The ERS-1 programme has been designed to serve a large variety of users with a comprehensive range of products and services. In response to this and other very challenging mission objectives the ERS-1 ground segment has been established using a systems approach.
The ground segment consists of an ensemble of facilities responsible for the acquisition, processing, distribution and archiving of the satellite data and of the derived products. Several factors have influenced the design of the ERS-1 ground segment:
The characteristics of the ERS-1 space segment in terms of its multi-sensor payload, orbit configurations and power requirements have imposed the implementation of a network of ground stations around the world to acquire the high bit rate SAR data (for which only direct readout is possible). In addition facilities have to be provided to permit the down-loading, once per orbit, of the on-board recorded low bit rate data.
Specific user requirements have called for the implementation of specific processing tools and fast delivery services at the ground stations operated by or for ESA to allow user centres to be furnished quickly with selected data products.
An important feature of the ground segment concept is that various user interfaces are considered key components. In practice the Central User Service (CUS) of the EECF will constitute the primary user gateway to the system.
Products will be disseminated either via fast delivery of selected products to nationally nominated user centres for operational applications or by off-line delivery to individual end users from the PAFs.
Data Acquisition and Fast Delivery Product Processing
ERS-1's orbit and the need for direct read-out of the SAR telemetry have necessitated a global network of ground stations, either within the ESA network or made available by national (ESA member) or foreign (non ESA members) entities. The ESA network, which has been established to ensure the acquisition of global LBR data and regional SAR data over Europe, consists of:
It should be noted that LBR data cannot be recorded on-board, while previously recorded data is being replayed. Therefore, during this period the LBR data is directly transferred. The instrument data is sent to the PAFs for archiving and off-line product generation - the SAR data and FD products directly, the LBR data via Fucino, where they are transcribed onto optical disks.
Data Dissemination FacilitiesERS data will be disseminated via various facilities at transmission and reception sites within the ground segment using satellite and telecommunication links. The low-rate fast-delivery products (LBRFDP) generated by the ESA ground stations will be centralised at the EECF (on the ISS) and re-distributed to nationally nominated user centres via standard land lines. An alternative of using a satellite link at low rate, e.g. 64 kbits/s, for quick dissemination, at least in Europe, is also being considered. One of the ERS-1 mission objectives is to provide to the user community FD products from ERS-1 within three hours from instrument observation. The nominal solution for the distribution of FD products distribution system, is using public network land lines. However, for the distribution of SAR products the capacity of the landlines is insufficient and satellite links are deemed necessary.
The Broadband Data Dissemination Network (BDDN) system is designed to transmit high rate FD products (HBRFDP) from Fucino, Kiruna and possibly Maspalomas ground stations to nominated receiving stations by means of a satellite telecommunication channel. Sources outside the footprint of the satellite will first transfer data to a suitable site within the footprint by appropriate point-to-point connections, e.g. land lines, packet switching networks etc. The Gatineau ground station will receive data through the dedicated line between the EECF and Canada. The EECF is connected with the other ESA Ground Stations and appropriate user centres via low speed land lines or equipment connections. Both Kiruna and Fucino ground stations are equipped with a SAR FD processor and with monitoring and control sub-systems for FD products distribution. In addition the stations will be connected through standard low speed lines with the EECF for schedule and control purposes.
Processing and archivingAs described above there are four PAFs:
A summary of the off-line products to be generated by each of the PAFs is shown in the figure and the services offered by each PAF are listed below it.
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