Range profiling with high resolution and accuracy can be accomplished using single-photon counting time-of-flight
techniques. Detection of target surfaces with high resolution is of importance for several remote sensing applications.
The use of laser pulses in the picosecond regime, single-photon avalanche photodiodes and acquisition electronics with
high timing resolution provides the tools for improving the range accuracy. This paper gives examples of measured
surface profiles and compares the results with simplified theoretical models. The results are discussed with respect to
Compared with other imaging approaches, high resolution angle-angle-range imagery provided by the three dimensional
imaging laser radar increases probability of target identification. Based on scannerless pulsed time-of-flight method, this
paper presents breadboard laser radar for proof-of-principle. A laser transmitter using laser diode flood illuminates a
target area with a relatively short pulse, then a receiver collects the returned energy on a 4x4 PIN diode array where each
pixel measures range respectively. Each of 16 channels consists of a TIA, main amplifier, timing discriminator and a
TDC channel. A processor based on microcontroller processes the output result of all pixels from two TDCs, then
transfers final range data to laptop for visualization. Here we present some preliminary intensity images of target
acquired through indoor experiments. Through these results, the feasibility of direct-detection imaging laser radar for
short-range target identification has been proved. Meanwhile, further development of this system is discussed.
Sigma Space Corporation has recently developed a compact 3D imaging and polarimetric lidar suitable
for use in a small aircraft or mini-UAV. A frequency-doubled Nd:YAG microchip laser generates 6
microjoule, subnanosecond pulses at fire rates up to 22 kHz. A Diffractive Optical Element (DOE)
breaks the 532 nm beam into a 10x10 array of Gaussian beamlets, each containing about 1 mW of laser
power (50 nJ @ 20 kHz). The reflected radiation in each beamlet is imaged by the receive optics onto
individual pixels of a high efficiency, 10x10 pixel, multistop detector. Each pixel is then input to one
channel of a 100 channel, multistop timer demonstrated to have a 93 picosecond timing (1.4 cm range)
resolution and an event recovery time of only 1.6 nsec. Thus, each green laser pulse produces a 100
pixel volumetric 3D image. The residual infrared energy at 1064 nm is used for polarimetry. The scan
pattern and frequency of a dual wedge optical scanner, synchronized to the laser fire rate, are tailored
to provide contiguous coverage of a ground scene in a single overflight. In both rooftop and
preliminary flight tests, the lidar has produced high spatial resolution 3D images of terrain, buildings,
tree structures, power lines, and bridges with a data acquisition rate up to 2.2 million multistop 3D
pixels per second. Current tests are aimed at defining the lidar's ability to image through water
columns and tree canopies.
Active optical remote sensing has numerous applications including battlefield target recognition and tracking,
atmospheric monitoring, structural monitoring, collision avoidance systems, and terrestrial mapping. The maximum
propagation distance in LIDAR sensors is limited by the signal attenuation. Sensor range could be improved by
increasing the transmitted pulse energy, at the expense of reduced resolution and information bandwidth. Coherent
detection can operate at low optical power levels without sacrificing sensor bandwidth.
Utilizing a high power LO laser to increase the receiver gain, coherent systems provide shot noise-limited gain thereby
increasing the sensing range. To fully exploit high LO powers without incurring performance penalties due to the RIN
of the LO, high power handling balanced photodiodes are used. The coherent system has superior dynamic range,
bandwidth, and noise performance than small-signal APD-based systems.
Coherent detection is a linear process that is sensitive to the amplitude, phase and polarization of the received signal.
Therefore, Doppler shifts and vibration signatures can be easily recovered. RF adaptive filtering following
photodetection enables channel equalization, atmospheric turbulence compensation, and efficient background light
We demonstrate a coherent optical transmission system using 15mA high power handling balanced photodetectors. This
system has an IF linewidth <1Hz, employing a proprietary phase locked loop design. Data is presented for 100ps pulsed
transmission. We have demonstrated amplitude and phase modulated 10Gb/s communication links with sensitivities of
132 and 72 photons per bit respectively. Investigations into system performance in the presence of laboratory induced
atmospheric turbulence are shown.
