DOI: 10.6078/d1bh9z
title: Data from: LiDAR-derived digital elevation model of Whale's Tail Marsh, San Francisco Bay, 2019

description: Data presented are a geospatially-aligned (NAD83) raster image with raster
 values as bare-earth elevation values (NAVD88) of mudflats, marsh, and
 levees around Whale's Tail Marsh, South San Francisco Bay
 (Hayward/Union City). Data presented are a subset of a larger LiDAR survey
 of the region contracted by the Alameda County Public Works Agency,
 trimmed to the region of study by Lukas WinklerPrins.  While
 these data have been tested for accuracy and are properly functioning,
 Alameda County and the Alameda County Flood Control and Water Conservation
 District disclaims any responsibility for the accuracy or correctness of
 the data. In addition, the use and/or reliance of the information by any
 other party shall be at their own risk.
description: ADF files of the study area were merged into a continuous raster
 and clipped to the region of interest using QGIS software. Methods for
 data collection and creation as reported by the contractor are as
 follows: 1. Flightlines and data were reviewed to
 ensure complete coverage of the study area and positional accuracy of the
 laser points. <br>2. Laser point return coordinates were computed
 using POSPac MMS 8.3 and RiProcess 1.8.5 software based on independent
 data from the LiDAR system, IMU, and aircraft. <br>3. The raw LiDAR
 file was assembled into flightlines per return with each point having an
 associated x, y, and z coordinate. <br>4. Visual inspection of swath
 to swath laser point consistencies within the study area were used to
 perform manual refinements of system alignment. <br>5. Custom
 algorithms were designed to evaluate points between adjacent flightlines.
 Automated system alignment was computed based upon randomly selected swath
 to swath accuracy measurements that consider elevation, slope, and
 intensities. Specifically, refinement in the combination of system pitch,
 roll, and yaw offset parameters optimize internal consistency.<br>6.
 Noise (e.g., pits and birds) was filtered using post-processing software,
 based on known elevation ranges and included the removal of any cycle
 slips. <br>7. Using TerraScan and Microstation, ground
 classifications utilized custom settings appropriate to the study
 area. <br>8. The corrected and filtered return points were compared
 to the ground survey points collected to verify the vertical
 accuracy. <br>9. TIN processing of the ground point returns was used
 to create this bare earth DEM.
description: # LiDAR-derived digital elevation model of Whale's Tail Marsh, San
 Francisco Bay, 2019 Data published are a geotiff (i.e. georeferenced
 raster data) of elevation values (in NAVD88 datum) of Whale's Tail
 Marsh in San Francisco Bay, with the surrounding mudflats, levees, ponds,
 and channels. These data were produced via LiDAR survey collected by the
 [Alameda County Public Works Agency ](https://www.acpwa.org/index.page)and
 were compiled and clipped to the region of interest by Lukas WinklerPrins,
 so as to contribute to a study of marsh-edge morphodynamics at the site.
 These data were set in context with other LiDAR surveys from 2004 and
 2010, in addition to structure-from-motion derived digital surface models
 over a 2021-2022 study year, and generally used to identify retreat rates
 and heterogeneity of the marsh-mudflat interface. ## Description of the
 data and file structure Data presented are in a single .tif file which
 includes additional metadata for georeferencing. We recommend loading the
 data into GIS software (e.g. QGIS or ESRI ArcGIS/ArcMAP) where it can be
 analyzed and manipulated as a raster surface in the correct geographic
 context. The file has a resolution of approximately 3 US Survey Feet
 (0.9144 m) to the side of each pixel. This earth surface is heterogeneous
 and mostly intertidal. Small perturbations in the surface due to
 vegetation or channels may be difficult to distinguish from measurement
 error in some places, and LiDAR returns from wet regions (generally low
 elevations and in the ponds on the eastern edge of the image) should be
 interpreted conservatively. ## Sharing/Access information Additional data
 generated from this LiDAR survey may be available via Alameda County
 Public Works Agency upon request. While the data published here have been
 tested for accuracy and are properly functioning, Alameda County and the
 Alameda County Flood Control and Water Conservation District disclaims any
 responsibility for the accuracy or correctness of the data. In addition,
 the use and/or reliance of the information by any other party shall be at
 their own risk. ## Code/Software Data were generally manipulated using
 QGIS 3.24.3 software, with some additional processing in python 3.10 using
 various common libraries but especially
 [tifffile](https://pypi.org/project/tifffile/).