Full-waveform LiDAR bathymetry of the La Baule bay

The LiDAR used is the Titan DW 600 from Teledyne Optech of the “Platform topo-bathymétrique aéroportée Nantes-Rennes”. Both 532-nm and 1064-nm LiDAR swath were acquired 6th and 7th of October 2017, at 400 m above ground with a FOV of 28° giving strip image width of 199.5 m with a nominal footprint of 0.49 m along-track and 0.29 m cross-track. A mirror compensation and a sidelap of 30% was used to prevent empty space between strips. The effective incident angle range was from 4 to 20°. The aircraft speed being 201.7 km/h the down track footprint rise up to 0.98 m on sideway what justify a final spatial resolution of 1 m. The laser pulse frequency was set to 50 kHz (100 kHz locally) giving an overall mean point density of 3.52 points/m². The full-waveform (FWF) was recorded only in 532-nm with a maximum length of 60 m, at 1 GHz frequency, resulting in a vertical resolution of 0.15 m. The Optech LiDAR Mapping Suite (LMS) combines a Global Positioning System (GPS) and Inertial Measurement Unit (IMU) to provide a georeferenced point cloud and associated FWF with strip optimization. To compute the complete point cloud, LMS uses an analogous approach to photogrammetric block adjustment. On overlap areas between each flight line, planes (typically roofs in land) are extracted and used in a least squares adjustment model provided by LMS. The trajectory accuracy provided by GEOFIT Company was better than 0.15 m in planimetry and 0.08 m on elevation. The set of data is stored in a zip file composed of the following image files associated with ENVI headers which are text files describing the image format. - LaBaule_2017106-7-orthophoto: contain the mosaic of RGB image acquired with the camera associated to the LiDAR. - LaBaule_2017106-7_536nm_raytracing-incident_angles_2m: contains the effective incident angle of each pixel retained in the mosaic with a pixel FOV of 0.3° and with a tilling of image strips in the top of each other from the North to the South. - LaBaule_2017106-7_1064nm_raytracing_discrete_echo_ranges_2m: contains the elevation of the water surface of each pixel. - LaBaule_2017106-7_536nm_raytracing_FWF_2m: contains the row FWF projected on the image plane at 0 m NGF with an offset of 30 m for easy spectral processing of the FWF (true range are stored in band names). - LaBaule_2017106-7_536nm_raytracing_FWF_2m_intensity_stats: contains the basic statistics of the FWF intensities. - LaBaule_2017106-7_536nm_raytracing_FWF_2m_range_stats: contains the min, max and thickness of the FWF ranges. - LaBaule_2017106-7_536nm_raytracing_FWF_2m_row_results: contains the row results of water surface and method 1 (dddNCFWF echoes) and method 2 (NCFWFT-1 bottoms) bathymetries as defined in https://doi.org/10.3390/rs11020117. - LaBaule_2017106-7_536nm_raytracing_FWF_4m_final_bathymetry: contains the final (cleaned NCFWFT-1 bottoms) bathymetry. The same data were acquired the 11th of August 2018 during a low tide with the same settings without RGB camera but with a new FWF recorder giving a lot less noisy signal allowing a constant spatial resolution of 1 m. The set of data is stored in a zip file composed of the following image files associated with ENVI headers which are text files describing the image format. - LaBaule_20180811_536nm_raytracing-incident_angles_1m: contains now 3 channels for the