Simultaneous three‐frequency (30, 401, and 800 Mc/s) radar studies of the aurora were made from a site in northern Scotland. A completely steerable 142‐foot‐diameter antenna was used at all frequencies, providing a 15° antenna beam at 30 Mc/s and identical scaled beams of 1.2° at 401 and 800 Mc/s. Detailed results on the position in space indicate that most echoes arise from a layerlike form of auroral scatterers whose thickness is about 10–20 km. The height distribution of the auroral return was peaked at about 100 to 120 km, but heights as great as 200 km were observed. The highest amplitude and greatest percentage of auroral echoes were found to arise from the intersection of the maximum of the visual auroral zone and the 100‐ to 120‐km orthogonality loci. Wavelength dependence and aspect sensitivity measurements at 401 and 800 Mc/s resulted in a power law dependence of λ7 and aspect sensitivity of 10 db per degree of off‐perpendicular angle. Interpretation of these results in terms of the Booker scattering formula indicates that the size of the irregularities is 45 to 90 meters along the magnetic field lines and 0.7 meter across the field lines. The wavelength dependence results from the 30‐ and 401‐Mc/s data indicate that questionable beam filling at 30 Mc/s introduces an unresolvable uncertainty of 45 db. The 30‐Mc/s aspect sensitivity results indicate an amplitude drop of 10 db per 5° of off‐perpendicular angle, or a length of the scatterers of 120 meters along the magnetic field line. Detailed comparison of magnetic activity auroral Doppler shifts and auroral echo amplitude indicates that the auroral Doppler spectrums and the amplitude of the echoes have a close relationship to the auroral current system. The auroral echoes seen at 401 Mc/s appear at times to be completely depolarized, possibly owing to Faraday rotation, but in general have a considerable degree of polarization retention. At 30 Mc/s, long‐range auroral echoes propagated by an intervening F‐layer reflection were seen as well as ground backscatter propagated by auroral sporadic E. The data indicate that the present theories for auroral scattering are insufficient to explain all the experimental characteristics observed. The plasma acoustic wave model developed for equatorial field‐aligned irregularities appears to fit most of the auroral data obtained but warrants further investigation.

During routine UHF auroral radar investigations an unusual daytime auroral effect has been discovered. It apparently occurs most frequently when: (1) the reflecting region is sunlit; (2) the atmosphere is undergoing its greatest change (early morning and late afternoon). There is a minimum of echo occurrence at noon when atmospheric conditions are stable. Daytime aurora is distributed over a larger region of space than the more commonly observed night‐time aurora. The night‐time and daytime echoes are labeled discrete and diffuse, respectively. They can be differentiated in several ways. Discrete echoes are identified by their relatively short duration, their occurrence only at night, and their orientation in the E‐layer along a plane at right angles to radar beam; hence, the echo does not shift in range with change in elevation angle of the radar antenna. Diffuse echoes last longer, occur only during the day, and are apparently oriented in the E‐layer along a plane almost parallel to the surface of the earth; hence, the echo does shift in range when the radar‐antenna elevation angle is changed. The primary effects of increasing the observation frequency are decreasing echo amplitudes and decreasing maximum off‐perpendicular angle. The observed aspect sensitivity and the wavelength dependence are interpreted in terms of the scattering approach of Booker. Using the experimental UHF results, a model of the underdense ionosphere has been developed consisting of irregularities which have dimensions of 0.1 meter across and 3.5 meters along the magnetic field lines. The echo results are compared with auroral zone effects, and described together with measurements of the frequency spectra (Doppler shift and spread) of an aurorally reflected continuous‐wave signal.

Auroral echoes have been detected using a radar at 106.1 Mc located at 43 ø geomagnetic latitude. The geometry of reflection for ionization aligned with the earth's magnetic field lines is such that, for a geomagnetic latitude of 43 ø, reflection can occur as high as 300 km. The results of these observations are presented, with an interpretation of the height of reflections and a discussion of the advisability of making low-latitude auroral echo investigations. Introduction--Considerable work has been done in the past on the investigation of the characteristics of auroral ionization by the radar technique. Much of this work has been at frequencies between 30 and 100 Mc [Curtie, Forsyth, and Vawter, 1953; Harang and Landmark, 1954(a); Booker, Garilein, and Nichols, 1955], and almost all of it has been at geomagnetic latitudes above 56 ø. Previous HF investigations of auroral echoes at the low geomagnetic latitude of 43 ø .have been conducted at only a very few locations to date [Leadabrand and Peterson]. This paper is a description of observations made at 106.1 Mc at a geomagnetic latitude of 43 ø .

Radar echoes from the moon have been observed at 400 Mc/s for the purpose of determining the scattering properties of the moon. The results go beyond the investigations of other authors who claim that the moon is a quasi‐smooth reflector having a range depth of less than 600 μsec. Results described in this report indicate that, although the moon behaves as a quasi‐smooth reflector in the 0‐ to 600‐μsec range depth, beyond this range the moon behaves as a uniformly rough scatterer, giving echoes out to 1 lunar radius or the limit of visibility of the moon's surface from the earth. An empirical fit to the integrated range versus time display provides an angular scattering law for each infinitesimal area of the surface given by: P(ϕ) ∝ [(sin  θ)/θ]20±6+1/10 A procedure for mapping the details of the moon's surface by radar, using range and Doppler shift coordinates, is suggested. This technique does not require angular resolution.