In: Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Yol. XXXVIII, Part 7B 
In: Wag 
but does not likewise cross the line of -6 dB. Potatoes have 
highest backscatter during the July and August acquisitions (>- 
9.2 dB and > -8.2 dB). In June and September they differ within 
huge ranges. This is very similar to potato fields in Fuhrberg 
with exception of June where the values of Gorajec seem 
randomly distributed. Backscatter values for both maize fields 
increase constantly from April to July. They remain on a level 
of >-10 dB until a significant decrease in October. In 
comparison, Fuhrberg backscatter values for maize fields 
increase to a higher level in June and July. Tobacco, which is 
also a broad-leaved crop, increases from April to July to a high 
level of above -7.3 dB. After reaching this peak, it turns to 
lower level but remains above -10 dB until harvest in October. 
The VV polarised backscatter value for broad-leaved crops 
decreases with a lower rate compared to the one of HH 
polarised signal. This is very similar to the results for Fuhrberg. 
The backscatter of broad-leaved crops is comparable to the one 
of Fuhrberg site, although they do not reach such high values. 
Grains: Grain crops mainly exhibit high backscatter values in 
March (Fig. 4). In April values are significantly lower. HH 
polarised backscatter increase within a wide range from April to 
July. In August, before harvest started, most values decrease to 
<-10dB. This is especially recognizable for wheat and rye. After 
the harvest the values increase in September and than decrease 
in October to <-8 dB. Compared to the grain crops in Fuhrberg 
area, grain fields in Gorajec vary within a wider range. An 
increment for grain crops in July can be observed likewise, but 
not as clearly as in Fuhrberg. Furthermore, there is an explicit 
difference between both June acquisitions with wide distributed 
values in Gorajec and low backscattering in Fuhrberg. There is 
a clear difference between VV and HH backscatter during the 
summer month. VV values are significantly lower. In June and 
July a strong decrease of backscatter values can be found. In 
June the mean decline is between 5.1 dB for rye and 3.2 dB for 
barley. In July the mean decrease ranges from 4.1 dB for rye 
and 2.2 dB for oat. In August decrease is less with mean 
declines from 1.2 dB (barley) to 2.1 dB (oat). VV backscatter 
during the summer month decreases stronger than for grains in 
Fuhrberg area. 
Grasslands and meadows: Measured backscatter for grasslands 
and meadows shows a constant value of <-10 dB. The only 
exceptions are two fields in March with clearly higher 
backscatter of >-10 dB and one measurement in June with - 
9.5 dB. Although grasslands do not reach values as low as the 
ones in Fuhrberg, they remain on a relatively low value 
compared to other crop types in the Gorajec region. An 
increment of values in July, similar to the one in Fuhrberg, 
cannot be found. The same effect as in Fuhrberg is observable 
in March, when most values are lower then grain crops or bare 
soils. The VV polarisation backscatter is lower during all month 
(average 1 dB). But during the summer month the decrease is 
stronger with about 2 dB. This is comparable to the Fuhrberg 
results for VV backscatter in grasslands and meadows. 
4. CONCLUSIONS 
The results of backscatter measurements for the different crops 
are very promising because individual backscattering patterns 
for the different crops can be found by using time series of 
images. As the images are available all over the year 
independent from the weather conditions, the phenological 
development of the plants during the year can be detected. This 
allows not only for a clear separation of broad-leaved crops 
from small leaved crops, but also for discrimination within the 
group of broad leaved crops (e.g. sugar beets and maize). The 
separation between the different grains still has some problems, 
with the exception of oats. But, due to its very specific 
reflection, especially in April, grasslands can be differentiated 
from all grains very clearly. This is not given for applications 
with optical data, when differentiation is often not available 
(Gonzalez-Sanpedro et al., 2008). 
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