2012 MEGIS Topographic Lidar: Statewide Lidar Project Areas 2 and 3 (Mid-Coastal Cleanup), Maine

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This graphic shows the lidar coverage for Maine Statewide Lidar: Areas 2 and 3 (Androscoggin, Sagadahoc, Kennebec, Lincoln, Waldo, Knox, Somerset,

Penobscot Counties).

Date that the source FGDC record was last modified.

Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using 'fgdc_to_inport_xml.pl' script. Contact Tyler Christensen (NOS) for details.

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Using a combination of Leica ALS60 and Optech Gemini LiDAR systems, 307 flight lines of high density data, at a nominal pulse spacing (NPS) of 1.5

meter, were collected over Maine (approximately 2327 square miles). Multiple returns were recorded for each laser pulse along with an intensity

value for each return. A total of twenty-one (21) missions were flown April 18, 2012 May 12, 2012. Two airborne global positioning system (GPS)

base stations were used in support of the LiDAR data acquisition. 34 ground control points were surveyed through static methods. The geoid used to

reduce satellite derived elevations to orthometric heights was Geoid09. The horizontal datum used for this survey is North American Datum 1983

(NSRS2007), UTM19, and expressed in meters. The vertical datum used for this survey is North American Vertical Datum 1988 (NAVD88), and expressed

in meters. 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. System

Parameters: - LIDAR data was collected using Leicas ALS60 and Optechs Gemini LiDAR Systems in Multi-Pulse mode. The ALS60 and Gemini LiDAR Systems

collect up to four returns (echo) per pulse, recording attributes such as time stamp and intensity data, for the first three returns. If a fourth

return was captured, the system does not record an associated intensity value. The aerial LiDAR was collected at the following sensor specifications:

Nominal Post Spacing: 4.92 ft / 1.5 m, AGL (Above Ground Level) average flying height: 7,800 ft / 2,377 m (Leica ALS60), 6,800 ft / 2,072 m

(Optech Gemini), MSL (Mean Sea Level) average flying height: Varies by terrain, Average Ground Speed: 150 knots / 172 mph, Field of View (full):

40 degrees, Pulse Rate: 99 kHz (Leica ALS60), 100 kHz (Optech Gemini), Scan Rate: 38 Hz (Leica ALS60), 32 Hz (Optech Gemini), Side Lap (Minimum): 25%.

The Leica ALS60 and Optech Gemini LiDAR system calibration and 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), unclassified data (Class 1), overlap

points (Class 11). 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 100 feet (30.5 meters), 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 100

feet (30.5 meters), 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 topographic files in .LAS V1.2 format. The files contained lidar elevation measurements, intensity

values, scan angle values, return information, and adjusted standard GPS time. The data were received in UTM Zone 19N, NAD83 coordinates and were

vertically referenced to NAVD88 using the Geoid09 model. The vertical units of the data were meters. OCM performed the following processing for

data storage and Digital Coast provisioning purposes:

1. Points in Class 11 (Overlap) were changed to Class 12 (Overlap).

2. The topographic las files were converted from orthometric (NAVD88) heights to ellipsoidal heights using Geoid09.

3. The topographic las files were converted from a Projected Coordinate System (UTM Zone 19N) to a Geographic Coordinate System (NAD83).

4. The topographic las files' horizontal units were converted from meters to decimal degrees.