axis thus it is possible to measure antenna temperature of water surface for 
incident angle ranging from 0° to 40° in both vertical and horizontal polari- 
zations. The experiment was conducted from October 19 through 27,1981 from the 
top of 20-m height tower. 
The coordinate system of the experiment is illustrated in Fig. 3. 
3. The results of the analysis of the data 
The results of the analysis of observed data indicate the following features 
1) Effect of incident angle (Fig..4) 
The correlation between antenna temperature and incident angle was positive for 
vertical polarization while it was negative for horizontal polarization. 
2) Effect of frequency (Fig. 4) 
Antenna temperature of 23.8 GHz was lower than that of 31.4 GHz regardless of 
polarization. This result is opposite to the theoretical characteristics. 
3) Variation of antenna temperature associated with polarization (Fig.5) 
The variation of antenna temperature associated with changing polarization 
indicated of sine function. 
4) Comparing with ‘the theoretical value 
The antenna temperature obtained in this experiment was higher than the theo- 
retical value. The offset value was as large as 40 K. 
The facts stated in 2) and 4) suggest necessity of further analysis. 
The effect of side-lobe is discussed in the following section. 
4, Antenna sidelobe correction 
In general, the antenna temperature TA is given by 
T Tg G(06,0) da 
A ls G(¢,6) da 
Where Tg is the brightness temperature of the target and G( à © ) is the an- 
tenna's pattern function, which is the fuction of azimuth and elevation angles 
+, 0 respectively. The contribution of the ground and sky is included in T 
besides the water surface when sidelobe and backlobe effects are taken into 
account therefore the expression for Tp is expressed by Eq. (2) 
= 3 | | | x 2TH 
AE a Y Gdgosl T 6 do T G de (2) 
A Gol Jaw B-W Ds 8:5 a B.G 
Where Tp iy , Tg. g and Tp,s are the brightness temperature of the water, ground 
and sky respectively,where Go is the denominator of Eq. (1). 
Due to the fact that the size of the pool is comparatively small , Tp M 
can be assumed to be nearly constant, the estimation of the value of Eq. (2) 
is reduced to the estimation of the terms de d $ for each integration area. 
In the actual computation, the magnitudé of G, antenna gain was read out at 
1/3? interval between 0° and 18°, and 2° interval between 18° and 180°. 
Now in the first term 1/8) fq, 6 d signifies the ratio of the contribution of 
water (pool), to the whole integration area including pool , ground and sky. 
The similar interpretation is applicable to other two terms 
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