Data Management Plan

Terrain data, as defined in FEMA Guidelines and Specifications, Appendix N: Data Capture Standards, describe the digital topographic data that were used to create the elevation data representing the terrain environment of a watershed and/or floodplain. Terrain data requirements allow for flexibility in the types of information provided as sources used to produce final terrain deliverables. Once this type of data is provided, FEMA will be able to account for the origins of the flood study elevation data.

NOAA OCM received a delivery from the FEMA Engineering Library which included a point shapefile filled with bare-earth points for the 2005 collection of Ulster County. Within this project was a .ASC DTM file which covered a larger area than the footprint of the shapefile. Ultimately, the smaller footprint was assumed to be validated bare-earth points and processed for public download through the Digital Coast. Final deliverables date to 2007 and cannot be assumed to meet later standards and specifications. Although data review suggests a DEM/DTM product would suffice as the vertical accuracy was tested thoroughly. Be advised that only portions of Ulster County were delivered and OCM is uncertain if more verified and classified data exist.

Process Steps:

• 2007-03-27 00:00:00 - SinkBreach is a linear spatial file representing sink breaches used to hydrologically correct terrain models. A comparison of flow path automatically generated by a GIS software using elevation data and known flow paths from existing maps and/or orthophotos shows sinks that need to be corrected. NoData, VoidArea, ExternalBoundary and Island are polygon spatial files created by reviewing elevation datasets. Flood*Ware processes were used to generate a surface model that is sampled at the center of each grid cell. For best results, the Bi-Linear Interpolation function should be used to extract elevations, rather than the standard Nearest-Neighbor function. The Bare-Earth LIDAR returns and vendor-supplied Break Lines are used to construct the un-corrected DEM using a 3rd-order, inverse distance- weighted Bi-Linear Interopolation over a neighborhood consisting of the twelve closest points within 50 meters of the center of the grid cell. See Watson, D.F. and Philip, G.M., A Refinement of Inverse Distance Weighted Interpolation. Geo-Processing, 2 315-327, 1985. For Detailed and Limited-Detail Studies the surveyed sections are used to constrct a bed elevation geometery to hydraulically correct the elevation model. The cross sectional area, wetted perimeter, stream slope, manning's N, and hydraulic radius are computed using an iterative numerical integration approach. An hydraulic-based approach is applied along flow tubes to interpolate surveyed bed elevations between surveyed sections. This approach uses a conservation of flow approach to vary the hydralulic radius, wetted perimeter, and cross sectional areas according to measured changes in top width and channel slope. The resulting matrix os bed elevation geometry is then applied to the area within the wetted-perimeter to replace the LIDAR returns from the water surface with the bed elevations. See Reed. C.J., Sanders B., and Lopez-Torrijios, R., LIDAR- Minimum Complements for a Hydraulically Correct Elevation Model Copyright 2003, American Society for Photogrammetry and Remote Sensing, Terrain Data- Applications and Visualization Conference Proceedings. For all study types, including Redelineation, corrections are made to the Elevation Model as dictated by the Hydarulic Model or the fit of an effective study to the terrain. Where voids in the Bare-earth LIDAR require better definition additonal LIDAR is extracted from the All Returns LIDAR and visaully compared to the Elevation Model. When additional points are deemed to be available in the All Returns the Bare-Earth LIDAR is augmented with the All Returns points and the Elevation Model is rebuilt.
• 2016-07-06 00:00:00 - The NOAA Office for Coastal Management (OCM) received a point shapefile containing lidar points without attributes as part of a FEMA delivery. The data was received in UTM Zone 18 in meters and were vertically referenced to NAVD88 using the Geoid03 model in meters. OCM performed the following processing for data storage and Digital Coast provisioning purposes: 1. The shapefile was converted to an LAS 1.2 file with LASTools' shp2las. 2. The LAS files were classified as Class 2 - Ground points. 3. The LAS files were converted from orthometric (NAVD88) heights to ellipsoidal heights using the Geoid03 model. 4. The LAS files were converted from UTM coordinates to Geographic Coordinates in decimal degree. 5. The LAS files were reviewed for outliers and removed accordingly.

This data can be obtained on-line at the following URL:

https://coast.noaa.gov/dataviewer/#/lidar/search/where:ID=5056;