Photon-Vegetation Interactions deals with the interaction of electromagnetic radiation with vegetation canopies. The approach to the various aspects is mainly theoretical and consequently the subject is being treated as a special branch of mathematical physics. A major emphasis is on the development of theoretical methods for determining the reflection function of vegetation canopies in optical remote sensing. Furthermore, the coupling of the radiative transfer theory with leaf photosynthesis to evaluate the productivity of vegetation canopies is treated as well as the theory of photon transport in phototropic and other biological media.

Stochastic and deterministic approaches to simulating the spectro reflectance of shortgrass prairie vegetation have been investigated. The stochastic approach uses randomly selected variates for incoming light flux, plant geometry, and intrinsic optical properties whereas the deterministic model is patterned after the familiar Kubelka-Munk theory for diffuse reflectance. The model results are compared with field and laboratory measurements of Blue grama (Bouteloua gracilis) and successfully predicts the non-Lambertian character of the canopy. The site of the field measurements was the Pawnee National Grasslands, the intensive study site of the International Biological Program. Direct solar and diffuse sky irradiance and the optical properties of Blue grama were measured in the 0.4 micrometer to 1.05 micrometers region of the spectrum using a field adapted EG and G spectroradiometer with a computer based digital acquisition system. Canopy geometry was measured with a laboratory photographic technique with subsequent digitization of the profile images. (Modified author abstract).

The development of a procedure to calculate the effect of certain environmental factors on the rate of photo-synthesis imposed mainly geometrical problems, which were solved in such a way that the actual calculation could be carried out by means of a computer. The calculation procedures have been used to study the. relative importance of the variables under various conditions. The results for a standard set of conditions, have been summarized in order to make it possible to estimate the daily photosynthesis at any time and place for a wide range of photosynthesis functions without a computer.