2009 Lidar DEM: Chatham, GA

Digital Elevation Model (DEM) generated from a lidar point cloud acquired in spring 2009 for Chatham County, for the Georgia for the Metropolitan Planning Commission.

This data is for planning purposes only and should not be used for legal or cadastral purposes.

Digital elevation model for planning purposes.

Support of FEMA's Floodplain Map Modernization Program and Florida Division of Emergency Management Disaster standards.

Elevation in NAVD88 feet for the center of each cell

The data represent the results of data collection and processing for a specific Metropolitan Planning Commission activity and indicates the general existing conditions at the time of the data collection. As such, it is only valid for its intended use, content, time, and accuracy specifications. The user is responsible for the results of any application of the data for other than its intended purpose. Any conclusions drawn from the analysis of this information are not the responsibility of the Office for Coastal Management or its partners.

This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer

The data set is dynamically generated based on user-specified parameters.

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this data may no longer represent actual surface conditions.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.

Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 2; ESRI ArcCatalog 9.2.4.1420

Lidar acquired and processed to meet 1 m (RMSE) horizontal accuracy.; Quantitative Value: 0.5 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.

The vertical accuracy is based on the Sanborn independent collection of 20 ground survey points distributed throughout the project.

The fundamental vertical accuracy at 95 percent confidence level in open terrain tested 0.07 meters (0.25 ft).

1. Vertical accuracy: Less than 0.30 feet RMSEz = less than 0.60 feet vertical accuracy at 95% confidence level, tested in flat,

non-vegetated terrain only, employing NSSDA procedures in Reference B.

2. Validation that the data also satisfies FEMA requirements.

3. Vertical units (orthometric heights) are in US Survey Feet, NAVD88.

; Quantitative Value: 0.07 meters, Test that produced the value:

Based on the vertical accuracy testing conducted by Sanborn using NSSDA and FEMA methodology, vertical accuracy at the 95%

confidence level (called Accuracyz) is computed by the formula RMSEz x 1.9600. The dataset for Chatham County, Georgia satisfies

the criteria:

Countywide lidar dataset tested 0.15 m (0.49 ft) vertical accuracy at 95% confidence level in open terrain, based on open terrain

RMSEz (0.25 ft) x 1.9600.

Countywide lidar dataset tested 0.24 m (0.78 ft) vertical accuracy at 95% confidence level in all land cover categories combined,

based on consolidated RMSEz (0.40 ft) x 1.9600.

A visual qualitative assessment was performed in the source Lidar dataset.

Data covers the tile scheme provided for the county.