Abstract:
In some particular time periods, fast response to flood and waterlogging monitoring is an issue of the first priority for satellite remote sensing or Earth observation satellite remote sensing. From the point of view of technology, at the same time when developing and utilizing multi-satellite data to resolve the problem of too long intervals of revisit and low resolution in order to make improvements in these affaires, it is key issue to lay emphasis on the integrated construction of system of data receiving and processing, so that intermediate procedures can be minimized, non -compatibility between different data and processing system, caused by various factors can be avoided. Thus, the time effect ( delay of time ) to the delivery of final merged/fused image products can be improved, making the image products be readable and usable for end-users with the particular requirements of fast response, which is very important and key issue, to which attention should be paid continuously.

Take the flood and waterlogging monitoring by satellite remote sensing in 1988 as an example, the effectiveness of satellite Earth observation technology was proved in respect of fast response of flood and waterlogging monitoring, i.e. goals of timely understanding of overall flood and waterlogging situation, accurate analysis after floods, dynamic monitoring construction of water conservancy facilities; forest drainage areas, preservation of water and soil were achieved. It is pointed in this paper that in order to achieve the above mentioned goals actually, under the realistic conditions of our country, the construction of multi-satellite Earth observation data receiving and processing systems must be intensified.

In this paper, it is taken as an example how China RSGS, the only one civilian satellite remote sensing station, functioned during the flood and waterlogging in 1998. analysis was made, taking in to account the key technique an system requirements of multi-satellite observation, data receiving, processing and correction, data fusing, and production of final image products. An idea of further integrated system construction to meet the requirements of flood and waterlogging mitigation and prevention is presented.

1. Foreword
Along with the very fast development of system of Earth observation technology, continuous improvement of satellite Earth observation operational systems , improvement of performance of sensors an there are more kinds of sensors, satellite Earth observation technology is playing more and more important role in areas of environment, resources, etc., and more concerns are shown by all sides of the society.

Take the fast response to flood and waterlogging monitoring as example, satellite Earth observation technology can play role in respect of

1. Timely understanding of overall flood and waterlogging situation.
2. Quick evolution and accurate analysis of flood and waterlogging.
3. Dynamic monitoring of construction of water conservancy facilities, forest drainage areas, and preservation of water and soil.

In order to play important role in the above mentioned three areas, especially if the firsts tow areas are concerned, the called time effectiveness and " regional characteristics " , i.e. to meet the requirements of cover given regions at given time are very important, and they are key points. Even for the first item. Which is not very critical in respect of time effectiveness, there are restrictions of seasons of low water season of water rising, raining season, or drought seasons. If guarantee of time effectiveness concerned, especially guarantee of time effectiveness during flood waterlogging application, it is a weak point of optical sensors.

When we start ot consider practical situation and take the fast response of flood and waterlogging monitoring to be implemented by a business operational system, we must analyze the problem in more details; is the problem of fast response to flood and waterlogging monitoring resoled, if we have got SAR satellites operational ? Besides factors, such as band selection, polarization, a and interference, which we are not going to discuss in this paper the key point is the length if interval of revisit time. Of course, from here, a great many of suggestions can be proposed, for example, if a constellation of 4 SAR satellites =, transmitting images of 100km width is operational, due to the feature of data acquisition of all weather and for all time of day a given place can be revisited one to two times per day.

If we consider the problem in more depth, it will be required , for whatever plan adopted, that the satellites and their sensors must be reliable. Their abnormality cannot appear quite often due to problem of technology, planning, and administration. It is so called commercialized operation . as pointed in [4], commercialized operation reflects a responsible commitment in respect of product delivery , quality control, turnaround time of products, technical services, etc.

If we consider the problem more comprehensively , we also need ground receiving and processing system, the capability of which can match that of the satellite observation . of courser, the system should not be abnormal due to any problem of any technical component, planning, and management.

2. Operational system and operation of system.
" Operational system and operation of system " includes tow aspects of a business engineering operational system : stability and reliability , and effectiveness . a system of high " Operationalizaiton " is a basis of reliable operation while high level of operation techniques is a guarantee of reliable operation. The combination of high system " Operationalization " and high level of operation techniques is the necessary condition of technical support to meet the requirements of fast response to flood and waterlogging monitoring etc.

The operational characteristics of a system are first of all reflected on the capability of uninterrupted, stable, and reliable operations with a meaning of being industrialized. From the stand point of view of technology, included are factors of various components of the system, such s the value of mean time between failure over a long period of time, reasonable configuration, design with redundancy, capability to fix problems, etc. second, for an operational system, quality control must be there to ensure quality of its products. What more important is, an operational system must also ensure that, in the entire work procedures, all of the links in the process must match and coordinate with each other orderly, so as to increaser the work efficiency of the entire system .

Take the work of China RSDS for flood and waterlogging monitoring in 1998 as a n example for the first step, our station achieved to cover a given are with a revisit period of 3-4 days, and we spent 4 hours (including 1.5 hours to transport the tapes ) totally to have digital products produced ( the data volume of one Scan SAR to be processed is 1 G Bytes ), beginning from the start of receiving image data. it took 6 hours to completer a digital product of an image merged with a TM and a SAR image, or merged with images of different times. it took 10 hours ot produce a large frame photographic composite product. Thereby, near real time services was implemented for different levels of products. It was implemented for different levels of products. It was achieved not only because there was an existing commercialized operational RADARSET, but also because there was an entire set of ground operational system, beginning from data planning to data distribution .

Earth observation is a kind of information industry by its nature. Its basic feature is : providing valuable information products to various departments of industries for daily use . where main factors, for the technical system to be qualified as an industry, are: " being operationalized ", of daily use, and the products are valuable " Operationalizaiton " is the basis, support, and it is of the nature of input, while the characteristics of daily use and the value produced by the system, are output, contribution, and reward . flood and waterlogging monitoring is one of the application of Earths observation. In particular time periods, it is required to use daily information, reflecting flood and waterlogging, that is to use valuable satellite images, while operational radar satellite technical system constitutes service system. This is also the fundamental reason, why the flood and waterlogging monitoring in 1998 was successful .