This PDF file contains the front matter associated with SPIE Proceedings Volume 7684, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

For a direct-detection 3D imaging ladar, the use of Geiger-mode avalanche photodiode (APD) could greatly enhance the detection efficiency of the receiver since each range measurement requires only one detected photon. Single photon sensitivity of the detector offers significant advantages in reducing receiver size, mass and power and reducing laser complexity. This paper studies the 3D imaging ladar using APDs which are actively quenched and gated to operate at Geiger-mode to detect short weak laser echo pulse. The detection model of this detector as well as the detection probability and false alarm probability for this ladar is analyzed and discussed. The analysis shows that the major factors influencing system design are the background light noise and the dead time of the Geiger-mode APD. Then the noise which affects the false alarm probability is analyzed and calculated and the measures to extract the weak signal echo from a high noise background are put forward. The research also shows that using a detector array instead of a single detector could reduce the false alarm probability by orders of magnitude. Finally a 3D imaging brassboard system which utilizes Geiger-mode APDs, a fast pulse, high repetition rate laser, and an optical scanner is described, and some experimental results obtained by this system are presented and analyzed. The results suggest that if the background light noise is sufficiently suppressed, 3D images of the targets could be successfully taken by the ladar using Geiger-mode APDs.

During the ESA Mars Sample Return (MSR) mission, a sample canister launched from Mars will be autonomously captured by an orbiting satellite. We present the concept and the design of an active 3D camera supporting the orbiter navigation system during the rendezvous and capture phase. This camera aims at providing the range and bearing of a 20 cm diameter canister from 2 m to 5 km within a 20° field-of-view without moving parts (scannerless). The concept exploits the sensitivity and the gating capability of a gated intensified camera. It is supported by a pulsed source based on an array of laser diodes with adjustable amplitude and pulse duration (from nanoseconds to microseconds). The ranging capability is obtained by adequately controlling the timing between the acquisition of 2D images and the emission of the light pulses. Three modes of acquisition are identified to accommodate the different levels of ranging and bearing accuracy and the 3D data refresh rate. To come up with a single 3D image, each mode requires a different number of images to be processed. These modes can be applied to the different approach phases. The entire concept of operation of this camera is detailed with an emphasis on the extreme lighting conditions. Its uses for other space missions and terrestrial applications are also highlighted. This design is implemented in a prototype with shorter ranging capabilities for concept validation. Preliminary results obtained with this prototype are also presented. This work is financed by the Canadian Space Agency.

Optical LADARs require high sensitivity near 1 nanowatt while also having fast recovery to overloads as high as 100W. Fast recovery is required in order to detect a secondary target from behind a bright target. In the current work, we have created a new family of LADAR receivers having a higher gain bandwidth product than most commercially available receivers. While maintaining the receiver bandwidth, a 4.8 × increase in responsivity can now be achieved. With cooling of the APD, these new receivers are offering more than a twofold time reduction of the NEP, allowing longer range coverage of the LADAR system. In addition, a new feature is the improvement of the overload recovery to 93ns from an laser pulse of 56mW, allowing close secondary target detection.

The theory and operation of Advanced Scientific Concepts, Inc.'s (ASC) latest compact 3D Flash LIDAR Video Cameras (3D FLVCs) and a growing number of technical problems and solutions are discussed. The solutions range from space shuttle docking, planetary entry, decent and landing, surveillance, autonomous and manned ground vehicle navigation and 3D imaging through particle obscurants.

In the present paper 3D range-gated imaging in scattering environments is investigated. Experiments were carried out in a fog chamber with different fog densities using a range-gated imaging system based on 532 nm laser illumination and an ICCD camera. Both, laser pulse width and exposure time were in the range of 500 ps. To evaluate the impact of scattering environment on the depth resolution capability of the imaging system the Lissajous eye pattern analysis was applied. This analysis gives experimental evidence of the reduction of depth accuracy in the presence of scattering media in the imaging range. Further, 3D information was reconstructed from tomography data using the least-square-fitting method. This 3D reconstruction verifies the results of the Lissajous eye pattern analysis.

A joint-service team led by the Air Force Research Laboratory's Munitions and Sensors Directorates completed a successful flight test demonstration of the 3D-LZ Helicopter LADAR Imaging System. This was a milestone demonstration in the development of technology solutions for a problem known as "helicopter brownout", the loss of situational awareness caused by swirling sand during approach and landing. The 3D-LZ LADAR was developed by H.N. Burns Engineering and integrated with the US Army Aeroflightdynamics Directorate's Brown-Out Symbology System aircraft state symbology aboard a US Army EH-60 Black Hawk helicopter. The combination of these systems provided an integrated degraded visual environment landing solution with landing zone situational awareness as well as aircraft guidance and obstacle avoidance information. Pilots from the U.S. Army, Air Force, Navy, and Marine Corps achieved a 77% landing rate in full brownout conditions at a test range at Yuma Proving Ground, Arizona. This paper will focus on the LADAR technology used in 3D-LZ and the results of this milestone demonstration.

In response to the 2010 Haiti earthquake, the ALIRT ladar system was tasked with collecting surveys to support disaster relief efforts. Standard methodologies to classify the ladar data as ground, vegetation, or man-made features failed to produce an accurate representation of the underlying terrain surface. The majority of these methods rely primarily on gradient- based operations that often perform well for areas with low topographic relief, but often fail in areas of high topographic relief or dense urban environments. An alternative approach based on a adaptive lower envelope follower (ALEF) with an adaptive gradient operation for accommodating local slope and roughness was investigated for recovering the ground surface from the ladar data. This technique was successful for classifying terrain in the urban and rural areas of Haiti over which the ALIRT data had been acquired.

