ارزیابی داده های زمینی و تصاویر ماهواره ای در تحلیل گرد و غبارهای نیمه غربی ایران

طوفان گرد و غبار فرایند پیچیده ای است که تحت تاثیر تعامل سیستم اتمسفر–زمین بوده و از نظر اقلیم شناسان و هواشناسانی که تغییرهای اقلیمی و اتمسفری را بررسی می کنند، پایش پوشش گرد و غبار یک پدیده دینامیکی مهم است. در این مطالعه با استفاده از داده های دید افقی و سنجش از دور ماهواره ای (modis) و شاخص nddi به آشکارسازی گردوغبار در نیمه غربی ایران پرداخته شده است. طبق بررسی های انجام شده، نقشه میانیابی تعداد روز غبارآلود در نیمه غربی ایران نشان داد که محدوده مورد مطالعه غرب ایران از لحاظ فراوانی وقوع پدیده گرد و غبار و چگونگی روند آن دارای نظام همگنی نیست و تعداد روزهای گرد و غباری از شمال به سمت جنوب افزایش می یابد. هسته بیشینه وقوع پدیده گرد و غبار در بخش جنوبغربی منطقه و بر روی اهواز، امیدیه و بوشهر  قرار دارد که با منشاٌ مناطق بیابانی در عراق سوریه و عربستان است. نتایج پراکنش فضایی دید افقی ایستگاه های زمینی با آشکارسازی شاخص nddi بر روی تصاویر مطابقت دارد و نشان داد که بیشترین سطح پوشش گردوغبار بر روی اتمسفر استان های فارس و بوشهر و کمترین مقدار آن در سطح استان های آذربایجان غربی و شرقی، قم و مرکزی مشاهده می شود.

assessment of ground based dataset and satellite remotely sensed images for analyzing of dust over western iran

introductiondust storm is a complex process affected by the earth atmophere system. the interaction between the earth and atmosphere is in the realm of the climatologists and meteorologists, who assess atmospheric and climatic changes, and monitor dust spread. dust is the main type of aerosols which affects directly and indirectly radiation budget. in addition, altogether they affect the temperature change, cloud formation, convection, and precipitation. the most important studies about dust analysis have considered the use of remote sensing technique and global models for analyzing the behavior and dynamics of dust in recent two decades. to achieve such a goal, this paper has used modis and nddi data to study and identify the behavior of atmospheric dust in half west of iran. materials and methodsthe western region of iran is the study area. the data used in this study are divided into two categories: ground based observations in 27 synoptic stations extracted from the iran’s meteorological organization during the period (1998 2010) and satellite modis images during the first to fourth days of july 2008 as atmospheric dust extremes. data was analyzed by using arcgis and envi software and nddi index.  results and discussionaccording to results, interpolated map for the number of dusty days during the study period over the western half of iran showed that the scope of study area does not involve an equal system aspect quantity of occurrences. the number of dusty days occurrences increase from north toward south and the sites located in northern proportions of the area have experienced lower dust events. in contrast, maximum hotspots are occurring over southwestern sites such as: ahvaz, ilam, boushehr and shiraz. therefore, principal offspring of dust input has been out of country boundaries and arrived at distant areas. also, based on results obtained using satellite remote sensing images and applied nddi index, maximum of intense dust cover is observed over fars, ilam, boushehr and ahvaz provinces on the first, second, third and fourth of july. however, the lowest rate of index situated in extent far such as: east and west azerbaijan provinces. thus, parts located on the north of the study area experienced less dusty days and the maximum dust cores were located in the southwestern (mostly khuzestan). the long term results were consistent with the daily average of nddi index in the whole study area and indicated the hotspot areas (ilam, ahvaz, omidyeh, bushehr and shiraz) during the first to fourth days of july 2008. however, the level of dust cover in the region has reduced when a wet and cloudy synoptic system passes over the central and northwestern parts of the study area. conclusionsthe climatic interpolated map interpretation indicated that increase of dust concentration based on ground based stations, which are consistent with dust concentration, is overshadowed by the latitude and proximity of sources of dust source in the middle east. also, the long term climatic results of ground based observations were consistent with the nddi index calculated on dust extremes in the whole study area and in the southern areas (ilam, ahvaz, omidyeh, bushehr and shiraz) during study days of july, 2008. therefore, dust occurrence increases from north to south and the maximum hotspots over southwestern confirm the proximity of the south western region of iran to deserts and sedimentary plains and their direct relationship with dust sources in the middle east. these regions highlight the volume and expansion of dust outbreaks, which were well detected due to the satellite imagery and spectral characteristics of modis for monitoring changes in the dust phenomenon.overall, the use of satellite remotely sensed data/images not only cover the ground based observation datasets gap to identify, highlight, and analyse the dust phenomenon, but also takes a much more geographical approach in analysing environmental hazards such as dust. it is also suitable for studies of atmospheric compounds such as atmospheric aerosols.