With the method of differential optical absorption spectroscopy (DOAS), average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one mont...With the method of differential optical absorption spectroscopy (DOAS), average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one month. The optical thickness at 550 nm is compared with the concentration of ground-measured suspended particulate matter (SPM). Good correlations are found between the DOAS and SPM data, leading to the determination of the aerosol mass extinction efficiency (MEE) to be possible in the lower troposphere. The average MEE value is about 7.6m^2.g^-1 , and the parameter exhibits a good correlation with the particle size as determined from the wavelength dependence of the DOAS signal intensity.展开更多
Mapping rice cultivation is indispensable for monitoring food supply conditions in Bangladesh because of the economical importance of the crop for supporting ever increasing population in the country. In this paper, w...Mapping rice cultivation is indispensable for monitoring food supply conditions in Bangladesh because of the economical importance of the crop for supporting ever increasing population in the country. In this paper, we extract the rice paddy field using the MODIS satellite data for five districts of Pabna, Manikganj, Sherpur, Sylhet, and Gazipur, each of which is characterized with its own aspects in terms of rice cultivation. Land classification is implemented using the vegetation index information derived from the red (band 1) and near-infrared (band 2) bands of MODIS 8-day composite time series data for the two time periods of 2001-2003 and 2011-2013. Results of unsupervised classification indicate that the paddy area coverage increased about 4% and 1% in Gazipur and Sylhet, respectively. In Pabna, Manikganj, and Sherpur, on the other hand, paddy area decreased by 10%, 2% and 5%, respectively, whereas notable increase of 12%, 2% and 7% was found in homestead area coverage, which is becoming more and more important for better management of small-scale agroforestry. At the same time, in Sherpur and Sylhet, forest area increased by 1% and 2% over the same time period. As a validation of these results, the changes detected in Gazipur are compared with those previously derived from the analysis of Landsat data with higher spatial resolution of 30 m as compared with that of MODIS (250 m). Also, the seasonal rice cropping pattern is studied in these five districts for discriminating cultivated rice types. These changes suggest that as a whole, efforts are being made to increase the food production, though the influence of population pressure and economic growth is apparent in these regions.展开更多
Land classification is conducted in Gazipur district, located in the northern neighborhood of Dhaka, the capital of Bangladesh. Images of bands 1 - 5 and 7 of Landsat 4 - 5 TM and Landsat 7 ETM+ imagery recorded in ye...Land classification is conducted in Gazipur district, located in the northern neighborhood of Dhaka, the capital of Bangladesh. Images of bands 1 - 5 and 7 of Landsat 4 - 5 TM and Landsat 7 ETM+ imagery recorded in years 2001, 2005 and 2009 are classified using unsupervised classification with the technique of image segmentation. It is found that during the eight year period, paddy area increased from 30% to 37%, followed by the increase in the homestead (55% to 57%) and urban area (1% to 3%). These changes occurred at the expense of the decrease in forest land cover (14% to 3%). In the category of homestead, the presence of different kinds of vegetation often makes it difficult to separate the category from paddy field, though paddy exhibits accuracy of 93.70% - 99.95%, which is better than the values for other categories. In addition, the analysis based on digital elevation model reveals that paddy cultivation is implemented in lowland rather than highland. Homestead areas have spread from south (low elevation) to north (high elevation), in association with the decrease in forest-covered areas.展开更多
Located on the mountainous area, Kelok Sembilan flyover area in West Sumatra, Indonesia has a long history of land deformation, therefore monitoring and analyzing as continuously is a necessity to minimize the impact....Located on the mountainous area, Kelok Sembilan flyover area in West Sumatra, Indonesia has a long history of land deformation, therefore monitoring and analyzing as continuously is a necessity to minimize the impact. Notably, in the rainy season, the land deformation occurs along this area. The zone is crucial as the center of transportation connection in the middle of Sumatra. Quasi-Persistent Scatterer (Q-PS) Interferometry technique was applied for extracting information of land deformation on the field from time to time. Not only does the method have high performance for detecting land deformation but also improve the number of PS point, especially in a non-urban area. This research supported by 90 scenes of Sentinel-1A (C-band) taken from October 2014 to November 2017 for ascending and descending orbit with VV and VH polarization in 5 × 20 m (range × azimuth) resolution. Both satellite orbits detected two critical locations of land deformation namely as zone A and Zone B, which located in positive steep slope where there is more than 500 mm movement in the Line of Sight (LOS) during acquisition time. Deformations in the vertical and horizontal direction for both zone, are 778.9 mm, 795.7 mm and 730.5 mm, 751.7 mm, respectively. Finally, the results were confirmed by ground truth data using Unmanned Aerial Vehicle (UAV) observation.展开更多
