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NASA NTRS1987

Comet thermal modeling

The past year was one of tremendous activity because of the appearance of Halley's Comet. Observations of the comet were collected from a number of sources and compared with the detailed predictions of the comet thermal modeling program. Spacecraft observations of key physical parameters for cometary nucleus were incorporated into the thermal model and new cases run. These results have led to a much better understanding of physical processes on the nucleus and have pointed the way for further improvements to the modeling program. A model for the large-scale structure of cometary nuclei was proposed in which comets were envisioned as loosely bound agglomerations of smaller icy planetesimals, essentially a rubble pile of primordial dirty snowballs. In addition, a study of the physical history of comets was begun, concentrating on processes during formation and in the Oort cloud which would alter the volatile and nonvolatile materials in cometary nuclei from their pristine state before formation.

Weissman, Paul R.↗

NASA NTRS1986

Thunderstorm cloud top dynamics as inferred from satellite observations and a cloud top parcel model

Thunderstorm top temperature-height structure and temperature-height conversion relations in the convective overshooting top region are examined using data from GOES IR, AVHRR, and aircraft overflights, and GOES stereoscopic observations. Using a Lagrangian one-dimensional cloud parcel model applied in the overshooting region, three classes of storm tops are described and the causes of their unique temperature-height structures are explored. Although the parcel model used does not fully reproduce the three-dimensional structure and dynamics of an evolving thunderstorm top, it is shown to crudely reproduce the parcel dynamics of updraft core parcels. The locations of cold points, high points, warm points, and the magnitude of cold-high offsets compare favorably between the model and the satellite observations.

Adler, Robert F.↗

NASA NTRS1989

IRAS results on outer galaxy star formation

An infrared defined (60 micron) sample of IRAS sources were systematically studied in order to investigate star formation in the outer Galaxy. Five percent of the sample are point sources with IRAS spectra that suggest the emission is from a dust shell surrounding a mature star. Ninety five percent have spectra where flux density strictly rises with wavelength. The sources are extended, and it is shown that Point Source Catalog fluxes seriously underestimate total fluxes. CO kinematic distances were reliably assigned to two thirds of the sources. Most of the infrared luminosities correspond to B spectral types. Six cm continuum emission were detected from all sources inferred to have spectral type B1 or earlier. The combined IRAS/CO/6 cm data show these sources are young, moderately massive stars that are embedded in interstellar clouds. The young embedded sources define a distinct band in an IRAS color-colar diagram. Normal IRAS galaxies fall in the same band, consistent with the interpretation that their infrared emission is due to star formation.

Terebey, Susan↗

NASA NTRS1993

A Fourier-Riccati approach to radiative transfer. I - Foundations

The three-dimensional equation of radiative transfer is formally solved using a Fourier-Riccati approach while calculations are performed on cloudy media embedded in a two-dimensional space. An extension to Stephens' work this study addresses the coupling between space and angle asserted by the equation of transfer. In particular, the accuracy of the computed radiation field as it is influenced by the angular resolution of the phase function and spatial discretization of the cloudy medium is discussed. The necessity of using a large number of quadrature points to calculate fluxes even when the phase function is isotropic for media exhibiting vertical and horizontal inhomogeneities is demonstrated. Effects of incorrect spatial sampling on both radiance and flux fields are also quantified by example. Radiance and flux comparisons obtained by the Fourier-Riccati model and the independent pixel approximation for inhomogeneous cloudy media illustrate the inadequacy of the latter even for tenuous clouds.

