Evaluation of Tea Tree Leaf Chlorophyll Content Retrieval Using Multi-Angle Polarized Remote Sensing

Quantitative delineation of leaf chlorophyll content (LCC) within tea plantations is fundamental for optimized management of cultivation practices. Abundant researches have advanced methods for LCC estimation in tea plants, nevertheless, mechanism and influence of polarization reflection caused by specular reflection to LCC retrieval process were less reported. Thus, the present study leveraged multi-angle polarized remote sensing to delve into polarization reflection modeling and characteristic analysis of tea plant canopy, and its impact on LCC estimation was further explored, utilizing vegetation index methods. Results suggested that Maignan (M) polarization reflection model accurately captured variations of polarized reflectance, RMSE values between simulated polarization reflectance and its measured equivalent within 400–1000 nm spectral domain hovered around 0.0013, under forward observation paradigms encompassing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0^{\circ}, 10^{\circ}20^{\circ}$</tex>, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$30^{\circ}$</tex>. Specular reflectance component, calculated from polarized reflectance, wielded the most substantial influence on LCC estimations via NDVI in forward <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$30^{\mathrm{o}}\text{observation}$</tex>, compared with backward <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20^{\circ}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0^{\circ}\text{observations}$</tex>. Separation of specular reflection component rendered a noteworthy enhancement in the inversion accuracies of NDVI model for LCC estimation, approximately by 25% under a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$30^{\circ}$</tex> forward observation condition. The improved model accuracy indicators were quantified as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{R}^{2}= 0.53,\text{RMSE}=12.67\mu \mathrm{g}/\text{cm}^{2}$</tex>, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{RPD} =1.45$</tex>, highlighting the criticality of specifying and adjusting for specular reflection components in the enhancement of LCC estimation models using NDVI methods.