2015 FEMA Lidar: Ashland County, WI

Create custom data files by choosing data area, product type, map projection, file format, datum, etc. A new metadata will be produced to reflect your request using this record as a base. Change to an orthometric vertical datum is one of the many options.

Bulk download of data files in LAZ format, geographic coordinates, orthometric heights. Note that the vertical datum (hence elevations) of the files here are different than described in this document. They will be in an orthometric datum.

This graphic displays the footprint for this lidar data set.

Link to data set report.

Link to data set report.

Link to the breaklines.

This data set is the project specified acquired point cloud data.

This data set is the project specified lidar deliverables.

Using two Leica ALS70 (lidar) systems on board a Cessna 404 and Cessna 310 aircraft, high density data, at a nominal pulse spacing (NPS) of 1.0 meter, were collected for this task order (approximately 1, square miles). AGL = 7800 feet - Aircraft Speed = 150 Knots, Field of View (Full) = 40 degrees, Pulse Rate = 230 kHz, Scan Rate = 34.4 Hz, with an average side lap of 25%. Multiple returns were recorded for each laser pulse along with an intensity value for each return. Three (3) missions were flown between November 1, 2014 and April 17, 2015. Two (2) Global Navigation Satellite System (GNSS) Base Stations were used in support of the lidar data acquisition. Specific information regarding latitude, longitude, and ellipsoid height to the L1 phase center is included in the lidar processing report. The geoid used to reduce satellite derived elevations to orthometric heights was GEOID12A. Data for the task order is referenced to the UTM Zone 15N, North American Datum of 1983 (2011) meters, and NAVD88, in US Survey Feet. 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 SBET was used to reduce the lidar slant range measurements to a raw reflective surface for each flight line. The ALS70 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.

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 surveyed ground control points provided by Compass Data are used to make vertical adjustments to the data set and to perform the accuracy checks and statistical analysis of the lidar dataset. This LAS 1.2 dataset contains return numbers beyond a 5th return (6th, 7th, 8th, etc). A fully compliant LAS 1.2 file only supports the encoding of up to and including 5 returns in the LAS header information. Any subsequent returns (6th, 7th, 8th, etc) cannot be encoded in the header and most lidar processing software will generate a warning stating "Number of points by return not equal point record count".

The scan angle rank in point data record is the angle at which the laser point was output from the laser system includes roll of the aircraft added by roll compensation. Due to the tiled nature of the LAS data, some LAS files may exhibit a lower scan angle rank than what the overall project was acquired at and/or contain only negative or positive scan angle ranks. This is due to the fact that when swath data is imported to a tiled format that tile assumes whatever scan angle rank values that fall within that tile boundary.

Scale Factor- The vertical scale factor of this lidar dataset is 0.01. The LAS generating software defaults the vertical scale factor to 0.001. The Z-value of a lidar point at 50.53 ft is stored by the software as 50.530 ft. This is what is known as “fluff”. There is nothing wrong with the data only that most lidar processing softwares are able to detect this “fluff” and display a warning. Supervisory QC monitoring of work ensured consistency of calibration and adjustments in adherence to project requirements across the entire project area. The resulting deliverables for this task order consist of unclassified LAS 1.2 files provided in a tiled format, fgdc metadata, and a post-flight aerial acquisition and calibration report. As part of this report, additional shape files were delivered and include flight line trajectories, planned flight lines, swath index, base station locations, tile index, and buffered AOI.

Tile Size: 1,500m x 1,500m. The tile file name was derived from the southwest corner of each tile.

NOAA OCM retrieved 1,276 las files from the WisconsinView wbestie (https://wisconsinview.org/). The files had intensity values, were in UTM 15N projection referenced to NAD83(2011) with linear units in meters, and orthometric heights having used geoid 12A with vertical units in US Survey feet.

OCM performed the following processing on the data for Digital Coast storage and provisioning purposes:

1. The las files were converted from las to laz format using LASTools laszip.

2. An internal OCM script was run to check the number of points by classification and by flight ID and the gps and intensity ranges.

3. Internal OCM scripts were run on the laz files to convert from orthometric (NAVD88) elevations to ellipsoid elevations using the Geoid 12A model, to convert from UTM 15N (NAD83 2011) coordinates in meters to geographic coordinates, to convert vertical units from feet to meters, to assign the geokeys, to sort the data by gps time and zip the data to database and to http.