摘要:

The ionospheric modification facility at Arecibo, Puerto Rico, has been used to study Langmuir waves excited in the lower ionosphere by a high‐power HF radio wave. Measurements of HF‐enhanced plasma lines have been made in the lowerFregion (<160 km altitude) and in theEregion using the 430‐MHz radar at Arecibo Observatory. These measurements complement observations made in the past at higher altitudes. Enhanced plasma line spectra observed in the lowerFregion peak at the so‐called “decay line” and contain additional spectral structure similar to that found in the upperFregion. In theEregion the spectra exhibit narrow peaks located at 430 MHz ±ƒHF, where ƒHFis the frequency of the modifying HF wave. While strong plasma line enhancements are commonly observed in sporadicE, only weak enhancements have been detected in the normal daytimeElayer. Candidate mechanisms for theEregion enhancements include the oscillating two‐stream instability and direct conversion of the HF wave int

ISSN:0048-6604    

DOI:10.1029/RS019i001p00383

年代:1984

数据来源: WILEY

摘要:

The Space Sciences Laboratory of The Aerospace Corporation is presently defining an experiment to test a loop antenna configuration for a VLF transmitter in the ionosphere. The primary objectives of the experiment are to validate existing models for radiation by a loop antenna and to study the performance of the antenna in the ionospheric plasma. A one‐third scale model of the antenna has been constructed. Impedance measurements have been made on the model in a 5‐m diameter space plasma simulation chamber at NASA Lewis Research Center. The measurements confirm that the reactance of the antenna in an ionospheric plasma is essentially identical to its free space self‐inductance. The effective series resistance of the circuit increases with frequency. The losses are attributed to power transferred to plasma turbu

ISSN:0048-6604    

DOI:10.1029/RS019i001p00395

年代:1984

数据来源: WILEY

摘要:

The behavior of a solid spherical probe immersed in a warm isotropic collisionless plasma, biased to plasma potential, and excited from an alternating current source, is investigated for frequencies below the ion plasma frequency. A hydrodynamic description of the plasma is used, together with absorptive boundary conditions for the electrons and ions at the probe surface. Expressions are derived for the alternating potential in the plasma, as a function of frequency, of radial distance, of probe radius, and of the plasma parameters. Much of this potential is due to ion acoustic waves, the amplitude of which depends strongly on the ratioRpof the probe radius to the Debye length. As soon asRpexceeds the ratio ƒ/ƒpeof the excitation frequency to the electron plasma frequency, the amplitude is reduced much below its value forRp= 0 corresponding to a point source. It is shown in particular that under some conditions, for values ofRpover a certain limited range, this reduction is independent ofRp. The smaller the ratio of the excitation frequency to the ion plasma frequency, the larger is this rang

ISSN:0048-6604    

DOI:10.1029/RS019i001p00400

年代:1984

数据来源: WILEY

摘要:

To support very long baseline interferometric experiments, the Jet Propulsion Laboratory has developed a system for estimating atmospheric water vapor path delay. The system consists of dual microwave radiometers, one operating at 20.7 GHz and the other at 31.4 GHz. The measured atmospheric brightness temperatures at these two frequencies yield the estimate of the precipitable water present in both vapor and droplets. To determine the accuracy of the system, a series of observations were undertaken comparing the outputs of two water vapor radiometers with the phase variation observed with two connected elements of the very large array (VLA). The results show that (1) water vapor fluctuations dominate the residual VLA phase and (2) the microwave radiometers can measure and correct these effects. The rms phase error after correction is typically 15° at a wavelength of 6 cm, corresponding to an uncertainty in the path delay of 0.25 cm. The residual uncertainty is consistent with the stability of the microwave radiometer but is still considerably larger than the stability of the VLA. The technique is less successful under conditions of heavy cloud

ISSN:0048-6604    

DOI:10.1029/RS019i001p00411

年代:1984

数据来源: WILEY

摘要:

The HF radar on Bribie Island, Australia, uses crossed‐fan beams produced by crossed linear transmitter and receiver arrays of 10 elements each to simulate a pencil beam. The beam points vertically when all the array elements are in phase, and is steerable by up to 20° off vertical at the central one of the three operating frequencies. Phase and gain changes within the transmitters and receivers are compensated for by an automatic system of adjustment. The 10 transmitting antennae are, as nearly as possible, physically identical as are the 10 receiving antennae. Antenna calibration using high flying aircraft or satellites is not possible. A method is described for using the ionospheric reflections to measure the polar diagram and also to correct for errors in the direction of pointi

ISSN:0048-6604    

DOI:10.1029/RS019i001p00423

年代:1984

数据来源: WILEY

摘要:

Electromagnetic wave propagation along a lossless, grounded, gyromagnetic slab, magnetized perpendicular or parallel to the ferrite‐air interface, is considered analytically for an arbitrary direction of propagation parallel to the slab surface. In addition to the usual surface waves, the present structure is found to support proper complex ones, which, corresponding to evanescent modes, carry no real power, but may store reactive energy. Propagation conditions are discussed and, also, dispersion relations and field intensity distributions for the supported modes are derived. A variety of related numerical results is presented in several plot

ISSN:0048-6604    

DOI:10.1029/RS019i001p00429

年代:1984

数据来源: WILEY

摘要:

On the basis of the experience obtained with the stationary SOUSY radar in the Harz mountains, a mobile VHF Doppler system was developed during the last two years. The electronic part is installed in a 20‐foot container and was tested for the first time during a joint experiment at the Arecibo Observatory (Puerto Rico) using a special log‐periodic aerial to illuminate the 300‐m dish. In 1982 this system was extended by designing a mobile phased antenna array with 576 Yagi elements. The grouping of the single Yagis, the feeding network, the phase shifters, the power splitters, and the transmit receive switch are described. A summary of results obtained during the first two campaigns is presented as well as a survey of future programs demonstrating the flexibility of this mobile s

ISSN:0048-6604    

DOI:10.1029/RS019i001p00441

年代:1984

数据来源: WILEY