Group for Earth Observation

The Independent Amateur Quarterly Publication for

Number 3

Earth Observation and Weather Satellite Enthusiasts

August/September 2004

Inside this issue . . .
GEO Symposium: Reportand photographs from
Leicester ...
... also included is Robert
Moore’s Symposium
presentation: ‘Observing
the Weather with MSG-1’
Rob Hollander presents
the first part of histreatise: ‘Antenna Theory
and Measurement’
Read about the Space andWeather activities at
Callington Space Centre
Lawrence Harris shares
his experience of thehistoric Venus Transit
David Painter attempts todemystify the role of DVB
in present-day weather
satellite reception
John Tellick details how
to get the most out of yourSatellite-TV dish using
multi-feed reception

Live Meteosat-8 reception on a laptop PC as demonstrated during the
GEO Symposium at the National Space Centre, Leicester, May 2004

The NOAA ‘2004 Satellite Direct Readout Conference:
A Decade in Transition’, takes place in Miami, Florida
in December 2004 — see page 4 for details

We have a beginners’
guide to using Satsignal,
David Taylor’s APT image
processing software
Mike Stevens describes
how he became involved
with weather satellites

Rob Hollander from Werkgroep Kunstmanen in expansive vein as he discusses the RQFH antenna with a visitor to GEO’s May 1
Symposium, held in the National Space Centre, Leicester. Read Rob’s article, Antenna Theory and Measurement, on page 26.
Photo: David Taylor

David Taylor (left) with Vibeke Thyness from the Norwegian
Meteorological Institute, who both received awards at the EUMETSAT
conference in Prague last May, David for for the best software
demonstration and Vibeke for the best poster (on the sea-ice SAF's work).

Sharonov Crater on MarsThis image was prepared using the 64 pixel/degree Mars
MOLA data. Douglas Deans explains how you can create
images like this in Software Showcase on page 38.

Photo: Cecilia Taylor

Image: Douglas deansGEO is led by
Francis Bell
Clive Finnis
Les HamiltonPeter WakelinWho would have thought at the beginning of this year that GEO
would become the success that it has? Here we are, with ourthird issue, thanks to the efforts of all those readers who have sokindly supported us. We have received many, many, messages ofcongratulations, and one point is pre-eminent among these: you
approve most wholeheartedly of GEO’s policy of addressing theneeds of beginners to the weather satellite field. This continues on
page 46 with an in-depth look at David Taylor’s Satsignal software
which creates NOAA APT images from WAV recordings.

B

ut GEO has to appeal to the full spectrum of enthusiasts. To
further this ideal, this issue contains the first part of a seminal
treatise by Rob Hollander on the RQHA antenna, aimed towards themore advanced user. You can read Rob’s authoritative account on
page 26.

E

veryone on the GEO team sends their congratulations to David
Taylor (Satsignal Software) for the award bestowed on him by
the delegates at last May’s EUMETSAT Meteorological Satellite
Conference in Prague. David was presented with a scale model of the
MetOp satellite after the software presentation he made at the event
was voted the best in show (see photo opposite).

F

inally, it is with sadness that we have to report the passing of
our respected contributor from Australia, Arthur Andrews.
Arthur’s articles in the Quarterly were highly thought of and will besorely missed. A brief tribute from his long-time friend Michael
Stubbs-Race appears on page 3.

Nigel Evans
Ray Godden
John Tellick

CONTACT INFORMATION
Public Relations and Education
Francis Bell,
Coturnix House,
Rake Lane,
Milford,Godalming,
Surrey GU8 5AB
EnglandTel:(01483) 416 897
e-mail: francis@geo-web.org.uk
General Information
John Tellick
Tel:(0208) 390 3315
e-mail: info@geo-web.org.uk
Articles and Images for Publication
Les Hamilton,
8 Deeside Place
Aberdeen AB15 7PW
Scotland, UKe-mail: editor@geo-web.org.uk
Membership and Subscriptions
Nigel Evans,
L’Eventail, 7 Gloster Ropewalk, Aycliffe,
Dover CT17 9ES
England, UKe-mail: members@geo-web.org.uk
Meteorological Consultant
Peter Wakelin
e-mail: meteo@geo-web.org.uk
Publisher

Contents
GEO News

Group for Earth Observation Ltd.

Francis Bell2

Obituary: Arthur Andrews

Michael Stubbs-Race4

2004 Satellite Direct Readout Conference

NOAA/NESDIS

4NASA’s Other Earth Observing Spacecraft - part I

Peter Wakelin

6

Forward Error Correction

Alan Sewards

8

Receiving Weather Satellites from Vietnam

Fred van den Bosch

9

Callington Space Centre

Beth Rose

11

The Transit of Venus

Lawrence Harris

15

Symposium 2004 - Report

Les Hamilton

16

Earth Imaging News

Peter Wakelin

19

A Storm to Remember

Hamilton & Teixeira

21

Copy Deadline for GEO Q4

22Digital Weather Satellites and DVBDavid Painter23

Antenna Theory and Measurement

Rob Hollander

26

Multi-feed Satellite Reception

John Tellick

33

Weather Satellite Frequencies

34

Weather Satellites ... How it all Began for Me

Mike Stevens

35

Software Showcase

Douglas Deans

38

GEO Helplines

39

Join the GEO-Subscribers News Forum

41

Observing the Weather with MSG-1

Robert Moore

42

Les Hamilton

46

In Tray - Readers’ Letters and Queries
APT Image Processing Using Satsignal

45

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Responsibility for Constructional
Projects and Software
Every effort is made to ensure that the technicaland constructional articles published in thisQuarterly are correct. However, the ultimate
responsibility is with the reader to ensure thesafety of constructions and for any interfacingwith other equipment. GEO cannot accept
liability for shortcomings in any published designor any constructions carried out by members orother third parties.
Copyright GEO © 2004
The contents of this Quarterly remain theintellectual property of the Group for Earth
Observation Ltd. and its contributors. Copying oftext or images, either from the printed Quarterly
or from any electronically stored source, isforbidden without permission from the editor.

GEO Quarterly No 3Group for Earth Observation

August/September 2004

Francis BellI know that elsewhere in this issue there is a report about our
Leicester symposium so my comments on this subject will bebrief. However, I do think it necessary for me to thank thosepeople associated with the day. The full management team of
GEO were there with the single exception of Peter Wakelin who
is still enduring a back injury. Peter continues to write for GEO
and looks after the dispatch of our Quarterly publication. Our
thanks to him and best wishes for a speedy recovery.
Others at Leicester must be thanked. The speakers are listed
elsewhere, but perhaps our main thanks should go to the 60
delegates who turned up to support the day. For a neworganisation such as GEO this level of support is mostencouraging. I cannot leave this topic without a special
acknowledgment of our friends from the Netherlands who went
to so much trouble and attended our symposium at their own
expense. I admire their skills and resourcefulness in weather
satellite reception; I just wish I was that good! They have theirown meeting in Utrecht on September 11, 2004 and if they willallow me (and others from GEO), I will try my best to attend.
One final point about Leicester—I have made a
provisional booking for next year—April 30 2005.
Please put this date in your diary now. Details will
follow much nearer the time, of course.
Still on the subject of meetings, AMSAT-UK invited GEO to theircolloquium in Guildford at the end of July where I provided live
weather satellite reception for all three days as well as making
presentations in their lecture programme on the Saturday. I
hope we can give a full report from Guildford in our next
Quarterly.
I have also noted that NOAA are
holding a conference in Miami in
December this year (see notice on
page 4). I will do my very best to
attend and promote the interestsof our membership. I consider thisto be a high priority for us, with amutual exchange of information
and an opportunity to learn about
NOAA’s plans for the future. I
hope to meet friends there again.
Ken Ashworth is EUMETSAT’s
man at NOAA and he has becomea good friend. He can keep us up
to date with NOAA’s programmes.
Of particular interest to us inEurope are the polar orbiting
satellites but I also recognise GEO
Page 2

has members in north and south America interested in NOAA’s
geostationary GOES satellites. Ken was recently in the UK
attending a EUMETSAT Council meeting in Exeter and I met
him at Heathrow airport together with John Tellick. For about
one hour Ken gave us a briefing about NOAA’s programmes.
It is a priority for GEO that we should represent the interests ofour membership to those agencies planning, launching andoperating weather satellite. I try to have a broad perspective
here and acknowledge that other groups exist whose interests
overlap those of GEO. I have addressed and actioned this issue
over the past month and I await responses. I was delighted toreceive AMSAT-UK’s unsolicited invitation for us to attend their
meeting in Guildford and I thank them for that. I hope GEO canmake a significant contribution.
Subscriptions
In looking at the finances of GEO I think the annual subscription
may be unsustainable for much longer. It was set at the lowest
possible level to attract membership and will remain there forthe remainder of 2004. Thereafter it must be reviewed. I still
think membership of GEO is stunning value and we will keep itthat way. However, please understand that it may be necessary
to raise the subscription in the future to keep us solvent.
Membership
Our membership is currently about 500. It would help if thisfigure increased. I feel sure I don’t have to explain that GEO’s
main cost is for the printing and distribution of our Quarterly. The
more members we have the more widely these costs can be
spread. Please encourage others to join GEO. I would not wish
members solely for the sake of increasing our numbers, but I do
sincerely believe there are many potential members out there
who just do not know about GEO. Please spread the word andask others to join if they show interest.
Here comes a disappointing note. I have previously indicated awish for GEO to have a higher profile in representing
educational interests. Some pages in this publication reporting
and reflecting education is my ambition. If you feel you can help
out in this area please get in touch with myself or any othermember of GEO’s management team. On the same issue, at
Leicester, a member pointed out to me the age structure of thedelegates. I expect you will be able to judge this for yourself
from the photographs elsewhere in this issue. Again this is amatter which I would like to address but I don’t know quite how.
Someone to volunteer please! These two issues are related.
Letters and Articles

Ken Ashworth (right) withJohn Tellick at Heathrow
AirportSprinkled through our previous publications, at our editor’s
discretion, are letters and articles written by me. I sometimes
write as an innocent. My question about ‘Forward Error

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August/September 2004

Group for Earth Observation

Correction’ was an example. It is very rewarding to receive
responses to these questions and my particular thanks to Alan
Sewards for his contribution which appears on page 8. I’m on alearning curve here but just about understand why Meteosat-8
data comes in blocks rather than scrolling images.
At other times I know I can be much more aggressive,provocative and rightly offer a kick in the groin to establishedviews. That was the style of my article about the death of ourplanet and global warming. I have received a letter from apotential member and my thanks to him, but I still defend every
word I wrote (except that Tokyo should have been Kyoto).
Atmospheric levels of carbon dioxide are dynamic but in myview global warming is electromagnetic not molecular. I offer astrong criticism of the media, particularly television, for notunderstanding these issues.
I do like watching science programmes on the TV but one
programme in June was hysterical beyond belief. The thread of
the story line was that the Gulf Stream will stop as a result of
melting polar ice. I certainly agree that the ice is melting but thepresent disposition of the continents and oceans coupled torotation of our planet will just not allow the Gulf Stream to stop.
I consider this media hysteria to be ill-judged. The authors of thisstory couldn’t even model clay yet alone ocean circulation.
Okay—I’ve done it again! But I’m right and unrepentant. What I
didn’t even tell our editor was that my article about planetarycarbon dioxide and global warming was refereed by four
distinguished scientists before I submitted it for publication. That
is not to say every item of content was agreed. The arguments
are mine alone and not written light-heartedly. This planet iswarming and we don’t know why! Of course I am supportive of
the scientific process: hypotheses, theories and laws—then theyturn out to be wrong, so we have to start over again. People
much more clever than I are good at doing this but what I don’t
like is media hysteria.
On the subject of oceans my sincere apology to Southampton
Oceanographic Sciences for not acknowledging the electron
micrographs they sent to me and which were published in GEO
Q2. From whatever your perspective they are beautiful images.

GEO Quarterly No 3

The Transit of Venus
I thought subscribers might be interested in this photograph I
took of my solar observatory during the recent transit of Venus.
Well you don’t often have a chance to do this. Just try! The
shadow from the tube of Pringles (sour cream and chive flavour)
gave me a regular check of azimuth. Elevation was moredelicate and required me to slacken the clamp on my workbench and tilt the binoculars. Focal length for the image was
90 cm. I was within three minutes of acquiring the publishedtime for the transit and three minutes for its loss. Okay, so mybinoculars have some chromatic aberration and edges are notalways perfect.

