Department
Home Page
About Us:
• Contact Info.
• Faculty
• Staff
• Students
Academic Program:
• Admission
• Undergraduate
• Graduate
• Certificates
Courses:
• Course Description
• Class Web Pages
• Class Syllabi
• Skills Tests
Research:
• Research Groups
• Colloquium
• Seminars
• News
Links:
| • Alumni Questionnaire |
| • Math Lab |
| • CAPA & Skills Tests |
| •Math Placement Test |
| • UCF Math Club |
| • Academic System Lab |
| • Careers |
| • American Mathematical Society |
| • Mathematical Association of America |
9/26/00 Colloquium
Laser Radar Group (Dr. Larry C. Andrews)
Mathematical Modeling of Atmospheric Effects on Laser Radar and Laser Communications
The
Laser Radar Group at CREOL (Prof.. L. C. Andrews
and Prof. R. L. Phillips)
is concerned with mathematical modeling and experimental verification
of optical propagation channels pertaining to optical communication
and laser radar applications. Optical systems
offer certain advantages over conventional microwave systems like
smaller antenna; less mass, power, and volume; and the narrow-beam
and high-gain nature of lasers.
However, when
an optical wave propagates
through the atmospheric it experiences distortions
caused by small
temperature variations related to the sun’s
heating of the Earth and the turbulent motion of the air due to winds
and convection. The most well known manifestation of this phenomenon
is the twinkling of stars (called scintillation). Atmospheric
effects like scintillation can adversely affect signal-to-noise
ratios and produce signal dropouts (called fading) that lead to
information loss in optical communication and radar systems.
Students and faculty at CREOL built an eight-aperture coherent receiver array and conducted outdoor experiments on a 1000-m range at Cape Kennedy during the past several years. The purpose of the study of this array receiver was to show through experimental data and theoretical analysis the benefit of using several small apertures to collect the echo signal from a target over that of a single large aperture system. The improvement in carrier-to-noise ratio of the coherent sum of the detector outputs compared with a single large aperture (same glass area) is shown in Fig. 1 below. Similarly, the improvement in lower probability of fade associated with the array is shown in Fig. 2. Solid curves in the figures are based on theoretical models.
Fig. 1 CNR Gain Factor vs No. of Apertures Fig. 2 Prob. Of Fade vs. Threshold below Mean
L. C. Andrews and R. L. Phillips, Laser Propagation through Random Media (SPIE Optical Engineering Press, Bellingham, 1999).
L. C. Andrews, Special Functions of Mathematics for Engineers, 2nd ed. (SPIE Optical Engineering Press, Bellingham, 1998).
L. C. Andrews, R. L. Phillips, C. Y. Hopen, and M. A. Al-Habash, “Theory of optical scintillation,” J. Opt. Soc. Am A 16, 1417-1429 (1999).
L. C. Andrews, R. L. Phillips, and C. Y. Hopen, “Aperture averaging of optical scintillations” power fluctuations and temporal spectrum,” Waves in Random Media 10, 53-70 (2000).
Figure: Equal-gain coherent array receiver.