Gabriel, P. M.↗

NASA NTRS2011

Water Ice Clouds and Dust in the Martian Atmosphere Observed by Mars Climate Sounder

The water ice clouds are primarily controlled by the temperature structure and form at the water condensation level. Clouds in all regions presented show day/night differences. Cloud altitude varies between night and day in the SPH and tropics: (1) NPH water ice opacity is greater at night than day at some seasons (2) The diurnal thermal tide controls the daily variability. (3) Strong day/night changes indicate that the amount of gas in the atmosphere varies significantly. See significant mixtures of dust and ice at the same altitude planet-wide (1) Points to a complex radiative and thermal balance between dust heating (in the visible) and ice heating or cooling in the infrared. Aerosol layering: (1) Early seasons reveal a zonally banded spatial distribution (2) Some localized longitudinal structure of aerosol layers (3) Later seasons show no consistent large scale organization

Mars Climate Sounder (MCS) instrument↗

NASA NTRS1973

On Lidar Sounding of the Atmosphere to Estimate Static and Dynamic Characteristics of Aerosol Inhomogeneities

1. A possible application of intensity fluctuations of a pulse light signal reflected by atmospheric aerosols is analyzed by the correlation method to evaluate static (medium sizes, shape) and dynamic (speed and direction of movement, lifetime) characteristics of aerosol inhomogeneities. The aerosol inhomogeneities are assumed to be expanded, pressed, disintegrated and originated constantly in accordance with random laws, the set of inhomogeneities as a whole traveling together with air masses and having predominant movement in wind direction. It is shown that the characteristics of aerosol inhomogeneities considered can be expressed by the coefficients of the correlation function expansion of the reflected signal fluctuation intensity in Tailor series. 2/ Correlation systems for evaluating static and dynamic characteristics of driving objects can be divided into two types according to the kind and quantity of used information: the systems with coordinates of the information removal "points" to be fixed in space, and the systems with a parallel simultaneous information removal at discrete moments of time. The systems for determination of wind direction considered in are the examples of the first type system. However, the operating information removal for two points is insufficient to estimate completely static and dynamic characteristics of inhomogenities, their quantity ought to be increased up to three of them for two-dimensional problem and up to four of them for three-dimensional problem as it is usually done in the ionospheric studies. The second type systems are used for the investigation of a medium shape and speed of the clouds according to photographs made from satellites. These systems are also used for solution of navigation problems. The use of optical quantum generators with a scanning beam is seen to increase greatly the working information removal in comparison with the first type systems. Nevertheless, scanning rate is not sufficient sometimes in order· to consider a general picture of aerosol inhomogeneities to be stationary. In this connection the use of the systems of second type treatment becomes a matter of essential difficulty. 3. Aerosol inhomogeneities simulation has been carried out on the basis of the digital computer experiments with the aim of estimating static and dynamic characteristics of inhomogeneities by an optical beam in the atmosphere at different scanning procedures. The dependence of determination accuracy of these characteristics on the type of chosen laws of aerosol particle distribution in the atmosphere, the parameters of inhomogeneities geometry, their speed and the law of scanning have been obtained.

Zuev, V. E.↗

NASA NTRS2018

Deep Space Observations of Sun Glint from Oceans

Every hour or two, the Earth Polychromatic Imaging Camera (EPIC) onboard the DSCOVR satellite provides unique full-color images of the sunlit side of the Earth from the L1 Lagrangian point, which is four times farther the Moon. Casual glances at such images often reveal bright colorful spots that stand out markedly from their surroundings. Such spots often appear not only over ocean but also over land. Tracking the colorful spots using an automated image analysis algorithm reveals that they are caused by specular reflection of sunlight, sometimes from ocean surfaces and other times from clouds containing horizontally oriented ice crystals. The presented study characterizes these spots in terms of prevalence, location, color, and brightness, and provides insights into the factors that lead to their appearance.

ice crystals↗

NASA NTRS1991

A survey for infrared excesses among high galactic latitude SAO stars

This project involves extending the previous analysis of infrared excesses among a volume-limited sample of 134 nearby A-K main-sequence stars to a magnitude-limited sample of stars, culled from the SAO Catalog, with excesses determined from the IRAS Point Source Catalog flux density ratios. This new sample includes 5706 B-M type stars, 379 of which have infrared excesses. The objective involved use of a statistically complete survey of objects in a standard catalog in order to assess the frequency with which different physical processes can affect the infrared output of stars. These processes include, but are not limited to, orbiting cold particle clouds and the onset of rapid mass loss. It is concluded that cold disks are consistent with the infrared excesses found among A-G dwarfs and G-K giants in the sample.

