3) The R/V Brown cruise from Honolulu to Sea of Japan sampled an aerosol optical depth gradient, with AOD(500 nm) extremes from 0.1 to 1.1. On the Pacific transit from Honolulu to Hachijo AOD(500 nm) averaged 0.2, including increases to 0.4 after several storms, suggesting the strong impact of wind-generated seasalt. The AOD maximum, found in the Sea of Japan, was influenced by dust and anthropogenic sources. (4) In Beijing, single scattering albedo retrieved from AERONET sun-sky radiometry yielded midvisible SSA=0.88 with strong wavelength dependence, suggesting a significant black carbon component. SSA retrieved during dust episodes was approx. 0.90 and variable but wavelength neutral reflecting the presence of urban haze with the dust. Downwind at Anmyon Island SSA was considerably higher, approx. 0.94, but wavelength neutral for dust episodes and spectrally dependent during non dust periods. (5) Satellite retrievals show major aerosol features moving from Asia over the Pacific; however, determining seasonal-average aerosol effects is hampered by sampling frequency and large-scale cloud systems that obscure key parts of aerosol patterns. Preliminary calculations using, satellite-retrieved AOD fields and initial ACE-Asia aerosol properties (including sulfates, soot, and dust) yield clear-sky aerosol radiative effects in the seasonal-average ACE-Asia plume exceeding those of manmade greenhouse gases. Quantifying all-sky direct aerosol radiative effects is complicated by the need to define the height of absorbing aerosols with respect to cloud decks.

Russell, Philip B.↗

NASA NTRS2000

Aerosol Radiative Forcing in Asian Continental Outflow

Aerosols in elevated layers were sampled with FSSP-probes and wire impactors over the Pacific ocean aboard the NASA DC-8 aircraft. Analyses of particle size and morphology identifies two distinctly different aerosol types for cases when the mid-visible extinctions exceed 0.2/km. Smaller sizes (effective radii of 0.2 um) and moderate absorption (mid-visible single scattering albedo of.935) are typical for urban-industrial pollution. Larger sizes (effective radii of 0.7 um) and weak absorption (mid-visible single scattering albedo of 0.985) identify dust. This aerosol classification is in agreement with its origin as determined by airmass back trajectory analysis. Based on lidar vertical profiling, aerosol dominated by dust and urban-industrial pollution above 3km were assigned mid-visible optical depths of 0.50 and 0.27, respectively. Radiative transfer simulations, considering a 50% cloud-cover below the aerosol layers, suggest (on a daily tP C)C> basis) small reductions (-4W/m2) to the energy budget at the top of the atmosphere for both aerosol types. For c' 0 dust, more backscattering of sunlight (weaker solar absorption) is compensated by a stronger greenhouse effect due to larger sizes. Forced reductions to the energy budget at the surface are 12W/m2 for both aerosol types. In contrast, impacts on heating rates within the aerosol layers are quite different: While urban-industrial aerosol warms the layer (at +0.6K/day as solar heating dominates), dust cools (at -0.5K/day as infrared cooling dominates). Sensitivity tests show the dependence of the aerosol climatic impact on the optical depth, particle size, absorptivity, and altitude of the layers, as well as clouds and surface properties. Climatic cooling can be eliminated (1) for the urban-industrial aerosol if absorption is increased to yield a mid-visible single scattering albedo of 0.89, or if the ocean is replaced by a land surface; (2) for the dust aerosol if the effective radius is increased from 0.7 to 1.2 um. The removal of low-level clouds doubles the cooling at the top of the atmosphere to about -8W/m2.

Pueschel, R.↗

NASA NTRS2023

Modeling Sea Ice Albedo and Transmittance Measurements With A Fully-Coupled Radiative Transfer Model

