The ASTER Ground Data System (ASTER GDS) is the ground system which performs the ASTER instrument operations,and does the data processing, archiving, distribution, etc., of ASTER data.
ASTER is the sensor mounted on EOS (Earth Observing System)- AM1 (renamed TERRA), the first platform of the Earth observation program from space (EOS program) which the National Aeronautics and Space Administration (NASA) promotes. TERRA is scheduled to be launched in 1999, in a sun-synchronous orbit, and passes the equator from north to south at 10:30 in the morning, local time.
The mission operation of TERRA, reception of data from the satellite, and the data transfer to Japan will be done in the United States. Therefore, close cooperation with NASA/EOSDIS (Earth Observing System Data and Information System) and GSFC (Goddard Space Flight Center) is needed for the operations of the ASTER GDS.
The necessity of solving some intrinsic technical problems different from the ones of past sensors arose for ASTER, because the performance of the spectrum decomposition and the S/N comparison, among other things, were improved. Therefore, the method of processing the data and the operation of the sensors are more complex than that of previous ones. Since there is a plan to accept not only data processing requests from the users, but also observation requests, the function of the ASTER GDS is large-scale.
ASTER GDS consists of three segments:
AOS (ASTER Operation Segment)
mainly performs the ASTER mission operation and monitoring the status of the ASTER sensor;
SDPS (Science Data Processing Segment)
provides the interface and controls of processing, analysis, archive and distribution;
CSMS (Communication and System Management Segment)
is responsible for networking and controls of the two segments mentioned above.
In addition, each segment is composed of some units (subsystems). This structure is almost identical to that of ECS (EOSDIS Core System) in EOSDIS, the ground system of the United States corresponding to the ASTER GDS of Japan.

Purpose of ASTER GDS

To process the data to contribute to the understanding of global environmental change (warming, desertification, destruction of the ozone layer, acid rain, and mineral research), in addition to geological research and natural resource exploitation.
To perform mission operations which reflects user requests regarding the data acquisition of the ASTER sensor.
Public data distribution of the ASTER data.
To establish interoperability with the United States EOSDIS.
The purpose of ASTER is to contribute to the profound understanding of local and regional scale phenomena, on and around the land surface. Some specific purposes are shown below:
(1) To promote research of geological phenomena, the history of the earth's crust, and topographic history; through detailed mapping of topographic and geologic features of the earth's surface This includes contributions to applied fields, such as resource investigation.
(2) To investigate the distribution of vegetation and its change.
(3) To elaborate the understanding of the interaction between the earth's surface and atmosphere, from an increased understanding of the distribution of the land surface temperature.
(4) To evaluate the influence of the discharge of volcanic gas into the atmosphere through monitoring of volcanic eruptions.
(5) To contribute to the understanding of the characteristics of aerosols in the atmosphere, and the classification of clouds.
(6) To contribute to clarifying the role of the coral reef in the carbon cycle, through an increased knowledge of coral reef classification and its global distribution.
Of the above, the first one should have the most emphasis.
The development project of ASTER GDS began in fiscal year 1994. The period of the development project lasts until the initial operations test following the launch of TERRA in fiscal year 1999.
Fiscal year 1994
Preliminary design
Fiscal year 1995
Detailed design
Fiscal year 1996
Development of each segment
Fiscal year 1997
Integration and test with the segments, the system, and the instruments
Fiscal year 1998
Test with U.S. and operation preparation
Fiscal year 1999
Initial operation test after the launch of TERRA
The operations project of ASTER GDS is scheduled to start in fiscal year 1999.
It is planned to operate for six years after the launch in December, 1999.

