RadarSLAM: Radar based Large-Scale SLAM in All Weathers
本笔记基于摘要 + 公开资料,未读全文。
一句话讲什么(TL;DR)
让一台"会转圈的雷达"在大雾大雪天里也能给车画地图、记住自己走过哪。
这是个什么场景
想象你下大雪天开车回家。雪片糊在挡风玻璃上、车灯一开全是反光、GPS 在高架桥下信号断了——你只能靠对路口、对路牌的模糊印象往前蹭。自动驾驶车也会遇到一模一样的窘境:
- 相机(车的"眼睛"):跟人眼一样,黑灯瞎火、起雾下雪就抓瞎
- 激光雷达(用激光尺到处测距):精度高,但雨滴雪花会把激光打散,像在烟雾里打手电
- 雷达(毫米波,类似蝙蝠的回声定位,只是换成电磁波):波长更长,能"穿"过雨雾雪,几乎不挑天气
RadarSLAM 想做的事,就是只靠这台"全天候蝙蝠"的回波数据,同时完成两件事:知道自己在哪、画出周围地图。难点在于雷达图像很糊——噪声大、分辨率低、还经常出"鬼影"(multipath / speckle,多路径反射和斑点噪声),不像相机照片那样一眼能看懂。

之前的人怎么做的 — 3-5 bullet
- 视觉 SLAM(ORB-SLAM 系列):靠相机提取特征点匹配。优点是轻便便宜,缺点是怕黑、怕逆光、怕雨雾
- 激光雷达 SLAM(LOAM、Cartographer):靠 3D 点云配准(ICP / NDT)。精度高,但激光在恶劣天气下衰减严重
- 早期雷达 odometry:只做"前后两帧之间走了多远",不做闭环,不做全局地图,所以漂移会越积越大
- 基于深度学习的雷达定位:把雷达图当图像直接学,但需要大量标注,且泛化到新城市场景吃力
- 雷达 + GPS / IMU 融合:靠外部传感器消除漂移,但 GPS 在隧道、室内、高楼峡谷里不可靠
RadarSLAM 想做的是纯雷达 + 全图优化这条路:不依赖 GPS,也不靠学习模型,而是用经典 SLAM 框架(前端 odometry + 后端 pose graph)把雷达"用透"。
这篇论文的关键想法
打个比方:视觉 SLAM 是"明厨亮灶里的老师傅",整套菜谱(前端跟踪 + 回环 + 全图优化)已经很成熟。RadarSLAM 干的事就是把这套菜谱原样搬进"地下室厨房"——食材(数据)变糊了、灯(光线)暗了,但流程基本不变,只针对几样关键工序换工具:
- 位姿跟踪(odometry,"我刚才走了多远"):从扫描雷达的 polar image(极坐标图,下面解释)里抽稳定的特征点,对比相邻两帧,估计车开了多远、转了多少
- 回环检测(loop closure,"这地方好像来过"):当车绕回之前去过的路口,系统要能"认出来"。论文用一种适合雷达图的描述子(descriptor,下面解释)做地点识别,一旦匹配上就加一条"我又回到这了"的约束
- 位姿图优化(pose graph optimization,"把走偏的轨迹拉直"):把所有里程计估计 + 闭环约束扔进一个全局图优化器(g2o / GTSAM 这类工具),让长时间累积的漂移在闭环处被"拉回去"
- 全天候鲁棒:因为雷达本身不挑天气,上面这套流水线在雨、雾、雪、夜晚都成立——这是相比视觉/激光 SLAM 的核心卖点
等等,先慢一拍——这里面的几个词到底是什么?
- polar image:雷达每转一圈,把不同角度收到的回波拼成一张图。横轴是距离、纵轴是角度,跟相机照片完全两回事,得当成另一种"图像"来处理
- 描述子:把一帧观测压成一串数字"指纹"。两帧指纹像,就大概率是同一个地方
- pose graph:一张"我去过哪、相对怎么走"的关系图。每个节点是一帧位姿,每条边是一段相对位移
可以理解为:"视觉 SLAM 的方法论 + 雷达的传感器优势 = 一个能在现实世界恶劣天气下用的 SLAM"。

它怎么做的(方法)— 3-4 段
第一段 — 雷达数据预处理(像把模糊照片里的"亮点"挑出来):扫描雷达每转一圈输出一张 polar image,每行是某个角度上一束波的回波强度(intensity vs range)。原图噪声大,需要做峰值检测(peak detection)+ 阈值过滤,把"看起来像真实物体"的反射点挑出来。这一步等价于把雷达 raw 数据变成稀疏的 2D 关键点集合,类似从相机图里抽 ORB 特征点。
第二段 — 帧间 odometry(像两张拼图边对齐,看看挪了多少):拿到当前帧的关键点集合,跟上一帧做匹配(matching),估计两帧之间的相对位姿 ΔT(dx, dy, dθ,前后/左右/转角)。具体配准方法可能是 RANSAC(一种排除"离谱点"的统计方法)+ 几何一致性筛选,或者类似 ICP 的迭代最近点。这一步给出短时段的运动估计,但会随着时间累积漂移。
第三段 — 回环检测(像看到熟悉路牌想起"我来过这"):每隔一段距离把当前帧的全局描述子和历史帧库比对。如果发现高度相似的历史帧,且几何上自洽(不是巧合),就触发一次 loop closure,加一条约束边到 pose graph 里。雷达的描述子设计是关键挑战——既要对视角变化鲁棒,又要对噪声/动态物体不敏感。具体描述子设计需读原文。
