RSI Publication Abstracts

N. Namazi, R. Burris, Jr., and G. C. Gilbreath, "Analytical approach to the calculation of probability of bit error and optimum thresholds in free-space optical communication," Optical Engineering, Volume 46, Issue 2, 025007, (2007).

Based on wavelet transformation and adaptive Wiener filtering, a new method was presented by the authors to perform synchronization and detection of binary data from a free-space optical (FSO) signal. It was shown prevlously that the Haar wavelet with a fixed scale is an excellent choice for this purpose. The output of the filter was zero mean and was closely related to the derivative of the binary data. In this effort, an analysis of the prior work is presented to obtain the probability of bit error using a Bayesian ternary hypotheses testing. The analysis also results in determining optimum thresholds for the detection of binary data. Simulation experiments are performed and presented to validate the results of the theoretical analysis.

M. F. Stell, C. I. Moore, H. R. Burris, M. R. Suite, M. J. Vilcheck, M. A. Davis, R. Mahon, E. Oh, W. S. Rabinovich, G. C. Gilbreath, W. J. Scharpf, and A. E. Reed, ``Passive optical monitor for atmospheric turbulence and windspeed,'' Proceedings of SPIE, Free-Space Laser Communication and Active Laser Illumination III, Vol. 5160, p. 422, (2004).

Measurement of atmospheric turbulence conditions is critical for predicting the performance of a free-space optical laser communication (FSO lasercomm) link. A Cn2 monitor based on angle-of-arrival (AOA) fluctuations has been built for characterization of atmospheric conditions at the NRL FSO Lasercomm Test Facility across the Chesapeake Bay. The monitor used existing lights in various locations as point sources for determining AOA fluctuations. Real time analysis of the AOA fluctuations was performed to determine the power spectrum of the fluctuations every few seconds. This additional power spectrum information allows much greater understanding of atmospheric conditions including estimation of average wind speed based on frequency shifts in the power spectrum distribution. The performance of the monitor was tested over short paths by comparison to a commercial scintillometer. In addition the monitor was used at other sites to determine atmospheric conditions at a variety of locations. Results of these experiments are presented.

B. McAndrew, J. Kline, and R. Miles, "Aerodynamic Control of a Symmetric Cone in Compressible Flow Using Heat Addition," 41st AIAA Aerospace Sciences Meeting and Exhibit, 2003.

The objectives of this work are to study the potential use of heat addition as a means of aerodynamic control and to make measurements suitable for comparison with CFD calculations. The experiments are conducted in a Mach 3 indraft wind tunnel with a 15° half angle instrumented cone used to measure aerodynamic perturbations. Free stream heat addition is achieved through the use of microwave driven discharges. Lift and drag changes over the cone are measured with a force balance. Asymmetric discharges produce changes in lift and drag as a function of microwave power.

C. I. Moore, H. R. Burris, M. R. Suite, M. F. Stell, M. J. Vilcheck, M. A. Davis, R. Smith, R. Mahon, W. S. Rabinovich, J. P. Koplow, S. W. Moore, W. J. Scharpf, and A. E. Reed, "Free-space high-speed laser communication link across the Chesapeake Bay,'' Proceedings of SPIE, Free-Space Laser Communication and Laser Imaging II, Vol. 4821, p. 474, (2002).

The Naval Research Laboratory (NRL) has established a free-space laser communication link across 16.2 km of the Chesapeake Bay between the Chesapeake Bay Detachment of NRL and Tilghman Island. The transmitter consists of a modulated 1550 nm oscillator amplified to 2 watts in an erbium doped fiber amplifier developed at NRL. The beam is fiber coupled to a 4 inch collimating lens on a remotely controllable gimbal mount. The beam is transmitted to a retro-reflector array at Tilghman Island and back to the receiver at CBD (32.4 km round trip). The receiver consists of a 16" Meade telescope either directly or fiber coupled to a variety of fast photo-detectors. Experiments have been conducted to study the stability and quality of the link. These include: bit-error rate measurements, probability density functions, power spectrum densities, and angle of arrival measurements of the received signal. Results of these experiments are presented.

J. Fisher, J. Antoniades, C. Rollins, and L. Xiang: “A hyperspectral imaging sensor for the coastal environment” in International Optical Design Conference, Proc. SPIE 3842, pp. 179-186 (1998).

Recent advances in large format detector arrays and holographic diffraction gratings have made possible the development of imaging spectrographs with high sensitivity and resolution, ideally suited for space-based remote sensing of earth resources. An optical system composed of dual spectrographs and a common fore-optic has been designed for the visible-near infrared (VNIR) and shortwave bands with 10-nm spectral resolution, providing 30-meter ground resolution from an altitude of 605 km. The spectrograph designs are based on a modified Offner 1-X relay with spherical mirrors and a convex spherical holographic grating for the secondary mirror. The fore-optic is a three-mirror anastigmatic telescope with a 360-mm focal length to match the pixel pitch of the respective 1024x1024 visible silicon CCD and SWIR HgCdTe FPAs. The primary advantages of this design are the relatively low f-number (f/3), large flat field (18mm), and low distortion. Preliminary performance results of a VNIR testbed grating and spectrograph are presented and compared to the design predictions.