In: Wagner W„ Szekely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010,1 APRS, Vol. XXXVIII, Part 7B 
In: Wagr 
70 
3. RESULTS 
3.1 Results of ground truthing 
The described differences of the study areas lead to different 
characteristics of crops with regard to the type of cultivated 
plants and their appearance. This is reflected by the results of 
taken ground truth on-site. 
15 (Fuhrberg) and 16 types of crops (Gorajec) have been 
recordered (Table 3). In the Fuhrberg area the presence of 
weeds is low on most fields. Nevertheless a gradient in the 
amount of weeds between different potato-fields has been 
detected. Some of them are completely free of weeds while 
others contain a certain amount of various species of weeds. 
The differences cannot be attributed to plant diseases. In 
Gorajec the amount of weeds is explicitly higher than in the 
Fuhrberg area. Most fields contain different kinds of weeds. 
Most potatoes in the Polish study area suffer from a disease. 
Fuhrberg (GER) 
Gorajec (PL) 
crop type 
count 
crop type 
count 
grasslands and 
meadows 
43 
grasslands and 
meadows 
4 
oat 
4 
oat 
7 
rye 
33 
rye 
12 
barley 
20 
barley 
24 
maize 
13 
maize 
2 
spelt 
1 
grain mixture: 
barley, wheat, oat 
18 
wheat 
9 
wheat 
25 
winter rape 
8 
turnip rape 
2 
sugar beets 
18 
sugar beets 
3 
potatoes 
24 
potatoes 
6 
fallow land 
5 
fallow land 
3 
strawberries 
3 
black currant 
5 
asparagus 
12 
tobacco 
13 
beans 
1 
beans 
4 
Lolium perenne 
4 
trefoil 
4 
grain mixture: 
wheat, rye 
3 
Table 3: Type and quantity of crops 
3.2 Measurement of signal backscatter 
Measured backscatter of radar signal differs for different crops 
and different acquisition times. Thus an individual pattern of 
backscatter can be derived for every single crop type. In the 
following, first results of backscatter patterns (means per field) 
for selected crops are presented. 
3.2.1 Fuhrberger Feld area 
Broad-leaved crops and asparagus: The comparison of HH 
polarised mean backscatter values per field exhibits high 
backscatter values for broad-leaved crops (Fig.l). Sugar beets 
have high backscatter values (-6 dB) during full development of 
leaves in June (BBCH-codes 31-39). In July, during full 
phenological development, values exceed -6 dB yet. Images 
with sugar beets have been available in June, July and October. 
Values of maize and potatoes rise up to -8 dB when leaves 
cover the ground. Potatoes reached this value in June when 
flowering started (BBCH-codes 60-65). In April, after sowing, 
backscatter values are dispersed over the whole range between - 
7.5 and -14 dB. Maize also reached the development state of 
closed canopy in June (BBCH-codes 30-32) and HH-polarised 
backscatter is equal to the one of potatoes. Backscatter distri- 
® -8 
3-10 
March , April . June 
July , October 
I 1 1 • « I 
-10 
sugar beets 
• à 
I t 
1 | 
1 i 
i | 
! [ 
potatoes 
CQ -8 
T3 
-10 
G I 
rape 
-10 
• 
• 
i i 
• 4 
• i 
• 
- * 
• 
• i 
1 * 
1 t 
: » 
. « 
• 
i : 
1 1 
• i 
A 
asparagus 
Mean backscatter per field 
* HH polarisation * VV polarisation 
Figure 1: Backscatter distribution for broad-leaved crops and 
asparagus in the Fuhrberg area 
bution for potatoes and maize has a wide range in October after 
harvesting due to differences in surface conditions. On winter 
rape fields, the ground was already covered in March when 
seven to nine leaves occurred (BBCH-codes 17-19). 
Accordingly, backscatter values average >-8 dB and remain on 
a high level of -10 dB or more up to July before harvesting 
started. The values for the different crops show that 
discrimination of broad leaved crops from those with narrow 
leaves is possible due to the clear difference in backscatter 
values. Furthermore, one can even differentiate within the 
broad-let 
ground c 
backscatt 
The max 
March, J 
noticed i 
and the 
strongly. 
The anal 
backscatt 
polarised 
dates. 
-10 
-10 
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Figure 
Grains: 1 
from brot 
to <-10 ( 
spring am 
developm 
grain fini: 
(BBCH-c.