Keywords: lidar, gmapd
Summary
This demonstrates a nadir viewing Geiger-mode Avalanche Photo-diode (GmAPD) laser radar system that whisk scans across the scene. The collection shoots 40 overlapping pulses over a scene composed of a tree on a background.
Details
This demo models a LIDAR system with a simple transmitter and a 32 x 128 GmAPD receiver array with 2 us long listening window and 1 ns time resolution (resulting in 2001 time bins). The multi pulse collection is then run through the advanced GmAPD detector model to produce an ASCII/Text XYZ point cloud. The advanced GmAPD detector model has a graphical interface available under Tools → Lidar Tools in the Simulation Editor, as well as a command-line interface.
Important Files
This section highlights key files important to the simulation.
Geometry and Materials
The scene is comprised of a single maple tree (see
geometry/Red_Maple_1.gdb) planted at the Scene ENU origin a flat plate.
The reflectance properties are spectrally flat and not realistic (see
materials/demo.mat and the optical property files in the materials
folder).
Platform
This section summarizes the properties of the transmitter and receiver components of the laser radar system used in this demo.
Transmitter
Laser wavelength: 1064 microns Pulse repetition rate (PRF): 20,000 Hz (20 kHz) Pulse length: 1 ns Pulse energy: 0.5 mJ
Receiver
Focal length: 1 m Array size: 32 x 128 elements @ 50 micron pitch Range gate width: 2 us Range gate resolution: 1 ns
Setup
Run the Radiometry Simulation
To run the simulation, perform the following steps:
-
Run the DIRSIG
demo.simfile
This produces the file demo.bin.
Run the Analysis Tool
It is always useful to verify the link budget (the number of photons arriving onto the pixels during a pulse). The BIN Analysis tool can be used to examine and summarize the radiometric values and supporting metadata in a BIN file. This tool can be run via the Analyze button in the detector model interface or via the command-line:
$ bin_analyze demo.bin
...
[header summaries deleted for documentation purposes]
...
Minimum total photons in a pixel = 0.549208
Maximum total photons in a pixel = 3.65245
Pixels with zero total photons = 0/4096 (0%)
Average background photons per pixel = 6.87829e-07
Average total photons per pixel = 1.08298
...
Pulse #40:
Minimum total photons in a pixel = 0.549208
Maximum total photons in a pixel = 3.80463
Pixels with zero total photons = 0/4096 (0%)
Average background photons per pixel = 2.00738e-06
Average total photons per pixel = 1.00801
Complete!
The Geiger-mode (Gm) Detector Model Database
The advanced Geiger-mode APD (GmAPD) detector model simulation uses detector specifications that mirror the commercial available products from Princeton Lightwave, Inc. (see http://www.princetonlightwave.com/mm-products/3d-ladar/128-x-32-gmapd-camera#specifications):
Photon detection efficiency (PDE)
Mean = 30 (typical)
Stddev = 5 (typical)
Dark Count Rate (DCR)
Mean = 5 (typical)
Stddev = 3 (typical)
This detector performance characteristics are captured in the GmAPD
database file (see demo.gmapd). Consult the Advanced GmAPD modeling
manual for details about creating these databases.
Run the Geiger-mode (Gm) Detector Model
Generating the Geiger-mode point cloud product can be accomplished using the graphical interface to the general detector model or via the command-line:
$ gmapd_processor --parameters demo.xyz.params
Results
Visualizations of the Geiger-mode point cloud in GNUplot (a simple 2D and 3D plotting tool) are shown below:
