• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.442-446
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• 1993

A flashlamp pumped Ti: sapphire laser was designed and fabricated in the laboratory. In order to find out the optimum pumping condition, three kinds of discharge circuits of which the pulse width are 10${\mu}s$, 45${\mu}s$, 65${\mu}s$ were designed. The fluorescent energy converter LD-490 of which the fluorescence spectra is coincident to the absorption band of Ti: sapphire was used to improve the laser efficiency. The laser output characteristics for three different concentrations of LD-490 and for three different pumping pulse widths were measured. As a result, the shorter the flashlamp pulse width, the higher the overall efficiency was achieved. When pumping light pulsewidth was 10${\mu}s$, the best efficiency was obtained at the concentration 1.0${\times}10^{-3}$mol/l of LD-490 dye. At lower concentrations the efficiencies were decreased.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.4
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• pp.347-357
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• 2003

This paper describes on the suppression of sea clutter on marine radar display using a cell-averaging CFAR(constant false alarm rate) technique, and on the analysis of radar echo signal data in relation to the estimation of ARPA functions and the detection of the shadow effect in clutter returns. The echo signal was measured using a X -band radar, that is located on the Pukyong National University, with a horizontal beamwidth of $$3.9^{\circ}$$, a vertical beamwidth of $20^{\circ}$, pulsewidth of $0.8 {\mu}s$ and a transmitted peak power of 4 ㎾ The suppression performance of sea clutter was investigated for the probability of false alarm between $l0-^0.25;and; 10^-1.0$. Also the performance of cell averaging CFAR was compared with that of ideal fixed threshold. The motion vectors and trajectory of ships was extracted and the shadow effect in clutter returns was analyzed. The results obtained are summarized as follows；1. The ARPA plotting results and motion vectors for acquired targets extracted by analyzing the echo signal data were displayed on the PC based radar system and the continuous trajectory of ships was tracked in real time. 2. To suppress the sea clutter under noisy environment, a cell averaging CFAR processor having total CFAR window of 47 samples(20+20 reference cells, 3+3 guard cells and the cell under test) was designed. On a particular data set acquired at Suyong Man, Busan, Korea, when the probability of false alarm applied to the designed cell averaging CFAR processor was 10$^{-0}$.75/ the suppression performance of radar clutter was significantly improved. The results obtained suggest that the designed cell averaging CFAR processor was very effective in uniform clutter environments. 3. It is concluded that the cell averaging CF AR may be able to give a considerable improvement in suppression performance of uniform sea clutter compared to the ideal fixed threshold. 4. The effective height of target, that was estimated by analyzing the shadow effect in clutter returns for a number of range bins behind the target as seen from the radar antenna, was approximately 1.2 m and the information for this height can be used to extract the shape parameter of tracked target..