Radiosondes

1
Radiosondes

1. History of upper air measurements
2. Radiosondes (sensors, calibration,
   telemetry,multiplexing)
3. The Vaisala radiosondes
4. Special radiosondes (Ozone,atmospheric
   electricity, radioactivity)

2
EuropeanUpper Air stations

• Operational stations launch 4 times per day

3
Requirements for upper air measurements
(1) To make accurate measurements of important
atmospheric parameters (usually temperature,
pressure and humidity) above the surface (2) To
send this information back in as close to
real-time as possible (1) and (2) usually
achieved by making a profile measurement, with a
balloon carried instrument, but aircraft data is
also used. (2) was once achieved using sondes
which dropped something (the lizardsonde), or
even exploded (the crackersonde) when a certain
condition was fulfilled.
4
Kite-carried sensors
Handbook of Meteorological Instruments (Part 2
Instruments for upper air observations), HMSO,
1961
5
Dines Kite Meteorograph
Handbook of Meteorological Instruments (Part 2
Instruments for upper air observations), HMSO,
1961
6
Dines balloon meteorograph (1907-1939)
Silvered recording plate
Hair humidity element
Bimetallic strip (temperature)
Aneroid capsule (pressure)
Handbook of Meteorological Instruments (Part 2
Instruments for upper air observations), HMSO,
1961
7
Radiosondes
Small and compact radio transmitters allow the
data obtained by a sensors carried on a balloon
to be transmitted back to a receiving
station. First successful radiosonde in the UK
was the Kew Met Office sonde, in use from
1939. Improvements followed, and the Mark2 was
used from 1945 up until the 1960s
Radiosondes require Sensors (with an electrical
output) Radiotelemetry (the data transfer
system) Batteries (which will work at low
temperatures) balloons and parachutes
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Sensors
The sensors must ultimately provide an electrical
output, which can be turned into a frequency for
the radio transmission. Mechanical sensors are
coupled to transducers to achieve this. An
example is a pressure sensor. Small mechanical
variations in an aneroid capsule are used to move
an iron core within an electrical inductor. The
inductance changes, which leads to a change in an
audio frequency, transmitted directly over the
radio link. Other sensors used include Temperature
bimetallic strips (mechanical), resistance wire
(electrical) Humidity hair or gold beaters skin
(mechanical), the humicap (electrical) Pressure
aneroid (mechanical or electrical)
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Radio Telemetry
A simple (carrier) radio wave requires a change
(modulation) to be applied for information to be
transmitted. This is usually either AM (amplitude
modulation) or FM (frequency modulation)
AM
Transmitted signal
Information
FM
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Multiplexing
If more than one signal is required, and in a
radiosonde, three different signals (humidity,
temperature and pressure) are usually sent, the
radio transmitter has to be switched between the
three sensors in turn. This is called
multiplexing. If the three signals are
sufficiently different, or the order of switching
is known, the individual signals can be recovered.
Handbook of Meteorological Instruments (Part 2
Instruments for upper air observations), HMSO,
1961
Multiplexing switch
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Mk2 MO radiosonde
sensors
Thermionic valves in radio transmitter
receiver
Multiplexing switch driven by wind mill
Handbook of Meteorological Instruments (Part 2
Instruments for upper air observations), HMSO,
1961
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Calibration

• Radiosonde sensors have to be calibrated if they
  are to produce accurate measurements over a range
  of conditions.
• Calibration requires the sensor to be exposed to
  the full range of variation they will receive in
  service, but in a controlled environment.
• The results of a calibration are used to
  construct a response function, which is an
  equation used to link the values found by a
  sensor to the magnitude of the parameter it is
  sensing.
• The precise response function is unique to each
  sensor, and is used by the receiving computer to
  turn the data received into meaningful physical
  values.
• The response functions are typically polynomial
  functions, with many coefficients to cover the
  range of values required. These coefficients are
  supplied with each radiosonde.

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Calibration
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Mk3 MO radiosonde
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View of Mk3 sonde
Thermometer (resistance wire)
Polystyrene housing
rotary multiplexing switch
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Vaisala RS80 Radiosonde
Temperature sensor
Relative Humidity sensor (humicap)
(Vaisala)
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RS80 Specification
(Vaisala)
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Windfinding

• If the location of a radiosonde is known, and
  recorded, its direction of motion can be
  determined from a set of the locations.
• This allows the wind directions to be found,
  often referred to as windfinding. The profile
  of wind direction and strengths can therefore
  also be plotted.
• The location of a radiosonde can be found by
  different methods
• Tracking it with radar
• Using a Global Positioning System (GPS) receiver
  on the sonde to send back its location
• Using the LORAN positioning system on the sonde
  to send back its location

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GPS satellite system
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RS90 radiosonde
(Vaisala)
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RS90 specification
(Vaisala)
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Special radiosondes
Radiosondes can carry a variety of sensors,
either instead of, or in addition to, the
standard meteorological sensors for temperature,
pressure, and humidity. Atmospheric properties
which have been extensively with modified
radiosondes include Ozone Atmospheric
electricity (the charges and electric fields
within clouds and thunderstorms) Radioactivity
Radiosondes for measuring the profile of ozone
in the atmosphere are known as Ozonesondes.
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Kew-Oxford Ozonesonde
Contains an ozone cell in which an electrolytic
reaction occurs, using potassium iodide. When
ozone is passed through iodine is formed, which
causes a small current to flow.
From Brewer and Milford, Proc Roy Soc, 256 1960
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Ozone profiles
From Brewer and Milford, Proc Roy Soc, 256 1960
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Atmospheric electricity radiosondes
Electric field probe-
measures change in voltage with height,
Potential Gradient
Haze layer
Venkiteshawaran S.P. Measurement of the
electrical potential gradient and conductivity by
radiosonde at Poona, India, pp89-100 In Smith
L.G. (1958) Recent advances in atmospheric
electricity, Pergamon Press
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Charge distribution in thunderclouds
Stolzenburg et al. (1998)
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In-cloud measurements

• Balloon-carried disposable instruments have been
  designed at Reading to make in-cloud
  measuerements. These have
• Detected charged particles emitted in aircraft
  exhausts
• Found thin and persistent, highly-charged layers

Sensor responds to changes in charge
Harrison R.G. Rev Sci Inst 72, 6 pp2738-2741
(2001)
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RS80 radioactivity sonde
Carries Geiger tubes, sensitive to beta and gamma
radioactivity, as well as standard temperature,
pressure and humidity
(Vaisala)