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Functions of the ASTER GDS are listed below.
Accepting the data acquisition requests:
Accepting acquisition requests from the users (domestic and overseas, except users authorized by NASA);
Accepting data acquisition requests from the users authorized by NASA through the IMS (Information Management Subsystem) of EOSDIS (EOS Data and Information System);
Operating the ASTER instrument:
Scheduling the instrument observing periods for data collection, and making the STS (Short Term Schedule) and the ODS (One Day Schedule);
Monitoring and archiving HK (housekeeping) data from electronic or physical media;
Analyzing the ASTER instrument status;
Supporting the Science Team with equipment operation, planning and supervising;
Data processing, archive, and distribution:
Receiving Level 0 data (electronically and by physical media);
Processing Level 0 data to Level 1A;
Processing and archiving of Level 1B and higher level products, based on user requests;
Sending back L1A and L1B data to the EDC DAAC;
Distributing the data based on user requests;
Retrieval of data and distribution of browse data;
Correspondence regarding changes in the processing algorithms;
Archive of the data for 20 years;
System management:
Performs network diagnosis and invokes contingency actions, when necessary;
Self-diagnosis of the system;
Managing information concerning the ASTER GDS, and performs the data exchange with the SMC (System Management Center);
Supporting software production:
Supporting specific users to generate processing and analysis algorithms and software;
Supporting specific users to analyze and process the data.
The ASTER GDS is configured with the following 3 segments and 8 (10) subsystems (units)

Diagram of the ASTER GDS structure

CSMS (Communication and System Management Segment)
GSMS (Ground System Management Subsystem)
GDS system management, monitoring, coordination and contact with the SMC.
ADN (ASTER Data Network)
Basic communication and network function.
AOS (ASTER Operation Segment)
ICC (Instrument Control Center)
Planning of instrument mission operations, and monitoring and analyzing the instrument status.
IST (Instrument Support Terminal)
Supports the SSSG in making their decisions during the above-mentioned planning.
SDPS (Science Data Processing Segment)
IMS (Information Management System)
Offers standardized access screens, DAR and DPR requests, and product search
DADS (Data Archiving and Distribution Subsystem)
Effective control, archive, and distribution of products and other data
PGS (Product Generation Subsystem)
Performs the generation and quality check of the products
SISS (Software Implementation Support Subsystem)
Supports the development by science users, and production of special products
DRS (Direct Receiving Station)
Onsite direct receiving facilities for direct downlink data, including antenna
Houses the antenna control and X-band data reception function
Performs Level 0 data production
Contains interface equipment on the GDS site to the DRS facilities.
The ASTER instrument observation time is limited to approximately 8 minutes per orbit. Therefore, 780 scenes of the ASTER data will be sent to the ground every day. Along the lines of the EOS Program policy, Japan, the instrument provider, must perform Level 1 processing (including geometric and radiometric correction) within 24 hours. To do this, a system to process huge amounts of data at high speed is being developed.
An outline of the ASTER GDS configuration is explained in the previous sections.
Level 1 processing is performed only on those scenes requested by users. The ASTER GDS and EOSDIS of the United States share the work of production processing of various higher level standard products produced from the Level 1 data.In addition, processing of semi-standard products and special products are done independently by Japan and the U.S.
Standard Product List
Products No. Standard Data Products
1A Reconstructed unprocessed instrument data 780
1B Radiance registered at sensor 310
2A02 Relative spectral emissivity (D-stretch) 0
2A03 Relative spectral reflectance (D-stretch) 0
2B01 Surface radiance 10
2B03 Surface temperature 10
2B04 Surface emissivity 10
2B05 Surface reflectance 10
Semi-Standard Product List
Products No. Semi-Standard Data Products
Production Japan
3A01 Radiance registered at sensor with orthophoto correction 30
4A01 Digital elevation model(Relative) 30
EOS Data and Operations System (EDOS)
EDOS sends the ASTER Level 0 data by physical media and electronically to ASTER GDS.
EROS Data Center (EDC)
EDC receives ASTER Level 1 data from ASTER GDS.
EOS Operations Center (EOC)
Receives the One Day Schedule (ODS) and sends the commands for the EOS satellite and the ASTER instrument.
This system and the operation team who run it are called the Flight Operations System (FOS) and the Flight Operations Team (FOT), respectively.
System Management Center (SMC)
Information is exchanged with the CSMS segment at the ASTER GDS.
Sends electronically the expedited d sets to ASTER GDS.
EOSDIS Core System (ECS)
Except for EDOS, the above-mentioned systems are developed by the ECS. Also, each data center is called a DAAC.

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