Coherent Technologies, Inc. has recently designed and developed an airborne Differential Absorption Lidar (DIAL) sensor that can rapidly and economically locate, identify, and quantitatively map hazardous chemical releases. The lidar was built under contract from Eastman Kodak Company and is capable of filling a broad range of chemical measurement needs. Topographic returns are used to provide simultaneous column content measurement of two (possibly three) chemical species with absorption features between approximately 2.4 microns and 3.5 microns. The system incorporates platform attitude correction and is optimized for mapping surface-source chemical plumes within swaths exceeding 50 m. This system can provide ground resolution better than 1 m at flight speeds in excess of 75 m/s. The 14-month transceiver design-and-build effort is currently in the final integration phase, and flight-testing is scheduled to begin this summer. A recently developed species-specific plume model developed by Kodak, enables reconstruction of the altitude distribution of the chemical plume and estimation of the source release rate, as well as providing realistic species-specific sensor performance predictions under differing environmental conditions. The paper discusses the system architecture, performance modeling, technology trades, and current status, and demonstrates the system measurement capabilities using modeled HCl plumes.

The Molecular Optical Air Data System (MOADS) is a compact instrument designed to measure aircraft airspeed as well as the density of the air surrounding the aircraft. Other air data products provided by the instrument include density altitude, angle of attack (AOA), angle of side-slip (AOS), and Mach number. MOADS is a direct-detection LIDAR that measures these air data products from fringe images derived from a Fabry-Perot etalon. Determination of airspeed and direction is achieved through three telescopes that view a fixed air volume ahead of the aircraft turbulent flow field. This method reduces the measurement error as compared to traditional measurements made from within this turbulent region. As a direct detection LIDAR instrument, MOADS is capable of collecting both molecular and aerosol LIDAR returns, which allows operation in clear air as well as in aerosol-filled atmospheric regions. A second prototype was designed, built and tested. This MOADS prototype has been validated in a laboratory wind tunnel. Presented here are the airflow velocity measurement results from ground testing and vibration test measurements.

A method for indirect determination of the refractive index profile in the atmospheric layer just above the sea surface with LIDAR is described. One important application is prediction of performance and particularly the maximum observation range of optical sensors. A lidar is placed near the sea surface and the lobe is scanned in a small vertical sector near the horizon. Returns from particles are recorded. The range to the point, where the laser beam reaches the sea surface, is determined from the lidar returns and stored together with the corresponding elevation angles. This information is compared to results from an optical propagation model to determine the vertical profile of the refractive index, which fits to the lidar results. Test measurements have been performed and results will be presented.

The use and scope of LADAR (laser detection and ranging) applications continues to expand as the technology matures. This growth is reflected in the National Institute of Standards and Technology's (NIST) experience with research into the applications of LADARs for construction, manufacturing, and autonomous vehicle navigation. However, standard protocols or procedures for calibrating and testing LADARs have yet to be developed. Currently, selections of LADAR instruments are generally based on the manufacturer's specifications, the availability of standard test procedures would promote more uniform definitions of these specifications and provide a basis for a better informed differentiation between LADAR instruments. Consequently, NIST's Construction Metrology and Automation Group (CMAG) has conducted exploratory experiments to characterize the performance of a LADAR instrument. The experiences gained in these efforts are summarized in this paper. These experiences also pointed to the need for an internal calibration/evaluation facility at NIST, as well as to the need for the development of uniform specifications and test procedures for characterizing LADARs. As a result, NIST convened a workshop on the establishment of a LADAR calibration facility. Discussions of some issues relating to the performance evaluation of LADARs, facility requirements, and similar efforts are presented in this paper.

Criss-crossing of focal images is the cause of a narrow dynamic range in Shack-Hartmann sensors. Practically, aberration range wider than ±3 diopters can not be measured. A method has been proposed for ophthalmologic applications using a rarefied lenslet array through which a wave front is projected with the successive step-by-step changing of the global tilt. The data acquired in each step are accumulated and processed. In experimental setup, a doubled dynamic range was achieved with four steps of wave front tilting.

