Operation Concepts and Requirements for Image Receiving Processing and Distribution System-Towards 300 Mbps Down-Link Data Rate and 1m Resolution

Taejung Kim, Young-Ran Lee, Min Nyo Hong, Tag-Gon Kim**
Remote Sensing Research Division, Satellite Technology Research Center
**Department of Electrical and Electronic Engineering
Korea Advanced Institute of Science and Technology
373-1 Kusung-Dong, Yusung, Taejon, KOREA 305-701
Email: tjkim@krsc,kaist.ac.kr, yllee@krsc,kaist.ac.kr, mnhong@krsc,kaist.ac.kr

Abstract.
As civilian remote sensing satellite programs are being professed rapidly, the roles of ground stations are increasing. In this paper, we describe an on-going work on the development of a new image receiving, processing and distribution system. This system aims for satellite image data at 1m resolution and transmitted at over 300 maps. Finally, we introduce existing image receiving, processing and distribution systems and discuss current trends of such systems. We then discuss operation concepts a new system should adopt and system requirements to implement such concepts. We describe our current design work for the new system in terms of the system context and operation design.

Introduction
In this decade, we have seen rapid technical advancements on civilian remote sensing satellites and sensor development. A number of high resolution remote sensing satellite program's is now being carried out, Such programs include the acquisition of 1m resolution spaceborne imagery, which used to be for military or reconnaissance only [ASPRS, 1997].

For the success of such programs, the roles of ground stations are important. A ground station must provide an efficient link between the spacecraft and image data users. Its roles can be divided into four major categories, image reception, image processing, image archiving and image distribution. For image reception, a station is required to track, receive and demodulate data signal from a satellite; retrieve image data from the signal; and store the data into appropriate media. For image processing (or pre-processing), a station is required to rectify image data to eliminate radiometric and geometric distortions inherent to the data. For image archiving, a station needs to handle a large quantity of image data in an efficient and reliable manner. For image distribution, a station must provide a tool for image data users to search for any images they need, to order image products and to have such products delivered to them as quickly as possible. 

With the emerging high resolution satellite programs, the roles of ground stations have also increased rapidly. New high-resolution satellites demand larger processing powers and data storage capacities of a ground station. At the same time, a ground station is required to have flexible equipment configuration to allow "smooth" upgrade for the reception of new satellite image data [Dti, 1995]. Data users need faster access of data archived at a ground station. They also prefer user friendlier environments for data search, product order and delivery. All of these are, in fact, challenging.

In this paper, we describe work on the development of a new image receiving, processing archiving and distribution system being carried out at author's affiliation. This system aims at receiving satellite image data transmitted at over 300Mbps; archiving and managing over 100 Tbytes of image data; and geo-referencing and rectifying images at 1m resolution. This work is still on going at the time of writing and we concentrate on the result of operation design and requirements study.

First, we introduce existing image receiving, processing, archiving, and distribution systems manufactured by commercial companies and discuss main features of such systems. We then discuss operation concepts a new system should adopt and system requirements to implement such concepts. We describe our current design work for the new system in terms of the system context and operation design. 

Overview of existing systems
There are a number of systems developed for receiving, processing and distributing spaceborne image data. Table 1 summarizes the most recent and representative products among them. The table figures each system in terms of maximum data rates for reception, frame synchronization scheme, main computer, catalogue generation and search and archive media.

Maximum data rate is a measure to describe how fast a system can receive and store signals from the spacecraft. Most systems aim at the data rate which 1m resolution satellite transmits its image data1. Frame synchronization is a produce required to retrieve image data from the signal received and to store the image data into storage media [SPOT Image, 1997]. This is a measure to describe the flexible of a station to allow "smooth" upgrades for reception of new satellite image data. If this is done by software control, the upgrade should be done without purchasing new (expensive) hardware components. As shown in the table, most systems adopt software control scheme for the flexibility. There seems no unified solution for selection of main computers.

An on-line catalogue search tool is important for users easy access to image data archive. Interestingly, there are several systems that do not have built-in on-line catalogue search tools. Such systems may employ search tools provided by third parties. There is a trend of using disk arrays for real time storage and DLT or D1 tapes for permanent archive.

Table 1. Characteristics of existing spaceborne image receiving, processing and archiving systems.