Cloud detection and classification form a basis in weather analysis. Split window algorithm (SWA) is one of the simple and matured algorithms used to detect and classify water and ice clouds in the atmosphere using sa...Cloud detection and classification form a basis in weather analysis. Split window algorithm (SWA) is one of the simple and matured algorithms used to detect and classify water and ice clouds in the atmosphere using satellite data. The recent availability of Himawari-8 data has considerably strengthened the possibility of better cloud classification owing to its enhanced multi-band configuration as well as high temporal resolution. In SWA, cloud classification is attained by considering the spatial distributions of the brightness temperature (BT) and brightness temperature difference (BTD) of thermal infrared bands. In this study, we compare unsupervised classification results of SWA using the band pair of band 13 and 15 (SWA13-15, 10 and 12 μm bands), versus that of band 15 and 16 (SWA15-16, 12 and 13 μm bands) over the Japan area. Different threshold values of BT and BTD are chosen in winter and summer seasons to categorize cloud regions into nine different types. The accuracy of classification is verified by using the cloud-top height information derived from the data of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). For this purpose, six different paths of the space-borne lidar are selected in both summer and winter seasons, on the condition that the time span of overpass falls within the time ranges between 01:00 and 05:00 UTC, which corresponds to the local time around noon. The result of verification indicates that the classification based on SWA13-15 can detect more cloud types as compared with that based on SWA15-16 in both summer and winter seasons, though the latter combination is useful for delineating cumulonimbus underneath dense cirrus展开更多
Differential optical absorption spectroscopy (DOAS) is a useful technique for measuring nitrogen dioxide (NO2) and aerosol, the most important species in urban environmental pollution. This paper reports on the result...Differential optical absorption spectroscopy (DOAS) is a useful technique for measuring nitrogen dioxide (NO2) and aerosol, the most important species in urban environmental pollution. This paper reports on the results of our dual path DOAS measurements recently conducted in Chiba City, Japan, using xenon flashlights equipped on tall constructions as aviation obstruction lights. Because of the proximity of the southern DOAS path to an industrial area, it is found that the level of air pollution generally increases with the dominance of westerly winds, from the plausible source area to the observation light path. This situation is consistent with the result of wind lidar measurement covering a sector of ±28? with the observation range of approximately 2.8 km. In spite of the fact that the two DOAS paths, having path lengths of 5.5 and 3.5 km each, are located in separated regions of Chiba City, the observed temporal behavior was similar for both nitrogen dioxide and aerosol, though the southern path tends to exhibit slightly higher pollution levels than the northern counterpart. Additionally it is confirmed that size information of aerosol particles can be derived from the DOAS data through the analysis of the wavelength dependence of the aerosol optical thickness, which shows fairly good correlation with the mass ratio between PM2.5 and suspended particulate matter (SPM) obtained from the in-situ sampling station measurement. Thus, the DOAS approach can also be utilized for obtaining information on PM2.5 that is considered to be more harmful to human health than SPM.展开更多
The understanding of aerosol properties in troposphere, especially their behavior near the ground level, is indispensable for precise evaluation of their impact on the Earth’s radiation studies. Although a sunphotome...The understanding of aerosol properties in troposphere, especially their behavior near the ground level, is indispensable for precise evaluation of their impact on the Earth’s radiation studies. Although a sunphotometer or a skyradiometer can provide the aerosol optical thickness (AOT), their application is limited to daytime under near cloud free conditions. In order to attain the multi-wavelength observation for both day- and night-time including cloudy conditions, here we propose a novel monitoring technique by means of simultaneous measurement using a nephelometer (450, 550, and 700 nm), an aethalometer (370, 470, 520, 590, 660, 880, and 950 nm), and a visibility meter (550 nm). On the basis of the multi-wavelength data of scattering and absorption coefficients from the nephelometer and aethalometer, respectively, first we calculate the real-time values of aerosol extinction coefficient in addition to the Angstrom exponent (AE). Then, correction of these values is carried out by comparing the resulting extinction coefficient with the corresponding value obtained from the optical data of visibility-meter. The major reason for this correction is the loss of relatively coarse particles due to the aerodynamic effect as well as evaporation of water content from particles during the sampling procedure. Then, with the ancillary data of vertical aerosol profile obtained with a lidar (532 nm), the temporal change of AOT is estimated. In this way, information from the sampling can be converted to the ambient properties in the atmospheric boundary layer. Furthermore, daytime data from a sunphotometer (368, 500, 675, and 778 nm) and a skyradiometer (340, 380, 400, 500, 675, 870, and 1020 nm) are used to validate the resulting AOT values. From the overall procedure, we can estimate the AE and AOT values from the sampling data, with uncertainties of approximately 5% for AE and 10% for AOT. Such a capability will be useful for studying aerosol properties throughout 24 hours regardless of the solar radiation and cloud coverage.展开更多
