This PDF file contains the front matter associated with SPIE Proceedings Volume 7324, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

The most commonly used altitude-dependent model for refractive index fluctuations, over long high-altitude slant paths or ground/space links, is the Hufnagel-Valley model. For the near-ground turbulence portion of the path, this model uses an exponential decay term suggested by Valley to connect ground level turbulence with the original Hufnagel model which was constructed for turbulence above 3 km. However, it has long been observed that refractive-index fluctuations in the first few hundred meters near the ground decrease with altitude raised to the -4/3 power rather than exponentially. Recent and some earlier measurements of refractive-index fluctuations are presented in this paper along with a theoretical modification of the Hufnagel model to account for low-altitude turbulence exhibiting this power-law behavior.

Using small-angle parabolic approximation and Feynman path-integral technique we derive the exact solution for optical beam propagation in the low-order turbulence consisting of the optical wedges and lenses distributed along the propagation path. We present complete solutions for some specific distribution of lenses, and discuss limitations of LOT as a proxy model for propagation in turbulence.

This paper presents theory of speckle noise for a frequency-modulation differential-absorption LIDAR system along with simulation results. These results show an unexpected relationship between the signal-to-noise ratio (SNR) of the speckle and the distance to the retro-reflector or target. In simulation, the use of an annular aperture in the system results in a higher SNR at midrange distances than at short or long distances. This peak in SNR occurs in the region where the laser's Gaussian beam profile approximately fills the target. This was unexpected since it does not occur in the theory or simulations of the same system with a circular aperture. By including the autocorrelation of this annular aperture and expanding the complex correlation factor used in speckle models to include conditions not generally covered, a more complete theoretical model is derived for this system. Obscuration of the center of the beam at near distances is also a major factor in this relationship between SNR and distance. We conclude by comparing the resulting SNR as a function of distance from this expanded theoretical model to the simulations of the system over a double-pass horizontal range of 10 meters to 10 km at a wavelength of 1.28 micrometers.

In this work a theoretical investigation regarding the availability of a Free Space Optical communication system was carried out. The statistical distribution of the photocurrent generated at the receiver by a Gaussian beam after propagating through the random medium was investigated. The photocurrent's relative frequencies were obtained by means of computer simulation and the cases where beam wandering was present were taken into account. An experimental set up was mounted for comparisons purposes. Finally, with the knowledge of the photocurrent statistical distribution, the system availability and the Bit Error Rate were estimated under several system configurations and impairments conditions.

We present a survey of apodization functions intended to suppress diffraction effects over a finite propagation distance and within a finite "score" region on the final plane. Such apodization functions would be suitable for use in numerical simulations as part of a scheme to reduce numerical computation cost without sacrificing numerical accuracy.

Similar to atmospheric propagation, the propagation of light underwater is affected by absorption and scattering. However, the scale of absorption and scattering in the underwater environment is much shorter, with extinction coefficients given in inverse meters rather than inverse kilometers. Such severe attenuation of light poses many challenges to optical imaging and free space optical communications in water. Although blue-green wavelengths can be selected to minimize absorption, multiple small angle forward scattering produces extended beam profiles that cannot be described by simple Gaussian shapes. This spatial spreading leads to image blurring and pulse stretching, which can limit the information capacity of underwater optical communication links. Scatter of the beam in the backward direction can also reduce the contrast of underwater imaging systems and modulating retroreflector-type communications links. Results from laboratory tank experiments and performance prediction models will be presented to illustrate the effects of the underwater environment on a propagating optical signal and on free space optical communication links.

