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At least 1,117 records · Page 62
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NASA NTRS1983

Interpretation of radar returns from clear air: Discrimination against clutter

Different kinds of inteference may cause problems to the proper detection and analysis of the atmospheric signals, when using VHF and UHF radars. These are separated into passive and active contributions. Passive contributions are existent in the receiving system without the radar transmitter switched on. Active contributions are due to scatter and reflection of the own transmitted radar signal from unwanted targets, which are called clutter. Of major importance to radar systems are active interference contributions. Different methods can be applied for elimination or at least suppressing unwanted effects. These are; (1) Directional filtering, i.e., applying optimum suppression of antenna sidelobes, (2) Range filtering, i.e., suppressing unwanted signals only in affected range gates, (3) selection by amplitude distributions, (4) Temporal filtering, i.e., recognizing typical temporal variations of the clutter signals, through spectral characteristics, and applying matched filters.

Rottger, J.↗
NASA NTRS1984

Characterization of LANDSAT-4 TM and MSS Image Quality for Interpretation of Agricultural and Forest Resources

Systematic analysis of both image and numeric data shows that the overall spectral, spatial, and radiometric quality of the TM data are excellent. Spectral variations in fallow fields are due to the vaiability in soil moisture and surface roughness resulting from the various stages of field preparation for small grains production. Spectrally, the addition of the first TM short wave infrared band (Band 5) significantly enhanced ability to discriminate different crop types. Bands 1, 5, and 6 contain saturated pixels due to high albedo effects, low moisture conditions, and high radiant temperatures of granite and dry, bare soil on south facing slopes, respectively. Spatially, the two fold decrease in interpixel distance and four fold decrease in area per pixel between the TM and MSS allow for improved discrimination of small fields, boundary conditions, road and stream networks in rough terrain, and small forest clearings resulting from various forest management practices.

Degloria, S. D.↗
NASA NTRS1984

Geophysical interpretation of satellite laser ranging measurements of crustal movement in California

As determined by satellite laser ranging the rate of contraction of a 900 kilometer baseline between sites located near Quincy in northern California and San Diego in southern California is about 61 to 65 mm/yr with a formal uncertainty of about 10 mm/yr. The measured changes in baseline length are a manifestation of the relative motion between the North America and Pacific tectonic plates. This long baseline result is compared to measurements made by more conventional means on shorter baselines. Additional information based on seismicity, geology, and theoretical modelling is also analyzed. Deformation lying within a few tens of kilometers about the major faults in southern California accounts for most, but not all of the observed motion. Further motion is attributable to a broader scale deformation in southern California. Data suggesting crustal movements north of the Garlock fault, in and near the southern Sierra Nevada and local motion at an observatory are also critically reviewed. The best estimates of overall motion indicated by ground observations lie between 40 and 60 mm/yr. This lies within one or two standard deviations of that deduced by satellite ranging but the possibility of some unresolved deficit cannot be dismissed. The long time scale RM2 plate tectonic model of Minster and Jordan predicts a contraction between 47 and 53 mm/yr depending on the extension rate of the Basin and Range. Thus the ground based observations, satellite laser ranging (SLR) results, and RM2 rates differ at about the 10 mm/yr level and are consistent with one another within the data and model uncertainties.

Cohen, S. C.↗
NASA NTRS1983

Methodology for interpretation of SST retrievals using the AVHRR split window algorithm

Intercomparisons of sea surface temperature (SST) products derived from the operational NOAA-7 AVHRR-II algorithm and in situ observations are made. The 1982 data sets consist of ship survey data during the winter from the Mid-Atlantic Bight (MAB), ship and buoy measurements during April and September in the Gulf of Mexico and shipboard observations during April off the N.W. Spanish coast. The analyses included single pixel comparisons and the warmest pixel technique for 2 x 2 pixel and 10 x 10 pixel areas. The reason for using multi-pixel areas was for avoiding cloud contaminated pixels in the vicinity of the field measurements. Care must be taken when applying the warmest pixel technique near oceanic fronts. The Gulf of Mexico results clearly indicate a persistent degradation in algorithm accuracy due to El Chichon aerosols. The MAB and Spanish data sets indicate that very accurate estimates can be achieved if care is taken to avoid clouds and oceanic fronts.

Barbieri, R. W.↗
NASA NTRS1983

The O(+) 834-A dayglow - Satellite observations and interpretation with a radiation transfer model

The observations were made with the EUV spectrometer on the Air Force satellite STP-78-1. The dayglow intensity was observed at an altitude of 600 km to vary with magnetic latitude from 30 R to 300 R in the near zenith direction (theta - 40 deg) and from 400 R to 500 R in the near nadir direction (theta = 140 deg). The correspondingly large near zenith to near nadir intensity ratio of 0.3-0.65 over much of the dayside is seen as suggesting that the O(+) ions in the topside ionosphere constitute an optically thick medium for resonance scattering of 834-A airglow emission even at this high altitude. The STP 78-1 airglow data are normalized by means of simultaneous measurements of the O(+) density from the Explorer AE-E spacecraft at 460-km altitude near the equator. It is noted that for the ionization excitation of atomic oxygen leading to the production of O(+) atoms in 4P state, a g value of 1.1 x 10 to the -8th/s at zero optical depth is required. The latitudinal distribution of O(+) density derived from the 834-A airglow data reveals a double peak surrounding an equatorial trough (characteristic of the equatorial anomaly) at altitudes below 1000 km and a single peak at the magnetic equator above 1000 km.

