• 한국정밀공학회지
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• 제31권11호
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• pp.999-1006
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• 2014

In this investigation, we explain the sub-sampling technique of white light scanning interferometry (WLSI) to improve the measurement speed. In addition to the previous work using Fourier domain analysis, several methods to extract the height from the correlogram of WLSI are described with the sub-sampling technique. Especially, Fourier-inverse Fourier transformation method adopting sub-sampling technique is proposed and the phase compensation technique is verified with simulation and experiments. The main advantage of sub-sampling is to speed up the measurements of WLSI but the precision such as repeatability is slightly poor. In case of measuring the sample which has high height step or difference, the proposed technique can be widely used to reduce the measurement time.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.109-113
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• 2007

The COMS provides the LRIT/HRIT services to users. The COMS LRIT/HRIT broadcast service should satisfy the 15 minutes timeliness requirement. The requirement is important and critical enough to impact overall performance of the LHGS. HRIT image data is acquired from INRSM output receiving but LRIT image data is generated by sub-sampling HRIT image data in the LHGS. Specially, since LRIT is acquired from sub-sampled HRIT image data, LRIT processing spent more time. Besides, some of data loss for LRIT occurs since LRIT is compressed by lossy JPEG. Therefore, algorithm with the fastest processing speed and simplicity to be implemented should be selected to satisfy the requirement. Investigated sub-sampling algorithm for the LHGS were nearest neighbour algorithm, bilinear algorithm and bicubic algorithm. Nearest neighbour algorithm is selected for COMS LHGS considering the speed, simplicity and anti-aliasing corresponding to the guideline of user (KMA: Korea Meteorological Administration) to maintain the most cloud itself information in a view of meteorology. But the nearest neighbour algorithm is known as the worst performance. Therefore, it is studied in this paper that the selection of nearest neighbour algorithm for the LHGS is reasonable. First of all, characteristic of 3 sub-sampling algorithms is studied and compared. Then, several sub-sampling algorithm were applied to MTSAT-1R image data corresponding to COMS HRIT. Also, resized image was acquired from sub-sampled image with the identical sub-sampling algorithms applied to sub-sampling from HRIT to LRIT. And the difference between original image and resized image is compared. Besides, PSNR and MSE are calculated for each algorithm. This paper shows that it is appropriate to select nearest neighbour algorithm for COMS LHGS since sub-sampled image by nearest neighbour algorithm is little difference with that of other algorithms in quality performance from PSNR.

• 한국전자파학회논문지
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• 제22권5호
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• pp.501-509
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• 2011

Software Defined Radio(SDR)에서는 ADC를 안테나 가까이에 위치시키는 것을 목표로 하고 있다. 하지만 실제 RF 대역의 신호를 ADC를 이용해 디지털화 하는 방법은 아직 어렵다. 그래서 RF 대역의 신호를 IF 대역으로 하향 변환 후 샘플링을 하는 방법이 연구되고 있다. 이런 방법의 하나로, Sub-Sampling 방식은 발진기 없이 RF 대역의 신호를 IF로 변환할 수 있는 방법이다. Sub-Sampling 방법을 이용한다면 2개 이상의 밴드를 하향 변환할 수 있지만, RF 필터의 성능으로 인해 하향 변환된 신호간에 간섭이 작용할 수 있어 성능을 저하시킨다. 본 논문에서는 time division multiplexing(TDM) 방식을 이용해 2개 이상의 신호를 시간적으로 분리시킴으로써 RF 필터의 좋지 않은 성능으로 인해 발생할 수 있는 신호간 간섭을 피할 수 있는 방법을 제안한다. 이 방식은 샘플앤홀더에서 두 신호에 대한 시간적 분리와 Sub-Sampling을 동시에 구현함으로써 하드웨어적인 큰 변화 없이 신호를 수신할 수 있다.

• ETRI Journal
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• 제23권3호
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• pp.129-137
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• 2001

A random sampling or systematic sampling method is commonly used to assess the accuracy of classification results. In remote sensing, with these sampling methods, much time and tedious work are required to acquire sufficient ground truth data. So, a more effective sampling method that can represent the characteristics of the population is required. In this study, fractal analysis is adopted as an index for reference sampling. The fractal dimensions of the whole study area and the sub-regions are calculated to select sub-regions that have the most similar dimensionality to that of the whole area. Then the whole area's classification accuracy is compared with those of sub-regions, and it is verified that the accuracies of selected sub-regions are similar to that of whole area. A new kind of reference sampling method using the above procedure is proposed. The results show that it is possible to reduce sampling area and sample size, while keeping the same level of accuracy as the existing methods.

• 대한수학회보
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• 제59권2호
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• pp.285-301
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• 2022

In this paper, we mainly study the random sampling and reconstruction of signals living in the subspace V^p(𝚽, 𝚲) of L^p(ℝ^d), which is generated by a family of molecules 𝚽 located on a relatively separated subset 𝚲 ⊂ ℝ^d. The space V^p(𝚽, 𝚲) is used to model signals with finite rate of innovation, such as stream of pulses in GPS applications, cellular radio and ultra wide-band communication. The sampling set is independently and randomly drawn from a general probability distribution over ℝ^d. Under some proper conditions for the generators 𝚽 = {𝜙_λ : λ ∈ 𝚲} and the probability density function 𝜌, we first approximate V^p(𝚽, 𝚲) by a finite dimensional subspace V^p_N (𝚽, 𝚲) on any bounded domains. Then, we prove that the random sampling stability holds with high probability for all signals in V^p(𝚽, 𝚲) whose energy concentrate on a cube when the sampling size is large enough. Finally, a reconstruction algorithm based on random samples is given for signals in V^p_N (𝚽, 𝚲).

