High-resolution Channel Research Articles

A low sidelobe technique for the direct measurement of scattering functions

Effective communication and echolocation depends strongly upon the coherence of the channel through which the signal is propagated. Under certain conditions, the average coherence or equivalently, the spreading of a random channel may be described by a scattering function (SF). This represents a second order (energy) measure of the average delay, Doppler, and more generally, the spatial (azimuthal) spread that the signal experiences. The SF is analogous to the point spread function (PSF) discussed in the image processing literature and likewise describes the amount of "blurring" imposed upon the signal or scene transmitted. The SF will be briefly reviewed and its measurement by both direct (high resolution channel probing) and indirect (deconvolution) methods will be discussed. A new direct method using specially designed waveform pairs and a twin or uncertainty product (UP) receiver structure is introduced. Unlike high resolution matched filter implementations for direct probing that are limited by the fixed volume constraint of ambiguity functions, the UP receiver produces vanishing sidelobes and hence more nearly approximates a desirable two-dimensional delta characteristic. The improvement gained in SF measurement is illustrated by the results of an experiment in which the UP receiver and traditional matched filter implementations were used to directly probe an ocean multipath channel.

CCS Observations of the Protostellar Envelope of B335

We present single-dish and interferometric spectral line observations of CCS at 22 GHz toward the core of B335, a classical example of a young protostellar region. We combined the VLA and DSN 70 m observations to produce high-resolution (6'' and 12'') channel maps at 0.04 km s-1 velocity intervals. These maps image for the first time the collapsing envelope around the protostar. These show that CCS emission arises primarily from the outer parts of the collapsing envelope down to half the infall radius and that CCS is clumpy throughout the core. LVG excitation analysis indicates that X(CCS) is ~3 × 10-9 in the outer envelope and less than 5 × 10-11 in the center of the infall region. The absence of CCS in the interior could be due to time-dependent chemical evolution. The velocity structure supports the evidence for inside-out collapse and the high-velocity features are consistent with accretion onto a rotating central disk. The asymmetric clumpy distribution of CCS emission implies that the physical conditions are not spherically symmetric, and that the gas falling onto the circumstellar disk may be episodic.

Optimized thermal neutron source for neutron radiography with a static DIANE device

The mobile neutron radiography DIANE device presented during the previous Denton accelerator conference and operating at Loral Vought Systems Corporation (USA) and IABG (Germany) is now also developed as a static device with a high resolution channel for parts inspection. For this purpose an optimized moderator has been designed which allows improvement in the thermal neutron flow. The theoretical approach and first experimental results are presented.

MOS - Modular optical scanner for remote sensing of oceans and atmosphere

For remote sensing of the oceans and the atmosphere 2 multispectral optoelectronic imaging spectrometers MOS are developed. They shall be utilized on board the Soviet orbital station MIR as part of the international environmental module PRIRODA in 1992. In order to meet the experimental requirements for remote sensing of the oceans and the atmosphere with high spectral and radiometric resolution the following characteristics must be realized: MOS-A has 4 high resolution channels (1, 4 nm halfwidth) for measurement of the atmospheric scattering in the O 2-A absorption band near 760 nm to determine the optical thickness of aerosol, MOS-B has 13 medium resolution channels (10 nm halfwidth) in the VIS-NIR region for dense spectral sampling of the ocean reflectance signature with a spatial resolution of 0.7×0.7 km 2 from an altitude of 350 km. The optical part consists of commercially available optics and gratings, specially developed CCD-focal-plane arrays and an internal in-flight control unit. For absolute calibration in orbit the full sun can be used. The radiation intensities are measured in 2 sensitivity ranges for ocean and land regimes resp, with 12 bit resolution and a data rate of 32.256 kByte/s.

Comparative utility of microwave and shortwave satellite data for all-weather charting of snow cover

Charting snow cover by shortwave imaging requires visual analysis which is complicated by cloud coverage and poor surface illumination1,2. Microwaves, however, being almost unaffected by clouds and independent of solar illumination, are potentially useful for monitoring the extent and variation in snow cover, in climatological and hydrological studies. Data from spaceborne passive microwave sensors have previously been used to chart regional overland snow cover3–5; but charting hemispherical snow coverage was not feasible until high spatial resolution and multiple channels were combined in the Scanning Multichannel Microwave Radiometer (SMMR) launched in 1978 on the Nimbus-7 satellite. Here we compare SMMR data with shortwave images obtained over Asia to justify further use of microwave sensors in automated charting of seasonal snow cover under all weather conditions. Agreement between the two methods is found in ∼75% of the tested grid points.

224 CM Variable Energy Cyclotron at Calcutta

Progress of work on the construction of the 224 cm. Variable Energy Cyclotron, being installed at Calcutta is described. The cyclotron, with maximum expected energies of 70 MeV protons, 65 MeV deuterons and 130 MeV alphas, follows the design of the 88? cyclotrons at the Lawrence Berkeley Laboratory and the Texas A & M University, with some modifications incorporated for facilitating indigenous fabrication and for improved performance. The yokes and yoke legs of the 250 tonne magnet have been cast and tested for composition and porosity. The machining of yokes, yoke legs and pole pieces is under way. The main coil winding has started. The trim and valley coils will be epoxy potted. The rf system, utilising the RCA 6949 oscillator tube, is a combination of a self-excited and a driven system. Power supply fabrication is nearing completion and two 89 cm diffusion pumps have been fabricated for the vacuum system. The building is in the final stages. Beam transport layout envisages three high intensity and six high resolution channels. A small 8k on-line computer is being planned. Various other facilities are also being planned.

An Experimental Approach to Video Bandwidth Compression by Multiplexing

A system is described, which is based on structural and perceptual redundancy. It employs the idle periods of one picture to introduce information from other pictures and integrates over several TV frames. The system is capable of multiplexing 15 high-resolution black and white TV channels.