摘要:

Radars have had a long and illustrious history in the investigation of the atmosphere. Beginning with verification of the existence of the ionosphere in the mid‐1920's [Appleton and Barnett, 1925;Breit and Tuve, 1926], radars have been operated in monostatic and bistatic modes to probe the atmosphere and have acquired names such as bottomside or topside ionosonde, meteor radar, auroral radar, meteorological radar, incoherent scatter radar, etc. It is therefore remarkable that such an old technique would warrant a special issue ofRadio Sciencein 1980. The reason seems to be that the scientific community was slow to recognize and exploit the potential of radar for sensing the nonionized clear atmospher

ISSN:0048-6604    

DOI:10.1029/RS015i002p00147

年代:1980

数据来源: WILEY

摘要:

It is now 15 years since radars were first used intensively to probe the atmosphere in clear‐air conditions. The first experiments were concerned with the nature of the targets and accounting for the intensity of the measured echoes. It was found that inhomogeneities in the refractive index field were responsible for a large proportion of clear‐air returns. Such returns were detected in characteristic patterns in association with sheared statically stable layers, convective thermals, air mass boundaries, and a variety of wave structures. More sensitive Doppler radars have been developed in recent years which are able to obtain usable signals from all heights in the troposphere. Such radars, as well as providing additional information about the clear‐air patterns observed previously, enable continuous measurements of wind profiles to be made. This paper describes the phenomena which have been observed and the measurements which have been made with radars under clear‐air conditions. A summary is given of the types of targets observed, and the kinds of radars used in clear‐air studies are briefly

ISSN:0048-6604    

DOI:10.1029/RS015i002p00151

年代:1980

数据来源: WILEY

摘要:

The use of high‐power radars for the observation of air motions and the occurrence of turbulence in the vicinity of the tropopause is reviewed. A model is presented for the interpretation of radar observations from the thin turbulent layers which occur in the stable regions of the upper troposphere and lower stratosphere. Radar observations are shown to be potentially important for the study of the transport processes that operate between the troposphere and the stratospher

ISSN:0048-6604    

DOI:10.1029/RS015i002p00177

年代:1980

数据来源: WILEY

摘要:

This paper reviews radar studies of the middle atmosphere at VHF and UHF frequencies. The mechanisms responsible for the scattering at both stratospheric and mesospheric heights are qualitatively discussed, and an attempt is made to evaluate the potential of the technique for inferring atmospheric parameters. A few applications of the technique to the study of atmospheric dynamics are then presented. Finally, some recommendations are made for future work.

ISSN:0048-6604    

DOI:10.1029/RS015i002p00195

年代:1980

数据来源: WILEY

摘要:

We describe the basic configuration of the Poker Flat, Alaska, MST (mesosphere‐stratosphere‐troposphere) radar currently under construction by NOAA's Aeronomy Laboratory. This 50‐MHz coherent radar consists of a 4 × 104m2phased dipole array, a 6.4‐MW peak power transmitter system (consisting of 64 separate 100‐kW peak pulse power transmitter modules distributed throughout the array), and an on‐line Doppler analysis/data recording system. With some limitations the system will be capable of measuring winds, waves, and turbulence throughout the 1‐ to 100‐km height range. Data obtained from the portion of the Poker Flat system already in operation are present

ISSN:0048-6604    

DOI:10.1029/RS015i002p00213

年代:1980

数据来源: WILEY

摘要:

A large MST radar for observing backscattering from refractive index fluctuations in the middle and upper atmosphere is now under design in Japan. The proposed system is a pulse‐modulated monostatic radar, working at a frequency near 48 MHz. The configuration will be quite different from the existing MST/ST radars. A quasi‐square array with an aperture of 104m2is composed of 456 Yagi antennas, each of which is provided with a low‐power amplifier. A peak output power of more than 1 MW is envisaged to be generated when the whole system is coherently activated. In this system a phase shift is obtainable at a low power level by variable phase shifters controlled by electronic means, which enable rapid and continuous scanning of the antenna. The whole system is monitored and controlled by a microcomputer ne

ISSN:0048-6604    

DOI:10.1029/RS015i002p00225

年代:1980

数据来源: WILEY

摘要:

