Monitoring Powdery Mildew of Winter Wheat by Using Moderate Resolution Multi- Temporal Satellite Imagery

Powdery mildew is one of the most serious diseases that have a significant impact on the production of winter wheat. As an effective alternative to traditional sampling methods, remote sensing can be a useful tool in disease detection. This study attempted to use multi- temporal moderate resolution satellite- based data of surface reflectances in blue ( B), green ( G), red ( R) and near infrared (NIR) bands from HJ-CCD ( CCD sensor on Huanjing satellite) to monitor disease at a regional scale. In a suburban area in Beijing, China, an extensive field campaign for disease intensity survey was conducted at key growth stages of winter wheat in 2010. Meanwhile, corresponding time series of HJ- CCD images were acquired over the study area. In this study, a number of single- stage and multi- stage spectral features, which were sensitive to powdery mildew, were selected by using an independent t- test. With the selected spectral features, four advanced methods: mahalanobis distance, maximum likelihood classifier, partial least square regression and mixture tuned matched filtering were tested and evaluated for their performances in disease mapping. The experimental results showed that all four algorithms could generate disease maps with a generally correct distribution pattern of powdery mildew at the grain filling stage ( Zadoks 72). However, by comparing these disease maps with ground survey data ( validation samples), all of the four algorithms also produced a variable degree of error in estimating the disease occurrence and severity. Further, we found that the integration of MTMF and PLSR algorithms could result in a significant accuracy improvement of identifying and determining the disease intensity ( overall accuracy of 72% increased to 78% and kappa coefficient of 0.49 increased to 0.59). The experimental results also demonstrated that the multi- temporal satellite images have a great potential in crop diseases mapping at a regional scale.