A rigorous treatment of the sea ice medium has been incorporated in the advanced Coupled Ocean-Atmosphere Radiative Transfer (COART) model. The inherent optical properties (IOPs) of brine pockets and air bubbles over the 0.25-4.0 μm spectral region are parameterized as a function of the vertical profile of the sea ice physical properties (temperature, salinity and density). We test the model performance using available albedo and transmittance measurements collected during the Impacts of Climate on the Ecosystems and Chemistry of the Arctic Pacific Environment (ICESCAPE) and the Surface Heat Budget of the Arctic Ocean (SHEBA) field campaigns. The observations are adequately simulated when at least three layers are used to represent bare (first-year and multi-year) ice, including a thin top layer characterized by low density and high scattering. Two layers can be sufficient to model isolated cases of multi-year ice, and apply well to ponded ice except for shallow ponds over thick ice. The albedo and transmittance of ponded ice in the visible are mainly determined by the optical properties of the ice underlying the water layer used to model the pond. Sensitivity results indicate that the air volume or ice density has the largest impact on the simulated fluxes. Possible contamination from light-absorbing impurities, such as black carbon or ice algae, is also implemented in the model and is able to effectively reduce the albedo and transmittance in the visible spectrum to further improve the model-observation agreement. The agreement between the observed and modeled spectra validates the parameterization of the sea ice IOPs, and endorses COART as an accurate tool for radiation studies in the cryosphere.

Coupled Ocean-9 Atmosphere Radiative Transfer (COA↗

NASA NTRS2011

Sensitivity of C-Band Polarimetric Radar-Based Drop Size Distribution Measurements to Maximum Diameter Assumptions

The estimation of rain drop size distribution (DSD) parameters from polarimetric radar observations is accomplished by first establishing a relationship between differential reflectivity (Z(sub dr)) and the central tendency of the rain DSD such as the median volume diameter (D0). Since Z(sub dr) does not provide a direct measurement of DSD central tendency, the relationship is typically derived empirically from rain drop and radar scattering models (e.g., D0 = F[Z (sub dr)] ). Past studies have explored the general sensitivity of these models to temperature, radar wavelength, the drop shape vs. size relation, and DSD variability. Much progress has been made in recent years in measuring the drop shape and DSD variability using surface-based disdrometers, such as the 2D Video disdrometer (2DVD), and documenting their impact on polarimetric radar techniques. In addition to measuring drop shape, another advantage of the 2DVD over earlier impact type disdrometers is its ability to resolve drop diameters in excess of 5 mm. Despite this improvement, the sampling limitations of a disdrometer, including the 2DVD, make it very difficult to adequately measure the maximum drop diameter (D(sub max)) present in a typical radar resolution volume. As a result, D(sub max) must still be assumed in the drop and radar models from which D0 = F[Z(sub dr)] is derived. Since scattering resonance at C-band wavelengths begins to occur in drop diameters larger than about 5 mm, modeled C-band radar parameters, particularly Z(sub dr), can be sensitive to D(sub max) assumptions. In past C-band radar studies, a variety of D(sub max) assumptions have been made, including the actual disdrometer estimate of D(sub max) during a typical sampling period (e.g., 1-3 minutes), D(sub max) = C (where C is constant at values from 5 to 8 mm), and D(sub max) = M*D0 (where the constant multiple, M, is fixed at values ranging from 2.5 to 3.5). The overall objective of this NASA Global Precipitation Measurement Mission (GPM/PMM Science Team)-funded study is to document the sensitivity of DSD measurements, including estimates of D0, from C-band Z(sub dr) and reflectivity to this range of D(sub max) assumptions. For this study, GPM Ground Validation 2DVD's were operated under the scanning domain of the UAHuntsville ARMOR C-band dual-polarimetric radar. Approximately 7500 minutes of DSD data were collected and processed to create gamma size distribution parameters using a truncated method of moments approach. After creating the gamma parameter datasets the DSD's were then used as input to a T-matrix model for computation of polarimetric radar moments at C-band. All necessary model parameterizations, such as temperature, drop shape, and drop fall mode, were fixed at typically accepted values while the D(sub max) assumption was allowed to vary in sensitivity tests. By hypothesizing a DSD model with D(sub max) (fit) from which the empirical fit to D0 = F[Z(sub dr)] was derived via non-linear least squares regression and a separate reference DSD model with D(sub max) (truth), bias and standard error in D0 retrievals were estimated in the presence of Z(sub dr) measurement error and hypothesized mismatch in D(sub max) assumptions. Although the normalized standard error for D0 = F[Z(sub dr)r] can increase slightly (as much as from 11% to 16% for all 7500 DSDs) when the D(sub max) (fit) does not match D(sub max) (truth), the primary impact of uncertainty in D(sub max) is a potential increase in normalized bias error in D0 (from 0% to as much as 10% over all 7500 DSDs, depending on the extent of the mismatch between D(sub max) (fit) and D(sub max) (truth)). For DSDs characterized by large Z(sub dr) (Z(sub dr) > 1.5 to 2.0 dB), the normalized bias error for D0 estimation at C-band is sometimes unacceptably large (> 10%), again depending on the extent of the hypothesized D(sub max) mismatch. Modeled errors in D0 retrievals from Z(sub dr) at C-band are demonstrated in detail and comparedo similar modeled retrieval errors at S-band and X-band where the sensitivity to D(sub max) is expected to be less. The impact of D(sub max) assumptions to the retrieval of other DSD parameters such as Nw, the liquid water content normalized intercept parameter, are also explored. Likely implications for DSD retrievals using C-band polarimetric radar for GPM are assessed by considering current community knowledge regarding D(sub max) and quantifying the statistical distribution of Z(sub dr) from ARMOR over a large variety of meteorological conditions. Based on these results and the prevalence of C-band polarimetric radars worldwide, a call for more emphasis on constraining our observational estimate of D(sub max) within a typical radar resolution volume is made

