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At least 883 records · Page 49

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NASA NTRS1978

A microwave radiometer spacecraft

A conceptual design for a future microwave-radiometer spacecraft is described. The intended remote-sensing mission is centered around soil moisture measurements and requires all-weather day and night observations at a low microwave frequency (less than 5 GHz) in order to penetrate clouds, haze, and ground covers. The specific mission requirements are summarized in terms of two broad mission objectives, the system design requirements are outlined, and three structural approaches are evaluated at the conceptual design level. The weights, Shuttle flights, and structural member lengths for the three concepts are compared. The dual momentum vector control concept for pointing and slewing control is examined.

Lovelace, U. M.↗

NASA NTRS1979

Effect of a neutral N2 cloud on the electrical charging of an electron beam-emitting rocket in the ionosphere - Echo IV

The interaction of 114 moles of neutral N2 and a 40-kV, 80 mA electron beam was studied during the Echo IV rocket flight. Neutralizing return currents to the rocket body preferentially followed a route back through the region where the electron beam interacted with the cloud. Photometric observations of a complex luminous discharge accompanying beam injection are reported. Observations of 3914-A emission produced by the beam indicated a maximum neutral N2 number density of nearly 10 to the 15th power per cu cm. An oscillatory discharge with a frequency somewhat lower than the N2 (+) ion gyrofrequency was noted at one point.

Israelson, G. A.↗

NASA NTRS1981

Application of millimeter-wave remote sensing to the investigation of comets

It is pointed out the despite years of investigation, the solid, quasi-permanent component of comets, the nucleus, remains largely a mystery. The composition and thermal properties of the nucleus determine the evolution of the more familiar and often spectacular cometary features, the coma and tail. Under certain circumstances, the nucleus may be obscured by a dust cloud of much higher temperature. The most appropriate technology for the investigation of the surface and subsurface layers of the nucleus is considered to be millimeter-wave sensing from an interplanetary spacecraft. Simple radiative transfer models, adapted from methods employed for the interpretation of remote-sensing data on terrestrial ice and snow fields, are used to predict the millimeter-wave spectra of representative model nuclei. The spectra determine the choice of the minimum set of observing frequencies that is required. An instrument configuration driven by these requirements and guided by available technology and the restraints of a proposed NASA spacecraft is then derived.

Hobbs, R. W.↗

NASA NTRS1990

The far-infrared polarization of the Orion nebula

Polarization of the 100 micron thermal emission from 10 points in the Orion nebula has been measured. At one of the positions the degree, 5.7 percent, is the largest far-infrared polarization yet discovered. Except at a position in the barlike structure to the south, the position angles of the polarization vectors are well-ordered, suggesting that a uniform magnetic field threads the cloud. The magnetic field strength is estimated to be between 0.7 and 4 mG. The relationship of the degrees of polarization to the physical conditions in the cloud is discussed.

Gonatas, D. P.↗

NASA NTRS1991

Spatial sampling errors for a satellite-borne scanning radiometer

The Clouds and Earth's Radiant Energy System (CERES) scanning radiometer is planned as the Earth radiation budget instrument for the Earth Observation System, to be flown in the late 1990's. In order to minimize the spatial sampling errors of the measurements, it is necessary to select design parameters for the instrument such that the resulting point spread function will minimize spatial sampling errors. These errors are described as aliasing and blurring errors. Aliasing errors are due to presence in the measurements of spatial frequencies beyond the Nyquist frequency, and blurring errors are due to attenuation of frequencies below the Nyquist frequency. The design parameters include pixel shape and dimensions, sampling rate, scan period, and time constants of the measurements. For a satellite-borne scanning radiometer, the pixel footprint grows quickly at large nadir angles. The aliasing errors thus decrease with increasing scan angle, but the blurring errors grow quickly. The best design minimizes the sum of these two errors over a range of scan angles. Results of a parameter study are presented, showing effects of data rates, pixel dimensions, spacecraft altitude, and distance from the spacecraft track.

Manalo, Natividad D.↗

NASA NTRS1993

The exciting young stellar object for the molecular outflow at the core of L1287

Using IR imaging, we demonstrate that a bipolar reflection nebula is associated with the nebula GN 00.33.9 at the core of the dark cloud L1287, and that these bipolar extensions are oriented with the molecular gas outflow lobes in this region. The polarization patterns in the high-resolution polarimetric maps indicate that the position of the primary source of illumination for these bipolar dust features lies to the north of both RNO 1B and RNO 1C. No NIR point source appears at the position in the images. In addition, the colors in the reflection nebulosity suggest the illuminating source is redder than either RNO 1B or RNO 1C. We suggest, therefore, that a previously unidentified young stellar object (YSO) is probably the driving source of the outflow. As the nominal position of IRAS 00338+6312 lies within 1.5 arcsec of the position of this newly identified YSO, we suggest that these are the same object. The colors and wavelength-dependent polarization levels in the vicinity of RNO 1C are most consistent with RNO 1C being a protostellar source.

