Indirect atmospheric measurements utilizing rake tropospheric scatter techniques—Part I: The rake tropospheric scatter technique

A computer‐controlled, coded‐pulse, step frequency, oblique sounder has been designed to probe the HF radio communication channel to a bandwidth of 1 MHz. The instrument monitors the complex pulse response of the channel over an extended period of time thus permitting simultaneous observation of the time and frequency behavior of the channel. A coherent time history presentation of the wide band data permits unequivocal identification of individual modes in situations involving several partially overlapping modes. Channel instantaneous bandwidth and mode Doppler shift can be estimated by inspection of the pulse response time history curves. Data presentation in the wide band time history format is also very informative in the description of signal fluctuation phenomena and in understanding their underlying causes. Measurements have been made over a short‐baseline (126 km), mid‐latitude path between an island off the southern California coast and the mainland. The response of the one‐hop F2 layer sky wave mode to a 1‐μs probing pulse is used to illustrate the unique capabilities of this instrument and the unusual effects that are observed with a high‐resolution probing pulse.

Section: Introductionmentioning

confidence: 99%

High‐resolution probing of the HF ionospheric skywave channel: F₂ layer results

Wagner¹,

Goldstein²

1985

“…The correlators employ synchronous radio-frequency detection, so that the Doppler spectrum can be measured at each of the 10-path delay outputs. Barrow et al [1968Barrow et al [ , 1969.) This power profile indicates a strong scattering or reflecting region at a relative delay of about 0.4 vsec at zero Doppler shift.…”

Section: Experimental Progressmentioning

confidence: 98%

Review of Techniques in Transhorizon Propagation Research and their Relationship to Parameters of the Troposphere

Cox¹

1969

Transhorizon propagation techniques and their usefulness in determining atmospheric parameters are discussed. It is concluded that the state or structure of the atmosphere cannot be inferred unambiguously from individual measurement techniques used in experiments reported to date. However, because of the sensitivity of the transhorizon radio signals to changes in the parameters of the troposphere, it is suggested that combinations of available techniques be pursued to determine the parameters uniquely.tional Academy of Sciences, Committee on Atmospheric Sciences, and was presented to the Panel in March 1968. Drift (wind) and internal motions as theyaffect the Doppler spectrum or fading of the radio signals; 2. Statistical characteristics or properties of the random fluctuations o.r variations in the atmosphere as they are related to frequency and angular dependence of the mean scattered power; 3. Nonuniformities in the statistical characteristics of the atmosphere such as inhomogeneity or anisotropy (including stratification tendencies) that exist to a scale resolvable by the measuring devices (sometimes antennas) or the technique. Much of the early work in transhorizon radio propagation was concerned with communications system applications, and the parameters measured in the experiments were usually averaged over long periods of time (many hours or even days) and over large regions of space (sometimes from just above the earth's surface to the top of the sensible atmosphere). These measurements were not very useful for determining atmospheric characteristics at any given time or location in space. For an experiment to be useful in determining atmospheric parameters, all information necessary for their determination should be contained in the radio measurements or in other measurements made simultaneously; that is, it should not be necessary to include in the interpretation any assumptions that are not supportable by the measurements themselves. Experiments that deal entirely with parameters of use only to communications system designers are not included in this review. Thus this review concerns itself with the subject of transhorizon propaga-905 906 DONALD C. COX tion only as it relates to the parameters of the atmosphere. BRIEF REVIEW OF THE THEORY Theories that attempt to describe transhorizon propagation phenomena can be classified into two groups. The models used to describe the variations or fluctuations in the refractive index of the asmosphere are the major distinguishing features of the groups. Turbulence theories. By far the greatest effort expended in describing transhorizon propagation phenomena has been based on a statistical description of turbulence in the atmosphere. A rather extensive review of this subject can be found in Staras and Wheelon, [1959]; it has been treated by many authors [e.g., ]. In this approach, the refractive index (or dielectricpermittivity) fluctuations are described as a small random change about mean level. Early work [e.g., Booker and Gordon, 1950] dealt with the time fluc...

“…In a bistatic system this region takes the shape of an ellipsoidal shell, since the surfaces of equipath delay are ellipsoids of revolution with the radio terminals as loci and the baseline between terminals as the axis of revolution (the beam-delay case). A related experiment based partially on delay resolution has been implemented [Barrow et al, 1969]. The third is a monostatic radar for which the common scatter volume is defined by the common transmitter-receiver antenna beam and the spatial region (spherical shell) of a constant range of path delay (the radar case).…”

mentioning

confidence: 99%

Imaging properties of monostatic and bistatic troposcatter radars

Lammers¹

1973

Three tropospheric scatter systems, featuring antenna-beam angular discrimination, or a combination of both antenna-beam angular discrimination and signal-delay temporal discrimination, are compared for sensitivity and spatial resolution as determined by theoretical calculations. Two of the radars used are bistatic; the third is monostatic or quasi-monostatic. Whenever practical, parameters are chosen equal for all three radars. The linear dimensions of the scatter volume and its size as a function of position in space are determined. The imaging properties of each radar are analyzed after the scatter integral (received power level) is numerically evaluated using a tropospheric multiple-layer model of turbulent refractive-index structure. Results are presented for a 500-km baselength in the bistatic case. Double layers of 100-m vertical width and 500-m vertical separation are displayed as seen with the angular beam resolution of 0.15 ø (between 3-db points) and 40-nsec temporal resolution corresponding to a 25-MHz system bandwidth. INTRODUCTIONElectromagnetic scatter systems have long proved their worth in remotely analyzing refractive-index structures of the troposphere. Weather radars responding to matter that is a condensate (cloud and precipitation particles in the liquid or frozen phase) are in common use. The scattering of gaseous inhomogeneities in the air, which at radio frequencies is due mainly to the water-vapor content and the temperature and pressure composition of the air, is the subject of extensive research that has already resulted in a better understanding of meteorologic processes [Hardy and Katz, 1969;Konrad, 1968; Ottersten, 1969; Richter, 1969] and will ultimately allow detection of such essential parameters as hazardous velocities and turbulences in the air.The performance of a scatter system in analyzing the gaseous refractive-index structure of the air is measured by three criteria' temporal resolution, spatial resolution, and sensitivity. This report deals with the latter two characteristics with reference to static models of the troposphere.Evaluation of the scatter integral for volume scattering from a refractively turbulent medium is quite involved, particularly in the bistatic case, due to the complicated shape of the scatter volume and the Copyright ¸ 1973 by the American Geophysical Union. 89 variability of most factors contributing to the scattering process. In the past, generally, simplifying assumptions were made about these parameters and were justified, for example, when calculating received-power levels in widebeam transhorizon communication links [Du Castel, 1966]. A statistical approach [Atlas et al., 1968] has given a somewhat refined analysis of forward-scattered power in a highresolution system. For a detailed evaluation of the mapping capabilities of scatter radars, however, such approximations are not satisfactory. The results presented in this paper are accurate, except for the constraint that narrowbeam antennas were used. The integration techniques, particularly t...