The analysis of radar echoes from the Moon

Rea, D. G.; Hetherington, N. S.; Mifflin, R.

doi:10.1029/jz069i024p05217

Cited by 30 publications

(20 citation statements)

References 10 publications

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“…For a smooth metal sphere (Po = 1) the echo power is reradiated isotropic ally and the value of g is 1.0 [Norton and Omberg, 1947]. As we have seen, the factor g is also unity in the case of a smooth dielectric sphere, but the scattering in this case is not isotropic and depends upon the dielectric constant k [Rea, Hetherington, and Mifflin, 1964].…”

Section: Theoretical Values Of the Cross Sectionmentioning

confidence: 60%

“…They refer to measurements made in the wavelength range 3 m to 10 cm and hence are roughly comparable. It seems that with the possible exception of the results published by Rea, Hetherington, and Mifflin [1964], non e of the values in tabl e 3 are close to the value that would be encountered by a landing vehi cle_ This follows because most authors have computed the average of the slopes e nco untere d when passing a vertical plane through the s urface. Thus, jn the geometric-optics approach, the mean slope ef> has been taken as…”

Section: Been Removed) Compared With the Best-fitt Ing Curves For Thementioning

confidence: 81%

“…If thi s is don e, th e di· rectivity factor g is automatically made the same as Gm. Rea, Hetherington, and Mifflin [1964] have pointed out that these approximations are certainly not valid for the case of a smooth dielectric sphere. 3.…”

Section: Theoretical Values Of the Cross Sectionmentioning

confidence: 99%

“…The simplest type of theory is one involving geometric optics and has been adopted by a number of authors [Brown, 1960;Muhleman, 1964;Rea, Hetherington, and Mifflin, 1964]. This has the virtue of avoiding a ditticulty encountered in the oth e r treat me nts, namely, that the reflection coe fficient will be a function of the angle of incidence and reflection .…”

Section: The Scattering Behavior Of An Irregular Surfacementioning

confidence: 99%

“…W e note that these airborne studies indicate that marked " quasi-specular" behavior is encountered only over deserts or moderately calm sea [Grant and Yaplee, 1957 Rea, Hetherington , and Mifflin [1964], and Daniels [1963b] have attempted to subtract out the diffuse component of the echo power before computing the slope. Differences also have arise n because most authors weight the values for the slope by the amount of area proj ected on to the mean surface asso ciated with that slope; yet others, e.g., R ea, Hetherington, and Mifflin [1964] weight by the actual amount of area at each slope.…”

Section: Been Removed) Compared With the Best-fitt Ing Curves For Thementioning

confidence: 99%

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Radar studies of the Moon

Evans¹

1965

J. RES. NATL. BUR. STAN. SECT. D. RAD. SCI.

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Accurate range measurements have been reported only by the group 'working at the Nava l Re· search Laboratory. Their most recent value for the mean center-to-center distance betwee n th e Earth and the Moon is 384,400.2 ± 1.1 km and is based upon a value for the Earth's radius of 6.378,170 m which seemed most cons istent with the observed diurnal variation in range.The absolut e cross section of the Moon has been determined over a wide range of wavelengths to a precision in most cases of ± 3 dB. Unfortunately, this uncertainty is too large to permit any definite conclusions to be drawn concerning the wavelength dependence in the cross section. The observations suggest th at the cross section remains cons tant at about 7 percent of the proj ec ted area of the Moon's disk at wavelengths in the range 1 cm to 1 m, and perhaps rises to 10 percent or higher at wavelengths in the range 1 to 10 m.Short-pulse observations ca n be used to exp lore th e angular dependence in the sca tterin g of radi o waves b y the lunar surface. Usefu l meas urem e nts have bee n tnade at wave le ngth s of 1130, 68,23, 10, and 3.6 em. The angu lar dependence has also been investigated at 8.6 mm , th ough here th e angu lar resolution afforded by a narrow pencil-beam a nte nna was e mployed. At all s ix 'wavele ngth s, it appears that part of th e ec ho arises from a hi ghli ght located at th e ce nt e r of the Moon 's visible disk_ A seco nd com ponent comes almost eq ually from th e re maining parts of th e surface. Th e divi sion of power in th e two compone nts changes mark ed ly as th e wavele ngth is red uced. At 68-cm wavele n gth, 80 percent of th e power is return ed fr om the highli ght , but at 8.6 mm only 15 percent ca n be associated with this co mp one nt. The angu lar power spec trum obse rved for th e power fro m th e highli ght also c ha nges with wavelength, indi cating that th e rm s slope of th e surface in c reases as th e wavelength is red uced. Th ese observations have been interpreted as indicat ing that there is a wid e range of structure sizes on the Moon.The deduced valu es of dielec tric co nstant ran ge from k = 2.79 down to k = 2.13. In view of th e greater experime nt al diffi c ulti es togeth e r with the doubtful validity of th e assumptions at 8.6-mm wavelength, this apparent wavelength dependence should be accepted with caution. If real, it may be ca used by the finit e co ndu ctivity of the mat erial (i.e., s "" a in (6)) or by inh omogeneity in th e surface layers -the den sit y pe rhap s in c reas ing sli ghtly with de pth. These val'ues ce rtainly indi ca te that th e surface is broke n or porous in texture -the material occupying perhaps about 30 percent of the available volume. In short, th e echo inte nsity and angular s pec trum is co mparable to that observed from aircraft over terrestrial des erts.

