Canopy architecture measured with a laser.

A laser based method was employed to measure and numerically describe the architecture of a corn canopy. Use of the method provides an interception coefficient for classes of vegetation in layers of the canopy viewed in various directions. Architectural data obtained for similar corn canopies but measured by differing methods are comparable to the results obtained using the laser based method. These results provide input data to mathematical models employed in remote sensing for describing the radiation environment in a plant canopy and predicting its reflectance.

Specular, diffuse, and polarized light scattered by two wheat canopies.

Using polarization measurements, the reflectance factor R(theta(i),phi(i),theta(r),phi(r)) of two wheat canopies is divided into components due to specularly and diffusely reflected light. The data show that two key angles may be predicted, the angle of the polarizer for minimum flux and the angle of incidence of sunlight specularly reflected by a leaf to a sensor. The results show that specular reflection is a key aspect to radiation transfer by two canopies. Results suggest that the advent of heading in wheat may be remotely sensed from polarization measurements of the canopy reflectance.

Influence of solar illumination angle on soybean canopy reflectance.

Remotely sensed spectral measurements taken over croplands are influenced not only by the cover type and condition, cultural practices, and environmental factors, but also by the solar illumination angle in relation to the scene. The reflectance of soybean canopies of differing row directions were measured at 15-min intervals during three clear days with a Landsat band radiometer to determine the interaction of the solar illumination angle and row azimuth angle on the measured reflectance factor of soybean canopies. Diurnal reflectance changes of as much as 140%, which were related to the fraction of shadow, were observed in the red wavelength region. As soil cover approached 100% the diurnal changes diminished. A function that describes the solar illumination angle with respect to the row azimuth explained most of the diurnal variation in the measured reflectance. Variation in near-infrared reflectance was much less and did not appear to be as strongly related to sun-row angle interactions as the visible region.

Avian eggs: thermoregulatory value of very high near-infrared reflectance.

Studies of the spectral reflectance of the eggs of 25 species of birds from nine families disclosed uniformly high reflectance (often above 90 percent) in the near infrared. This property is associated with the presence of the eggshell pigments protoporphyrin and the bilins. These pigments allow coloration for cryptic or other purposes with minimum solar heating, a combination not possible with the melanin pigments typical of vertebrates.