In this paper we present our Spectral LADAR concept, an augmented implementation of traditional LADAR. This sensor uses a polychromatic source to obtain range-resolved 3D spectral images which are used to identify objects based on combined spatial and spectral features, resolving positions in three dimensions and up to hundreds of meters in distance. We report on a proof-of-concept Spectral LADAR demonstrator that generates spectral point clouds from static scenes. The demonstrator transmits nanosecond supercontinuum pulses generated in a photonic crystal fiber. Currently we use a rapidly tuned receiver with a high-speed InGaAs APD for 25 spectral bands with the future expectation of implementing a linear APD array spectrograph. Each spectral band is independently range resolved with multiple return pulse recognition. This is a critical feature, enabling simultaneous spectral and spatial unmixing of partially obscured objects when not achievable using image fusion of monochromatic LADAR and passive spectral imagers. This enables higher identification confidence in highly cluttered environments such as forested or urban areas (e.g. vehicles behind camouflage or foliage). These environments present challenges for situational awareness and robotic perception which can benefit from the unique attributes of Spectral LADAR. Results from this demonstrator unit are presented for scenes typical of military operations and characterize the operation of the device. The results are discussed here in the context of autonomous vehicle navigation and target recognition.

Image chain analysis is a systems engineering tool which allows imaging system designers to understand how different components of the imaging chain affect the quality and derivable information of generated data products. In this paper, we apply image chain analysis techniques to formulate a product chain for airborne three-dimensional (3D) imaging laser radar systems that employ arrays of Geiger-mode avalanche photodiode detectors. The processes involved in 3D data generation and subsequent information extraction are described. These processes are grouped into five groups (Data Capture, Raw Point Cloud Formation, Noise Filtering, Advanced Post-Processing and Data Analysis) to form the proposed product chain. For each group, key parameters that affect 3D data quality are identified along with synthetic data examples of their respective impact to 3D data quality and information extraction. In addition, we discuss on-going and future work intended to continue our understanding o3 3D data quality and interpretability.

Some episodes are reviewed of the early development of laser radar in Ukraine and Russia being the parts of the former Soviet Union, including laser radars for Navy applications, anti-missile defense experiments, and medical applications. Some details are pointed out on spatial suppression of the backscattered light, on laser radar for fire control systems, and long-range multi-channel laser radar. Double-circuit tracking is discussed for high-precision designator. High-power multi-channel ruby laser transmitter with high pulse repetition rate and matrix multi-channel photodetector were tested at Sary-Shagan in the mode of missile and satellite ranging and tracking. Specular target identification is analyzed which uses polarization parameters. Studies of speckle propagation in the atmosphere resulted in their dual application for speckle suppression and for selection of the fluctuating retroreflecting targets. An aberrometer - instrument for wave front measurements using the principles of laser radar is described with its application in the field of ophthalmology.

For the wide applications of LAser Detection and Ranging (LADAR) imaging with large format Geiger-mode (GM) avalanche photodiode (APD) arrays, it is critical and challenging to develop a LADAR camera suitable to volume production with enough component tolerance and stable performance. Recently Spectrolab and Black Forest Engineering developed a new 32x32 Read-Out Integrated Circuit (ROIC) for LADAR applications. With a specially designed high voltage input protection circuit, the ROIC can work properly even with more than 1 % of pixels shorted in the APD array; this feature will greatly improve the camera long-term stability and manufacturing throughput. The Non-uniform Bias circuit provides bias voltage tunability over a 2.5 V range individually for each pixel and greatly reduces the impact of the non-uniformity of an APD array. A SMIA high speed serial digital interface streamlines data download and supports frame rates up to 30 kHz. The ROIC can operate with a 0.5 ns time resolution without vernier bits; 14 bits of dynamic range provides 8 μs of range gate width. At the meeting we will demonstrate more performance of this newly developed 32x32 Geiger-mode LADAR camera.

Intensified Imaging Photon Counting (I²PC) is a new approach to flash lidar that employs direct coupling of a photocathode and microchannel plate front end to a high-speed, pipelined, all-digital ASIC to achieve photon-counting temporal waveform capture in each pixel on each laser return pulse. A unique characteristic of the Ball architecture is the absence of analog components that limit temporal resolution and dynamic range. Implemented in 65nm CMOS technology, the current generation I²PC is expected to record up to 300 photon arrivals in each pixel with 100 ps resolution on each pulse return, and with up to 6000 range bins in each 55 μm pixel. Additional advantages of this architecture are operation at any wavelength where photocathodes are available, intrinsically low f/# and high fill factor capability, array sizes to >3000×3000 pixels with COTS components, extremely high dynamic range, and extremely low false alarm rates. In addition to long-range and low-power hard target imaging, I²PC extends the scannerless capabilities of flash lidar to distributed target applications such as range-resolved waveform captures for atmospheric aerosol and chemistry sensing, vegetation canopies, and camouflage penetration. As a passive imager, I2PC also brings unprecedented speed and dynamic range to low-light and UV imaging applications.

Three-dimensional (3D) Light Detection And Ranging (LIDAR) systems designed for foliage penetration can produce good bare-earth products in medium to medium-heavy obscuration environments, but product creation becomes increasingly more difficult as the obscuration level increases. A prior knowledge of the obscuration environment over large areas is hard to obtain. The competing factors of area coverage rate and product quality are difficult to balance. Ground-based estimates of obscuration levels are labor intensive and only capture a small portion of the area of interest. Estimates of obscuration levels derived from airborne data require that the area of interest has been collected previously. Recently, there has been a focus on lacunarity (scale dependent measure of translational invariance) to quantify the gap structure of canopies. While this approach is useful, it needs to be evaluated relative to the size of the instantaneous field-of-view (IFOV) of the system under consideration. In this paper, the author reports on initial results to generate not just average obscuration values from overhead canopy photographs, but to generate obscuration probability density functions (PDFs) for both gimbaled linear-mode and geiger-mode airborne LIDAR. In general, gimbaled linear-mode (LM) LIDAR collects data with higher signal-to-noise (SNR), but is limited to smaller areas and cannot collect at higher altitudes. Conversely, geiger-mode (GM) LIDAR has a much lower SNR, but is capable of higher area rates and collecting data at higher altitudes. To date, geiger-mode LIDAR obscurant penetration theory has relied on a single obscuration value, but recent work has extended it to use PDFs1. Whether or not the inclusion of PDFs significantly changes predicted results and more closely matches actual results awaits the generation of PDFs over specific ground truth targets and comparison to actual collections of those ground truth targets. Ideally, examination of individual PDFs for specific collections will provide insight into how collection operations can be optimized in general and whether or not a generation of representative PDFs of various forest types will be useful for collection planning.