Atmospheric absorption, scattering, and turbulence are impairments in practical high-speed free-space laser communications. These atmospheric effects can be mitigated by choosing the proper transmission wavelength. It is well known that the MWIR (~3.8 μm) has many low-absorption spectral lines suitable for low-loss propagation. Also, MWIR can be more robust to turbulence in the weak-turbulence regime. Since high-speed laser transceivers are not available in the MWIR, a 3.8-μm signal can be generated and detected using a 1.55-μm telecom transceiver via wavelength conversion. Free-space transmission of optical homodyne RZ-QPSK through a turbulent channel at 3.8 μm has been investigated. A pair of Ti:PPLN-based nonlinear wavelength converters were used to down- and up-convert from 1.55 to 3.8 and back to 1.55 μm at the transmitter and at the homodyne receiver, respectively. The converted RZQPSK signal was transmitted through a tabletop wind tunnel that produces a weak turbulent path. Comparison of 1.55 and 3.8 μm transmission through the wind tunnel shows that under weak-turbulence 3.8 μm transmission is more robust than 1.55 μm. Under the same turbulence condition, the scintillation index measured at 3.8 μm is consistently lower than that at 1.55 μm. Extrapolated scintillation indexes for 3.8 and 1.55 μm using the Rytov variance (~ λ^-7/6 ) and independent measurement at 632.8 nm are consistent with the RZ-QPSK scintillation data for 3.8 and 1.55 μm. Under the most severe turbulence condition, the average bit-error-rate of 3.8-μm transmission is better than that of 1.55-μm giving an estimated receiver sensitivity improvement of at least 6 dB.

The path-integrated turbulence strength is usually thought of as a parameter that varies slowly with time. In a recent free-space communications experiment the C_n² n value over a 5-km horizontal path was monitored almost continuously for a period of nearly a month. In addition to well defined and repeatable diurnal fluctuations, strong short-term fluctuations were observed in which the turbulence strength changed by an order of magnitude within a period of minutes. These rapid changes were independently measured by a commercial scintillometer and the high-rate output from the communications transceiver. The characteristics and probable causes for these dynamic atmospheric events and their impact on the design of free-space communication systems are discussed in this article.

The Georgia Tech Research Institute (GTRI) has developed a turbulence profiling lidar system based on the differential image motion concept. The lidar measures a profile of mean square wave front tilt differences by focusing a laser guide star at multiple ranges and then computing the differential image motion variance of guide star images collected through multiple sub-apertures on the receiver. Direct inversion of the resulting integrals suffers from high noise gain, so several different techniques were investigated to determine the refractive turbulence profile. The best inversion method uses a non-linear fitting algorithm to fit a collection of functions to the differential image motion profile. Each of the fitted functions then maps to a profile of refractive turbulence.

Free-space optical (FSO) links typically carry digital data over short to moderate distances (100m - 50 km). From a military perspective, FSO links have the advantages of low probability of interception, inherent anti-jam capability and a reasonable degree of covertness. In certain applications it is desirable to minimize size, weight and power of the transmitter and this pushes the designer to eliminate power-hungry digitizers and to transmit raw analog, instead of digital, information. However, the transmission of analog signals presents significant technical challenges due to strong fluctuations in received optical power resulting from atmospheric turbulence. In this case the standard RF link properties of gain, noise factor, and linearity must be described entirely in statistical terms. In this paper we present preliminary experimental results from a short (500m), single-tone, 5 MHz analog FSO link and compare the data to theoretical predictions. Theory suggests, and our preliminary experimental results confirm, that the statistical properties of all the RF performance metrics of a FSO analog link are determined entirely by the statistical properties of the received optical power. We show that the distribution of values of RF link parameters can be obtained directly from the distribution of received optical power, without the need for modeling the received power with a continuous function.

