Richard D. Richmond

Direct-Detection LADAR Systems

This text is designed to introduce engineers-in-training to the basic concepts and operation of 3D imaging LADAR systems. The book covers laser range equations; sources of noise in LADAR signals; LADAR waveforms; the effects of wavefront propagation on LADAR beams through optical systems and atmospheric turbulence; algorithms for detecting, ranging, and tracking targets; and comprehensive system simulation. Computer code for accomplishing the many examples appearing throughout the text is provided. Exercises appear at the end of each chapter, allowing students to apply concepts studied throughout the text to fundamental problems encountered by LADAR engineers. Also included is a CD-ROM with the MATLAB code from the examples.

Eye-safe laser radar focal plane array for three-dimensional imaging

Previous efforts to develop 3-D laser radar (ladar) imagers have required multiple laser pulses and complex stable scanning and timing systems in order to generate images. This paper describes the progress that has been made in program developing an approach that will enable a complete 3-D ladar image (angle-angle-range) to be captured with a single pulse. It has been previously reported that a unique processor chip was designed and fabricated that was intended to be bump bonded directly behind a detector array, the sensor provides separate independent range finder circuitry for each pixel. The time-of-flight for each pixel is recorded on the chip and the values are then read out serially. This approach allows the range resolution to be determined by the laser pulse width and electronics bandwidth and to be independent of image framing rates. The original version of this concept is a 32 X 32-pixel device. A silicon photo-diode array was bonded to the processor chip. This limited the useful wavelength of the sensor 1 micron and below. Images generated using this sensor will be presented. The effects of shot-to-shot fluctuations, turbulence and scintillation on image quality will be discussed. The next generation, under development at this time, will also be presented. This sensor will be a 64 X 64-pixel device. The detectors will be electron-capture anode plates and the device will be sealed into an image intensifier tube. The photocathode material will be InGaAs, engineered to be sensitive to 1.5 microns. Results from the photocathode development effort, including quantum efficiency and micro-channel plate gain will be presented.

Flash light detection and ranging range accuracy limits for returns from single opaque surfaces via Cramer-Rao bounds

A Cramer-Rao lower bound on the range accuracy obtainable by a Flash light detection and ranging (LADAR) system receiving a return from a single surface in the instantaneous field of view of each detector is developed and verified with experimental data. The bound is compared to the performance of a new algorithm and that of a matched filter receiver by using both simulated and measured LADAR data. The simulated data are used to show that the estimator is nearly unbiased and efficient for systems that match the negative paraboloid model used in its derivation. It is found that the achievable range accuracy for the LADAR system and for the target geometry used to collect the measured data is of the order of 2.5 in. while the bound predicts a range accuracy limit of approximately 0.6 in.

Laser radar focal plane array for three-dimensional imaging

Previous efforts to develop 3D laser radar (ladar) imagers have required multiple laser pulses and complex stable scanning and timing systems in order to generate images. This paper describes an approach that will enable a complete 3D ladar image (angle-angle-range) to be captured with a single pulse. Using a unique processor chip that is bump bonded directly behind the detector array, the sensor provides separate independent range finder circuitry for each pixel. The time-of-flight for each pixel is recorded on the chip and the values are then read out serially. This approach allows the range resolution to be determined by the laser pulse width and electronics bandwidth and to be independent of image framing rates. This paper will discuss the design, laboratory tests and present the status of the imager that will be assembled for field demonstrations. The specifications of the demonstration unit are for a 64 X 64 pixel imager with a resolution of .3 X .3 X .3 meters (1 X 1 X 1 feet). The system is expected to operate at approximately video framing rates (30 frames per second) and the resulting image will be displayed in a false color picture on the processor monitor.

The application of iterative closest point (ICP) registration to improve 3D terrain mapping estimates using the flash 3D ladar system

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.