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.295-298
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• 2000

In this research, a novel sampling strategy for a CMM to inspect freeform surfaces is proposed. Unlike primitive surfaces, it is not easy to determine the number of sampling points and their locations for inspecting freeform surfaces. Since a CMM operates with slower speed in measurement than optical measuring devices, it is important to optimize the number and the locations of sampling points in the inspection process. When a complete inspection of a surface is required, it becomes more critical. Among various factors to cause shape errors of a final product, curvature characteristic is essential due to its effect such as stair-step errors in rapid prototyping and interpolation errors in NC tool paths generation. Shape errors are defined in terms of the average and standard deviation of differences between an original model and a produced part. Proposed algorithms determine the locations of sampling points by analyzing curvature distribution of a given surface. Based on the curvature distribution, a surface area is divided into several sub-areas. In each sub-area, sampling points are located as further as possible. The optimal number of sub-areas. In each sub-area, sampling points are located as further as possible. The optimal number os sub-areas is determined by estimating the average of curvatures. Finally, the proposed method is applied to several surfaces that have shape errors for verification.

• 음성과학
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• 제12권2호
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• pp.153-170
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• 2005

The sub-Nyquist nonuniform sampling (SNNS) and the perfect reconstruction (PR) formula are proposed for the development of a systematic method to obtain minimal representation of a speech signal. In the proposed method, the instantaneous sampling frequency (ISF) varies, depending on the least upper boundary of spectral support of a speech signal in time-frequency domain (TFD). The definition of the instantaneous bandwidth (IB), which determines the ISF and is used for generating the set of samples that represent continuous-time signals perfectly, is given. Also, the spectral characteristics of the sampled data generated by the sub-Nyquist nonuniform sampling method is analyzed. The proposed method doesn't generate the redundant samples due to the time-varying property of the instantaneous bandwidth of a speech signal.

• 분석과학
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• 제37권3호
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• pp.174-188
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• 2024

본 연구에서는 토양 및 지하수 중 미세플라스틱(MP) 분석법 표준화를 위해 관련 국내·외 연구동향을 검토하고 매체 별 시료채취 방법, 전처리 방법 및 분석 장치의 종류 등에 관한 대표적인 방법을 리뷰하였다. 토양 시료채취는 시료채취 지점선정, 채취 깊이 및 시료량을 고려하고 있으며 대부분 15 cm 이내(표토) 깊이에서 약 1 kg의 시료를 혼합채취하는 것으로 파악되었다. 지하수 시료채취는 정치방법과 연속흐름방법 중 연속흐름방식이 대표적이고 채취량 300~1,000 L 구간에서 유량 2~6 L/min로 채취하며 현장 여과하였다. 처리 방법은 두 매체에 공통적으로 유기물 분해와 밀도차 분리로 나뉘며 유기물 분해방법인 H₂O₂, 산, 알칼리, 효소 활용 중 H₂O₂가 추천된다. 밀도 분리는 NaCl, ZnCl₂, ZnBr₂ 등의 시약 중 NaCl이 주로 사용되나 분석하고자 하는 MP의 밀도에 따라 시약을 선택적으로 활용할 수 있다. 분석 기기는 비파괴적 분석법인 FTIR, Raman과 파괴 분석법인 Py-GC/MS가 대표적이다. µ-FTIR은 직경 10 ㎛ 이상 Raman은 1 ㎛ 이상의 MP 재질과 개수 분석이 가능하나 전처리를 통해 유기물과 같은 분광분석의 방해요소를 충분히 제거해야 한다. Py-GC/MS는 복잡한 전처리가 필요 없고 특정 재질의 정량분석이 가능하여 지속적으로 연구되어지고 있다.

• 한국통신학회논문지
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• 제40권7호
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• pp.1234-1238
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• 2015

본 논문에서는 Sub-Nyquist 샘플링 기반의 협력 스펙트럼 센싱 기법을 제안한다. 최근 압축 센싱 (Compressive Sensing) 기술이 많은 주목을 받으면서 원본 신호의 성긴 정도 (Sparsity)를 추정하는 기법도 활발히 연구되고 있다. 따라서 본 논문에서는 주파수 대역의 Sparsity를 안다고 가정할 때 다양한 샘플링율과 협력 센싱 기법에 따른 Sub-Nyquist 샘플링 기법의 검출 성능을 수학적으로 분석한다. 또한 모의실험 결과를 통해 제안된 기법의 성능을 입증한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(5)
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• pp.9-12
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• 2002

The problem of sub-Nyquist nonuniform sampling for the perfect reconstruction of signals with time-varying spectral contents is studied. The signals are assumed to have a known instantaneous bandwidth in time-frequency domain. As the function of time, the nonuniform sampling pattern of a given signal, that is, the instantaneous sampling frequency is determined by the observation of instantaneous bandwidth based on time-frequency analysis. The proposed sampling pattern guarantees the perfect reconstruction of nonuniform sampled signals under Nyquist-sampling rate in average.