摘要:

AnX‐band radar designed and built by the Naval Research Laboratory and capable of continuously variable transmitted pulse durations down to 1 nsec is being flown on a NASA Wallops Flight Center C‐54 aircraft to investigate the interaction of radar altimeter signals with the sea surface. There is good agreement between the observed radar altimeter leading edge rise time for a 1‐nsec transmitted pulse and the rise time predicted from the radar parameters and the sea state determined by a laser profilometer. Using a threshold tracker on 29‐pulse averages for a transmitted pulse of 24 nsec, we found that the range noise varied linearly with the power level of the threshold over a considerable range. The altimeter range quantization was 9.35 cm and a minimum range noise of 3.9 cm was obtained. A comparison of pulse‐to‐pulse correlation observed in the radar data with that predicted by a Monte Carlo simulation is used to obtain a measure of sea surface scatt

ISSN:0048-6604    

DOI:10.1029/RS009i008p00711

年代:1974

数据来源: WILEY

摘要:

Spherical wave weak‐scattering propagation theory is employed to show that the resolution of multifrequency atmospheric probing techniques is limited to inhomogeneity scale sizes that are larger than a certain cutoff scale sizelc. The magnitude oflcdepends on the frequency separation and the path geometry. Inhomogeneities smaller thanlccannot be resolved and inevitably contribute to measurement errors. Propagation experiments performed at radio and acoustic wavelengths confirm the existence of the predicted cutoff and are in good agreement with the theory. An example is given to illustrate how this cutoff limits the ultimate accuracy of a radio‐optical comparison measurement aimed at determining path‐averaged water vapor varia

ISSN:0048-6604    

DOI:10.1029/RS009i008p00723

年代:1974

数据来源: WILEY

摘要:

The results of the dispersion analysis of the spaced receiver records of fading for an equatorial station in the Indian zone are discussed. It is shown that the apparent drift speed increases almost linearly with the frequency of fading in all the cases studied for both theEandFregions. The dispersion of drift speed is larger for theFregion than for theEregion in general. Furthermore, theFregion shows a larger dispersion during the daytime whereas it is of the same order in the day and nighttimes for theEregion. The drift speed corresponding to the highest Fourier frequency present in a particular record is found to be close to the apparent drift speedVaas determined from the shift of the peak of cross correllograms while the total frequency spread of the speed is linearly related to the random drift speedVcderived by the full correlation analysis.Several possible causes of dispersion in the ionosphere such as gravity waves, independently moving reflecting screens, height gradient of the horizontal drift and size of irregularities, the dispersive nature of the vertical drift velocity, and the variability of the drift during the course of record are discussed. Interference of the signals reflected from two or more highly aspect‐sensitive areas in the ionosphere is suggested as a possible mechanism resulting in the positive and linear dispersion observed on the ground at an equatorial statio

ISSN:0048-6604    

DOI:10.1029/RS009i008p00733

年代:1974

数据来源: WILEY

摘要:

Tests are performed over a 4300‐km path to determine the accuracy of reverse path loss estimates using the step‐frequency sounder of the Navy Tactical Sounder System. The objective is to develop computational techniques for real‐time estimates of communication channel performance. Experimental results are presented which indicate the statistical performance of several path loss estimation techniques. It is concluded that, for Navy applications, reverse path loss can be predicted to within 6 db for 90% of the

ISSN:0048-6604    

DOI:10.1029/RS009i008p00741

年代:1974

数据来源: WILEY

摘要:

The effect of the daily variability off0F2andhmF2on the propagation conditions of an HF communication circuit has been studied in an empirical manner. The daily variability off0F2andhmF2was determined by a detailed statistical analysis and the results were incorporated into a three‐dimensional ionospheric model and ray‐tracing program. During hours surrounding local noon, the relative day‐to‐day changes seen in bothf0F2andhmF2are comparable while at all other times the daily variability off0F2substantially exceeds that ofhmF2. In terms of HF propagation changes resulting from these changes inf0F2andhmF2, it can be concluded that a knowledge of the critical frequency of theF2region is much more important than that ofhmF2if account must be taken of the propagation changes resulting from the normal daily variability of theF

