CONCEPTUAL DESIGN AND FIRST RESULTS OF A DIRECTED BALLOON SOUNDING SYSTEMCecilia M.I.R. Girz and A.E. MacDonaldNOAA Forecast Systems Laboratory Boulder, Colorado
Improvements in weather forecasts for the western half of the lower 48 States can only come through better specification of atmospheric conditions over the eastern Pacific Ocean. Over land, the traditional workhorse of atmospheric observing systems, the radiosonde, provides input to numerical weather models at high vertical resolution (although at low horizontal and temporal resolution). Supplemental wind and temperature data with higher temporal resolution but lower spatial sampling are produced over both land and ocean by commercial jet aircraft along flight routes, and from satellite soundings. The larger area of Earth's atmosphere over the ocean, however, is not as well observed, either in space or in time, as the land areas. A new concept for routinely sounding Earth's atmosphere over oceanic areas is under development at NOAA's Forecast Systems Laboratory (FSL). The Directed Balloon Sounding System proposes to take in-situ observations of oceanic atmospheres by combining sounding balloon technologies developed more 15 years ago with more recent technological advances in electronics and materials. Recovery and reuse of these balloons is a key feature of the system. Components of the system are discussed in this paper and initial results from prototypes will be presented at the conference. 2. SYSTEM COMPONENTS The system is composed of: a "cannibal-loon" and pump by which the altitude of the balloon can be varied; electronics to run the pump, balloon-to-ground communications, and location hardware; and instrumentation to sense internal and environmental pressure, temperature and moisture. In the prototype, off-the-shelf components capable of meeting the functionality, performance and weight criteria of the system were used where ever available. The safety of this system to aircraft was a major consideration. The system conformed to Federal Aviation Administration Regulations (FAR 101) for mass-density requirements, and contained several independent mechanisms for terminating the flight. 2.1 Balloon Shell The balloon is of the "cannibal-loon" design (Lally, 1967), consisting of concentric helium and air bladders inside a synthetic-fabric shell. Helium provides the lift, as in operational soundings, and the air bladder allows control over the balloon's altitude. Introducing ambient air into the air bladder increases the weight of the balloon causing it to lose altitude; venting air permits the balloon to rise. The shell used in the 1995 tests was a 2.4-m diameter sphere, capable of withstanding superpressures of 20 to 40 mb. Temperature and pressure sensors kept track of the internal state of the balloon. 2.2 Pump and Batteries The pump is the most critical component of the system. It must be able to deliver a high flow of air against high backpressures in order to bring the balloon down from maximum altitude in a reasonable period of time (under 2 hours). Several candidate pumps were tested before one was found that was minimally adequate to meet the test objectives. Temperature sensors recorded the state of the pump package. Lithium batteries provided power for all electrical components of the balloon. 2.3 Electronics 2.3.1 Global Positioning System Balloon location was determined by the Global Positioning System (GPS). Information from the onboard GPS was telemetered to the ground. Accurate location information was crucial for flight decisions, such as determining when to begin landing procedures, and where to direct the recovery team. 2.3.2 Telemetry Communications between the balloon and the ground permitted regular monitoring of the balloon's state and allowed control of the flight from the ground as necessary. Onboard pressure and temperature information on the pump, batteries, and balloon shell, as well as the balloon's GPS location were telemetered to the ground at scheduled times. Commands that could be sent from the ground were those to open or close the helium vent, start or stop the air pump, and query the balloon position. 2.3.3 Computer An onboard computer monitored the state of the hardware, sent scheduled messages to the ground, executed a predetermined flight script, and updated this script as commands from the ground were issued. The script automatically terminated the flight if certain preset criteria were exceeded; these conditions included the location of the balloon being outside the target area of operations and the length of the flight being longer than a predetermined period. 2.3.4 Meteorological Instrumentation A standard sounding package returned an environmental temperature, pressure and moisture sounding to the ground. Winds were determined from successive GPS locations. 3. FIELD TESTS The following set of limited objectives were tested with a prototype system:
4. CONCLUDING REMARKS For the long term, FSL plans to demonstrate the feasibility of in-situ soundings at 6-hourly intervals from the surface to 8 km for the eastern Pacific, with at least one balloon residing in every 10 by 10 latitude-longitude square. In 1996 we will continue testing over land with day-night flights and further developments in the balloon shell, power and pumping subsystems. By the late 1990s we anticipate running a demonstration network over the ocean. With this demonstration we will be able to assess the benefit of these data sets on forecasts from numerical weather models. 5. REFERENCE Lally, V.E., 1967: Superpressure balloons for horizontal soundings of the atmosphere. Rept. No. NCAR-TTN-28, June 1967, 167 pp. NCAR, Boulder, Colo.
Last modified: Mon Oct 2 10:43:19 1995 |
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Prepared by Randall Collander, randall.s.collander@noaa.gov |