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All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Propagation effects on satellite systems at frequencies below 10 GHz, a handbook for satellite systems design, 1st edition

Satellite communications below about 6 GHz may need to contend with ionospheric effects, including Faraday rotation and ionospheric scintillation, which become increasingly significant with decreasing frequency. Scintillation is most serious in equatorial, auroral, and polar latitudes; even the 4 to 6 GHz frequency range turns out to be subject to scintillation to a significant degree of equatorial latitudes. Faraday rotation, excess range or time delay, phase advance, Doppler frequency fluctuations, and dispersion are proportional to total electron content (TEC) or its variation along the path. Tropospheric refraction and fading affects low angle satellite transmissions as well as terrestrial paths. Attenuation and depolarization due to rain become less important with decreasing frequency but need consideration for frequencies of about 4 GHz and higher. Empirically derived relations are useful for estimating the attenuation expected due to rain for particular percentages of time. Aeronautical, maritime, and land mobile satellite services are subject to fading due to multipath propagation.

Flock, W. L.↗
NASA NTRS1984

Natural radio noise - A mini-review

Natural radio noise in telecommunication systems can be accounted for by the contribution which it makes to antenna noise temperature. Attenuation due to water vapor and oxygen, clouds, and precipitation is accompanied by thermal noise which further degrades the applicable signal-to-noise ratio. Extraterrestrial noise may be of thermal or nonthermal origin and may cover a continuum of frequencies or occur at discrete frequencies. The spectral index n (the exponent giving the variation of noise power density with wavelength) is -2 for a black body and between 0 and -2 for thermal emission in general. The mechanism responsible for much of the extensive nonthermal extraterrestrial noise is synchrotron radiation, characterized by a positive spectral index.

Flock, W. L.↗
NASA NTRS1986

Propagation through Martian dust at 8.5 and 32 GHz

Independent studies of attenuation of X-band (8.5 GHz) and Ka-band (32 Ghz) radio signals when traversing Martian dust were carried out. These analyses turned out remarkably similar. The computational method is essentially that of T. S. Chu but uses observed optical depth at 0.67 microns rather than visibility as the measure of optical attenuation from which to derive the microwave attenuation. An awkwardness in the approach is that the size distribution of Martian dust particles is not well known, but the mean is probably around 4 microns, whereas in the terrestrial case it is nearer 10 microns. As a consequence, there will be a larger tail of particles still in the Mie regime in the Martian case as compared to the terrestrial one. The computational error will, therefore, be somewhat larger for Martian than Earth-bound dust. Fortunately, the indicated attenuations are small enough for the worst case (1.3 dB at 32 GHz) that the error is academic.

Smith, E. K.↗
NASA NTRS1987

Propagation effects on satellite systems at frequencies below 10 GHz: A handbook for satellite systems design

Frequencies below 10 GHz continue to be used for a large portion of satellite service, and new applications, including mobile satellite service and the global positioning system, use frequencies below 10 GHz. As frequency decreases below 10 GHz, attenuation due to precipitation and gases decreases and ionospheric effects increase. Thus the ionosphere, which can be largely neglected above 10 GHz, receives major attention. Although attenuation and depolarization due to rain are less severe below 10 GHz than above, they are nevertheless still important and constitute another major topic. The handbook emphasizes the propagation effects on satellite communications but material that is pertinent to radio navigation and positioning systems and deep-space telecommunications is included as well. Chapter 1 through 7 describe the various propagation impairments, and Chapter 9 is devoted to the estimation or calculation of the magnitudes of these effects for use in system design. Chapter 10 covers link power budget equations and the role of propagation effects in these equations. Chapter 8 deals with the complex subject of interference between space and terrestrial systems.

Flock, Warren L.↗
NASA NTRS1988

Propagation effects on spread-spectrum mobile satellite systems

In contrast to the situation at L-band, wide bandwidths of 500 MHz or more have been allocated for mobile satellite service at frequencies between 20 and 50 GHz. These broad bandwidths are well suited for the use of spread-spectrum. Certain system considerations about the use of such high frequencies for mobile satellite service are mentioned first, and attention is then given to propagation effects on high-frequency broad-band systems. Attenuation due to rain is a constant at 20 to 50 MHz, but would not be a serious problem if outages occurring for one to three percent of the time, depending on location, are considered to be acceptable. Clear air absorption becomes a significant factor above 40 GHz, but should not exceed 2 dB at a 10 degree elevation angle and frequencies below 40 GHz. Spread-spectrum provides a form of frequency diversity that helps to minimize the effects of multipath.

