CS 
Mv 
Fig.2 shows the relationship between spectral features and 
different rating of area with the symptom of progress 
disease. 
In the spectral region of 640nm, the reflectance decreased 
with rating of the damaged area, those were almost whole 
area damaged, over 20 percent area damaged, less than 20 
percent, less than 5 percent and none by turn. 
In the middle infrared region more than 1,400nm, it had 
also same order as the visible region. 
On the other hand, it had reverse order of the above 
mentioned wavelength in the near infrared region of 800 
nm. 
3. SPECTRAL INDICES AND SYMPTOM OF 
DISEASE 
3.1 Why and How to Calculate Indices ? 
Through the spectral feature measurement, it was identified 
to have peak reflectance in the region of 340, 640, 800, 
1,450 and 1,940nm. 
Rationing is known as one of the spectral enhancement 
methods. NDVI(Normalized Difference Ve getation Index) 
is the typical index using spectral rationing. 
As the effect of rationing, it is possible to reduce some of 
influences based on the environmental condition such as 
sunlight illumination angle, shadow and etc.. 
According to the results of spectral measurement, the 
relationship between spectral indices and the different 
rating of damaged area was discussed. The damaged area 
had progress symptom of disease. 
As first, in order to enhance spectral information, 
following three indices based on the five reflectance peaks 
were used: 
( R640 - R340 ) / ( R640 4 R340 ) 1) 
( R800 - R640 ) / ( R800 + R640) 2) 
RidS0 eR 19405 Ale ten 3) 
0.9 p 
EE A ETT 
Equation 1) is the normalized difference of maximum and 
minimum reflectances in the region of visible wavelength. 
Particularly 340nm had lowest reflectance in the whole 
measurement spectral region. 
Equation 2) is also the normalized difference by 
combining the reflectance in visible red and near infrared 
region, it seems to have almost same physical 
characteristics of Normalized Difference Vegetation Index. 
Equation 3) is the summation of lowest two reflectances in 
water absorption regions, those are 1,450 and 1,940nm. 
3.2 Indices and Different Rating of Damaged 
Area 
Fig.3.1 and 3.2 show the relationship between the index 
and different rating of damaged area. 
Indices' values from 1) increased with increasing of the 
damaged area. 
The value based on 3) had also same trend as 1). 
On the other hand, the value from 2) was identified to have 
an inverse trend as the other two indices. 
As the results, the differences based on the difference of 
rating damaged area were more clear or accurate than the 
comparison of reflectance. 
Accordingly the above mentioned indices were proved to 
be effective for not only spectral information 
enhancement but also target feature extraction. 
  
  
  
Index Value 
oo 
QN - 
  
oo 
5 Wn 
, 
  
e? 
- 
m - 
  
- 
-—7 
- 
- 
  
see 
m h2 UJ 
---dÀ--- (R640-R340)(R640«R340) 
  
— 7dà—— — (R800-R640)/(R800--R640) 
  
  
  
0 | : à; ; 
None less than 5% less than 20% over than 20% Almost Whole 
Rating of Damaged Area 
Fig.3.1 Relationship between Index and Different Rating Damaged Area 
809 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996