effective incident angle, the strip number and the GPS time. - LaBaule_20180811_1064nm_raytracing_discrete_echo_ranges_1m: contains the elevation of the water surface and all echoes above it in each pixel. - LaBaule_20180811_536nm_raytracing_FWF_1m: contains the row FWF projected on the image plane at 0 m NGF with an offset of 30 m for easy spectral processing of the FWF (true range are stored in band names). - LaBaule_20180811_536nm_raytracing_FWF_1m_intensity_stats: contains the basic statistics of the FWF intensities. - LaBaule_20180811_536nm_raytracing_FWF_1m_range_stats: contains the min, max and thickness of the FWF ranges. - LaBaule_20180811_536nm_raytracing_FWF_1m_row_results: contains the row results of water surface and method 1 (dddNCFWF echoes) and method 2 (NCFWFT-1 bottoms) bathymetries as defined in https://doi.org/10.3390/rs11020117. - LaBaule_20180811_536nm_raytracing_FWF_1m_final_bathymetry: contains the best of dddNCFWF echoes and NCFWFT-1 bottoms simply presented with the application of a 5x5 median filter. -本次实验所用的激光雷达（LiDAR, Light Detection and Ranging）为Teledyne Optech公司生产的Titan DW 600型，搭载于“南特-雷恩机载地形测深平台（Platform topo-bathymétrique aéroportée Nantes-Rennes）”。2017年10月6日至7日采集了532nm与1064nm两个波段的激光雷达条带数据，飞行高度距地面400m，视场角（Field of View, FOV）为28°，单条带成像宽度为199.5m，标称沿航迹向光斑尺寸（footprint）为0.49m，跨航迹向为0.29m。采用反射镜补偿方案与30%的旁向重叠率，以消除条带间的空白区域。有效入射角范围为4°至20°。机载平台航速为201.7km/h，导致侧方航迹向光斑尺寸增至0.98m，因此最终空间分辨率设定为1m。激光脉冲重复频率设为50kHz（局部区域为100kHz），整体平均点云密度为3.52点/m²。仅在532nm波段采集全波形（Full-Waveform, FWF）数据，采样频率为1GHz，最大记录长度为60m，垂直分辨率达0.15m。 Optech激光雷达测绘套件（LiDAR Mapping Suite, LMS）集成全球定位系统（Global Positioning System, GPS）与惯性测量单元（Inertial Measurement Unit, IMU），可生成地理配准点云与配套全波形数据，并支持条带优化。LMS采用与摄影测量区域网平差类似的方法完成点云拼接：在各飞行航线的重叠区域，提取平面特征（通常为陆地屋顶），并代入LMS提供的最小二乘平差模型进行解算。GEOFIT公司提供的轨迹精度为：平面位置精度优于0.15m，高程精度优于0.08m。 第一批次数据存储于压缩包中，所有影像文件均附带ENVI格式头文件（文本格式，用于描述影像格式参数），具体文件如下： 1. LaBaule_2017106-7-orthophoto：搭载于激光雷达的相机采集的RGB正射影像镶嵌图。 2. LaBaule_2017106-7_536nm_raytracing-incident_angles_2m：镶嵌图中有效像素对应的入射角数据，像素视场角为0.3°，影像条带由北至南依次堆叠。 3. LaBaule_2017106-7_1064nm_raytracing_discrete_echo_ranges_2m：每个像素对应的水面高程数据。 4. LaBaule_2017106-7_536nm_raytracing_FWF_2m：将原始全波形投影至0m NGF基准面的影像平面上，偏移量为30m以简化全波形的光谱处理流程（真实距离值存储于波段名称字段中）。 5. LaBaule_2017106-7_536nm_raytracing_FWF_2m_intensity_stats：全波形强度的基础统计数据。 6. LaBaule_2017106-7_536nm_raytracing_FWF_2m_range_stats：全波形距离的最小值、最大值与厚度统计数据。 7. LaBaule_2017106-7_536nm_raytracing_FWF_2m_row_results：水面高程、方法1（dddNCFWF回波）与方法2（NCFWFT-1水底）反演的测深结果，具体定义参见https://doi.org/10.3390/rs11020117。 8. LaBaule_2017106-7_536nm_raytracing_FWF_4m_final_bathymetry：经清洗的NCFWFT-1水底最终测深成果。 2018年8月11日在低潮时段采集了第二批次数据，采用相同的飞行参数，未搭载RGB相机，但更换了全新的全波形记录仪，信号噪声显著降低，可实现稳定的1m空间分辨率。该批次数据同样存储于附带ENVI格式头文件的压缩包中，具体文件如下： 1. LaBaule_20180811_536nm_raytracing-incident_angles_1m：包含3个通道，分别为有效入射角、条带编号与GPS时间戳。 2. LaBaule_20180811_1064nm_raytracing_discrete_echo_ranges_1m：每个像素对应的水面高程及所有高于该水面的回波数据。 3. LaBaule_20180811_536nm_raytracing_FWF_1m：将原始全波形投影至0m NGF基准面的影像平面上，偏移量为30m以简化全波形的光谱处理流程（真实距离值存储于波段名称字段中）。 4. LaBaule_20180811_536nm_raytracing_FWF_1m_intensity_stats：全波形强度的基础统计数据。 5. LaBaule_20180811_536nm_raytracing_FWF_1m_range_stats：全波形距离的最小值、最大值与厚度统计数据。 6. LaBaule_20180811_536nm_raytracing_FWF_1m_row_results：水面高程、方法1（dddNCFWF回波）与方法2（NCFWFT-1水底）反演的测深结果，具体定义参见https://doi.org/10.3390/rs11020117。 7. LaBaule_20180811_536nm_raytracing_FWF_1m_final_bathymetry：通过对dddNCFWF回波与NCFWFT-1水底结果择优，并经5×5中值滤波得到的最终测深成果。