Two things puzzle me. Why was my image upside down
compared with published images? And when can I see the nexttransit of Mars?—No answers please, the answers areembedded in the text!—And yes, I did eat the Pringles. For a
more in-depth report on this Venus transit, read Lawrence
Harris’s article on page 15.
Key WestThanks must go the Stephen Padar for the image of Key Westshown here. Stephen lives in Florida and is experienced inweather satellite reception.

Snow
I’m still interested in snow. On a Meteosat-8 image I thought I
could see snow on Sicily. I telephoned Peter Wakelin. ‘Peter,
does it ever snow on Mount Etna?’. Reply: ‘Well the last time I
cycled up Etna I had to turn back because of the slush andsnow’. I’m still looking for an image of snow on the Troodos
mountains. Look out for an article from Peter Bradley in
GEO Q4 on the subject of the ‘East African Glaciers and Ice
Fields’, a follow-up to my ‘Snows of Kilimanjaro’ piece in GEO’s
Launch Issue.
ThanksFinally more thanks. I have a very good friend, David Simmons,
who will be embarrassed to read this. David was at Leicesterand is planning to come to Guildford. When I get stuck withtechnical problems he comes to my house and helps me out. My
thanks to him. But GEO’s biggest vote of thanks must be to ourcontributors. I hope they are satisfied to see their work in sucha fine publication—which is also a tribute to our editor.

I spent some time with him at a NOAA conference in Miami
about two years ago. It is very encouraging when GEO
members respond to small questions posed in our Quarterly
publication. It shows that people actually read our Quarterly
rather than just looking at the pictures. It was in GEO Q1 that I
asked: ‘Could anybody submit an image of Key West?’ (Thatwas my Ernest Hemmingway connection; he had a housewww.geo-web.org.uk

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

there). Stephen has done just that and our thanks to him. The
Image is HRPT from NOAA-16 from March 4, 2004.
Although I have been there, Stephen’s image prompted me to
examine a map of Key West, which is an island connected to themainland by bridges and causeways. It is about 6 km long and1.5 km wide so not easy to image from a weather satellite. It has
a small airport. If you’re not sure of Key West’s location, it is themost southerly tip of Miami State, and is the southernmost pointof the contiguous USA; that is you can get to it by road! Although
the climate there is delightful it is not tropical. My map revealed
that Key West is about 120 km north of the tropic of Cancer.
There is one state in the USA which is tropical and that is
Hawaii. It’s about 200 km south of the tropic of Cancer.
American sugar-cane barons annexed the islands against thewishes of the indigenous Polynesians on July 7, 1898. If you
want to know the importance of sugar-cane as a crop re-read
GEO Q2 page 27. Well British colonial history isn’t perfect eitherand Hawaii does now give the Americans somewhere warm to
go to and get married—several times!

Darrell R Robertson
NOAA invites Direct Readout users to its upcoming “2004Satellite Direct Readout Conference: A Decade in Transition”,
scheduled for December 6-10, 2004 at the Hilton Miami Airport
and Towers Hotel, Blue Lagoon Drive in Miami, Florida.
NOAA expects more than 250 participants from more than 40
countries to attend. NOAA and NASA are cooperating in thisyear’s conference to bridge the L-Band and X-Band user
community with the goal of serving as an information exchange.
The conference will also provide a forum for vendors to display
and discuss their products and services. NOAA is currently
working on a web site where more details will be available in thenear future, at:
http://DirectReadout.noaa.gov/miami04/

Silent Key - Vale VK2AAE.
by Michael Stubbs-Race VK2ASR (G3JYE)
It is with profound regret I have to record thepassing of Arthur Andrews VK2AAE (Andy),
following a heart-attack, on May 19, 2004, at the ageof 67 years.

During the next decade, the transitioning into new technologies
for NOAA satellite systems will result in significant changes.
These will affect all current and future users of NOAA satellites,
particularly those who receive data directly from the satellites. In
time, all users will have to modify or replace current receiving
equipment and basic processing software as the next
generations of satellites begin operation. The purpose of thisDirect Readout Conference is part of a continuing effort toprepare all users for these changes.

A friend of mine for many years now, we enjoyedputting the world to right several evenings throughthe week. Andy was a keen amateur and mostprofessional in his conduct on air.
He was widely known for his many articles written
on weather satellite imaging and farming mattersfor the various magazines he had served for the past
15 years at least.
Andy had wide-ranging interests, including an
excellent grasp of satellite imaging, which would
have been his favourite subject. He was engaged inproving trials for a new satellite receiving system up
until the time of his death.
I shall indeed miss his friendly voice, as I am sure
his vast readership will miss his many readerfriendly articles and advice.
Our heartiest condolences go to Hazel, his wife of 42
years, daughter Helen and son Nigel (VK4FNA).
Requiescat in Pace

Page 4David Taylor sent us both the HRPT and APT versionsof the 16:06 UT channel-2 (vis/near IR) pass fromNOAA-12 on June 25 this year, which shows a ridge ofhigh pressure over Great Britain (opposite page).
When launched in 1991, NOAA-12’s evening passes ataround 18:30 UT were too under-illuminated to
produce good channel-2 images. But now, as a result of
the continuous precession of the satellite’s orbit,
NOAA-12 is providing some exceptional afternoon
imagery.
David makes an interesting comparison between the
APT image (inset top, and enlarged, lower right) andthe HRPT image. The enhanced HRPT detail, where
the maximum ground resolution is one kilometre per
pixel is clearly apparent. The APT images have amaximum ground resolution of only 4 km per pixel.

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NOAA-12 channel-2 image acquired by David Taylor on June 25, 2004 (16:06 UT)
The main image is from the HRPT data stream. The APT image is shown at upper right using the same
resolution, and at lower right, a strip is enlarged to provide a direct comparison with the HRPT image.
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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Peter Wakelin
The NOAA polar-orbiters and the GOES geostationary weather
satellites are familiar to our readers but there are numerous
other NASA Earth observing spacecraft either in operation or in
the design and construction phase. These spacecraft areproviding huge amounts of data for NASA’s Earth Science
Enterprise (ESE), and others, to increase our knowledge ofatmospheric composition, the carbon cycle, climate variability
and change, the Earth’s surface and interior and the water andenergy cycle as well as the weather.
NASA joined the Coordination Group for Meteorological
Satellites (CGMS) in 2003 and at the 32nd annual meeting of the
CGMS held in Sochi, Russia in May 2004, provided informationon their present and future research and development
spacecraft. That information has been used as a basis for thisarticle and I am grateful to the CGMS Secretariat for making it
available so promptly.
ACRIMSAT(Active Cavity Radiometer
Irradiance Monitor Satellite)
Launched in December 1999,
this satellite measures total
solar irradiance to determine
the character and variabilityof solar radiation.
ACRIMSAT
Terra(Measurement of Earth’s climate system)
Some readers will be familiar with imagery from the Moderate
Resolution Imaging Spectroradiometer (MODIS) carried on thissatellite but it also incorporates the instruments CERES (Clouds
and the Earth’s Radiant Energy System), MISR (Multi-angle
Imaging Spectro-Radiometer), MOPITT (Measurement of
Pollution in the Troposphere) and ASTER (Advanced
Spaceborne Thermal Emission and Reflection Radiometer).

Aqua(Collects information about the Earth’s water cycle)
Like Terra, Aqua carries MODIS and CERES. It also carries
infrared and microwave measuring devices to derivetemperature and humidity profiles of the atmosphere and has
been orbiting since May 4, 2002.
ERBS(Earth Radiation Budget Satellite)
Launched from the Space Shuttle Challenger nearly 20 years
ago, this satellite is still returning useful data. It was designed toinvestigate how energy from the Sun is absorbed and re-emitted
by the Earth and to determine the effects of human activities(such as the burning of fossil fuels and the use of CFCs) andnatural occurrences (such as volcanic eruptions) on the Earth’s
radiation balance.
Landsat 7(Acquires 30 m resolution imagery of the Earth)
The Landsat series of imaging spacecraft started in 1972 andhas been very successful. The latest one, now nearing the endof its five-year design life, provides moderate resolution digital
imagery of the Earth’s continental and coastal areas with global
coverage on a seasonal basis using the ETM+ (Enhanced
Thematic Mapper Plus) instrument. Operated by the US
Geological Survey since the year 2000, its data applications
include agricultural efficiency, air quality, aviation safety, coastalmanagement, public health and water management.
Landsat’s sun-synchronous orbit repeats the same ground track
after 16 days and, on the daylight side of its orbit, passes
overhead in mid-morning when average cloud cover over land is
at its minimum.

This is an international mission, launched in late 1999, with
instruments supplied by Japan and Canada as well as the USA
and provides global data on the state of the land, oceans andatmosphere.

NMP EO-1(New Millennium Program Earth Observing-1)
EO-1 was designed to demonstrate and validate advanced
instruments and spacecraft systems but has returned usefulscientific data as a by-product of its testing. ALI (Advanced
Land Imager) data is used to measure land use changes. It was
launched in November 2000 into an orbit similar to that ofLandsat 7.

Jason-1(Ocean surface topography)
This is a joint mission between the US and France and carries
equipment to measure sea surface height with great precision.
In addition to an array of laser retroreflectors and a solid stateradar, it carries a microwave radiometer and a DORIS (Doppler
Orbitography and Radiopositioning Integrated by Satellite)
receiver as well as a GPS tracking system. It has been in orbit
since December 7, 2001 and is a follow-on mission to the highly
successful TOPEX/Poseidon.

ICESat(Ice, Cloud and Land
Elevation Satellite)
The primary goal of ICESat is
to quantify ice sheet massbalance and understand howchanges in the Earth’s
atmosphere and climate
affect polar ice masses andPage 6www.geo-web.org.uk

ICESatAugust/September 2004

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GEO Quarterly No 3

global sea level. ICESat also measures the distribution of clouds
and aerosols, as well as land topography, sea ice andvegetation cover. The sole scientific instrument on ICESat is theGeoscience Laser Altimeter System (GLAS) which combines a
precision surface lidar (LIght Detection And Ranging) with asensitive dual-wavelength cloud and aerosol lidar. The lidar
technique requires the satellite’s position to be known precisely
and ICESat collects data for calculating its position in space byusing onboard GPS receivers augmented by a network ofground GPS receivers and satellite laser ranging stations.
ICESat was launched on January 13, 2003 into a near-polar
600 kilometre circular orbit with a ground track repeat cycle ofprecisely half a year.
QuikSCAT(Quick Scatterometer)
Launched in June 1999, this satellite carries SeaWinds, a
specialised microwave radar for measuring sea surface windspeed and direction for global climate research and operational
weather forecasting and storm warning. An almost identical
instrument was launched on Japan’s ADEOS 2 spacecraft in
December 2002 to provide similar observations beyond the
QuikSCAT mission.
TOPEX/Poseidon(Topographic Experiment/Poseidon)
This joint mission between France and the US began its global
ocean monitoring in August 1992. It carries a dual-frequency
NASA radar altimeter, a single frequency CNES (Centre
National d’Etudes Spatiales) radar altimeter and a microwave
radiometer. To measure the spacecraft’s precise position it isequipped with GPS receivers, a laser retroreflector array and a
DORIS (Doppler Orbitography and Radiopositioning Integrated
by Satellite) receiver.
TRMM(Tropical Rainfall Measuring Mission)
TRMM is a joint mission between NASA and JAXA (Japan
Aerospace Exploration Agency) to measure tropical rainfall andthe associated release of energy that helps to power the global
atmospheric circulation which shapes both weather and climate
around the globe. Launched in November 1997, the satellite isoperating well beyond its three year design life. Its instruments
include CERES (Clouds and the Earth’s Radiant Energy
System), LIS (Lightning Imaging Sensor), TMI (TRMM
Microwave Imager), VIRS (Visible and Infrared Scanner) and a
precipitation radar.
Its low inclination orbit means it operates only between latitudes
35°N and 35°S but around 90 percent of the 1,100 cubic
kilometres of rainwater that reaches the surface every day fallwithin this area.
SORCE(Solar Radiation and Climate Experiment)
Launched in January 2003, SORCE is a joint project with the
University of Colorado’s Laboratory for Atmospheric and Space
Physics in Boulder. The 290 kg spacecraft was orbited by aPegasus XL rocket which was carried aloft by a modified L-1011
carrier plane. The drop over the Atlantic Ocean was followed bysuccessful burns of all three Pegasus XL stages. SORCE

The launch of SORCE in 2003
carries two main instruments; TSIM (Total Solar Irradiance
Monitor) and SOLSTICE (Solar-Stellar Intercomparison
Experiment) to measure the total solar output for climate
studies.
UARS(Upper Atmosphere Research Satellite)
The Space Shuttle Discovery lifted off on September 12, 1991
carrying this very large, complex spacecraft. It was released
three days later and began many years of gathering data on thehigh atmosphere including measurements of solar UV
irradiance and solar flux as a function of time, energetic electron
atmospheric energy input and the mapping of atmosphericwinds.

