• 대기
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• 제20권4호
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• pp.483-494
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• 2010

The vertical profiles of the extinction coefficient, the backscatter coefficient, and the lidar ratio (i.e., extinction-to-backscattering ratio) for Asian dust and pollution aerosols are determined from Raman (inelastic) and elastic backscatter signals. The values of lidar ratios during two polluted days is found between 52 and 82 sr (July 22, 2009) and 40~60 sr (July 31, 2009) at 52 nm, with relatively low value of particle depolarization ratio (<5%) and high value of sun photometer-derived Angstrom exponent (> 1.2). However, lidar ratios between 25 and 40 sr are found during two Asian dust periods (October 20, 2009 and March 15, 2010), with 10~20% of particle depolarization ratio and the relatively low value of sun photometer-derived Angstrom exponent (< 0.39). The lidar ratio, particle depolarization ratio and color ratio are useful optical parameter to distinguish non-spherical coarse dust and spherical fine pollution aerosols. The comparison of aerosol extinction profiles determined from inelastic-backscatter signals by the Raman method and from elastic-backscatter signals by using the Fernald method with constant value of lidar ratio (50 sr) have shown that reliable aerosol extinction coefficients cannot be determined from elastic-backscatter signals alone, because the lidar ratio varies with aerosol types. A combined Raman and elastic backscatter lidar system can provide reliable information about the aerosol extinction profile and the aerosol lidar ratio.

• Journal of the Optical Society of Korea
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• 제15권3호
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• pp.209-215
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• 2011

A new iterative algorithm is developed to estimate LIDAR ratio for a thin cirrus cloud over an aerosol layer. First, the thin cirrus cloud is screened out and replaced by a modeled LIDAR signal and the extinction coefficients of the aerosol layer are derived using the Fernald backward method. These aerosol coefficients are referred as the "actual values". Second, the original LIDAR signal which includes the thin cirrus cloud is also inverted by the Fernald backward method down to the aerosol layer but using different LIDAR ratio for the thin cirrus cloud. Depending on the different assumptions about the LIDAR ratio of the thin cirrus cloud, different sets of aerosol extinction can be derived. The "actual values" which are found in the first step can be used to constrain this iterative progress and the correct LIDAR ratio of the thin cirrus cloud can be found. The detailed description of this method and retrieval examples are given in the paper. The cases compared with other methods are presented and the statistical result is also shown and agrees well with other studies.

• Journal of the Optical Society of Korea
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• 제14권3호
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• pp.174-177
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• 2010

The rotational Raman LIDAR technique has been used to accurately measure aerosol optical properties such as backscatter coefficient, extinction coefficient, and LIDAR ratio. In the case of the vibrational Raman technique, the ${\AA}$ngstr$\ddot{o}$om exponent, which has wavelength dependence on the particle properties, is assumed to obtain the extinction coefficient. However, this assumed ${\AA}$ngstr$\ddot{o}$m exponent can cause systematic errors in retrieving aerosol optical properties. In the case of the rotational Raman technique, the aerosol optical properties can be measured without any assumptions about the ${\AA}$ngstr$\ddot{o}$m exponent. In this paper, the LIDAR ratio was measured by using the rotational Raman LIDAR and vibrational Raman LIDAR in the troposphere. And, the LIDAR ratios measured by these two methods were compared.

• 한국대기환경학회지
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• 제22권1호
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• pp.1-14
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• 2006

Tropospheric aerosols are highly variant in time and space due to non-uniform source distribution and strong influence of meteorological conditions. Backscatter lidar measurement is useful to understand vertical distribution of aerosol. However, the backscatter lidar equation is undetermined due to its dependence on the two unknowns, extinction and backscattering coefficient. This dependence necessitates the exact value of the ratio between two parameters, that is, the lidar ratio. Also, Iidar ratio itself is useful optical parameter to understand properties of aerosols. Tropospheric aerosols were observed to understand variance of lidar ratio at Anmyeon island ($36.32^{/circ}N$, $126.19^{/circ}E$), Korea using a multi-wavelength raman lidar system developed by the Advanced Environmental Monitoring Research Center (ADEMRC), Gwangju Institute Science and Technology (GIST), Korea during measurement periods; March 15$\sim$April $16^{th}$, 2004 and May 24$\sim$ $8^{th}$ 2005. Extinction coefficient, backscattering coefficient, and lidar ratio were measured at 355 and 532 nm by the Raman method. Different types of aerosol layers were distinguished by the differences in the optical properties such as Angstrom exponent, and lidar ratio. The average value of lidar ratio during two observation periods was found to be $50.85\pm4.88$ sr at 355 nm and $52.43\pm15.15$ sr at 532 nm at 2004 and $57.94\pm10.29$ sr at 355 nm and $82.24\pm15.90$ sr at 532 nm at 2005. We conduct hysplit back-trajectory to know the pathway of airmass during the observation periods. We also calculate lidar ratio of different type of aerosol, urban, maritime, dust, continental aerosols using OPAC (Optical Properties of Aerosols and Clouds), Remote sensing of atmospheric aerosol using a multi-wavelengh lidar system with Raman channels is quite and powerful tool to characterize the optical propertises of troposheric aerosols.