Flock, Warren L.↗
NASA NTRS1988

The Propagation Information Center at the University of Colorado

A Propagation Information Center is in the process of being established at the University of Colorado with connections to NAPEX and to the NASA program at Colodado University (CU) for Interdisciplinary Research in Telecommunications Policy and Technology Issues. The Propagation Information Center was conceived as a response to several items in the Science Review of the NASA Propagation Program carried out in September of 1986 by a distinguished panel of experts. The program for the Center is conceived as including archival aspects: a memory of past work by NAPEX members; accounts of relevant research activities around the world; papers published in pertinent areas of propagation; and pertinent propagation data files. Duties of the Center should include: exchanging information on future plans with research organizations around the world; scanning the literature for possible contributions; carrying out quick response studies requested by program management; conducting customer surveys of users; preparing a quarterly newsletter to help maintain communication amongst program participants; and assisting students and faculty who are working on policy issues for NASA in the propagation field.

Smith, Ernest K.↗
NASA NTRS1989

NASA Propagation Information Center

The NASA Propagation Information Center became formally operational in July 1988. It is located in the Department of Electrical and Computer Engineering of the University of Colorado at Boulder. The Center is several things: a communications medium for the propagation with the outside world, a mechanism for internal communication within the program, and an aid to management.

Smith, Ernest K.↗
NASA NTRS1990

NASA propagation information center

The NASA Propagation Information Center became formally operational in July 1988. It is located in the Department of Electrical and Computer Engineering of the University of Colorado at Boulder. The center is several things: a communications medium for the propagation with the outside world, a mechanism for internal communication within the program, and an aid to management.

Smith, Ernest K.↗
NASA NTRS1992

WARC 92 and some thoughts as to its impact on the NASA propagation program

The World Administrative Radio Conference of 1992 (WARC 92) was held in Torremolinos, Spain, 3 Feb. - 3 Mar. 1992. Major topics considered included shortwave broadcasting, mobile and mobile-satellite service, broadcasting satellite service (sound and HDTV), space services above 20 GHz, and space research. Considerable attention was given to the congested 1-3 GHz band in general and to Low Earth Orbit (LEO) Mobile-Satellite Service, including 'little' LEO's operating below 1 GHz and to 'big' LEO's operating above 1 GHz. Significant new allocations were made for generic Mobile-Satellite Services (MSS). Proposals for allocations for uplink power control beacons and for space research received favorable treatment.

Flock, Warren L.↗
NASA NTRS1991

Natural noise above 50 MHZ from terrestrial and extraterrestrial sources

This paper offers a brief overview of natural radio noise for frequencies above 50 MHz in terms of brightness temperature as observed from two vantage points. The first is from an Earth station located at 40 degrees north latitude and observing at elevation angles from 0 to 90 degrees with an ideal antenna. The second is a satellite in geostationary orbit communicating with the Earth. Earth station noise at VHF and UHF is dominated by galactic and solar noise. Emission from the atmosphere, gases and hydrometeors, are dominant at EHF and SHF. Radiative transfer theory is invoked in the calculation of brightness temperature from the atmosphere. The situation is not vastly different from geostationary orbit if communications is with the Earth. Emission from the land and sea, even under idealized conditions, enters significantly. Land is a much more effective emitter than sea water, but at frequencies above 30 GHz the differential becomes much less due to the increasing significance of atmospheric emission.

Smith, E. K.↗
NASA NTRS1993

Effects of the equatorial ionosphere on L-band Earth-space transmissions

Ionosphere scintillation can effect satellite telecommunication up to Ku-band. Nighttime scintillation can be attributed to large-scale inhomogeneity in the F-region of the ionosphere predominantly between heights of 200 and 600 km. Daytime scintillation has been attributed to sporadic E. It can be thought of as occurring in three belts: equatorial, high-latitude, and mid-latitude, in order of severity. Equatorial scintillation occurs between magnetic latitudes +/- 25 degrees, peaking near +/- 10 degrees. It commonly starts abruptly near 2000 local time and dies out shortly after midnight. There is a strong solar cycle dependence and a seasonal preference for the equinoxes, particularly the vernal one. Equatorial scintillation occurs more frequently on magnetically quiet than on magnetically disturbed days in most longitudes. At the peak of the sunspot cycle scintillation depths as great as 20 dB were observed at L-band.

