713 
The strength of such a formulation over that used by Ahmad and Deering directly on the albedo variation, is 
that this parameterization of R H allows the albedo to be calculated under varying degrees of diffuse 
irradiance, whereas the former does not. 
30° (662 nm) 
90° (662 nm) 
30° (826 nm) 
90° (826 nm) 
prairie (June) 
0.037 
0.031 
0.471 
0.397 
prairie (August) 
0.046 
0.042 
0.415 
0.342 
alkali flat 
0.655 
0.601 
0.675 
0.621 
bare soil 
0.116 
0.275 
0.163 
0.179 
desert scrub 
0.518 
0.549 
0.635 
0.585 
Table I. Summary of albedo values for various cover types for two solar elevation angles 
30° (662 nm) 
90° (662 nm) 
30° (826 nm) 
90° (826 nm) 
E, atmosphere 1 / 
Wm' 2 
680 
1525 
433 
993 
Ej atmosphere 2 / 
Wm 2 
462 
1287 
302 
852 
Table II. Summary of E, values for two solar elevation angles for atmospheres 1 and 2 
4.2. Effect of Aerosols 
Simulations were also run for a sky radiance distribution calculated with atmospheric parameters relevant to a 
relatively high concentration of aerosols typical of urban/industrial areas (atmosphere 2). The sky radiance 
distribution of this atmosphere varies significantly from that used in the simulations described above, especially 
at low solar elevation angles. The percentage of diffuse irradiance from both atmospheres (SKYL) is presented 
in Figure 2. One can see that SKYL for the 826 nm wavelength is typically of the order of 0.05 less than that 
for 662 nm, and that there is a significantly higher proportion of diffuse irradiance for atmosphere 2 than 
atmosphere 1. the values for 90° solar elevation being around 0.26 and 0.17 respectively (662 nm). 
From Figure 4, it can be seen that the albedo values do not vary significantly with aerosol loading, except at low 
Sun angles where the sky for atmosphere 2 has a higher proportion of diffuse irradiance than atmosphere 1.