GRACE(Gravity Recovery and Climate Experiment)
GRACE is a cooperative mission with Germany to obtain an
accurate global determination of both the static and the timevariable components of the Earth’s gravity field. It was launchedon a Russian rocket on March 17, 2002 and carries the Star
Camera Assembly and SuperSTAR accelerometers as well as
instruments to measure its precise position.
The above is just a brief outline of some of NASA’s researchsatellites; much more can be learned by entering a spacecraft’s
name in an Internet search engine. Part two will give somedetails of spacecraft nearing launch and others currently underdevelopment.

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Alan Sewards
In the column ‘In Tray’ in the launch issue of GEO Quarterly,
Francis Bell asked about forward error correction. ‘How can you
correct an error which has not happened yet?’ he asked. This
short article aims to demystify the subject without getting into
the detail of how the error-correction codes work.
ARQ Anyone?
In earlier days of communications, the normal method of copingwith errors in transmission or reception of a message was to ask
for a repeat. This procedure, known later as ARQ (automatic
repeat request), involved the use of a back channel to send therequest over. With two operators involved in an exchange, thisis of course no problem, but if there is no back channel (such as
in the case of DTH TV—direct to home television), or if there aremany receivers for a message, some of whom may havereceived it OK and others not, the ARQ procedure cannot be
used. It is interesting to note that, although ARQ is regarded bysome as impossibly archaic, all the traffic on the Internet stilluses it, embedded in the familiar TCP/IP protocol.
Forward Error Correction
To cope with the exceptions, the idea was developed ofincluding additional information with the transmitted signal: thiswould enable any errors to be corrected at the receiving end.
This was done by passing the transmitted digital bit-stream
through an encoder which added redundant parity bits
according to an algebraic algorithm, outputting a longer
sequence of code bits called a codeword. The codewords werethen transmitted to the receiver which used a suitable decoder
to extract the original bit sequence. Suitable choice of thealgorithm permitted errors to be detected and corrected. Thisapproach was known as forward error correction (FEC).
Improved Coding Schemes
In 1955, another scheme of coding was introduced, known as
convolutional coding, in which the data is processed as a
stream of bits rather than blocks of data. The advantage of thisapproach is that the encoding of any bit is strongly influenced by
the bits that preceded it—in other words, the scheme has
memory. The decoder can then take into account this memory
when trying to estimate the most likely sequence of data thatwould have produced the observed sequence of code bits. Early
decoders used a process known as sequential decoding thatused a systematic procedure to search for a good estimate of
the message sequence, but this procedure was complex andtime-consuming and did not offer graceful degradation.
Improved Decoding Schemes
In 1967 Andrew Viterbi invented a decoding scheme which has
become the standard for decoding convolutional codes. At eachcode interval, the decoder compares the actual received code
bits with those which might have been produced for eachpossible memory state transition. It chooses the most likely
sequence within the particular time frame, using metrics ofsimilarity. The Viterbi algorithm requires less memory andprocessing than the earlier approach and performs robustly.
Deep Space Needs FEC
Later developments included the concatenated code, in whichan algebraic coder is followed by a convolutional coder, with thereverse for decoding. This approach combined the advantages
Page 8of the algebraic code in handling burst errors with those of the
convolutional code with random errors. Thus any burst errors
resulting from the convolutional decoder would be effectively
corrected by the algebraic decoder. Performance was further
improved by using an interleaver between the two stages tomitigate any bursts that might be too long for the algebraic
decoder to handle. Codes of this type were used by Voyager 2
on its encounter with Uranus in 1986 and are used for the DeepSpace Network and the US Air Force Satellite Control Network.
Extra Bits Needed
The encoding process used in forward error correction
produces a number of additional bits for each given number ofdata bits and these are added to the transmitted bit-stream,
which increases the amount of data to be transmitted. For
example, a 40 MHz bandwidth satellite transponder may have
only 23 MHz available for TV data as the remaining 17 MHz areused for parity bits. Other schemes produce one parity bit foreach data bit—this is known as a rate code. Other common
codes use rate , rate , rate . Generally, the more parity bits
added, the more powerful the code, but at some point theadditional data to be sent begins to cut into the channel
capacity, and a compromise is necessary.
FEC Is Everywhere
FEC coding is becoming very common today as it offers
significant improvements in performance and the required
processing power is available cheaply on chips. The common
Compact Disk, for example, uses block coding FEC to protect
against read errors (no back channel available here!), as doDVDs and computer hard drives. Common coding schemes
used are the Reed-Solomon, Golay, BCH and Hamming codes.
DTH TV would be quite impracticable without FEC as thesatellite transponder power would have to be hundreds of watts
or the receive antenna several metres in size. Cellular (portable)
telephones also make use of FEC to obtain adequate range
performance with the low output power that has become thenorm.
Turbo Coding
The most recent development in FEC is turbo coding, invented
in the early 1990s by two French engineers. This scheme uses
two relatively simple convolutional codes and an interleaver toproduce a block code. The interleaver is designed such that thesecond encoder gets an interleaved version of the same datathat went into the first encoder, thus the second encoder
generates an independent set of code bits. It has the great meritthat it performs within a fraction of a decibel (dB) of thetheoretical limit calculated by Shannon. Such codes are
beginning to be introduced into DTH TV systems.
How Much Do You Get?
To put some real numbers on the table, assume that we have achannel for which we require a bit error rate of 10 to thepower –6 (i.e. 10-6). Convolutional codes can provide an
improvement of about 5.5 dB compared with an uncoded
system, while concatenated codes manage 7.75 dB. The turbo
code, on the other hand, can produce an improvement of 10 dB.
When you think of antenna diameters or transponder output
powers in terms of decibels, these are powerful numbers!

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August/September 2004

Group for Earth Observation

GEO Quarterly No 3

Fred van den BoschAt least once a year we visit thefamily of my Vietnamese wife
Minh. They live in Nha Trang, anice quiet bathing village on theeast coast of Vietnam, about 400
km north of Ho Chi Minh City.
Since last year I have been trying

to receive weather satellites there.
That first year I had a lot of
problems finishing my equipment
due to a lack of time and a harddisk crash of my laptop.
Fortunately I was able to borrowan antenna and receiver so that I

could receive some pictures. This
year I planned to do it better. I
started earlier with rebuilding theantenna and receiver but thetravelling for my job cost me a lotof time so I finished everything justshortly before our leaving.

Figure 2 - NOAA-17 at 02:16 UT

Figure 3 - NOAA-17 at 04:07 UT

Figure 4 - NOAA-17 at 03:07 UT on March 16, 2004
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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Antenna

Program

The antenna I used was the PITA 137, a QFH antennadeveloped by Ruud Jansen and described in the Dutch
magazine De Kunstmaan of April 2000. The filars are
made from measuring tape (figure 1). My antenna isbasically the same as Ruud Jansen’s but I changed acouple of things, based on the borrowed antenna andmy experiences in using it.

I use WXtoImg for decoding the signals. An advantageof this program is that it gives pass lists in both UT
and local time for those who want to see which areas
are shown on the images. As Ground Station Location
I used latitude 12.25°N and longitude 109.18°E. The
time difference compared with with UT is +7 hours. In
my original experiments, I used a minidisk for storing
the satellite signals but the colours of my MSApictures were terrible. I haven’t looked for the reason
yet. In Vietnam I choose the easiest solution: I sent thesignals directly to my laptop and obtained much moresatisfying colours.

The Images

Figure 1 - The antenna mounted on a roof-top ladder

Very bad weather in Holland shortly before ourdeparture meant that I could only test the antennaindoors. In general reception results in my house arevery bad. But I put the antenna in front of a windowand set out to see if I could receive a signal. Thatturned out to be possible so I decided to take the risk
and do further testing in Vietnam in a much better
temperature. And the results there were surprisingly
good. The antenna was placed on a ladder on the roofof the house, about 12 metres above the ground.
During a couple of days there was a storm and it
became clear that my antenna was not really stormproof—the filars became all twisted and bent. The
whole antenna was leaning over by about 30 degrees
because the small tripod I used could not stand thepressure of the wind. Nevertheless the images I madethat day (March 9, 2004) are rather good. You canhardly see any difference compared with ‘normal’ days
(figures 2,3). Figure 3 shows more noise because thiswas a rather low pass and in that direction there aremountains.
Figure 4 shows an image taken after righting theantenna. At the top is China, Vietnam is prominent at
centre while most of Indonesia can be seen to thesouth.

I was a bit limited in the number of useful passes
available. Rising early during my holiday is in general‘out of discussion’. In the evening the darkness comes
rather early. Beside that there were also the social
duties. Family and friends often visited or invited us
out just at those times when the best passes were due(indeed, having a holiday is a tough task!). But I
succeeded in receiving some nice images. And that wasof course the main reason of doing all the ‘hard work’:receiving pictures from a part of the world you don’t get
so often.

Suggestions for Articles
Finally, I would like to finish with a ‘wish list’ for thekind of articles I would like to see appearing in futureissues of GEO Quarterly (to help me improve myimages).
How can you improve your images with photoprograms like Paint Shop Pro or Photoshop. I don’tmean combining images in the way that Ferdinand
Valk described in his recent article but the more ‘basic’things, such as:• what options are useful and how to use them
• what colours to use (because I am a bit colour
blind)• how to remove noise etc. from the images. I use
WXtoImg but there are perhaps better ways.
• how to give all your images the same colour /brightness / contrast (as a start for combining
images - WXtoImg does not work completely
satisfactorily here).
Of course there are books about this but my idea is tohave an article with operations specific for weather
satellite images. At least I can use the hints!

ReceiverWell, what about it! [Editor]

The receiver is an RX137 from the Dutch bookHandboek Weersatelliet-ontvangst of Rene Reudink. I
bought it second hand. The receiver was originallybuilt in a rather big cabinet, so I rebuilt it in thesmallest possible cabinet and added a few features—
like a switch for predefined frequencies.

Here’s a great opportunity for some of you moreexperienced GEO readers to share your techniqueswith Fred and other relative newcomers to weather
satellite imaging. Please send your contributions to:editor@geo-web.org.uk

Page 10

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Group for Earth Observation

GEO Quarterly No 3

Beth Rose
Callington Space Centre ispositioned 50° 30”N, 4° 19”W in
Cornwall, UK. It is dedicated tothepromotionofSpace,
Astronomy, and the awarenessand use of science and technology.
It seeks to motivate and educate
the students and the communityof today. The centre runs a wide
variety of courses ranging fromresidential overnight experiences
and open days, to courses directed
at talented students. The Centre
also runs adult astronomy
workshops using the latest
telescopes,
andwishestoencourage their use by everyonein the local community.
The centre is also engaged insetting up a weather station forreception
of
APT
and
Geostationary satellites, withsome equipment donated by
Dartcom (a local company). There
are also plans to receive directly
data from the latest EUMETSATMSG digital satellite and toprovide direct reception of theNASA and ESA television
services. This will provide ahigher degree of technicalbackground information for the
students.
These future developments willallow the development of the
Callington Space Centre as across-curriculum resource andenable it to keep abreast of all thelatest advances and space-related
developments. The Centre has
fostered a wide variety of local
support, and is encouraging
interest within the community bydemonstrating the extent of thework that is going on at theCentre by its open days and otheractivities.
New educational modules havebeen written with the focus on
primary students, aiming to

make them more aware of thetechnology we use to gather dataon Earth. This will hopefully
provoke students to take up
technical courses having left
college, and help in maintaining
the countries leading role inremote observing and spacetechnology development.
The centre has applied to
EUMETSAT for educational data
access to the newly launched
Meteosat Second Generation
Satellite (Meteosat-8), which
would not have been possible
without the continued lobbying ofcertain individuals within theamateur community to keep thedata access free for educationaluse. This will provide a massive
amount of data for use by the
whole
of
the
Callington
Community College.

