摘要:

Knowledge of the absolute, versus relative, performance characteristics of VHF and UHF radars used in geophysical applications is often important. We suggest that the Moon may form a convenient, easily tracked calibration target for many such radars. The lunar absolute radar scattering crosssection is large, reasonably well known (∼7% of the visible disk) and is essentially wavelength independent over 6 m>λ>1 cm. The Arecibo 430‐MHz radar system was calibrated using the Moon as the target. These measurements, which are discussed in detail, yielded cross sections of 4.0% and 4.6% for a special 6 W and the main 1.6‐MW transmitters, respectively. We develop and present the radar equation appropriate to all total power calibration procedures including the Arecibo “worst case” calibration. We also discuss error levels, the necessity for averaging to obtain valid cross sections, and other practical difficulties associated with the

ISSN:0048-6604    

DOI:10.1029/RS023i001p00001

年代:1988

数据来源: WILEY

摘要:

A mathematical model is presented which links the dynamical properties of microwave radio signal attenuation to the spatial rain rate structure of intensive showers. The theoretical relation found between attenuation and its rate of change is verified by radio wave propagation measurements on a satellite‐Earth path at 11.5 GH

ISSN:0048-6604    

DOI:10.1029/RS023i001p00013

年代:1988

数据来源: WILEY

摘要:

The Geophysics Laboratory of McGill University investigated the use of UHF‐EM transillumintion measurements in geophysics through the construction of a prototype 445‐MHz continuous‐wave transillumination instrument designed for underground use in geophysics. Test surveys with this instrument were conducted at the Big Nickel Mine in Sudbury, Ontario, to obtain through‐rock electromagnetic absorption rates. Measurements were made at several sites between underground drifts and the surface. The results of the field surveys indicate that the UHF‐EM transillumination technique is feasible and, under strictly defined field conditions, can provide useful information on the in situ electrical properties

ISSN:0048-6604    

DOI:10.1029/RS023i001p00023

年代:1988

数据来源: WILEY

摘要:

A new integral equation has been obtained for the attenuation factor of a radio wave launched by an elevated element, as the wave propagates over a radially inhomogeneous surface of varying height, with an elevated current element as a receiver. In the analysis use is made of the vector form of compensation theorem, using the concept of a real surface impedance on the irregular surface together with that of an equivalent normalized surface impedance in air, at points which follows the contour of the irregular surface. The new integral equation generalises previous work to treat arbitrary terrain, so that both gradual and sharp changes of terrain height, such as a cliff and a knife edge are considered. The validity of the integral equation has been tested theoretically by comparison with alternative solutions for particular cases, and also by experiment.

ISSN:0048-6604    

DOI:10.1029/RS023i001p00033

年代:1988

数据来源: WILEY

摘要:

An image method for computing the static magnetic field due to an arbitrary current injected into a conducting and polarizable half‐space is derived. The advantage of this approach is that the magnetic field is given in terms of a Biot‐Savart integral over only the impressed current sources and their finitely many images. Integration over the conducting currents, which are distributed in the entire conductive half‐space, is avoided. The magnetic field is evaluated in closed form when the conductors that feed current to the electrodes are laid out in a rectilinear

ISSN:0048-6604    

DOI:10.1029/RS023i001p00041

年代:1988

数据来源: WILEY

摘要:

We have developed a meteor echo detection and collection system (MEDAC) that can be attached to many ST or MST radars operating in the VHF range. The system can be operated in parallel with the normal data collection of turbulent echoes. The use of the meteor echoes extends MST mesosphere observations into the night and extends ST capabilities into the mesosphere and lower thermosphere. This paper describes the system and presents preliminary wind measurements using the Platteville, Colorado, ST radar.

ISSN:0048-6604    

DOI:10.1029/RS023i001p00046

年代:1988

数据来源: WILEY

摘要:

A brief discussion is presented of “forward” and “backward” electrostatic ion‐cyclotron waves in the high‐latitude ionosphere. The need for additional measurements by HF radars is

ISSN:0048-6604    

DOI:10.1029/RS023i001p00055

年代:1988

数据来源: WILEY

摘要:

Wind measurement by MST/ST radars may be accompanied by a systematic error due to a finite range volume effect which works when a thin turbulent layer is simultaneously located in several adjacent range volumes. The error occurs when the layer coincides with a cross section through the range volume which is not symmetric with respect to the center of the beam. The finite range volume effect appears as a false vertical shear of horizontal wind in a vertical scale of the order of a few hundred meters, even if the ambient wind field is uniform. The false wind shear sometimes exceeds 40 ms−1km−1in magnitude or the critical value to induce the Kelvin‐Helmholtz instability. Also the effect leads to a false temporal variation of the wind measurement, although the wind field does not change at all. The false wind shear with a magnitude less than 40 ms−1km−1cannot be discriminated from a true one in the observed data. It seems hard to indicate directly that the finite range volume effect appears as theoretically conceived. Judging from wind velocity and echo intensity data obtained by the MU radar in Japan, this effect appears quite frequently in the atmosphere. The small vertical scale wind shear as well as the temporal variation found only at a specific range should be treated with great care except when the ambient wind field is weak, where the finite range volume effect is not so

ISSN:0048-6604    

DOI:10.1029/RS023i001p00059

年代:1988

数据来源: WILEY

摘要:

A finite range volume effect causes a systematic error in MST/ST radar wind measurement when a thin turbulent layer is simultaneously located in several adjacent range volumes. This error appears as a false vertical shear of horizontal wind or as a false temporal wind variation at some ranges even if the ambient wind field is uniform with height and does not change at all. Also, because of this effect the observed Doppler power spectrum becomes asymmetric, and a noticeable error is induced in estimation of echo power, mean Doppler velocity, and spectral width. The present investigation will show that these errors are well explained by a simple numerical model which is made to simulate an actual observational situation. The observed wind velocity is more reliable at ranges where the echo intensity is relatively larger compared with adjacent ranges. The finite range volume effect is negligibly small for weak ambient wind velocities less than approximately 10 ms−1and/or for an antenna beam width less than one degre

ISSN:0048-6604    

DOI:10.1029/RS023i001p00074

年代:1988

数据来源: WILEY

摘要:

It has recently been suggested that the observed tendency for intense turbulence to occur in thin layers in the atmosphere introduces an error in horizontal wind measurements with MST radars, even in the absence of wind shear. This effect, called the finite range volume effect, is a consequence of the tilted pulse volume when using the Doppler technique. A model is shown which illustrates that this effect may be very important in MST radar measurements when wide antenna beam widths are used. These model results are supported by observations performed with the MU radar in Japan, where wind measurements with different beam widths have been performed. The impact of these measurements on MST radar design and possible methods to minimize the error are discussed.

ISSN:0048-6604    

DOI:10.1029/RS023i001p00083

年代:1988

数据来源: WILEY