3-D Lidar systems are capable of measuring complex three-dimensional scenes. Like traditional two dimensional imaging systems, 3-D lidar systems have limitations that limit the spatial resolution of the measured data. Herein two types of lidar resolution targets are presented, a point reflector target and an MTF bar target, for the calculation of spatial resolution. Supporting analysis points to their utility and indicates the results derived via MTF for the point source and CTF derived from the bar target are well within similarity expectations and are consistent with typical comparisons of CTF and MTF curves.

A sensor for measuring scattering at multiple wavelengths and multiple angles has been designed and is being tested for the characterization of atmospheric aerosols. Charge coupled device (CCD) imagers are used to record scattering measurements at two polarizations and as a function of angle relative to the co-aligned laser beams. A diffraction grating is used to spatially separate the wavelengths across the field-of-view of the CCD array, allowing simultaneous measurements at multiple wavelengths. Experiments are conducted to measure the scattering intensities for two polarizations at discrete wavelengths that span the visible spectrum. The data from the CCD images are inverted using a genetic algorithm and Mie scatter equations to determine aerosol properties of artificially generated fog. The results are compared with in-situ measurements of the aerosol size distribution and concentration using an aerodynamic particle sizer spectrometer and a condensation particle counter.

Several laser remote sensing techniques are used to characterize the properties of aerosols. The various techniques include: backscatter, optical extinction using Raman scatter, and bistatic/multistatic scattering using the polarization ratio of the scattering phase function. The number density, size, and size distribution are obtained under the assumption of spherical scatterers. Other measurements can be used to describe additional properties, such as aerosol type based upon approximate refractive index and detected departure from spherical, when simultaneous measurements at several wavelengths and several angles are analyzed. Examples are shown to demonstrate our present capability to characterize aerosol particles using recently developed techniques.

With the dramatically climate changing we are facing today atmospheric monitoring is of major importance. Several atmospheric monitoring instruments are used for measuring atmospheric composition, optical coefficients, PM2.5, aerosol optical depth, size distribution, PBL height and many other parameters. However an inexpensive method of determining these parameters is by use of models and one model that depicts the aerosol dynamics in the atmosphere is the Community Multi-scale Air Quality (CMAQ) model. Our paper is comparing the lidar, sunphotometer and TEOM measurements performed at City College of the City University of New York against CMAQ model.

The Enhanced Photodissociation Fluorescence method is a novel approach to overcome several limitations associated with remote optical detection of vapors emanating from NO containing explosives. By using an additional laser source to enhance their evaporation, a sufficient concentration-level is achieved to extend the scope of optically detected materials. The enhanced system has successfully demonstrated detection of low vapor pressure explosives (RDX, PETN, C4, Composition B and SEMTEX) from a distance of 30m in outdoor, day-light conditions.

The primary purpose of this research was to develop an effective means of creating a 3D terrain map image (point-cloud) in GPS denied regions from a sequence of co-bore sighted visible and 3D LIDAR images. Both the visible and 3D LADAR cameras were hard mounted to a vehicle. The vehicle was then driven around the streets of an abandoned village used as a training facility by the German Army and imagery was collected. The visible and 3D LADAR images were then fused and 3D registration performed using a variation of the Iterative Closest Point (ICP) algorithm. The ICP algorithm is widely used for various spatial and geometric alignment of 3D imagery producing a set of rotation and translation transformations between two 3D images. ICP rotation and translation information obtain from registering the fused visible and 3D LADAR imagery was then used to calculate the x-y plane, range and intensity (xyzi) coordinates of various structures (building, vehicles, trees etc.) along the driven path. The xyzi coordinates information was then combined to create a 3D terrain map (point-cloud). In this paper, we describe the development and application of 3D imaging techniques (most specifically the ICP algorithm) used to improve spatial, range and intensity estimates of imagery collected during urban terrain mapping using a co-bore sighted, commercially available digital video camera with focal plan of 640×480 pixels and a 3D FLASH LADAR. Various representations of the reconstructed point-clouds for the drive through data will also be presented.

In this paper a new image processing technique for flash LIDAR data is presented as a potential tool to enable safe and precise spacecraft landings in future robotic or crewed lunar and planetary missions. Flash LIDARs can generate, in real-time, range data that can be interpreted as a 3-dimensional (3-D) image and transformed into a corresponding digital elevation map (DEM). The NASA Autonomous Landing and Hazard Avoidance (ALHAT) project is capitalizing on this new technology by developing, testing and analyzing flash LIDARs to detect hazardous terrain features such as craters, rocks, and slopes during the descent phase of spacecraft landings. Using a flash LIDAR for this application looks very promising, however through theoretical and simulation analysis the ALHAT team has determined that a single frame, or mosaic, of flash LIDAR data may not be sufficient to build a landing site DEM with acceptable spatial resolution, precision, size, or for a mosaic, in time, to meet current system requirements. One way to overcome this potential limitation is by enhancing the flash LIDAR output images. We propose a new super-resolution algorithm applicable to flash LIDAR range data that will create a DEM with sufficient accuracy, precision and size to meet current ALHAT requirements. The performance of our super-resolution algorithm is analyzed by processing data generated during a series of simulation runs by a high fidelity model of a flash LIDAR imaging a high resolution synthetic lunar elevation map. The flash LIDAR model is attached to a simulated spacecraft by a gimbal that points the LIDAR to a target landing site. For each simulation run, a sequence of flash LIDAR frames is recorded and processed as the spacecraft descends toward the landing site. Each run has a different trajectory profile with varying LIDAR look angles of the terrain. We process the output LIDAR frames using our SR algorithm and the results show that the achieved level of accuracy and precision of the SR generated landing site DEM is more than adequate for detecting hazardous terrain features and identifying safe areas.

