Radiosondes
1. History of upper air measurements
2. Radiosondes (sensors, calibration,
telemetry,multiplexing)
3. The Vaisala radiosondes
4. Special radiosondes
(Ozone,atmospheric electricity,
radioactivity)
1
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
2
condition was fulfilled.]
Kite-carried sensors
Handbook of Meteorological Instruments
(Part 2: Instruments for upper air
observations), HMSO, 1961
3
Dines’ Kite
Meteorograph
Handbook of Meteorological Instruments
(Part 2: Instruments for upper air
observations), HMSO, 1961
4
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
5
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…
6
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)
7
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
“Information”
Transmitted
signal
FM
8
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
9
Multiplexing switch
Mk2 MO radiosonde
sensors
Thermionic
valves in
radio
transmitter
Multiplexing
switch driven
by wind mill
receiver
10
Handbook of Meteorological Instruments (Part 2:
Instruments for upper air observations), HMSO, 1961
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.
11
Calibration
12
Mk3 MO radiosonde
13
View of Mk3 sonde
Thermometer
(resistance
wire)
Polystyrene
housing
14
rotary multiplexing switch
Vaisala RS80 Radiosonde
Temperature
sensor
Relative
Humidity
sensor
(“humicap”)
(Vaisala)
15
RS80 Specification
(Vaisala)
16
“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
17
GPS satellite system
18
RS90 radiosonde
(Vaisala)
19
RS90 specification
(Vaisala)
20
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.
21
“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
22
Ozone profiles
From Brewer and Milford, Proc Roy
Soc, 256 1960
23
Atmospheric electricity
radiosondes
Electric
field probemeasures
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
24
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 respond
to changes in
charge
Harrison R.G. Rev Sci Inst 72, 6
pp2738-2741 (2001)
25
Charge measurements using
radiosondes
• The disposable
electrometer has
detected charged
aerosol layers in an
apparently cloudless
troposphere at 500
mb
Zeroing
cycle
+ve
aeros
ol
measurement
“The housing is that
originally supplied to house
the small plastic toy
contained within a
children's confectionery
KinderEgg. The outer
chocolate enclosure and
foil coating must first be
removed.”
Sensor hanging
beneath balloon
at launch
26
RS80 radioactivity
sonde
Carries Geiger tubes, sensitive to beta
and gamma radioactivity, as well as
standard temperature, pressure and
humidity
(Vaisala)
27