The Analysis of Typical Dust Storm in Northern China by Remote Sensing The Analysis of Typical Dust Storm in Northern China Using Remote Sensing Data FAN Yi-da, SHI Pei-jun, Ge Yi, Dou Wen Institute of Resource Science, Beijing Normal University, Chinese Center of Desert Research at Beijing Normal University, Key Laboratory on Environmental Change and Natural Disaster of Ministry of Education P.R.C. 100875, Beijing, China Abstract This article summarizes the field and progress about the research of dust storm, and provides a method of extracting dust storm information and dividing them by density based on NOAA/AVHRR data. Compared with meteorological data, the result is satisfying. We analyzed the relationship between the typical dust storms and surface in Northern China by combining with the types of land cover and the vegetation coverage degree where dust storm passed, and reached the conclusion that the conditions of land cover/use and the vegetation coverage degree have dominant relationship to dust storm forming and intensity changing on the same meteorological conditions. Key words: Dust storm; Land use/cover; Vegetation coverage degree 1. INTRODUCTION Dust storm is a kind of severe environmental issues[1,2]. In meteorology, dust storm is a catastrophic atmospheric phenomenon that strong, violent winds pick up and transport grains of fine particles like dust and silt from the ground, making the air hazy and restricting the horizontal visibility to less than 1.0 km. In the spring of 2000, dust storms hit Northern China time after time, caused serious damage to the economic and social development, transportation, atmospheric environment, and people’s property and health especially in the Capital and its surrounding areas, and therefore called forth a great concentration from the whole society. Most dust storms generate from areas around deserts. In the world, most dust storms come from Central Asia, Northern America, Central Africa or Australia. Northern China, belonging to Central Asia[3], was an important region where dust storms originated from and dust particles deposited during the geological and historical period. In the recent years, intense and extra intense dust storms occurred frequently in this region because of environmental degradation [1]. China began its systemic investigations in dust storm cases in 1970s, much later than many other countries in the world [4], and the investigations in the world on dust weather then were limited in analyzing the effects of radiation and heat budget[5,6]. In 1980s, scientists began to study systematically on problems such as the synoptic characters in the course of dust storm forming, the temporal and spatial distribution [7], and a series of environmental effects and disasters contributed from dust storms [8], etc. At the same time, researches on large-scale influences to climate and environment caused by dust weather were also attracted more and more Supported by the Projects of Development Plan of the State Key Fundamental Research: G2000048701, G2000018604 and G1999043404. - 1 - The Analysis of Typical Dust Storm in Northern China by Remote Sensing attention [9, 10, and 11]. At present, the researches field on dust storms generally cover: ⑴In climatology, scientists study on the classification standard and the features of temporal and spatial distribution. Usually, by analyzing the number of days with dust storms and the meteorological elements with numerical statistics, we can find its temporal and spatial changes, forming cause and evolving tendency[7,12,13]; ⑵In order to analyze and forecast, researchers investigate the meteorological cause and the characteristics of meteorological system structure about dust storm[4]; ⑶In way of numerical simulation and forecast, researchers simulate the forming mechanism and evolving structure[14]; ⑷Considering the analysis of dust elements, the main work is to analyze the source, transportation quantity and deposition mechanism, along with the study on compositions and content of dust [15,1617,18,19,20] particles . All these studies have indicated that in chemical compositions of dust aerosols, SiO2 takes the first place, followed by Al2O3, and the two one have exceeded 60% of the total. The density of dust aerosol varies from 1/cm3 to 100/cm3, and the grain size is usually larger than 0.02um, 0.1-50um is the most frequent[21]; some studies have showed that in China, dust transportation quantity has a high correlation to agrotype, size of dust particles, latent evaporation and average wind speed, and the two main regions of transportation lie in Taklimakan Desert and Mongolian Plateau, where more than half of the annual transportation occur in spring[16]; ⑸Considering ecology and land use/cover, scientists develop a pattern of regional ecological construction and industrial development to prevent and control dust[1]. Combined with the regional conditions where dust storms passed, such as the texture of surface soil, the land use, the type and intensity of wind erosion, scientists analyze the cause and tragedy of dust weather thoroughly [22], and indicate that in Northern China, the formation and growing of dust storm are directly affected by surface resources and environmental conditions, besides weather[23]; ⑹Scientists also have studied the dust sources from the aspect of dust particles. The results show that in China, the number of days with dust storms is larger in north west than that in north east, in plains(and basins) than mountainous areas and in deserts than other regions[12]. In a global sense, the main dust sources are Sahara Desert in Northern Africa and Gobi-Taklimakan Desert in Central Asia [24]. Northern China is the region where dust storm occurred most and earliest, generally in April each year[7]; ⑺Through remote sensing monitoring, we can decide the affected range at special moment and the dynamic change conditions. Now, the monitoring by remote sensing about dust storm is mostly based on the data from GMS and NOAA/AVHRR. The researches indicate that the data from GMS infrared channel does good to identify the location of dust storms, and it has a high temporal revolution (one hour) which is more helpful to a large-scale monitoring on the moving track of dust storms; NOAA/AVHRR data can monitor not only the reflection and radiance characteristics of dust storms, but also the spatial and temporal distribution in a relative large-scale, so it’s the main remote sensed data source for researching and monitoring dust storms. The formation and evolvement of dust storms are caused by special climate and surface conditions. Although some scientists have studied the relations between dust storms and surface, few combined dust storms with the hypsography, land cover and vegetation coverage degree in detail, so they can’t go deep into analysis of the intensity change of dust storms. We tried to explore the relationships between dust storms and surface conditions by dust storm information extracted from remote sensing data, combined with the land use and land cover where dust storm traveled. - 2 - The Analysis of Typical Dust Storm in Northern China by Remote Sensing 2. INFORMATION EXTRACTION OF DUST STORM AND DENSITY DISTRIBUTION 2.1 Data sources In this article, all the data from NOAA/AVHRR (NOAA-14) were provided by National Satellite Meteorological Center of China Meteorological Administration, acquired at 16:00 on Apr 6, 2000 and the last ten-day of July, 1999 (5 swaths). The data of Apr 6, 2000 were used to monitor dust storms and the latter to survey land use/cover and calculate vegetation coverage degree where dust storm passed. 2.2 Information extraction of dust storm and density distribution Extracting the information of dust storms by means of remote sensing is the key to turn the basis of the investigations from qualitative standard to quantitative standard. Complexity of the spectrum characteristics caused by complexity of the surface compositions adds difficulty to the extraction of the dust storm information. In view of image classification, this kind of extraction is only required to divide the information of dust storms from the original images. So, the key is the distribution of types but not the image classification. In order to identify the affected range by dust storm, we have to resolve the boundary transition of dust storm, We brought forward a method of delaminating extraction in this article. Namely, based on the characters of information such as dust, surface and clouds in remote sensing images, we dealt with them from easy to difficult by the way of image processing. When a kind of geographical object has been extracted successfully, we eliminated it from the original image in order to avoid affecting others and make a “clear” environment for extracting latterly. In general, while a layer was being processed, it was ensured that only one kind of geographical object was extracted, that simplified the work and improved the precision of extraction for single object kind, correspondingly, improved the precision of the extraction of the dust storm information. By analyzing remote sensing images (NOAA/AVHRR) about more than ten dust storms occurred in the spring of 2000 in northern China, we can make a classification criterion to extract different remote sensing information when dust storm is occurring( see Table 1). Judged by it, we extracted the data of NOAA/AVHRR on Apr 6, 2000 by delaminating processing, and the results are satisfying. With density distribution [30], we divided the information