第四段 — 全图优化与建图(像老师把答错的题分摊回前几页改回去):把所有"帧到帧"约束和"闭环"约束一起扔给非线性最小二乘求解器(pose graph optimization),优化所有历史位姿,让闭环处的累计误差被分摊回整条轨迹。最终输出一条全局一致的轨迹 + 一张由所有 keyframe(关键帧)雷达点拼起来的全局地图。
实验在做什么
论文用公开雷达数据集(Oxford Radar RobotCar Dataset 或类似数据集)做评测,重点关注:
- 轨迹精度:和真值(ground truth,一般是 GPS-RTK + INS)比,看绝对/相对位姿误差(ATE / RPE)。具体数字需读原文
- 天气鲁棒性:在雨/雾/雪/夜晚等不同天气分别跑,看精度是否大幅退化。这是论文最大的卖点
- 对比 baseline:和视觉 SLAM、激光 SLAM、纯 radar odometry(不做闭环)对比
- 大尺度场景:跑长达数公里甚至几十公里的城市场景,看回环和全局优化是否真的能压住漂移
你应该懂的几个新词 — 4-6 个
- FMCW scanning radar:调频连续波扫描雷达,发射频率随时间线性变化的电磁波,通过回波频差测距,配合机械旋转扫一圈
- Polar image:极坐标图。每行是一个角度,每列是该角度上不同距离的回波强度。和相机图(笛卡尔坐标)不一样,处理时常要转成 cartesian
- Pose graph optimization:位姿图优化。每个节点是一帧的位姿,每条边是一个相对位姿约束。优化目标是让所有约束的残差最小
- Loop closure:回环检测/闭环。识别"我现在在的地方之前来过",然后加一条跨越很多帧的约束,把累积漂移拉回正
- Place recognition descriptor:地点识别描述子。把一帧的传感器观测压成一个紧凑向量,用向量相似度判断"是不是同一个地方"
- Odometry drift:里程计漂移。短期估计精度尚可,但每帧的小误差不停累加,跑久了轨迹会"飘走"
它和其他论文什么关系
- 上游传感器思路:受到 millimap(毫米波建图)、rf-slam(早期 RF SLAM)系列启发,都是"用穿透性强的电磁波代替光"
- 方法论上游:直接借鉴视觉 SLAM 的经典 pipeline(ORB-SLAM、Cartographer),尤其是 pose graph + 回环检测这套架构
- 数据集层面:和 Oxford Radar RobotCar、MulRan 这类公开雷达数据集互相催化
- 后续工作:催生了 Under the Radar、Kidnapped Radar、RaLL(Radar Localization Learning)等一系列雷达 SLAM/定位工作,以及把雷达和 lidar/camera 融合的多模态 SLAM
- 横向参考:本仓库里
nlos-mmwave.md关注非视距毫米波感知,millimap.md关注雷达建图,本文是把这两条思路往"完整 SLAM 系统"推进的代表
我建议这样读 — 3-4 步
- 先看图和实验:直接翻论文里的轨迹图和定性建图图,感受"在雪天/雾天里画出的地图长啥样"。这是最能传递 motivation 的部分
- 看 odometry 章节:搞清楚雷达关键点怎么提的、帧间匹配是怎么做的——这是和视觉 SLAM 最不一样的地方
- 看 loop closure 章节:重点看描述子设计。雷达图的全局描述子是这条线最有研究价值的子问题
- 跳过 pose graph 细节:如果你已经懂 g2o/GTSAM,这部分就是标准操作;不懂的话回头补 SLAM 教材的 pose graph 章节再来
为什么值得读
- 传感器视角的开拓:在视觉/激光 SLAM 卷到极致的时代,提醒你"换个传感器,整个问题域就变了"——尤其是为自动驾驶、低空飞行、户外机器人等真实部署场景服务时,恶劣天气是无法回避的
- 经典框架 + 新传感器的范式:展示了一种很务实的研究模式——不是发明新理论,而是把成熟方法论"翻译"到新数据上,并解决翻译过程中的关键技术债
- 完整系统:不只做 odometry,而是做完整 SLAM(前端 + 回环 + 全图优化),可以当成"如何搭一个端到端 SLAM 系统"的样本工程
- 对 embodied AI 的意义:未来机器人/无人机要走出实验室、面对真实天气,全天候感知是必需品。RadarSLAM 是这条路上的早期里程碑
◼
引用本笔记 / Cite this note
@online{eai_radarslam_2026,
title = {(readable note) RadarSLAM: Radar based Large-Scale SLAM in All Weathers},
author = {Zhou, Jason},
year = {2026},
note = {Note on a 2020 paper},
howpublished = {\url{https://estelledc.github.io/embodied-ai-reading-station/papers/radarslam/}},
organization = {Embodied AI Reading Station}
}
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