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Training school pupils in the scientific method: student participation in an international VLF

radio experiment

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School pupils and the scientific method: a VLF radio experiment

of space physics and the SunEarth system. Fol-

lowing this a process was put in place by which

deployment of the equipment to Headlands Schoolcould begin. After construction of the hardware by

Sodankyla Geophysical Observatory (SGO), Fin-

land, and initial testing at Lancaster University, the

experiment was deployed at Headlands School in

November 2010 (Kavanagh et al 2011). The ex-

periment is now part of the international AARD-

DVARK network of similar experiments deployed

around the world (e.g. Clilverd et al 2009).

Background to VLF waves

VLF waves can be detected with relatively simple

equipment, which can be constructed with areasonably low budget requiring little more than a

PC, a commercial sound card and an antenna (see,

for example, Fullerkrug (2009) or www.vlf.it/

obs1/monitoringstation.html). More sophisticated

experiments, such as that deployed at Headlands,

aim to increase the signal-to-noise ratio, and

to record data at high time resolution from a

number of different narrow-band sources. Two

prominent signals dominate the VLF spectrum

between3 and 50 kHz: the natural VLF waves

generated by lightning and the artificial VLF

waves from various high power transmitters used

to communicate with the worlds submarine fleets.VLF waves can travel large distances (thou-

sands of kilometres) due to their relatively low at-

tenuation. Whilst some researchers are interested

in the study of lightning using VLF (see, for ex-

ample, the World Wide Lightning Location Net-

work: http://wwlln.net/) the primary focus for the

Lancaster scientists is in using the artificial signals

generated by high power transmitters to probe the

geospace environment.

VLF waves are ducted between the Earths

surface and either the lower portion of the

ionospheric D region at an altitude of

75 kmduring sunlit hours or the lower portion of the

ionospheric E region at an altitude of 90 km

during darkness. This cavity between the Earths

surface and the lowest conducting layer in the

atmosphere acts as a natural waveguide (see

figure 1).

The measured amplitude and phase of these

signals fluctuates in response to changes in the

atmosphere on the path between the transmitter

and the receiver. By analysing artificial VLF

transmissions it is possible to monitor the charged

Figure 1. The cavity between the Earth's surface andfree electrons in the lower ionosphere forms a naturalwaveguide. VLF transmissions propagate large

distances along this waveguide, between transmitter(TX) and receiver (RX). The amplitude and phase ofthe signal can be studied to derive information aboutthe ionosphere between transmitter and receiver.

free electrons in the atmosphere form aconducting layer that extends above

7590 km, known as the ionosphere

VLF signals travel along the naturalwaveguide between the ground and the

bottom of the ionosphere

received signals provide information on theionosphere between TX and RX

TX RX

VLF

portion of the atmosphere along this path. In

general the more energy the particles from space

have, the deeper they will penetrate into the

atmosphere, and the most energetic particles may

reach ground level. However, most incoming

particles collide with neutral atomic species

such as oxygen or nitrogen at altitudes between

60 and 400 km. Since most of the particles

and radiation incident on the Earth originate from

the Sun, the VLF experiment at Headlands School

allows us to study changes in different regions of

the ionosphere which are due directly to so-called

space weather effects.

The VLF wave properties of the signals from

these transmitters are analysed and can detect the

presence of high-energy charged particles from

space which can precipitate or rain down into

the atmosphere (Clilverd et al 2006, Rodger

et al 2007, Longden et al 2008, Gamble et al

2008) under certain conditions (Kavanagh and

Denton 2007, Denton et al 2009). A selection ofpropagation paths from various VLF transmitters

to the Headlands receiver in Bridlington are shown

in figure 2.

Relevance to international projects

Members of the AARDDVARK project, involv-

ing nine different institutes from seven coun-

tries, operate a network of VLF receivers around

the globe (see www.physics.otago.ac.nz/space/

AARDDVARK homepage.htm). Each partner

January 2012 P H Y S I C S E D U C A T I O N 65

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J J Denton et al

Figure 2. A selection of ray paths between VLFtransmitters and the Bridlington receiver at HeadlandsSchool. Information can be derived about the upperatmosphere along these ray paths.

