Characteristics Of Radar Echoes Research Articles

Raindrop-size Distribution from Individual Storms

Raindrop data from 34 storms, taken at the University of Miami, Florida, using a raindrop camera, have been analyzed. The relationship between the parameters A and b of the radar reflectivity equation Z=ARB, and the type of drop-size distribution has been investigated. Parameters A and b control not only the pattern of the family of size-distribution curves but also the type of the individual curves. Cases have been plotted against logA and b as rectangular co-ordinates. Reviewed in relation to rainfall types, these showed thunderstorms occupying a region of larger A (300 to 1000) and moderate b (from 1.25 to 1.65). Both A and b are smaller for rainshowers; for continuous rains the value of b ranges widely, from 1.0 to 2.0, while A never exceeds 600. The same sort of data-display has been reviewed in relation to radar echo characteristics to provide a more comprehensive and continuously varying relation between the parameters and the storm-pattern characteristics.

Coordinate method of converting radar echoes to digital form

Radar echoes can be converted to digital form by means of a sequence of (x, y) coordinates obtained around the periphery of the echo. Procedures for computing echo areas and centroids from the (x, y) coordinates are presented. Computations are made by a high-speed computer. Other radar echo characteristics can also be computed and summarized.

Field-alignedE-region irregularities identified with acoustic plasma waves

This paper describes some measurements related to the nature of field-aligned irregularities in the E region. The measurements were performed near the magnetic equator, and the irregularities are attributed to the equatorial electrojet. It is shown that the irregularities are most likely to consist of plane acoustic waves generated by an instability resulting from the flow of current in the electrojet. Reference is made to a recent theory of Farley in which the existence of such waves is predicted. The characteristics of auroral radar echoes are shown to be similar to those of the equatorial echoes. It is inferred that the auroral field-aligned irregularities are also caused by the flow of electrojets.

Some radar observations of meteors and aurorae at 300 and 500 Mc/s using a large radio telescope—I Observations of meteors

Abstract The characteristics of radar echoes from meteor trails have been studied at 500 and 300 Mc/s with a high power transmitter used in conjunction with a large radio telescope. At the higher frequency the sporadic meteor rate varied between one every few hours up to about two per hour depending on the elevation of the beam, the time of year and the time of day. During the Perseid meteor shower the average rate increased to about three times the sporadic rate. At the lower frequency the sporadic rate was about twenty times that at 500 Mc/s. It is concluded that the echoes arose from meteor trails having initial linear densities in the region 10 13 –10 14 electrons per cm. A class of echoes has been identified in which the specular condition for reflection is relaxed. The echoes were characterized by a symmetrical rise and fall of amplitude in time. It is believed that these echoes were obtained from short lengths of highly ionized trail moving immediately behind the larger meteors and that the amplitude variation arose from either the reradiating polar diagrams of the short trail or the main beam of the aerial.

The electrical characteristics of the atmosphere and surface of Venus from radar observations

Radar observations of Venus were made at wavelengths of 12.5 cm and 68 cm during several months around the 1961 inferior conjunction. These observations have been quantitatively compared for possible dispersion effects caused by the atmosphere of Venus and the interplanetary medium. A possible effect of the plasma has been observed at 68 cm through correlations of the radar echo characteristics with solar activity. On the assumption that this correlation was real, a crude model for the ionosphere of Venus has been developed. The model yields a maximum electron density at Venus of order 10 7 cm −3 corresponding to a plasma frequency of about 27 Mcs. The absence of relative dispersion and absorption effects between the two propagation frequencies is interpreted to indicate that all plasma phenomena were small, however. In particular, the proposed “ionospheric” model as the source of the Venusian radio spectrum is shown to be inconsistent with the radar observations. An analysis of the observed echo power indicates the average dielectric constant of the Venusian surface material to be less than 7 but greater than 3 with no large upward variations during the observations. This low value of the dielectric constant and the absence of measurable variations in the echo power (and consequently, in the dielectric constant) is interpreted to indicate that there are no large bodies of water on the Venusian surface.