In the past decade arrays of Geiger-mode Avalanche Photodiode (GmAPD) detectors have increased in size from 4×4 to 128×32, resulting in significant increases in data rates. If not handled appropriately, data collected with larger arrays and higher laser pulse repetition frequencies could potentially stress existing data dissemination and storage infrastructures. Data compression techniques that reduce storage requirements by taking advantage of data redundancies could be used to mitigate this problem. In this paper we present an analysis of the coding redundancy that exists in raw data captured with three dimensional imaging laser radar systems that employ arrays of Geiger-mode Avalanche Photodiode (GmAPD) detectors. The data we analyzed was collected in three different scanning modes, namely: mapping-mode, target-mode and stare-mode. We found that there is a significant amount of coding redundancy in raw GmAPD data which can be used to minimize storage sizes. We demonstrate that a trivial and simple approach reduces data for some scan patterns. This work represents a first step towards developing robust compression algorithms for raw GmAPD data. We present considerations for future work.

In many laser radar systems the intensity value's strength is dependent on the reflectivity of the measured surface. High intensity values are necessary for accurate range measurements. When measuring a low-reflectivity surface the returning laser intensity will be low. This, in turn, results in high uncertainty in the range estimate. In this paper, an approach to correct the intensity values are presented which results in more accurate range estimates even on lowreflecting surfaces. Examples are shown using the ASC (Advanced Scientific Concepts) FLASH 3D LADAR sensor. During a data collection several series of measurements characterizing the shape of the return laser pulse from surfaces with known reflectivity were performed. Using principal components analysis (PCA), variation in pulse shape as a function of laser intensity was determined. These data were then used to identify a parametric model that described the variation in intensity values relative to the surface's reflectivity. Based on the model, an approach to systematically adjust intensity values has been developed. In this paper we will also examine laser timing jitter, intensity, and their effects on range estimation.

The Eyesafe Ladar Test-bed (ELT) is a raster scanning, single-beam, energy-detection ladar with the capability of digitizing and recording the return pulse waveform at 2 GHz in the field for off-line 3D point cloud formation research in the laboratory. The ELT serves as a prime tool in understanding the behavior of ladar waveforms. Signal processing techniques have been applied to the ELT waveform in an effort to exploit the signal with respect to noise reduction, range resolution improvement, and ability to discriminate between two surfaces of similar range. This paper presents a signal processing method used on the ELT waveform. In the processing, three deconvolution techniques were investigated-the Wiener filter, Richardson-Lucy deconvolution, and a new method that synthesizes the surface response using least squares minimization. Range error and range resolution are reported for these methods.

We demonstrate a numerical technique for registering multiple frames of point cloud data from an airborne 3D flash ladar system that we have designed, built, and flown. This technique stitches together ladar data even in the presence of inaccuracies in the line-of-sight pointing knowledge as well as instabilities in the time-of-flight clock frequency. The technique performs frame-to-frame in-track as well as cross-track stitching of multiple flight line data to create large area maps of urban areas and vegetation. Filters remove data with spurious range values and high intensity specular back flashes such as those from bodies of water. Signal averaging of nearly overlapping pixel data creates monolithic, wide area 3D maps that are geo-located and thus readily superimposable with other types of sensor data, such as hyperspectral images, for fused-data exploitations. The accuracy of the numerical technique used for stitching data from different target types, such as urban, vegetation, or bare earth, was studied. This analysis provides guidance for future improvements of algorithms used for registering airborne 3D flash ladar point cloud data sets.

This paper relates a short history of laser radar development in the United States. It starts in the 60's, shortly after the invention of the laser. Initially laser radars used various lasers, until CO2 became the popular choice for coherent laser radar and NdYag for laser range finders and designators. CO2 reigned as the coherent laser radar of choice from the early 70's until the 80's or 90's. Most CO2 laser radars were at a wavelength of 10.6 μm, although to avoid atmospheric CO2 absorption some CO2 laser radars used different isotopes of CO2 to avoid 10.6 μm operation. The exception to the early laser radar development being CO2 were laser designators, which can be considered a form of bi-static laser radar, and laser range finders. NdYag, at 1.064 μm wavelength, was the laser of choice for laser designators and range finders. Laser designators started in the late 60's. In the 80's to 90's solid state lasers came more into their own for laser radar application, including coherent solid state laser radars. The main development was the ability to eliminate heat from solid state material, thus allowing higher power operation. Laser diodes also became prominent, allowing a reliable and efficient method of pumping. Wind sensing, navigation, terrain following, 2D, and 3D imaging, and velocity detection are some of the other laser radar uses that have been pursued. CO2 based navigation laser radar was deployed, but with the advent of GPS has become less popular.

Coherent high resolution imaging of distant targets is a challenging problem whose complexity involves understanding of diffractive properties of the optical imaging system, speckle properties of target, statistical properties of the atmospheric refractive index variations, coherence properties of the light source and noise limtations of the detector array to mention a few major issues. In a coherent laser radar imaging system, the target is illuminated with a laser beam, and the scattered light wave from the target light wave is mixed with a local oscillator wave from the same source. The system is referred to as spatial heterodyne imaging system. The sparse aperture imaging approach is based on reducing the total irradiance collection area using smaller sub-apertures, while the resulting resolution of the sparse aperture imaging array is equivalent to an aperture larger than the subapertures. The Ladar and Optical Communications Institute (LOCI) currently has a prototype of the high resolution sparse aperture imaging testbed with an indoor and outdoor range capability. In collaboration with industry partners, academic institutions, and the government this testbed is becoming an innovative research tool in the field of high resolution coherent ladar imaging.