Weintraub, David A.↗

NASA NTRS1984

Energetics of the protonation of CO - Implications for the observation of HOC(+) in dense interstellar clouds

A number of molecular species on the H3CO(+) energy hypersurface is examined. Ab initio molecular orbital theory is used to determine the structures and relative energetics of the two isomers of HCO(+) and HOC(+) together with the affinity of CO for protonation at either end. The proton affinities of H2 and H2CO are also examined. The calculations are performed using large basis sets and include the effects of electron correlation. The calculated vibrational frequencies are used to correct for zero point energy differences. The results show that the proton affinities of H2 and CO to form HOC(+) are within 1 kcal of each other. The calculations demonstrate that there is no thermodynamic driving force to form HOC(+) in collisions of H3(+) with CO, and that the formation of HCO(+) in such collisions is very exoergic. A plausible mechanism is suggested to explain the differences observed between the laboratory and the interstellar medium.

Dixon, D.↗

NASA NTRS1983

Computation of potential flows with embedded vortex rings and applications to helicopter rotor wakes

A finite difference scheme for solving the motion of a number of vortex rings is developed. The method is an adaptation of the 'cloud-in-cell' technique to axisymmetric flows, and is thus a combined Eulerian-Lagrangian technique. A straightforward adaptation of the cloud-in-cell scheme to an axisymmetric flow field is shown to introduce a grid dependent self-induced velocity to each vortex ring. To correct this behavior the potential is considered to consist of two parts, a local and a global field. An improved difference formula is derived, allowing the accurate calculation of the potential at points near vortex locations. The local potential is then subtracted before calculating the velocity, leaving only the influences of the remaining vortices. The correct self-induced velocity is then explicitly added to the vortex velocity. Calculations of the motion of one and two vortex rings are performed, demonstrating the ability of the new method to eliminate the grid dependence of the self-induced velocity. The application of the method to the calculation of helicopter rotor flows in hover is attempted.

Roberts, T. W.↗

NASA NTRS1991

The spatial variations of lightning during small Florida thunderstorms

Networks of field mills (FM's) and lightning direction finders (LDF's) were used to locate lightning over the NASA KSC on three storm days. Over 90 percent of all cloud-to-ground (CG) flashes that were detected by the LDF's in the study area were also detected by the LDF's. About 17 percent of the FM CG events could be fitted to either a monopole or a dipole charge model. These projected FM charge locations are compared to LDF locations, i.e., the ground strike points. It was found that 95 percent of the LDF points are within 12 km of the FM charge, 75 percent are within 8 km, and 50 percent are within 4 km. For a storm on 22 Jul. 1988, there was a systematic 5.6 km shift between the FM charge centers and the LDF strike points that might have been caused by the meteorological structure of the storm.

Oram, Timothy D.↗

NASA NTRS2015

Radiation Budget Instrument (RBI) for JPSS-2

Radiation Budget Instrument (RBI) will be one of five instruments flying aboard the JPSS-2 spacecraft, a polar-orbiting sun-synchronous satellite in Low Earth Orbit. RBI is a passive remote sensing instrument that will follow the successful legacy of the Clouds and Earth's Radiant Energy System (CERES) instruments to make measurement of Earth's short and longwave radiation budget. The goal of RBI is to provide an independent measurement of the broadband reflected solar radiance and Earth's emitted thermal radiance by using three spectral bands (Shortwave, Longwave, and Total) that will have the same overlapped point spread function (PSF) footprint on Earth. To ensure precise NIST-traceable calibration in space the RBI sensor is designed to use a visible calibration target (VCT), a solar calibration target (SCT), and an infrared calibration target (ICT) containing phase change cells (PCC) to enable on-board temperature calibration. The VCT is a thermally controlled integrating sphere with space grade Spectralon covering the inner surface. Two sides of the sphere will have fiber-coupled laser diodes in the UV to IR wavelength region. An electrical substitution radiometer on the integrating sphere will monitor the long term stability of the sources and the possible degradation of the Spectralon in space. In addition the radiometric calibration operations will use the Spectralon diffusers of the SCT to provide accurate measurements of Solar degradation. All those stable on-orbit references will ensure that calibration stability is maintained over the RBI sensor lifetime. For the preflight calibration the RBI will view five calibration sources - two integrating spheres and three CrIS (Cross-track Infrared Sounder ) -like blackbodies whose outputs will be validated with NIST calibration approach. Thermopile are the selected detectors for the RBI. The sensor has a requirement to perform lunar calibration in addition to solar calibration in space in a way similar to CERES instruments approach. To monitor climate change and to get stable and traceable results, it is critical to assure stable calibration over instrument lifetime.