A dust or aerosol cloud represents a convenient target to examine the capabilities of range-resolved Doppler and
intensity (RRDI) or inverse synthetic aperture ladar (ISAR) imaging coherent laser radar, known as coherent "lidar" for
optically thin targets. The poly-phase P4 ladar waveform and its RRDI images are described and compared with
previous pulse-burst, linear-FM chirp pulse-compression, pseudo-random phase modulation waveforms, and several
other waveforms which have not been utilized to date. A "dust cloud" has very many independently moving point
scatterers with velocities that are approximately Gaussian randomly distributed in x,y,z with standard deviations of about
10% of the mean wind + aerosol velocity. This is contrary to a hard-target where the point scatterers are rigidly attached
and moving together. The dust cloud produced speckle effects for the various ladar waveforms are compared. In
addition, a reference set of four corner-cube retro-reflectors within the dust cloud further illustrates the differences in the
various waveform capabilities and resolution.
Raman scattering techniques have long been used as unique identifiers for spectral fingerprints of chemical and
biological species. Raman lidar has been utilized on a routine basis to remotely measure several constituents in the
atmosphere. While Raman scattering is very reliable in uniquely identifying molecules, it suffers from very small
scattering cross sections that diminish its usefulness at increased ranges and decreased concentrations of the species of
interest. By utilizing a resonance Raman technique, where the laser excitation is tuned near an electronic absorption
band, it is possible to increase the Raman scattering cross section. An optical parametric oscillator (OPO) with a UV
tuning range of ~220 nm - 355 nm has been utilized to explore the wavelength dependence of Raman scattering for
diamond, water, benzene, and toluene. Resonance enhancements of the Raman spectra have been studied.
Recent advances in the field of supercontinuum lasers have provided a unique opportunity for developing lidar
instruments that cover a wide spectral range. These instruments permit many simultaneous measurements of differential
absorption spectra (DIAL and DAS techniques) to determine species density. Application of MODTRANTM 5 and other
simulation software has allowed us to design and validate the findings of supercontinuum lidar systems developed at
Penn State Lidar Laboratory. The multiple line differential absorption concepts have been demonstrated with various
system topologies for a host of atmospheric windows in the visible to near infrared regions. During the past three years,
we have developed and demonstrated several systems that are capable of measuring concentrations of various
atmospheric constituents at background or elevated levels through long path absorption by transmitting only milliwatts
of optical power. Our most recent supercontinuum lidar system utilizes a nanosecond supercontinuum laser fiber
optically coupled to a transceiver system for remote sensing of atmospheric species concentrations. Due to the flexibility
of the design, the operational prototype is currently being used to demonstrate the capability for accurately measuring
real world open path atmospheric concentrations across the Penn State campus. The purpose of this study is to develop
the technology and to demonstrate the capability for accurately measuring species concentrations without the
complexities and uncertainties inherent in hyper-spectral remote sensing using the sun as a source, or the limitations and
errors associated with using pairs of laser lines for DIAL measurements of each species. Initial simulations and
measurements using this approach are presented.
Retro-reflection can be used for the detection and classification of optical systems. The probability of detecting sights
over large ranges depends on parameters of the laser, the sight, the detector and the atmosphere. We have developed a
software tool that simulates a sight detection system. With the use of this tool we can 'test' different sight detection
system designs and make estimations on detection ranges of optical systems. In this paper we give a short overview of
the physical aspects that have been implemented in the model and discuss the experimental validation of our model.
Manifold extraction techniques, such as ISOMAP, are capable of projecting nonlinear, high-dimensional data to a lower-dimensional
subspace while retaining discriminatory information. In this investigation, ISOMAP is applied to 3D
LADAR range imagery. Selected man-made objects are reduced to sets of spin-image feature vectors that describe object
surface geometries. At various spin-image support scales, we use the distribution-free Henze-Penrose statistic test to
quantify differences between man-made objects in both the high-dimensional spin-image vector representation and in the
low-dimensional spin-image manifold extracted using ISOMAP.
Small-footprint airborne laser scanners with waveform-digitizing capabilities are becoming increasingly available.
Waveform-digitizing laser scanners seize the physical measurement process in its entire complexity. This leads the way
to the possibility of deriving the backscatter cross section which is a measure of the electromagnetic energy intercepted
and reradiated by objects. The cross section can be obtained by firstly decomposing the echo waveform in several
distinct echoes, whereas for each echo its range, amplitude and width are known. Then the radar equation can be used for
calibrating the waveform measurements using external reference targets with known backscatter cross sections. The final
outcome is a 3D point cloud where each point represents one scatterer with a given cross section and echo width. Using
these physical attributes and various geometric criteria the point cloud can be segmented or classified. In this paper this
procedure is demonstrated based on waveform measurements acquired by the RIEGL LMS-Q560 sensor. The cross
section of the homogenous reference targets is estimated with a RIEGL reflectometer and Spectralon® targets.
