H. Sari

Validation of refractive index structure parameter estimation for certain infrared bands

Variation of the atmospheric refraction index due to turbulent fluctuations is one of the key factors that affect the performance of electro-optical and infrared systems and sensors. Therefore, any prior knowledge about the degree of variation in the refractive index is critical in the success of field studies such as search and rescue missions, military applications, and remote sensing studies where these systems are used frequently. There are many studies in the literature in which the optical turbulence effects are modeled by estimation of the refractive index structure parameter, C(n)(2), from meteorological data for all levels of the atmosphere. This paper presents a modified approach for bulk-method-based C(n)(2) estimation. According to this approach, conventional wind speed, humidity, and temperature values above the surface by at least two levels are used as input data for Monin-Obukhov similarity theory in the estimation of similarity scaling constants with a finite difference approximation and a bulk-method-based C(n)(2) estimation. Compared with the bulk method, this approach provides the potential for using more than two levels of standard meteorological data, application of the scintillation effects of estimated C(n)(2) on the images, and a much simpler solution than traditional ones due to elimination of the roughness parameters, which are difficult to obtain and which increase the complexity, the execution time, and the number of additional input parameters of the algorithm. As a result of these studies, Atmospheric Turbulence Model Software is developed and the results are validated in comparison to the C(n)(2) model presented by Tunick.

Design of a cost-effective laser spot tracker

One of the most important aspects of guided systems is detection. The most convenient detection in the sense of precision can be achieved with a laser spot tracker. This study deals with a military grade, high performance and cost-effective laser spot tracker for a guided system. The aim is to develop a high field of view system that will detect a laser spot from a distance of 3 kilometers in which the target is designated from 3 kilometers with a laser. The study basically consists of the system design, modeling, producing and the conducting performance tests of the whole system.

A computer modelling approach to decrease stray light in low light non imaging optical designs

Opto-mechanical structures (objectives) are employed to transfer photons which are collected from their field of view (FOV) to the detector plane. The sensors used in such systems have high gain which causes them to detect stray light originated from the mechanical body of the objective. This type of stray light is a major problem in low light nonimaging optical systems used in laser seekers which employ four quadrant position sensors to determine laser illumination reflected from a target surface positioned kilometers away. This work, mainly concentrates on reducing unwanted stray light caused by inner mechanical structure of large FOV objectives with the use of software tools. Stray light in an optical system can not be totally eliminated. However, it can often be reduced to a level at which it is tolerable. This works focuses on reducing unwanted stray light originating from mechanical structure of the objective in a cost efficient way. In order to prevent this unwanted stray light a sample laser seeker objective is designed in ZEMAX software environment together with its mechanical mount. Black delrin is used as the objective material. Its specular and diffused reflective properties are measured with spectrophotometer and defined in the software environment. Ten objectives with different baffle height/pitch ratio (h/p) are designed and used in the same optic design. In order to show that a software model can be used to find the optimum h/p ratio for eliminating stray light, prototype objectives are manufactured and tested with readout electronics. After making measurements with different angles on incidence values best applicable objective with a certain baffle h/p ratio is found. It is verified that the h/p ratio found in software model is in very good agreement with the measurement results. This helps us not use more baffles than necessary since increasing baffle h/p astronomically increases production and workmanship costs. This study shows that, instead of manufacturing expensive prototypes computer simulation can be used to identify and also take necessary precautions to prevent or decrease stray light before production. This prevents loss of significant amount of time, work, and cost.