2010 ARRA Lidar: 4 Southeast Counties, MI

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This graphic shows the lidar coverage for the 2010 Michigan ARRA Lidar collection for Monroe, Saint Clair, Livingston and Macomb counties.

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Using a LH Systems ALS50 Light Detection And Ranging (LiDAR) system, 130 flight lines of high density data, one and one half point per square meter, were collected over Livingston, Monroe, St. Clair, and Macomb counties (approximately 2,351 square miles). Multiple returns were recorded for each laser pulse along with an intensity value for each return. A total of thirteen missions were flown over a 10 day period: March 22, 2010 through April 1, 2010. A minimum of two airborne global positioning system (GPS) base stations were used in support of the LiDAR data acquisition. 62 ground control points were surveyed through static methods. The geoid used to reduce satellite derived elevations to orthometric heights was Geoid03. All data for the task order is referenced to Michigan State Plane South Zone (2113), NAD83/2007, NAVD88, in international feet. Airborne GPS data was differentially processed and integrated with the post processed IMU data to derive a smoothed best estimate of trajectory (SBET). The SBET was used to reduce the LiDAR slant range measurements to a raw reflective surface for each flight line. The coverage was classified to extract a bare earth digital elevation model (DEM) and separate last returns. Two layers of coverage were delivered in the ArcINFO ArcGrid binary format: bare-earth and intensity. System Parameters: - Type of Scanner = LH Systems ALS50 - Data Acquisition Height = 7,800-feet AGL - Scanner Field of View = 40 degrees - Scan Frequency = 35.3 Hertz - Pulse Repetition Rate - 99.0 Kilohertz - Aircraft Speed = 130 Knots - Swath Width = 5,678-feet - Number of Returns Per Pulse = Maximum of 4 - Distance Between Flight Lines = 3,974-feet

The ALS50 calibration and system performance is verified on a periodic basis using Woolpert's calibration range. The calibration range consists of a large building and runway. The edges of the building and control points along the runway have been located using conventional survey methods. Inertial measurement unit (IMU) misalignment angles and horizontal accuracy are calculated by comparing the position of the building edges between opposing flight lines. The scanner scale factor and vertical accuracy is calculated through comparison of LiDAR data against control points along the runway. Field calibration is performed on all flight lines to refine the IMU misalignment angles. IMU misalignment angles are calculated from the relative displacement of features within the overlap region of adjacent (and opposing) flight lines. The raw LiDAR data is reduced using the refined misalignment angles.

Once the data acquisition and GPS processing phases are complete, the LiDAR data was processed immediately to verify the coverage had no voids. The GPS and IMU data was post processed using differential and Kalman filter algorithms to derive a best estimate of trajectory. The quality of the solution was verified to be consistent with the accuracy requirements of the project.

The individual flight lines were inspected to ensure the systematic and residual errors have been identified and removed. Then, the flight lines were compared to adjacent flight lines for any mismatches to obtain a homogeneous coverage throughout the project area. The point cloud underwent a classification process to determine bare-earth points and non-ground points utilizing "first and only" as well as "last of many" LiDAR returns. This process determined bare-earth points (Class 2), Noise (Class 7), Water (Class 9) Ignored ground (Class 10) and unclassified data (Class 1). The bare-earth (Class 2 - Ground) LiDAR points underwent a manual QA/QC step to verify that artifacts have been removed from the bare-earth surface. The surveyed ground control points are used to perform the accuracy checks and statistical analysis of the LiDAR dataset.

The NOAA Office for Coastal Management (OCM) received the files in laz format from USGS via an FTP online repository. The files contained lidar elevation and intensity measurements. The data were in State Plane Zone 2113, NAVD88 (orthometric) heights in (international) feet. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. The data were converted from State Plane coordinates in International Feet to geographic coordinates in decimal degrees.

2. Erroneous elevations were removed.

3. The data were converted from NAVD88 (orthometric) heights in feet to GRS80 (ellipsoid) heights in meters using Geoid 03.