THE PARAMETERS INVOLVED IN HAPKE'S MODEL FOR ESTIMATION OF THE COMPOSITION OF THE EJECTA LUNAR TERRAINS. S.G. Pugacheva, V.V. Shevchenko. Sternberg State Astronomical Institute, Moscow University, 13 Universitetsky pr., 119992 Moscow, Russia, pugach@sai.msu.ru. Introduction. In the previous papers we were estimated the surface roughness of the ejecta lunar terrains by means comparison of the local phase function and the average integrated lunar indicatrix. The difference between the modeled and observed phase functions was obtained for surface having various degree of the surface roughness. We were investigated the surface of the lunar landing sites. The great difference between the modeled and observed phase functions demonstrates for phase angle in range about 18o and corresponds a high degree of the surface roughness [1]. The value of this difference of intensities was used as a photometric parameter of the surface roughness I. In this article we compared the values photometric parameter of the roughness I with the parameters the Hapke's model. The Hapke's theoretical model of the lunar surface reflection. The Hapke's formula is well known model for the estimation of the surface roughness [4, 5, 6]. The model allows to define of the physical and chemical characteristics of the lunar surface by means phase function. This model is the only existing one, which accurately represents the reflection properties of the Moon. The photometric function by Hapke of the bidirectional reflectance (R) may be written in the general form: R={wo/[4(o+)]}{[1+B(g)]P(g)+ +H(o)H()1}S(), where o, are cosines of incidence (o) and emergence () angles, g is the phase angle, i, e are angles of incidence and emergence, w is the single scattering albedo, B(g) is the opposition effect function, P(g) is the phase function, H() is the multiple scattering function, S() is the function for macroscopic roughness. The function B(g) describes the brightness of a surface near zero phase angle. The parameters of the function B (g) describe the backscatter due to blocking and shadowing within the soil. B (g) = Bo/[1+(1/h) tan (g/2)]. The parameter h characterizes compaction of the regolith and size of the particle. The parameter Bo defines amplitude of the opposition effect. The function P(g) includes two parameters b and c, which determines the phase function form and the nature of scattering (c<0.5 corresponds to forward scattering and c>0.5 to backward scattering). P(g)=(1-c)[(1-b2)/(1+2bcos(g)+b2)3/2]+ +c[(1-b2)/(1-2bcos(g)+b2)3/2], where g is the phase angle, b and c are the parameters with the material properties of the lunar regolith. The function of the isotropic multiple scattering H(x) includes angles incidence and emergence and the single scattering albedo w. H(x) (1+2x)/[1+2x(1-w)1/2], where x is either o or . The equation S() allows to calculate the effects of macroscopic roughness on light scattered by a surface having an arbitrary diffuse-reflectance function [3, 6]. The parameter is a mean topographic slope angle of the surface. The effects of macroscopic roughness will modify the reflectance. The geometry of the reflectance is shown in figure 1. The signal r(i,e,g) is interpreted as if it came from a smooth, horizontal area, the bidirectional reflectance from sloping area is r(ie,ee,g). The expressions for r(i,e,g), r(ie,ee,g) and S() will make the following equation true: R(i,e,g,)=r(ie,ee,g)S(). The mean slope angle equal A=1/(tan2) and B=1/(tan2), where A and B are empirical coefficients of the equation described by a Gaussian [6]. The Hapke's theoretical integral phase function involves six parameters: w, Bo, h, , and two parameters to describe P(g). For