Analysis of hyperspectral singularity of rice under Zn pollution stress

The aim of this study is to detect the stress levels of rice under Zn pollution by analyzing the characteristics of hyperspectral singularity. Hyperspectral reflectance and heavy metal concentration from different growth stages of rice in two consecutive years were collected in the field experiment. Wavelet transform was performed to hyperspectral reflectance (350-1 300 nm) by using “Daubechies 5” wavelet function, and three categories of singularity parameters as indicators of hyperspectral singularity of rice under Zn stress were explored, including singularity range (SR), singularity amplitude (SA) and singularity exponent (SE). The results showed that the wavelet coefficient of the fifth decomposition level of “Daubechies 5” wavelet function proved successful for accurately identifying the hyperspectral singularity of rice under Zn stress. SR of rice was concentrated on the region around 480-850 nm of spectral signal under Zn stress. Maximum value of SA occurred at the tillering stage, and the SA increased sharply from seeding stage to tillering stage and then decreased from jointing stage to anthesis stage and to mature stage, while the SE increased constantly from seeding stage to mature stage when rice was growing. Zn concentration in rice leaves had better linearity with the SA and SE with correlation coefficient (R2) of 0.8445 and root mean square error (RMSE) of 5.60. The hyperspectral singularity applying wavelet transform technique has been shown to indentify and quantitatively analyze the stress levels of rice under Zn pollution effectively and provide important reference for detecting other metal-induced stress on crop.