needed to adjust for small temperature differences between the black body used in the field 
and target surface. Usually both of these corrections are less than 0.1 C. The correction for 
C0 2 absorption is 0.0088 C at a C0 2 concentration of 370 pmol mol ' 1 for every meter of path 
length and 1 C temperature difference between the target and the intervening air. Thus, for 
a 1-m path at 370 pmol mol ' 1 with the air temperature 3 C above target temperature, the cor 
rection is 0.026 C. For small canopies (wheat, alfalfa etc.) or bare soil, the angle device is 
constructed so that the path length between the sensors and the surface is fixed at 1 m for all 
angles and the same spot on the ground (0.14 m in diameter) is viewed from all directions. 
For large canopies such as com, the path length may vary with view angle and corrections of 
a few tenths of degrees C can occur. 
This method for measurement of soil and vegetation emissivities typically has errors less 
than 0.005 if appropriate care is taken with calibration and corrections. 
5 - RESULTS 
5.1. Directional Temperature 
Comparisons between predictions of directional brightness temperature from Cupid and mea 
surements from FIFE are contained in Figures 1 and 2. The MMR measurements are in the 
10.5-12.5 pm wavelength band and hand-held infrared thermometer measurements in the 8-14 
pm wavelength band. The model simulation is in the MMR wavelength band. 
Figure 1. Comparison between brightness temperature predicted from Cupid and 
measurements from the MMR instrument at the FIFE site 11 on Day 156 at 12:15 
Central Standard Time (leaf area index is 1.6).