Influence of land surface effects on MODIS aerosol retrieval using the BAER method over Korea

Kwon Ho, Lee,Young Joon, Kim,von Hoyningen‐,Huene, Wolfgang,Burrow, John P. TaylorFrancis 2006 International journal of remote sensing Vol.27 No.14

<P>As satellite receiving signals are affected by complex radiative transfer processes in the atmosphere and on land surfaces, aerosol retrieval over land from space requires the ability to determine surface reflectance from the remote measurements. To use the Bremen Aerosol Retrieval (BAER) method for aerosol optical thickness (AOT) retrieval over land at a spatial scale of 1×1 km<SUP>2</SUP> from Moderate Resolution Imaging Spectroradiometer (MODIS) data, a linear mixing model with a vegetation index was used to calculate surface reflectances. As the vegetation index is affected by the aerosol present in the atmosphere, an empirical linear relationship between short wavelength infrared (SWIR) channel reflectance and visible reflectance was estimated to calculate a modified aerosol free vegetation index (AFRI) value. Based on a modified AFRI obtained from MODIS SWIR channel reflectance, an improved linear mixing model was applied for aerosol retrieval. A comparison of results between calculated and apparent surface reflectance was satisfactory, with a linear fit slope above 0.94, correlation coefficients above 0.84, and standard deviation below 0.008 for the study area. These results can therefore be used for improved aerosol retrieval over land by the BAER method with MODIS Level 1 data.</P>

Spatio-temporal variability of satellite-derived aerosol optical thickness over Northeast Asia in 2004

Lee, Kwon Ho,Kim, Young Joon,von Hoyningen-Huene, Wolfgang,Burrow, John P. Elsevier 2007 Atmospheric environment Vol.41 No.19

<P><B>Abstract</B></P><P>In this study a modified Bremen aerosol retrieval (BAER) method was used to retrieve aerosol optical thickness (AOT) over both land and ocean using moderate resolution imaging spectro-radiometer (MODIS) data over Northeast Asia for a full year during 2004. Retrieved MODIS AOT data were in good agreement with data obtained from a ground-based AERONET sunphotometer (<I>r</I>=0.90, linear slope=0.89). Seasonal variation analysis of AOT revealed maximum values in summer (∼0.41) and minimum values in winter (∼0.25). The contribution of each aerosol type to total AOT was estimated for each pixel. A spectral shape fitting procedure was used to select the optimum aerosol model for AOT retrieval among six aerosol types: urban, rural, maritime, tropospheric, Asian dust, and biomass burning. The spatio-temporal distribution of average AOT was analyzed for the following five sectors in Northeast Asia: (I) East China, (II) Yellow Sea, (III) Korea, (IV) East Sea, and (V) South Sea plus a part of Japan. Maximum AOT values of 0.75±0.18 were measured over sector (I) in summer, while minimum values of 0.10±0.02 were recorded over sector (IV) in winter. AOT estimates over sector (I) were much higher than those of other sectors due to an increased contribution to the total AOT by fine urban aerosol, which contributed up to 56.5% of the total AOT.</P>

AN X-RAY STUDY OF SUPERNOVA REMNANT N49 AND SOFT GAMMA-RAY REPEATER 0526-66 IN THE LARGE MAGELLANIC CLOUD

Park, Sangwook,Hughes, John P.,Slane, Patrick O.,Burrows, David N.,Lee, Jae-Joon,Mori, Koji IOP Publishing 2012 The Astrophysical journal Vol.748 No.2

<P>We report on the results from our deep Chandra observation (120 ks) of the supernova remnant (SNR) N49 and soft gamma-ray repeater (SGR) 0526-66 in the Large Magellanic Cloud. We firmly establish the detection of an ejecta 'bullet' beyond the southwestern boundary of N49. The X-ray spectrum of the bullet is distinguished from that of the main SNR shell, showing significantly enhanced Si and S abundances. We also detect an ejecta feature in the eastern shell, which shows metal overabundances similar to those of the bullet. If N49 was produced by a core-collapse explosion of a massive star, the detected Si-rich ejecta may represent explosive O-burning or incomplete Si-burning products from deep interior of the SN. On the other hand, the observed Si/S abundance ratio in the ejecta may favor Type Ia origin for N49. We refine the Sedov age of N49, tau(Sed) similar to 4800 yr, with the explosion energy E-0 similar to 1.8 x 10(51) erg. Our blackbody (BB) + power law (PL) model for the quiescent X-ray emission from SGR 0526-66 indicates that the PL photon index (Gamma similar to 2.5) is identical to that of PSR 1E1048.1-5937, the well-known candidate transition object between anomalous X-ray pulsars and SGRs. Alternatively, the two-component BB model implies X-ray emission from a small (R similar to 1 km) hot spot(s) (kT similar to 1 keV) in addition to emission from the neutron star's cooler surface (R similar to 10 km, kT similar to 0.4 keV). There is a considerable discrepancy in the estimated column toward 0526-66 between BB+PL and BB+BB model fits. Discriminating these spectral models would be crucial to test the long-debated physical association between N49 and 0526-66.</P>

