15 min. and are within reception range of a PTT for an average of 10 min. during each 

 pass. The Argos system is administered by Service Argos which charges users by the 

 number of days it collects data for each PTT. Information is retransmitted immediately 

 and also stored on the satellite for later transmission to earth stations. The re- 

 transmitted information can be received by local user terminals (LUTs), and positions 

 can be calculated immediately. The stored information is downloaded from the satellite 

 to one of three ground stations and then sent to the NOAA Data Concentrator in 

 Suitland, Maryland before going into the user-accessible Service Argos computer. 



Data were retrieved from Service Argos with an IBM PC-compatible computer 

 and modem. In general, Argos-acquired locations were available within 3.5 hours of a 

 satellite passing overhead. Because there is a LUT at Wallops Island, Virginia, which is 

 part of the Argos system, some locations were available within 20 min. of a satellite pass. 

 We also obtained monthly backup summaries from Service Argos on floppy disks. 



Service Argos locations are categorized by location accuracy, which increases as 

 the number of messages received and the time between the first and last message 

 increases. Argos-determined location accuracies vary from unknown to ±_ 150 m. 

 Table 1 summarizes the location class requirements and accuracies. 



Table 1. Accuracy and required conditions for Argos location classes. 



