Low-cost field goniometer for multiangular reflectance measurements

A low-cost field goniometer was constructed for multiangular reflectance measurements using a spectral radiometer. The goniometer consists of a circular base made of plywood approximately 4 m in diameter. A rotating arch carries a sled with the radiometer, which can be positioned at any angle relative to the test object at the center of the goniometer. Data from the radiometer are downloaded to a portable computer via a serial cable. The goniometer was tested on a typical lawn, and spectral measurements were collected in the solar plane and at right angles to the solar plane. Spectral characteristics of the test lawn differed significantly from idea lawn grass. Maximum reflectance was measured at the antisolar point in visible light, but maximum infrared reflectance took place at a different position. These results demonstrate the value of collecting in-situ spectral data for evaluation of ground-cover conditions.