A free-space quantum key distribution system is being developed by the National Institute of Information and Communications Technology (NICT) in Koganei, Japan. Quantum cryptography is a new technique for transmitting information where the security is guaranteed by the laws of physics. In such systems, a single photon is used for the quantum information. However, since the transmission distance in optical fibers is limited by the absorption of photons by the fiber, the maximum demonstrated range has been limited to about 100 km. Free-space quantum cryptography between an optical ground station and a satellite is a possible solution to extend the distance for a quantum network beyond the limits of optical fibers. At NICT, a laser communication demonstration between the NICT optical ground station and a low earth orbit satellite was successfully conducted in 2006. The use of free-space quantum key distribution for such space communication links is considered an important future application. This paper presents conceptual designs for the onboard transceivers for satellite quantum cryptography

In the context of the increasing demand in high-speed data link for scientific, planetary exploration and earth observation missions, the Italian Space Agency (ASI), involving Thales Alenia Space as prime, the Polytechnic of Turin and other Italian partners, is developing a program for feasibility demonstration of optical communication system with the goal of a prototype flight mission in the next future. We have designed and analyzed a ground level bidirectional Free Space Optical Communication (FSOC) Breadboard at 2.5Gbit/s working at 1550nm as an emulator of slant path link. The breadboard is full-working and we tested it back-toback, at 500m and 2.3km during one month. The distances were chosen in order to get an equivalent slant path cumulative turbulence in a ground level link. The measurements campaign was done during the day and the night time and under several weather conditions, from sunny, rainy or windy. So we could work under very different turbulence conditions from weak to strong turbulence. We measured the scintillation both, on-axis and off-axis by introducing known misalignments at the terminals, transmission losses at both path lengths and BER at both receivers. We present simulations results considering slant and ground level links, where we took into account the atmospheric effects; scintillation, beam spread, beam wander and fade probability, and comparing them with the ground level experimental results, we find a good agreement between them. Finally we discuss the results obtained in the experimentation and in the flight mission simulations in order to apply our experimental results in the next project phases.

The Naval Research Laboratory (NRL) in collaboration with the Defence Science and Technology Organisation (DSTO) of Australia has performed long distance experiments with analog modulated free space optical communication links across the Chesapeake Bay. Results will be presented on estimating the probability density functions of the RF parameters of gain, noise factor, and linearity after propagating an RF modulated, 1550nm laser beam over a 32km distance (folded round-trip across Chesapeake Bay). In addition, results from the transmission of video using analog FM modulation of a 1550nm laser beam over the link will be presented.

In order to track, acquire and maintain a free-space optical link between mobile platforms experiencing misalignment due to movement and atmospheric turbulence requires a different approach than traditional free-space optical transceivers. Recently, an investigation of alternative receiver configurations found that a small focal length lens combined with larger core fibers significantly expanded the range of angular and translational misalignments tolerated by the receiver. The trade-off for this increased misalignment tolerance was a smaller receiving area, typical of short focal length lenses, which limited the collected power. This paper investigates a novel approach using a lens array coupled to an array of large-core fibers in an effort to maximize both misalignment tolerance and optical power collected. The approach is evaluated on the key parameters of maximum allowable lateral, allowable angular misalignment, and collected power for both collimated and divergent beams. Both experimental and theoretical analyses of the system are presented to characterize the system performance. The investigation finds that the lens array provides superior performance over a single lens combined with a fiber bundle.

As part of a free-space optical communications experiment over a 5km horizontal path, an extensive database of tilt-stabilized receiver data was collected for C_n² n conditions ranging from benign to very strong. This paper focuses on the scintillation measurements made during those tests. Ensemble probability distributions are compiled from these results, and are subsequently compared with standard channel models such as the log-normal and gammagamma distributions. Statistical representations of temporal behavior are also developed from this database. Accurate statistical models of atmospheric channel effects have proved to be invaluable in the development of high-performance free-space transceivers.

In order to track, acquire and maintain a free-space optical link between mobile platforms experiencing misalignment due to movement and atmospheric turbulence requires a different approach than traditional free-space optical transceivers. Recently, a fiber-bundle approach for beam steering at the transmitter was proposed and investigated that allowed tracking of the receiver without the use of mechanical devices. This reduced the size and weight of the transmitter by reducing the dependence on stabilization systems. This paper investigates different approaches for controlling the distribution of light to the bundle to facilitate tracking of the receiver and hence maximizing up time of the link. These approaches include switching light between individual fibers in the bundle, splitting of light amongst multiple fibers and switching between groups of fibers, and splitting light between all of the fibers. Each approach is evaluated on key parameters including power availability at the receiver, switching time, projected up time between switches, and coverage area at the receiver plane. Both experimental and theoretical analyses of the system are presented to address the key parameters. The investigation finds that a combination of switching combined with splitting of the light between at most three fibers is a suitable solution for the target application of a hybrid disaster area wireless network.

