Remote sensing of vegetation and soil using microwave ellipsometry

A method of determining the water content and thickness d of a layer of vegetation on a soil substrate of known refractive index n.sub.m comprising:

• transmitting a circularly polarized train of microwaves of wave length .lambda. to a layer of vegetation at a predetermined angle of incidence .theta., the orthogonal components of the electric field of said microwaves having equal intensities I.sub.i.sup.p and I.sub.i.sup.s and in quadrature in the plane of incidence and normal to it;
• receiving the orthogonal components of the train of microwaves reflected from the layer of vegetation and the soil substrate;
• detecting the intensities I.sub.r.sup.p and I.sub.r.sup.s of the orthogonal components of the electric field of the received reflected train of microwaves;
• determining the ratio I.sub.r.sup.p /I.sub.r.sup.s of the intensities of the detected orthogonal components of the electric field of the received reflected train of microwaves;
• measuring the phase difference 90.degree. + .DELTA. of the orthogonal components of the electric field of the received reflected train of microwaves;
• and
• computing the refractive index n.sub.f and the thickness d of the layer of vegetation from the formula:
• ##EQU5## wherein r.sub.f.sup.p, r.sub.m.sup.p, r.sub.f.sup.s and r.sub.m.sup.s are the Fresnel coefficients and are functions of .theta., .lambda., d, n.sub.f and n.sub.m ;
• and the refractive index of the vegetation n.sub.f is given essentially by the water content of the vegetation.