Spectrogonio radiometer for the study of the bidirectional reflectance and polarization functions of planetary surfaces. 1. Design and tests.

We have developed a spectrogonio radiometer to measure in the laboratory (-35 degrees C to +30 degrees C) the bidirectional reflectance and polarization distribution functions of various types of planetary material from the UV to the near-IR (310-4800 nm). The major, to our knowledge, novel feature of this instrument is that it is capable of measuring dark to translucent materials with a high degree of radiometric accuracy under most viewing geometries. The sample surface is illuminated with a large monochromatic and polarized parallel beam (incidence: 0 degrees-90 degrees ), and the total intensity and the two polarized components of the reflected light are measured (observation, 0 degrees-80 degrees; azimuth, 0 degrees-180 degrees). The scientific and technical constraints, the design, and the performances and limitations of the system are presented in this first paper.