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Showing 4 results for Optical Depth

Dr Sara Karami, Dr Nasim Hossein Hamzeh, Dr Abbas Ranjbar,
Volume 0, Issue 0 (3-1921)

Today, dust storms affect the lives of many people around the world and cause a lot of financial and human losses. Every year, Iran is affected by dust storms caused by internal sources and external dust sources located in neighboring countries. Semnan province has several dust-producing sources due to its geographical location, that affect not only this province, but also the neighboring provinces. The purpose of this study is to investigate the dust phenomenon of Semnan province and its monthly changes in the 15-year period, between 2003 and 2017. For this purpose, meteorological stations data of the province and the aerosol optical depth of satellite product have been investigated. Also, GOCART model has been used to estimate the amount of dust emissions from this region and to determine the vertical dust flux in Semnan province. The study of average dust flux showed that the highest values ​​of dust flux was in the southeast of Shahroud and then in the south of Shahroud, Damghan and Sorkheh. A monthly investigation showed that in all months, the average AOD in the southern half of Semnan province was higher than in the northern half. The highest levels of AOD were in May, April and June, and the highest amounts of dust flux were observed in March, June and July. Also, the prevailing wind direction was northeast and northeast, and this factor causes dust particles rising from this region and dust loading in the south of Semnan province and areas of Isfahan, Yazd and South Khorasan provinces.
Dr. Ali Bayat, Mr. Ahmad Assar Enayati , Mrs. Azimeh Toshani,
Volume 21, Issue 62 (10-2021)

In this paper, aerosol optical depth measured by Caliop, MODIS, MISR, and OMI satellite sensors is compared with Sun-photometer data located in the Institute for Advanced Studies in Basic Sciences (IASBS) from December 2009 to December 2013 over Zanjan city. We computed figures for root mean square error (RMSE), mean absolute error (MAE) and root mean bias (RMB) between space-born and ground-based sensor measurements. The results show that the Caliop and MISR sensors have the highest correlation (0.61 and 0.54), respectively, with Sun-photometer measurements over Zanjan area. MISR, Caliop, and OMI sensors have the closest aerosol optical depth data to the Sun-photometer measurements (the fitted line slope is 0.68, 0.61 and 0.59, respectively) which represents the appropriate model used in the sensors to extract the aerosol optical depth. The variable monthly AOD figures obtained with different sensors indicate underestimation by MODIS and Caliop instruments (0.32 and 0.83 respectively) over Zanjan city relative to the Sun-photometer data, and overestimation by OMI and MISR instruments (1. 23 and 1.08 respectively).

Dr. Ruhallah Moradhaseli, Dr. Ali Bayat, Mrs. Fateme Radmehri,
Volume 23, Issue 70 (10-2023)

Aerosol optical depth in 550 nm and angstrom exponent measurements with MODIS have been studied with 1-degree resolution for the period 2006-2017 in the middle east. Moreover, tropospheric aerosol optical depth and depolarization ratios measured at 532 nm with CALIOP have been studied for same area and same period of time too. These parameters have been classified seasonally. Optical depth results show high values for the region especially in spring and summer seasons. During the cold seasons, optical depth values are much less compared with their values at warm seasons. At spring, dust sources located in northern Iraq and those located in central and northern parts of Arabian Peninsula are much more active. Sources located in southern parts of Arabian Peninsula get more active by summer. Angstrom exponent results show that in arid and semi-arid parts of middle east, aerosol sizes are mainly in coarse mode. In arid parts of Iraq and Arabian Peninsula coarse mode particles are dominant during 4 seasons, but for arid parts inside Iran coarse mode is dominant during warm seasons and a modification in suspended particle sizes can be seen during cold seasons. Depolarization measurements of CALIOP show that almost in all seasons, non-spherical particles are ready in middle east atmosphere which is usual for an area inside the dust belt.

Kaveh Mohammadpour, Mohammad Saligheh, Tayeb Raziei, Ali Darvishi Bloorani,
Volume 24, Issue 72 (6-2024)

Mineral Dust, the most important type of aerosol, has a significant direct and indirect role in weather and climate. In this case, it intend to investigate the capability and capability of MACC model validated by MODIS for detection of dust episodes in the Kurdistan province during 2003-2012. To achieve that, we analysis satellite and model data using Man-Kendall trend and statistical tests. The results of the temporal distribution indicated that the mean Aerosol Optical depth (AOD) in 2008 was 0.36 and its lowest was 29.04 for 2004. In addition, average AOD in menthioned year was 0.036, 0.335, 0.385, 0.377 and 0.3368 for the cities of Sanandaj, Saqez, Ghorveh, Kamyaran, Marivan, respectively. The spatial distribution of AOD average in different seasons showed that winter and autumn had the lowest amount and spring, and summer season had the highest AOD. AOD's monthly spatial distribution showed that high dust belonging to April-August period to covers completely interested area.The results of the Man-Kendall test showed that the area had a significant positive trend in the spring season throughout the province and the summer season in the east of the province. Therefore, the spring season in the area known Extreme Season and June 19, 2009 between the five days of the dust extreme is as an extreme episode with an average AOD of 1.16 and a horizontal visibility of less than two kilometers that it have the highest and most widespread mineral dust. In general, the results of the MACC with multidimensional approach showed that optical depth (AOD, DOD) is a more appropriate criterion than horizontal visibility in determining dust storm.

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