06 May 2022
27 May 2020
What is A-DCS
The Metop A-DCS contributes to the Argos worldwide location and data collection system dedicated to studying and protecting the environment. Argos provides environmental monitoring from remote stations, either fixed or mobile, fitted with an Argos transmitter. Sensors on Argos platforms collect data on atmospheric pressure, sea temperature, animal heart rates, alarm management or water level of a river. Data from the Metop A-DCS is provided directly the the Argos centre for onward processing and dissemination.
How A-DCS works
The A-DCS consists of two units, RPU (Receiver Processing Unit) and TXU (Transmit unit). Both contain a nominal and cold redundant sub-system, the selection is made via an RPU interface card, which has a pair of relays for each unit.
The data are transmitted to the user community through the Argos network. Flying the Argos system aboard polar-orbiting satellites provides worldwide coverage.
On transmission of an Argos Beacon the signal is received by the RPU via an antenna (401.650MHz). The RPU, having the ability to process 12 messages simultaneously (three 4,800bps and nine 400bps), converts the incoming signal to an IF signal and ascertains the location of each Data Collection Platform (DCP) or small transmitter using the Doppler Effect (accurate timing allows a location accuracy of between 150–1000m).
The RPU processing software performs the following signal functions: acquisition of carrier, signal demodulation, bit and frame synchronisation, Doppler counting, time tagging, and message formatting.
Once the 12 buffers are full, the RPU encoder commands the data to be transferred to memory ready for transfer to the spacecraft. On receipt of a data transfer request from the spacecraft the data is available for real-time transmission or delayed transmission, as determined by the orbit.
Unlike previous generations, the A-DCS instrument is able to send messages to the users' mobile terminals through its UHF transmitter (TXU, 465.9875MHz bi-phase PM 200 or 400bps). This provides the ability for message acknowledgement, time sync of the beacon, update of the beacon activity profile, and updating of the satellite status/position for the beacon.
The up-link occurs via Argos Master Beacons (Svalbard, Toulouse and Fairbanks). The up-link Argos message is analysed/processed and prepared for down-link by the RPU, which is then transmitted by the UHF transmitter.
This transmission is independent of the satellite operations and has no impact on them, since the down-link is permanent — that means that when there is no message, the down-link contains filler code.
The Argos programme is administered under a joint agreement between NOAA and CNES. The A-DCS instrument is provided under a cooperative agreement by CNES and was developed by Thales Elancourt. Data processing is performed by CLS Argos, Toulouse and Service Argos Inc, USA.