A direct detection time-of-flight ladar simulator has been developed to synthesize noisy realizations of true range for the purpose of testing the performance of target recognition algorithms. The simulator can model either peak report or peak report above a threshold using computationally efficient analytic models. In addition, the simulator can also model arbitrary detection logic by direct simulation for cases where analytic models do not exist. Two types of range estimates can occur, local and global. Local errors represent error about the true target range and are described by a Gaussian distribution whose width is given by the Cramer-Rao lower bound. Global errors represent errors that occur because the noise, in one or more bins within the range search interval, is stronger than the target echo. These errors are called "anomalies" and, for peak detection logic, are uniformly distributed over the range search interval. In this paper, the probability density function (PDF) that accounts for both local and global errors is derived. The PDF is a function of signal-to-noise ratio (SNR), range search interval (RSI), and level of speckle diversity. The signal synthesizer uses these PDFs to synthesize the range errors much faster than via direct simulation. Simple approximations to the anomaly probability are derived for high SNRs. The predicted range precision is compared to the results of Monte Carlo simulations of the noisy received signals.

High-energy 2-micron lasers have been incorporated in a breadboard coherent Doppler lidar to test component technologies and explore applications for remote sensing of the atmosphere. Design of the lidar is presented including aspects in the laser transmitter, receiver, photodetector, and signal processing. Sample data is presented on wind profiling and CO₂ concentration measurements.

The U.S. Army Research Laboratory (ARL) has developed a number of near-infrared, prototype laser detection and ranging (LADAR) Systems based on the chirp, amplitude-modulated LADAR (CAML) architecture. The use of self-mixing detectors in the receiver, that have the ability to internally detect and down-convert modulated optical signals, have significantly simplified the LADAR design. Recently, ARL has designed and fabricated single-pixel, self-mixing, InGaAs-based, metal-semiconductor-metal detectors to extend the LADAR operating wavelength to 1.55 mm and is currently in the process of designing linear arrays of such detectors. This paper presents fundamental detector characterization measurements of the new 1.55 mm detectors in the CAML architecture and some insights on the design of 1.55 μm linear arrays.

This paper reviews the progress of Advanced Scientific Concepts, Inc (ASC). flash ladar 3-D imaging systems and presents their newest single-pulse 128 x 128 flash ladar 3-D images. The heart of the system, a multifunction ROIC based upon both analog and digital processing, is described. Of particular interest is the obscuration penetration function, which is illustrated with a series of images. An image tube-based low-laser-signal 3-D FPA is also presented. A small-size handheld version of the 3-D camera is illustrated which uses an InGaAs lensed PIN detector array indium bump bonded to the ROIC.

This paper examines several characteristics and phenomenon associated with the optimization of diode pumped erbium ytterbium glass microlasers. Test results indicate that within an erbium ytterbium glass gain element, the excited erbium (laser) ion effective pump depth is larger than the excited ytterbium (sensitizer) ion effective pump depth. Designed specifically for diode pumping, JD phosphate laser glass host material exhibits high rare earth and sensitizer ion solubility. This enhanced doping capability allows the JD glass to be used in a variety of diode pump architectures that are not possible with most conventional crystal & glass laser materials. Our study has shown that new small gain element composite laser glass architectures & designs may be made used to more efficiently capture, contain and uniformly distribute the diode laser pump light. We expect this work to will lead to the next generation of high peak & average power "eye-safe" diode pumped microlasers for use in rangefinding, imaging, illumination tracking and targeting applications.

InAlAs/InGaAs avalanche photodiodes (APDs) have been fabricated and characterized in linear mode operation as photon counting detectors. Dark current, dark count, dynamic range, pulse shapes, and counting statistics are presented on 75 μm and 200 μm diameter APDs.

