Water level is an important indicator of wetland hydrological regime. Detection of wetland water levels through interferometric synthetic aperture radar (InSAR) has outstanding advantage, including high spatial resolution, high accuracy, low cost, and high efficiency. We introduced prerequisites for the monitoring of wetland water levels with InSAR, discussed the types of InSAR techniques, the influencing factors for monitoring wetland water levels and their advantages and disadvantages. There are three prerequisites for effectively detecting wetland water levels with InSAR techniques: 1) the presence of emergent aquatic plants; 2) the main backscattering mechanism is double bounce scattering; and 3) the interferometric coherence exceeds a certain threshold. Current water level monitoring techniques have been developed from traditional InSAR techniques to advanced InSAR techniques, such as STBAS, MM, and DSI. These techniques evolve from detecting relative water level changes to estimate absolute water level and water depth time series. The influencing factors of InSAR techniques for monitoring wetland water levels include operating para-meters of the synthetic aperture radar (SAR) and characteristics of the wetlands themselves. Finally, we proposed the key directions for future research in this field: i) investigating the potential use of specific water level monitoring techniques in other regions with different backscattering and interferometric coherence characteristics; ii) developing new algorithms to integrate multi-sensor, multi-track, multi-band, multi-polarization, and multi-temporal InSAR repeat-pass observation; iii) considering alternative sources of SAR data; and (iv) strengthening research on "by-products" of wetland water level monitoring with InSAR, such as wetland hydrological connectivity, flow direction, and flow regime.
湿地水位是表征湿地水文情势的重要指标,干涉合成孔径雷达(InSAR)监测湿地水位具有空间分辨率高、精度高、成本低和效益好等突出优势。本文简要介绍了InSAR监测湿地水位的先决条件,系统阐述了InSAR监测湿地水位技术的类型及其优缺点,重点探讨了InSAR监测湿地水位的影响因素。InSAR监测湿地水位须满足三大前提条件:1)存在非淹没水生植被;2)主要后向散射机制为双回波散射;3)干涉相干性超过一定的阈值。目前,该水位监测技术已从传统的InSAR技术发展到STBAS、MM和DSI等改进的InSAR技术,已由监测相对水位变化发展到监测绝对水位和水深时间序列。InSAR监测湿地水位的影响因素包括合成孔径雷达(SAR)的工作参数和湿地本身的特性。最后,指出该领域未来亟待加强的研究方向为:探讨该水位监测技术应用于更多具有不同后向散射特性及干涉相干性特征的其他生态区的潜力;开发多传感器、多轨道、多波段、多极化和多时相的InSAR新算法;引入新的SAR数据源;加强InSAR监测湿地水位的“副产品”,如湿地水文连通性、流向和流态等研究。.
Keywords: InSAR; backscattering; hydrological connectivity; interferometric coherence; water level; wetland.