Testing a multispectral full waveform lidar for vegetation canopy characterization

陆地激光扫描仪(TLS)通过对关键生物物理变量进行快速、半自动的测量，具有前所未有的精度，有可能给植被冠层结构的测量带来革命性的变化。叶面积指数、方向间隙分数、丛生指数和垂直叶分布等变量可以通过使用轻型、坚固耐用的野外便携式设备在几分钟内记录的数百万个激光采样点的反向散射能量来确定。申请者最近使用商业上可用的TLS测量和模拟森林和林地树冠结构的研究已经确定了这种测量技术的优点和缺点，最重要的是突出了对背向散射激光能量进行全波形数字化的多光谱激光系统的需要，以实现其全部潜力。这一概念验证应用的目标是开发和测试一种具有全波形数字化的多光谱激光系统，用于表征植被冠层结构和组成。索尔福德大学(丹森)和Halo Photonics Ltd.(Pearson)目前正在开发第一台定制的多光谱半球扫描激光器，用于表征植被树冠。这个野外便携式系统将记录两个回波，第一个和最后一个脉冲，最初在1550和1040 nm的激光波长下工作，以利用植被成分(叶、针、茎、枝)在中红外和近红外中的光谱反射差异。该系统的开发由大学通过其资本投资基金提供支持，并从Halo Photonics研发预算中拨出一小笔资金。为了实现这一概念验证的目标，建议在开发这一系统的同时，开发一个多光谱全波形原型，以测试这种系统是否能够比目前的离散回波系统提取更准确的植被冠层特征三维信息。这一概念验证的三个要素是：(I)基于计划中的离散回波系统的类似组件测试全波形数字化和信号处理模块；(Ii)在Lewis、Disney和Hancock所做工作的基础上对多光谱全波形激光扫描仪进行基于模型的模拟；以及(Iii)在一系列植被目标和校准对象上以静态模式使用该系统，以验证模型并测试模型反演的可能性。

Terrestrial laser scanners (TLS) have the potential to revolutionise measurement of vegetation canopy structure by making rapid, semi-automatic measurements of key biophysical variables with unprecedented levels of accuracy. Variables like leaf area index, directional gap fraction, clumping index and vertical foliage distribution can be determined by recording the backscattered energy from several million laser sample points recorded within a few minutes using lightweight, rugged and field portable devices. Recent research by the applicants to measure and model forest and woodland canopy structure, using commercially available TLS, has identified the strengths and weaknesses of this measurement technique and most significantly has highlighted to the need for multispectral laser systems with full waveform digitization of the backscattered laser energy to realize its full potential. The objective of this Proof of Concept application is to develop and test a multispectral laser system with full waveform digitization for characterizing vegetation canopy structure and composition. University of Salford (Danson) and Halo Photonics Ltd. (Pearson) are currently developing the first custom-built multispectral hemispherical scanning laser for vegetation canopy characterization. This field-portable system will record two returns, first and last pulse and operate at laser wavelengths of 1550 and 1040nm initially, to exploit spectral reflectance differences in vegetation components (leaves, needles, stems, branches) in the middle infrared and near infrared respectively. The development of the system is supported by the University through its Capital Investment fund with a small allocation from the Halo Photonics R&D budget. To achieve the objectives of this Proof of Concept it is proposed that, in parallel with the development of this system, a multispectral full waveform prototype will be developed in order to test whether such a system may be capable of extracting more accurate three-dimensional information on vegetation canopy characteristics than the current discrete-return systems. The three elements to this proof of concept are (i) testing a full waveform digitization and signal processing module based similar components of the planned discrete return system, (ii) performing model-based simulations of a multispectral full waveform laser scanner building on the work done by Lewis, Disney and Hancock, and (iii), using the system in static mode, on a range of vegetation targets and calibration objects, in order to validate the model and test the potential for model inversion.