NASA Scholarship
On a personal level, my time attheCentrehas
been
extraordinary, and ten months
ago I had the opportunity totravel to America. A scholarshipplacement with NASA is not theconventional work experience forstudents studying the first year of
their A levels! However throughthe Callington Space Centre this
proposal became a reality andthrew up a landscape ofopportunities to all involved.
For a chance to experience thewonders of NASA, each student
had to go through a six monthselection process to demonstrate
to the judges that they possessed‘The Right Stuff’. The fifteen
candidates varied hugely and all
had qualities which might securethem a place. The selection was
tough and enduring involving
intelligence tests, endurance runs
and many other disciplines
bringing out both the best in
www.geo-web.org.uk

The Weather Station
Mike Grocott

The Weather station we are setting
up within the Space Centre isdesigned to encourage the public tobecome more aware of the benefits
that satellite technology gives us.
Most people think of space as being
either shiny things in the night sky
or astronauts; many do not realise
the leading role the UK has in thefield of remote observation. The
Space Centre and the weather
branch hope to address that lack ofunderstanding.
The whole system was brought
sharply into focus on the afternoon
of Friday, March 26 this year, when
one of our students switched on thesystem and captured the image of acyclone heading towards the coastof South America, a classic image ofa natural phenomenon. The easewith which the image came down
and its clarity were exceptional andas we all realise, people love
anything that is easy. The event
was made more special when, on
the news that night, the students
heard the report of the cyclone.
They understood the excitement of
discovering news before anyone
else around them. The image is
now on the college intranet where
it is provoking more interest thanever in the idea of watching the
Earth from above.
Although still in its early stages theidea is for me to get the students tostart learning how to use thesoftware to develop the colour
imaging etc. I have found thatstudents tend to find more time touse computers than I can!. We arealways looking for support andadvice so please let us know of any
good sites or tips to make life easier
for a busy teacher and information
hungry students.
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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Figure 1 - The ISSET Champions 2003 (Beth's Team).
Beth is pictured at far right of the group as thecrew prepare to launch their rocket at Johnson
Space Centre.

Figure 2 - Students of St.Mellion Primary school, Mike Grocott
Director of the Space Centre, Portreeve of
Callington. Front row - Dr. Martynov, Interplanetary
Scientist and Cosmonaut Alexander Volkov (right).

Figure 3 - Callington Space Centre students Beth,Zak and Julia, with Mike Grocott, present
a book of condolence to Astronauts
Bonnie Dunbar and Andy Thomas.

Figure 4 - The Weather Station at Callington Space Centre

Figure 5 (above)
The Meteosat-7 image
pictured during reception
Figure 5 - The APT antenna and Meteosat dishPage 12Figure 6 - The Meteosat-7 image of the cyclone in the south Atlantic Ocean
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August/September 2004

Group for Earth Observation

people, and sometimes the worst, each discipline
carefully constructed so that all areas of skill could betested. After months of waiting my name wasannounced as one of three students who would
represent the Space Centre, County and Country
embarking on the adventure of a lifetime to experience
the extraordinary!
Two other students, Zak Bourn, Julia Geall and myself
travelled with Mike Grocott, Director of the Space
Centre to the USA. Mike had helped lead this trip
several times in the past, returning each year with anocean of enthusiasm. Every year the experiences where
spectacularly different, from watching a launch as a
VIP at the exclusive VIP observation point, toparticipating in a BBC documentary.
After a short flight (sitting next to the ex-mayor of San
Francisco!) we arrived in Florida to experience the firstweek working with employees at the Kennedy Space
Centre. There was a huge difference from the tour wewere on to the usual tours that excite thousands ofvisitors each year. A presidential pass ensured that wewould see the highly restricted zones and watch how
the Rocket Scientists really work.
An exclusive look inside the VAB (Vehicle Assembly
Building) caused an outburst of gasps at the sheer
height and volume of this fascinating building. The
VAB is where the Space Shuttle Orbiters, such as
Columbia and Endeavour are assembled before launch,and it is thick with the history of space travel andexploration. This building has fascinated many anaudience at presentation evenings with its wonderfularray of facts and stories. The flag painted on the sideof the building is the largest hand-painted American
flag in the world, and the roof could accommodate an
American football stadium, with an acre’s worth ofparking!
Launch pad 39A, is where the shuttles spend their
final hours on Earth before being launched in to space
and is an inspiring place to be. The general public are
positioned on a lookout tower just over a mile from theactual launch pad peering through binoculars.
However the Space Centre team, being guests ofimportance (!) were driven up to the final VIP
observation point where NASA employees are allowed
to stand. From this angle it was hard to imagine howmuch power is dissipated on launch as there are few
signs of stress on the framework, and it was strange torealise that this was the final stop before the moon,and probably the closest I would ever get.
The second day of the trip proved to be the most
exciting. The team of NASA employees who werechaperoning the students managed to arrange a rarevisit to view the Mars Rover before its launch to the
Red Planet. This is a phenomenal piece of technology!
We were told that this ‘wondrous object’ has only been
witnessed by as few as one thousand people—and I was

GEO Quarterly No 3

one of them! Any human contact with the sensors on
the Rover would distort the results obtained from
Mars, and millions of dollars would be wasted.
It is hard to describe what it was like to see the Rover,being at the very forefront of science, technology andspace exploration. There is nothing to compare it with
due to it being so unique, and the best explanation
would not convey the fascination that gripped me andthe other students. There was great excitement back in
the UK when we heard news of the successful landingof the two Rovers, Spirit and Opportunity, knowingthat what I had seen was now on Mars.
Physics took on a whole new meaning whilst studying
with rocket scientists, as I could see the result of
calculations and measurements, and the lesson
experienced whilst on a roller-coaster is one I shallnever forget! However even a good roller-coaster could
not compare with the astronaut training facilities,some of which enabled us to push our bodies to thelimit.
The Centrifuge was probably the most memorable partof Astronaut Training. This machine simulates theeffect of being launched in an Orbiter putting 3G’s ofpressure on your body, and it was extraordinary to feelthe blood draining from your arms. 3G’s were great toexperience: however the first astronauts had to endure
16G. Your body can continue functioning for a split
second at 12G but after that you pass out.
The second week introduced the academic element as
we became Texan Aerospace Scholars at the Johnson
Space Centre in Houston. The group was presented
with a three-day challenge involving presentations,analysing rocks, driving Rovers and launchingchemical rockets. Three teams emerged with eachmember taking on a different role; from rock analyser
to Rover Control Man. One team captain was also
required with each team electing a Callington Space
Centre student introducing extra rivalry!
One of my responsibilities as captain was overseeing
the distribution of the $330 million budget with which
to make Landers and rockets, and to spend on
experiments we wished to conduct. Throughout thechallenge we had to cope with pay-cuts, the occasional
bonus and declaration of materials that had beenclassified as unsafe. With each memo new plans had tobe formulated and every idea carefully discussed untila solution was found.
It was a fun but sometimes fraught couple of days as
each team fought to become the International Space
School Educational Trust (ISSET) champions of 2003
(which eventually resulted in my team winning!).
A poignant and reflective opportunity in Houston was
the presentation of a book of condolence to NASA for thecrew of Columbia; tragically killed during February

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GEO Quarterly No 3Group for Earth Observation

2003. The book was signed by members of the local
community and presented to Bonnie Dunbar (STS 61A, STS-32, STS-50, STS-71, STS-89) and Andy
Thomas (STS-77, STS-89, Mir, STS-102 next flight
STS-114) two of NASA's most prolific astronauts. An
assurance from Bonnie Dunbar that the book would begiven to Sean O'Keefe Head of NASA emphasised thepresence and strong links with NASA that Callington
Space Centre is forging.
The final day of the trip was utterly astonishing. Eachstudent had been given a personal invitation fromJohnson Space Centre to watch the live video link-up
of the launch of the Russian Soyuz carrying one
American Astronaut and one Russian Cosmonaut. This
event was hugely important to NASA and the Russian
Space Programme, as it was the first launch since
Columbia and the first time that only two astronauts
would be sent to the International Space Station(usually three are sent).
As we drove into Johnson Space Centre, passing thearmed security, we saw television crews lining the roadwatching the build-up to the launch and waiting for theslightest bit of information. I could not believe thatthey were ‘staking out the place’ and likewise they
could not believe that students from the UK wereattending the launch as invited guests of NASA. It wasat that point that I realised I would be the only
journalist to witness the event as it happened, frominside NASA Headquarters!
The launch was the most exciting and exhilarating
moment of the trip, and yet it was excruciatingly slow.
As the countdown commenced, the auditorium fellsilent, and everyone became fixated on the screen until
eventually the Soyuz exploded with a tremendous
amount of power and started to gradually lift from the
Earth. There were a few stunned silent seconds before
the auditorium erupted with cheers and camera
flashes catching the historic moment. The Callington
Space Centre students had not only watched but had
also become part of space travel history. This is justone of the many interesting opportunities the Space
Centre offers annually for students who aredetermined enough to gain a place!
It is not just NASA that the Centre has links with, it
has strong relations with the Russian space
programme as well. The Callington Space Centre was
opened on the 22nd of January 2004 by Colonel
Alexander Volkov who has spent a total of over 13
months in space aboard the MIR Space Station as a
Cosmonaut, he was accompanied by his friend andtranslator Dr Martynov who is a Chief Scientificadvisor and Interplanetary Scientist, as well as having
been the head of Ballistics in Russian Mission Control(Energia). Our guests were exceptionally impressedwith the set-up of the Centre, and enjoyed speaking to
the students about their perceptions of science andspace exploration after they had unveiled a plaque toPage 14

August/September 2004

commemorate the opening of the Callington Space
Centre.
Students can gain scholarships to represent the United
Kingdom in Moscow as part of the Russian Space
Olympics. Like the NASA scholarship, there is alengthyselection
procedurewith
Physics,
Mathematics, Literature and Computing Exams to becompleted, but the resulting lifetime experience
exceeds by far the little pressure felt by sitting a coupleof small exams.(honest!)
It was not just the trip which has made me so excitedabout Space, Science and Technology, but also working
at the Space Centre with younger and older membersof the community. Residential courses have to top mylist of Space Centre activities. Children are now on
waiting lists to try the Callington Space Centre
experience, building rockets, learning about the latest
telescopes and astronomy; and hopefully soon they will
be able to see live weather pictures from space via the
new weather station.
The community is becoming excited about science andspace and students are volunteering to sit GCSE
Astronomy several years earlier than they will besitting their compulsory exams. Becoming anastronaut or rocket scientist is now more achievable.
Space is the future and the Callington Space Centre ispart of that.
If anybody is interested in any of the courses on offer
or the public open evenings, they should contact Mr.
Mike Grocott, Director of the Space Centre, our contact
details are on the website at:www.callingtonspacecentre.co.uk

Peter Wakelin provided this Meteosat-7 infrared image received at
1200 UTC on 23 June 2004. It depicts an unusually vigorous summer
depression crossing Britain. The central pressure dropped to 982 hPa
which is within 5 hPa of the June UK record which occurred on June 5,
1944 (that storm delayed the D-Day landings by 24 hours). High winds
on 23 and 24 June felled many trees and road, rail and sea traffic wasdisrupted. In some places, June’s average rainfall fell in just 24 hours.

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August/September 2004

Group for Earth Observation

GEO Quarterly No 3

Lawrence Harris
It is amazing to realise just how many objects cross theface of the sun: artificial Earth satellites, such as theISS; the Moon (during a solar eclipse); a few asteroids
and of course the two inner planets, Mercury and
Venus. When early astronomers first realised, bylaborious calculation, that the inner planets could
cross the disc of the sun, they also realised that thisgave a rare opportunity to calculate the Earth-sun
distance. This was of extreme importance at that time
because this fundamental distance was not accurately
known: there had been a few estimates but what weknow now as the true distance (about 93 million miles)
was simply unknown.
Transits of Venus are rare. They happen in pairs over
one hundred years apart. No-one alive today saw thelast one—in 1882.
Much has been commented about the safe viewing oftransits—and rightly so. Unlike a solar eclipse thetransit of a planet across the face of the sun is not easy
to see. The planet itself is very small against the brightbackdrop. Mercury is smaller than Venus and further
away from Earth, so when it transited the sun last year
few people without suitably equipped telescopes wereable to see it. Venus is larger and also nearer, but I
personally doubt whether anyone would have seen thetiny black circle without optical aid. A much better way
to view most solar phenomena is to project the sun’s
image from a refracting telescope.

the transit—but, hey.—I just wanted to watch. I
therefore decided to observe the early stage of Venus
entering the sun’s disc so that I could look out for theBlack Drop effect. This was reported by Venus transit
watchers of previous centuries and took the form of a
black elongation between the disc of the planet and theedge of the sun’s limb. It has been reported to last
several seconds. I watched the separation of Venus
during ingress but hardly anything like a black drop
appeared. The image was so clear that I was reluctant
to fit the web camera, but I did so anyway. Rememberthat these days, astronomers are using telescopes with
optics of a quality unobtainable in previous years. I
suspect that the Black Drop effect may have been afunction of imperfect optical systems.