Significant research efforts are underway to investigate the application of Free-Space Optics (FSO) for the provision of high-bandwidth communications links between mobile platforms. The use of FSO between mobile platforms introduces several interesting challenges in addition to those found in traditional fixed link FSO systems. In this paper, some of the major hurdles facing fixed FSO communications that carry over into links between mobile platforms are analyzed. These topics include: issues with alignment and tracking, an investigation into the weather and its affect on the link, and a study of the feasibility of having uninterrupted communications links. Other topics presented unique to mobile applications include: the security risks during link alignment, maintaining the link while tracking and optical power and beam divergence variations that are introduced into the system. In this paper the results from simulation work performed on some of these issues along with proposed solutions to the challenges are presented.

Delay-diversity transmission employing two orthogonal polarizations in turbulent media has been shown to be effective in combating fading. The technique employs simultaneous transmission of two orthogonal polarizations carrying the same information but delayed relative to each other by an amount (Td) equal to or greater than the turbulence correlation time (τc). At the receiver, the polarization signals are detected separately with Td compensated on the delayed polarization, resynchronizing the two signals, and they are then combined. Because Td is comparable to τc, scintillation suffered by the two resynchronized polarization signals is essentially independent in a statistical sense. As a result, the average bit-error-rate (BER) of the polarization-combined signal is less than the average BER of either one of the polarization signals. The signal-to-noise ratio (SNR) is effectively improved. We describe here an experiment and test results of fading mitigation via polarization delay-diversity reception in homodyne optical RZ-QPSK transmission at 1.55 μm through a tabletop wind tunnel and phase plates. The wind tunnel and the phase plates produce, respectively, weak and strong turbulence with scintillation indexes less than and greater than one. The turbulence correlation time for the wind tunnel is less than 1 ms. The homodyne detected optical RZ-QPSK signals in the two orthogonal polarizations were captured and stored for off-line processing. Test results show that the computed BER of the polarizationcombined signal is lower than the BER of either polarization signals. As a result, an equivalent signal-to-noise ratio improvement of at least 2 dB was deduced.

We present theoretical and experimental results for the expected impact on high-throughput optical communication systems of pulse broadening effects from scattered light propagating through water-based clouds. Existing analytical models are compared with experimental results. A preferred Monte Carlo model is developed and validated from field measurements of off-axis scattering through clouds, using a low-power continuous wave laser source at 1550 nm wavelength. This model is used in the time domain to examine the effects of pulse broadening for Gigabit and higher systems with practical apertures and fields of view. Results indicate that, for most current scenarios, pulse stretching may not cause significant inter-symbol interference.

The Georgia Tech Research Institute (GTRI) is developing a transportable multi-lidar instrument known as the Integrated Atmospheric Characterization System (IACS). The system will be housed in standard shipping containers that will be transported to remote sites by tractor-trailer. IACS will comprise three lidars: a 355 nm imaging lidar for profiling refractive turbulence, a 355 nm Raman lidar for profiling water vapor, and an aerosol lidar operating at both 1.06 and 1.625 microns. All of the lidar transmit/receive optics will be co-aligned on a common mount, pointable at any elevation angle from horizontal to vertical. The entire system will be computer controlled to facilitate pointing and automatic data acquisition. The purpose of IACS is to characterize optical propagation paths during outdoor tests of electro-optical systems. The tests are anticipated to include ground-to-ground, air-to-ground, and ground-to-air scenarios, so the system must accommodate arbitrary slant paths through the atmosphere with maximum measurement ranges of 5-10 km. Elevation angle scans will be used to determine atmospheric extinction profiles at the infrared wavelengths, and data from the three wavelengths will be used to determine the aerosol Angstrom coefficient, enabling interpolation of results to other wavelengths in the 355 nm to 1.6 micron region. The imaging lidar for profiling refractive turbulence is based on a previously-reported project known as Range Profiles of Turbulence.