The U.S. Army Research, Development and Engineering Command (RDECOM) is developing approaches and processes that will exploit the characteristics of current and future Laser Radar (LADAR) sensor systems for critical man-in-the-loop tactical processes. The importance of timely and accurate target detection, classification, identification, and engagement for future combat systems has been documented and is viewed as a critical enabling factor for FCS survivability and lethality. Recent work has demonstrated the feasibility of using low cost but relatively capable personal computer class systems to exploit the information available in Ladar sensor frames to present the war fighter or analyst with compelling and usable imagery for use in the target identification and engagement processes in near real time. The advantages of LADAR imagery are significant in environments presenting cover for targets and the associated difficulty for automated target recognition (ATR) technologies.

The ability to extract target features from a ladar Range Resolved Doppler Image (RRDI) can enable target detection, identification, discrimination, and status assessment. Extraction of these features depends on the image processing algorithms, target characteristics, and image quality. The latter in turn depends on ladar transmitter and receiver characteristics, propagation effects, target/beam interactions, and receiver signal processing. In order to develop hardware systems and processing algorithms for a specific application, it is necessary to understand how these factors interact. A modular, high fidelity ladar simulation has been developed which provides modeling of each step from transmitter, through feature extraction.

The analysis of particles produced by solid rocket motor fuels relates to two types of studies: the effect of these particles on the Earth's ozone layer, and the dynamic flight behavior of solid fuel boosters used by the NASA Space Shuttle. Since laser backscatter depends on the particle size and concentration, a lidar system can be used to analyze the particle distributions inside a solid rocket plume in flight. We present an analytical model that simulates the lidar returns from solid rocket plumes including effects of beam profile, spot size, polarization and sensing geometry. The backscatter and extinction coefficients of alumina particles are computed with the T-matrix method that can address non-spherical particles. The outputs of the model include time-resolved return pulses and range-Doppler signatures. Presented examples illustrate the effects of sensing geometry.

The Army Research Laboratory (ARL) has developed a three dimensional (3D) imaging ladar based on an amplitude modulated laser for which the frequency of the amplitude modulation (AM) is linearly increased and/or decreased with time (i.e., chirped). The frequency chirped waveform is a standard radar and coherent ladar waveform for high resolution ranging and Doppler frequency shift measurement. ARL first demonstrated the use of this waveform with laser amplitude modulation and optical direct detection for high range resolution 3D imaging ladar. The Doppler frequency shift measurement capability of the AM direct detection ladar had been known previously, but had not been demonstrated until recently. This paper contains the first report of an experimental demonstration of the capability of an AM direct detection ladar to measure the frequency and amplitude of surface vibrations via the phase/frequency modulation induced on the return waveform by the surface motion. In addition, we present data demonstrating the measurement of line-of-sight translational velocities via the Doppler shift of the chirped AM waveform using the same apparatus. We first briefly describe the operating principles of ARL's chirped AM ladar for range and translational Doppler measurement with references to previous papers. We then present the classic theory for vibration induced phase/frequency modulation to explain the operating principles of the AM direct detection ladar vibrometer. We then describe the experimental demonstration of the AM direct detection ladar vibrometer, including descriptions of the experimental setup, data processing and analysis methods, and results.

We present a hybrid sensor consisting of a high-performance 3D imaging laser sensor and a high-resolution digital camera. The laser sensor uses the time-of-flight principle based on near-infrared pulses. We demonstrate the performance capabilities of the system by presenting example data and we describe the software package used for data acquisition, data merging and visualization. The advantages of using both, near range photogrammetry and laser scanning, for data registration and data extraction are discussed.

We report on the demonstration of an InGaAs PIN and Avalanche Photodiode (APD) based "FLASH" 3-dimensional imaging system. The system utilizes a unique LADAR readout integrated circuit (ROIC) designed to operate using either PIN or APD based devices fabricated on a common cathode substrate. In addition to a digital range count that is output from each of the 1024 pixels, on-chip signal processing enables sub-six inch range resolution in a single FLASH image. The uniformity of the breakdown voltage, gain, and dark current of the InGaAs APDs fabricated for this demonstration greatly simplifies the ROIC architecture, as input offset voltage trimming is unnecessary. The ROIC architecture enables advanced LADAR applications such as first pulse suppression, programmed range interrogation, and return pulse shape sampling enabling dramatic improvements in range accuracy using advanced ranging algorithms.