Figure 3. The figure shows construction of the VLFantenna at Headlands School and a selection of pupilswho are custodians of the experiment.

shares data to enable all participants to utilize the

largest dataset possible for application to individ-

ual research projects. Lancaster University is the

most recent institute to join the AARDDVARK

network with the deployment of the Bridlington

VLF receiver. The site has reasonably low radio

noise and its location on the east coast of the UK

ensures that the transmitter-to-receiver paths com-

plement existing AARDDVARK receivers.

One exciting opportunity for further interna-

tional collaboration will arise with the launch of

the NASA Radiation Belt Storm Probes (RBSP)

mission in 2012. One aim of this mission is to

study how particles from the Earths radiation belts

Figure 4. An example of the data analysed by pupilsat Headlands School. The figure shows the level ofwave power between 0 and 48 kHz during a 10 speriod on 14 April 2011. VLF transmitters broadcaston specific narrow frequencies and are easilyidentified. Lightning strikes produce short-lived VLFwaves with wave power spread over a number offrequencies. Broadband intermittent noise can alsobe identified in the data. The cause of this is underinvestigation.

0

time (s)

intermittent broadbandnoise: cause unknown

high power, narrow band signalsfrom VLF transmitters

intermittent broadbandsignals from lighting orunknown sources

0 2 4 6 8 10

10

20

30

40

0

5

10

15

5

10

15

power(dB)

frequency(kHz)

may be lost via collisions with the upper atmo-

sphere (e.g. Ukhorskiy et al 2011). The equipment

deployed at Headlands School is able to detect thisparticle precipitation and can thus provide ground-

based support for missions such as RBSP. The con-

nections between Headlands School and the above

international projects mean that there are many op-

portunities to stimulate pupils with the real-world

applications of their knowledge.

Methodology, student interaction andlearning

The hardware for the experiment was assembled

at Headlands School in November 2010 (figure 3).

Despite initial plans to include students in buildingthe antenna itself, this proved unworkable given

health and safety considerations due to the

rooftop location. After initial testing the system

started producing meaningful data in January

2011 and this allowed student interaction with

the equipment to begin. An example of raw

data recorded at Headlands School is shown in

figure 4. The signatures of lightning strikes, VLF

transmitter signals, and broad-band noise are

all present. In the few months that the project

has been running mixed gender students aged

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School pupils and the scientific method: a VLF radio experiment

1418 have been encouraged to plan and carry

out (in their own time!) a variety of tasks and

experiments based on the VLF data. A sixthform special interest group of 25 students has

been particularly active in analysing data and

attempting to determine the sources of the noise

seen in the data. Their learning objectives were

primarily based around greater understanding of

waves and the electromagnetic spectrum, and

the principles of scientific enquiry. The GCSE

science specification contains a large section on

the use of waves for communication and the

equipment deployed at Headlands School has

given staff the opportunity to enrich and enlighten

students, broadening their understanding of the

electromagnetic (EM) spectrum whilst exploringthe theme of How Science Works.

The pupils suggested a testable hypothesis

that interference from local electrical devices

caused some of the noise recorded in the

dynamic spectra. This hypothesis was based

upon (a) the reasonably high strength of the

noise, (b) regular pattern spacing, and (c) a clear

start point, suggesting an anthropogenic source.

As part of the experimental design pupils listed

numerous potential local independent variables

(electrical sources) and dependent variables (local

harmonics), along with other non-local sourcesof VLF emissions beyond their control (e.g.

electrical sub-stations which were presumed to

remain static through the course of an experiment).

The initial experimental phase involved the

identification of a test area and a synchronized

deactivation of electrical equipment within that

area. The pupils designed a spreadsheet to plan

the deactivation and ensure that it was carried out

in a timed manner such that any reduction in noise

in the data could be attributed to a particular piece

of equipment. The initial experiment returned a

null result, neither supporting nor disproving the

original hypothesis. Hence, further tests are beingplanned to explore radio-noise sources in the area

surrounding the school. In addition the students

are themselves designing an experiment to test

whether electrical discharges from a Van der Graff

generator will produce a VLF signature in the data

in a manner analogous to lightning.