So-called "free-space" laser communication systems working near the surface of the Earth must operate in the presence of atmospheric turbulence. The effects of the atmospheric turbulence on the laser beam which are relevant to optical communications are a broadening of the laser footprint, random jitter of the laser beam, and high spatial frequency intensity fluctuations referred to as scintillation. The overall goal of our program is to improve performance and extend the range of optical communications systems by exploring the use of adaptive optics and channel coding. To better model the performance of a real system operating in the real world, we have developed an outdoor turbulence-measurement and monitoring system. In this paper we describe an atmospheric turbulence monitoring system for three kilometers, partially over water path. The laser transmitter operates at 808 nm with a source power of 2mW. The receiver consists of relay optics, a Hartmann wave front sensor (WFS), and a CCD camera. The WFS is used to monitor atmospheric turbulence-induced phase aberrations, and the camera is used for both conventional imaging studies and measurements of anisoplanatic effects. In this paper we describe this system and present some preliminary results obtained from the measurements.

The scientific method applies to more than science or technology. It has application equally to processes of technical development, invention, innovation, communications, practical application and, ultimately, operations. Differences between the practice of pure science and the themes of effective operations exist only in terms of the ultimate objective and the standards by which success is measured. The standard for science is proof of concept; the standard for operations is a particular utility or effectiveness in solving an operational problem. The scientific method is ideally able to manage each process against distinct objectives and still achieve the desired success. This paper discusses the tension between the two orientations and argues for the application of the scientific method to the urgent need for changes to obsolete organizational structures and processes that impede the effective implementation of new capabilities into operations. This must occur even as, simultaneously, we must operate within these obsolete structures to achieve the transition results we desire.

Hyperspectral ground mapping is being used in an ever-increasing extent for numerous applications in the military, geology and environmental fields. The different regions of the electromagnetic spectrum help produce information of differing nature. The visible, near-infrared and short-wave infrared radiation (400 nm to 2.5 μm) has been mostly used to analyze reflected solar light, while the mid-wave (3 to 5 μm) and long-wave (8 to 12 μm or thermal) infrared senses the self-emission of molecules directly, enabling the acquisition of data during night time. Push-broom dispersive sensors have been typically used for airborne hyperspectral mapping. However, extending the spectral range towards the mid-wave and long-wave infrared brings performance limitations due to the self emission of the sensor itself. The Fourier-transform spectrometer technology has been extensively used in the infrared spectral range due to its high transmittance as well as throughput and multiplex advantages, thereby reducing the sensor self-emission problem. Telops has developed the Hyper-Cam, a rugged and compact infrared hyperspectral imager. The Hyper-Cam is based on the Fourier-transform technology yielding high spectral resolution and enabling high accuracy radiometric calibration. It provides passive signature measurement capability, with up to 320x256 pixels at spectral resolutions of up to 0.25 cm-1. The Hyper-Cam has been used on the ground in several field campaigns, including the demonstration of standoff chemical agent detection. More recently, the Hyper-Cam has been integrated into an airplane to provide airborne measurement capabilities. A special pointing module was designed to compensate for airplane attitude and forward motion. To our knowledge, the Hyper-Cam is the first commercial airborne hyperspectral imaging sensor based on Fourier-transform infrared technology. The first airborne measurements and some preliminary performance criteria for the Hyper-Cam are presented in this paper.