Georgieva, Elena↗

NASA NTRS1980

The effect of radiation pressure on the restricted three-body problem

The classical restricted three-body problem is extended to account for the effects of radiation pressure and the Poynting-Robertson effect on a particle with a surface-to-volume relation such that radiation pressure forces are nonnegligible moving in the gravitational field of two larger, orbiting bodies. The positions of the L4 and L5 Lagrangian points are found as functions of the ratio of radiational to gravitational forces. The inclusion of the Poynting-Robertson effect, however, is found to render the L4 and L5 points unstable on a time scale which is long compared to the rotation period of the two massive bodies. The results imply that space colonies with solar facing adjustable sails may be able to remain stationary at any heliocentric distance between a planet and the sun, and may provide a mechanism for producing asymmetries in the interplanetary dust cloud.

Schuerman, D. W.↗

NASA NTRS1983

The influence of coastal shape on winter mesoscale air-sea interaction

In cold air outbreaks, the combination of coastal shape and sea surface isotherms has a profound effect in the establishment of mesoscale atmospheric circulation, due to differential heating resulting from both overwater path length and underlying sea surface temperature (SST) variations. Where coastal effects are dominant, a mesoscale front forms downstream of the point which marks the major bend in the coastline's orientation. The strength of the induced mesoscale circulation depends on the original contrast between the land air temperature and the SST. It is noted that where the coastline and the isotherm pattern are approximately normal to the mean boundary layer flow, and thermal contrast is sufficiently large, the cloud streets formed downstream will be convective in nature, and oriented with the axis of roll vortices along the wind direction.

Atlas, D.↗

NASA NTRS1985

Application of the Man-computer Interactive Data Access System (McIDAS) to aerospace meteorology

The Man-computer Interactive Data Access System (McIDAS) considered in this paper has been in use at Marshall Space Flight Center (MSFC) since 1981. The MSFC McIDAS system is primarily employed as a research tool, taking into account rainfall estimates as deduced from Scanning Multichannel Microwave Radiometer (SMMR) data, remote sensing sensor development (MAMS), Doppler-lidar derived winds, cloud tracked winds, and analysis of lightning ground strike data. With respect to the SMMR data analysis, passive microwave satellite data are displayed on McIDAS as images. Two major research efforts are concerned with the determination of mesoscale winds. These efforts are based on a utilization of a Doppler-lidar system, and GOES multispectral imagery. It is pointed out that future plans include increased usage of the McIDAS system.

Meyer, P. J.↗

NASA NTRS2000

How do Polar Stratospheric Clouds Form?

SOLVE measurements have been compared with results from a microphysical model to understand the composition and formation of the polar stratospheric clouds (PSCs) observed during SOLVE. Evidence that the majority of the particles remain liquid throughout the winter will be presented. However, a small fraction of the particles do freeze, and the presence of these frozen particles can not be explained by current theories, in which the only freezing mechanism is homogeneous freezing to ice below the ice frost point. Alternative formation mechanisms, in particular homogeneous freezing above the ice frost point and heterogeneous freezing, have been explored using the microphysical model. Both nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) have been considered as possible compositions for the solid-phase nitric acid aerosols. Comparisons between the model results and the SOLVE measurements will be used to constrain the possible formation mechanisms. Other effects of these frozen particles will also be discussed, in particular denitrification.

Drdla, Katja↗

NASA NTRS2002

Understanding the Long-Term Spectral Variability of Cygnus X-1 with Burst and Transient Source Experiment and All-Sky Monitor Observations

We present a comprehensive analysis of all observations of Cyg X-1 by the Compton Gamma Ray Observatory Burst and Transient Source Experiment (BATSE; 20-300 keV) and by the Rossi X-Ray Timing Explorer all-sky monitor (ASM; 1.5-12 keV) until 2002 June, including approximately 1200 days of simultaneous data. We find a number of correlations between fluxes and hardnesses in different energy bands. In the hard (low) spectral state, there is a negative correlation between the ASM 1.5-12 keV flux and the hardness at any energy. In the soft (high) spectral state, the ASM flux is positively correlated with the ASM hardness but uncorrelated with the BATSE hardness. In both spectral states, the BATSE hardness correlates with the flux above 100 keV, while it shows no correlation with the 20-100 keV flux. At the same time, there is clear correlation between the BATSE fluxes below and above 100 keV. In the hard state, most of the variability can be explained by softening the overall spectrum with a pivot at approximately 50 keV. There is also another, independent variability pattern of lower amplitude where the spectral shape does not change when the luminosity changes. In the soft state, the variability is mostly caused by a variable hard (Comptonized) spectral component of a constant shape superposed on a constant soft blackbody component. These variability patterns are in agreement with the dependencies of the rms variability on the photon energy in the two states. We also study in detail recent soft states from late 2000 until 2002. The last of them has lasted thus far for more than 200 days. Their spectra are generally harder in the 1.5-5 keV band and similar or softer in the 3-12 keV band than the spectra of the 1996 soft state, whereas the rms variability is stronger in all the ASM bands. On the other hand, the 1994 soft state transition observed by BATSE appears very similar to the 1996 one. We interpret the variability patterns in terms of theoretical Comptonization models. In the hard state, the variability appears to be driven mostly by changing flux in seed photons Comptonized in a hot thermal plasma cloud with an approximately constant power supply. In the soft state, the variability is consistent with flares of hybrid, thermal/nonthermal, plasma with variable power above a stable cold disk. The spectral and timing differences between the 1996 and 2000-2002 soft states are explained by a decrease of the color disk temperature. Also, on the basis of broadband pointed observations simultaneous with those of the ASM and BATSE, we find the intrinsic bolometric luminosity increases by a factor of approximately 3-4 from the hard state to the soft one, which supports models of the state transition based on a change of the accretion rate.