ISSN:0048-6604    

DOI:10.1029/RS009i008p00749

年代:1974

数据来源: WILEY

摘要:

Normal‐run magnetograms for the year 1967 from seven Canadian observatories were scaled to study the amplitude characteristics of Pc 5 pulsations. The results of the statistical analysis are: (1) Large amplitude Pc 5's occur in a limited region located on the poleward side of the auroral zone. (2) The diurnal variation of Pc 5 amplitude maximizes in the postnoon period at Resolute Bay and this peak tends to appear earlier and earlier in the day at the lower latitude stations, e.g., it appears in the morning at Great Whale River. An additional midnight peak in the diurnal variation of amplitude is noted at auroral zone stations. (3) The amplitude attains a maximum value at Great Whale River near the central line of the auroral zone. It decreases at a faster rate toward the lower latitudes than toward the higher latitudes. In quiet intervals an additional peak in the amplitude‐latitude profile is noted near the cusp region at Baker Lake. (4) The diurnal variation pattern of amplitude shows no clear relationship with the seasons or with magnetic activity. (5) Under disturbed magnetic conditions a much larger amplification of the amplitude of Pc 5's has been at Great Whale River than at high or low latitude stations. Pc 5 amplitudes correlate very well withKpup to a level of 6−. (6) With increasing solar elevation angle the region of maximum amplitude of Pc 5 is found to move toward the northern border of the auroral zone. (7) From the data analyzed, amplitudes of Pc 5 do not show a 27‐day recurrence t

ISSN:0048-6604    

DOI:10.1029/RS009i008p00757

年代:1974

数据来源: WILEY

摘要:

High resolution incoherent scatter electron density data using Barker‐coded pulses are presented for two separate 24‐hr periods of very different magnetic conditions. The first period in April 1972 was magnetically quiet while the second period spanned parts of two of the five most magnetically disturbed days in July 1972. Solar activity was low with 2800‐MHz indices of 129 and 128 for the April days and indices of 109 and 117 for the July days. Contour plots and selected profiles are presented which show larger sporadic‐Elayers and stronger gravity wave effects during the disturbed night than during the quie

ISSN:0048-6604    

DOI:10.1029/RS009i008p00769

年代:1974

数据来源: WILEY

摘要:

Measurements on laminar and turbulent flames indicate that refraction effects can be calculated in a turbulent flame if the refractive index is assumed to depend on the mean electron density. Refraction effects are important when incoherent scattering cross sections of turbulent wakes are calculated at small aspect angles. Incoherent cross sections were measured at aspect angles of 20° and 40°, for backscatter and bistatic scatter. The measured cross sections deviated from a square‐law dependence on electron density in a way that was not well accounted for by a refraction calculation. Both cross‐section data and spectral data agreed better with a “modified” refraction calculation in which some energy was said to scatter from the “shadow zone” predicted

ISSN:0048-6604    

DOI:10.1029/RS009i008p00777

年代:1974

数据来源: WILEY

摘要:

A Monte Carlo technique is described for finding the response of a horizontally stratified cold plasma to a plane impulsive wave at vertical incidence. The effects of electron collisions with neutral particles and a vertical magnetic field are included in the analysis. The technique is arrived at by replacing a continuous scattering process (by continuous we mean the electrons are uniformly distributed through any horizontal plane in the plasma ( with a sequence of scatters. All orders of scatter are computed from this sequence of scatters, and the Monte Carlo approximation to the exact solution is the sum over these orders of scatter. The method is applicable for any electron density functionN(z), collision frequency, or cyclotron frequency. The Monte Carlo solution presented here is valid only for small and intermediate values of time; the solution diverges for large values of time. The Monte Carlo method is applied to the uniform half‐space problem since there are exact and approximate analytical solutions to compare with the Monte Carlo result

ISSN:0048-6604    

DOI:10.1029/RS009i008p00789

年代:1974

数据来源: WILEY

ISSN:0048-6604    

DOI:10.1029/RS009i008p00799

年代:1974

数据来源: WILEY