Characterizing the fundamental response and operational parameters of a deformable mirror is a critical first step in the design of an adaptive optics system. This paper describes the characterization of the influence function and training of a piezoelectric deformable mirror (PDM) at 632 nm. We scale the results to 1550 nm for low to mid order aberration correction for free space laser communications applications in the Short Wave Infrared (SWIR). A modified Twyman-Green interferometer was used to measure the influence functions and to characterize the mirror. The data was analyzed using commercial and customized software.

Active sensing has long been used for autonomous navigation in ground vehicles and involves the classification of objects based primarily on 3D spatial information. Differentiating critical targets such as humans from other objects and terrain has proven difficult due to the diversity of human spatial configurations that could be present in a given scene. Our approach to this problem and classification in general is to augment existing sensor technology with spatially independent information. In this paper we report on new signatures-based enhancements to the current technology to enhance classification with additional aspects of discrimination. The experimental investigation involved the measurement and evaluation of the polarization characteristics of objects of importance to short range autonomous ground mobility. A monostatic polarimeter was constructed to operate at 1550 nm and analyze the backscatter from materials over a wide range of incident angles. Several materials were analyzed with special focus on discerning humans from foliage clutter. The results are discussed here in the context of current UGV perception technology and applications. We have further interest in extending this concept to include active spectropolarimetric sensing and present results from numerical calculations.

Spider webs were shown to be effective collectors of bioaerosols and airborne microorganisms. Spider webs were collected and analyzed for microbial content using two general microbial culture mediums. To be considered suitable passive collectors, webs had to satisfy three basic conditions; (1) collection of microorganisms without discrimination based on species or size, (2) collection under variable environmental conditions, and (3) saturation avoidance in the presence of strong microbial launching sources. Samples were collected from four locations near Wright-Patterson Air Force Base, OH, a waste water treatment facility, a commercial garden center, a secluded state park area, and a parking garage located within a medium size metropolitan area. These four locations provided appropriately varied environmental and physical conditions to test the collection parameters previously stated. A simple collection methodology was devised; microscopy cover glass slides were used as collection instruments. The methodology assured sterility during collection and permitted in situ microbial growth, observation, and enumeration. Microbial growth, both bacteria and fungi, were recovered from all collected spider web samples.

The multiple coincidence technique uses 14.1 MeV neutrons to produce (n, multiple-γ) coincidences to detect fissile and fissionable materials. Measurements of n-γ-γ coincidences with targets of depleted uranium (DU), W, and Pb, show that the counting rate for the DU is substantially above that for the non-fissionables. Also, the data involving prompt neutrons and delayed gammas in the DU time spectra provide a signature for fissionables that is distinct from that of non-fissionables.

It has been observed that electronic devices emit unintentional electromagnetic energy. These emissions can create a passive radio frequency signature that can be used to characterize and eventually detect and identify the device. In support of this concept, the authors have integrated high fidelity models and simulations into a framework used to perform collection feasibility studies of unintentional electronic emissions in relevant detection scenarios. This paper will discuss the elements involved in simulating realistic electronic emissions in a complex environment, including near earth propagation, terrain model effects, and visualization techniques.

Terahertz (THz) spectral signatures have been measured for a variety of explosive materials and precursors. These signatures were measured by THz Time Domain Spectroscopy, using ultrashort pulsed lasers coupled with electro-optic materials to generate and detect THz radiation. Transmission and reflection spectra were measured across a frequency range from 0.2 to 2.5 THz for solid and liquid materials. These spectra are reported in terms of index of refraction and absorption coefficient, both of which can be calculated from transmission or reflection data. The value of THz spectral signatures for the development of future explosives sensing systems is discussed.