We have developed a mono-static staring 3-D laser radar based on gated viewing with range accuracy below 1 mm at 10 m and 1 cm at 100 m. We use a high sensitivity, fast, intensified CCD camera, and a Nd:YAG passively Q-switched 32.4 kHz pulsed green laser at 532 nm. The CCD has 752×582 pixels. Camera shutter is controlled in steps of 100 ps. Camera delay is controlled in step of 100 ps. Each laser pulse triggers the camera delay and shutter. A 3-D image is constructed from a sequence of 50-100 2-D reflectivity images, where each frame integrates ~700 laser pulses on the CCD. In 50 Hz video mode we record a 2-D sequence in a second and process a 3-D image in few seconds. We compare 3-D images with a system performance model.

The Army Research Laboratory is researching system architectures and components required to build a 32x32 pixel scannerless ladar breadboard. The 32x32 pixel architecture achieves ranging based on a frequency modulation/continuous wave (FM/cw) technique implemented by directly amplitude modulating a near-IR diode laser transmitter with a radio frequency (RF) subcarrier that is linearly frequency modulated (i.e. chirped amplitude modulation). The backscattered light is focused onto an array of metal-semiconductor-metal (MSM) detectors where it is detected and mixed with a delayed replica of the laser modulation signal that modulates the responsivity of each detector. The output of each detector is an intermediate frequency (IF) signal (a product of the mixing process) whose frequency is proportional to the target range. Pixel read-out is achieved using code division multiple access techniques as opposed to the usual time-multiplexed techniques to attain high effective frame rates. The raw data is captured with analog-to-digital converters and fed into a PC to demux the pixel data, compute the target ranges, and display the imagery. Last year we demonstrated system proof-of-principle for the first time and displayed an image of a scene collected in the lab that was somewhat corrupted by pixel-to-pixel cross-talk. This year we report on system modifications that reduced pixel-to-pixel cross-talk and new hardware and display codes that enable near real-time stereo display of imagery on the ladar's control computer. The results of imaging tests in the laboratory will also be presented.

NASA has developed a sensor suite to inspect the Space Shuttle Thermal Protection System while the Shuttle is flying in orbit. When the Space Shuttle returns to flight, it will carry a 3D Imaging Laser Radar as part of the sensor suite to observe the Thermal Protection System and indicate any damages that may need to be repaired before return to earth. The 3D laser sensor provides accurate images that include precise measurement of the depth of any flaws that may be present. This paper describes the 3D laser sensor for the next shuttle flight and indicates the remaining challenge to industry to provide a sensor that can be even more capable for future flights.

Recently-developed airborne imaging laser radar systems are capable of rapidly collecting accurate and precise spatial information for topographic characterization as well as surface imaging. However, the performance of airborne ladar (laser detection and ranging) collection systems often depends upon the density and distribution of tree canopy over the area of interest, which obscures the ground and objects close to the ground such as buildings or vehicles. Traditionally, estimates of canopy obscuration are made using ground-based methods, which are time-consuming, valid only for a small area and specific collection geometries when collecting data from an airborne platform. Since ladar systems are capable of collecting a spatially and temporally dense set of returns in 3D space, the return reflections can be used to differentiate and monitor the density of ground and tree canopy returns in order to measure, in near real-time, sensor performance for any arbitrary collection geometry or foliage density without relying on ground based measurements. Additionally, an agile airborne ladar collection system could utilize prior estimates of the degree and spatial distribution of the tree canopy for a given area in order to determine optimal geometries for future collections. In this paper, we report on methods to rapidly quantify the magnitude and distribution of the spatial structure of obscuring canopy for a series of airborne high-resolution imaging ladar collections in a mature, mixed deciduous forest.

