Directional Thermal Infrared Exitance Distributions from a Leafless Deciduous Forest

The directional thermal infrared exitance distributions of a 21.5-m-tall leafless deciduous forest were measured using a rotating 7-detector array suspended 33 m above the forest floor. These distributions are presented for several illumination conditions. Strong directional thermal infrared distributions were observed at high solar elevations on a clear day. Temperature gradients frequently exceeded 3°C per 10-degree change of view angle. At low sun angles and the early evening, change of observed temperature with nadir angle was more moderate and was negligible with azimuth angle. At night and on a cloudy morning, uniform temperature distributions were observed. An interpretation of these directional temperature distributions is given.