Observation of optical properties of atmospheric aerosols, especially their behavior near the surface level, is indispensable for better understanding of atmospheric environmental conditions. Concurrent observations o...Observation of optical properties of atmospheric aerosols, especially their behavior near the surface level, is indispensable for better understanding of atmospheric environmental conditions. Concurrent observations of ground-based instruments and satellite-borne sensors are useful for attaining improved accuracy in the observation of relatively wide area. In the present paper, aerosol parameters in the lower troposphere are monitored using a plan position indicator (PPI) lidar, ground-sampling instruments (a nephelometer, an aethalometer, and optical particle counters), as well as a sunphotometer. The purpose of these observations is to retrieve the aerosol extinction coefficient (AEC) and aerosol optical thickness (AOT) simultaneously at the overpass time of Landsat-8 satellite. The PPI lidar, operated at 349 nm, provides nearly horizontal distribution of AEC in the lower part of the atmospheric boundary layer. For solving the lidar equation, the boundary condition and lidar ratio are determined from the data of ground sampling instruments. The value of AOT, on the other hand, is derived from sunphotometer, and used to analyze the visible band imagery of Landsat-8 satellite. The radiative transfer calculation is conducted using the MODTRAN code with the original aerosol type that has been determined from the ground sampling data coupled with the Mie scattering calculation. Reasonable agreement is found between the spatial distribution of AEC from the PPI lidar and that of AOT from the blue band (band 2) of Landsat-8. The influence of AOT on the values of apparent surface reflectance is also discussed.展开更多
Statistical mechanics and semi-empirical molecular orbital theory (PM6) are used to calculate the surface coverage of CO2 and H2 molecular species chemically adsorbed on the surface of Cu and Zn micro clusters. The ca...Statistical mechanics and semi-empirical molecular orbital theory (PM6) are used to calculate the surface coverage of CO2 and H2 molecular species chemically adsorbed on the surface of Cu and Zn micro clusters. The calculation shows that CO2 is adsorbed well both on the surface of Cu and Zn micro clusters. Although H2 is adsorbed well on the surface of Zn micro clusters, H2 absorption on the surface of Cu micro clusters is much more limited in the pressure range of 20 - 100 atm and temperature range of 200 - 1000 K. Reaction rates are also estimated for some chemical adsorption process of H2 gas using theory of absolute reaction rates. It is found that the values of the reaction rate calculated in the present paper agree reasonably well with the experimental values.展开更多
Since the volcanic eruption in 2000, continuous monitoring of sulfur dioxide (SO2) gas has been conducted with in-situ samplers located along the seashore road in Miyakejima, a volcano island around 180 kmsouth of Tok...Since the volcanic eruption in 2000, continuous monitoring of sulfur dioxide (SO2) gas has been conducted with in-situ samplers located along the seashore road in Miyakejima, a volcano island around 180 kmsouth of Tokyo. The purpose of these sampling measurements has been to issue warning on the hazardous air pollution to the local residents. Therefore, the resulting data do not provide direct information on pollution levels inside the restricted areas where high concentration of SO2 still takes place frequently. From the ecological point of view, it is desirable to have pollution data covering wider regions of the island. In this paper we report on our differential optical absorption spectroscopy (DOAS) measurements carried out inside the highly-polluted, restricted areas in Miyakejima in December 2009 and September 2010. The system is based on continuous light emitted from a xenon light sources, while detector setups consisting of a telescope and a compact spectrometer detect the light after passing a nearly horizontal optical path of460 m-1300 m. By virtue of the portability of the DOAS observation systems, we achieved the measurement of the concentrations inside the restricted districts in the eastern and southwestern parts of the island. The DOAS results in both of these districts revealed the occurrence of pollution of volcanic gas even when no pollution was observed at nearby sampling stations. In addition, simultaneous measurements with two nearly orthogonal DOAS paths were conducted for examining the spatial distribution of the volcanic gas over the spatial range of several hundred meters. The result of this two paths measurement has indicated the importance of orography, in addition to the wind speed and wind direction, in determining the spatial concentration of SO2 emitted from the volcano crater.展开更多
基金Project supported by National Natural Science Foundation of China (Grant No 10274080).