This paper wil give an overview of 3D laser sensing and related activities at the Swedish Defence Research Agency (FOI) in the view of system needs and applications. Our activites include data collection of laser signatures for target and backgrounds at various wavelengths. We will give examples of such measurements. The results are used in building sythetic environments, modellin of laser radar systems and as training sets for development of algorithms for target recognition and weapon applications. Present work on rapid environment assessment includes the use of data from airborne laser for terrain mapping and depth sounding. Methods for automatic target detection and object classification (buildings, trees, man-made objects etc.) have been developed together with techniques for visualisation. This will be described in more detail in a separate paper. The ability to find and correctly identify "difficult" targets, being either at very long ranges, hidden in the vegetation, behind windows or under camouflage, is one of the top priorities for any military force. Example of such work will be given using range gated imagery and 3D scanning laser radars. Different kinds of signal processing approaches have been studied and will be presented more in two separate papers. We have also developed modeling tools for both 2D and 3D laser imaging. Finally we will discuss the use of 3D laser radars in some system applications in the light of new component technology, processing needs and sensor fusion.

Over the years imaging laser radar systems have been developed for both military and civilian (topographic) applications. Among the applications, 3D data is used for environment modeling and object reconstruction and recognition. The data processing methods are mainly developed separately for military or topographic applications, seldom both application areas are in mind. In this paper, an overview of methods from both areas is presented. First, some of the work on ground surface estimation and classification of natural objects, for example trees, is described. Once natural objects have been detected and classified, we review some of the extensive work on reconstruction and recognition of man-made objects. Primarily we address the reconstruction of buildings and recognition of vehicles. Further, some methods for evaluation of measurement systems and algorithms are described. Models of some types of laser radar systems are reviewed, based on both physical and statistical approaches, for analysis and evaluation of measurement systems and algorithms. The combination of methods for reconstruction of natural and man-made objects is also discussed. By combining methods originating from civilian and military applications, we believe that the tools to analyze a whole scene become available. In this paper we show examples where methods from both application fields are used to analyze a scene.

This paper presents our ongoing research activities on target recognition from data generated by 3-D imaging laser radar. In particular, we focus on future full flash imaging 3-D sensors. Several techniques for laser range imaging are applied for modelling and simulation of data from this kind of 3-D sensor systems. Firstly, data from an experimental gated viewing system is used. Processed data from this system is useful in assisting an operator in the target recognition task. Our recent work on target identification at long ranges, using range data from the gated viewing system, provides techniques to handle turbulence, platform motion and illumination variances from scintillation and speckle noise. Moreover, the range data is expanded into 3-D by using a gating technique that provides reconstruction of the target surface structure. This is shown at distances out to 7 km. Secondly, 3-D target data is achieved at short ranges by using different scanning laser radar systems. This provides high-resolution 3-D data from scanning a target from one single view. However, several scans from multiple viewing angles can also quite easily be merged for more detailed target representations. This is, for example, very useful for recognizing targets in vegetation. Hereby, we achieve simulated 3-D sensor data from both short and long ranges (100 meters out to 7 km) at various spatial resolutions. Thirdly, real data from the 3-D flash imaging system by US Air Force Research Lab (AFRL/SNJM), Wright Patterson Air Force Base, has recently been made available to FOI and also used as input in the development of aided target recognition methods. High-resolution 3-D target models are used in the identification process and compared to the 3-D target data (point cloud) from the various laser radar systems. Finally, we give some examples from our work that clearly show that future 3-D laser radar systems in cooperation with signal- and image analysis techniques have a great potential in the non-cooperative target recognition task and will provide several new and interesting capabilities, for example, to reveal targets hidden in vegetation.

