2011 MDEQ Tennessee-Tombigbee Waterway Lidar Survey

Collect and deliver high-density elevation point data derived from multiple-return light detection and ranging (LiDAR) measurements for use in supporting topographic analysis, including applications such as flood plain mapping. The Nominal Point Spacing Value for the final lidar is 3.2 ft (~1 m). Deliver LiDAR Bare Earth and Contour lines within the areas designated in areas of Clay, Itawamba, Monroe, and Lowndes Counties to aid in visual interpretation of Flood Basin elevations and for addition to the MDEM elevation dataset. Comply with mapping guidelines and specifications as stated in the FEMA Procedure Memorandum No. 61

Updating DFIRM maps, hydrologic modeling, transportation routing, floodplain mapping and assessment of natural hazards. Furthermore, the data sets can be utilized by the general public including engineers, surveyors, appraisers and others interested parties to evaluate transportation and land use planning.

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Reflective surface data represents the DEM created by laser energy reflected from the first surface encountered by the laser pulse. Some energy may continue beyond this initial surface to be reflected by a subsequent surface as represented by the last return data. Intensity information is captured from the reflective surface pulse and indicates the relative energy returned to the sensor as compared to the energy transmitted. The intensity image is not calibrated or normalized but indicates differences in energy absorption due to the interaction of the surface materials with laser energy at the wavelength transmitted by the sensor. Points are classified as water, bare ground or not bare ground to support creation of a bare earth model from the data.

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

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/2560/supplemental/ms2011_mdeq_tenn_tombigbee.KMZ

The MDEQ Tennessee-Tombigbee report may be accessed at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/2560/supplemental/ms2011_mdeq_tenn_tombigbee.pdf

Any conclusions drawn from the analysis of this information are not the responsibility of the following: MDEQ, The Atlantic Group, 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=2560

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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.

LiDAR data horizontal accuracy is met as contracted. The Nominal Point Spacing Value for the final LiDAR is 3.2 ft (0.97 m).; Quantitative Value: 0.649 meters, Test that produced the value: Horizontal point accuracy is a function of angular origination of the pulse; IMU orientation; the scanner encoder and ranging function and will vary depending on the proposed point density selected for the collection. Statistically, the error is roughly 1/3 of the illuminated foot print on the ground and is a function of the beam divergences. This gives a final horizontal accuracy value of 2.13 feet (0.649 m).

LiDAR vertical data accuracy determination shall employ the National Standard for Spatial Data Accuracy (NSSDA).The Nominal Point Spacing Value for the final LiDAR is 3.2 ft.; Quantitative Value: 0.07 meters, Test that produced the value: Based on the vertical accuracy testing conducted by The Atlantic Group, LLC using NSSDA methodology, the dataset tested for vertical accuracy at 95% confidence level in open terrain, based on open terrain. This gives a final vertical accuracy value of 0.24 feet (0.07 m).

Cloud Cover: 0

All data is complete to standards as specified. LIDAR raster data is visually inspected for completeness to ensure that any gaps between flight lines of required collection area. LIDAR is self-illuminating and has minimal cloud penetration capability. Water vapor in steam plumes or particulates in smoke may cause reflection of LIDAR signals and loss of elevation information beneath these plumes. Glass structures and roofs may appear transparent to the LIDAR signal and therefore may not register on the reflective surface.

QC/QA process includes review of flight alignments and completeness of supporting data. The MDEQ or its designee may perform additional QC/QA testing. The root mean square error (RMSE) is used to estimate both horizontal and vertical accuracy. RMSE is the square root of the average of the set of squared differences between dataset coordinate values and coordinate values from an independent source. Bare-earth processed data for this acquisition block comply with the following accuracy requirements for Artifact/Feature removal: artifacts - 90%; outliers - 95%; vegetation - 95%; buildings - 98%. All LAS formatted LIDAR data are validated using commercial GIS software to ensure proper formatting and loading before delivery. This validation procedure ensures that data on delivery media is in correct physical format and is readable. Higher accuracy for identical points. If those differences are normally distributed and average zero, 95 percent of any sufficiently large sample should be less than 1.96 times the RMSE. Therefore 9-centimeter RMSE can be referred to as "18-centimeter accuracy at the 95-percent confidence level." Following that convention, the vertical accuracy of any DEM is defined as 1.96 times the RMSE of linearly interpolated elevations in the DEM, as compared with known elevations from high-accuracy test points. DEMs should have a maximum RMSE as specified to meet its required vertical accuracy.