Smith, Ernest K.↗
NASA NTRS1998

Hydrogen Radicals, Nitrogen Radicals, and the Production of O3 in the Upper Troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HO, required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production Of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about I part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more 03 than expected.

Wennberg, P. O.↗
NASA NTRS2003

Measurement of Peroxyacetyl Nitrate (PAN), Peroxypropionyl Nitrate (PPN) and Peroxymethacryloyl Nitrate (MPAN) during TRACE-P

In Fall 2000, the PANs gas chromatograph (GC) was improved and prepared for installation on the NASA P-3. A number of experiments were conducted in conjunction with the NCAR NO,, instrument (B. Ridley) to settle some of the fine details of the output of the calibration system for each instrument. In addition, the sampling frequency was improved.

Flocke, Frank↗
NASA NTRS2007

Reactive Nitrogen Distribution and Partitioning in the North American Troposphere and Lowermost Stratosphere

A comprehensive group of reactive nitrogen species (NO, NOz, HN03, HOzN02, PANs, alkyl nitrates, and aerosol-NO3) were measured over North America during July/August 2004 from the NASA DC-8 platform (0.1 - 12 km). Nitrogen containing tracers of biomass combustion (HCN and CH3CN) were also measured along with a host of other gaseous (CO, VOC, OVOC, halocarbon) and aerosol tracers. Clean background air as well as air with influences from biogenic emissions, anthropogenic pollution, biomass combustion, convection, lightning, and the stratosphere was sampled over the continental United States, the Atlantic, and the Pacific. The North American upper troposphere (UT) was found to be greatly influenced by both lightning NO, and surface pollution lofted via convection and contained elevated concentrations of PAN, ozone, hydrocarbons, and NO,. Observational data suggest that lightning was a far greater contributor to NO, in the UT than previously believed. PAN provided a dominant reservoir of reactive nitrogen in the UT while nitric acid dominated in the lower troposphere (LT). Peroxynitric acid (H02N02) was present in sizable concentrations peaking at around 8 km. Aerosol nitrate appeared to be mostly contained in large soil based particles in the LT. Plumes from Alaskan fires contained large amounts of PAN and aerosol nitrate but little enhancement in ozone. A comparison of observed data with simulations from four 3-D models shows significant differences between observations and models as well as among models. We investigate the partitioning and interplay of the reactive nitrogen species within characteristic air masses and further examine their role in ozone formation.

Singh, H. B.↗
NASA NTRS2007

Reactive Nitrogen Distribution and Partitioning in the North American Troposphere and Lowermost Stratosphere

A comprehensive group of reactive nitrogen species (NO, NO2, HNO3, HO2NO2, PANs, alkyl nitrates, and aerosol-NO3) were measured in the troposphere and lowermost stratosphere over North America and the Atlantic during July/August 2004 (INTEX-A) from the NASA DC-8 platform (0.1-12 km). Less reactive nitrogen species (HCN and CH3CN), that are also unique tracers of biomass combustion, were also measured along with a host of other gaseous (CO, VOC, OVOC, halocarbon) and aerosol tracers. Clean background air as well as air with influences from biogenic emissions, anthropogenic pollution, biomass combustion, and stratosphere was sampled both over continental U. S., Atlantic and Pacific. The North American upper troposphere was found to be greatly influenced by both lightning NO(x) and surface pollution lofted via convection and contained elevated concentrations of PAN, ozone, hydrocarbons, and NO(x). Under polluted conditions PAN was a dominant carrier of reactive nitrogen in the upper troposphere while nitric acid dominated in the lower troposphere. Peroxynitric acid (HO2NO2) was present in sizable concentrations always peaking at around 8 km. Aerosol nitrate appeared to be mostly contained in large soil based particles in the lower troposphere. Plumes from Alaskan fires contained large amounts of PAN and very little enhancement in ozone. Observational data suggest that lightning was a far greater contributor to NO(x) in the upper troposphere than previously believed. NO(x) and NO(y) reservoir appeared to be in steady state only in the middle troposphere where NO(x)/NO(y) was independent of air mass age. A first comparison of observed data with simulations from four 3-D models shows significant differences between observations and models as well as among models. These uncertainties likely propagate themselves in satellites derived NOx data. Observed data are interpreted to suggest that soil sinks of HCN/CH3CN are at best very small. We investigate the partitioning and interplay of the reactive nitrogen species within characteristic air masses and further examine their role in ozone formation.

