INTRODUCTIONIt is of great interest to compare the results of the chemical analysis of the lunar surface material made by 'Surveyor' with that based on the data of the radio astronomical investigations of the electromagnetic properties of the lunar material. The method of determining the chemical composition by the equipment brought onto the moon by Surveyor 7 has been described by Turkerich et al. [1968].From ground-based optical observations of the moon, attempts to estimate the chemical composition of the lunar surface material have been made, for example, by comparing the polarization properties with those observed for terrestrial rocks. Yet, optical methods are not very effective, as their results depend chiefly on the geometrical properties of the surface (i.e. the roughness). Radar measurements provide the reflection coefficient and some limited data on the nature of the lunar material. They allow, for example, one to distinguish between a metallic and a dielectric reflector.
The development o.f radioastronomical investigations enables us to determine a new characteristic'a material loss tangent angle at the centimeter wavelength. As is known, the loss angle in dielectrics depends to a great extent on the nature of the material. Thus attempts may be made to identify the lunar material by comparing the value of the loss angle with that found for terrestrial rocks.
Initially it was not recognized that the loss angle of rock depends on the material density • and that the comparison cannot be a single-valued one. Thus one has to find the loss tangents and dielectrical constants of various rocks at an invariant density. To circumvent this problem Troitskii [1960] introducedthe specific tangent of the loss angle, tan/v/v, which he used as an invariant for the comparison. Later ex-perimental investigations of terrestrial rocks confirmed that the specific tangent of the loss angle remains practically constant over a wide range of density. The value a = [(E) x/2 -1]/t• has also been established to. be invariant of the rock density (or porosity) [ Krotikov, 1962]. These measurements help us to obtain a rather clear dependence of b = tan /x/t• on the content of SiO2 in rock. RELATIONSHIP BETWEEN ELECTRICAL AND CHEMICAL PROPERTIES OF ROCKS Ground-based radio astronomical measurements of b make it possible to estimate the content of SiO• in the lunar material, the weight being equal to 55-65% [Krotikov a,nd Troitskii, 1964]. A special experimental investigation of rocks made at NIFRI at frequencies from 1.5 to 500 MHz shows that the values b -tan/x/o and a -[(•)•/• -1]/• depend essentially on the chemical composition of the rock [Troitskii and Bondar', 1969] and to some extent on the type of crystalline structure (intrusive and effusive rocks). (The measurements at • -500 MHz were made by S. A. Shmulevich.) Of about 40 different rocks measured by us at a frequency of 100 MHz, the specific loss tangent angle was found to vary by a factor of 20 between the acidic and the basic ones. The value a varies from 0.45 for the a...
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