Zdziarski, Andrzej A.↗

NASA NTRS2004

An on-board processor for a spaceborne Doppler precipitation radar : requirements and preliminary design

Use of Doppler velocity measurement in spaceborne precipitation radar is highly desirable, since it can allow more accurate retrieval of atmospheric latent heating, which depends on both cloud and rain microphysical processes and on dynamical processes, namely, vertical updrafts and downdrafts. However, if the rain within the antenna beam is very non-uniform, biases can result with conventional pulse-pair processing, and more sophisticated processing is required. The solution is a time-frequency approach, which uses the full Doppler spectrum at each point in time. Since precipitation radars normally operate continuously and collect large amounts of data, real-time, on-board processing of data is needed to reduce the data rate. The objective of this work is to develop an on-board data processor for spaceborne Doppler precipitation radar, using field-programmable gate array (FPGA) technology. This paper describes the simulations and analysis that have been completed during the first year of the project. This includes both analytical calculations and bit-true simulations that allow the effects of finite word length to be explored. Tradeoffs have also been considered between speed and space within the chosen FPGA part. The results of these analyses have been used to develop a complete set of requirements for the processor. Initial design work has begun, based on these requirements. The design is being implemented in Verilog, and a description of this early design effort is also be given.

on-board processing↗

NASA NTRS2009

Integrating and Visualizing Tropical Cyclone Data Using the Real Time Mission Monitor

The Real Time Mission Monitor (RTMM) is a visualization and information system that fuses multiple Earth science data sources, to enable real time decision-making for airborne and ground validation experiments. Developed at the NASA Marshall Space Flight Center, RTMM is a situational awareness, decision-support system that integrates satellite imagery, radar, surface and airborne instrument data sets, model output parameters, lightning location observations, aircraft navigation data, soundings, and other applicable Earth science data sets. The integration and delivery of this information is made possible using data acquisition systems, network communication links, network server resources, and visualizations through the Google Earth virtual globe application. RTMM is extremely valuable for optimizing individual Earth science airborne field experiments. Flight planners, scientists, and managers appreciate the contributions that RTMM makes to their flight projects. A broad spectrum of interdisciplinary scientists used RTMM during field campaigns including the hurricane-focused 2006 NASA African Monsoon Multidisciplinary Analyses (NAMMA), 2007 NOAA-NASA Aerosonde Hurricane Noel flight, 2007 Tropical Composition, Cloud, and Climate Coupling (TC4), plus a soil moisture (SMAP-VEX) and two arctic research experiments (ARCTAS) in 2008. Improving and evolving RTMM is a continuous process. RTMM recently integrated the Waypoint Planning Tool, a Java-based application that enables aircraft mission scientists to easily develop a pre-mission flight plan through an interactive point-and-click interface. Individual flight legs are automatically calculated "on the fly". The resultant flight plan is then immediately posted to the Google Earth-based RTMM for interested scientists to view the planned flight track and subsequently compare it to the actual real time flight progress. We are planning additional capabilities to RTMM including collaborations with the Jet Propulsion Laboratory in the joint development of a Tropical Cyclone Integrated Data Exchange and Analysis System (TC IDEAS) which will serve as a web portal for access to tropical cyclone data, visualizations and model output.

Goodman, H. Michael↗

NASA NTRS1993

Infrared Cirrus and Discrete Sources in the Outer Galaxy

Studies of Galactic infrared cirrus have been based on observations of individual high latitude clouds, analysis of large scale emission at high latitudes in the Solar Neighborhood and complete linear decomposition of the global emission from IRAS and other observations over the entire Galaxy.

IRAS infrared cirrus linear decomposition Point So↗