07:51 UT

09:04 UT

From then on, everything was recorded for posterity. I
collected a large number of 30-second video sequencesusing a Toucam Pro webcam and K3CCDTools, afreeware program (at least the version that I used),and collected about 4 Gb of video.

On the evening before the transit I was using mytelescope under clear skies but decided to finish about
midnight because I had to be up for the transit for 6 am
BST. Where was the sun going to rise? I have some
unwelcome trees surrounding my observatory; a huge
one due south that cuts weather satellite signals until
they reach over 30 degrees elevation, and two on myeast. At 6 am I was looking across the garden andsmiling because the sun had risen between these trees
and was clearly going to give me a good view for somehours.

Rather unfortunately, the sun was devoid of sunspots
and faculae. These can act as reference points duringtransits. Instead, I tried to include some of the sun’s
limb for many of the sequences, though during the
middle phase this was not possible.

I opened the observatory, powered up the telescope andcomputer, fitted the solar filter and web camera, andfocused the instrument.
Locating the sun took me an
unusually long time—about
5 minutes—and by the time
I finally found the solarlimb, Venus had justentered. This ‘first contact’(ingress) is of great interest
to those doing projects about
Ingress - 05:49 UTC

The next transit is in eight years’ time but it won’t bevisible from Britain. We were therefore very lucky withthis one, even though not allareas of Britain had clear
skies. For me, it was thebest astronomical event that
I have been able to record –and I was able to produce a
picture in the early stages,
for my 5-year old grandson
to take to school to show theEgress - 11:02 UTC
teacher. It made his day.

As the end of the transit approached, I took moresequences because I wanted to include all of the egress,
especially any Black Drop effect. This proved
successful and my final sequence included the last few
seconds of Venus in front of the sun.

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Les Hamilton
The dust has settled, the computers, antennas anddisplay tables have gone: all that remains of GEO’s
inaugural Symposium at the National Space Centre in
Leicester last May 1 are fond memories of a truly
wonderful day. The packed program featured no fewer
than three separate systems downloading live DVB
reception of Meteosat-8 imagery, demonstrations ofbending copper-pipe filars for the RQHA antenna,talks from a wide range of speakers, the chance todiscuss problems with experts and, not least, theopportunity to visit the Space Centre itself, with its
topical Beagle-2 display and its amateur radio station
operating GEO’s own GB0GEO callsign.
First impressions are always important. Visitors to
Symposium 2004 were held spellbound the instantthey entered the auditorium by David Taylor’s
projections of stunning Meteosat-8 imagery on to a big
screen. Another major point of focus was Francis Bell’s
display of live MSG imagery on a laptop PC, illustrated
on the front cover of this issue, which emphasised just
how rapidly improving technology is bringing highquality imaging from the digital satellites withineveryone’s reach. There was also an impressive displayof official Meteosat-8 images in the form of colour
posters, courtesy EUMETSAT’s Gordon Bridge.
The Symposium was opened by Francis Bell, whowelcomed over 60 delegates and speakers. We weredelighted to welcome a strong representation from theDutch weather satellite organisation, Werkgroep
Kunstmanen, but our most travelled visitor was C S
Loh from Kuala Lumpur in Malaysia. Congratulations
were offered to EUMETSAT on the occasion of the firstanniversary of operational imagery from Meteosat-8(which fell the previous day). It was emphasised that
GEO’s overriding philosophy was that ‘this is ameeting of friends’—we should all enjoy the occasion.

The Speakers
Charles Bishop
Fittingly, the day’s proceedings were opened by
Charles Bishop, Chief Executive of the Space Centre,
who started by explaining that he is not a scientist, but
a professional in the field of visitor attraction
management—and had previously worked at both
Alton Towers and Madame Tussauds in this capacity.
Charles traced the development of the National Space
Centre from the mid 1990’s, when it was but a merebrainchild of Leicester University, through to its
realisation on the site of a former sewage works.
Construction commenced during 1999 and the Centre
Page 16

doors first opened to the public in summer 2001, when
it proved so popular that there were regularly 2-hour
queues of visitors awaiting admission.
Currently, pride of place in the Centre goes to theBeagle-2 display, and we learned how this 65 kg Marslander had developed, through miniaturisation, froman original concept design the size of a family car!
Despite the lander’s ultimate demise, the Beagle
Project really had captured the interest of the public,
and the launch of the parent Mars Express craft waswatched, within the Centre, via a live video feed from
Kazakhstan. All this is just part of the Centre’s drive
to excite people about Space and the next major projectwill be the building of the Human Spaceflight Gallery
in time for opening in June 2005.
Geoff Griffiths
An amateur radio station, manned by volunteers,
operates within the National Space Centre. Its main
purpose is to educate the public in the use of amateur
radio through satellites, not just in the field of voicetraffic, but also the decoding of satellite transmissions
to learn about diagnostics of onboard instruments.
Free training courses are offered to radio amateurs,
where they are instructed how to operate throughsatellites. The station has also been able to offer
opportunities for school groups to question astronauts
aboard the International Space Station. Geoff pointed
out that, for Symposium Day, they were operating asan HF station under GEO’s own GB0GEO callsign, andAnn-Marie Evans took the opportunity to visit thestation during the afternoon to make a contact with
Poland !
Gordon Bridge
We were specially pleased to welcome EUMETSAT’srepresentative, Gordon Bridge, to the Symposium.
Gordon outlined the Meteosat-8 story from its funding
by a consortium of European national weather services
to its role in providing the regular 15-minute scans ofweather cover over the oceans of the Earth that are
essential for today’s short-range forecasting. Gordon
described the Meteosat ground segment and revealed
that the extent of automation is such that only two or
three people are needed to control all three operating
Meteosats. The EUMETCast dissemination systemcurrently in place for Meteosat-8 will continue for
future MSG satellites, even though they will also
provide a concurrent direct broadcast facility.
Gordon’s talk was well illustrated with slides showing
various stages in the development of Meteosat-8 andthe appearance of images from all its data channels.

www.geo-web.org.uk

Nadine Bell signing in delegates attending the Symposium

Nigel Evans and Rob Hollander (right) bending RQHF filars

Photo: David Taylor

Photo: Cecilia Taylor

Model of the ill-fated Beagle-2
Mars lander on display at
the National Space Centre

David Taylor (2nd left) discussing his
MSG Data Manager software withdelegates during the GEO Symposium

Ruud Jansen from Werkgroep
Kunstmanen holding an impromptu
discussion during the afternoon session

The amateur radio station at the National Space Centre,
operating GEO’s GB0GEO callsign for the day

Visitors enjoying hands-on experience of live MSG reception

Symposium visitors enjoying a display ofMeteosat-8 imagery on the big screen

The display of posters and images by EUMETSAT

Photo: Ray Godden

Photo: David Taylor

GEO Quarterly No 3Group for Earth Observation

But the highlight was a presentation of animations,many in colour, from Meteosat-8. We were regaled,inter alia, by developing thunderstorms over east
Africa, a swarm of aeroplane contrails sweeping
laterally across Europe, Cyclone Gafilo swamping
Madagascar, sand blowing from the western Sahara
over the Atlantic, diurnal fog waxing and waning over
the Mediterranean, and smoke and hotspots from lastsummer’s forest fires in Portugal.
Finally, Gordon looked to the future and revealed thatplanning for Meteosat Third Generation, targeted for2015, was already under way. New features of MTG
were likely to include lightning detection and both IR
and UV/Vis atmospheric sounding.
Gordon Bridge’s entire presentation, including someamazing weather movies, is available from GEO as a2-CD set. Anyone interested should send a request toFrancis Bell, enclosing three first-class postage stamps.
David Taylor
David explained, with the aid of a Powerpoint PC
slideshow, the latest developments in using his MSG
software suite to create images from the DVB
EUMETCast relays of MSG data from the Hot Bird-6
satellite. David described features of the 2-PC system
initially recommended by EUMETSAT, where acomputer of relatively moderate specification could be
used to download the data but then pass it to a second
networked PC of higher specification for processing
and image storage. These systems work well, butadvances in design now mean that a single PC with a
2- to 3-GHz processor plus a gigabyte of memory canhandle the entire task on its own. David also explained
the functionality of each program in his MSG software
suite, suitably illustrated by both still slides andanimation sequences.
David Taylor has kindly made his entire
presentation available to GEO readers on a CD
ROM. This is a Powerpoint slideshow which
covers all the hardware and software issues
needed to set up a PC for reception of Meteosat-8
imagery; specifications of various PC systems(twin/single), hardware components, DVB card
installation and many useful tips. If you would likea copy of David’s presentation, which includes anumber of images and animations, please send the
Editor £5 for your copy, which includes the cost of
P&P. Cheques and postal orders should be madepayable to ‘Group for Earth Observation’. (Youmay also send cash, but at your own risk).
Robert Moore
Robert has been an enthusiastic user of Meteosat data
for many years, and described his experiences insetting up his MSG station. He detailed how his
location in north Wales had proved ideal for studying
weather arriving from the Atlantic Ocean, and how theincreased resolution of Meteosat-8 has furthered thesestudies. Robert’s talk is presented in full starting on
page 42
Page 18

August/September 2004

Arne van Belle
We were privileged to have several members of the
Dutch Werkgroep Kunstmanen present, all well known
for their pioneering work in the field of MSG reception.
Arne opened by presenting live Meteosat-8 images on
his laptop, projected on to a large screen. Amazingly,
this was accomplished using a 35 cm dish withstandard 0.6 dB ALPS LNB!. With the MSG softwarestill running in the background, Arne proceeded toshow us an animation detailing the launch of NASA’s
Terra satellite and continuing to show, in animation,
how the instrumentation aboard it operated.
Next followed Arne’s own illustrated presentation
detailing how to set up an MSG station, covering boththe hardware side, and a walk-through of setting up
the Tellique software. He then returned to MSG DataManager to illustrate how both HRIT and LRIT images
build up, and concluded by running the current day’s
animation showing the cloud over England.
This was followed by a series of archived animations
created using GeoSatsignal: a 24-hour June 2003
global animation, dust storms over the Mediterranean
and the Canary Islands, the birth of a hurricane offwest Africa and the Brazil cyclone.
Arne then simultaneously brought up a satellite-TV
channel via the DVB link and followed up by treating
us to several movie sequences created by a Spaceflight
Simulator program. Finally, he returned to MSG DataManager, which had continued to operate flawlessly inthe background all this time—without compromisingsynchronisation or image acquisition: all possible
thanks to a 3.5 GHz Pentium 4 processor!
Rob Hollander
Rob, another member of Werkgroep Kunstmanen, gavea presentation on QFH antennas and their radiation
patterns. Rob made the point that a half-turn QFH
provided better reception for satellites close to thehorizon than the alternative quarter-turn version.
Most of Rob’s presentation, and much more, is detailed
in his article on page 26.

Open ForumFrancis Bell set the forum in motion with a brief
overview of GEO, detailing the group’s creation in
November 2003 and its status as a limited company.
Discussions ensued on matters as diverse as upgrading
the RX2 PIC to handle the new APT frequencies for the
NOAA N and NOAA N-prime satellites, the likelihoodof ‘pager’ problems on the higher 137.9125 MHz
channel, using David Taylor’s ATOVS Reader
program, preferences for a paper Quarterly rather thenan electronic CD version etc. etc.
Finally, with everyone’s queries answered, Francis
Bell concluded the day with a vote of thanks toeveryone who had contributed towards making the day
such an unqualified success.

www.geo-web.org.uk

August/September 2004

Group for Earth Observation

GEO Quarterly No 3

Peter Wakelin
Weather Satellite Explodes
The Defense Meteorological Satellite Program (DMSP) F-11
spacecraft exploded during April. It was launched on
November 28, 1991 and retired four years later. USSTRATCOM
catalogued 56 fragments large enough to be detected by the US
space surveillance network. Orbital data for the DMSPs are notmade public but two-line elements are maintained by hobbyist
visual observers. Greg Roberts, in Capetown, observed thissatellite after the explosion and found it to be more or less on
track with no change to its visual appearance, indicating that theenergy from the explosion was insufficient to significantly
change the orbit or shatter the satellite completely. Surprisingly,
two-line data for the fragments were released, which made iteasy to establish that the explosion occurred at about 1500 UTC
on April 15.
It is probable that the build-up of pressure in a battery or gas
tank caused the explosion. Shortly after launch, DMSPs, andtheir NOAA cousins, use hydrazine thrusters to trim their orbits.
These thrusters are then rendered inoperative. Unspent
hydrazine has caused many fragmentations in the past but thisis believed to be the first time that a weather satellite has
suffered such a fate.

