2 com- 
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394. 06-21-81  Ox«30? v ' 9041 06—23-81 X=10"H 
  
  
   
8 12 18 28 24 4 8 e 12 18 2a 24 4 8 
Fig. 2e Fig. 2f 
Fig. 2 - Brightness and infrared Trig temperatures during the day compared with 
soils Ts and air T4 temperatures (Tbl=36GHz, Tb2-10GHz) T4 is at top 
of vegetation. Data refer to 6 days: June 11th, 14th, 15th are clear 
days, 19th and 21th overcast, 23th cloudy. (a = angle of observation 
H and V horizontal and vertical polarization). 
The different observational conditions (angle of observation and 
polarization) don't alter the possibility of comparing data of different days. 
From the figures is clear that after June 19th (the day of watering) there 
is much less difference between day and night brightness temperature. This 
however corrispond to an equivalent behaviour of the physical temperature. 
The variation of the brightness temperature as measured by a radio- 
meter from the observation angle o may be related to the temperature profile 
of air in the vegetation (6). During the period of stress the curves Tb 
(a) recorded at different times from 8.00 a.m. to 5.00 p.m. are clearly sepa- 
rated, while data recorded for well watered conditions show smaller variation 
in temperature and no appreciable modification of the shape. 
As an example the dependence of Tb from a , data recorded at 12.00 
a.m. in two different days (June 14th and June 19th) are given in Fig.3a and 
3b. 
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