This study quantifies terahertz (THz) or sub-millimeter imaging performance during simulated rotary-wing brownout or whiteout environments based on geographic location and recent/current atmospheric weather conditions. The atmospheric conditions are defined through the Air Force Institute of Technology Center for Directed Energy (AFIT/CDE) Laser Environmental Effects Definition and Reference or LEEDR model. This model enables the creation of vertical profiles of temperature, pressure, water vapor content, optical turbulence, and atmospheric particulates and hydrometeors as they relate to line-by-line layer extinction coefficient magnitude at wavelengths from the UV to the RF. Optical properties and realistic particle size distributions for the brownout and whiteout particulates have been developed for and incorporated into LEEDR for this study. The expected imaging performance is assessed primarily at a wavelength of 454 μm (0.66 THz) in brownout conditions at selected geographically diverse land sites throughout the world. Seasonal and boundary layer variations (summer and winter) and time of day variations for a range of relative humidity percentile conditions are considered to determine optimum employment techniques to exploit or defeat the environmental conditions. Each atmospheric particulate/hydrometeor is evaluated based on its wavelength-dependent forward and off-axis scattering characteristics and absorption effects on the imaging environment. In addition to realistic vertical profiles of molecular and aerosol absorption and scattering, correlated optical turbulence profiles in probabilistic (percentile) format are used. Most evaluated scenarios are brownout environments over ranges up to 50 meters. At submillimeter wavelengths and the short ranges studied, preliminary results indicate the main source of image degradation in brownout conditions is water vapor content, even with visibility less than 10 m and strong optical turbulence.

From 1996 through 2008, the NIST Speaker Recognition Evaluations have focused on the task of automatic speaker detection based on recorded segments of spontaneous conversational speech. Earlier evaluations were limited to English language telephone speech. More recent evaluations (2004-2008) have included some conversational telephone speech in multiple languages, with the 2008 evaluation including 24 different languages. These recent evaluations have also explored cross channel effects by including phone conversations recorded over multiple microphone channels, and the 2008 evaluation also examined interview type speech recorded over multiple microphone channels. The considerable progress observed over the period of these evaluations has made the technology potentially useful for detecting individuals of interest in certain applications. Performance capability is measurably affected by a number of situational factors, including the number and duration of the training speech segments available, the durations of the test speech segments available, the language(s) spoken in these segments, and the types and variability of the recording channels involved.

The dissemination formats for multimodal signature data generally favor either formats with extreme interoperability, such as Extensible Markup Language (XML), portable binary formats with very high levels of interoperability, such as Hierarchical Data Format 5 (HDF5), or proprietary binary formats, often optimized for a specific application but which offer very low levels of interoperability across various computer platforms. The lack of Free and Open Source Software (FOSS) tools for proprietary or application specific file formats, tends to make such formats inappropriate for sharing signature data across organizations such as U.S. Army Research Laboratory (ARL), Signatures Support Program (SSP), and other government agencies. Sharing signature data for computational purposes is of extreme interest to the scientific community. An initial study of similar signatures in two different popular data file formats (HDF5 and XML) and using three popular computational environments (MATLAB, Octave, and Python) reveals definite advantages of HDF5 over XML, especially for larger data sets. HDF5 provides several key benefits for scientific applications without sacrificing interoperability across many computer platforms. The combination of HDF5 and XML for dissemination of signature data and information may yield the best solution for data consumers and providers.

The Signatures Support Program (SSP) leverages the full spectrum of signature-related activities (collections, processing, development, storage, maintenance, and dissemination) within the Department of Defense (DOD), the intelligence community (IC), other Federal agencies, and civil institutions. The Enterprise encompasses acoustic, seismic, radio frequency, infrared, radar, nuclear radiation, and electro-optical signatures. The SSP serves the war fighter, the IC, and civil institutions by supporting military operations, intelligence operations, homeland defense, disaster relief, acquisitions, and research and development. Data centers host and maintain signature holdings, collectively forming the national signatures pool. The geographically distributed organizations are the authoritative sources and repositories for signature data; the centers are responsible for data content and quality. The SSP proactively engages DOD, IC, other Federal entities, academia, and industry to locate signatures for inclusion in the distributed national signatures pool and provides world-wide 24/7 access via the SSP application.