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摘要: 星载合成孔径雷达(SAR)以卫星等空间飞行器为运动平台,具有全天时、全天候、全球观测能力,已成为一种不可或缺的对地观测手段。当前,我国星载SAR已实现分辨率从米级到亚米级、系统体制从正侧视条带向方位扫描聚束、从单通道向多通道、极化方式从单一极化到全极化的技术跨越。随着技术的不断进步,未来星载SAR将在体制、概念、技术、模式等方面取得突破,包括高分辨率宽幅成像、多基地、轻小型化、智能化等,从而不断拓展星载SAR的观测维度,实现多维度信息获取。该文将围绕星载SAR的技术发展趋势展开论述。Abstract: Spaceborne Synthetic Aperture Radar (SAR), which can be mounted on space vehicles to collect information of the entire planet with all-day and all-weather imaging capacity, has been an indispensable device for earth observation. Currently, the technology of our spaceborne SAR has achieved a considerable technological improvement, including the resolution change from meter to submeter, the imaging mode from stripmap to azimuth beam steering like the sliding spotlight, the practical application of the multichannel approach and the conversion of single polarization into full polarization. With the development of SAR techniques, forthcoming SAR will make breakthroughs in SAR architectures, concepts, technologies and modes, for example, high-resolution wide-swath imaging, multistatic SAR, payload miniaturization and intelligence. All of these will extend the observation dimensions and obtain multidimensional data. This study focuses on the forthcoming development of spaceborne SAR.
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图 1 不同分辨率SAR图像对比(X波段,分辨率自左至右分别为0.1 m, 0.5 m和2.0 m,场景分别为电塔和农田,中国科学院空天信息创新研究院(下文简称AIR-CAS)航天微波遥感系统部供图)
Figure 1. SAR image comparison between different resolution (tower and farm at X band, the resolution are 0.1 m, 0.5 m and 2.0 m. Images are provided by the Department of Space Microwave Remote Sensing System, AIR-CAS)
图 35 机载P波段混合极化SAR(圆极化发射/双线极化接收)极化分解图像:红色表示偶次散射,蓝色表示表面散射,绿色表示体散射(AIR-CAS供图)
Figure 35. Polarimetric decomposition image of airborne P-band hybrid polarimetric SAR (circularly polarized on transmit and dual-circularly polarized on receive) Red for double-bounce scattering, blue for single-bounce scattering and green for volume scattering (Image provided by AIR-CAS)
表 1 SAR图像分辨率与典型军事目标关系(m)
Table 1. The relationship between the resolution and typical military targets (m)
目标 发现 识别 确认 描述 雷达 3 0.9 0.3 0.15 无线通讯设施 3 1.5 0.3 0.15 部队单位或营地 3 3 1.2 0.3 机场设施 6 4.5 3 0.3 火炮兵器/火箭 0.9 0.6 0.15 0.05 飞机 4.5 1.5 0.9 0.15 司令部 3 1.5 0.9 0.15 导弹阵地 3 1.5 0.6 0.3 中小型船只 7.5 4.5 0.6 0.3 车辆 1.5 0.6 0.3 0.05 表 2 DEM指标划分标准(m)
Table 2. Index classification criteria of DEM(m)
空间分辨率 绝对高程精度 相对高程精度 HRTI-1 90 ×90 < 30 < 20 HRTI-2 30 ×30 < 18 < 12 HRTI-3 12 ×12 < 10 < 2 HRTI-4 6 ×6 < 5 < 0.8 HRE-4 4 ×4 < 5 < 0.8 表 3 不同体制的优缺点对比
Table 3. Advantages and disadvantages comparison between different systems
信号体制 优点 缺点 传统脉冲体制 收发天线共用 占空比低,发射功率大 连续波体制 占空比~100%,峰值功率低 收发天线无法共用 间断连续波体制 占空比90~100%,结合脉冲与连续波的优势 回波信号部分缺失,需要估计重构 -
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