2019-2021 USGS Lidar: Alameda County Lidar

This metadata reflects the combination of three lidar collections over Alameda County, CA. These are: 1) a 2019 QL1 collection upgraded to 3DEP specifications; 2) a 2021 QL1 collection; and 3) a 2021 QL0 collection. Each dataset has an Entwine Point Tile version that makes the data accessible by the Digital Coast Data Access Viewer. This metadata is to support that use by the Data Access Viewer.

Geographic Extent: The three collections and derived products encompass areas covering approximately 216, 376, and 186 square miles of Alameda County, California, respectively.

Dataset Description: The Alameda County Lidar 2019 Upgrade Lidar project called for the reprocessing of lidar data collected in a 2019 acquisition to meet current 3DEP specifications outlined in the U.S. Geological Survey National Geospatial Program Lidar Base Specification 2020, Revision A document. The QL1 and QL0 Alameda County Lidar 2021 Lidar projects called for the planning, acquisition, and processing of lidar data collected to Quality Level 1 (QL1) and Quality Level 0 (QL0) standards, also based on the U.S. Geological Survey National Geospatial Program Lidar Base Specification 2020, Revision A. Lidar data was delivered as calibrated and classified LAS 1.4 files. These files were subsequently converted to Entwine Point Tile format in Web Mercator projection, NAVD88 Geoid12b meters.

Ground Condition: Ground condition was free of snow and acquisition occurred free of smoke, fog and cloud cover.

The purpose of the lidar data was to produce a high accuracy 3D dataset that meets all necessary standards laid out by the 3D Elevation Program and the Alameda County Lidar 2021 contract.

USGS Contract No. G16PC00016

CONTRACTOR: NV5 Geospatial

Ground Control Points were acquired and calibrated by NV5 Geospatial

All lidar data acquisition, calibration, and follow-on processing were completed by NV5 Geospatial.

The following are the USGS lidar fields in JSON:

{

"ldrnote" : "The lidar section reflects the QL0 collection.",

"ldrinfo" : {

"ldrspec" : "U.S. Geological Survey National Geospatial Program Lidar Base Specification 2020, Revision A",

"ldrsens" : "Riegl 1560ii/ii-s",

"ldrmaxnr" : "15",

"ldrnps" : "0.254",

"ldrdens" : "15.5",

"ldranps" : "0.127",

"ldradens" : "61.92",

"ldrfltht" : "1100",

"ldrfltsp" : "145",

"ldrscana" : "58.2",

"ldrscanr" : "245",

"ldrpulsr" : "2000",

"ldrpulsd" : "3",

"ldrpulsw" : "0.9",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "0.18",

"ldrswatw" : "1232",

"ldrswato" : "20",

"ldrgeoid" : "Geoid 18"

},

"ldraccur" : {

"ldrchacc" : "0",

"rawnva" : "0",

"rawnvan" : "66"

},

"lasinfo" : {

"lasver" : "1.4",

"lasprf" : "6",

"laswheld" : "Withheld (ignore) points are identified in these files using the standard LAS Withheld bit.",

"lasolap" : "Swath "overage" points were identified in these files using the standard LAS overlap bit.",

"lasintr" : "16",

"lasclass" : {

"clascode" : "1",

"clasitem" : "Processed, but Unclassified"

},

"lasclass" : {

"clascode" : "2",

"clasitem" : "Bare earth ground"

},

"lasclass" : {

"clascode" : "7",

"clasitem" : "Low Noise"

},

"lasclass" : {

"clascode" : "9",

"clasitem" : "Water"

},

"lasclass" : {

"clascode" : "17",

"clasitem" : "Bridge Decks"

},

"lasclass" : {

"clascode" : "18",

"clasitem" : "High Noise"

},

"lasclass" : {

"clascode" : "20",

"clasitem" : "Ignored Ground Near Breaklines"

}

}}

Users should be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations. This product is for informational purposes and may not have been prepared for or be suitable for legal, engineering, surveying, or site specific purposes. Users of this information should review or consult the primary data and information sources to ascertain the usability of the information.

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA, the Office for Coastal Management or its partners

QL0 area

QL1 2021 area

2019 QL1 upgraded collection area

Data is available online for bulk or custom downloads

None

Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

Applanix PosPac MMS, RiProcess, RiWorld, Microstation CONNECT, TerraScan Version 21, TerraModeler Version 21, ESRI ArcGIS 10.7, LAS Product Creator (NV5 Proprietary), LAS Projector (NV5 Proprietary), LAS Monkey (NV5 Proprietary), Windows 10 Operating System

This data set was produced to meet ASPRS Positional Accuracy Standard for Digital Geospatial Data (2014) for a 5-cm RMSEz Vertical Accuracy Class. The NVA was tested with 106 independent check points located in open terrain and distributed throughout the project as feasible. These check points were not used in the calibration or post processing of the lidar point cloud data. Specifications for this project require that the NVA be 0.098 meters or better AccuracyZ at 95% confidence level.

Vegetated Vertical Accuracy (VVA) is also to be computed from the classified las. The VVA was tested with 60 check points in tall grass, forest, and shrub land cover types. These check points were also withheld from the calibration and post processing of the lidar point cloud data and distributed throughout the project area as feasible. Specifications for this project require that the VVA be 0.150 meters or better AccuracyZ at the 95th percentile.Quantitative value: 0.042 0.096, Test that produced the value: The 106 independent NVA check points were surveyed using the closed level loop technique. Elevations interpolated from the unclassified lidar surface were compared to the elevation values of the surveyed NVA check points. The RMSE was computed to be 0.021 meters resulting in an AccuracyZ at the 95% confidence level of 0.042 meters. The 60 VVA check points were surveyed using the closed level loop technique. Elevations for these points were compared to the elevations of the classified lidar surface resulting in an AccuracyZ of 0.096 meters at the 95th percentile.

These LAS data files include all data points collected. No points have been removed or excluded. A visual qualitative assessment was performed to ensure data completeness. No void areas or missing data exist. The raw point cloud is of good quality and data passes Non-Vegetated Vertical Accuracy specifications.

Classified LAS files were tested by USGS for vertical accuracy. All data is seamless from one tile to the next, no gaps or no data areas.

Data is backed up to cloud storage.