Carey, Lawrence D.↗

NASA NTRS1973

Optical potential approach to the electron-atom impact ionization threshold problem

The problem of the threshold law for electron-atom impact ionization is reconsidered as an extrapolation of inelastic cross sections through the ionization threshold. The cross sections are evaluated from a distorted wave matrix element, the final state of which describes the scattering from the Nth excited state of the target atom. The actual calculation is carried for the e-H system, and a model is introduced which is shown to preserve the essential properties of the problem while at the same time reducing the dimensionability of the Schrodinger equation. Nevertheless, the scattering equation is still very complex. It is dominated by the optical potential which is expanded in terms of eigen-spectrum of QHQ. It is shown by actual calculation that the lower eigenvalues of this spectrum descend below the relevant inelastic thresholds; it follows rigorously that the optical potential contains repulsive terms. Analytical solutions of the final state wave function are obtained with several approximations of the optical potential.

Temkin, A.↗

NASA NTRS2001

Columnar Aerosol Single-Scattering Albedo and Phase Function Retrieved from Sky Radiance Over the Ocean: Measurements of African Dust

The single-scattering albedo and phase function of African mineral dust are retrieved from ground-based measurements of sky radiance collected in the Florida Keys. The retrieval algorithm employs the radiative transfer equation to solve by iteration for these two properties which best reproduce the observed sky radiance using an assumed aerosol vertical structure and measured aerosol optical depth. Thus, no assumptions regarding particle size, shape, or composition are required. The single-scattering albedo, presented at fourteen wavelengths between 380 and 870 nm, displays a spectral shape expected of iron-bearing minerals but is much higher than current dust models allow. This indicates the absorption of light by mineral dust is significantly overestimated in climate studies. Uncertainty in the retrieved albedo is less than 0.02 due to the small uncertainty in the solar-reflectance-based calibration (12.2%) method employed. The phase function retrieved at 860 nm is very robust under simulations of expected experimental errors, indicating retrieved phase functions at this wavelength may be confidently used to describe aerosol scattering characteristics. The phase function retrieved at 443 nm is very sensitive to expected experimental errors and should not be used to describe aerosol scattering. Radiative forcing by aerosol is the greatest source of uncertainty in current climate models. These results will help reduce uncertainty in the absorption of light by mineral dust. Assessment of the radiative impact of aerosol species is a key component to NASA's Earth System Enterprise.

Cattrall, Christopher↗

NASA NTRS2006

Near Sun Free-Space Optical Communications from Space

Free-space optical communications offers expanded data return capacity, from probes distributed throughout the solar system and beyond. Space-borne and Earth-based optical transceivers used for communicating optically, will periodically encounter near Sun pointing. This will result in an increase in the scattered background light flux, often contributing to degraded link performance. The varying duration of near Sun pointing link operations relative to the location of space-probes, is discussed in this paper. The impact of near Sun pointing on link performance for a direct detection photon-counting communications system is analyzed for both ground- and space-based Earth receivers. Finally, impact of near Sun pointing on spaceborne optical transceivers is discussed.

free-space↗