2014 PSLC Lidar: City of Redmond

In February 2014, Quantum Spatial (QSI) was contracted by the Puget Sound LiDAR Consortium (PSLC) to collect Light Detection and Ranging (LiDAR) data for the City of Redmond site in western Washington. Data were collected to aid PSLC in assessing the topographic and geophysical properties of the study area.

The accompany report discusses the delivered LiDAR data and documents contract specifications, data acquisition procedures, processing methods, and analysis of the final dataset including LiDAR accuracy and density.

This project covers the City of Redmond located in King County. The data was acquired in April 2014.

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A footprint of this data set may be viewed in Google Earth at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4735/supplemental/wa2014_pslc_redmond_m4735.kmz

A project report for this data set may be accessed at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/4735/supplemental/wa2014_pslc_redmond_m4735_surveyreport.pdf

LiDAR points in LAS 1.1 format

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

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

https://coast.noaa.gov/dataviewer/#/lidar/search/where:ID=4735;

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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be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions.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. These data depict the heights at the time of the survey and are only accurate for that time.

The accuracy of the LiDAR data collection can be described in terms of absolute accuracy (the consistency of the data with external data sources) and relative accuracy (the consistency of the dataset with itself). See Appendix A in the report for further information on sources of error and operational measures used to improve relative accuracy.

When collecting RTK and PPK data, the rover records data while stationary for five seconds, then calculates the pseudorange position using at least three one-second epochs. Relative errors for the position must be less than 1.5 cm horizontal and 2.0 cm vertical in order to be accepted.; Quantitative Value: 0.02 meters, Test that produced the value: Value reported as RMSE in meters, not tested

Lidar accuracies were tested for vertical accuracy. Watershed Sciences collected 222 ground control points for use in verifying the vertical accuracy of the classified LiDAR data in King County, surrounding Redmond.; Quantitative Value: 0.019 meters, Test that produced the value: Value reported as RMSE in meters. FVA (RMSE x 1.96) reported as 0.037 m in open terrain

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Absolute accuracy was assessed using Fundamental Vertical Accuracy (FVA) reporting designed to meet guidelines presented in the FGDC National Standard for Spatial Data Accuracy. FVA compares known RTK and PPK ground control point data collected on open, bare earth surfaces with level slope (+/- 20 degrees) to the triangulated ground surface generated by the LiDAR points. FVA is a measure of the accuracy of LiDAR point data in open areas where the LiDAR system has a high probability of measuring the ground surface and is evaluated at the 95 percent confidence interval (1.96 x RMSE).

The mean and standard deviation (sigma) of divergence of the ground surface model from ground survey point coordinates are also considered during accuracy assessment. These statistics assume the error for x, y and z is normally distributed, and therefore the skew and kurtosis of distributions are also considered when evaluating error statistics. For the City of Redmond survey, 224 ground survey points were collected in total resulting in an average accuracy of 0.004 feet (0.001 meters) (Figure 7 in the lidar report).