We discuss the architecture and performance of compact, robust, alignment-free, homodyne vibrometers using telecom diode lasers as the illumination source. The technical challenges and performance of implementations using conventional macroscopic optical components are compared with ultra-miniature micro-bench components and assembly methods. Focused sensitivity exceeding 4.6 pm/SQRT(Hz) at 1m range, 23 pm/SQRT(Hz) at 5m range, and useful operation to >20m have been demonstrated with COTS 1550 nm sources, 1.5 cm transmit/receive beam diameter and 32 mW transmitted power. Vibrometer measurement bandwidth exceeds 100 kHz with current electronics. Demonstrated performance is suitable for a variety of defense, security, and inspection applications.

In this paper we develop spectral models for windowed speckle-modulated continuous coherent ladar signals with arbitrary coherence time as a function of the window duration and shape. This processing chain (compute the spectrum of the window random signal) is typical for many coherent ladar applications where the target is distributed in range, such as wind lidar. We link the peak of the spectrum to the signal's carrier-to-noise ratio (CNR) and the number of integrated signal photoelectrons. We also develop theoretical models for the SNR of the integrator output and the resultant coherent integration efficiency. In addition, we generalize Goodman's rectangular integrator diversity model to arbitrary window functions and show that the product of diversity and efficiency is close to one for arbitrary integration times and window functions. These general models are then applied to various signal autocorrelation functions and window functions. The analysis demonstrates that the shape of the window function has little impact on the output SNR, efficiency and speckle diversity. We show that if the coherence time is long compared to the integration time then the conventional CNR expression is valid, and the signal has unit diversity and the coherent integration efficiency is 100%. However, when the coherence time is short compared to the integration time, the CNR is reduced by roughly the ratio of these times and the diversity is increased by roughly the same factor. Finally, we also show how signal detectivity is related to SNR and diversity.

The ability of multiple-return airborne lidar systems to resolve fine details has grown significantly since their introduction, and many modern instruments are capable of footprint sizes under a half meter. Because most systems scan at near-nadir angles, the pulse origin is often ignored and not recorded with the return point cloud data. By recording this additional position information over multiple focused collects we show how properties such as occlusion can be derived using voxel aggregation of the return data. The voxel map allows us to exploit this new information in scenes with significant spatial structure, such as under tree canopies. Results are presented which show the accuracy of our approach under canopies of varying occlusion levels. Our findings are validated using simulated data provided by the Rochester Institute of Technology through the DIRSIG software.

The three-dimensional (3-D) nature and the unorganized structure of topographic LIDAR data pose several challenges for target recognition tasks. In the past, several approaches have applied two-dimensional transformations such as spinimages or Digital Elevation Maps (DEMs) as an intermediate step for analyzing the 3-D data with two-dimensional (2-D) methods. However, these techniques are computationally intensive and often sacrifice some of the overall geometrical relationship of the target points. In this paper, we present a simple and efficient 3-D spatial transformation that preserves the geometrical attributes of the LIDAR data in all its dimensions. This transformation permits the utilization of well established statistical and shapebased descriptors for the implementation of an automatic target recognition algorithm. We evaluate our transformation and analysis technique on a set of simulated LIDAR point clouds of ground vehicles with varied obstructions and noise levels. Classification results demonstrate that our approach is efficient, tolerant to scale, rotation, and robust to noise and other degradations.

For many decades attempts to accomplish Automatic Target Recognition have been made using both visual and FLIR camera systems. A recurring problem in these approaches is the segmentation problem, which is the separation between the target and its background. This paper describes an approach to Automatic Target Recognition using a laser gated viewing system. Here laser-flash illumination is used in combination with a gating viewer such that only a small part in the distance domain is seen in a single image. In our approach, using an Intevac LIVAR 4000 imaging system, we combined several images with different gate settings to construct a 3D data cube. This paper describes the preprocessing and filtering steps taken to obtain a range image for which pixel values represent the distance between camera and objects in the illuminated scene. Depth segmentation is performed using the global histogram of this range image. After this depth segmentation very good 2D object segmentations can be obtained which can be used to classify persons and vehicles. An outlook will be given towards operational application of this procedure.

Laser Radar, also referred to as lidar, has become widely available and is an established contributor to the military and intelligence community by providing precise elevation data using 3-dimensional measurements. The utilization of customized algorithms designed for lidar data exploitation provides the capability to determine corridors or gaps in areas of vegetation cover. These capabilities lend themselves as geospatial tools for mobility applications and tactical planning. This effort uses elevations derived from small-footprint (airborne) lidar surveys to create accurate surface models and corresponding canopy characterization maps. The canopy height models are based on elevation voxels above ground level and are used as input into a tree finding algorithm. Corridors under the canopy are then predicted using the obstruction identification technique and neighboring point characteristics. Path determination can also be performed using the obstruction maps and a modified A-star algorithm. A lidar survey over Camp Shelby, MS was chosen as the test case for the obstruction detection utilities as it provides fairly dense vegetation cover and interesting topographic features. The survey was completed using both a full-waveform lidar and a discrete return system which offers a coincident comparison of the obstruction methodology for differing data types. It is determined that the fullwaveform data provides a more complete and accurate assessment of the surface, the canopy and potential obstruction detection than the discrete return system.

A simple Monte Carlo model of laser propagation through a tree is presented which allows the simulation of fullwaveform LIDAR signatures. The model incorporates a LIDAR system and a 'natural' scene, including an atmosphere, tree and ground surface. The PROSPECT leaf reflectance model is incorporated to determine leaf radiometric properties. Changes in the scene such as varying material reflectance properties, sloped vs. flat ground, and comparisons of tree 'leaf-on' vs. 'leaf-off' conditions have been analyzed. Changes in the LIDAR system have also been studied, including the effects of changing laser wavelength, shape and length of transmitted pulses, and angle of transmission. Results of some of these simulations are presented.

