Multiple-source localization using GPS technology and receivedarrival time structure analysis in an air-deployed system

An efficient and robust method has been developed to locate multiple impulsive sources in an ocean environment. Global position system (GPS) receivers were installed on sonobuoys to obtain their locations within a few meters of accuracy. A sonobuoy field was deployed in a ring-type pattern. Charges were then set off at arbitrary locations within the ring, High-resolution plots were used to obtain direct path and/or first bottom bounce arrivals on each buoy. A model grid of arrival times was constructed, corresponding to the dimensions of the buoy field. A ray model previously developed here at the Applied Research Laboratories at the University of Texas at Austin (ARL:UT) was used to obtain model travel times. The minimum value of the least-square-type error between the real arrival times and the modeled travel times resulted in an unambiguous location of the source, within the limits of the grid spacing chosen. This value was calculated by picking one receiver as the reference and then summing the timing errors of the remaining receivers relative to the reference. Successive iterations with finer grid spacings result in source localization within the accuracy of the buoy locations. The localization routine was extended by allowing permutations of the pulse arrivals on each buoy to account for multiple sources closely separated in time and/or space. An automated correlation technique is presented as an alternative to the leading edge-detection method used here for obtaining relative arrival times. Two proof-of-concept experiments were performed and some results of data obtained at Lake Travis and the Gulf of Mexico are presented     

TEMPORAL TRENDS IN SOIL PRODUCTIVITY EVALUATIONS*

Studies of soil productivity must compensate for the effects of temporal trends in order to examine the pattern of crop yields along spatial gradients. An analysis of the published yield estimates for 30 soils in 233 counties, however, did not find consistent yield increases over the past three decades. On the contrary, the yield estimates for many soils were markedly uniform since 1972. The uniformity appears to have two causes: the acknowledged difficulty of making yield estimates in a time of increasing variability in soil and crop management, both within and between regions, and surveyors' awareness of data stored in a national soils data base. The effect is to cast doubt on soil productivity data reported in county soil surveys published between 1973 and 1988.     

A comparison of theoreticalCIV emission line strengths with active region observations obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

Theoretical line ratios involving 2s ² S - 3p ² P, 2p ² P - 3s ² S, and 2p ² S - 3d ² D transitions inCiv between 312 and 420 Å are presented. A comparison of these with solar active region observational data obtained during a rocket flight by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals good agreement between theory and experiment, with discrepancies that average only 22%. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar data from the S082A instrument on boardSkylab. The potential usefulness of theCIV line ratios as electron temperature diagnostics for the solar transition region is briefly discussed.     

Transient phenomena in the energetic behind-the-limb solar flare of september 29, 1989

The powerful cosmic ray flare of Sept. 29, 1989 occurred behind the limb and was observed over a wide spectral range. The analysis of optical, radio, and other relevant data suggest two phases of energy release. After an impulsive phase a prolonged post eruption energy release occurred in an extended region of the corona following the eruption of a large coronal mass ejection (CME). This phase is responsible for numerous coronal and interplanetary phenomena including the ground-level increase of cosmic rays.     

Chromospheric evolution and the flare activity of super-active region NOAA 6555

Super-active region NOAA 6555 was highly flare productive during the period March 21st–27th, 1991 of its disk passage. We have st udied its chromospheric activity using high spatial resolution Hα filtergrams taken at Udaipur along with MSFC vector magnetograms. A possible relationship of flare productivity and the variation in shear has been explored. Flares were generally seen in those subareas of the active region which possessed closed magnetic field configuration, whereas only minor flares and/or surges occurred in subareas showing open magnetic field configuration. Physical mechanisms responsible for the observed surges are also discussed.     

HST/NICMOS Observations of M82

The irregular galaxy M82 is known as the archetypal starburst galaxy. Its proximity (3.5 Mpc) makes this galaxy an ideal laboratory for studying the properties of its starburst. The detailed morphology of the [FeII] 1.644 μm and emission Pa_α (at 1.87 μm) is revealed by the NICMOS images. The peak of the 2.2 μm continuum brightness(evolved population) lies very close to the dynamical centre. Most of the Pa_α emission (which traces the young population) is distributed in a ring of star formation (with a `hole' lacking line emission at the centre of the galaxy). These observations support the scenario in which the starburst in M82 is propagating outwards. It has long been suggested that the [FeII] emission in starburst galaxies can be used as a measure of supernova (SN) activity. M82 shows a large number of radio supernova remnants (SNRs), approximately 50, lying in the plane of the galaxy. The comparison of the positions of the bright compact [FeII] emitting regions with the location of the radio SNRs shows that there is no one-to-one spatial correspondence between the two emissions, suggesting that the radio and [FeII] emissions trace two populations of SNRs with different ages. Young (a few hundred years) SNRs are best traced by their radio emission, whereas the [FeII] stage lasts for at least a few 10⁴ yr. The compact [FeII] sources contribute only some 20 % of the total [FeII] emission observed in M82. However, much of the remaining unresolved [FeII] emission in the plane of the galaxy may arise from SNRs that expanded and merged into a general interstellar medium within a few 10⁴ yr. Presumably, as much as 70% of the total extinction-corrected [FeII]1.644 μm in M82 is associated with SNRs. The extended and diffuse [FeII] component in M82 seems to be related with the superwind above and below the disc of the galaxy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinematics of Gas and Stars in 20 Disc Galaxies

In this paper we present the kinematics of the gas and/or the stars of a sample of 20 disc galaxies. We investigate whether there is any relation between the kinematics of the gas and stars and the classical morphological type of the galaxies in the sample. We deduce that, in most of the late-type spirals we have studied, the stars and the ionized gas are moving with virtually circular velocity, except when the spectroscopic slit crosses a bar region. On the other hand, we found in the central parts of early-type disc galaxies a wider variety of different behaviour of stars and gas. We find many possible factors that complicate the classification of the kinematical properties of the galaxies by their morphological type: the presence of counter-rotations (star vs. stars or star vs. gas), misalignment between the different kinematic components present in the galaxy, the presence of a bar structure and its orientation with respect to the line of nodes of the galaxy, and interactions and mergers or external accretion processes are some of the problems we find in the study of the kinematics of a galaxy.     

CCD Polarimetric Imaging Of Comet Hale-Bopp (C/1995 O1)

Polarimetric observations of the light scattered by dust have been carried out at Pic-du-Midi Observatory with the 2 m telescope in June and September–October 1996, and at Haute-Provence Observatory with the 0.80 m telescope in April 1997. They cover a total number of 11 nights and a large (6.9°–47.7°) phase angle range. The spatial resolution allows to underline structures in the coma, as well in the brightness images as in the polarization maps, with a correlation between the regions of bright structures and the regions of higher polarization. A clear difference appears between the sunward and antisunward side, with higher polarization on the antisunward side. The phase angle coverage allows us to obtain a polarimetric phase curve for the whole coma and to compare it with other cometary phase curves. The degree of polarization is higher for Hale-Bopp than for the comets previously observed. This revised version was published online in July 2006 with corrections to the Cover Date.