|Argos Newsletter N° 52 - July 1997|
Stanley M. Tomkiewicz, Jr.
Director, Environmental Programs
The effect of Argos system enhancements
Our firm includes approximately 100 engineers, technicians, and field support specialists engaged in developing fully integrated systems for data transfer, acquisition, and processing through the use of state-of-the-art micro-power and micro-miniaturization techniques. Our laboratory is located in Mesa, Arizona. We work extensively with the research community to provide information on technical advances, and to develop new products and applications which help researchers balance study goals with their critical budget and time considerations. We have been developing technologies associated with the Argos system since the late 1970s.
Over the past 20 years we have watched the Argos system develop from a system designed specifically for collecting meteorological and oceanographic information to a system also utilized extensively by wildlife professionals on a worldwide basis to track and recover data from free-ranging wildlife. To accommodate the wildlife community, the system had to develop specific processing and dissemination approaches which accommodate the requirements of the wildlife field. In addition, modification of Argos PTT (transmitter) specifications have been made to accommodate low power, micro-miniaturized "smart" Argos PTTs which can be successfully used to track and study a variety of wildlife species. Although many early Argos ptts were suitable only for large animals, new ptt designs now exist and units in the 30g weight range allow for tracking of relatively small birds.
Several enhancements to the Argos system have been proposed, or are now being implemented, which will aid most users and which will have a very positive and significant impact on wildlife studies. Among the notable improvements are the deployment of a new satellite receiver with increased sensitivity, deployment of the Argos satellite receiver on additional satellites, and the possibility for a specialized low power band to be used with PTTs which have power output of less than 300 mW (into a 50 ohm antenna). All of these enhancements should make tracking wildlife easier, increase the number of species which could be tracked with the system, and increase the operational life of ptts deployed on wildlife.
PTTS deployed on wildlife are unique among Argos PTTs.A series of special problems face researchers attempting to apply this sophisticated technology to a free-ranging animal. First, these units are among the smallest Argos transmitters deployed. Consequently, these ptts must be powered by very small battery subsystems which can support only relatively low power transmissions. To further reduce power consumption, duty-cycling is often critically important to obtaining a reasonable and adequate operational life for the ptt. Further, since these Argos transmitters are placed on the animal as part of a collar, backpack, wing mount, or implant, the antennas are of necessity simple and generally detuned by the presence of the animal's body, the result of which are antennas that are poor radiators.
Under the proposed sensitivity enhancements for the Argos satellite receiver, units with small batteries and poor antennas deployed on wildlife should have greater success in achieving a link with the satellite. Further, additional satellite overpasses (a result of having the receiver on board additional satellites) can effectively reduce the required "on air" time for obtaining position fixes. This is especially important in wildlife applications where battery capacity is extremely limited and long operational life is often required. Another benefit to having the additional satellites carrying the Argos receiver is that they will help fill in the time periods when the noaa satellites are not overhead. The result is more continuous coverage over the 24-hour period.
One additional enhancement under consideration which holds promise involves utilizing a specialized frequency band for low power transmitters. The separation of units based on power level could help prevent the low power units with limited antennas from being masked by higher power 1 watt units, with efficient antennas. In general, these enhancements will allow studies which were impractical a few years ago a means to become operational in the near future.
Also among the future proposed system enhancements is the utilization of the two-way communication system which essentially allows the user, through a satellite down-link, to communicate with the transmitters. This feature allows commands to be issued to the transmitter after deployment, such as turning the unit on and off, and/or reprogramming duty-cycles or data collection schemes. Although the exact specifications for the receiving system have not yet been completely determined, a two-way system is more likely to emerge in the oceanographic and meteorological fields first. The additional circuitry and antenna requirements necessary for the system will increase ptt size and complexity of the unit for the foreseeable future initially making it impractical for use in the wildlife field.
The technological constraints associated with this early receiver may preclude putting them on board Argos ptts designed for animals. As with all technologies, maturation and miniaturization often go together and at some point in the future it may be possible that Argos PTTs, including a downlink receiver, can be incorporated in specific wildlife applications.
In general, then, these enhancements open the door to the further development of wildlife applications using the Argos system, which is today the only practical satellite system available to monitor and track