The 53.5‐MHz radar of the Max‐Planck‐Institut für Aeronomie (SOUSY‐VHF‐Radar) was specifically designed for the study of the dynamics of the troposphere, stratosphere, and mesosphere including turbulence and other small‐scale phenomena. Transmitter and receivers were designed for a pulse width and altitude resolution of the order of 75–150 m. Such high resolution corresponds to sampling rates of the order of 2 million complex samples per second. Maximum sensitivity calls for the use of coded pulse schemes (pulse compression). The digital decoding and processing requirements of such a high information rate are beyond the capabilities of a general purpose digital computer and demanded a special purpose preprocessor. A programable preprocessor was designed and built, and it is the subject of this paper. It can decode an arbitrary sequence and perform coherent integrations for as many as 1024 altitudes. The coherent integration reduces the data rate into the computer to reasonable values. Also, by performing the coherent integration before decoding (they are linear operations and can be permuted), the necessary decoding operations in the preprocessor are reduced by 2 orders of magnitude. The master controller for the device is programed by a 1024 4‐bit instruction PROM. There are 16 different instructions allowing the necessary flexibility for different code and sampling schemes. The transmitter and analog‐to‐digital converter are also controlled by the same device. Stratospheric and mesospheric echoes obtained with the help of this device are presented for illustration. The detection of layers as thin as 150 m or less at both stratospheric and mesospheric heights justified the efforts to achieve the maximum

ISSN:0048-6604    

DOI:10.1029/RS015i002p00233

年代:1980

数据来源: WILEY

摘要:

With the advent of the MST (mesosphere‐stratosphere‐troposphere) radar technique the atmosphere from 0 to 100 km can be observed with a single radar system. Several different mechanisms have been identified as causing the echoes observed by MST radars. Two primary mechanisms are scattering from turbulent irregularities and Fresnel (or partial) reflection from horizontal strata. Two additional mechanisms that apply primarily to the upper mesosphere are meteor scatter and thermal (or incoherent or Thomson) scatter. Below the stratopause the refractive index structure responsible for the echoes arises solely from neutral atmosphere fluctuations; above the stratopause the radar cross section of such fluctuations is enhanced by the presence of free electrons (moreover, in the absence of small‐scale neutral fluctuations the electrons alone can provide the scattered signal). This paper is an attempt to unify the scattering and reflection theories in the light of observational st

ISSN:0048-6604    

DOI:10.1029/RS015i002p00243

年代:1980

数据来源: WILEY

摘要:

Very high frequency (VHF) radar echoes received with a quasi‐vertical antenna beam from the troposphere and stratosphere are caused by reflection and scattering. The essential difference between these mechanisms is described by different atmospheric refractivity structures, viz., stable laminae and turbulent irregularities. Several methods for discriminating between reflection and scattering are described and tested experimentally. These involve comparing estimates of the reflection coefficient and the turbulence refractive index structure constant using acceptable models. They also involve the wavelength and volume dependence, as well as the angular distribution of the radar echoes. Doppler spectra, phase and amplitude distributions, temporal and spatial correlation functions, and the dependence between radar echo power and coherence are examined. Diffuse reflection from refractivity laminae, corrugated by turbulence, appears to be an appropriate model for many observations. Finally, the implications of this process for VHF radar investigations of the atmosphere are outline

ISSN:0048-6604    

DOI:10.1029/RS015i002p00259

年代:1980

数据来源: WILEY

摘要:

In the derivation of Booker‐Gordon scattering cross sections in a turbulent atmosphere, certain assumptions have been made so that the power scattered within the scattering volume will add coherently. This results in a scattered power that is proportional to the effective scattering volume. As the scattering volume increases without bound, it leads to a physically unreasonable result of infinite scattered power. In this paper we examine these assumptions. In particular, we study the scattering cross sections, taking into account the possible phase incoherence of the scattered fields within the scattering volume. In addition, the effect of a thin turbulent layer on the complex autocorrelation function is investigated. The turbulence is assumed to be locally frozen. Expressions for both the Doppler shift and the correlation time have been derive

ISSN:0048-6604    

DOI:10.1029/RS015i002p00277

年代:1980

数据来源: WILEY