New Chinese Satellites Under Construction
The first two spacecraft in the next-generation Feng Yun 3
series of polar-orbiters are being built and the first, FY-3A, is
expected up in 2006. There are to be 7 spacecraft in this series
and they will operate until 2020.
In addition to a suite of atmospheric sounders, there will bethree imagers, one of which, the Visible and Infrared
Radiometer, will transmit real-time data in the new AHRPT
format on 1704.5MHz. Transmission characteristics will be very
similar to those of the European METOP which will transmit on
1701.3MHz but, unlike METOP, there will be no LRPT broadcast
at 137MHz.
The other imagers are the 20-channel Medium Resolution
Spectral Imager (MERSI) which is very similar to the MODIS onsome Western spacecraft and a Microwave Radiation Imager(MWRI).

NOAA-N’ (N-prime) Future Still Unclear
NOAA N’ was severely damaged in a factory accident last year
and, at the time of writing, a decision on the future of the Nprime mission is still awaited. There would appear to be three
options: Repair the damaged satellite, build a new one, or scrap
the mission completely. Some sources indicate that the damage
was too severe to be repaired. The second option is expensive
and would take several years. If the third option is taken, thenthe demise of APT could come several years sooner than
anticipated as NOAA-N, due up next February, would be the last
to carry APT.
Should the N-prime mission not go ahead, then the risk of the
NOAA series failing before the next-generation NPOESS
becomes operational (2010 at the earliest) is greatly increased.
Three military DMSP craft (now operated by NOAA) are
believed to be operational and a further four await launch sosome data would still be available. However, the direct-readout
data stream from the DMSP craft is not available to hobbyists.

In the meantime, the European METOP data should come onstream and the NPOESS Preparatory Project (NPP) is due tofollow.

NOAA N-prime lies prostrate after its fall at the Lockheed
Martin plant on September 6, 2003.
Image: NASA/NOAA/Lockheed Martin

MSG-2 Launch Preparation Under Way
MSG-2 was taken out of storage in April and Arianespace will
launch it early in 2005. The month of launch is dependent on theavailabity of the various versions of the Ariane-5 launch vehicle
and possible co-passengers but should be known bySeptember.
Following the failure of one SSPA (Solid State Power Amplifier)on MSG-1, the design was modified and extensively tested. The
SSPAs for MSG-2 were subsequently delivered in May.
Retrofitting to correct other anomalies encountered during
MSG-1 commissioning has also taken place.
An anomaly encountered on the SEVIRI MDU (Main Detector
Unit) on MSG-2 during an optical vacuum test resulted in theunit being replaced by the one destined for MSG-3.
The MSG-2 system validation test is currently under way toensure compatibility between the satellite and the groundsegment which has been upgraded to cater for two operational
spacecraft.

Forthcoming Weather Satellite Launches• The next NOAA polar-orbiter, NOAA N, has been delayed
until February, 2005.
• GOES N is due up on December 1, 2004.
• At the CGMS 32 meeting held in Sochi, Russia in May, theRussians reported that Sich 1M would be launched in
September, 2004.
• The Chinese give October 2004 for the launch of their next
geostationary satellite, Feng Yun 2C, which will bestationed above 105E longitude.
• November 2004 is the earliest that the Japanese could
launch MTSAT 1R following the failure of the H-IIA rocket
at its last launch attempt.

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Page 19

GEO Quarterly No 3Group for Earth Observation

Figure 1 - A true-color MODIS image of ‘Cyclone Catarina’
acquired by NASA’s Aqua satellite on March 27.
Image: Jeff Schmaltz, MODIS Land R R Team at NASA GSFC.

August/September 2004

Figure 2 - NASA's QuikSCAT spacecraft and its Seawinds
instrument produced this image of the first hurricane
ever recorded in the southern Atlantic on March 27.
The white arrows represent wind speed anddirection: the colours indicate mean wind speeds.
Image: W. Timothy Liu at JPL, Project Scientist of QuikSCATFigure 3 (left) and Figure 4 (right) - TRMM representations of ‘Cyclone Catarina’
Images produced by Hal Pierce (SSAI/NASA GSFC)

Figure 5 - A NOAA-16 image of the storm acquired on
March 25 by Raul Teixeira from Ceará, Brazil.
Page 20

Figure 6 - This image was taken from the International Space
Station just as the storm was about to make landfall.

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August/September 2004

Group for Earth Observation

GEO Quarterly No 3

Les Hamilton and Raul Fritz Teixeira
Just days before GEO Q2 went to press
there occurred one of the most amazing
and unexpected weather events. Almost
certainly the first of its type since
weather satellites started revealing the
Earth’s weather patterns in the 1960’s,
a cyclonic storm developed in the south
Atlantic Ocean off the coast of southern
Brazil. The theories behind such an
event were recounted by Peter Wakelinin our previous issue [1]. Here we look at
the event in more detail.
This particular storm was first observedin a NOAA-16 image acquired at the
Ceará State Department of Meteorology
in Funceme, Brazil by Raul Teixeira.
Raul told us:‘A rare cyclone/hurricane is visible
near the coast of the south of Brazil inthis NOAA image which I obtained at
my site near the equator in northnortheastern Brazil. It is a NOAA-16
AVHRR channel-1 (visible) image,overlayed with the mcsst/NOAA sea
surface temperatures (figure 5). The redand orange colours indicate thewarmest areas. The letters ‘RJ’ show
the position of Rio de Janeiro City. The
image was obtained at 17:14 UT on
March 25 when the eye of the cyclone
was at 28°42 S and 41°55 W. The storm
travelled westward almost 300 km
during the following 24 hours. The
processing of the image was made by
the ‘TeraScan’ System. Unfortunately
the image doesn´t show all thecyclone/hurricane because it was
situated at the end of the pass.’
The very next day, the MODIS
instrument aboard NASA’s Terrasatellite alerted the world thatsomething highly unusual was taking
place by acquiring a startling image
showing what appeared to be a
hurricane in the south Atlantic Ocean;
an image that appeared on the inside
front cover of GEO Q2. Figure 1 shows asecond MODIS image taken by the Aqua
satellite shortly before the storm
smashed into Brazil on March 27.

This part of the world experiences
cyclonic storms so rarely that althoughBrazil has weather stations along its
southern coast, it lacks the meteorological buoys and instrumented
aeroplanes for in-situ measurement ofwind and rain from tropical storms over
the Atlantic—the main reason why thestorm was unnamed. Such storms that
do occur in this area rarely makelandfall anyway.
The winds were estimated to be a little
greater than 120 kph and the US
National Hurricane Center in Miami
considered the storm to be a full-fledged
Category-1 hurricane. Previously, only
two tropical cyclones had ever been
noted in the south Atlantic basin. Some
Brazilian meteorologists disagreed
however, stating that the storm had
weaker maximum winds and therefore
classified it as an extratropical cyclone.
The two sides based their estimates onsatellite data only, due to the lack ofground-based wind measuring devices.
CPTEC (the Center for Weather
Forecasts and Climatic Studies) and
INMET (the National Institute for
Meteorology in Brazil) produced atechnical note stating that the storm,
had displayed hybrid characteristics.
During the first days following its
formation the storm, unofficially named
Catarina by meteorologists, exhibited acold nucleus with winds rotating aroundit in the same direction at both low andhigh levels (extra-tropical cyclone) while
in its final phase it developed into a‘hurricane’, with winds characteristically rotating around the eye in
opposite directions at upper and lower
levels. Analysis of damage indicatedwind velocities which were close to
150 kph. However, Catarina displayed aclear, well-defined eye for well over 36
hours, a feature that would be unusual
for any storm below hurricane-strength.

QuikSCAT
NASA’s Quick Scatterometer satellite(QuikSCAT) carries the Seawinds
www.geo-web.org.uk

These five NOAA-17 images
above show the progress of thestorm between March 26-30.
Images: NOAA SAA
Processing: L Hamilton(using HRPT Reader/Groundmap)
Page 21

GEO Quarterly No 3Group for Earth Observation

instrument, designed to measure wind speeds over theworld’s oceans. Although surface winds of about
90 kph were indicated on March 26, the satellite was
not ideally positioned to measure the eye where thehighest wind speeds occur. But it was a different
matter on March 27, when the storm was confirmed as
Category-1 and bordering on Category-2 on the
Saffir–Simpson 5-level scale (figure 2).

TRMM
The Tropical Rainfall Measuring Mission spacecraft(TRMM), which is a joint venture between NASA and
the Japanese space agency, monitored the storm using
its precipitation radar several times during the days
leading up to landfall. This radar penetrates the clouds
and detects falling rain within the spiralling bands ofcloud to generate false colour images of the storm that
depict rain-rates throughout the cyclone (figure 3).
Figure 4 is a vertical slice through the storm which
reveals mainly moderate intensity rain (yellow) with
an embedded area of heavy rain (red) in the westerneye-wall. A single area of intense rain (darker red)appears in an outer rain band east of its centre.

LandfallCatarina made landfall near Criciúma, a town of some
180,000 inhabitants, situated at the southern coast ofSanta Catarina. It then moved on to Torres, a famous
beach resort (whose population swells to 400,000
during the summer) on the northern coast of theneighbouring state of Rio Grande do Sul, about 520
miles southwest of Rio de Janeiro.

August/September 2004

The storm lashed Brazil’s southern coast with strongly
gusting winds and heavy rain during the night ofSaturday to Sunday, March 27-28. Some 500 homes
were completely destroyed and an estimated 32,000
more damaged, rendering some thousands of terrified
residents—who had never experienced such a storm
before—homeless. Many buildings were damaged byfalling trees and in the town of Ararangua at least
5,500 buildings lost their roofs. Over the region as awhole several hundred thousand people suffereddisruption to power and water supplies while
communications between many towns and villages
were severed as trees brought down telephone wires.
Overall, at least two people were killed and over 30
injured on land while 12 more were lost at sea after
two fishing boats sank nine miles offshore in waves
four to five metres high. Two fishermen were rescued
from the sea after many hours drifting in the water inlifebelts. By Sunday March 28 it was generally agreed
that winds had exceeded the 118 kph hurricane
threshold, with some estimates reaching 150 kph,
which is well above hurricane strength.

Acknowledgments• Thanks to Peter Bartlett for additional information used incompiling this report.
• ISS Image ISS008-E-19646 on page 20 courtesy of Earth
Sciences and Image Analysis Laboratory, Johnson Space
Center (http://eol.jsc.nasa.gov

Reference
1 Why are South Atlantic Hurricanes so Rare? - Peter
Wakelin, GEO Q2, page 45, May 2004

Copy Deadline for GEO Q4 - Thursday, September 30, 2004
The Editor is always on the lookout for articles and images for
the GEO Quarterly. These can relate to all aspects of Earth
Imaging, especially:
•
•
•
•
•
•
•
•

Technical articles concerning relevant hardware
Construction projects
Weather satellite images
Reports on weather phenomena
Description of readers’ satellite imaging stations
Activities from overseas
Letters to the Editor
Problems and Queries for our experts to answer

Images and Diagrams
Images can be accepted in any of the major bitmap formats, e,g,
JPG, BMP, GIF, TIFF etc. Images in both monochrome andcolour are welcomed for inclusion. Line drawings and diagrams
are also welcome in Windows metafile and postscript formats.
We can also scan original photographs, negatives and slides.
Please note that we do require individual copies of each of yourimages/drawings (which are not embedded within your article)
for make-up.

Contributions should of course be original and, where possible,
should be submitted to the editor in electronic format (floppy
disc, CD or e-mail attachment). But we will also accept
handwritten or typed copy should the need arise.

Submission of Copy

Please note, however, that major articles containing numerous
illustrations should be submitted earlier than the date above sothat they can to be prepared and made up into pages in time forpublication.

Materials may also be sent as attachments to the following
e-mail address:

Page 22All materials for publication should be sent to the Editor, Les
Hamilton, 8 Deeside Place, Aberdeen, AB15 7PW, Scotland.

www.geo-web.org.uk

editor@geo-web.org.uk

August/September 2004

Group for Earth Observation

GEO Quarterly No 3David PainterThe first of the new Meteosat Second Generation(MSG) weather satellites is already launched and inorbit, and it is the first in a succession of ‘Digital’
weather satellites. What are the implications for thosewishing to receive weather images? And what does
‘DVB’ mean?

This meant a massive cost saving for all users in the
hardware required to physically receive the signal; theminimum required dish size was reduced, the LNB
became a universal domestic one and the receiver
became the off-the-shelf, well proved and available
Skystar2 PC card.

