The National Weather Service (NWS) is developing the Radiosonde Replacement System (RRS) to replace its antiquated Microcomputer Automatic Radio-theodolite (Micro-ART) system, which has been in operation since the late 1980s. The RRS is comprised of a new Global Positioning System (GPS) tracking antenna referred to as the telemetry receiving system or TRS, 1680 MHz GPS radiosondes, and a new NT-based workstation. In addition to the deployment of the RRS, a new surface weather observing system and precision digital barometers will be deployed at 102 locations from the Caribbean to Guam and from Alaska to Pago Pago, American Samoa in the Southern Hemisphere.

The figure below delineates the RRS configuration as it will be deployed at NWS field sites. The basic system components include: the Telemetry Receiving System (TRS), interactive workstations where upper air data is collected, processed and World Meteorological Organization (WMO) TEMP messages are prepared and disseminated to the meteorological community and the public; The RRS communicates these products through an interface to the Advanced Weather Interactive Processing System (AWIPS) for transmission to the external community.

To meet the continuing requirement of a broad base of users for atmospheric sounding data, the NWS will replace its entire current upper air network with RRS to:

Comply with Congressional direction to reduce the use of radio-frequency spectrum and implement the Federal Communications Commission’s (FCC’s) plan to vacate the 1670-1675 MHZ frequency band,

Maintain or increase system availability and data accuracy,

Require less operator interaction and maintenance,

Provide a complete high-resolution data archive to users,

Provide consistent and accurate measurement of surface weather parameters at the point of balloon release using the Radiosonde Surface Observing Instrumentation System (RSOIS).

Increase amount of data provided to users (at 1 second resolution or about every 5 meters through the atmosphere).

One of the major features of the RRS is its use of state-of-the-art GPS radiosondes operating in the 1680 MHz radiosonde frequency. Until recently, commercial systems/radiosondes sold around the world were based on the 403 MHz frequency. Unfortunately, this band is very congested with thousands of licenses already issued. The NWS has been using the 1680 MHz band with its Radio Direction Finding systems, almost exclusively, for over 50 years with minimal interference from other users. The NWS decided to require radiosonde vendors interface their GPS signal processing with the 1680 MHz frequency radiosonde as part of the RRS. This caused a number of technological challenges for the commercial vendors. Sippican® has developed operational radiosondes of this new design. One significant impact this radiosonde will have on operations will be changes to sensors for temperature, pressure, and relative humidity measurements, which have differing characteristics than current radiosondes fielded.

Upper-air Operations

The radiosonde is prepared for flight in the weather office where the Workstation is located, and released at the inflation shelter. As the radiosonde transmita data, the TRS tracks the signal and sends it to the Signal Processing System (SPS), which is furnished by the radiosonde vendors. The SPS then decodes the transmitted radiosonde telemetry to recover the meteorological data, and compute pressure, temperature, humidity and winds.

During the radiosonde flight, the Workstation continuously monitors the course of the flight. The design of the RRS maximizes data acquisition capabilities whether the radiosonde is at low level elevation angles, or at the zenith relative to the ground receiving antenna. The Workstation displays tabular and graphical radiosonde flight data to aid the operator in evaluating the accuracy, completeness, and consistency of the meteorological data. The operator may delete or edit data, or choose to perform another flight. RRS then generates upper air coded messages for transmission to data users.

The first software build (Build 1) will provide the standard WMO messages. Later builds may include a high resolution (i.e., 1-sec.) real-time data product in the BUFR format.

In addition to the standard archive data set produced today for Micro-ART, a high resolution data archive will also be generated and electronically sent to NCDC. The plan is to use the BUFR format to produce this high-resolution data set of the upper air parameters. When transmitted to NCDC, it will provide researchers and other users of upper air data a complete summary of the data collected and flags for data inconsistencies. Of special interest, will be the high resolution winds calculated from the GPS data.

The RRS will be deployed in a phased approach starting with first article production units and followed by full production to the remaining 102 locations. Implementation of the first system occurred in August, 2005, and the current plan is to have between one and two systems deployed per month, depending on funding.