Updated: 07 Mar 2005
TERSS Technology
The TERSS data acquisition facility is remotely-operated. It does not require personnel to be on-site to position the antenna dish correctly to capture data from passing polar-orbiting Earth resources satellites. This means the facility operates at a lower cost than manned stations thereby allowing further investment in the technology.The software that drives the automatic data capture was developed by the CSIRO in Hobart. An upgrade developed by ACRES supports downlinks from Landsat 5, Landsat 7, as well as ERS 1 and 2 and RADARSAT 1.
See the automatic data capture system diagram.
TERSS technology can be divided into five areas:
Antenna and Control System
The primary reflector and feedhorn support structure was supplied by AOTC. It is a version of a standard 9 metre communications antenna with modifications to lighten it and adapt it for use with a full motion tracking system. The primary reflector and subreflector are shaped to provide an aperture efficiency of 75%, giving a gain of about 56 dB at X-Band.Data Acquisition and Control System (DACS)
Conventional remote sensing ground stations use high density digital tape recorders (HDDRs) for data acquisition. The resulting high density tapes (HDDTs) are used as the archive media and for data exchange purposes.TERSS is configured to directly record data to disk during satellite reception. Once reception is complete, this data is written to digital linear tape cartridges for transfer to ACRES. This approach has advantages compared to the use of HDDTs. The advantages include reduced capital and operating costs, higher reliability and operational convenience. In particular, this model allows a high level of automation of ground station operation, one of our design goals was that the ground station can operate unattended for several days at a time.
Downloading time for completed reception from disk to DLT is in the order of half an hour.
Data Cataloguing
TERSS acquisitions are processed via accelerated acquisition cataloguing, a system developed by ACRES. This means that, not only the usual data sets for Landsat 5 TM, but also browse and metadata for Landsat 7, and the SAR data sets of ERS and RADARSAT will be available in the ACRES on line Digital Catalogue within 4 hours of the acquisition of the pass. This applies to business days only, weekend and public holiday passes are available by noon next working day.Data Storage System
Once a reception is completed and offloaded onto DLT, it is shipped to ACRES Data Processing Facility at Bruce in Canberra. On arrival at ACRES, the DLT is logged and then stored in the archive.Mission Planning
The mission planning for data acquisition from the TERSS antenna is carried out by the ACRES Satellite Operations Services (SOS) section in Canberra. Customers submit programming requests for TERSS data well in advance of the overpass date. In addition to acquiring client requested areas ACRES has its own background program to acquire TERSS coverage for its archive for public interest purposes. These two requirements have to be met using software tools to analyse and model the future overpasses and regions for acquisition from the Landsat 5 and 7, RADARSAT 1 and the ERS satellites.Once the ground track location and data times for a satellite are known, the next step is to map the programing requests for each satellite for each day using geographic information systems (GIS) techniques. In this way an "optimum solutions" model can be applied by utilising satellite transmission time, granted by the overseas satellite operators, to achieve satisfactory coverage of programming request areas on any particular day. The end product is a daily TERSS reception schedule that is compiled in advance of the planned overpass day. The reception schedule is often altered in the days proceeding the actual overpass day to accommodate last minute requests or to accomodate changes requested by the overseas satellite operator.