marin52_tbsm50cm_20131218f
Revsion 2013.12.18 of County of Marin digital topographic-bathymetric surface model: This is a 50cm gridded surface exported from ESRI Terrain Dataset with natural neighbor interpolation. The Terrain Dataset was used to fuse airborne LiDAR ground-classified points, multibeam sonar bathymetric grids, and depth survey soundings, and elevation-interpolated historical flow paths. The multibeam bathymetric surface was obtained as 1-meter grids in San Francisco Bay and as 2-meter grids offshore; these grid cells were converted to masspoints for use in the fusion process.The original motivation for the surfaces was a countywide implementation of HAZUS-MH, with a surface to support modeling of riverine and coastal flooding peril as well as tsunami inundation. Funding for this dataset has been provided by a series of MarinMap.org projects to map countywide creeks, wetlands, and watersheds at parcel-scale accuracy as a set of model-derived features. This surface is the fifth edition of an integrated countywide terrain model of Marin County, California.VERSION HISTORY:0) 2009.09 ver. 0.85 Demonstration Edition "tsm30cm" The fusion of photogrammetric topographic contours and breaklines was the initiative for the first edition of the terrain surface, gridded at resolutions as small as 30cm and stabilized as "2009.09". 1) 2010.03 ver. 1.0 "tsm40cm" The further fusion of FEMA LiDAR data in the urban areas and NCALM GeoEarthScope LiDAR along the San Andreas Fault in the western county was the initiative for the second edition of the terrain surface, stabilized as "2010.01" and distributed to a number of engineering companies and published as default terrain in Google Earth by 2010 03.2) 2010.08 ver. 2.0 "tbsm45cm" The fusion of all data sets previously integrated with bathymetry data was the initiative for the third edition, called "2010.08", With use of the NOAA VDatum Java-based application, it became possible to reprocess the ITRF-2000-based NCALM point cloud directly, along with all NOAA depth surveys from 1931 to the most recent public sets, and the California Seafloor Mapping Project gridded models of multibeam sonar soundings in San Francisco Bay and out to the 3-nautical-mile limit offshore. An additional LiDAR dataset was provided by the Marin Municipal Water District for lower Lagunitas Creek below Kent Reservoir. The original photogrammetric break lines were segregated into sets of ridgelines and road edge lines, with ridges and water lines used as soft contraints, and road edges used as hard constraints in the fusion of points and breaklines in the ESRI Terrain Dataset into the 2010.08 terrain model. This grid has been produced in WGS84 UTM zone 10 North, meters, with elevations in WGS84 NAVD88 (CONTUS Geoid 2003) positioning.3) 2011.08.18 ver. 3.0 "tbsm50cm_20110818c" This grid made first use of the ARRA LiDAR, and kept all pre-existing datasets including legacy ALACE LiDAR flights along the coastal shoreline that were not ground-classified, as well as photogrammetric break lines from 2004 that were abandoned in later grids. This grid was extended toward the west to fully include Bodega Head to support hillshades required by the Marin Community Map multi-scale base map, although it did not include the Farallon Islands. Hillshades were developed in both WGS 1984 US National Grid (UTM) and Web Mercator. The benefits of 50cm gridding were recognized during collaboration with USGS scientists who were compiling SF Bay topo-bathy data at 2m gridding. The 50cm grid made a better source for 1m, 2m, and 4m downsampling than did earlier resolutions.4) 2012.11.30 ver. 4.0 "tbsm50cm_20121130g" After the arrival of ARRA-funded countywide 2ppsm airborne LiDAR, several months of experimentation and discussions with creek-mapping colleagues identified that the photogrammetric contours and breaklines from a 2004 survey should be deprecated and not used further in county terrain models. Likewise, the early ALACE coastal LiDAR which did not have ground classification was deprecated and discontinuted from the county terrain models. This surface was the first in the series to only fuse aerial LiDAR surveys wherever available for topographic surface modeling. On land, FEMA 2007 (urban east 2 ppsm), NCALM 2008 (San Andreas Fault 7 ppsm), MMWD/Airborne 1 2009 ( lower Lagunitas Creek 2 ppsm), NOAA 2010 ( urban