Shading Inverted Pyranometers and Measurements of Radiation Reflected from an Alfalfa Crop

Field experiments were made to determine if pyranometers require shading when inverted to measure reflected radiation, and if the view angle of such instruments may be restricted to allow for measurement over small plots. Results indicate that shade must be provided for inverted Eppley pyranometers to prevent radiation from entering the glass bulb above the plane of the sensor. It does not appear necessary to shade the entire bulb. Reflection from a well‐developed alfalfa crop was found anisotropic, indicating that shades which reduce the view angle significantly should not be used.