文摘With the method of differential optical absorption spectroscopy (DOAS), average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one month. The optical thickness at 550 nm is compared with the concentration of ground-measured suspended particulate matter (SPM). Good correlations are found between the DOAS and SPM data, leading to the determination of the aerosol mass extinction efficiency (MEE) to be possible in the lower troposphere. The average MEE value is about 7.6m^2.g^-1 , and the parameter exhibits a good correlation with the particle size as determined from the wavelength dependence of the DOAS signal intensity.
文摘Mapping rice cultivation is indispensable for monitoring food supply conditions in Bangladesh because of the economical importance of the crop for supporting ever increasing population in the country. In this paper, we extract the rice paddy field using the MODIS satellite data for five districts of Pabna, Manikganj, Sherpur, Sylhet, and Gazipur, each of which is characterized with its own aspects in terms of rice cultivation. Land classification is implemented using the vegetation index information derived from the red (band 1) and near-infrared (band 2) bands of MODIS 8-day composite time series data for the two time periods of 2001-2003 and 2011-2013. Results of unsupervised classification indicate that the paddy area coverage increased about 4% and 1% in Gazipur and Sylhet, respectively. In Pabna, Manikganj, and Sherpur, on the other hand, paddy area decreased by 10%, 2% and 5%, respectively, whereas notable increase of 12%, 2% and 7% was found in homestead area coverage, which is becoming more and more important for better management of small-scale agroforestry. At the same time, in Sherpur and Sylhet, forest area increased by 1% and 2% over the same time period. As a validation of these results, the changes detected in Gazipur are compared with those previously derived from the analysis of Landsat data with higher spatial resolution of 30 m as compared with that of MODIS (250 m). Also, the seasonal rice cropping pattern is studied in these five districts for discriminating cultivated rice types. These changes suggest that as a whole, efforts are being made to increase the food production, though the influence of population pressure and economic growth is apparent in these regions.
文摘Land classification is conducted in Gazipur district, located in the northern neighborhood of Dhaka, the capital of Bangladesh. Images of bands 1 - 5 and 7 of Landsat 4 - 5 TM and Landsat 7 ETM+ imagery recorded in years 2001, 2005 and 2009 are classified using unsupervised classification with the technique of image segmentation. It is found that during the eight year period, paddy area increased from 30% to 37%, followed by the increase in the homestead (55% to 57%) and urban area (1% to 3%). These changes occurred at the expense of the decrease in forest land cover (14% to 3%). In the category of homestead, the presence of different kinds of vegetation often makes it difficult to separate the category from paddy field, though paddy exhibits accuracy of 93.70% - 99.95%, which is better than the values for other categories. In addition, the analysis based on digital elevation model reveals that paddy cultivation is implemented in lowland rather than highland. Homestead areas have spread from south (low elevation) to north (high elevation), in association with the decrease in forest-covered areas.