This article was written to give an introduction to DVB
and will hopefully help answer some of the questions
you may have. It will also introduce you to theminefield of abbreviations that ‘pepper’ our new Digital
Weather satellite system. Please see the Glossary at
the end to help ease the pain.

EUMETSAT still had software issues to resolve but
the difficult matter of how to receive the signal had
already been cheaply solved for us. This does not meanthat the trusty soldering iron is redundant yet: it justmeans that there will, hopefully, be other projects for it
to do later.

EUMETSAT’s original aim was to broadcast the MSG1
data from it’s satellites directly to users using it’s own
complete data transmission system. This system wasdeveloped by EUMETSAT to suit it’s own specificneeds and required specific hardware and software
designed to integrate into its existing distribution
system. This meant that to receive the data as
originally intended, users would be required to obtainor build ‘unique’ hardware to physically receive thenew data stream.

Because the DVB standard is really a group of
standards that ‘knit’ together, it allows an operator to‘pick and choose’ or ‘tweak’ the parts that suit theneeds of the operator. The versatile DVB standard
allowed EUMETSAT to rapidly tailor the systemneeded to deliver a data ‘package’ to an end user orcustomer, without loss or corruption of that data via adomestic system.

The Good News (for us)
The failure of one of the solid state power amplifiers(SSPA’s) on board the MSG1 satellite during thetesting phase caused a major rethink within
EUMETSAT about how to redistribute the data fromthe new satellite. The eventual solution was tointegrate the MSG1 data stream into the existing
ATOVS ‘broadcast standard’ downlink from the Hot
Bird-6 broadcast satellite. This meant using anotheroperator’s system, so the data had to fit within thespace available to it and be compatible with someone
else’s system hardware and not fit EUMETSAT’s
original MSG1 dissemination plan.
The result of this was that the hardware required by
the end users would now no longer need to be ‘unique’to the EUMETSAT system, and could be an ‘off-theshelf’ receiver/decoder unit built to an industry
standard already in use. But why did EUMETSAT
choose DVB?
It is extremely lucky for the amateur fraternity thatthe majority of European digital satellites are basedaround the Digital Video Broadcasting standard (DVB
for short), as this meant that the MSG data downlink
had now to became compatible with the satellites inorbit and domestic DVB equipment.

EUMETSAT chose to broadcast a special format data
stream called Tellicast, that uses the Tellique software.
This Tellique software is vital as it manages thedelivery of the data streams and reassembles the DVB
data packets transmitted by the DVB satellite backinto computer data files that can be accessed by theusers’ software.
The reconstituted computer data files are reformed
into the three separate data ‘channels’ that comprise
the Tellicast data stream:• Channel 1-ATOVS- Rapid Scan data
• Channel 2-HRIT data
• Channel 3-LRIT data
However, the data format used for the ‘transport’ partof the distribution from the Hot Bird-6 satellite to thereceiver conforms to the DVB standard as alreadymentioned.
The outstanding advantage of the DVB standards arethat the data contained within the ‘packets’ produced
by a DVB multiplexer can be a variety of formats, data
rates and types, and come from a wide variety ofsources. The DVB ‘transport’ system chosen by
EUMETSAT is based around an MPEG2 data stream
but the data within that stream does not have to be
MPEG data.

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GEO Quarterly No 3Group for Earth Observation

It’s rather like getting on a plane; when you board theplane at the start of your journey both you and yourbaggage are together. During the trip, your baggage iscarried separately, in a separate container. You andyour baggage are not turned into parts of the
aeroplane, you are merely in it. At the destination
airport, you and your baggage will be reunited(hopefully), though possibly after a considerable delay.
The DVB transport stream does not change the data
within, it just transports it with a measurable delay.
Specialised software is then required to reconstitute acontinuous data stream from the separated anddelayed DVB data packets. There are many functions
carried out by the Tellique software, not least theprioritisation of the data packets, to ensure timely
arrival of the most important data first. It is thisreconstituted data stream that your data manager anddecoding software can cope with.
The Tellicast data to be carried is put into a ‘virtual
container’ (VC) or data ‘packet’. Each data packet has
two different types of error protection to protect it enroute between the broadcast satellite and the end
user’s receiver: Reed Solomon (inner coding) and
Viterbi (outer coding), which are applied within an RF
modulator.

DVB – The history

August/September 2004

DVB-S (‘S’ for satellite)
The specification that was produced in 1994 was called
DVB-S, and was based around a method of modulating
data on to a single RF carrier using a method called
QPSK (Quadrature Phase Shift Keying).
This has now been adopted worldwide and has formed
the basis for many other standards. It can use a data
stream that has been MPEG encoded or it can carrydata, audio or video signals encoded in a variety ofways, including IP (Internet style data). The hardware
standard is designed to deliver a data ‘packet’ to its
destination with a specification of less than one
uncorrected error event per hour. Effectively error-freeat the destination.- So long interference(.)

EUMETCast
The details for the EUMETCast DVB Ku band signal,
which carries the Tellicast data, are listed as:
The Hot Bird-6 SatelliteThis is a digital satellite equipped with its own
multiplexers, which means it can incorporate manysmall DVB-compatible uplinks from many sources into
one single DVB compliant multiplex for transmission.
It is unknown at this time if the EUMETCast data ismultiplexed on board the satellite or whether it isuplinked already integrated into one large multiplex atUsingen in Germany.

The DVB group was founded in 1992 by a number ofinternational companies whose aim was to produce apractical, universal digital transmission standard
that would be adopted globally for all methods ofdigital broadcasting. The first aim was to produce a
standard specification that would be adopted by theinternational satellite operators for the latest
generation of broadcast and telecommunications
satellites.

Current details of what else is on Hot Bird-6 can befound at:

The unusual thing about all the DVB standards is thatthey were to be ‘open-source’, meaning that there were
to be no intellectual property rights issues. The DVB
standards could be used freely worldwide without any
licence agreement. This helped to ensure that thestandard was very widely and easily integrated into allsorts of applications. The development of mass
produced chip-sets was critical to its success as a global
standard.

Downlink Frequency: 1.346Ghz
This is the transponder frequency minus the LNB local
oscillator frequency (9.75Ghz). This is the ‘real’frequency that the DVB card tunes in to after down-conversion to extract the data.

To date there are over 300 companies involved directlywith the DVB project and who make thousands ofproducts to the DVB standards that have now been
established. There are now about forty standards
covering everything from Digital Terrestrial Television(DVB-T) to DVB-C for Cable-To-Home. All thesestandards are being adopted and regulated by theEuropean Telecommunications Standards Institute(ETSI) and each DVB standard gets it’s own number.
(The DVB-S standard is EN 300 421).

Page 24http://www.lyngsat.com/hb6.shtml

Transponder centre frequency: 11.096Ghz
This is the exact RF frequency of the centre of themultiplex channel. (Transponder 129). Uplink source
T-Systems, Germany.

Symbol rate: 27500 ks/sec
This is the data-rate transmitted by the transponder towhich the card is tuned. It means the same as 27.5
mega symbols per second ( i.e. the same as domestic
Astra DVB).
It must be noted that a ‘symbol’ is one phase/amplitudestate of the RF carrier, so the actual data rate is not
the same as bits per second. (each symbol can transmit
more than one bit of information).
FEC = Auto
FEC stands for Forward Error Correction. Based upon
the DVB standard you wish to use, and the data rate
you wish to transmit, there are known degradations

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August/September 2004

Group for Earth Observationthat can affect your signal. The ‘operator’ can then‘tweak’ the specification of the DVB signal according towhom they want to be able to receive an error-freesignal. This can affect service area and required dishsize, as well as the ‘robustness’ of the signal withinthat area. The target specification is one error-event
per transmission-hour at the input of the receiver.
Generally, Forward Error Correction adds into thesignal a proportion of error-correction data. The moreerror-correction data you send, the lower your ‘useful’data rate is. The more Forward Error Correction you
add, the more robust your signal is. Typical values of
FEC are , , ,and .
PID (Packet IDentifier)
Each data stream within the multiplex is made up of
packets of information that are identified exactly with
their function and where they ‘belong’. A sort ofaddress label and time stamp.
The information that is compiled to make a DVB
multiplex can arrive at a multiplexer from manydifferent data sources and in many differing formats
and rates. The multiplexer can be thought of as arotary kitchen knife that slices up all the data streams
depending upon certain rules.
Data for a particular stream is chopped up and packed
into a VC without any additional error correction. A
PID is added to the packet to give it a unique label
stating from which data stream it has come. This data
packet then passes through the multiplexer where it is
Forward Error Corrected by a QPSk modulator.
You must configure your computer to select just one of
the many data streams that may be present within themultiplex, which are being simultaneously received byyour DVB card, by specifying which PID packets you
want to use. PID values can be specified inhexadecimal (HEX) or decimal (e.g. FFFF or 1634). The
PID determines which packets you will pick out fromthe hundreds of channels that may be contained within
one DVB data stream.
Modulation of the Information
The data is Reed/Solomon coded (inner coding) toprevent ‘random’ losses of data, and Viterbi Coded(outer coding or convolutional coding) to protect thatdata from being destroyed by ‘burst’ type noise en routeto the user’s receiver. Finally, the data is output fortransmission as a modulated RF signal which is then‘upconverted’ (multiplied to the correct transmitter
frequency) and amplified for onward transmission by
the satellite.
Your receiver needs to be set up with the same
parameters as the encoding modulator or it will not beable to distinguish the ‘true’ data from the error
correction data and be unable to decode it correctly.

GEO Quarterly No 3

The DVB compatible Skystar2 card and currently
available software will hopefully open the door to otherexciting possibilities as more ‘digital’ satellites arelaunched. It is not known yet if the new NOAA
satellites when launched will be compatible and be
DVB compliant but, as DVB standards are presently
the ones most widely used in digital transport systems
today, we can but hope.
The future for digital weather satellites has started
and there are a whole lot more things to learn, fromsetting up your ‘new’ PC, DVB card and software, tounderstanding the new data that has been madefreely available to you. There is also an ever more
focussed awareness of the effects the weather can havein the media and in education, so it is an exciting time
for the amateur who has access to millions of pounds
worth of technology through the humble PC.

Reference• Digital Television Broadcasting (DVB) via terrestrial andsatellite channels - Dr. Mario Cominetti and Dr. Alberto
Morello, R.A.I.

Glossary (or Pain Killers?)• DVB - Digital Video Broadcast - a specification for doing
various things in a European Digital way.
• MSG1 - Meteosat Second Generation, satellite number
one.
• SSPA - A precision amplifier that cost a lot of money andfailed during testing.
• LNB - Low Noise Block converter - a device that converts
high RF frequencies into lower ones.
• Tellique - A proprietary software package devised by
T-Systems of Germany to re-assemble data packets into
something a computer may understand from the Tellicast
data.
• ATOVS - Data provided by NOAA satellites from a suite of
instruments providing environmental data about the Earth’s
atmosphere.
• HRIT - High Rate Information Transmission – as it says on
the packet.
• LRIT - Low Rate Information Transmission – not as many
packets as HRIT.
• MPEG - Moving Picture Expert Group - a consortium ofcompanies that produced standards for data transmissionof video/audio. The standards produced are called
MPEG/MPEG2 etc.
• PID - Packet IDentifier- information within a DVB data
packet, that identifies the packet as being part of a data
stream or ‘channel’ or as performing some other function
within the DVB system (synchronisation, time stamp etc.)• Reed Solomon - a method of error correction applied to adata stream, that protects it against interference that may
cause the loss of single packets of data from that stream.
(referred to as ‘inner coding’)• Viterbi - a method of error protection applied to a data
stream that protects against interference that may cause
the loss of groups of data packets (referred to as‘convolutional coding’).
Concluded on page 41 ...

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Rob Hollander
Introduction
The measurement of the radiation pattern, sensitivity
and polarisation of my RQHA has been on my wish-list
for years. The Resonant Quadrafilar Helical Antenna
is described in detail in Technote-1999-1, which can befound onwww.kunstmanen.nl

under ‘downloads’. The RQHA is, in theory, an ideal
antenna for APT-reception in the 137 MHz band. In
2003 an ‘antenna measuring group’ was formed byseveral members of the Dutch Werkgroep Kunstmanen:
Harrie van Deursen, Arne van Belle, Peter Smits andmyself combining our skills and instrumentation. Afterhalf a year of preparations we were able to make thefirst measurements in November 2003. This article
deals with antenna theory, measurement set-up andprotocol, and the first results. A second article will
describe the results of measurements planned for April
and May 2004. The preliminary results gave us
confidence in the used procedures. Moreover welearned how to adapt these procedures so that themeasured results could be compared with theory.

