350 
Table 1. Dates in 1983, 19^4, and 1^85 of 
measurements of equation [1 ] and [2 ] variables 
(Days of year, in parentheses, follow calendar 
date). 
Measurements 
Reflectance 
Factor 
PAR 
LAI 
YIELD 
11 Apr(101) 
18 Apr(108) 
25 Apr(115) 
2 May( 122) 
Cotton (1983) 
28 Apr(118) 
4 May(124) 4 May(l24) 6 May(126) 
16 May(136) 16,17 May(136,137) 
23 May(143) 23 May(143) 23 May(143) 
1 Jun(152) 2 Jun(153) 1 Jun(152) 
9 Jun(160) 
15 Jun(166) 14 Jun(165) 
20 Jun(171) 
27 Jun(178) 27 Jun(178) 
8 Jun(159) 
20 Jun(171) 
6 Jul(187) 
14 Jul(195) 
22 Jul(203) 
28 Jul(209) 
3 Aug(215) 
3 Aug(215) 
17 Aug(229) 
5 Dec(339) 
12 Dec(346) 
29 Dec(363) 
6 Jan(006) 
i^Teat TTSFJ-fSSi )' ' 
6 Dec(340) 
15 Dec(349) 13 Dec(347) 
11 Jan(011) 11,12 Jan(011,012) 
3 Feb(034) 
16 Feb(047) 13 Feb(044) 13,14 Feb(044,045) 
24 Feb(055) 
29 Feb(060) 28 Feb(059) 
8 Mar(068) 8 Mar(068) 8 Mar(068) 
16 Mar(076) 
22 Mar(082) 
28 Mar(088) 29 Mar(089) 28 Mar(088) 
3 Apr(094) 
9 Apr(100) 
16 Apr( 107) 
24 Apr(115) 
27 Apr(118) 
30 May( 150)-^/30 
3 Jun(154) 
10 Jun(161) 11 
21 Jun(172) 21 
25 Jun(176)^/25 
26 Jun(177) 26 
1 Jul(182)-^/ 1 
9 Jul(190) 9 
12 Jul(193)^/12 
17 Jul(198) 16 
18 Ju1(199)-§/18 
1 Aug(213)^/ 1 
8 Aug(220)^/ 8 
20 Aug(232)-3/20 
Corn 
May(150) 
(1985) 
Jun(162) 
Jun(172) 
Jun(176) 
Jun(177) 
Jul(182) 
Jul(190) 
Jul(193) 
Jul(197) 
Jul(199) 
Aug(213) 
Aug(220) 
Aug(232) 
10 Jun(161) 
17 Jun(168) 
24 Jun(175) 
1 Jul(182) 
9 Jul(190) 
12 Jul(193) 
22 Jul(203) 
1 Aug(213) 
8 Aug(220) 
20 Aug(232) 
6 Sep(249) 
Diurnal reflectance factor and PAR 
interception measurments were made in one 
irrigated and nonirrigated plot on these dates; on 
other dates measurements were made at two sites 
in each of three replicates of each treatment. 
optical-physical rationale of the spectral 
components analysis (SCA) approach is consistent 
with the concept that plants integrate the soil and 
aerial environments and the stresses experienced and 
express their responses through the canopies 
achieved. The spectral components analysis 
identities of equations [1] and [2] describe the 
interrelationships among leaf area index (LAI), the 
spectral vegetation indices (VI), absorption of 
photosynthetically active radiation (APAR), and 
Table 2. Equations for each term of the spectral 
components analysis identify of equation [1 ] 
for cotton, wheat, and corn. Z-| and Z2 
designate solar zenith angles at time of VI and 
APAR observations, respectively. 
Equation 
n Coeff. of 
Deter. 
(LAl/cosZ^) vs VI71 
[1st term] 
Cotton 
LAl/cosZ-]=0.001 exp 9.14 (ND Z1 ) 
=4.99 (NDzi) 7 * 14 
=0.078 exp .113 (PVT z1 ) 
=0.001 (PVI Z -|) 2 - 31 
20 
.959 
.956 
.922 
.961 
Wheat 
LAl/cosZ-j =0.050 exp .440 (ND Z -| ) 
=3.21 (ND 71 ) 2 - 60 
=0.220 exp'.100 (PVI z i) 
=0.036 (PVT Z -|) 1 - 35 
30 
.795 
.771 
.961 
.947 
Corn 
LAl/cosZi=0.032 exp 5.17 (ND Z1 ) 
=3.34 (ND Z1 ) 2 - 33 
=0.122 exp .138 (PVI Z -|) 
=0.074 (PVI z i) 1 - 13 
10 
.894 
.856 
.940 
.936 
APAR79 vs (LAI/cosZ 2 ) [2nd term] 
Cotton 
APAR Z 2=1-.858 exp-.514 (LAI/COSZ2) 
=0.494 (LAI/cosZ2)* 436 
20 
.967 
.978 
Wheat 
APAR z2 =1-.888 exp-.540 (LAl/cosZ 2 ) 
=0.444 (LAI/cosZ 2 )*486 
30 
.930 
.887 
Corn 
APAR z2 =1-.914 exp-.347(LAl/cosZ 2 ) 
=0.298 (LAI/cosZ 2 )* 811 
10 
.961 
.953 
(APAR7,2) vs (VIcosZi/cosZ2) [right hand side] 
Cotton 
APAR z2 = 0.802 (NDcosZ-|/cosZ 2 ) 2 * 93 
=-0.864 + 1.67 (NDcosZ-|/cosZ 2 ) 
= 0.022 (PVIcosZ-|/cosZ2) 1 * 02 
= 0.028 + 0.023 (PVIcosZ-|/cosZ 2 ) 
20 
.867 
.857 
.969 
.942 
Wheat 
APAR z2 = 0.758 (NDcosZ l /cosZ 2 ) 1 -42 
J =-0.128 + 0.902 (NDcosZ-|/cosZ2) 
= 0.069 (PVIcosZi/cosZ 2 )- 746 
= 0.201 + 0.022 (PVIcosZi/cosZ 2 ) 
30 
.581 
.469 
.835 
.825 
Corn 
APARz2= 0.787 (NDcosZ-|/cosZ2) ^ 
=-0.205 + 0.961 (NDcosZ-|/cosZ 2 ) 
= 0.040 (PVIcosZi/cosZ 2 )-886 
= 0.008 + .028 (PVIcosZ-|/cosZ2) 
10 
.878 
.751 
.986 
.969 
economic yield (YIELD) of the crops inherent 
in the 
rationale. 
Relationships between the numerator variable (y) 
and the demonimator variable (x) were presented for 
4 - . 
2 - 
4 . 
each t 
expert 
light 
for co 
vegeta 
as fra 
(Resul 
for wh 
vegeta 
photos 
Thus A 
Altern 
insert 
litera 
estima 
close 
ground 
VI a 
large 
APAR v 
crop ( 
ships 
absorp 
growir 
size c 
indie