• Current Optics and Photonics
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• 제2권2호
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• pp.119-124
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• 2018

The errors in retrieved aerosol backscattering coefficients due to different lidar ratios are analyzed quantitatively in this paper. The actual calculation shows that the inversion error of the aerosol backscattering coefficients using the Fernald backward-integration method increases with increasing inversion distance. The greater the error in the lidar ratio, the faster the error in the aerosol backscattering coefficient increases. For the same error in lidar ratio, the smaller actual aerosol backscattering coefficient will get the larger relative error of the retrieved aerosol backscattering coefficient. The errors in the lidar ratios for dust or the cirrus layer have great impact on the retrievals of backscattering coefficients. The interval between the retrieved height and the reference range is one of the important factors for the derived error in the aerosol backscattering coefficient, which is revealed quantitatively for the first time in this paper. The conclusions of this article can provide a basis for error estimation in retrieved backscattering coefficients of background aerosols, dust and cirrus layer. The errors in the lidar ratio of an aerosol layer influence the retrievals of backscattering coefficients for the aerosol layer below it.

• 대기
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• 제25권1호
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• pp.169-177
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• 2015

Vertical distribution of particle mass concentrations was estimated from 8-year elastic-backscatter lidar and sky radiometer data, and from ground-level PM10 concentrations measured in Seoul. Lidar ratio and mass extinction efficiency were determined from aerosol optical depth (AOD) and ground-level PM10 concentrations, which were used as constraints to estimate particle mass concentration. The mean lidar ratio (with standard deviation) and mass extinction efficiency for the entire 8-year study period were $60.44{\pm}23.17$ sr and $3.69{\pm}3.00m^2g^{-1}$, respectively. The lidar ratio did not vary significantly with the ${\AA}ngstr{\ddot{o}}m$ exponent (less than ${\pm}10%$); however, the mass extinction efficiency decreases to $1.82{\pm}1.67m^2g^{-1}$ (51% less than the mean value) when the ${\AA}ngstr{\ddot{o}}m$ exponent is less than 0.5. This result implies that the particle mass concentration from lidar measurements can be underestimated for dust events. Seasonal variation of the particle mass concentration estimated from lidar measurements for the boundary layer, was quite different from ground-level PM10 measurements. This can be attributable to an inhomogeneous vertical distribution of aerosol in the boundary layer.

• 대기
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• 제21권1호
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• pp.57-67
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• 2011

2006년 3월부터 4년간 서울대학교에서 관측한 라이다와 스카이 라디오미터 관측 자료로부터 에어러솔의 라이다 비를 산출하고 그 계절 변화 특성을 살펴 보았다. 서울지역의 라이다 비는 여름철에 $68.1{\pm}16.8$ sr로 가장 높고 점차 감소하여 겨울철에 $57.2{\pm}17.9$ sr로 가장 낮았으며 다시 증가하는 경향을 보였다. 그러나 전 기간 동안 산출된 라이다 비가 30 sr에서 최대 110 sr까지의 범위에서 분포하며 관측 전 기간의 표준편차가 16.46 sr인 것을 감안하면 계절변동은 두드러지지는 않았다. 이처럼 계절 변동이 약하게 나타나는 이유는 도심지역에 해당하는 서울의 지리적 특성에 기인한 것으로 연중 인위적인 오염물질이 지속적으로 배출되어 영향을 미치기 때문으로 판단된다. 라이다와 스카이 라디오미터 관측으로 얻은 옹스트롬 지수, 편광소멸도 및 에어러솔 광학두께와 산출된 라이다 비의 관계도 살펴 보았다. 옹스트롬 지수와 편광소멸도는 음의 상관관계가 뚜렷하게 나타나 에어러솔 입자의 크기가 클 경우 비구형을 띄며 크기가 작을수록 구형에 가까워 짐을 확인할 수 있었다. 또한, 라이다 비가 작게 나타나는 깨끗한 날을 제외하면 라이다 비는 옹스트롬 지수가 증가할수록 (편광소멸도가 감소할수록) 증가하는 경향을 가졌다. 이를 바탕으로 에어러솔 광학두께가 하위 10%에 해당하는 깨끗한 날과 옹스트롬 지수가 하위 10%에 해당하는 황사입자가 우세한 사례, 옹스트롬 지수가 상위 10%에 해당하는 오염물질이 우세한 사례로 나누어 라이다 비의 특성을 살펴보았다. 오염물질이 우세한 사례에서의 라이다 비는 $62.2{\pm}13.2$ sr로 기존의 오염물질에 의한 라이다 비와 잘 일치하는 모습을 보였다. 그러나 깨끗한 날과 황사가 우세한 사례의 경우는 각각 $45.0{\pm}9.5$ sr와 $51.7{\pm}13.7$ sr로 나타나 선행 연구 결과보다는 다소 높은 값을 보였다. 이는 앞에서 언급하였다시피 도심지역에 해당하는 서울은 항상 주변에서 발생하는 인위적인 오염물질의 영향을 받기 때문인 것으로 판단할 수 있다.

