Upper-air sounding systems have historically been designed as closed systems, where the receiving equipment on the ground operates only with radiosondes designed specifically for it. The key benefit is that these systems are completely integrated in order to optimize performance. The primary disadvantage is that once the ground station investment has been made, users must work with a sole-source supplier of disposables. This eliminates competition for sonde re-orders and can lead to unacceptably high operating costs. Users may also be required to continue purchasing a specific radiosonde model that has become obsolete.

With upper-air soundings already representing one of the highest cost operations for budget-constrained met services, the high cost of disposables has contributed to shutting down some synoptic sites with the resulting gaps in global data.

International Met Systems has adopted an open, or "universal" system philosophy in its 1680 MHz RDF ground stations that allows them to track any sondes produced by co-operating manufacturers. By opening up the ground station, InterMet allows operators to purchase long-lived ground equipment without being locked into any one manufacturer’s disposables.

In August of 2004, InterMet installed an IMS-1600B system in Dar es Salaam, Tanzania as part of the WMO program to close the gaps in the global upper-air observing network. This system can fly InterMet, Sippican and Modem radiosondes including 1680 MHz GPS models. With this installation, the Tanzania Meteorological Agency will have complete flexibility in future years deciding what type of sondes to fly and where to buy them.

In India, the InterMet IMS-1500 has allowed the India Meteorological Department to fly the locally produced MK-IV radiosonde as well as Sippican and InterMet sondes. The ground station will also be able to readily accommodate the IMD MK-V sonde currently under development.

This paper presents the technological challenges of developing the Universal System and discusses both the advantages and drawbacks of this approach. Preliminary data from the Tanzania installation will be included.