NHD and Lidar : Development of Common Guidelines and Practices

1. NHD and Lidar:Development of Common Guidelines and Practices NHD/WBD Technical Architecture Planning Meeting USGS - Denver, CO May 11-13, 2010 Ricardo Lopez-Torrijos Ricardo.Lopez.inAlbany@gmail.com NHD Consultant

2. Lidar Vocabulary • Lidar: Point data representing the X-Y-Z location, with other attributes, of any terrestrial target reflecting the laser pulse. • Not limited to bare-earth points • Points grouped into classes according to target type (ground, water, vegetation, etc.) • Not a surface such as raster DEM or TIN • DEM: Digital Elevation Model of the bare-earth surface, almost always raster. • DEMs derived from Lidar are still just DEMs. • ‘LiDARHydrography’ is derivative of a derivative.

3. All-Return Lidar (Points) Inferred Channel? Building? Flowline?

4. Bare-Earth DEM (Surface)

5. Example of Lidar collection record • Pennsylvania State-wide data“PAMAP Program - 3.2 ft Digital Elevation Model … consists of a raster digital elevation model with a horizontal ground resolution of 3.2 feet. The model was constructed from PAMAP LiDAR (Light Detection and Ranging) elevation points.” I.e. • ‘Lidar’ is actually the derived DEM • Point cloud & intensity info left behind

6. Example of Lidar collection record, 2 • LiDAR Processing/Contour Enhancement Lines “… consists of vectors used to classify LiDAR points and aesthetically enhance contour lines. The vectors are commonly delineated along features such as… double line hydro (20' wide and greater), lakes and ponds, swamps and marshes,…” I.e. • ‘Ground truth’ is most often aerial imagery • Hydro breaklines poorly defined

7. LidarCollection Specifications • Appropriately dictated by topography, landcover, and primary use of the data • Post Spacing/Point Density • Spatial Accuracy (Vertical & Horizontal) • Classifications • Others… Primary use never hydrography compilation • Cannot realistically be uniform across the nation • Mohave Desert, Great Smokey Mountains, Gulf Coast… • Floodplain Mapping, forestry, 3D urban models… • Accepted that specifications will vary within a national collection effort

8. LiDAR Collection Practices • Currently unique to project, data producer, software, and instrument • Some variations are inevitable, acceptable, and healthy for continued innovation in the industry • Others pose significant impediments to a “seamless” National Lidar effort: • Point delivery - completeness • Classification – completeness • Accuracy – assessment and reporting • Metadata – consistency and completeness • Calibration & Boresighting – consistency • Adjacent Project Registration

9. LiDARProcessing Practices • Some pose challengessto NHD compilation from Lidar: • Rarely synchronus with imagery collections • Undefined Horiz/Vert co-registration with imagery, • Poorassessment and reporting • Missing Intensity signal • Classification – ground class accuracy? water? • Metadata – consistency and completeness • Consistency & Registration w/ Adjacent Projects • Currently unique to project, data producer, software, and QA/QC protocol

10. USGS-NGP Lidar Guidelinesand Base Specification • Prompted by ARRA funding for lidar to support the NED • Clarify USGS-NGP minimum requirements for NED usage • Identify common buy-up options • Improve consistency across lidar point deliveries • Allow waivers for flexibility (previous collections; science) • Addresses both point cloud data and derived products • Assures delivery of bare-earth DEMs suitable for use in the NED (what does this mean from NHD viewpoint?) • Assures delivery of more consistent point cloud data for use in other scientific and mapping applications • Specs to remain durable beyond ARRA projects

11. NHD and the Base Specification • Although planned to be finalized and published this year, periodic updates are presumed • NDEP Expects that a broader Federal Lidar Spec will be developed • Common body dealing with point clouds and practices • Appendices specific to individual agencies/projects • Still a draft, the Spec has already been tentatively embraced by numerous other organizations: • NHD could develop its own specs

12. A Possible National Lidar System Delivery Cache NHD? Common Product Cache User Interface Software XML Metadata & Reduced Resolution Views User Request for Data, Analysis, & Derived Products Data Delivery Management Software Systems Check for Existing Data/Product Hydro enforcing? Flow line extraction? Data Analysis and Processing Software Systems Finished Products Data Access and Control Software Systems Points Needed to Fulfill User Request LAS Data Stores (petabytes) Metadata and Index Stores

13. LidarBest Practices • Growing movement for national lidar is adding urgency to the need for industry “standards” and Best Practices • Agreement for the need across system manufacturers, collection vendors, users • Upcoming ASPRS Airborne Lidar Manual includes sections on Best Practices (volunteer authors!!) • Endorsed Best Practices expected to be drawn from multiple sources: • ASPRS Airborne Lidar Manual • USGS-NGP Lidar Guidelines and Base Specification • Other inputs … (NHD?)

14. Areas for an NHD and Lidar Best Practice • Collection: relation between ground point spacing, land cover and breaklines • Processing and delivery: • ‘Water’ Class, assessment of vegetation removal • Breakline compilation and delivery • Given age of NHD/NED, where are projects more needed/efficient? I.e. coordination with NDEP • Culverts vs. bridges • Include Z in flowline • Hydro enforcing? NHD Plus vertical integration? • Engage ASPRS in manual development?

15. Topics for an NHD and Lidar Best Practice • Concurrent temporal and Horiz/Vert accuracy specs for lidar and imagery • (X,Y,t) registration conflict resolution • Point density as a function of ground cover • Vegetation removal assessment, dirty areas • Water point class and breaklines • Capture Conditions • NED/NHD/EDNA Update sequence, source coordination with NDEP • Dissemination of practice across lidar partners