Singh, H. B.↗
NASA NTRS2007

Surface and Lightning Sources of Nitrogen Oxides over the United States: Magnitudes, Chemical Evolution, and Outflow

We use observations from two aircraft during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign over the eastern United States and North Atlantic during summer 2004, interpreted with a global 3-D model of tropospheric chemistry (GEOS-Chem) to test current understanding of the regional sources, chemical evolution, and export of nitrogen oxides. The boundary layer NO(x) data provide top-down verification of a 50% decrease in power plant and industry NO(x) emissions over the eastern United States between 1999 and 2004. Observed 8-12 8 km NO(x) concentrations in ICARTT were 0.55 +/- 36 ppbv, much larger than in previous United States aircraft campaigns (ELCHEM, SUCCESS, SONEX). We show that regional lightning was the dominant source of this NO(x) and increased upper tropospheric ozone by 10 ppbv. Simulating the ICARTT upper tropospheric NO(x) observations with GEOS-Chem require a factor of 4 increase in the model NO(x) yield per flash (to 500 mol/flash). Observed OH concentrations were a factor of 2 lower than can be explained from current photochemical models, and if correct would imply a broader lightning influence in the upper troposphere than presently thought.An NO(y)-CO correlation analysis of the fraction f of North American NO(x) emissions vented to the free troposphere as NO(y) (sum of NO(x) and its oxidation products PAN and HNO3) s shows observed f=16+/-10 percent and modeled f=14 +/- 8 percent, consistent with previous studies. Export to the lower free troposphere is mostly HNO3 but at higher altitudes is mostly PAN. The model successfully simulates NO(y) export efficiency and speciation, supporting previous model estimates of a large U.S. contribution to tropospheric ozone through NO(x) and PAN export.

Hudman, Rynda C.↗
NASA NTRS2006

Establishing Lagrangian Connections between Observations within Air Masses Crossing the Atlantic during the ICARTT Experiment

The International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)-Lagrangian experiment was conceived with an aim to quantify the effects of photochemistry and mixing on the transformation of air masses in the free troposphere away from emissions. To this end attempts were made to intercept and sample air masses several times during their journey across the North Atlantic using four aircraft based in New Hampshire (USA), Faial (Azores) and Creil (France). This article begins by describing forecasts using two Lagrangian models that were used to direct the aircraft into target air masses. A novel technique is then used to identify Lagrangian matches between flight segments. Two independent searches are conducted: for Lagrangian model matches and for pairs of whole air samples with matching hydrocarbon fingerprints. The information is filtered further by searching for matching hydrocarbon samples that are linked by matching trajectories. The quality of these coincident matches is assessed using temperature, humidity and tracer observations. The technique pulls out five clear Lagrangian cases covering a variety of situations and these are examined in detail. The matching trajectories and hydrocarbon fingerprints are shown and the downwind minus upwind differences in tracers are discussed.

Methven, J.↗
NASA NTRS2009

Emissions from Biomass Burning in the Yucatan

In March 2006 two instrumented aircraft made the first detailed field measurements of biomass burning (BB) emissions in the Northern Hemisphere tropics as part of the MILAGRO project. The aircraft were the National Center for Atmospheric Research C-130 and a University of Montana/US Forest Service Twin Otter. The initial emissions of up to 49 trace gas or particle species were measured from 20 deforestation and crop residue fires on the Yucatan peninsula. This included two trace gases useful as indicaters of BB (HCN and acetonitrile) and several rarely, or never before, measured species: OH, peroxyacetic acid, propanoic acid, hydrogen peroxide, methane sulfonic acid, and sulfuric acid. Crop residue fires emitted more organic acids and ammonia than deforestation fires, but the emissions from the main fire types were otherwise fairly similar. The Yucatan fires emitted unusually amounts of SO2 and particle chloride, likely due to a strong marine influence on the peninsula.

Yokelson, R.↗