Information Content Of Canopy Bdrf: A Monte Carlo Approach

Abstract

PO2444 Observatory Toravere. Tartu, Estonia, U.S.S.R, For calculation of the plant BDRF the Monte Carlo method is used. The plant canopy architecture is given by a universal geometrical model allowing to consider structural parameters, such as canopy density and height, number of leaves per plant, distance between single leaves on the stem, dimensions and orientation of leaves and stems, etc and their influence on the shape of the BDR 8s a function of solar and view directions. The most valuable information about plant architecture contains the BDRF on the principal plene in the near-nadir directions, in the hot-spot area, and around specular directions of the solar beam. Bidirectional reflectance function, Monte Carlo method, plant canopy architecture.For the calculation of the plant canop bidirectional reflectance factor BDRFY the Monte Carlo method is used [ 6 , 7 j . The plant canopy architecture is given by a rather universal geometrical model which allows to coneider such structural parameters as canopy density and height, the number of leaves per plant, distance between leaves, dimensions and orientations of leaves and stems etc. and their influence on the shape of the BDR as a function on solar and view directions. The model plant consist of a vertical cylindrical stems with a diameter dst and a height H , of N L elliptical leaves with a length dL1 and a width d,. The Height of the first leaf above the soil Z is a random quantity given by normal bution with the mathematical expectation Q and the variance LT .Let the distances between neighbouring leaves be equal, then the height of the j-th leaf is zj = z l + (j-1) H / N L , d = 1,. . . ,NL. The azimuth angle of the first leaf is uniformly distributed on the '' interval [ o * 23r] , the azimuth of the d-th leaf is F j = $ , + ( j -l ) f s v where \9 is the azimuth angle between succeseive leaves on the genetic spiral. The leaf inclination angle 6' is described by the probability dlstridensity function* of leaf angle distribution (LAD) yL (e,), 0 d e L < n / 2 , 3i/2 0 according to one of the three rules: 1. all leaves have a constant and equal inclinat ion angle @* : $ ( Q~I = & ( e L -e * ) , where 8 is a Dirac delta function; 2. trigonometrical orientation l i 3 3. beta-distribution 131 ,-p,) = ~3 -+ 6c0S28, + c ~0 3 4 6~; where 6 ( p , v ) = r ( p ) r(v)/r (p+v> is the beta function. The plant canopy is simulated as an infinite field of model plants grown in rows. The row effect is characterized by the parameter Let LL be the given leaf area index. tien the distance between plants in one row A is uniquely defined by the equality L, = n N,d,f d L 2 / 4 A 2 p and Apis the distance between the rows. If A is known, we can find the stem area index L = d,t.TH/2AT> and the total area index LA1 2 L,+ L,. The following simple optical leaf model is proposed: isotropic transmission is characterized by the spectral coefficient t L ; the reflection consists of two components : the diffuse component by the spectral coefficient r , and the specular component. The lea...