A SUPER-SOLAR METALLICITY FOR THE PROGENITOR OF KEPLER'S SUPERNOVA

Park, Sangwook,Badenes, Carles,Mori, Koji,Kaida, Ryohei,Bravo, Eduardo,Schenck, Andrew,Eriksen, Kristoffer A.,Hughes, John P.,Slane, Patrick O.,Burrows, David N.,Lee, Jae-Joon IOP Publishing 2013 ASTROPHYSICAL JOURNAL LETTERS - Vol.767 No.1

<P>We have performed deep X-ray observations of the remnant of Kepler's supernova (SN 1604) as a Key Project of the Suzaku Observatory. Our main goal is to detect secondary Fe-peak elements in the supernova (SN) ejecta to gain insights into the Type Ia SN explosion mechanism and the nature of the progenitor. Here, we report our initial results. We made a conclusive detection of X-ray emission lines from highly ionized Mn, Cr, and Ni as well as Fe. The observed Mn-to-Cr line flux ratio is similar to 0.60, similar to 30% larger than that measured in Tycho's remnant. We estimate an Mn-to-Cr mass ratio of similar to 0.77, which is strongly suggestive of a large neutron excess in the progenitor star before the onset of the thermonuclear runaway. The observed Ni-to-Fe line flux ratio (similar to 0.03) corresponds to a mass ratio of similar to 0.06, which is generally consistent with the products of the explosive Si-burning regime in Type Ia explosion models, and rules out contamination from the products of neutron-rich nuclear statistical equilibrium in the shocked ejecta. Together with the previously suggested luminous nature of the explosion, these mass ratios provide strong evidence for a super-solar metallicity in the SN progenitor (similar to 3 Z(circle dot)). Kepler's SN was likely the thermonuclear explosion of a white dwarf formed in the recent past that must have exploded through a relatively prompt channel.</P>

SNR 0104-72.3: A remnant of Type Ia Supernova in a Star-forming region?

이재준,Sangwook Park,John P. Hughes,Patrick Slane,David Burrows 한국천문학회 2011 天文學會報 Vol.36 No.1

인공위성(SCIAMACHY) 데이터를 이용한 대류권 SO₂, NO₂ 측정

이철규(Chulkyu Lee),Andreas Richter,John P. Burrows,김영준(Young J. Kim) 한국대기환경학회 2008 한국대기환경학회지 Vol.24 No.2

Anthropogenic emissions of nitrogen oxides and sulfur dioxide in Northeast Asia are of great concern because of their impact on air quality and atmospheric chemistry on regional and intercontinental scales. Satellite remote sensing based on DOAS (Differential Optical Absorption Spectroscopy) technique has been preferred to measure atmospheric trace species and to investigate their emission characteristics on regional and global scales. Absorption spectra obtained by the satellite-born instrument, SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) have been utilized to retrieve the information of SO₂ and NO₂ over Northeast Asia. SO₂ levels over Northeast Asia were in order of East China, Yellow Sea, South Sea and Korean Peninsula with mean vertical columns of 1.78(±1.0)×10<SUP>16</SUP>, 1.11(±0.67)×10<SUP>16</SUP>, 0.60(±0.63)×10<SUP>16</SUP>, 0.71(±0.65)×10<SUP>16</SUP> molecules/㎠, respectively. NO₂ levels were in order of East China, Yellow Sea, Korean Peninsula, and South Sea with mean vertical columns of 1.2(±0.56)×10<SUP>16</SUP>, 0.38(±0.19)×10<SUP>16</SUP>, 0.48(±0.28)×10<SUP>16</SUP>, 0.26(±0.16)×10<SUP>16</SUP> molecules/㎠, respectively. High levels of SO₂ and NO₂ were observed over East China, in particular in winter by the contribution of heating fuel combustion exhausts. The SO₂ and NO₂ levels over East China were the highest in January with 34% and 42% higher over the annual means. Low levels of SO₂ ranged over Korean peninsula, while NO₂ levels were relatively high, in particular in winter. The SO₂ and NO₂ levels over Yellow Sea were relatively higher compared to those over Korean peninsula and South Sea, which could be mainly attributed to their transport from East China.