实验技术与管理

动态水面的电磁散射特性对于研究海洋微波遥感机理和应用具有重要意义。水槽实验是定量测量水面电磁散射特性的重要手段，但传统雷达观测设备在水槽实验中难以实现多角度同时观测，对于捕捉动态水面电磁散射特性的连续变化存在局限。为此，该研究设计了一种基于多输入多输出合成孔径雷达（multiple-input multiple-output synthetic aperture radar,MIMO-SAR）的动态水面电磁散射特性水槽实验方法。利用微波暗室中的大型风浪水槽产生不同海况的动态水面，通过MIMO-SAR获得多角度下的散射信号，分析角度、海况参数对电磁散射特性的影响规律。该实验方法可以同时观测不同入射角度下的水面电磁散射特性，为定量研究动态水面电磁散射特性与海况参数、观测角度之间的关系提供了有效的技术手段。

[Objective] Understanding the electromagnetic scattering characteristics of dynamic water surfaces is fundamental for advancing microwave remote sensing in ocean environments. The backscattering response of ocean surfaces is highly dependent on the incidence angle, with notable differences in the scattering mechanisms across nadir-, low-, and medium-incidence geometries. At low incidence angles, the surface interactions are dominated by specular and quasi-specular reflections, exhibiting strong angular dependence and nonlinearity, and are particularly sensitive to the surface roughness. However, the existing theoretical models and satellite-derived empirical approaches often fall short in characterizing complex scattering behaviors for dynamic sea states, especially at low incidence angles. In-situ field measurements face limitations in cost, flexibility, and environmental variability. To overcome these challenges, this study proposes a laboratory-based experimental method for observing multi-angle microwave scattering from dynamic water surfaces using the Multiple-Input Multiple-Output Synthetic Aperture Radar(MIMO-SAR) system. The objective is to establish a controlled, high-resolution, and multi-angle observation framework for capturing the intricate variations in radar backscatter induced by wind, waves, and swell, thereby supporting the development of scattering models and quantitative remote sensing applications. [Methods] The experimental setup was implemented in a large-scale ocean dynamics simulation tank housed within a microwave anechoic chamber, enabling the generation of repeatable wind and wave conditions while minimizing electromagnetic interference and multipath effects. The MIMO-SAR radar system, equipped with multiple transmit and receive antennas, was deployed above the tank for high-resolution imaging of the water surface across a wide angular range. By tilting the main beam direction off-nadir and utilizing virtual aperture synthesis, the radar system captured simultaneous backscatter signals at different incidence angles. The dynamic water surfaces were generated using various combinations of wind speeds and long-period regular waves to simulate typical sea states. Auxiliary sensors, including wave gauges and anemometers, were employed to provide ground-truth measurements of the environmental parameters. For each test case, radar echo signals were collected over a continuous 20 s period and averaged over time to extract the statistical characteristics of the scattering intensity. The signal processing chain included calibration of channel mismatches, compensation of array errors, and generation of the SAR image, resulting in two-dimensional range-azimuth scattering intensity maps under each experimental condition. [Results] The experimental results revealed distinct differences in the scattering behavior of smooth versus rough water surfaces. For calm water, scattering was concentrated in a narrow region near the specular direction, consistent with mirror-like reflection. As the wind speed increased, the surface roughness intensified, expanding the observable backscatter region and weakening the central bright spot, thereby forming arc-shaped streaks that extended as the incidence angle increased. When long-period waves were introduced, multiple bright-scatter zones appeared in the SAR images, corresponding to the wavefronts aligned with the radar illumination. The spatial separation of these zones matched the wavelength of the imposed swell, confirming that they originate from periodic slope modulation. Statistical analysis showed a strong angular dependence of the averaged backscatter intensity across the incidence angles, where the peak values were obtained near nadir and rapid decay was apparent beyond 10–15°. Higher wind speeds broadened the effective range of observation angles and enhanced backscatter at off-nadir angles owing to the increased quasi-specular reflection. The presence of swell modified the slope distribution, enabling significant returns from angles farther from nadir, particularly under low-wind conditions. Furthermore, asymmetry between the upwind and downwind directions was observed, with more stable backscatter trends in the downwind side and pronounced fluctuations upwind, highlighting the directional modulation effect induced by the wave orientation and slope distribution. [Conclusions] This study presents a novel laboratory approach for quantitative assessment of multi-angle microwave scattering from dynamic water surfaces using the MIMO-SAR system. The surface roughness, wave structure, and incidence geometry jointly influence the spatial and angular distribution of radar backscatter. The proposed method successfully captures complex scattering features under various wind-wave combinations, revealing nonlinear, asymmetric, and directionally modulated behaviors, especially near nadir. These findings provide valuable experimental evidence for validating and refining electromagnetic scattering models at low incidence angles, offering new insights into the design of remote sensing instruments and the interpretation of microwave backscatter data.