EFFECT OF FRIED PARAMETERS RESULTS OF DIFFERENTIAL IMAGE MOTION MONITOR-CORRECTED METHOD IN ADAPTIVE OPTICAL SIMULATION OF STAR CLUSTER OBJECTS

• Main Author: Andryan R A, Rezzal
• Format: Theses
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/47362
• Institution: Institut Teknologi Bandung

Measuring stellar objects based on optical methods can’t be separated from the atmospheric turbulence’s effect. Especially if optical-based measurements are used in advanced astronomical objects, atmospheric turbulence becomes a disturbance in the measurement process. Adaptive Optics (AO) present a measurement solution for reducing the effects of atmospheric turbulence. Even so, AO's pefromance is affected by sky conditions. One parameter of the sky condition is the fried parameter (????0). The commonly method used to find the value of the fried parameter are Differential Image Motion Monitor (DIMM), Multi-Aperture Scintillation Sensor (MASS) and Star Trail. In this study, the DIMM method was used to find the value of the fried parameter. The difference with other DIMM methods is in the data correction process in the study, the Median Absolute Deviation (MAD) method was used in correcting the observation data. This method can detect extreme outlier data caused by noise that arises during measurement. Later, the outlier data is omitted and replaced with the average data value.. Then, the value of ????0 was used as an atmosphere parameter in the adaptive optics type Laser Tomography Adaptive Optics (LTAO) simulation to restore AO images from cluster star objects. The AO device performance is calculated from the restoration image using the sterhl-ratio and encircled energy. In simulation, the star cluster object is described as a 25-star object with a range of 0.13 arcsec, 1 arcsec and 7.5 arcsec. Then, the value of ????0 (5.03 cm) from historical data of seeing observation at the Bosscha Observatory is used as a comparison variable. From the results of the observation, the value of corrected ????0 is 6.89 cm. Then, this result is used as a sky parameter in the AO simulation with a target of 25 stars. After that, the restored AO image is obtained for the star range 0.13 arcsec and 1 arcsec. Different results for the 7.5 arcsec star range. In that range, AO can’t restore the image properly. But, there is one image of a star from 25 stars that is restored well and then the rest, speckle still appear on the image.. The simulation results then measure quality of image resolution using Strehl Ratio and Encircled Energy. In strehl ratio, the value obtained from corrected fried parameter for range 0.13 arcsec and 1 arcsec has a stable value in 70-80%. While the strehl-ratio value for the 7.5 arcsec range has a fluctuate value. Then, the encircled-energy graph is obtained from the distribution of the PSF energy in the image that describes the aberration from the location of the first diffraction ring from the PSF. From the encircled-energy graph shows that the encircled-energy graph for range 0.13 and 1 arcsec in the corrected fried parameter and the comparator fried parameter shows the location of the first diffraction ring at a radius of ± 2 [in units ? / D]. Meanwhile, the encircled energy graph for the 7.5 arcsec range on the fried parameter looks unstable. However, there is one graph that shows the location of the first diffraction ring of PSF at radius 2 [in units ? / D].