This paper reports the successful application of automatic target recognition and identification (ATR/I) algorithms to
simulated 3D imagery of 'difficult' military targets. QinetiQ and Selex S&AS are engaged in a joint programme to build
a new 3D laser imaging sensor for UK MOD. The sensor is a 3D flash system giving an image containing range and
intensity information suitable for targeting operations from fast jet platforms, and is currently being integrated with an
ATR/I suite for demonstration and testing.
The sensor has been extensively modelled and a set of high fidelity simulated imagery has been generated using the
CAMEO-SIM scene generation software tool. These include a variety of different scenarios (varying range, platform
altitude, target orientation and environments), and some 'difficult' targets such as concealed military vehicles. The
ATR/I algorithms have been tested on this image set and their performance compared to 2D passive imagery from the
airborne trials using a Wescam MX-15 infrared sensor and real-time ATR/I suite.
This paper outlines the principles behind the sensor model and the methodology of 3D scene simulation. An overview of
the 3D ATR/I programme and algorithms is presented, and the relative performance of the ATR/I against the simulated
image set is reported. Comparisons are made to the performance of typical 2D sensors, confirming the benefits of 3D
imaging for targeting applications.
In 2006, ASTM committee E57 was established to develop standards for the performance evaluation of 3D imaging
systems. The committee's initial focus is on standards for 3D imaging systems typically used for applications
including, but not limited to, construction and maintenance, surveying, mapping and terrain characterization,
manufacturing (e.g., aerospace, shipbuilding), transportation, mining, mobility, historic preservation, and forensics.
ASTM E57 consists of four subcommittees: Terminology, Test Methods, Best Practices, and Data Interoperability.
This paper reports the accomplishments of the ASTM E57 3D Imaging Systems committee in 2007.
3D LIDAR imaging is a key enabling technology for automatic navigation of future spacecraft, including landing,
rendezvous and docking and rover navigation. Landing is typically the most demanding task because of the range of
operation, speed of movement, field of view (FOV) and the spatial resolution required. When these parameters are
combined with limited mass and power budget, required for interplanetary operations, the technological challenge
becomes significant and innovative solutions must be found. Single Photon Avalanche Photodiodes (SPADs) can reduce
the laser power by orders of magnitude, array detector format can speed up the data acquisition while some limited
scanning may extend the FOV without pressure on the mechanics. In the same time, SPADs have long dead times that
complicate their use for rangefinding. Optimization and balance between the instrument subsystems are required. We
discuss how the implementation of real-time control as an integral part of the LIDAR allows the use of SPAD array
detectors in conditions of high dynamics. The result is a projected performance of more than 1 million 3D pixels/s at a
distance of several kilometers within a small mass/power package. The work is related to ESA technology development
for future planetary landing missions.
The Advanced Ladar Signal Simulator (ALASS) is a comprehensive laser radar simulator that synthesizes ladar signals
for complex three dimensional dynamic diffuse targets in the presence of a dynamic turbulent atmosphere. ALASS
provides single realization random signals (speckle) or the associated mean signals (ensemble rough target average).
ALASS is radiometrically correct, accurately models receiver diffraction and defocus for both coherent and direct
detection transceivers with single or multi-element detectors, and generates signals with correct three dimensional
speckle statistics. Signals are computed using the target plane formulism; for coherent detection this involves the
calculation of the back propagated local oscillator (BPLO) while for direct detection the back propagated impulse
response (BPIR) is used. ALASS's primary functions are to serve as a laser radar sensor design tool, data product
generator for exploitation, and a decision aid for implementing system designs. This paper provides an overview of
ALASS, describes its functionality, presents validation results, and displays example imagery.
Holographic optical elements have found many applications in imaging systems, optical wireless communication, data
storage etc. We have developed filter for Lidar receiver which includes holographic optical elements (HOEs) - volume
diffraction grating (VDG) and holographic lens. HOEs were designed and recorded to meet system requirements.