Vendor(Nationality)	Max. data rate	Frame sync. Scheme	Main Computer	Catalogue generation & search	Archive media
Dti(USA)	~ 170 Mbps	Software control	SUN SPARC 20	Unspecified	Disk Array->DLT
MDA(Canada)	~ 170 Mbps	Software control	SGI Challenge 10000	Automatic Generation Web-based search	Disk Array->DLT
Matra/SPOT Image (France)	~ 160 Mbps	Software control	Digital Symmetric Multiprocessing	Unspecified	Disk Array - > Tape
ASC (Canada)	~ 200 Mbps	Hardware control	Unspecified	Web-based search	Tape
IAI (Israel)	~ 87.5 Mbps	Hardware control	Unspecified	No search Tool	D1
ACS (Italy)	Unspecified	Software control	SGI Challenge Server	No search Tool	Disk Array - > D1/DLT
Anite (UK)	Unspecified	Software control	SGI Challenge Server	No search Tool	Disk Array - > DLT
Vexcel (USA)	~ 180 Mbps	Software control	UNIX W/S 256 Mb Memory	No search Tool	Disk Array - > DLT

Operation concept and requirements for a new system
So far, we have summarized existing systems. Most of them are aiming at 1m resolution satellites and designed to increase the flexibility. However, we feel there are several other aspects to consider. We state our operation concepts or principles of a new image receiving, processing, distribution, system and requirements of such a system to meet the principles.

A system or a ground station needs to be operated according to the principles of user friendliness, fast processing, reliability, easy maintenance, cost effectiveness, flexibility and security. 

For user friendliness and fast processing, a system should be designed to automate as many components as possible. Data users should be able to generate product orders on-line and such orders be executed automatically. Catalogue generation should also start automatically after reception of image data. There should be a tool to aid image acquisition planning in advance, which most existing systems do not possess. In particular, authors feel this tool is very important since most ground stations do not merely receive image data but "request" image acquisition to a spacecraft control station. Currently such tools very limited and nor not user friendly. 

For reliability, a system should be designed to check validity of operators' or users' input and perform corrective actions. A system should also provide means to monitor its status, current processing jobs and the quality of image data being processed. A system may be designed to have redundancy at the expense of cost. 

For easy maintenance, a system should produce and maintain a history of operation. Archives and back ups should be carried pout periodically without operators ' intervention. For cost, effectiveness, among others, a system should be operated such that it processing power is scheduled and distributed efficiently and its storage devices and archive media are maintained economically. For flexibility, a system should be designed for easy upgrade and easy modification. As other existing systems, frame synchronization should be done by software control. For security, a system should have a mean to prohibit unauthorized access. 

Current Work
After the definition of operation concepts of a new system and brief definition of system requirements, we have performed thorough system operation design and requirements study. The new system is for 1m resolution satellite transmitted at 300 Mbps down link data rate. The new system shall be operated in the system context in Figure 1. 

The system will receive image data from the spacecraft at 33 Mbps down link rate. Users will generate on line orders and the system will provide output to users. Output will be delivered on line for some users and off line for others. The system will issue image acquisition requests with the aids from an acquisition planning tool and a satellite control center will confirm the requests. The system may acquire auxiliary data, such as ground control points, from unnamed data sources. 



The system shall have nine major operation processes of catalogue search and order generation, order management, image acquisition planning, image reception, image archiving, catalogue generation, image pre-processing, value added processing and output handling. We have combined series of these processes and defined them as operational scenarios. According to users' orders the system shall be executed automatically as defined in the scenarios. In particular, we have included value added processing in the processing chain of scenarios since this process may be one of the major tasks for 1m resolution imagery.

Conclusion 
So far we have described the work being carried out at authors' affiliation for the development of a new image receiving, processing and distribution system for 1m resolution spaceborne imagery transmitted at 300 Mbps down link rate. Since this work is on going, we concentrated on the description of operation concepts and system requirements of the new system. We also provided a brief review of existing systems and our operation concepts.

Since a number of remote sensing satellite programs are being carried out and more will start in near future, the roles of ground stations shall be emphasized. The operation concepts and system requirements stated here, we hope, can help when designing such stations. 

Acknowledgements
The work described here is supported by the Ministry of Science and Technology of the government of the Republic of Korea. 

References

• ARPRS, 1997, Proceedings of Land Satellite Information II
  
  
• DTi, 1995, "OPEN 2000 Remote Sensing Satellite Data Acquisition Facility" , Proposal No. B0101
  
  
• SPOT Image, 1997, SPOT to Direct Receiving Station Interface Document", S-IF0/E-10-SI, Appendix 1, section 3.1.3.2