ES A EEE ESS 
2. Microwave Scanning Radiometer (MSR) 
The bread board model of MSR is modified for the experiment. Major modifi- 
cations are containing of the the instrument in a thermal blancket to maintain 
the instrument at a constant temperature and the removal of antenna scanning 
mechanism to fix the antenna with 50 cm diameter to the instrument. 
The specification of MSR used in the experiment is shown in Table 1. MSR 
operates with two channels; 23.8 GHz with horizontal polarization and 31.4 GHz 
with vertical polarization. The output signal is integrated for 10 msec and 
47 msec simultaneously at the two frequencies. It has an antenna temperature 
resolution of 1.0 K at 300 K 
The functional block diagram of MSR is indicated in Fig. 1. MSR is consisted 
of two Dicke type receivers, which are fed by an antenna and calibration sources. 
"Hot" calibration source is an ambient temperature of calibration load, while 
"cold" calibration source is not available on the ground since it would be pro- 
vided by a deep space temperature as viewed by sky horn on orbit. Radiometric 
calibration method using the "hot" calibration source only is described in the 
next section. 
3. Radiometric calibration 
(1) General Calibration 
In order to relate the radiometric output digital values to the input bright- 
ness temperature, a calibration equation is used which makes use of data from 
hot and cold calibration sources. On orbit, cold calibration source is a deep 
space viewed by sky horn and hot calibration source is an ambient temperature 
of calibration load. 
The brightness temperature T at Dicke switch is given by equation (1) 
N. - N 
7 N) ------------------ (1) 
where T temperature from cold calibration source at Dicke switch 
T. temperature from hot calibraion source at Dicke switch 
N digital count corresponding to T 
N. " T. 
N, i T 
For the actual calibration, temperatures have to be corrected for loss and 
physical temperature of the each component. A simplified radiometric correction 
model is shown in Fig. 2. The output temperature of a component with loss L is 
given by equation (2). 
1 
1 
out L Tin + ( 1 "Xv Te TAOA Ta 1TARZa3l 3? (2) 
where the first term is from the loss in the component and the second term is the 
radiation from the physical temperature of the component Te: 
(2) Calibration of field experiment data 
Due to unavailability of deep space for cold calibration source in the field 
SE cn ct cn RES 
  
    
  
    
     
      
   
   
   
   
     
    
   
  
  
    
    
  
   
   
     
   
  
   
   
   
    
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4. Method of 
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5. Results 
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(2) Polariza: 
In MSR « 
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