Argos is a satellite-based system which collects, processes and disseminates environmental data from fixed and mobile platforms worldwide. What makes Argos unique is the ability to clearly geographically locate the source of the data anywhere on the Earth utilizing the Doppler effect. Argos was established in 1978 and since that time, it has provided data to environmental research and protection communities that, in many cases, was otherwise unobtainable. The system is fully proven and highly reliable. Many remote automatic weather stations report via Argos. Argos is a key component of many global research programs including: Tropical Ocean-Global Atmosphere program, Tagging of Pacific Pelagics, World Ocean Circulation Experiment, Argo, and others. There are currently 22,000 active transmitters, 8,000 of which are used in animal tracking, and over 100 countries utilize the Argos system. Since the late 1980s Argos transmitters have routinely been deployed on a large number of marine mammals and sea turtles and it continues to serve as the most important tool for tracking long distance movements of both coastal and oceanic species. Through upload of data from, for example, pressure transducers, it has also been possible to obtain a wealth of knowledge about dive and foraging behavior from unrestrained animals in the wild. Argos was developed under a Memorandum of Understanding between the Centre National d'Etudes Spatiales, the National Aeronautics and Space Administration and the National Oceanic and Atmospheric Administration. The system utilizes both ground and satellite-based resources to accomplish its mission. These include:
instruments carried aboard the NOAA polar orbiting environmental satellites, the EUMETSATMetOp satellites, and ISRO satellites,
This fully integrated system works to conveniently locate and deliver data from the most remote platforms to the user's desktop, often in near real-time. Argos is operated by CLS/Argos, based in Toulouse, France, and its U.S. subsidiary, CLS America. Since June 2019, a new subsidiary named Kinéis has taken over operations and plans to launch a constellation of 16U CubeSats in 2022.
Most current day use of the Argos System makes use of one way data transmission on 401.65MHz using Argos 2. Each Argos platform features a unique 28-bit ID and the ability to transmit a short 3 to 31 byte message for each transmission. Each platform is restricted to a specified interval, such as every 60 seconds, allowing for a few hundred bytes total per satellite pass. This is enough to contain a couple elements of GPS coordinates or other sensor data. Argos 1 is no longer supported. One of the most unique capabilities of the Argos System is that it can determine transmitter position using doppler shift on a single satellite. In order to do this accurately, approximately 4-6 transmissions are required in succession during a satellite pass. Accuracy can vary between several hundred meters to several kilometers. Newer versions of the Argos System, called Argos 3 and Argos 4, offer most robust modulations, higher symbol rates, larger packet sizes and interactive data capability. Some near satellites feature Argos 3, with varying degrees of functionality. The Argos 3 system features a new downlink signal at 465.9875MHz. However, due to ground based alarm system interference issues in the United States, the downlink was disabled on the NOAA-19 satellite. Other newer satellites still transmit on this frequency. The downlink contains current date and time, Argos System satellite ephemeris data, and the downlink portion of the newer two-way communication link. Data collected from the Argos System is transmitted to the ground using two possible methods. If an Argos System ground receiving station is in view of the satellite while the transmitter is also in view, the data is transmitted and processed in near real time. If a ground station is not in view or operational, data is additionally transmitted from the satellite to one of several polar based ground stations. This can introduce additional delay in receiving messages.
Satellite Constellation
The Argos System is currently served by 7 polar orbiting satellites at an altitude of 850 km and completes a revolution around earth approximately every 100 minutes. At a vantage point of 850 km, satellites cover approximately 5000 km of earth at any given time. Each satellite was intended to be sun synchronous, with passes almost at the same solar time each day. Although due to the age of some satellites, minor drifting does occur. Due to the satellite constellations polar orbit, 100% of the earth is covered by the Argos System. Since pass overlap increase with latitude, the number of daily passes over a transmitter also increase with latitude.