Kumar, S.↗
NASA NTRS1983

Interpretation of vector magnetograph data including magneto-optic effects. I - Azimuth angle of the transverse field

In this paper, the presence of Faraday rotation in measurements of the orientation of a sunspot's transverse magnetic field is investigated. Using observations obtained with the Marshall Space Flight Center's (MSFC) vector magnetograph, the derived vector magnetic field of a simple, symmetric sunspot is used to calculate the degree of Faraday rotation in the azimuth of the transverse field as a function of wavelength from analytical expressions for the Stokes parameters. These results are then compared with the observed rotation of the field's azimuth which is derived from observations at different wavelengths within the Fe I 5250 A spectral line. From these comparisons, it is found: the observed rotation of the azimuth is simulated to a reasonable degree by the theoretical formulations if the line-formation parameter is varied over the sunspot; these variations are substantiated by the line-intensity data; for the MSFC system, Faraday rotation can be neglected for field strengths less than 1800 G and field inclinations greater than 45 deg; to minimize the effects of Faraday rotation in sunspot umbrae, MSFC magnetograph measurements must be made in the far wings of the Zeeman-sensitive spectral line.

West, E. A.↗
NASA NTRS1983

A thermal interpretation of the X-ray spectra of quasars, active galactic nuclei, and Cygnus X-1

It is shown that spherically accreting black hole models emitting bremsstrahlung radiation provide an excellent fit to the observed X-ray spectrum of typical active galactic nuclei, as well as of 3C 273 and Cygnus X-1. The spectral slope remains approximately constant under changes of luminosity, as required by observations. Only one parameter, T(max), is needed for the fit.

Meszaros, P.↗
NASA NTRS1983

Nitric oxide in the upper stratosphere - Measurements and geophysical interpretation

A rocket-borne parachute-deployed chemiluminescence instrument has obtained seven new measurements of atmospheric nitric oxide for altitudes between 30 and 50 km at mid-latitudes. These results, when combined with profiles measured by an earlier version of the instrument, cover all four seasons and provide a more comprehensive picture of upper stratospheric nitric oxide than has been available previously. At the highest altitudes studied, the vertical gradient in mixing ratio displays positive and negative values during different observations, with the largest values tending to appear at the greatest heights in summer. Examination of the differences among the profiles, which exceed a factor of 3 near the stratopause, suggests that they arise from the action of transport processes which carry air into the mid-latitude upper stratosphere from regions of the atmosphere that contain widely different odd-nitrogen abundances.

Harvath, J. J.↗
NASA NTRS1983

On the interpretation of kernels - Computer simulation of responses to impulse pairs

A method is presented for the use of a unit impulse response and responses to impulse pairs of variable separation in the calculation of the second-degree kernels of a quadratic system. A quadratic system may be built from simple linear terms of known dynamics and a multiplier. Computer simulation results on quadratic systems with building elements of various time constants indicate reasonably that the larger time constant term before multiplication dominates in the envelope of the off-diagonal kernel curves as these move perpendicular to and away from the main diagonal. The smaller time constant term before multiplication combines with the effect of the time constant after multiplication to dominate in the kernel curves in the direction of the second-degree impulse response, i.e., parallel to the main diagonal. Such types of insight may be helpful in recognizing essential aspects of (second-degree) kernels; they may be used in simplifying the model structure and, perhaps, add to the physical/physiological understanding of the underlying processes.

Hung, G.↗
NASA NTRS1983

Interpretation of the 6818.9-A methane feature observed on Jupiter, Saturn, and Uranus

High-resolution (0.1-A) spectra of the 6818.9-A methane feature obtained for Jupiter, Saturn, and Uranus by Baines, Schempp, and Smith (1969) are modeled using a doubling and adding code after Hansen (1983). The feature's rotational quantum number is estimated using the relatively homogeneous atmosphere of Saturn, with only J = 0 and J = 1 fitting the observational constraints. The aerosol content within Saturn's northern temperate region is shown to be substantially less than at the equator, indicating a haze only half as optically thick. Models of Jupiter's atmosphere are consistent with the rotational quantum-number assignment. Synthetic line profiles of the 6818.9-A feature observed on Uranus reveal that a substantial haze exists at or above the methane condensation region with an optical depth eight times greater than previously reported. Seasonal effects are indicated. The methane column abundance is 5 + or - 1 km-am. The mixing ratio of methane to hydrogen within the deep unsaturated region of the planet is 0.045 + or - 0.025, based on an H2 column abundance of 240 + or - 60 km-am (Smith, Macy, and Pilcher /1980/), thus indicating that methane comprises between one-sixth and one-half of the planet's mass. However, proper reevaluation of H2 quadrupole features accounting for the haze reported here may significantly reduce the relative methane abundance.

