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Spectral Feature of Rice Leaves Infected by Blast 
Mitsunori Yoshimura 
Remote Sensing Technology Center of Japan 
Toshihiko Nakajima, Ichiro Arakawa, Kazutoshi Nemoto, Masanao Homma, Hiroyuki Tojo, 
Fukushima Prefecture Agricultural Experiment Station 
Yoichi Torigoe, Eiji Kanda 
Tohoku National Agricultural Experiment Station 
Commission VII, Working Group 1 
KEY WORDS: Remote Sensing, Agriculture, Application 
ABSTRACT: 
The rice blast, caused by Pyricularia oryzae Bri. et Cav., is one of the most serious diseases in rice production of Japan. The 
final objective of our study is to construct the modeling for predicting the damage of disease using remote sensing. In this 
paper, the relationship between spectral feature and symptom of the disease was discussed as the preliminary report, using the 
measurement of spectral characteristics for the infected rice leaves with blast. As the results of this measurement, it was 
identified to have peak reflectance in the regions of 340, 640, 800, 1,450 and 1,940 nm (R340,R640,R800,R 1,450,R 1,940). 
According to this fact, the relationship between the following three kinds of spectral indices and the different rating of 
damaged area were discussed: 
1) (R640-R340) (R640--R340), 2) (R800-R640)/(R800+R640), 
3) R1,450+R1,940 
As the results of this study, combining five reflectances using indices operation was proved to be effective for the 
identification of diseased symptom. In near future, more detail discussion and the modeling for predicting the damage of disease 
would be possible by accumulating the data for spectral feature and their physical characteristics for infected leaves. 
1. INTRODUCTION 
1.1 Food Problem and Rice Blast 
The food problem, the population problem, these are 
necessary to be solved at the global scale and important 
for human being. 
In Asian countries including Japan, people can live on rice 
and its stable provision is discussed at each countries 
together. Particularly in Japan, the food problem related to 
rice, is reported in newspaper every few years. 
The bad rice crop in 1993, is known as the worst harvested 
after world war II. In this year, at the main rice production 
regions such as Miyagi, Fukushima and Kanto, the 
outbreak of rice blast has occurred by the record-breaking 
cool summer and continuous unseasonable weather so that 
the worst yield has recorded. Some of social problems such 
as an imported rice, rice price upswing and etc., have 
occurred in succession by this worst yield. 
1.2 What is Rice Blast ? 
Generally the rice blast is infected on rice leaves or its ear 
and proceeds to occurrence, infection and to almost dead in 
the worst case. 
Rice blast is classified to following two main types, one is 
leaves blast, disease infected on leaves, the other is ear 
blast, disease infected at an ear of rice. 
The spores of the disease stay over the winter season with 
straw and unhealed rice. It begins to be active at the same 
time as the beginning of rice cultivation in the next crop 
year. Furthermore not only the weather but also the sort of 
rice, manuring and the site specification are influence to 
the occurrence of disease. It has high probability of the 
sudden outbreak under the cool summer condition with 
high humidity. 
Particularly serious disasters by rice blast often occur at 
Fukushima prefecture and it's surrounding region. In this 
study, the authors investigated the disease symptom of 
leaves blast and its spectral feature. 
2. SPECTRAL FEATURE MEASUREMENT 
2.1 Diseased Rice Leaves with Blast as 
Measurement Target 
The infected leaves with blast and healthy leaves of rice as 
the measurement targets were collected at farmer's rice 
fields on 16th July, 1995. Its field was located at Funahiki- 
town, tamura-district, Fukushima-prefecture. 
At about the same time, blast had already started to proceed 
so that the rice leaves infected by blast could be easily 
identified around its rice field. 
The type collected rice was "Hatsuboshi". Collected rice 
leaves had different symptom of disease. 
2.2 How to Measure Spectral Feature ? 
The measurement of spectral feature for the infected rice 
leaves with blast was carried out under the uniform 
condition with 20 degree centigrade using four lamps with 
2,500 candela, 80 degree irradiation angles respectively in 
the phytotron that located in Fukushima Prefecture 
Agricultural Experiment Station. 
The used measurement instrument was multi-purpose 
spectral-radiometer MSR-7000 that produced by OPTO 
research corporation. The spectral region of this 
measurement was from 280 to 2,500nm and its interval 
was 5nm. The reflectance from target can be calculated by 
relative reflective energy from the target based on the 
standard white board. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996