Keywords : Sandstorm Remote Sensing Monitoring System Disaster Assessment

Abstract
The paper is a draft introduction of the sandstorm disaster and the on-going development of "The Satellite Remote Sensing Monitoring and Disaster Loss Estimation System of Sandstorm" project. This project has been set up for promoting the spatial technology application in the efforts of preventing disaster and reducing disaster losses. In view of that sandstorm is a kind of nature disaster with small probability, huge harmfulness and caused by complicated factors, The research and development of this system is really a challenging task with a great practical value.

Significance of the system research and development
The sandstorm has always occurred in the areas of vast desert and seriously affected areas by desertification that is mainly caused by multiple natural and human factors. The sandstorm is an unexpected meteorological disaster under a complicated natural condition and always led to a substantial devastating to the ecological environment and brought about tremendous social economic losses. However, owing to the worsening ecological environment, it had in turn promoted the possibility of the occurrence of the sandstorm. The China's northwest area is a part of the Central Asian sandstorm area in one of the global four sandstorm regions. On May 5, 1993, a catastrophic sandstorm occurred in the northwest part of China and contributed grave losses, meanwhile it had also raised the attention and concern of China Government as well as the whole society of the country. Since then, the Ministry of Forestry and related departments had in succession organized and completed a series research topics in this regard. Owing to its proruption and a short sustained period of the sandstorm, it has therefore much difficult to make an exact monitoring and forecast for its occurrence. Furthermore, the sandstorm has always been occurred in the areas with poor traffic and communication conditions, and a strong process has always affected considerable regional scope. Thus, the assessment with routine approach is hard to achieve the anticipated objectives and thereby a proper deployment for the disastrous relief activities has been seriously impacted. For promoting the role of remote sensing, GIS and network technology in disaster prevention and reduction, the Academy of Forest Inventory & Planning / the China National Desertification Monitoring Center ,SFA and had undertaken the Project :" Research and Development a Satellite Remote Sensing Monitoring and Disaster Assessment System of Sandstorm". In addition, the China National Satellite Meteorological Center, Lanzhou Desert Institute and Inner Mongolian Forestry College also participated the activities of tackling some key technical problems and the system research and development.

Sandstorm and its classified criteria
Sandstorm is referred in particular to the disastrous weather phenomenon of the strong wind raising a cloud sand and dust from the ground, and the visibility is lower than 1000 meters. By research, it shows that drought, short of rain, frequent gale and unstable air as well as wide-spread desert, gobi and the desertified land were all provided abundant substantial sources for the sandstorm, plus the special natural conditions of topographic features and landform, it had composed of several major factors of the formation of the sandstorm.

In accordance with the criteria of WMO and based on the degree of the horizontal visibility, the strength of the sandstorm can be divided into four grades of special strength, strength, moderate and light. The indicators of the corresponding visibility are separately as 50, 200, 500 and 1000 meters.

Source of remote sensing information and the key technologies

The information source of remote sensing monitoring for the sandstorm
Since the frequented sandstorm areas have rare meteorological stations, by using the meteorological satellite to conduct remote sensing monitoring, it should be of an effective approach. The NOAA/AVHRR data has a rather higher spatial resolution and if in an appropriate occasion, it can be effectively used for collecting the information of sandstorm. The geo-stationary meteorological satellite, such as GMS/VISSR data, has lower spatial resolution, but it can provide a sheet of 1/3 global disc picture per hour. It is quite suitable for real time detection and monitoring for the sandstorm. The CH1 and CH2 channels of NOAA/AVHRR are located at the visible and near infrared waveband and can be used to measure and calculate the albedo of the underneath. The CH3,CH4,CH5 channels are the thermal infrared channels which can be used to measure and calculate the brightness temperature of the underneath. Since there are some differential in albedo and temperature for the sandstorm, the cloud system and the ground surface, thus the information of the sandstorm can be separated out from the satellite cloud image. The albedo data of the visible channel of GMS-5/VISSR has 64 grades, of which, the grade 0-47 reflect only the targets with low albedo, such as sandstorm and the ground surface, also, it has more meticulously distinguishing power. However, for the availability of the real albedo, it must do some additional work of corrections in the light of the change of the angle of depression.