Backscatter effects of surfaces composed of dry biological particles

We present the backscattering of particulate surfaces consisting of dry biological particles using two laboratory photopolarimeters that measure intensity and degree of linear polarization in a phase-angle range 0.2-60°. We measure scattering properties from three samples composed of dry biological particles, Bacillus subtilis var. niger (BG) spores and samples of fungi Aspergillus terreus and Sporisorium cruentum spores. We find that the surfaces display a prominent brightness opposition effect and significant negative polarization near backscattering angles. The brightness and polarimetric phase curves are different for B. subtilis and the fungi.