Detailed 3D environment models for visualization and computer based analyses are important in many defence and homeland security applications, e.g. crisis management, mission planning and rehearsal, damage assessment, etc. The high resolution data from airborne laser radar systems for 3D sensing provide an excellent source of data for obtaining the information needed for many of these models. To utilise the 3D data provided by the laser radar systems however, efficient methods for data processing and environment model construction needs to be developed. In this paper we will present some results on the development of laser data processing methods, including methods for data classification, bare earth extraction, 3D-reconstruction of buildings, and identification of single trees and estimation of their position, height, canopy size and species. We will also show how the results can be used for the construction of detailed 3D environment models for military modelling and simulation applications. The methods use data from discrete return airborne laser radar systems and digital cameras.

Structural segmentation of 3-D point-cloud data is an important step in the acquisition, recognition and visual representation of objects from point data. Associating groups of points that are consistent with structural surface elements allows decision making based on object components that are much more meaningful that the points alone. Processing begins by filtering the 3-D point-cloud data to smooth surfaces and remove noise. Filtering is essential for accurate surface-normal estimation. Our point filtering algorithm steps a 3-D box through the data, using an efficient search algorithm that employs priority queues for sequential sorting in x, y, and z. Filtering is based on the computation of a best planar fit at each box location. After filtering, processing continues by again stepping through the data and computing local surface normals at each filtered point. We then compute a Minimum Spanning Tree (MST) with nodes consisting of the filtered points, edges established by proximity, and edge weights set as the Euclidean distance between local surface normals. A modified range tree that is computed on the fly from unsorted point data is used in implementing the MST. We then employ a novel procedure to determine the edges that should be broken, leaving subgraphs that represent structural surfaces. These surfaces have been used for visual display of 3-D LADAR data, extraction of surfaces for automatic detection of buildings, and differentiation between man-made and natural objects.

Using LiDAR data collected on the levees along the Rio Grande River in New Mexico and Texas, an algorithm has been developed to automatically extract longitudinal elevation profiles. This algorithm consists of a series of filters, interpretation of geophysical properties, and digitized levee centerlines. The series of filters, in order of operation, include an alignment buffer filter, bare-earth filter, sampling filter and a maximum value filter. The result of the filter configuration is a 3-D polyline that models the levee crest. This algorithm allows for efficient identification of portions of levee that are lower than original design specifications. A comparison between the LiDAR levee crown extraction filter and a least-cost-path technique are offered.

The LADAR simulation tool described in this paper is designed to propagate optical fields from the laser transmitter to the target and back to the receiver. This simulation tool differs from other wave optics simulation codes as they propagate fields using the Fresnel approximation to approximate diffraction between planes in the optical train. The approach taken here involves the use of the Rayleigh-Sommerfeld propagation integral for computing the field at one field plane due to another. The proposed modeling technique can be used to model both 2-D and 3-D data collected with different sensors. The probability of detection is estimated from the modeled data and is compared to that estimated from the measured data. Both the average probability of detection over the whole target and the error variance of the probability of detection are used to compare the modeled and measured data. These experiments show that the model can successfully estimate the performance of the 3-D sensor to within 6.5 percent of its measured value.

We present results from experimental investigations on different laser sources for 3D imaging lidars. The lasers investigated include microchip lasers and fiber lasers and the results are compared to results obtained with diode lasers. The potential of the laser candidates for spaceborne 3D imaging sensors based on the pulsed time-of-flight principle is analyzed. Analysis include limitations in radar key parameters such as peak power, pulse width, beam divergence, parameter stability, efficiency, and impact on sensor mass and volume. After trade-off and selection of suitable laser sources, breadboard models have been realized and tested.