Baines, K. H.↗
NASA NTRS1984

Interpretation of microwave active region structures using SMM soft X-ray observations

A new kind of sunspot-associated microwave source was detected by Alissandrakis and Kundu (1982). The observed emission came predominantly from a ring structure with a size between that of the umbra and the penumbra. It was thought that the newly discovered structure could be the product of the low gyroresonance opacity when the angle between the magnetic field and the line of sight is close to zero. The present investigation has the objective to study the roles played by the geometrical effect of gyroresonance absorption and by the low-temperature flux tubes above the relevant sunspot, taking into account 6 cm observations made with the aid of a radio telescope and X-ray observations conducted with the X-ray Polychromator (XRPO on the Solar Maximum Mission) (SMM) satellite.

Strong, K. T.↗
NASA NTRS1984

The energy spectrum of electrons and cosmic-ray confinement A new measurement and its interpretation

Measurements of the cosmic ray flux and electron energy spectrum from 5 GeV to 300 GeV, with an absolute uncertainty in the flux level of + or - 10 percent at low energies and + or - 30 percent at 100 GeV, are described. The measured spectrum appears to represent the competing processes of radiative energy loss in the interstellar medium and leakage out of the Galaxy. In the framework of the leaky box model and diffusion models, the result is most consistent with the picture of cosmic ray electrons spending an average of 10 million years in the Galaxy independent of electron energy, probably propagating in a halo as well as in the galactic disk.

Tang, K.-K.↗
NASA NTRS1984

Interpretation of the number versus diameter distribution for supernova remnants in the Large Magellanic Cloud

An examination is conducted of the cumulative number versus diameter relation for an X-ray selected sample of supernova remnants in the Large Magellanic Cloud in an attempt to understand the evolutionary state of these objects. Previous studies have suggested that the observed linear N(D) relation requires the remnants in the cloud to be freely expanding. Detailed calculations have been carried out to determine the effect of a luminosity threshold on the observed distribution and it is shown that the observations can be fitted by remnants which are in the adiabatic or later stages of evolution. The implications of the results for the supernova creation rate in the LMC are discussed.

Hughes, J. P.↗
NASA NTRS1983

Remote assessment of ocean color for interpretation of satellite visible imagery: A review

An assessment is presented of the state-of-the-art of remote, (satellite-based) Coastal Zone Color (CZCS) Scanning of color variations in the ocean due to phytoplankton. Attention is given to physical problems associated with ocean color remote sensing, in-water algorithms for the correction of atmospheric effects, constituent retrieval algorithms and application of the algorithms to CZCS imagery. The applicability of CZCS to both near-coast and mid-ocean waters is considered, and it is concluded that while differences between the two environments are complex, universal algorithms can be used for the case of mid-ocean waters, and site-specific algorithms are adequate for CZCS imaging of the near-coast oceanic environment. A short description of CVCS and some sample photographs are provided in an appendix.

Gordon, H. R.↗
NASA NTRS1984

Resonant heating - An interpretation of coronal loop data

It is shown that the resonant heating theory of Hollweg can be used to organize the coronal loop data of Golub et al. (1980). When combined with a reasonable form for the input power spectrum, the resonant heating theory is fully compatible with the loop data.

Hollweg, J. V.↗
NASA NTRS1984

Magnetic Alignment Theory and the Interpretation of Polarization

The theory of magnetic spinning alignment is outlined. It is shown that a classical enhanced thermal Davis and Greenstein mechanism may be considered as a limiting case of Purcell's suprathermal spinning alignment theory when the number of active sites on a given grain becomes very important and/or for very short lived suprathermal sites. The results are applied to the interstellar medium and some problems in which it may be important are discussed.

Cugnon, P.↗
NASA NTRS1983

An investigation of the crustal properties of Australia and surrounding regions derived from interpretation of MAGSAT anomaly field data

The 2 deg averaged data set was analyzed and filtered to produce a magnetic anomaly map of the Australian continental region. The map was overlain on a tectonic map of Australia and correlations were made. A data set was selected that is dominated by relatively low elevation profiles with small changes of elevation within the Australian area in an effort to maximize the crustal anomaly field signal and reduce the effect of variation in satellite elevation. Support systems, both hardware and software are described and best-worst case errors encountered during processing of MAGSAT investigator tapes are summarized. The Broken Ridge anomaly was studied for model development purposes.

Johnson, B. D.↗