植被冠层辐射散射信号中蕴含了丰富的植被信息,通过构建植被冠层辐射散射模型,可以实现植被结构等生物物理参数的遥感定量反演。迄今为止,可见光/近红外、热红外、微波波段均已发展了大量的模型,这些模型在参数反演方面各具优势,但不同波段的模型又有其自身的局限性。跨波段的联合模拟可以实现模型间的优势互补,进而提高地表参数的反演精度,近年来已有学者专注于可见光/近红外与热红外模型,热红外与微波模型,主被动微波模型,以及可见光/近红外与微波模型的联合模拟和协同反演,但多是两两联合,且主要是基于经验模型或解析模型。基于3维场景的植被冠层辐射散射特性模拟模型可以细致刻画不同组分的结构和空间分布特征,对于由植被结构引起的多次散射和组分比例变化的考虑具有优势。本文主要介绍了3维模拟模型在可见光/近红外、热红外和微波波段,以及跨波段联合模拟方面的研究进展,从模型机理、场景统一、以及组分理化参数的统一的角度,探讨了构建多波段3维模拟系统的可行性,展望了多波段3维模拟模型的发展趋势。

Canopy radiation and scattering signal contain high amounts of vegetation information. Biophysical parameters can be quantitatively retrieved by establishing a canopy radiation and scattering model and inverting this model. Thus far, models in visible/near infrared(VIS/NIR), thermal infrared(TIR), and microwave(MW) regions have been developed. Each model suitable to a specific spectral(frequency) domain is characterized by advantages and disadvantages in terms of parameter inversion. Joint simulation models can produce complementary advantages and improve inversion precision. Although joint simulation and inversion research area has been improved, studies are mostly based on semi-empirical models or analytical models. A three-dimensional model is more suitable to characterize multiple scattering caused by vegetation structures and specified distribution of different components.This article presents a review on advances in three-dimensional canopy radiation and scattering characteristic simulation models specifically used for VIS/NIR, TIR, and MW regions, as well as a joint simulation model. The three-dimensional VIS/NIR Bidirectional Reflectance Distribution Function(BRDF) model can be divided into two categories, namely, Monte Carlo ray tracing and radiosity models. The model is improved in terms of the ability to simulate remote sensing images with kilometer pixels and to simulate non-lambert characteristic of components. The three-dimensional TIR directional radiation model can be extended from the three-dimensional BRDF model by considering self-emission. The three-dimensional MW backscatter model includes incoherent and coherent models. A coherent model can export phase information and is more accurate, especially at low frequencies, than an incoherent model. MW emission can be simulated by calculating bistatic scattering with a three-dimensional MW backscatter model. In addition to this VIS/NIR and TIR joint simulation model and the active and passive MW joint simulation model, VIS/NIR and active MW joint simulation models were discussed. These models were listed and described in this paper. Based on our analysis, three scientific issues and corresponding solutions were proposed using the three-dimensional joint simulation models. One issue involved scene unification. Models suitable for different spectral(frequency) domains describe a specific scene in different details. A standard should be established to perform simulations based on the same scene. Another issue involves the unity of physical and chemical parameters of components. Driving parameters vary. Therefore, transformation is required, and some models(e.g., PROSPECT and dual-dispersion models) should be coupled to convert various parameters into few but unified parameters. The last issue is the choice of efficient inversion methods. three-dimensional models require more calculation than other models. Look-up table and neural network methods are two of the commonly used approaches. However, these methods should be improved to satisfy three-dimensional joint simulation models. Other prospects are developed for further advancements of the joint three-dimensional simulation model. Three-dimensional joint simulation systems should be developed and used by researchers in future studies, considering that remote sensing platforms of the mechanism models(http://210.72.27.51:83/ModelCategory/All/) developed by the State Key Laboratory of Remote Sensing Science are constantly improved.