We have designed, fabricated and characterized InGaAs/InP Geiger-mode avalanche photodiode (APD) 32 x 32 arrays
optimized for operation at both 1.06 and 1.55 μm wavelengths Single element devices with a thick multiplication layer
thickness showed dark count rate as low as 60 kHz at a 3 V overbias, while photon detection efficiencies at a wavelength
of 1.55 μm exceed 30% at 2 V overbias. Back illuminated 32 x 32 detector arrays exhibited breakdown uniformity of
greater than 97% and excellent dark current uniformity. Detector arrays were integrated with low-noise read-out
integrated circuits for an imaging demonstration. 3D imaging was demonstrated using 1.06 micron detector arrays.
A novel InGaAs structure has been developed specifically for use in high-speed applications that require large active
area diodes with greater than 3mm diameter size. The device design is based on a thick and fully depleted PIN structure.
The intrinsic layer thickness is 2 to 4 times thicker than that of the conventional PIN detectors. Greater than 3-fold
reduction in detector capacitance per unit area and the corresponding RC time constant has been demonstrated. Even
with such significant speed enhancement, other diode performance characteristics such as dark current and breakdown
voltage of these novel InGaAs PIN detectors remain comparable to those of the conventional structure. Front- and
backside-illuminated InGaAs detectors are fabricated. Both show equally high-quality spectral response and spatial
uniformity. Comprehensive electro-optical tests are performed and the data and analysis are presented. Temperature
dependent performance characteristics are also reported. Well-behaved performance characteristics are observed from
TE-cooled temperatures to elevated temperatures above ambient.
We have developed low-cost LADAR imagers using photon-counting Geiger avalanche photodiode (GPD) arrays, signal
amplification and conditioning interface with integrated active quenching circuits (AQCs) and readout integrated circuit
(ROIC) arrays for time to digital conversion (TDC) implemented in FPGA. Our goal is to develop a compact, low-cost
LADAR receiver that could be operated with room temperature Si-GPD arrays and cooled InGaAs GPD arrays. We
report on architecture selection criteria, integration issues of the GPD, AQC and TDC, gating and programmable features
for flexible and low-cost re-configuration, as well as on timing resolution, precision and accuracy of our latest LADAR designs.
New measurements are presented for multi-stage InGaAs avalanche photodiodes (APDs) which have the potential to
perform GHz-rate single photon counting in linear mode. No increase in dark current was measured for an 11-device
sample of 5-stage APDs following 717 hours of accelerated aging under bias at 50°C, during an initial lifetime study.
Impulse response times of 0.45 ns, 0.9 ns, and 1.1 ns were measured directly for 6-, 8-, and 10-stage APDs, respectively,
operated at a nominal gain of M=10. To assess the suitability of the technology for a NASA optical communications
application, separate samples of 5-stage APDs were irradiated by 1- and 2-MeV protons at the University of
Washington's Center for Experimental Nuclear Physics and Astrophysics (UW CENPA) and by 63.5-MeV protons at
the University of California Davis, Crocker Nuclear Laboratory (UCD CNL). Good agreement between calculated non-ionizing
energy loss (NIEL) and observed damage was found for the low-energy protons at fluences of 1010 and 1011 cm-2. A NIEL calculation successfully predicted the damage observed following a 5×1010 cm-2 dose of 63.5-MeV protons by
extrapolating from 2 MeV data, which suggests that displacement damage is the dominant mechanism.
Laser-based 3D sensors measure range with high accuracy and allow for detection of several reflecting surfaces for each
emitted laser pulse. This makes them particularly suitable for sensing objects behind various types of occlusion, e.g.
camouflage nets and tree canopies. Nevertheless, automatic detection and recognition of targets in forested areas is a
challenging research problem, especially since foreground objects often cause targets to appear as fragmented.
In this paper we propose a sequential approach for detection and recognition of man-made objects in natural forest
environments using data from laser-based 3D sensors. First, ground samples and samples too far above the ground (that
cannot possibly originate from a target) are identified and removed from further processing. This step typically results in
a dramatic data reduction. Possible target samples are then detected using a local flatness criterion, based on the
assumption that targets are among the most structured objects in the remaining data. The set of samples is reduced
further through shadow analysis, where any possible target locations are found by identifying regions that are occluded
by foreground objects. Since we anticipate that targets appear as fragmented, the remaining samples are grouped into a
set of larger segments, based on general target characteristics such as maximal dimensions and generic shape. Finally,
the segments, each of which corresponds to a target hypothesis, undergo automatic target recognition in order to find the
best match from a model library. The approach is evaluated in terms of ROC on real data from scenes in forested areas.
