<title>Pointing accuracy improvement using model-based noise reduction method</title>

Abstract

A new method for improving centroid accuracy, thereby pointing accuracy, is proposed. Accurate centroid estimation is critical for free-space optical communications where the number of photons from the reference optical sources such as stars or an uplink beacon is limited. It is known that the centroid accuracy is proportional to the SNR. Presence of various noise sources during the exposure of CCD can lead to significant degradation of the centroid estimation. The noise sources include CCD read noise, background light, stray light, and CCD processing electronics. One of the most widely used methods to reduce the effects of the noise and background bias is the thresholding method, which subtracts a fixed threshold from the centroid window before centroid computation. The approach presented here, instead, utilizes the spot model to derive the signal boundary that is used to truncate the noise outside the signal boundary. This process effectively reduces both the bias and the noise. The effectiveness of the proposed method is demonstrated through simulations.

Centroid Error Analysis of Beacon Tracking under Atmospheric Turbulence for Optical Communication Links

“…Regardless of sensor type (i.e., image sensors or position-sensitive detectors), the centroid error is dominated by not only the angular size of the beacon image, but also SNR. Assuming there is no intensity fluctuation due to atmospheric turbulence, the instantaneous centroid error of a CMOS detector is expressed as [21,22]…”

“…The limited accuracy of beacon detectors has been analyzed in terms of the noise equivalent angle, known as the random centroid error [20][21][22], particularly in the field of adaptive optics to evaluate the Shack-Hartmann wavefront sensors [23][24][25][26][27]. However, the intensity fluctuations resulting from atmospheric turbulence were not taken into consideration in these reports to precisely assess the centroid error.…”

An improvement of stars' centroid determination using PSF-fitting method

“…To improve determination of stars' centroids, an utilisation of PSF-fitting method [16,17] is proposed. In particular observation session, a test image is acquired and registered in order to determine current function PFS describing atmospheric conditions and registering equipment.…”

Accurate Real-Time Laser Spot Locating Based on Template Correlation in Intersatellite Laser Communications

“…The CG algorithm has a weak noise robustness [15] and contains systematic error that introduced by discrete sampling [16]. The CGT algorithm can strengthen noise robustness to a certain extent [17,18], but the truncation error [19] limits its accuracy. The FCG algorithm changes the gray-scale distribution of the spot and inevitably introduces a centroiding error.…”