National Institute for Research and Development in Forestry "Marin Dracea", 128 Blvd. Eroilor, Voluntari 077190, Ilfov, Romania; Department of Geology, Geography and the Environment, University of Alcala, c/Colegios 2, 28801 Alcala de Henares, Spain.
Center for the Study of the Biosphere from Space, University of Paul Sabatier, 18 av. Edouard Belin, Toulouse 2801, France.
Sci Total Environ. 2019 Nov 1;689:1104-1114. doi: 10.1016/j.scitotenv.2019.06.494. Epub 2019 Jun 29.
Natural and anthropogenic disturbances pose a significant threat to forest condition. Continuous, reliable and accurate forest monitoring systems are needed to provide early warning of potential declines in forest condition. To address that need, state-of-the-art simulations models were used to evaluate the utility of C-, L- and P-band synthetic aperture radar (SAR) sensors within an integrated Earth-Observation monitoring system for beech, oak and coniferous forests in Romania. The electromagnetic simulations showed differentiated sensitivity to vegetation water content, leaf area index, and forest disturbance depending on SAR wavelength and forest structure. C-band data was largely influenced by foliage volume and therefore may be useful for monitoring defoliation. Changes in water content modulated the C-band signal by <1 dB which may be insufficient for a meaningful retrieval of drought effects on forest. C-band sensitivity to significant clear-cuts was rather low (1.5 dB). More subtle effects such as selective logging or thinning may not be easily detected using C- or L-band data with the longer P-band needed for retrieving small intensity forest disturbances. Overall, the simulations emphasize that additional effort is needed to overcome current limitations arising from the use of a single frequency, acquisition time and geometry by tapping the advantages of dense time series, and by combining acquisitions from active and passive sensors. The simulation results may be applicable to forests outside of Romania since the forests types used in the study have similar morphological characteristics to forests elsewhere in Europe.
自然和人为干扰对森林状况构成重大威胁。需要连续、可靠和准确的森林监测系统，以便对森林状况的潜在下降发出预警。为满足这一需求，使用最先进的仿真模型评估了 C、L 和 P 波段合成孔径雷达（SAR）传感器在罗马尼亚山毛榉、橡树和针叶林综合地球观测监测系统中的效用。电磁仿真结果表明，SAR 波长和森林结构对植被含水量、叶面积指数和森林干扰的敏感性存在差异。C 波段数据主要受叶量影响，因此可能有助于监测落叶。含水量的变化使 C 波段信号的调制幅度<1dB，这对于从森林干旱效应中获取有意义的信息可能是不够的。C 波段对大规模皆伐的敏感性相当低（1.5dB）。使用 C 波段或 L 波段数据，由于需要更长的 P 波段来获取小强度的森林干扰，可能难以检测到诸如选择性采伐或间伐等更微妙的影响。总体而言，这些仿真结果强调需要克服当前由于使用单一频率、采集时间和几何形状所带来的限制，利用密集的时间序列的优势，并结合主动和被动传感器的采集来实现。由于研究中使用的森林类型与欧洲其他地区的森林具有相似的形态特征，因此模拟结果可能适用于罗马尼亚以外的森林。