• Journal of the Optical Society of Korea
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• 제14권3호
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• pp.215-220
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• 2010

Aerosol observation with Raman LIDAR in NIES (National Institute for Environmental Studies, Japan) LIDAR network was conducted from 17 April to 12 June 2008 over Beijing, China. The aerosol optical properties derived from Raman LIDAR were compared with the retrieved data from sun photometer and sky radiometer observations in the Aerosol Robotic Network (AERONET). The comparison provided the complete knowledge of aerosol optical and physical properties in Beijing, especially in pollution and Asian dust events. The averaged aerosol optical depth (AOD) at 675 nm was 0.81 and the Angstrom exponent between 440 nm and 675 nm was 0.99 during experiment. The LIDAR derived AOD at 532 nm in the planetary boundary layer (PBL) was 0.48, which implied that half of the total AOD was contributed by the aerosol in PBL. The corresponding averaged LIDAR ratio and total depolarization ratio (TDR) were 48.5sr and 8.1%. The negative correlation between LIDAR ratio and TDR indicated the LIDAR ratio decreased with aerosol size because of the high TDR associated with nonspherical and large aerosols. The typical volume size distribution of the aerosol clearly demonstrated that the coarse mode radius located near 3 ${\mu}m$ in dust case, a bi-mode with fine particle centered at 0.2 ${\mu}m$ and coarse particle at 2 ${\mu}m$ was the characteristic size distribution in the pollution and clean cases. The different size distributions of aerosol resulted in its different optical properties. The retrieved LIDAR ratio and TDR were 41.1sr and 19.5% for a dust event, 53.8sr and 6.6% for a pollution event as well as 57.3sr and 7.2% for a clean event. In conjunction with the observed surface wind field near the LIDAR site, most of the pollution aerosols were produced locally or transported from the southeast of Beijing, whereas the dust aerosols associated with the clean air mass were transported by the northwesterly or southwesterly winds.

• Journal of the Optical Society of Korea
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• 제14권4호
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• pp.444-450
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• 2010

The traditional approach to inverting aerosol extinction makes use of the assumption of a constant LIDAR ratio in the entire Mie-LIDAR signal profile using the Fernald method. For the large uncertainty in the cloud optical depth caused by the assumed constant LIDAR ratio, an not negligible error of the retrieved aerosol extinction below the cloud will be caused in the backward integration of the Fernald method. A new algorithm to determine aerosol extinction below a cirrus cloud from Mie-LIDAR signals, based on a new cloud boundary detection method and a Mie-LIDAR signal modification method, combined with the backward integration of the Fernald method is developed. The result shows that the cloud boundary detection method is reliable, and the aerosol extinction below the cirrus cloud found by inverting from the modified signal is more efficacious than the one from the measured signal including the cloud-layer. The error due to modification is less than 10% taken in our present example.

• 대한원격탐사학회지
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• 제32권2호
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• pp.97-104
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• 2016

본 연구에서는 일본 오사카에서 AERONET 선포토미터로 관측된 데이터를 분석하여 440, 675, 870, 1020 nm 파장에서의 입자 편광소멸도를 산출하였다. 산출된 결과는 같은 지역에서 측정된 라이다 자료로부터 얻어진 532 nm에서의 입자 편광소멸도와 비교하였다. 두 값은 440 nm를 제외하고는 잘 일치되는 결과를 보였고, 상관계수($R^2$)는 440, 675, 870, 1020 nm에서 각각 0.28, 0.81, 0.88 0.89의 값을 보였다. 가장 높은 상관계수를 보인 1020 nm에서의 입자 편광소멸도를 기준으로 값의 변화에 따른 입자의 혼합정도를 확인하였을 때, 순수 황사의 경우 높은 편광소멸도를 보이고 오염입자가 혼합될수록 값이 낮아짐을 보였다. 이는 단산란 알베도와 입자 크기 분포를 통하여 확인하였다.