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Section: Theoretical Values Of the Cross Sectionmentioning

confidence: 60%

Section: Been Removed) Compared With the Best-fitt Ing Curves For Thementioning

confidence: 81%

Section: Theoretical Values Of the Cross Sectionmentioning

confidence: 99%

Section: The Scattering Behavior Of An Irregular Surfacementioning

confidence: 99%

Section: Been Removed) Compared With the Best-fitt Ing Curves For Thementioning

confidence: 99%

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Radar studies of the Moon

Evans¹

1965

J. RES. NATL. BUR. STAN. SECT. D. RAD. SCI.

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A Study of the Depolarization of Lunar Radar Echoes

Hagfors

1967

Radio Science

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The radar backscattering characteristics of the lunar surface are examined in detail at a wavelength of 23 cm. The backscattered waves are studied both for circular and for linear polarization of the transmitted wave. Effects relating to the orientation of the local plane of incidence on the moon with respect to the polarization of transmitted or scattered waves are investigated. The experimental results appear to strongly support the hypothesis that the returns at oblique angles of incidence arise through single scattering from discrete objects, as opposed to the returns at near normal incidence which are dominated by quasi‐specular reflection.

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Planetary characteristics from radar observations

Muhleman

1966

Space Sci Rev

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Meaningful radar experiments have been achieved with the planets Venus, Mercury, and Mars since the first successful radar detection of Venus in early 1961. Venus in particular has been carefully studied radarmetrically in the wavelength range from 3.6 cm to 7 meters, with several spectacular results yielding both fundamental information concerning the planet as well as corollary data for synthesizing a complete physical picture of Venus from all of the astronomical measuring techniques. It has been discovered that the Venusian axial rotation is retrograde with a period of about 250 days, the atmosphere is essentially transparent at wavelengths longer than 10 cm and that radar echos are an order of magnitude weaker at 3.6 cm than at the longer wavelengths suggesting a considerable atmospheric effect in the short centimeter region.Observations of Mercury and Mars are far less complete owing to the planets' relatively great distances from the Earth which effect the radar detectability through an inverse R fourth law. However, it appears that an accurate rotational period of Mercury of 59 _+ 5 days has been established as opposed to the long accepted synchronous period of 88 days. Furthermore, significant variations in the reflectivity of Mars with the Martian-centered coordinates of the subearth point have been observed, some of which are strongly correlated with visual markings on the planet's surface.Finally, through straining the available radar facilities to their limits a vast catalogue of range and doppler velocity data for Venus and Mercury has been assembled for the study of the motions of the Earth and planets and for the computation of greatly improved values of the fundamental solar system constants, the most notable of which is the astronomical unit.The purpose of this paper is to review the interpretation of the radar observations from the standpoint of the above and to outline the direction of current radar astronomical research. The questions of celestial mechanics, however, will not be discussed. Fundamental ConceptsWe will take the basic photometric approach as developed by MUHLEMAN et al. (1965) as opposed to that of conventional radar engineering since it appears to allow a smoother integration with other astronomical measurements. The planets may be studied in terms of how the measurements differ from the radar response of an ideal

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The analysis of radar echoes from the Moon

Cited by 30 publications

References 10 publications

Radar studies of the Moon

Radar studies of the Moon

A Study of the Depolarization of Lunar Radar Echoes

Planetary characteristics from radar observations

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