Several multiple-hypothesis range-rate algorithms are investigated to determine initial target acquisition capabilities of a direct detection ladar operating under low photo-electron return conditions. During initial acquisition of an object, the location of the object is not known, therefore the ladar returns cannot be simply summed in order to improve detection statistics. Analogous to classical radar multiple hypothesis algorithm approaches a "shift and sum," a "shift and accumulate," and a "numerically shift and histogram" algorithm are investigated. The probability density function for the maximum of the multiple-hypothesis range-rate algorithm matrix output is developed so that a threshold crossing probability can be determined and a "detection" declared (receiver-operating-characteristic). This is expressed as a function of false alarm rate which is a function of the number of ladar returns processed in the acquisition process and the length of the acquisition window.

Very accurate geo-location (geo-coding) of imagery taken at long range is a very large challenge. Whereas GPS can supply a very accurate sensor position, the hardware for the required precision pointing can have a very large cost. Roth, et al (2005) showed that because of the accuracy of lidar range-data, a tri-lateration method (called Multi-Look Lidar or Multi-Look Geo-Coding) can achieve very accurate geocoding at very long ranges and very low cost by using data-driven processing. This paper presents extensive flight-testing results using commercial airborne lidar. Because the tri-lateration method produces a large number of control points, the resulting accuracy of the geo-coded lidar data is somewhat better than that predicted for a single control point due to control-point averaging.

It is shown through physics-based Monte Carlo simulations of avalanche photodiode (APD) LADAR receivers that under typical operating scenarios, Geiger-mode APD (GmAPD) flash LADAR receivers may often be ineffective. These results are corroborated by analysis of the signal photon detection efficiency and signal-to-noise ratio metrics. Due to their ability to detect only one pulse per laser shot, the target detection efficiency of GmAPD receivers, as measured by target signal events detected compared to those present at the receiver's optical aperture, is shown to be highly particular and respond nonlinearly to the specific LADAR conditions including range, laser power, detector efficiency, and target occlusion, which causes the GmAPD target detection capabilities to vary unpredictably over standard mission conditions. In the detection of partially occluded targets, GmAPD LADAR receivers perform optimally within only a narrow operating window of range, detector efficiency, and laser power; outside this window performance degrades sharply. Operating at both short and long standoff ranges, GmAPD receivers most often cannot detect partially occluded targets, and with an increased number of detector dark noise events, e.g. resulting from exposure to ionizing radiation, the probability that a GmAPD device is armed and able to detect target signal returns approaches zero. Even when multiple pulses are accumulated or contrived operational scenarios are employed, and even in weak-signal scenarios, GmAPDs most often perform inefficiently in their detection of target signal events at the aperture. It is concluded that the inability of the GmAPD to detect target signal present at the receiver's aperture may lead to a loss of operational capability, may have undesired implications for the equivalent optical aperture, laser power, and/or system complexity, and may incur other costs deleterious to operational efficacy.

Laser imaging offers potential for observation, for 3D terrain-mapping and classification as well as for target identification, including behind vegetation, camouflage or glass windows, at day and night, and under all-weather conditions. First generation systems deliver 3D point clouds. The threshold detection is largely affected by the local opto-geometric characteristics of the objects, leading to inaccuracies in the distances measured, and by partial occultation, leading to multiple echos. Second generation systems circumvent these limitations by recording the temporal waveforms received by the system, so that data processing can improve the telemetry and the point cloud better match the reality. Future algorithms may exploit the full potential of the 4D full-waveform data. Hence, being able to simulate point-cloud (3D) and full-waveform (4D) laser imaging is key. We have developped a numerical model for predicting the output data of 3D or 4D laser imagers. The model does account for the temporal and transverse characteristics of the laser pulse (i.e. of the "laser bullet") emitted by the system, its propagation through turbulent and scattering atmosphere, its interaction with the objects present in the field of view, and the characteristics of the optoelectronic reception path of the system.

A two-part method for calibrating a laser high definition profiler is presented. The profiler consists of laser line sources and a video camera, and it is designed to be deployed on a remotely operated vehicle (ROV). In the first part, distortions in the digital image were measured using images of a test grid, and corrected by an interpolation method based on a virtual pinhole camera model. In the second part, the equations of the laser planes were determined according to their intersections with a target of known geometry, whose position and orientation were obtained by a registration process.

The development of new asymmetric threats to civilian and naval ships has been a relatively recent occurrence. The bombing of the USS Cole is one example and the pirate activities outside Somalia another. There is a need to recognize targets at long ranges and possibly also their intentions to prepare for counteractions. Eye safe laser imaging at 1.5 μm offers target recognition at long ranges during day and night. The 1.5 μm wavelength is suitable for observing small targets at the sea surface such as boats and swimmers due to the low reflectivity of water compared to potential targets. Turbulence and haze limits the sensor performance and their influence is estimated for some cases of operational interest. For comparison, passive EO images have been recorded with the same camera to investigate the difference between sun illuminated and laser illuminated images. Examples of laser images will be given for a variety of targets and external conditions.Image segmentation for future automated recognition development is described and examplified. Examples of relevant 1.5 μm laser reflectivities of small naval targets are also presented. Finally a discussion of system aspects is made.

This paper discusses the simulation and flight test results of an integrated dual airborne laser scanner (DALS)/inertial navigation system (INS) navigator onboard Ohio University's DC-3 aircraft over Athens, Ohio. The use of two airborne laser scanners, integrated with an INS form an alternative means of navigation in non-GPS and unknown terrain environments. In these environments the usual integration of GPS and INS will no longer be a viable option. This paper will address both a feed-forward and a feedback coupled method without an available terrain database and show flight test results onboard Ohio University's DC-3.

