2012 USGS NRCS Somerset and Wicomico Lidar

Create custom data files by choosing data area, product type, map projection, file format, datum, etc.

Bulk download of data files in LAZ format, geographic coordinates, orthometric heights.

Information on the NOAA Office for Coastal Management (OCM)

The Data Access Viewer (DAV) allows a user to search for and download elevation, imagery, and land cover data for the coastal U.S. and its territories. The data, hosted by the NOAA Office for Coastal Management, can be customized and requested for free download through a checkout interface. An email provides a link to the customized data, while the original data set is available through a link within the viewer.

This graphic displays the footprint for this lidar data set.

Download page for the Maryland iMAP lidar data by block.

Data for the NRCS Maryland LiDAR project was acquired by Aerial Cartographics of America, Inc.

A Riegl LMS-Q680i Full Waveform LiDAR sensor was utilized to collect the data. A calibration flight was flown on February 15, 2012 to obtain current boresight misalignment angles defining the relationship between the scanner and the Inertial Measurement Unit (IMU). A site was selected in Salisbury, Maryland. The 1320 ft X 1320ft site was surveyed to provide twelve (12) horizontal and vertical control locations for assessing the calibration. The area was flown at 1,600 feet AGL at 400 kHz with 50 percent sidelap in the recommended configuration of four (4) north south lines flown in alternating directions and four (4) east west lines flown in alternating directions. Refer to document NCRS Maryland Riegl Calibration.docx for additional information.

The project laser data were collected on February 17, 18, 23, 24 and March 12, 2012 utilizing a Riegl LMS-Q680i full waveform laser scanner (Serial Number 9997848) mounted in a Cessna 208 Grand Caravan aircraft at an approximate altitude of 3,300 feet above ground level (AGL) with a ground speed of 120 knots per hour, 30 percent sidelap, a pulse rate repetition (PRR) of 320 kHz, a scan half angle of 30 degrees resulting in a point spacing of 0.64 meters. The data were collected under cloud-, fog-, and snow-free conditions with no unusual flooding. No data were collected within 72 hours of rainfall that measured more than 0.25 inches. All data were acquired within 2 hours of low tide as predicted by tidal stations located on the bay and inland rivers. Tidal Stations used to determine tidal activity are Sharptown, Vienna, Salisbury, Roaring Point, Whitehaven, Great Shoals Light, Chance, Teague Creek, Long Point, Ewell, Crisfield, Ape Hole, and Shelltown

The GPS data from the ground base stations and the airborne platform were processed using Applanix POSPac 4.4 software module POSGPS. The Inertial Measurement Unit (IMU) solution was processed to provide information regarding the attitude of the sensor platform using the Applanix POSPac 4.4 software module POSProc. This solution was integrated with the Airborne GPS and adjusted using a Kalman filter in a forward/reverse solution to provide a Smoothed Best Estimate of Trajectory (SBET). The ground base stations were set up at the Salisbury-Ocean City Wicomico Regional Airport (ACA001) and on control point 111 enabling the aircraft to be within 25 miles of ground base station at all times.

Receivers for base station during Airborne Data Capture:

1. Leica GX123 464483 Dual frequency reciever

2. Leica AX1220GG 0632001 Dual Frequency GPS Antenna

3. Leica GX1230 464495 Dual Frequency GPS Reciever

4. Leica AX1220GG 0632002 Dual frequency GPS Antenna

Two base stations locations were used for the ABGPS processing 111 and ACA001, located at

the Salisbury Municipal airport.

1. station 111 easting 426121.404 northing 4216147.508 height 0.627

2. station ACA001 easting 343022.014 northing 4185037.17 height 38.948

Coordinate information for 13 aerial targets distributed throughout the project site was provided by Greenman Pedersen Incorporated, Annapolis Junction, MD for ground validation. The validation is for the acquisition portion of this project only. The control points were taken in flat, open areas to determine a fundamental vertical accuracy. Horizontal and vertical was established at the calibration site in Salisbury, Maryland and throughout Somerset and Wicomico Counties on the Eastern Shore of Maryland. The horizontal datum for the project is referenced to NAD 83 (2007), Maryland State Plane Coordinate System, U.S. survey feet and UTM Zone 18, meters. The vertical datum for the project is referenced to NAVD 88, U.S. survey feet and meters. Geoid 2009 was used as the reference model for all GPS computations.

Using TerraSolid Ltd. software, an output control report was produced by comparing a triangulated irregular network of the laser points at the horizontal location of the known ground control points and measuring the vertical difference. The Vertical Root Mean Square Error (RMSEz) is 0.0246 meters. Accuracyz (RMSEz*1.96) is calculated at 0.048meters at 95% confidence level with no outliers.

Dewberry utilizes a variety of software suites for inventory management, classification, and data processing. All LiDAR related processes begin by importing the data into the GeoCue task management software. The swath data is tiled according to project specifications (1,500 m x 1,500 m). The tiled data is then opened in Terrascan where Dewberry uses proprietary ground classification routines to remove any non-ground points and generate an accurate ground surface. The ground routine consists of three main parameters (building size, iteration angle, and iteration distance); by adjusting these parameters and running several iterations of this routine an initial ground surface is developed. The building size parameter sets a roaming window size. Each tile is loaded with neighboring points from adjacent tiles and the routine classifies the data section by section based on this roaming window size. The second most important parameter is the maximum terrain angle, which sets the highest allowed terrain angle within the model. Once the ground routine has been completed a manual quality control routine is done using hillshades, cross-sections, and profiles within the Terrasolid software suite. After this QC step, a peer review and supervisor manual inspection is completed on a percentage of the classified tiles based on the project size and variability of the terrain. After the ground classification corrections were completed, the dataset was processed through a water classification routine that utilizes breaklines compiled by Dewberry to automatically classify hydrographic features. The water classification routine selects ground points within the breakline polygons and automatically classifies them as class 9, water. During this water classification routine, points that are within 1 meter of the hydrographic features are moved to class 10, an ignored ground due to breakline proximity. In addition to classes 1, 2, 9, and 10, there is a Class 7, noise points . This class was only used if needed when points could manually be identified as low/high points.

The fully classified dataset is then processed through Dewberry's comprehensive quality control program.

The data was classified as follows:

Class 1 = Unclassified. This class includes vegetation, buildings, noise etc.

Class 2 = Ground

Class 7= Noise

Class 9 = Water

Class 10=Ignored

The LAS header information was verified to contain the following:

Class (Integer)

GPS Week Time (0.0001 seconds)

Easting (0.003 m)

Northing (0.003 m)

Elevation (0.003 m)

Echo Number (Integer 1 to 4)

Echo (Integer 1 to 4)

Intensity (8 bit integer)

Flight Line (Integer)

Scan Angle (Integer degree)

NOAA OCM downloaded the point cloud data from the Maryland iMAP (imap.maryland.gov). Data were reprojected to geographic coordinates and vertical values were transformed to meters above the ellipsoid. Vertical transformation used the geoid09 model. Data were then compressed to LAZ format using the laszip program. Data were ingested into the Digital Coast Data Access Viewer for custom download.