Stencel, Robert E.↗

NASA NTRS2015

Planetary Science with Balloon-Borne Telescopes

The National Aeronautics and Space Administration (NASA) and the planetary science community have recently been exploring the potential contributions of stratospheric balloons to the planetary science field. A study that was recently concluded explored the roughly 200 or so science questions raised in the Planetary Decadal Survey report and found that about 45 of those questions are suited to stratospheric balloon based observations. In September of 2014, a stratospheric balloon mission called BOPPS (which stands for Balloon Observation Platform for Planetary Science) was flown out of Fort Sumner, New Mexico. The mission had two main objectives, first, to observe a number of planetary targets including one or more Oort cloud comets and second, to demonstrate the applicability and performance of the platform, instruments, and subsystems for making scientific measurements in support planetary science objectives. BOPPS carried two science instruments, BIRC and UVVis. BIRC is a cryogenic infrared multispectral imager which can image in the.6-5 m range using an HgCdTe detector. Narrow band filters were used to allow detection of water and CO2 emission features of the observed targets. The UVVis is an imager with the science range of 300 to 600 nm. A main feature of the UVVis instrument is the incorporation of a guide camera and a Fine Steering Mirror (FSM) system to reduce image jitter to less than 100 milliarcseconds. The BIRC instrument was used to image targets including Oort cloud comets Siding Spring and Jacques, and the dwarf planet 1 Ceres. BOPPS achieved the first ever earth based CO2 observation of a comet and the first images of water and CO2 of an Oort cloud comet (Jacques). It also made the first ever measurement of 1Ceres at 2.73 m to refine the shape of the infrared water absorption feature on that body. The UVVis instrument, mounted on its own optics bench, demonstrated the capability for image correction both from atmospheric disturbances as well as some of the residual motion from the gondola that was not addressed by the gondolas coarse pointing systems. The mission met its primary science and engineering objectives. The results of the BOPPS mission will feed into the body of science knowledge but also feed into future planning for more science from balloon-borne platforms. A notional platform called Gondola for High-Altitude Planetary Science (GHAPS) has been explored and this concept platform can address a number of important decadal questions. This paper provides a summary of the assessment of potential balloon borne observations for planetary science purposes including where potential science contributions can be expected, the necessary performance characteristics of the platform, and other features required or desired. The BOPPS mission is summarized including descriptions of the main elements and key science and engineering results. The paper then briefly describes GHAPS, and the salient features that can make it a valuable tool for future planetary observations.

Telescope↗

NASA NTRSDate not supplied

Space-borne Doppler Weather Radar Modeling for Radar Design Evaluation

A model has been developed to predict the reflectivity and Doppler performance of a spaceborne weather radar for atmospheric aerosol and cloud monitoring. The goal is to predict radar sensitivity, resolution, uncertainties and other key performance metrics vs. radar design parameters and hardware nonidealities. Analytical formulas are readily available to predict key performance metrics of a space-borne radar system as a function of design parameters such as antenna size, spacecraft velocity, transmit power, and receive noise figure. Effects of some system nonidealities such as antenna pointing errors, power amplifier nonlinearity and phase noise can be estimated using idealized methods. These analytical formulas use idealized forms of the antenna radiation pattern and weather statistics to predict system performance. However, it is desirable to have a more physical model based on discretized weather volumes in which the particle size distribution, Doppler distribution, and other parameters can be varied to study how the radar hardware design parameters and nonidealities affect the measurement of the weather reflectivity and Doppler characteristics. This would allow the radar designers to have more insight into what is being measured and the hardware parameters and errors that need to be carefully controlled to achieve best radar performance, as well as potential methods to calibrate the system or correct errors. This presentation will demonstrate some proof-of-concept Ka-band simulations where the discretized model agrees with the analytical formulas for a simple case where the elements in the discretized weather volume are defined by a constant reflectivity and simple velocity vectors. In particular, the system sensitivity and Doppler uncertainty are evaluated by analytical formulas as well as the discretized model. Future work will expand on this to include more complex weather scenarios and the addition of system nonidealities.

