Multifunction laser radar systems can collect two-dimensional target images of intensity, range, or velocity, and many such systems augment their active-sensor channel with a FLIR channel. This paper addresses the problem of optimal target detection using such an active-passive sensor, focusing on the performance benefits that accrue when multidimensional data-active-sensor range, velocity, and intensity, plus passive-sensor intensity - are combined in the detection processor. Generalized likelihood ratio tests are derived for active-passive detection processing, and quantitative performance results - receiver operating characteristics - are obtained through computer simulation of pixel-level statistics. The performance predictions for the gamut of multidimensional, multipixel detection processors are confirmed via experiments performed using a multidimensional laser radar test bed.
This paper deals with the theory of monopulse angle tracking with a laser radar employing heterodyne detection. The detector is assumed to be of the quadrant type. The target's angular location is inferred from the location of its diffraction pattern in the detector plane. A generalized gain characteristic for the detector can be used to relate the strength of the matched filter outputs, which correspond to the spatial regions (halves) of the detector surface, to the corresponding angular location of the target. The maximum likelihood angle estimator is derived for a speckle target. The performance of an approximation to the maximum likelihood angle estimator is evaluated for both the speckle and glint targets. The angle estimator performance is also evaluated in the presence of atmospheric turbulence and beam jitter.
This paper shows how these signal probability density functions in power and in voltage propagate down the signal processing electronics chain using data from the Army Missile Optical Range (AMOR) facility. The AMOR targets considered here are 'analytical targets' consisting of rotating diffuse disks and rotating diffuse spheres illuminated by a CO2 laser. It is hoped that the analyses presented will clarify and clearly illustrate the origins of these various signal probability density functions with the added benefit that the signal processing calculations are performed on data from a coherent laser radar system.
This paper extends techniques of convex set reconstruction from support line measurements, assesses their performance with respect to various parameters, and applies these to laser radar data. Specifically, the techniques are applied to both range-resolved and Doppler-resolved data, which provide one and two support line measurements, respectively. The resulting reconstructions provide size and shape estimates of the targets under observation. While such information can be obtained by other means (e.g., from reconstructed images using tomography), the present methods yield this information more directly. Furthermore, estimates obtained using these methods are more robust to noisy and/or sparse measurement data and are much more robust to data suffering from registration errors. Finally, the present methods are used to improve tomographic images in the presence of registration errors.
The signal isolation capabilities of rotating wave plate type single sideband electrooptic modulators operating in different configurations are analyzed. Discussion includes a broadband configuration in which the microwave pump wave travels in the backward direction. Experimental results confirming the feasibility of a simple configuration are presented.
In this work, the issues of broadband tuning in the design of a high average power Ti:Sapphire amplifier for a chromatic scanning lidar system are addressed. A novel pump delay and staging scheme is used to maintain high extraction efficiency with flat temporal and spatial pulse profiles while tuning over a 700-900 nm range. The effects of the chromatic scanning scheme on ASE suppression and beam pointing are discussed in relation to the amplifier optical system. The average power scaling for three power amplifier geometries (zigzag slabs, parallel plates, and active mirrors) was investigated to determine the limitations of each. Pump light is provided by diode laser-pumped Nd:GGG slab lasers which make up over 60 percent of the system weight. Predicted electrical to light laser efficiency was 3-4 percent over the wavelength tuning range.
The global winds measurement application of coherent Doppler lidar requires intensive study of the global climatology of atmospheric aerosol backscatter at infrared wavelengths. An airborne backscatter lidar is discussed, which has been developed to measure atmospheric backscatter profiles at CO2 laser wavelengths. The instrument characteristics and representative flight measurement results are presented.
A low average power, pulsed, solid-state, 1.06-micron coherent laser radar (CLR) for range and velocity measurements of atmospheric and hard targets has been developed. The system has been operating at a field test site near Boulder, CO since September, 1988. Measurements have been taken on moving targets such as atmospheric aerosol particles, belt sanders, spinning disks, and various stationary targets. The field measurements have shown that this system exhibits excellent velocity measurement performance. A fast-tuning CW Nd:YAG oscillator has also been developed which has a frequency tuning range of greater than 30 GHz (which spans a target radial velocity range of over 16 km/s) and a tuning speed greater than 30 GHz/ms.
A CW CO2 lidar sytem developed to determine the feasibility of using such a system for detecting and measuring low-level wind shear is discussed. The system was constructed from off-the-shelf components at a relatively low cost. Results of preliminary testing of the system are included. Wind shear measurements have been achieved but the capability of the system to measure large-scale microburst-generated wind shear has not been determined at this time.
System considerations and the design of infrared coherent lidars utilizing tropospheric backscatter are discussed. Requirements regarding power measurement, Doppler measurement, antenna and laser energy considerations are addressed. A design for an improved CO2 laser source is proposed that meets these requirements and is compact and capable of unattended operation.
The system level issues that any Doppler ladar, operating from a polar orbiting platform, will confront are described. Emphasis is given to signal-to-background issues. It is found that the ladar behavior is quite distinctive depending on the relationship between viewing direction and satellite motion. The relativistic correction to the Doppler shift is analyzed and compared to the signal. The results indicate the need for taking account of the relativistic effect.
The Lidar In-Space Technology Experiment (LITE) is a Shuttle experiment that will demonstrate the first use of a lidar system in space. Its design process must take into account not only the system design but also the unique design requirements for spaceborne experiment.
An overview of some of the developments completed on an alexandrite laser for making water vapor DIAL measurements is presented in this paper. A computer control for active stabilization of the two intracavity etalons has been implemented and recently tested in an aircraft environment. Long-term frequency drift (i.e., 2 hours) of less than 0.7 pm has been observed in the laboratory. An alignment technique to get the optimum free spectral range ratio for the two etalons is also developed.
A differential absorption lidar (DIAL) system developed at NASA Langley Research Center for the remote measurement of atmospheric H2O and aerosols from an aircraft is briefly discussed. This DIAL system utilizes a Nd:YAG laser-pumped dye laser as the off-line transmitter and a narrowband, tunable Alexandrite laser as the on-line transmitter. A 1-m monochromator and a multipass absorption cell are used to position the on-line laser to the center of the H2O line. The receiver system has a 14-in. diameter, f/7 Celestron telescope to collect the backscattered laser light and focus in into the detector optics. Return signals are converted to electrical signals by the optical detector and are digitalized and stored on magnetic tape. The results of fligh tests of the system are shown.
A multiwavelength CO2 direct-detection DIAL system has been designed and developed to produce range-resolved vapor concentration contour plots of a 1 x 1 km grid at 20-m spatial resolution in 10 s intervals.
The design and operation of a differential absorption lidar (Light Detection and Ranging) system capable of remotely measuring
the vertical stmcture oftroposphenc pressure and temperature is described. The measurements are based on the absorption
by atmospheric oxygen of the spectrally narrowband output of two pulsed alexandrite lasers. Detailed laser output spectral
characteristics, which are critical to successful lidar measurements, are presented.