Helicopter pilots in military and civilian operations need visual assistance for safe flight and landing under adverse
conditions, especially during white-out condition or brown-out condition, in which it is difficult for a pilot to see
obstacles or ground through snow or dust generated by the helicopter's rotorwash. There have been intensive efforts to
develop a sensor that can detect obstacles or ground inside aerosols in recent years.
LIDAR can use the gating function of timing discrimination to suppress the effect of scattering from aerosols, it can
generally "see" farther than passive sensors such as human eyes and cameras inside aerosols. The challenge of using a
LIDAR under aerosol conditions is not only the requirement of high laser power for penetrating aerosols, but also the
requirement of high detection dynamic range and the suppression of aerosol scattering in front of a LIDAR. Neptec's
Obscurant Penetrating Autosynchronous LIDAR (OPAL) uses an autosynchronized optical design, which utilizes a
triangulation relationship to control the amount of return beam accepted by the TOF (time-of-flight) receiver as a
function of target range. The design also maintains this property during high-speed optical scanning. As a result, OPAL
can suppress the return signals from nearby aerosol scattering and, at the same time, have a sensitivity and dynamic
range to detect obstacles or ground inside aerosol. Neptec has conducted experiments to study the effect of atmospheric
aerosol scattering on LIDAR, FLIR and human vision by using a propagation and aerosol evaluation corridor. Neptec
has also carried out flight tests of a prototype of OPAL on a NRC Bell 412 helicopter. In this paper, the concept of the
OPAL that is uniquely designed to penetrate aerosols will be described and its applications in helicopter landing will be
Direct detection laser radar systems with echo signal digitization and subsequent full waveform analysis supply
additional information on the target's properties compared to conventional time-of-flight-based first-pulse / last-pulse
systems. We present a new generation of commercial 3D laser scanners relying on this technology, providing an
improved measurement capability and thus enabling to cover challenging applications even under unfavorable
conditions, e.g., targets partly obscured by camouflage. We will discuss the features of the instruments and we will give
examples on field data to demonstrate the superiority of full-waveform-analysis data.
Naval operations in the littoral have to deal with threats at short range in cluttered environments with both neutral and
hostile targets. There is a need for fast identification, which is possible with a laser range profiler. Additionally, in a
coastal-surveillance scenario a laser range profiler can be used for identification of small sea-surface targets
approaching the coast. A field trial in June 2007 at the coast of Norway was conducted to validate the concept of ship
identification with a laser range profile. A laser range profiler with a high bandwidth, fast laser receiver was used to
perform tests on the capability of a laser range profiler for identification. The ships in the field trial were of frigate size.
Good laser range profiles could be obtained up to a range of 10 km. The experimental results were compared with the
geometry of the ships and a simulated range profile based on a 3D target model. The good match between experimental
and simulated laser range profiles means that a database of laser range signatures can be constructed from 3D-models,
thus simplifying the database creation. It is shown that sea-surface targets can be distinguished by their laser range
profiles. A neural net approach could distinguish five ships with no false identification.
Coastal surveillance and naval operations in the littoral both have to deal with the threat of small sea-surface targets.
These targets have a low radar cross-section and a low velocity that makes them hard to detect by radar. Typical threats
include jet skis, FIAC's, and speedboats. Lidar measurements at the coast of the Netherlands have shown a very good
signal-to-clutter ratio with respect to buoys located up to 10 km from the shore where the lidar system was situated. The
lidar clutter is much smaller than the radar clutter due to the smoothness of the sea surface for optical wavelengths. Thus,
almost all laser light is scattered away from the receiver. These results show that due to the low clutter a search lidar is
feasible that can detect small sea-surface targets. A search-lidar demonstrator is presented and experimental results near
the coast of Holland are presented. By using a high rep-rate laser the search time is limited in order to be useful in the
operational context of coastal surveillance and naval surface surveillance. The realization of a search lidar based on a
commercially available high power and high rep-rate laser is presented. This demonstrator is used to validate the system
modeling, determine the critical issues, and demonstrate the feasibility.