Sara Tucker↗

NASA NTRS1978

Infrared radiation of Venusian clouds

The thermal infrared emission of Venus measured by Venera-9 and Venera-10 is analyzed. The emission of the night side corresponds to a brightness temperature of 244 K. The brightest temperature of the day side is 233-234 K. The extent of the upper layer of clouds, in which the thermal emission is formed, is 4-6 km. The altitude of the emitting layer above the surface of the planet (64-67 km) is determined from the brightness temperature and the existing models of the atmosphere of Venus. In some cases, correlation is noted between the inhomogeneity and the details of the ultraviolet image. The day side temperatures strangely coincide with the freezing point of sulfuric acid at a concentration of 66-77%.

Ksanfomaliti, L. V.↗

NASA NTRS1995

Interstellar Grain Surface Chemistry

Chemistry on grain surfaces plays an Important role in the formation of interstellar Ices, It can also influence the composition of the gas phase through outgassing near luminous, newly formed stars. This paper reviews the chemical processes taking place on Interstellar grain surfaces with the emphasis on those transforming CO into other hydrocarbons. At low, molecular cloud temperatures (approximately equal to 10K), physisorption processes dominate interstellar grain surface chemistry and GO is largely hydrogenated through reactions with atomic H and oxidized through reactions with atomic O. The former will lead to the formation of H2CO and CH3OH ices, while the latter results in CO2 ice. The observational evidence for these ices in molecular clouds will be discussed. Very close to protostars, the gas and grain temperatures are much higher (approximately equal to 500K) and chemisorption processes, including catalytic surface reactions, becomes important. This will be illustrated based upon our studies of the Fischer-Tropsch Synthesis of CH4 from CO on metallic surfaces. Likely, this process has played an important role in the early solar nebula. Observational consequences will be pointed out.

Tielens, Alexander G. G. M.↗

NASA NTRS2021

Deep Space Observations of Terrestrial Glitter

Deep space climate observatory (DSCOVR) spacecraft drifts about the Lagrangian point ≈1.4–1.6 × 106 km from Earth, where its Earth polychromatic imaging camera (EPIC) observes the sun-lit face of the Earth every 1 to 2 hours. At any instance, there is a preferred (specular) spot on the globe, where a glint may be observed by EPIC. While monitoring reflectance at these spots (terrestrial glitter), we observe occasional intense glints originating from neither ocean surface nor cloud ice and we argue that mountain lakes high in the Andes are among the causes. We also examine time-averaged reflectance at the spots and find it exceeding that of neighbors, with the excess monotonically increasing with separation distance. This specular excess is found in all channels and is more pronounced in the latest and best-calibrated version of EPIC data, thus opening the possibility of testing geometric calibration by monitoring distant glitter.

DSCOVR↗

NASA NTRS1991

The structure and evolution of rich star clusters in the Large Magellanic Cloud

The present evaluation of surface brightness profiles and color-magnitude diagrams for 18 rich star clusters in the LMC, whose ages range from 10 million to 1 billion years, notes that while the profiles of the older clusters are representable by models with King-like cores, those of many younger clusters resist such modeling in virtue of bumps, sharp 'shoulders', and central dips. If the clusters have undergone violent relaxation, then the small cores of the youngest ones may be indicative of formation from relatively 'cool' initial conditions. The sharp shoulders would then point point toward 'warmer' initial conditions, although they are alternatively explainable as signatures of merging subcondensations.

