LiDAR Survey Project Report
Applying ALSM to scale up rainfall interception before and after
removal of pinon and juniper in a woodland-encroached sagebrush
ecosystem
Project executed for PI: Devon Snyder
University of Nevada, Reno e-mail: devonsnyder@cabnr.unr.edu
Department of Natural Resources and Phone: 484-844-0764
Environmental Science Fax: 775-784-1375
1. LiDAR System Description and Specifications
This survey was performed with an Optech Gemini Airborne Laser Terrain Mapper (ALTM)
LiDAR serial number 06SEN195 mounted in a twin-engine Piper Chieftain PA-31 with Tail
Number N154WW. The instrument nominal specifications are listed in table 1.
Operating Altitude 150-4000 m, Nominal
Horizontal Accuracy 1/5,500 x altitude (m AGL); 1 sigma
Elevation Accuracy 5 - 35 cm; 1 sigma
Range Capture Up to 4 range measurements, including 1st, 2nd, 3rd, last returns
Intensity Capture 12-bit dynamic range for all recorded returns, including last returns
Scan FOV 0 - 50 degrees; Programmable in increments of ±1degree
Scan Frequency 0 – 70 Hz
Scanner Product Up to Scan angle x Scan frequency = 1000
Roll Compensation ±5 degrees at full FOV – more under reduced FOV
Pulse Rate Frequency 33 - 167 kHz
Position Orientation System Applanix POS/AV 510 OEM includes embedded BD960 72-channel
10Hz (GPS+GLONASS) receiver
Laser Wavelength/Class 1064 nanometers / Class IV (FDA 21 CFR)
Beam Divergence nominal (full angle) Dual Divergence 0.25 mrad (1/e) or 0.80 mrad (1/e)
See http://www.optech.ca for more information from the manufacturer.
Table 1 – Optech GEMINI specifications
(http://www.optech.ca/pdf/Gemini_SpecSheet_100908_Web.pdf).
LiDAR Survey Project Report
2. Areas of Interest.
The survey area consisted of a polygon located about 180kms east of Carson City, Nevada. The
polygon is approximately 6.5 km on each side, enclosing approximately 42 km². The polygon
layout and location are shown with red outline below in Figure 1.
Figure 1 – Shape and location of survey polygon (Google Earth).
3. Data Collection
a) Survey Dates: The survey flight took place on July 14, 2015, DOY 195. The airport that served
as the base of operation for the flights was Carson City Airport (KCXP). The total flight time
was 3.5 hrs. with a total laser on time of 1.2 hrs.
b) Airborne Survey Parameters: The nominal survey parameters are provided in Table 3 below.
Nominal Flight Parameters Equipment Settings Survey Totals
Flight Altitude 600 m Laser PRF 100 kHz Total Flight Time 3.5 hrs
Flight Speed 65 m/s Beam Divergence 0.25 mrad Total Laser Time 1.2 hrs
Swath Width 390 m Scan Frequency 40 Hz Total Swath Area 60 km2
Swath Overlap 50 % Scan Angle ± 18° Total AOI Area 42 km2
Point Density 7 p/m² Scan Cutoff 2.0°
Table 2 – Survey Parameters and Totals.
LiDAR Survey Project Report
c) Ground GPS: Four GPS reference station locations were used during the survey, which are
part of UNAVCO’s PBO network. All reference GPS observations were logged at 1 Hz.
Table 3 gives the coordinates of the stations and Figure 2 shows the project area and the
reference GPS station locations.
GPS station P136 P134 P130 P133
Agency UNAVCO UNAVCO UNAVCO UNAVCO
Latitude 38.76136 38.98087 39.26803 38.7326
Longitude -119.45851 -118.9304 -118.93774 -118.4602
Height 1773.84 1886.57 1380.65 1782.41
Table 3 – GPS Coordinates of ground reference stations. Ellipsoid height (NAD83) in meters.
4. GPS/IMU Data Processing
Reference coordinates for all stations are derived from observation sessions taken over the
project duration and submitted to the NGS on-line processor OPUS which processes static
differential baselines tied to the international CORS network. For further information on OPUS
see http://www.ngs.noaa.gov/OPUS/ and for more information on the CORS network see
http://www.ngs.noaa.gov/CORS/
Airplane trajectories for this survey were processed using KARS (Kinematic and Rapid Static)
software written by Dr. Gerald Mader of the NGS Research Laboratory. KARS kinematic GPS
processing uses the dual-frequency phase history files of the reference and airborne receivers to
determine a high-accuracy fixed integer ionosphere-free differential solution at 1 Hz. All final
aircraft trajectories for this project are blended solutions from the four stations.
After GPS processing, the trajectory solution and the raw inertial measurement unit (IMU) data
collected during the flights are combined in APPLANIX software POSPac MMS (Mobile
Mapping Suite Version 7.1). POSPac MMS implements a Kalman Filter algorithm to produce a
final, smoothed, and complete navigation solution including both aircraft position and
orientation at 200 Hz. This final navigation solution is known as an SBET (Smoothed Best
Estimated Trajectory).
LiDAR Survey Project Report
5. LiDAR Data Processing Overview
The following diagram (Figure 2) shows a general overview of the NCALM LiDAR data processing
workflow
Figure 2 NCALM LiDAR Processing Workflow
NCALM makes every effort to produce the highest quality LiDAR data possible but every
LiDAR point cloud and derived DEM will have visible artifacts if it is examined at a sufficiently
fine level. Examples of such artifacts include visible swath edges, corduroy (visible scan lines),
and data gaps.
A detailed discussion on the causes of data artifacts and how to recognize them can be found
here:
http://ncalm.berkeley.edu/reports/GEM_Rep_2005_01_002.pdf .
A discussion of the procedures NCALM uses to ensure data quality can be found here:
http://ncalm.berkeley.edu/reports/NCALM_WhitePaper_v1.2.pdf
NCALM cannot devote the required time to remove all artifacts from data sets, but if researchers
find areas with artifacts that impact their applications they should contact NCALM and we will
assist them in removing the artifacts to the extent possible – but this may well involve the PIs
devoting additional time and resources to this process.
Classification done by automated means using TerraSolid Software
http://www.terrasolid.fi/en/products/4
LiDAR Survey Project Report
6. Data Deliverables
a) Horizontal Datum: NAD83
b) Vertical Datum: NAVD88 (Geoid 12A)
c) Projection: UTM Zone 11N
d) File Formats:
1. Point Cloud in LAS format, points classified as ground and non-ground, in 1 km
square tiles.
2. ESRI format 1-m DEM from first-return points.
3. ESRI format 1-m bare earth DEM from ground classified points only.
4. ESRI format 1-m Hillshade raster from First-return points.
5. ESRI format 1-m bare earth Hillshade raster from ground classified points only.
e) File naming convention: 1 Km LAS tiles follow a naming convention using the lower
left coordinate (minimum X, Y) as the seed for the file name as follows:
XXXXXX_YYYYYYY. For example if the tile bounds coordinate values from easting
equals 447000 through 448000, and northing equals 4368000 through 4369000 then the
tile filename incorporates 447000_4368000. These tile footprints are available as an
AutoCAD DXF or ESRI shapefile. The ESRI DEMs are single mosaic files created by
combining together the 1KM tiles.
