# Identification of Rice Sheath Blight through Spectral Responses Using Hyperspectral Images
## 3 Results
### Construction of the Spectral Feature Library with Disease Symptom Proportions  
#### 3.2.1 Statistical Analysis of \"Three-Edge\" Parameters  
\"Three-edge\" parameters can quantitatively express spectral variations of diseased leaves in the blue edge, green peak, red valley, red edge and near-infrared band. Table 1 and Figure 3  
Figure 2: The spectrums of healthy and diseased leaf blade fractions: (**a**) original reflectance; (**b**) the ratio spectrum of diseased and healthy reflectance; (**c**) first derivative and (**d**) second derivative. illustrated statistical differences of the position, amplitude, area, ratio indices and normalized indices of \"three parameters\" between healthy and diseased leaf blade fractions, respectively. As shown in Table 1, variation coefficients of diseased leaf blade fractions were greater than those of healthy leaf blade fractions in various parameters of amplitude and area, except for yellow edge amplitude (Dy), yellow edge area (SDy) and near-infrared area (SDnir). The highest was red edge amplitude (Dr), which reached 0.365, followed by red edge area (SDr), red valley amplitude \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Variables**} & \multicolumn{2}{c}{**Maximum**} & \multicolumn{2}{c}{**Minimum**} & \multicolumn{2}{c}{**Mean**} & \multicolumn{2}{c}{**C.V.**} \\ \cline{2-9}  & **Diseased** & **Healthy** & **Diseased** & **Healthy** & **Diseased** & **Healthy** & **Diseased** & **Healthy** \\ \hline
**Db** & 0.002 & 0.004 & 0.001 & 0.003 & 0.001 & 0.003 & 0.222 & 0.105 \\
**BEP** & 530 & 523 & 501 & 515 & 517 & 520 & 0.017 & 0.002 \\
**Rg** & 0.209 & 0.173 & 0.076 & 0.111 & 0.148 & 0.132 & 0.196 & 0.106 \\
**GPP** & 560 & 555 & 553 & 548 & 560 & 551 & 0.002 & 0.003 \\
**Dy** & 0.001 & 0.000 & 0.000 & 0.000 & 0.001 & 0.000 & 0.221 & 1.527 \\
**YEP** & 583 & 555 & 550 & 550 & 558 & 551 & 0.016 & 0.001 \\
**Dr** & 0.008 & 0.011 & 0.001 & 0.008 & 0.003 & 0.009 & 0.365 & 0.080 \\
**REP** & 734 & 723 & 690 & 698 & 699 & 702 & 0.012 & 0.008 \\
**Ro** & 0.267 & 0.057 & 0.067 & 0.029 & 0.174 & 0.037 & 0.248 & 0.140 \\
**RTP** & 677 & 677 & 641 & 669 & 654 & 672 & 0.020 & 0.003 \\
**SDb** & 0.020 & 0.043 & 0.007 & 0.026 & 0.012 & 0.032 & 0.198 & 0.119 \\
**SDg** & 0.020 & 0.032 & 0.009 & 0.019 & 0.013 & 0.025 & 0.155 & 0.103 \\
**SDy** & 0.012 & \(-\)0.014 & \(-\)0.005 & \(-\)0.022 & 0.006 & \(-\)0.017 & 0.481 & \(-\)0.087 \\
**SDr** & 0.147 & 0.207 & 0.030 & 0.124 & 0.058 & 0.157 & 0.282 & 0.136 \\
**SDnir** & 0.048 & 0.007 & 0.008 & \(-\)0.007 & 0.027 & 0.002 & 0.287 & 1.102 \\ \hline \hline \end{tabular}
\begin{tabular}{c} C.V.: Coefficient of variation; Db: Blue edge amplitude; BEP: Blue edge position; Rg: Green peak amplitude; GPP: Green peak position; Dy: Yellow edge amplitude; YEP: Yellow edge position; Dr: Red edge amplitude; REP: Red edge position; Ro: Red valley amplitude; RTP: Red valley position; SDb: Blue edge area; SDg: Green peak area; SDy: Yellow edge area; SDr: Red edge area; SDnir: Near-infrared area.  
\end{table} 
Table 1: Descriptive statistics of spectral position, amplitude and area. Figure 3: Descriptive statistics of some ratio and normalized indices with spectral amplitude and area parameters. (Ro), blue edge amplitude (Db), blue edge area (SDb), green peak amplitude (Rg), and green peak area (SDg). This resulted from the different levels of ShB severity. Nevertheless, according to the maximum and minimum values of each parameter, it was clear that the whole ranges of Db, SDb, Dr, Ro, SDy, and SDnir were completely non-overlapping between ShB-infected and healthy leaf blade fractions, while these parameters of Rg, SDg, and SDr showed an inclusive or overlapping relationship. This finding suggests that the parameters of Db, SDb, Dr, Ro, SDy, SDnir facilitate the recognition of rice ShB. The positions of blue edge, green peak, yellow edge, red valley and red edge can move with changes in the biophysical and biochemical traits of vegetation.