rature in the range of 110 to 120 K for calm fresh water 
and sea water. The emissivity of water measured by remote 
sensing tests is 0.37 to 0.40. The brightness temperature of 
marshland is situated between that of water bodies and of 
dry land. The difference of brightness temperature of marsh 
lands mainly depend on the moisture content and density of 
covering vegetations. It is worthy to be noted that, firstly, 
the radiometric temperature of the marginal water bodies is 
higher somewhat than that of the center water bodies, as a 
result of the contribution of aquatic plants growing at sh 
allow waters along the bank; secondly, there is a lower tem 
perature belt lies in the center parts outside the dyke, 
contrasting sharply with surrounding targets. The anomaly 
of the brightness temperature is probably concerned with the 
seepage of the reservoir judging from the image. In situ 
observations showed that this belt is a former riverbed and 
became a paddy field after the dam was erected. A fully wet 
of soil is kept as a result of the seepage of the reservoir 
to a certain extent. Fig.3 is a grey level image of another 
marshland. It can be seen that the waterlogged depressions 
presenting the dark tones are scattered over the grassland 
the light tones. 
Fig. 3,A grey level image 
of Xinlicheng marshland, 
Changchun, at an altitude 
of 2000 m acquired on 
August 20, 1979. 
A, Water bodies, 
B, Grassland. 
Soil and Vegetation 
Microwave radiation of soils are dependent on a number of 
geophysical properties. These include moisture content, sur 
face roughness, vegetable layer, thermometric temperature, 
etc. Compositional variations are of less importance in de 
termining the microwave characteristics of soils, except in 
circumstances where significant amounts of metallic or mag 
netic minerals are present. With the exception of the ther 
mometric temperature dependence, these parameters are all 
associated with the dielectric properties of the soils. The 
dielectric constant of water at microwave frequencies is 
auite large. For example, the real part of the dielectric 
constant of water at L band or below is about 80, and that 
of most dry soils is about 3 (7). Thus the addition of water 
to dry soils causes significant changes in the dielectric 
properties. A set of curves in Fig. 4 are the results of 
experimental measurement for various soils type of China(8). 
Fig. 4, The dielectric 
constant (real part) g/of 
soils as function of mois 
ture content. ( 1,meadow 
soil, 2, drab soil, 3,rice 
paddy soil, 4, red earth, 
5, yellow soil, 6, brown 
earth. ) 
10 20 
moisture content (%) 
1 
30