Elson, Rebecca A. W.↗

NASA NTRS1983

The GEMPAK Barnes interactive objective map analysis scheme

The analysis scheme and meteorological applications of the GEMPAK data analysis and display software system developed by NASA are described. The program was devised to permit objective, versatile, and practical analysis of satellite meteorological data using a minicomputer and a display system with graphics capability. A data area can be selected within the data file for the globe, and data-sparse regions can be avoided. Distances between observations and the nearest observation points are calculated in order to avoid errors when determining synoptic weather conditions. The Barnes (1973) successive correction method is employed to restore the amplitude of small yet resolvable wavelengths suppressed in an initial filtering pass. The rms deviation is then calculated in relation to available measured data. Examples are provided of treatment of VISSR data from the GOES satellite and a study of the impact of incorrect cloud height data on synoptic weather field analysis.

Koch, S. E.↗

NASA NTRS1984

First Results of Submillimeter Polarimetry

Airborne results of submillimeter polarization at one wavelength, 270 micro m for just three points in the sky are presented. Polarizations of 1.7% at each of two points in Orion are shown. A null result at 400 micro m from ground-based observations of Mars at opposition is also presented. A null result for W3(OH) is given. The Kleinmann-Low Nebula (KL) was chosen for one of the measurements because it is bright and polarization had been observed 10 micro m. Airborne results of submillimeter polarimetry indicate that: (1) Cool, dense interstellar clouds can emit polarized submillimeter radiation; (2) The direction of the magnetic field, averaged over the 90 beams, is the same for the Kleinmann-Low Nebula and the 400 micro m peak 1.5 south of the Nebula; and (3) The effectiveness of the grain alignment mechanism, averaged over the 90 beams, is the same for the Kleinmann-Low Nebula and the 400 micro m peak.

Hildebrand, R. H.↗

NASA NTRS1993

Orbit determination and orbit control for the Earth Observing System (EOS) AM spacecraft

Future NASA Earth Observing System (EOS) Spacecraft will make measurements of the earth's clouds, oceans, atmosphere, land and radiation balance. These EOS Spacecraft will be part of the NASA Mission to Planet Earth. This paper specifically addresses the EOS AM Spacecraft, referred to as 'AM' because it has a sun-synchronous orbit with a 10:30 AM descending node. This paper describes the EOS AM Spacecraft mission orbit requirements, orbit determination, orbit control, and navigation system impact on earth based pointing. The EOS AM Spacecraft will be the first spacecraft to use the TDRSS Onboard Navigation System (TONS) as the primary means of navigation. TONS flight software will process one-way forward Doppler measurements taken during scheduled TDRSS contacts. An extended Kalman filter will estimate spacecraft position, velocity, drag coefficient correction, and ultrastable master oscillator frequency bias and drift. The TONS baseline algorithms, software, and hardware implementation are described in this paper. TONS integration into the EOS AM Spacecraft Guidance, Navigation, and Control (GN&C) System; TONS assisted onboard time maintenance; and the TONS Ground Support System (TGSS) are also addressed.

Herberg, Joseph R.↗

NASA NTRS2014

A Classification Scheme for Young Stellar Objects Using the WIDE-FIELD INFRARED SURVEY EXPLORER ALLWISE Catalog: Revealing Low-Density Star Formation in the Outer Galaxy

We present an assessment of the performance of WISE and the AllWISE data release in a section of the Galactic Plane. We lay out an approach to increasing the reliability of point source photometry extracted from the AllWISE catalog in Galactic Plane regions using parameters provided in the catalog. We use the resulting catalog to construct a new, revised young star detection and classification scheme combining WISE and 2MASS near and mid-infrared colors and magnitudes and test it in a section of the Outer Milky Way. The clustering properties of the candidate Class I and II stars using a nearest neighbor density calculation and the two-point correlation function suggest that the majority of stars do form in massive star forming regions, and any isolated mode of star formation is at most a small fraction of the total star forming output of the Galaxy. We also show that the isolated component may be very small and could represent the tail end of a single mechanism of star formation in line with models of molecular cloud collapse with supersonic turbulence and not a separate mode all to itself.

WIDE-FIELD↗