east 1 ppsm), CA-OPC 2010 ( coastal 1 ppsm), and ARRA 2010 (countywide 2 ppsm) provided LiDAR sources. Some NED 10m grid values were retained for infill of adjacent areas outside of Marin County. The 50cm model grid is projected to WGS 1984 UTM 10 north meters, and positioned WGS84 / NAVD 1988 (CONTUS Geoid 2003). Typical distribution is in single seamless ERDAS Imagine file format. Gridding was performed on six large rectangular patches with minimal 20m overlap. The study area was split into 14 rectangular sub-areas for terrain building, and separate ESRI File Geodatabases were prepared for each with only input data needed for each sub-area incluced. An ESRI Terrain Dataset was built with a single pyramid layer in each of the separate File GDB, and then ESRI 3D Analyst's Terrain to Raster conversion was performed with 50cm gridding. The 14 sub-area grids were mosaicked using ERDAS Imagine to a single full-extent grid from which various derviative products will be drawn.5) 2013.08.30 ver. 5.0 "tbsm50cm_20130830a" During 2013, the 20121130g surface was intensively analyzed to model surface drainage, and slope surfaces were derived for QA evaluation, which led to several patches of the surface where berrain blocks had been mosaicked and adjacent edges had artifacts from inconsistent interplation across some boundaries. Data from a 2011 QA 1m grid of ARRA LiDAR prepared by Bill Kruse were used along these match edges. As drainage processing has evolved to production of USGS National Hydrography Dataset (NHD) Local Resolution flow lines and USGS Watershed Boundary Dataset (WBD) HUC-16 polygon areas, contour sets are routinely produced as part of the formal WBD review protocol. 6) 2013.11.21 ver. 5.1 "tbsm50cm_20131121e" was patched to responsd to (what had only then become) routine generation of a percent-slope analysis for each new terrain version. As part of Marin NHD generation of candidate WBD watershed areas, it was required to generate a set of contour lines for the reviewers, and these highlighted issues at the boundaries of grids in the ver. 4.0 surface. Also, the slope analysis identified that the boundary issues extended beyond areas with anomalous contours. For this version, smoother areas from ver. 3.0 surface were overlaid along the grid boundaries.7) 2013.12.18 ver. 5.2 "tbsm50cm_20131218f" To better support the QA requirements of WBD HUC-16 production, pre-inundation topography beneath reservoirs was modeled with reference to USGS 1895 quad sheets and elevations interplated along enforcement lines traced through each pool and out to all its tributaries. Dam structures are retained and flow paths are modeled through current spillways, but this method supports WBD definitions that join tributaries at their historic confluence, as required in Federal Standards and Procedures for the National Watershed Boudnary Dataset (WBD), Fourth Edition. The five reserovirs near Mount Tamalpais, Soulajule and Stafford reservoirs, and Laguna Lake have been given this treatment.Input datasets not positioned in the project's reference vertical datum were exported to ASCII comma-spaced values for adjustment with NOAA VDatum into WGS84 UTM meters-XY, NAVD88 (Geoid 2003) meters-Z. Exported datasets were filtered to remove NULL Z-values, and reloaded as multipoint-Z features in the Terrain Dataset. Project work was begun in 2009 with ESRI ArcGIS 9.3.1, proceeded for several months in early 2010 using ArcGIS 9.4 beta 1 and beta 2, and completed with ArcGIS 10.0, 10.1, and 10.2 by 2014. LiDAR data published by FEMA were flown and processed by Dewberry in 2007 and provided by FEMA to County of Marin. The GeoEarthScope LiDAR data were obtained from OpenTopography.org as a bare-earth grid (for edition 2010.01) and as a full point clound (for edition 2010.08) and positioned with NOAA VDatum. Sounding data were obtained from the National Geophysical Data Center, National Ocean Survey Hydrographic Survey Data portal map.ngdc.noaa.gov and positioned into WGS84_NAVD88 (CONTUS Geoid 2003) using NOAA VDatum. ARRA LiDAR data were provided on disk by San Francisco State University, CSMP bathymetry were obtained from Cal State Monterey Bay website, CA-OPC and NOAA LiDAR were obtained from NOAA Digital Coast website. Channel soundings were purchased from USACE by FOIA request in 2010.
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