Compact mid-infrared DIAL lidar for ground-based and airborne pipeline monitoring

We report the progress in the development of a compact mid-infrared differential absorption lidar (DIAL) for ground-based and airborne monitoring of leaks in natural gas pipeline systems. This sensor, named Lidar II, weighs approximately 30 kg (70 lbs) and occupies a volume of 0.08 m3 (3.5 ft3). Lidar II can be used on the ground in a topographic mode or in a look-down mode from a helicopter platform. The 10-Hz pulse repetition rate and burst-mode averaging currently limit the airborne inspection speed to 30 km/h. The Lidar II laser transmitter employs an intracavity optical parametric oscillator. Wavelength tuning is accomplished through two mechanisms: a servo-controlled crystal rotation for slow and broad-band tuning and a fast piezo-activated wavelength shifter for on-line/off-line switching in less than 10 ms. The sensor operates in the 3.2-3.5-μm band with the primary focus on hydrocarbons and volatile organics. In the pipeline inspection work, the two main targets are methane and ethane, the latter chemical being important in preventing false positives. Initial results of Lidar II testing on actual pipeline leaks are reported. To supplement the mapping capabilities of Lidar II with range-resolved information, a short-range (less than 300 m) aerosol backscatter lidar is currently under development.

U.S. Air Force Ballistic Winds program

The Air Force Wright Laboratory has successfully flown two micron laser radars and is preparing to fly a third. These systems are designed to provide real-time 3D maps of the wind fields between the aircraft and the ground. This paper briefly describes these systems and the demonstrated performance of each. Future measurement efforts of this program ar also discussed.

Worldwide assessments of laser radar tactical scenario performance variability for diverse low altitude atmospheric conditions at 1.0642 μm and 1.557 μm

Spatial, spectral and temporal variations in operating conditions are major contributors to the expected variability/uncertainty in system performance. The ratio of signal-to-noise ratio (SNR) based on climatological data to a standard atmosphere is the primary performance metric used, with results presented in the form of histograms and maps of worldwide LADAR performance variation. This metric is assessed at 2 wavelengths, 1.0642 μm and 1.557 μm, for a number of widely dispersed land and maritime locations worldwide over oblique and vertical air to surface paths in which anticipated clear air aerosols and location specific heavy rain and 150 m thick fog occur. Seasonal, boundary layer, and time of day variations for a range of relative humidity percentiles are also considered. In addition to realistic vertical profiles of molecular and aerosol extinction, air-to-ground cloud free line of sight (CFLOS) probabilities as a function of location for this geometry are computed. Observations from the current study strongly indicate that use of the standard atmosphere to predict performance will produce overly optimistic, in many cases extremely so, estimates of expected performance. Locally heavy rain, when present, severely limits LADAR system performance at these wavelengths. Some operational capability exists for vertical looks through fog.

Characterization measurements of ASC FLASH 3D ladar

As a part of the project agreement between the Swedish Defence Research Agency (FOI) and the United States of Americans Air Force Research Laboratory (AFRL), a joint field trial was performed in Sweden during two weeks in January 2009. The main purpose for this trial was to characterize AFRLs latest version of the ASC (Advanced Scientific Concepts [1]) FLASH 3D LADAR sensor. The measurements were performed essentially in FOI´s optical hall whose 100 m indoor range offers measurements under controlled conditions minimizing effects such as atmospheric turbulence. Data were also acquired outdoor in both forest and urban scenarios, using vehicles and humans as targets, with the purpose of acquiring data from more dynamic platforms to assist in further algorithm development. This paper shows examples of the acquired data and presents initial results.

Detection and Estimation Theory Applied to LADAR Signal Detection

This chapter presents techniques for processing LADAR data to accomplish the tasks of detection and range estimation. Section 4.1 introduces the theory of Bayesian reasoning for making an optimal detection decision from a single photocount measurement. The decision process requires criteria for making the decision, which is discussed in Sec. 4.2. Section 4.3 covers methods of detecting targets from a collection of measurements or a waveform. Section 4.4 describes a method for comparing the performance of different LADAR target detectors known as the receiver operating characteristic. Finally, Sec. 4.5 discusses range estimation algorithms. 4.1 Simple Binary Hypothesis Testing Many LADAR applications involve the detection of a target in air or space. In these cases, the laser pulse is transmitted upward into the sky and the receiver waits for a signal to return to determine if a target is present. This scenario is known as the simple binary hypothesis problem, because at any time there are two possible conclusions from the signal measured by the receiver. The first possibility is that a target is present, and the second possibility is that no target is present. If a signal is present, it may not be detectable, given the noise that is also present in the measurement. The probability mass function (PMF) of the number of photoelectrons in the measurement D is denoted as P(D|H1), where H1 denotes hypothesis number one, in which the target is present. When the signal in its raw form (no data processing) is present and amplified by an APD, the noise will usually be dominated by laser speckle and photon noise.