David H. Terry

Free-space optical channel characterization in the maritime environment

The performance of a free-space optical (FSO) communications link in a maritime environment was evaluated during two field trials conducted off the mid-Atlantic coast near Wallops Island, VA, in July and September 2009. Bidirectional, ship-to-shore data links operating at 2.5 Gbps and utilizing commercial, single-mode adaptive optics terminals were set up between a lookout tower located on Cedar Island, VA and a Johns Hopkins University Applied Physics Laboratory research vessel over a range of 2-22 km (optical horizon). This paper presents the test configuration, discusses the overall performance of the FSO channel, and compares it to the available turbulence and weather measurements. Additionally, modeling of the link configuration is presented, and comparisons are made to data measured throughout the experiment such as received power, received beam diameter, and local The performance of a free-space optical (FSO) communications link in a maritime environment was evaluated during two field trials conducted off the mid-Atlantic coast near Wallops Island, VA, in July and September 2009. Bidirectional, ship-to-shore data links operating at 2.5 Gbps and utilizing commercial, single-mode adaptive optics terminals were set up between a lookout tower located on Cedar Island, VA and a Johns Hopkins University Applied Physics Laboratory research vessel over a range of 2-22 km (optical horizon). This paper presents the test configuration, discusses the overall performance of the FSO channel, and compares it to the available turbulence and weather measurements. Additionally, modeling of the link configuration is presented, and comparisons are made to data measured throughout the experiment such as received power, received beam diameter, and local Cn2.

Imaging pyrometry of oxides

A technique for imaging pyrometry of oxides will be presented which is capable of remotely determining the temperatures of an oxide surface with useful accuracy. The technique relies on the near-blackbody emittance properties of most oxides in the two-phonon spectral region. Most oxides in the longwave IR region are very highly emitting with an emittance that is almost temperature independent and Lambertian. We present a generalized calibration procedure for longwave cameras that allows spatially resolved surface temperature to be obtained from radiance measurements. Experimental results from a sapphire disk will be presented as a demonstration of the technique.

Detection of DNA sequence symmetries using parallel micro-optical devices

In order to search for symbolically encoded sequences of DNA base information, we have constructed an incoherent optical feature extraction system. This approach uses video display, spatial light modulation, and detection components in conjunction with microlenslet replicating optics, to expedite the recognition of symbol sequences based on their symmetry properties. Multichannel operation is achieved through the replication of input scenery, making possible a higher throughput rate than for single channel systems. A notable feature of our arrangement has been the exchanged positions of input scenery and the filter set. The conventional treatment has been to display the input scene on a monitor for projection onto a set of feature extraction vectors realized as amplitude modulated LCTV devices or lithographically prepared masks. We have chosen instead to provide the filter set as input to the system and to correspondingly place the sequence data in the filter plane of the system, relying on the commutativity of projection to allow this role reversal. A class of DNA sequences known as palindromes are known to have special regulatory functions in biological systems; this class is distinguished by the antisymmetric arrangement of bases in palindromic sequences. We have designed our optical feature extractor to classify short (6 bases in length) sequences of DNA as palindrome or nonpalindrome. We note that this classification is made on the basis of the sequence symmetry, independent of base composition. We discuss the design of this architecture and the considerations that led us to the sequence representation. Initial results of this work are presented. Finally, the integration of this optical architecture into a complete system is discussed.

Photonically enabled Ka-band radar and infrared sensor subscale testbed

A subscale radio frequency (RF) and infrared (IR) testbed using novel RF-photonics techniques for generating radar waveforms is currently under development at The Johns Hopkins University Applied Physics Laboratory (JHU/APL) to study target scenarios in a laboratory setting. The linearity of Maxwell’s equations allows the use of millimeter wavelengths and scaled-down target models to emulate full-scale RF scene effects. Coupled with passive IR and visible sensors, target motions and heating, and a processing and algorithm development environment, this testbed provides a means to flexibly and cost-effectively generate and analyze multi-modal data for a variety of applications, including verification of digital model hypotheses, investigation of correlated phenomenology, and aiding system capabilities assessment. In this work, concept feasibility is demonstrated for simultaneous RF, IR, and visible sensor measurements of heated, precessing, conical targets and of a calibration cylinder. Initial proof-of-principle results are shown of the Ka-band subscale radar, which models S-band for 1/10th scale targets, using stretch processing and Xpatch models.

Verification and validation of an atmospheric boundary layer passive remote sensing technique using midwave infrared downwelling radiance

Passive radiometric remote sensing of the lower atmospheric is an attractive alternative to conventional techniques such as balloonsondes and active radiometric sensing with lidars. Measurements can be made with high sampling frequency, with complete safety and covertness, and with no loss in performance during day or night operation. A recently developed inversion algorithm generates vertical profiles of temperature and water vapor partial pressure from midwave infrared downwelling radiance to a ground based spectroradiometer. The technique is fast allowing real-time profile computation. Profiles up to 1 km altitude can be obtained for temperature and up to 0.5 to 1 km altitude for water vapor depending on the level of relative humidity. As with any new technique a verification and validation process must be performed to achieve acceptance. The verification is based on the fact that sound physical principles are employed with accepted databases (HITRAN spectroscopic database). The validation is based on comparisons with balloonsonde, MET tower, and Raman lidar measurements, and comparisons with MODTRAN 4 calculations of downwelling radiance using known profiles. An introduction to the inversion algorithm emphasizing verification is presented. This is followed by a discussion of the results from the comparison study.

Measurement technique for obtaining the extraordinary-ray absorption coefficient of uniaxial crystals

A novel experimental technique for obtaining the extraordinary-ray absorption coefficient of uniaxial crystals is presented. The infrared multiphonon e-ray absorption edge of sapphire and quartz is measured as a function of frequency and temperature for the first time.

Optical properties of polycrystalline magnesium fluoride

A common window material for midwave IR systems is polycrystalline magnesium fluoride. This material is now only available from a French manufacturer, Ceramiques Techniques Desmarquest. The optical constant database on this material is based on samples produced by Kodak and Bausch and Lomb. Because the optical constants are extrinsically dominated in the midwave IR, a new characterization study is needed. The IR absorption coefficient is presented as a function of temperature and frequency. Also, the scatter properties are determined by the bidirectional scatter distribution function.

Extraction of features from images using video feedback

This paper describes the results of using video feedback to support the calculation of the radon transform and angular correlation. Application of this type of optical processor to the extraction of features from synthetic aperture radar imagery of ships is described. By theoretical analysis and experimental evaluation of the optical architecture outputs (using some digital post processing) it is shown that the internal structure of objects, their primitive dimensions, and even their boundary can be obtained. In particular, the power of angular correlation to extract object length, width, area, aspect ratio, orientation and boundary from suitably thresholded images is shown. Alternative techniques to extract the object boundary based on angular correlation are discussed, including direct optical computation as well as digital deconvolution. Simple optical shapes, such as squares, rectangles, and triangles were used to initially compare the optical architecture outputs with digital baseline calculations. In addition, the test and evaluation of the optical processor using simple synthetic models of ship data is discussed. The results of a study that uses object primitives (derivable from angular correlation) in conjunction with the Radon transform (along the longitudinal axis) to classify ships using a backpropagation neural network also are described. A discussion of these results is presented pertaining to their broader application to optical parts inspection and to feature extraction from imaging infrared surveillance sensors. The practical implementation of such a processor in compact form using lenslet array optics also is discussed.