Radiosondes ATS 351 - May 5th Balloon Launch. What is a Radiosonde? A radiosonde is a balloon-based instrument platform with radio transmitting capabilities.

Radiosondes

ATS 351 - May 5th Balloon Launch

What is a Radiosonde?

• A radiosonde is a balloon-based instrument platform with radio transmitting capabilities.• “radio” for the onboard radio transmitter• “sonde” from French, meaning sounding line

• Contains instruments capable of making direct in-situ measurements of air temperature, humidity, and pressure as a function of height up to about 30 km

• The device provides an indirect measure of wind speed and direction by recording time and position.

Purpose

• To make accurate measurements of atmospheric parameters above the surface and send this information back in as close to real-time as possible

• It is important to know weather aloft in order to forecast accurately

History• 18th and 19th centuries

– A kite with a thermometer (began around 1749)• A few years later, Benjamin Franklin flew a kite near a thunderstorm to demonstrate the electrical nature of lightning

– Manned hot air and hydrogen balloons in 1800’s– Kite observation network in U.S. by end of 1800’s

• Early 1900’s– Meteorographs carried by free, unmanned balloons that could reach the stratosphere

– Aircraft soundings from Army Air Corps in 1925-1940’s

– However, both methods could not provide real-time data

History• 1930’s-1950’s

– First radio-meteorographs (“radiosondes”) in early 1930’s

– 1937: U.S. NWS established radiosonde network (still exists today)

– Automated radio-theodolites (“rawinsondes”) by the 1950’s (theodolite=positional triangulation device)

• 1960’s-1980’s– Computerized reduction of rawinsonde data: almost fully automated by 1980’s• Processing time greatly reduced and data quality improved

– Radio-navigation aids (NAVAID): LORAN and Omega for wind

• 1990’s– Improved sensors, data processing and NAVAID system

– GPS for wind measurements

Radiosonde NetworkWeather balloons are launched world-wide.The US has a decent network of daily radiosonde launches but more would always be helpful for forecasting and research.

Each location generally launches twice a day in order to help with forecasting.

What Makes Up the Balloon System?

The Balloon• The balloon is filled

with helium to an amount specified by the mass of the balloon and the mass of the radiosonde so that it will achieve a certain rate of ascent. (~6 m s-1)

• It is attached to the radiosonde via a plastic hook/tether unwinder with cable ties.

• The balloon is about 5 feet in diameter at the time of launch.

• Becomes 24-32 feet before bursting

• Allows sonde to reach altitudes exceeding 25 miles (~10 mb).

What is a radiosonde?

1. Housing for Pressure Sensor and Transducer Electronics

2. Temperature Sensor3. Humidity Sensors4. Sensor Boom5. Balloon Tether Mast6. GPS Receiver7. Interface

Connection Port8. UHF Transmitter9. Battery Pack

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What is Measured?

• Temperature• Humidity/moisture• Wind speed• Pressure

The Temperature Sensor• Capacitance: property of

storing an electrical charge between two separate conductors

• The capacitance between the electrodes is dependent upon temperature.

Platinum Wire

Glass Encapsulation

Glass-CeramicDielectric

Relative Humidity Sensors

• Capacitance between electrodes is also dependent on relative humidity

Heating Resistor

Dielectric Polymer

Relative Humidity Sensors

• Defrosting method with two heated sensors

• Two sensors are heated alternately• While first sensor is measuring, the second is heated. After a recovery phase to ambient conditions the latter is measured.

How the Data is Used

• Most routine radiosonde launches occur at 0000 UTC and 1200 UTC to provide a snapshot of an instant in the atmosphere which is very useful for forecasting

• Input for weather prediction models• Input for air pollution models• Climate change research• Ground truth for satellite data• Research of weather phenomena like downdrafts, gravity and mountain waves, low-level jets, hurricanes, etc.

How the Data is Used• The pressure locations of the recorded data depend on the balloon’s rate of ascent.• Additionally, data are recorded at the standard pressure levels of 1000, 925, 850, 700, 500, 400, 300, 250, 200, 150,100, 70, 50, 30, 20 and 10 mb.

• The upper air data are routinely ingested by numerical models to be used in forecasting the weather.

Problems

• Humidity readings– Measurements very high in atmosphere are not very accurate

– In extreme dry environments, measurements from radiosonde are too dry

– In relatively humid environments, the radiosonde is slow to respond to dry layers and therefore sounding is too wet

Problems• Both the thermistor and hygrister are poorly vented and both are easily wetted, leading to a plethora of problems caused by the latent heat effects of condensation, evaporation, freezing, and sublimation

• Often missing winds through significant layers

• Other problems, again probably related to internal electronics, cause high to veryhigh frequency noise leading sometimes to many many "special" points - in bothT and Td