Summary and future work

We consider the project to date to have been a

great success, both in terms of student learning and

from a research perspective. Enrichment activities,

such as this project, allow students the chance

to experience non-curricular activities they wouldnot normally have access to. Discussions with

the students indicate that they enjoy being part

of the project and are intellectually stimulated by

the challenges involved. In the future we aim

to involve other pupils in further experimental

studies to support core activities at Key Stages

35. This will involve year 711 students

carrying out observations and photography of

the Sun using specialized equipment. Students

in year 1213 will perform similar observations

and also carry them further by studying the

subsequent effects of solar activity on the VLF

measurements. Headlands School will also carryout outreach work within the community and with

Key Stage 2 pupils from local feeder primary

schools. Lancaster University Faculty of Science

and Technology (FST) has funded the purchase

of a solar telescope and camera equipment for

Headlands School to facilitate these activities.

Such projects aim to reinforce and strengthen

the learning the students undertake as part of

the National Curriculum, and to enhance their

understanding of the SunEarth system. However,

given the scope of experimental research carried

out in UK universities in numerous subject areas,many other opportunities must be available for

forming productive partnerships with schools in

the community. We encourage such efforts

which, in our opinion, stimulate an interest in

and appreciation of science in the upcoming

generation.

Acknowledgments

We thank Mark Clilverd (British Antarctic Sur-

vey), Craig Rodger (University of Otago, New

Zealand), Andrew Senior (Lancaster), and Steve

Marple (Lancaster) for useful discussions and ad-vice during the project. We gratefully acknowl-

edge the assistance of Markku Postila and the

workshop and staff at Sodankyla Geophysical

Observatory (SGO), Finland, during construction

of the VLF receiver. MHD acknowledges the

hospitality extended by SGO during his visit in

May 2011. We thank Bob Bunce (Headlands

School) for help during deployment of the equip-

ment. Special thanks are due to all pupils in-

volved with the VLF receiver at Headlands School

for their help and support of this project. This

January 2012 P H Y S I C S E D U C A T I O N 67

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J J Denton et al

work was part-funded by a Lancaster Univer-

sity Small Award and FST Grant to M H Den-

ton.

Received 5 June 2011

doi:10.1088/0031-9120/47/1/64

References

Clilverd M A, Rodger C J and Ulich T 2006The importance of atmospheric precipitation instorm-time relativistic electron flux drop outsGeophys. Res. Lett. 33 L01102

Clilverd M A et al 2009 Space Weather 7 S04001Denton M H, Borovsky J E, Horne R B,

McPherron R L, Morley S K and Tsurutani B T2009 Introduction to special issue on high speed

solar wind streams and geospace interactionsJ. Atmos. Sol.-Terr. Phys. 71 10113

Fullerkrug M 2009 Exploration of the electromagneticenvironment Phys. Educ. 44 1337

Gamble R J, Rodger C J, Clilverd M A, Sauvaud J A,Thomson N R, Stewart S L, McCormick R J,Parrot M and Berthelier J J 2008 Radiation beltelectron precipitation by man-made VLFtransmissions J. Geophys. Res. 113 A10211

Kavanagh A J and Denton M H 2007 High speed solarwind streams and geospace interactions Astron.Geophys. 48 6.246

Kavanagh A J, Denton M H, Denton J J and Harron H2011 Probing geospace with VLF radio signals

Astron. Geophys. 52 2.2730

Longden N, Denton M H and Honary F 2008 Particleprecipitation during ICME-driven and CIR-drivengeomagnetic storms J. Geophys. Res. 113 A06205

Rodger C J, Clilverd M A, Nunn D, Verronen P T,Bortnik J and Turunen E 2007 Storm time,short-lived bursts of relativistic electronprecipitation detected by subionospheric radiowave propagation J. Geophys. Res. 112 A07301

Ukhorskiy A Y, Mauk B H, Fox N J, Sibeck D G andGrebowsky J M 2011 Radiation belt storm probes:resolving fundamental physics with practicalconsequences J. Atmos. Sol.-Terr. Phys.73 141724

Further informationThe Lancaster VLF experiment http://vlf.lancs.ac.ukThe AARDDVARK network of VLF receivers www.

physics.otago.ac.nz/space/AARDDVARK homepage.htm

Live data from Sodankyla Geophysical Observatorywww.sgo.fi/Data/latest.php

Build your own VLF receiver www.vlf.it/obs1/monitoringstation.html also Fullerkrug (2009)

The NASA Radiation Belt Storm Probes (RBSP)Mission http://rbsp.jhuapl.edu/

Real-time Space-Weather www.swpc.noaa.gov/

68 P H Y S I C S E D U C A T I O N January 2012

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