A parousiameter having a dual beam setup and method for use thereof is provided for producing measurements of optical parameters. The dual beam parousiameter includes a hemispherical dome enclosure 318 sealed at the bottom with a base 320. A radiation source 302 produces radiation in two beams, an illumination beam 304 for illuminating a sample surface 308 and a calibration beam 330 for providing optical characterization information about the illumination beam 304. Each beam is guided into the hemispherical dome enclosure 318 via separate optical paths. An optical imaging device 324 is positioned to acquire an image of scatter radiation 314 scattered by the sample surface 308 illuminated by the illumination beam 304, and acquire an image of the calibration beam, simultaneously. The calibration beam image is used to compensate for variability in optical output of the radiation source 302 when analyzing the scatter radiation data.