Dust storm monitoring with MODIS data on the Multan region (Pakistan)

Dust storm is a complex process influenced by the interaction of earth-atmosphere system, mainly caused by high wind speed, bared soil and dry air condition. It often takes place in arid and semi-arid areas caused usually by dry and cold front, resulting in ascending airflows and in turn raising dust to upper levels of atmosphere (Omidvar K. and Khosravi Y 2012). In recent years, the frequency of dust storm is rising causing more impact on the climate change over regional and global scale due to its interaction with the solar and terrestrial radiative fields (Shi and Zao, 2003). Since the 1970s, scientists have succeeded in identifying the outbreaks of dust storms from satellite images by use of two different techniques, the VIR (visible and near-infrared) and the TIR (thermal infrared) window technique. It has been shown that the TIR technique has the distinct advantage in detecting dust storms over high albedo surfaces and in night-times (Zhang P. et al., 2006). Multan City is a city in the Punjab Province of Pakistan and capital of Multan District, located in the southern part of the province on the east bank of the Chenab River. Multan city is famous not only for its history but also for its blinding dust storms. These dust storms occur mainly between May and June due to a moving western disturbance over the northern areas of Pakistan. To monitor dust storm in the Multan area MODIS data has been used. MODIS senses the Earth’s entire surface in 36 spectral bands, spanning from the visible (0.415 μm) to the infrared (14.235 μm) regions of the spectrum with spatial resolutions of 1 km, 500 m, and 250 m at nadir respectively. MODIS data were acquired from NASA DB web service. The data were georeferenced and reprojected to correct the Bow Tie effect. When the dust storm happens, lots of dusts particles get together to form a dust cloud. The thick dust layer can absorb and reflect surface radiation and solar radiation, emitting and radiating at the same time, so the values of sensors change (Ochirkhuyag and Solmon, 2008). Among the 36 channels of MODIS, the visible and near infrared channels are used to measure objects reflection while the thermal infrared channels are used to measure objects brightness temperature.