We present experimental results on two breadboard systems developed within ESA contracts dealing with a long-range rendezvous and docking sensor on one hand and a high precision relative attitude control sensor on the other. A rendezvous and docking sensor to be used in a Mars sample return mission has been developed and recently tested over a range of 5 km. A high-speed 3-D laser scanner with range noise below 1 mm was realized and demonstrated. A critical assessment of the performance and potential for further developments of both systems is given.

The NLFM waveform resulting from a tunable integrated optical ring resonator is simulated and compared with the well known tan-FM waveform. The metrics of interest are the first sidelobe levels and FWHM times of the autocorrelation, as these directly relate to the long-range performance and fine range resolution of a LADAR system, and should ideally be as small as possible. Through simulation, the sidelobe level of the autocorrelation of an NLFM waveform generated by a series of tunable integrated optical ring resonators is shown to be lower than the autocorrelation sidelobe level of an equivalent optimized tan-FM waveform with an equal FWHM time. A proof of concept experiment employing thermally tunable Silicon Nitride integrated optical ring resonator is shown to generate NLFM chirped waveforms with frequency chirps of 28 kHz.

Single Longitudinal Mode (SLM) lasers are of interest for various coherent LIDAR techniques that utilize the Doppler wavelength shifting effect. Also, narrow linewidth lasers are of interest for Differential Absorption LIDAR (DIAL) which can precisely identify trace chemical species. However, such SLM lasers are often limited to low (~100Hz) rep rates due to laser seeding limitation. We report the development of a seeded SLM technology that enables us to achieve up to 85W of power at 1064nm with a linewidth less than 100 MHz. Furthermore, such SLM powers can be realized at rep rates up to 10 kHz enabling a myriad of next generation of narrow linewidth laser applications. We have built both watercooled and air-cooled versions of theses SLM lasers for various power level requirements.

An extension of the solution for the propagation of modulated beams through homogeneous media in cylindrical coordinates which results in a wave function described by Bessel Beams is the basis for this analysis of modulated beams through non homogeneous media in cylindrical coordinates]. By solving the wave equation analytically, including functions that describe the non-homogeneity, and using computer algebra software such as MAPLE©, we formulate new kinds of beams defined by special functions such as Airy, Kummer,and Hypergeometric functions. We also present convergence issues around the axis of propagation and possible applications for these new beams in telecommunication systems.

The Army Research Laboratory (ARL) is researching a short-range ladar imager for small unmanned ground vehicles for navigation, obstacle/collision avoidance, and target detection and identification. To date, commercial ladars for this application have been flawed by one or more factors including, low pixelization, insufficient range or range resolution, image artifacts, no daylight operation, large size, high power consumption, and high cost. In the prior year we conceived a scanned ladar design based on a newly developed but commercial MEMS mirror and a pulsed Erbium fiber laser. We initiated construction, and performed in-lab tests that validated the basic ladar architecture. This year we improved the transmitter and receiver modules and successfully tested a new low-cost and compact Erbium laser candidate. We further developed the existing software to allow adjustment of operating parameters on-the-fly and display of the imaged data in real-time. For our most significant achievement we mounted the ladar on an iRobot PackBot and wrote software to integrate PackBot and ladar control signals and ladar imagery on the PackBot's computer network. We recently remotely drove the PackBot over an inlab obstacle course while displaying the ladar data real-time over a wireless link. The ladar has a 5-6 Hz frame rate, an image size of 256 (h) × 128 (v) pixels, a 60° x 30° field of regard, 20 m range, eyesafe operation, and 40 cm range resolution (with provisions for super-resolution or accuracy). This paper will describe the ladar design and update progress in its development and performance.

Newest developments in laser scanner technologies put surveyors in the position to comply with the ever increasing demand of high-speed, high-accuracy, and highly reliable data acquisition from terrestrial, mobile, and airborne platforms. Echo digitization in pulsed time-of-flight laser ranging has demonstrated its superior performance in the field of bathymetry and airborne laser scanning for more than a decade, however at the cost of somewhat time consuming off line post processing. State-of-the-art online waveform processing as implemented in RIEGL's V-Line not only saves users post-processing time to obtain true 3D point clouds, it also adds the assets of calibrated amplitude and reflectance measurement for data classification and pulse deviation determination for effective and reliable data validation. We present results from data acquisitions in different complex target situations.

Research groups at Rochester Institute of Technology and Carnegie Institution for Science are studying savanna ecosystems and are using data from the Carnegie Airborne Observatory (CAO), which integrates advanced imaging spectroscopy and waveform light detection and ranging (wLIDAR) data. This component of the larger ecosystem project has as a goal the fusion of imaging spectroscopy and wLIDAR data in order to improve per-species structural parameter estimation. Waveform LIDAR has proven useful for extracting high vertical resolution structural parameters, while imaging spectroscopy is a well-established tool for species classification. We evaluated data fusion at the feature level, using a stepwise discrimination analysis (SDA) approach with feature metrics from both hyperspectral imagery (HSI) and wLIDAR data. It was found that fusing data with the SDA improved classification, although not significantly. The principal component analysis (PCA) provided many useful bands for the SDA selection, both from HSI and wLIDAR. The overall classification accuracy was 68% for wLIDAR, 59% for HSI, and 72% for the fused data set. The kappa accuracy achieved with wLIDAR was 0.49, 0.36 for HSI, and 0.56 for both modalities.

A new technique to improve the accuracy of direct detection time-of-flight (TOF) laser radar using a Geiger-mode avalanche photodiode (APD) by reducing range walk error is presented. The range walk error refers to the change of the measured distance as a function of the waveform and energy of the laser-return pulse scattered from the target. The technique is based on the theoretical model, established with Poisson statistics, of the system and it enables to overcome the inherent limitation of Geiger-mode APD so that the mean number of photons of the laser-return pulse is expectable within the range in which the target detection probability varies. The theoretical model for the detection probability of each time bin in a TOF histogram is derived after it is experimentally proved that the creation of primary electrons in the Geiger-mode APD is Poisson-distributed. It is shown that the range walk error depends on the energy of the laser-return pulse at the Geiger-mode APD with the theoretical model regarded as the TOF histogram of multiple laser pulses in a single-hit case. The method which reduces the range walk error with the center of mass detection in the TOF histogram is then proposed, and the experiment for its proof is carried out. The experimental results show that the theoretical model is appropriate and the range walk error is reducible within the range in which the detection probability varies.