文摘Located on the mountainous area, Kelok Sembilan flyover area in West Sumatra, Indonesia has a long history of land deformation, therefore monitoring and analyzing as continuously is a necessity to minimize the impact. Notably, in the rainy season, the land deformation occurs along this area. The zone is crucial as the center of transportation connection in the middle of Sumatra. Quasi-Persistent Scatterer (Q-PS) Interferometry technique was applied for extracting information of land deformation on the field from time to time. Not only does the method have high performance for detecting land deformation but also improve the number of PS point, especially in a non-urban area. This research supported by 90 scenes of Sentinel-1A (C-band) taken from October 2014 to November 2017 for ascending and descending orbit with VV and VH polarization in 5 × 20 m (range × azimuth) resolution. Both satellite orbits detected two critical locations of land deformation namely as zone A and Zone B, which located in positive steep slope where there is more than 500 mm movement in the Line of Sight (LOS) during acquisition time. Deformations in the vertical and horizontal direction for both zone, are 778.9 mm, 795.7 mm and 730.5 mm, 751.7 mm, respectively. Finally, the results were confirmed by ground truth data using Unmanned Aerial Vehicle (UAV) observation.
文摘Cloud detection and classification form a basis in weather analysis. Split window algorithm (SWA) is one of the simple and matured algorithms used to detect and classify water and ice clouds in the atmosphere using satellite data. The recent availability of Himawari-8 data has considerably strengthened the possibility of better cloud classification owing to its enhanced multi-band configuration as well as high temporal resolution. In SWA, cloud classification is attained by considering the spatial distributions of the brightness temperature (BT) and brightness temperature difference (BTD) of thermal infrared bands. In this study, we compare unsupervised classification results of SWA using the band pair of band 13 and 15 (SWA13-15, 10 and 12 μm bands), versus that of band 15 and 16 (SWA15-16, 12 and 13 μm bands) over the Japan area. Different threshold values of BT and BTD are chosen in winter and summer seasons to categorize cloud regions into nine different types. The accuracy of classification is verified by using the cloud-top height information derived from the data of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). For this purpose, six different paths of the space-borne lidar are selected in both summer and winter seasons, on the condition that the time span of overpass falls within the time ranges between 01:00 and 05:00 UTC, which corresponds to the local time around noon. The result of verification indicates that the classification based on SWA13-15 can detect more cloud types as compared with that based on SWA15-16 in both summer and winter seasons, though the latter combination is useful for delineating cumulonimbus underneath dense cirrus
文摘Differential optical absorption spectroscopy (DOAS) is a useful technique for measuring nitrogen dioxide (NO2) and aerosol, the most important species in urban environmental pollution. This paper reports on the results of our dual path DOAS measurements recently conducted in Chiba City, Japan, using xenon flashlights equipped on tall constructions as aviation obstruction lights. Because of the proximity of the southern DOAS path to an industrial area, it is found that the level of air pollution generally increases with the dominance of westerly winds, from the plausible source area to the observation light path. This situation is consistent with the result of wind lidar measurement covering a sector of ±28? with the observation range of approximately 2.8 km. In spite of the fact that the two DOAS paths, having path lengths of 5.5 and 3.5 km each, are located in separated regions of Chiba City, the observed temporal behavior was similar for both nitrogen dioxide and aerosol, though the southern path tends to exhibit slightly higher pollution levels than the northern counterpart. Additionally it is confirmed that size information of aerosol particles can be derived from the DOAS data through the analysis of the wavelength dependence of the aerosol optical thickness, which shows fairly good correlation with the mass ratio between PM2.5 and suspended particulate matter (SPM) obtained from the in-situ sampling station measurement. Thus, the DOAS approach can also be utilized for obtaining information on PM2.5 that is considered to be more harmful to human health than SPM.
文摘The understanding of aerosol properties in troposphere, especially their behavior near the ground level, is indispensable for precise evaluation of their impact on the Earth’s radiation studies. Although a sunphotometer or a skyradiometer can provide the aerosol optical thickness (AOT), their application is limited to daytime under near cloud free conditions. In order to attain the multi-wavelength observation for both day- and night-time including cloudy conditions, here we propose a novel monitoring technique by means of simultaneous measurement using a nephelometer (450, 550, and 700 nm), an aethalometer (370, 470, 520, 590, 660, 880, and 950 nm), and a visibility meter (550 nm). On the basis of the multi-wavelength data of scattering and absorption coefficients from the nephelometer and aethalometer, respectively, first we calculate the real-time values of aerosol extinction coefficient in addition to the Angstrom exponent (AE). Then, correction of these values is carried out by comparing the resulting extinction coefficient with the corresponding value obtained from the optical data of visibility-meter. The major reason for this correction is the loss of relatively coarse particles due to the aerodynamic effect as well as evaporation of water content from particles during the sampling procedure. Then, with the ancillary data of vertical aerosol profile obtained with a lidar (532 nm), the temporal change of AOT is estimated. In this way, information from the sampling can be converted to the ambient properties in the atmospheric boundary layer. Furthermore, daytime data from a sunphotometer (368, 500, 675, and 778 nm) and a skyradiometer (340, 380, 400, 500, 675, 870, and 1020 nm) are used to validate the resulting AOT values. From the overall procedure, we can estimate the AE and AOT values from the sampling data, with uncertainties of approximately 5% for AE and 10% for AOT. Such a capability will be useful for studying aerosol properties throughout 24 hours regardless of the solar radiation and cloud coverage.
