2010 USGS Lidar: Southeastern Michigan (Hillsdale, Jackson, Lenawee Counties)

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This graphic shows the coverage of the 2012 USACE Lake Michigan lidar in Wisconsin and on the upper peninsula of Michigan.

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Using a LH Systems ALS50 Light Detection And Ranging (LiDAR) system, 83 flight lines of high density data, one and one half point per square meter, were collected over Jackson, Hillsdale, and Lenawee counties in Michigan (approximately 2,093 square miles). Multiple returns were recorded for each laser pulse along with an intensity value for each return. A total of five missions were flown over a 3 day period: November 19, 2010, November 20, 2010, and November 28, 2010. A minimum of two airborne global positioning system (GPS) base stations were used in support of the LiDAR data acquisition. 28 ground control points were surveyed through static methods. The geoid used to reduce satellite derived elevations to orthometric heights was Geoid09. All data for the task order is referenced to UTM 16N for the area within its zone and UTM 17N for the area within its zone, NAD83, NAVD88, in meters. Data located in tiles along the UTM zone border was processed in both UTM 16N and UTM 17N. 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. In addition to the LAS deliverables, one layer of coverage were delivered in the ArcINFO ArcGrid binary format: bare-earth. 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 = 3,943-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 homogenous 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.

Breaklines defining lakes, greater than two acres, and double-line streams, wider than 30.5 meters (100 feet), were compiled using digital photogrammetric techniques as part of the hydrographic flattening process and provided as ESRI Polyline Z and Polygon Z shape files. Breaklines defining water bodies and streams were compiled for this task order. The breaklines were used to perform the hydrologic flattening of water bodies, and gradient hydrologic flattening of double line streams. Lakes, reservoirs and ponds, at a nominal minimum size of two (2) acres or greater, were compiled as closed polygons. The closed water bodies were collected at a constant elevation. Rivers and streams, at a nominal minimum width of 30.5 meters (100 feet), were compiled in the direction of flow with both sides of the stream maintaining an equal gradient elevation. The hydrologic flattening of the LiDAR data was performed for inclusion in the National Elevation Dataset (NED).

The NOAA Office for Coastal Management (OCM) received the topographic files in LAS format from USACE. The files contained lidar easting, northing, elevation, intensity, return number, etc. The data was received in Geographic Coordinates (decimal degrees). OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. A datum shift was performed for all tiles found in UTM Zone 17N and shifted to UTM Zone 16N in order to eliminate duplicate points and tiles.