We report the results of experiments demonstrating large-format coherent imaging at a range of 1.5 km. For this work, we use digital holographic detection to record coherent data and are thus able to measure the complex-valued optical field from a flood-illuminated scene over an extended aperture. Images are formed using digital Fourier processing. The return light is interfered with a coherent reference beam, and the intensity of the interference pattern is recorded using a conventional large-format detector array. Experimental results obtained using a coherent, pulsed laser source operating at 1.6 microns are presented. We also demonstrate the utility of this technique for advanced imaging functions such as 3D imaging.

The need to characterize in a robust way Planetary Boundary Layer (PBL) heights is crucial as in air quality forecast and transport models. In particular, incorrect determination of PBL heights can severely distort the surface air quality predictions such as PM2.5. Local properties and morphological features can influence PBL dynamics through local circulation phenomena such as the sea-breeze development as well as influences from the Urban Heat Island Canopy resulting in multiple layers that need to be resolved. In this paper, based on a combination of wavelet and image processing methods, we develop methods to quantify multilayer PBL's and assess their dynamics with meteorological measurements including temperature, wind and humidity profiles. In particular, meteorologically based PBL heights based on both the Potential Temperature Gradient and Richardson Number are compared against both lidar and ceilometer measurements. It is shown that in general, the Potential Temperature Gradient method is better correlated to the PBL dynamics. Meanwhile, the Hysplit model provides sounding data which can be used for comparison between actual sounding and lidar measurements. On the other hand, when strong atmospheric instability is present or layering develops, the comparison between different methods can provide information about the PBL internal structure. Further comparisons with air quality models such as MM5 are also made and illustrate the difficulty in these models properly predicting the PBL dynamics seen in urban areas.

We report on remote measurements of cross-wind and atmospheric turbulence, using a one-station scheme. As most remote wind-sensing methods, our method is based on observing the drift of the scintillation pattern across the line of sight. The scintillations are caused by naturally-occurring turbulence-induced refractive index irregularities in the atmosphere, which drift at wind speed. Analyzing spatial-temporal cross-correlation function of the signals of two elements in the array, it is possible to obtain the cross-wind speed. We use the zero-crossings technique for measuring the cross-wind value, while the cross-wind direction is determined by comparing areas from both sides of the peak of the cross-correlation function. Here we present results obtained using these techniques in comparison to independent measurements of the anemometers. The experiments were performed along a uniform path over a flat beach parallel to the Mediterranean Sea shore. Four white-screen diffusive targets were placed at distances of 300, 600, 850 and 1200m. Five anemometers were placed along the laser beam path, one near each target and at the measurement station. Each target was illuminated with a beam from a glass fiber pulsed infrared laser with a repetition rate of several thousand Hz, and a sub-microsecond pulse-length, and output beam divergence of ~300 μrad. The receiver has an entrance aperture of 80mm, and the incoming radiation is focused onto an array of four 50×250um InGaAs detectors by a lens with f=500mm. The results show good agreement. From the fluctuations of the signal on the detector array, our system also measures the turbulence structure parameter Cn 2, using the angle-of arrival technique. The obtained results show reasonable agreement with independent scintillometer measurements of C_n², performed with a CW He-Ne laser in a two-station setup with a detector at a distance of 60m from the laser.

We report on developing of a prototype LIDAR for remote measurements of cross-wind profile, using backscattering from aerosol in a single-ended scheme. The system contains a pulsed Nd:YAG laser with 500 Hz repetition rate and ~20 nsec pulse width, as a transmitter, and a matrix of 7 detectors, placed at the focus of Cassegrain-type telescope, as a receiver. To realize detection of signals with high-sampling resolution, a high-sampling-rate digitizer with 8 simultaneously sampled channels and 60 Msamples/sec-per-channel sampling rate was incorporated into the system. To check the ability to detect a local cross-wind flow, we performed an experiment using the cooling tower of Soreq reactor as a vertical wind simulator. We recorded the detector signals from aerosol scattering at different distances, and analyzed the temporal-spatial cross-correlation function. The analysis of the asymmetry and shift of the cross-correlation function shows good ability for qualitative mapping of local cross-wind. Next development steps will include improvement of the electronic circuits, in order to increase the sampling resolution along the line of sight, performing of additional controlled experiments and developing of wind-profile algorithm.

Long range, combined UV-IR LIDAR system was built and tested. The system was developed to operate as a multi-wavelength DIAL in the IR (8-11 μm), dual exciting wavelengths LIF LIDAR in the UV, and aerosol map and track at 1.5 μm. The IR transmitter is a continuous tunable solid-state Tandem Optical Parametric Oscillator (OPO) [1]. The first OPO stage generates the 1.5 μm beam and the second OPO stage pumped by the first, generates the IR band. In the UV the transmitter generates and transmits either the 266 nm or the 355 nm wavelengths sequentially. All the outgoing laser beams are prealigned to ensure geometric overlap over the measured paths. Energy references are measured for each beam on every pulse. The receiver is based on a single reflective telescope with coatings optimized for both the UV and the IR. The optical signal is routed between the different detection packages by means of a computerized optical scanner mirror. The receiver-transmitter layout is based on periscope geometry and is equipped with a large θ-φ scanner. Computer control enables fast switching between the different measurements and wavelengths, data acquisition and spatial scan as well. The system was built inside a mobile trailer and was field tested to descriminate aerosol types in a complex enviroment [2].