Coherent laser radars observing a resolved (larger than the incident laser mode) target vibrating surface can estimate the target's piston-mode displacement motion from the target's Doppler produced frequency spectrum. We review recent work showing that a newly developed joint time-frequency transform algorithm is superior to older joint time-frequency transforms, the common short-time-Fourier transform (spectrogram) algorithm, and other elementary spectral estimation algorithms for resolving the target's spectra. In this paper we extend these approaches when the ladar is observing an unresolved (smaller than the incident laser mode) piston-mode vibrating object situated on the ground. Because the target is smaller than the laser spot, the surrounding ground produces a narrow-band constant frequency "clutter" signal at the baseband frequency. We show that a recently developed "sech-window" joint time-frequency transform is superior to other algorithms for separating the frequency modulated target piston motion signal from the narrow-band ground return. The analysis in this case includes a "signal-to-clutter ratio" (SCR) parameter variation as well as a "carrier-to-noise ratio" (CNR), or target signal strength to LO-laser noise strength, parameter variation.

A general methodology for a spectroscopic continuous-wave, frequency-modulated ladar (CW-FM-ladar) concept based on principles of both CW-FM-range-finding and modulation spectroscopy, together with modern techniques of optical signal transmission using tunable laser diodes, signal detection and heterodyne processing are presented. A mathematical description of trace gas detection using CW-LD ladar is developed including the relationship between the heterodyne echo-signal amplitudes and frequencies and trace gas concentration for each range. In particular, precise range and gas retrieval resolution limits based on the transmitting signal modulation and absorption line parameters are developed.

This paper reviews work done at Trex Enterprises Corporation over the past 18 years on electro-optic surveillance and tracking systems. The range of objects that can be detected and tracked cover awide range of brightness and velocities, from slower moving mortars to fast moving bullets.

The SHOALS-1000T is the first generation of coastal mapping systems which incorporates both airborne lidar bathymetric (ALB) and airborne topographic subsystems. Its predecessor, the SHOALS (Scanning Hydrographic Operational Airborne Lidar Survey) system went operational in 1994 and was retired in 2003 after a history of successful worldwide surveys. The SHOALS-1000T has 2.5 times the data collection rate of the previous SHOALS system and yet is about one-third the size and consumes about half the power. A description of the system design will be given, along with a summary of extensive field testing carried out in Florida in August of 2003. It will be shown that despite the reduction in size and power requirements, the basic system performance matched the previous system very well. The increased collection rate also increases other capabilities such as target detection. The addition of a digital camera has enhanced the SHOALS-1000T system as a premier coastline mapping tool.

When using airborne passive spectral data for underwater imaging, inversion of radiative transfer models is often based on the simplifying assumptions that spectral diffuse attenuation and path radiance do not vary horizontally across the project area. We have developed a technique which does not require these assumptions. In it, we use a combination of SHOALS pseudoreflectance images and passive spectral images to manually identify areas of homogeneous bottom type. At these locations, we use the measured depths from the SHOALS bathymeter to estimate the spectral diffuse attenuation coefficients, the additive path radiance of the water column, and the bottom radiance (or reflectance) at each homogeneous patch. The parameters estimated at these patches are then used as control points in the interpolation of surfaces for each parameter. In this paper, we show early results using this approach to solve the radiative transfer equations for calibrated radiance data acquired with a casi-2 imaging spectrometer, and describe our procedure for producing SHOALS pseudoreflectance images.

Small target detection and tracking are important for laser systems in many applications such as Directed Infrared Countermeasures (DIRCM), fire control, target recognition and free-space laser communication. In order to evaluate performance of these applications in a marine environment we have performed laser propagation studies over the Baltic Sea during May to October 2003. The laser system consisted of a CO₂ laser, a pointing and tracking head, a quadrant laser receiver, a TV and 3-5 μm IR camera and a laser range finder. The laser system was placed in a building 18m above water and corner cube targets and separate receivers were placed on islands at 2.5, 5.5 and 17 km range. Together with the laser registration, separate instruments such as a scintillometer and a weather station were recording the meteorological parameters. From the received signals irradiance fluctuation parameters for different beam offsets relative to the beam centre, temporal and amplitude signal distributions, probability and meant time of fade were derived. Results from single- and double-ended paths will be compared. The results will be discussed in relation to theoretical modelling and evaluated in view of some system aspects.