文摘Observation of optical properties of atmospheric aerosols, especially their behavior near the surface level, is indispensable for better understanding of atmospheric environmental conditions. Concurrent observations of ground-based instruments and satellite-borne sensors are useful for attaining improved accuracy in the observation of relatively wide area. In the present paper, aerosol parameters in the lower troposphere are monitored using a plan position indicator (PPI) lidar, ground-sampling instruments (a nephelometer, an aethalometer, and optical particle counters), as well as a sunphotometer. The purpose of these observations is to retrieve the aerosol extinction coefficient (AEC) and aerosol optical thickness (AOT) simultaneously at the overpass time of Landsat-8 satellite. The PPI lidar, operated at 349 nm, provides nearly horizontal distribution of AEC in the lower part of the atmospheric boundary layer. For solving the lidar equation, the boundary condition and lidar ratio are determined from the data of ground sampling instruments. The value of AOT, on the other hand, is derived from sunphotometer, and used to analyze the visible band imagery of Landsat-8 satellite. The radiative transfer calculation is conducted using the MODTRAN code with the original aerosol type that has been determined from the ground sampling data coupled with the Mie scattering calculation. Reasonable agreement is found between the spatial distribution of AEC from the PPI lidar and that of AOT from the blue band (band 2) of Landsat-8. The influence of AOT on the values of apparent surface reflectance is also discussed.
文摘Statistical mechanics and semi-empirical molecular orbital theory (PM6) are used to calculate the surface coverage of CO2 and H2 molecular species chemically adsorbed on the surface of Cu and Zn micro clusters. The calculation shows that CO2 is adsorbed well both on the surface of Cu and Zn micro clusters. Although H2 is adsorbed well on the surface of Zn micro clusters, H2 absorption on the surface of Cu micro clusters is much more limited in the pressure range of 20 - 100 atm and temperature range of 200 - 1000 K. Reaction rates are also estimated for some chemical adsorption process of H2 gas using theory of absolute reaction rates. It is found that the values of the reaction rate calculated in the present paper agree reasonably well with the experimental values.
文摘Since the volcanic eruption in 2000, continuous monitoring of sulfur dioxide (SO2) gas has been conducted with in-situ samplers located along the seashore road in Miyakejima, a volcano island around 180 kmsouth of Tokyo. The purpose of these sampling measurements has been to issue warning on the hazardous air pollution to the local residents. Therefore, the resulting data do not provide direct information on pollution levels inside the restricted areas where high concentration of SO2 still takes place frequently. From the ecological point of view, it is desirable to have pollution data covering wider regions of the island. In this paper we report on our differential optical absorption spectroscopy (DOAS) measurements carried out inside the highly-polluted, restricted areas in Miyakejima in December 2009 and September 2010. The system is based on continuous light emitted from a xenon light sources, while detector setups consisting of a telescope and a compact spectrometer detect the light after passing a nearly horizontal optical path of460 m-1300 m. By virtue of the portability of the DOAS observation systems, we achieved the measurement of the concentrations inside the restricted districts in the eastern and southwestern parts of the island. The DOAS results in both of these districts revealed the occurrence of pollution of volcanic gas even when no pollution was observed at nearby sampling stations. In addition, simultaneous measurements with two nearly orthogonal DOAS paths were conducted for examining the spatial distribution of the volcanic gas over the spatial range of several hundred meters. The result of this two paths measurement has indicated the importance of orography, in addition to the wind speed and wind direction, in determining the spatial concentration of SO2 emitted from the volcano crater.