TheoryThe radiation pattern, polarisation and gain of atransmitting antenna are the same as the sensitivity
pattern, polarisation and gain of this antenna inreceiving mode. It is however much easier to calculate
the radiation pattern than to calculate the sensitivity
pattern. So we start with a feed-current in our antenna
and calculate the corresponding EM-field instead of
calculating the current induced in it by an EM-field.
There are many computer programs to calculateantenna performance but the real problem is not thecalculation (a few lines of program code) but defining
the geometry of the antenna in 3D and the input andoutput (several pages of code). Moreover, if you want tounderstand what is going on, it is much more
instructive to write the program yourself.
With the new generation of programs that use vector
calculations like Matlab, it is a pleasure to write thecode. All efforts can be directed to the solution of the
problem, the solution of the Maxwell equations for the
EM-field of a current element in vector notation andthe description of the antenna geometry in vector
notation as well. A full description would be beyond thescope of this article but interested readers may have alook at the web-site www.kunstmanen.nl under‘downloads’ in the pdf-file TechNote-2004-1.
Page 26

The basics of EM-theory can be found in many
textbooks like Jackson [1]. An alternating current
produces EM-waves consisting of alternating electricand magnetic fields. The electric field vector isperpendicular to the magnetic field vector and both
vectors are perpendicular to the propagation direction.
The waves travel with the speed of light from theantenna outward, and beyond a certain distance (morethan 2.5 wavelengths) a more or less spherical wave isformed. From that point on, the ‘far field’
approximation can be used. In order to calculate thefield of an antenna, the antenna is divided into small
elements, each carrying an alternating current. At
resonance this current is a standing wave and can be
described by:(1)

where k = 2π/λ = ω/c gives the wave number, λ is the
wavelength, ω = 2πf gives the radial frequency and c isthe speed of light. The current at any position s along
the antenna has an amplitude of IA(s) = I0 cos(ks),alternates with a radial frequency ω, and has a relative
phase angle of δ. To simplify the calculations thecomplex notation exp(jα) is used instead of sin(α) orcos(α) wherever possible, with j the imaginary unit.
Since EM-fields are linear, we can find the field of anantenna by summation of the fields produced by all
individual small current elements. We have to keep inmind that EM-fields are transverse fields, which
implies that the radial component of the field in the
propagation direction is zero. We can write (in vector
notation) for the θ and ϕ components of the electricfield vector at position r in space, indicated by the polar
co-ordinates (r, θ, ϕ), due to a current element ds at theposition rs indicated by polar co-ordinates (rs, θs, ϕs):
(2)

The vectors ûθ, ûϕ, ûs, ûr and rs are respectively:• the unit vector in the θ-direction• the unit vector in the ϕ-direction• the unit vector in the direction of the current at
position s• the unit vector in the r-direction• the vector from the origin to the current element at
position s.

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Group for Earth Observation

We have dropped the common factor exp(jωt), so theamplitude of the field strength is shown. These fieldcomponents Eθ and Eϕ produced by the current areorthogonal and can be measured with a simple dipole
antenna, which is linearly polarised. Using thedefinition of the polar co-ordinates from figure 1, we
see that Eθ corresponds with the vertical component
and Eϕ with the horizontal component of the field, if weare looking in the r-direction.

GEO Quarterly No 3

The electric field is now split into two orthogonal fields
ER, the RCP-field, and EL, the LCP-field:(5)

The components ER and EL can be expressed as:(6)

Figure 1 - Co-ordinates used in the calculations. The antenna
axis is in the z-direction and the imaginary cylinder
formed by the helical parts has radius r0.
(see also fig.2)

If we want to measure Eθ we need a vertical dipole andto measure Eϕ a horizontal one. If Eθ and Eϕ are equal,
then the field can be linear or circularly polarised
depending on their phase relation. If the measured
field strength is independent of the orientation of ourreceiving dipole (thus independent of being horizontal,
vertical or of all orientations in between) then thepolarisation is circular: RCP or LCP. Now the role ofthe transmitting antenna and the receiving antenna
can be interchanged; we can measure the sensitivity of
our RQHA for the direction of polarisation with arotating transmitting dipole. However, this gives us
only an idea of the degree of circular polarisation. If wewant to measure both RCP and LCP polarisation
contributions separately, another method has to be
used.
The field can be described not only by the two
orthogonal components Eθ and Eϕ where the orthogonal unit vectors ûθ and ûϕ form the orthonormal
base,
(3)

but any orthonormal base can be used; e.g. ûR and ûL
defined as:(4)

The RCP field has its electric field vector rotating CW
when looking towards the oncoming (!) wave. Thismeans that a right-hand circularly polarised wave is
propagating as a left-hand screw—this is called‘negative helicity!’ This definition comes from classical
optics, was adopted for EM-waves as well, but is
nowadays sometimes confusing. Please note that thesigns used in the equations in this article form a
consistent set. If the definition of the time in thecurrent is reversed another consistent set of signs
should be used, as some people prefer, because they
think that it is more elegant that an outgoing wave has
a positive sign for its radial phase-factor instead of thenegative sign in exp(-jkr).
The axial ratio, a measure of circular polarisation, canbe defined in several ways. If we use:
(7)

then we have pure circular polarisation for AR = 1 andpure linear polarisation for AR = 0.
There are two representations: one based on unit
vectors ûθ and ûϕ is appropriate for the description of
linearly polarised fields; the other based on ûR and ûL
is appropriate for the description of circularly polarised
fields. The information from measurements only
applies to the absolute value of the field strength (orthe square root of the emitted power). The relation
between these two representations (equation 6) looks
simple but is in fact complex.

Simulation Results
The calculation is performed by taking integrals overall current elements starting at one point along a full
loop. The distal point at the bottom was chosen, as in
the Kilgus article [2]. The four half-loops are each one
half wavelength in length. A cosine function isassumed for the amplitude of the current along theloops, corresponding with a ‘phase’ along the loops thatruns from zero to 2π, which brings us back to the distal
point after one full loop:(8)

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

with maximal values at the distal-point at the bottom(JA(0) = JA(λ) = +J0) and at the feed-point at the top(JA(λ/2) = –J0). For resonant antennas and a feed at thecurrent maximum this model is close to reality.

there is one possibility out of four to get the correctantenna by chance. It is thus possible to turn the
RQHA upside down with its terminals at the bottom, if
you want another BALUN design!

The program can calculate the E-fields for full-turn,half-turn and quarter-turn quadrafilar antennas. The
design parameters are:• frequency• number of turns (1,or )• ratio of diameter over axial length• the distance from the centre of the RQHA to thepoint where the field strength is calculated• the ‘helicity’ of the helix• the phase of half-loops 2 and 4 relative to halfloops 1 and 3,• the azimuth angle ϕ for the elevation scan
performed in the θ-direction.

The code for the Matlab program is
supplied in TechNote 2004-1. With
the program it is easy to tailor theratio of diameter over axial length
to the desired radiation pattern
and the required circular polarisation at the horizon.

The fields are calculated as a scan over all angles θ forthe selected angle ϕ. The fields of an RQHA are
independent of ϕ, as was stated by Kilgus, which isonce more verified by these calculations. The relevant
polar plots of Eθ, Eϕ, ER and EL are shown in figure 3.
Although it is simple to calculate the absolute fieldstrength at a selected distance (as long as the ‘far field’
approximations are valid), this is not done. Only the
angular dependence is shown as this is the relevant
information for radiation patterns. The factor:(9)in equation (2) is ignored. This makes the choice of the
distance and frequency as design parameters a bit
strange since the presented results do not depend onthese parameters. However, these parameters areincorporated in the program so that, when not only theradiation pattern but also the absolute field strength iswanted, the program is able to calculate this simply bymultiplication of the results with the above mentioned
factor.
In the calculations, the origin is taken as the centre of
the antenna (Kilgus [2] takes the distal point at thebottom as origin). The half-loops are numbered 1,2,3,4
counting counter-clockwise, looking from the top
downward (Kilgus counts 1,3,2,4). The phase, δ, of thecurrent in half-loops 2 and 4 (inductive large loop) has
to be –π/2 relative to half-loops 1 and 3 (capacitive
small loop) to get the RCP (right-hand circularpolarisation) in the upper hemisphere.
Note that the twist of an RQHA for RCP-APT reception(helicity of helix = –1) is the opposite of the LCPexample in Kilgus’s article [2] where helicity = +1! If thehelicity is –1 and the phase, δ, is +π/2 we have RCP in
the lower hemisphere; if the helicity is +1 and thephase is –π/2, we have LCP in the lower hemisphere
while for +π/2 we get LCP in the upper hemisphere. So
Page 28

The radiation pattern of an RQHA
is the result of a delicate balance ofconstructive
anddestructive
Figure 2interference of the fields of the
The RQHA on myindividual parts. The field at theroof under thehorizon is produced by the helical
Dutch skyparts while the fields up and down
are produced by the radial parts (more or less). The
field in the upper hemisphere is the result ofconstructive interference and the absence of the field in
the lower hemisphere is the result of destructive
interference. Addition of the fields of the parts has tobe done by adding the real and imaginary components
individually; then the absolute value can be calculated
and shown in graphs like figure 3.

Measurement Set-up
A mobile, battery operated set-up was made by thegroup, partly from existing units, although some newunits also had to be built. A small transmitter and
impedance matching network feed the transmitting
antenna, which is a crossed dipole, to produce
circularly polarised fields. Flipping the antennachanges the direction of polarisation from LCP to RCP.
An attenuator is used to adjust the power so that thereceiver, approximately 100 yards away, is notoverloaded. About 1 µW was used in the experiments.
The AUT (antenna under test) was the RHQH-12,
connected by a 50 Ω cable with an electrical length oflambda to an antenna amplifier (HRA-137). This
lambda is the total length of the cable from the top of
the antenna to the amplifier, thus including the‘internal’ cable of the ‘infinite BALUN’ and the ‘length’of the connectors. This cable transforms the real
impedance of the antenna (at its feed point at the top)from 31.5 Ω @ 137.5 MHz to a real impedance of 79 Ω,
suitable for the antenna amplifier input.
The receiver was an HRX-137, fitted with a special
buffered signal strength output. The output voltage
was calibrated as a function of the input voltage.
Although the output is approximately a log-function of
the input, several wiggles show up in the curve due tothe internal circuit of the CA3089. There are better
signal monitor ICs, but a 9-th order polynomial fit
represented our calibration curve nicely, so that thisfitted curve could be used in the analysis of themeasurements.

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GEO Quarterly No 3

Figure 3 - Radiation patterns for an RQHA with a diameter over length ratio of 0.444. At the top the patterns for aquarter-turn antenna are shown. In the middle the results for my design with a half turn are shown andat the bottom the results for a full turn antenna.

The output voltage was measured
with an 8-input ADC-unit made
from
a
kit
from
ConradElektronika. This ADC-unit iscontrolled by the control lines DTR
and RTS from the serial port of alaptop and read out by the statuslines DSR and CTS. A measuring
program has been written in Pascal
to collect the data and store them on
disk. At intervals of selectable

length, e.g. one second, a selectable
number of samples, e.g. 10, areconverted and averaged to suppress
noise to less than 1-mV. Not only
the signal strength is recorded but
also the voltages representing theangles of the AZ (azimuth) and EL(elevation) rotors. These areproduced with multi-turn linear
pot-meters coupled to the rotor
shafts and are sampled at almost
www.geo-web.org.uk

the same instant as the signal
voltage. This procedure gives threevaluespersamplerecord,completely defining the required
information independently of the
speed of the rotors and without
synchronisation problems. The
relations between readings andangles were calibrated and proved
to be very linear (high impedance
loading of the pot-meters was used).
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GEO Quarterly No 3Group for Earth Observation

A 12 V battery, from which a stabilised 15 V d.c. ismade by a dc-dc converter (specially built for thisoccasion) powers the whole set-up. It is the supply forthe laptop, the receiver, the ADC-unit and the rotor
steering. The receiver has an additional internal 12 V
stabiliser and the ADC-unit a 9 V stabiliser, a second
5V stabiliser for the pot-meters and a 5 V reference for
the ADC. Recordings are ± 1mV on a range of 5 V.
In future measurement sessions, a rotating dipole will
be used for the measurement of Eθ and Eϕ, while twodipoles at 90°, placed a quarter of a wavelength
distant, will be used to measure ER and EL. This isshown below in figure 8.

August/September 2004

To make pure circularly polarised antennas is not
simple. The best approach is to use two identical,
linearly polarised dipole antennas, fed in phase, one aquarter wavelength behind the other, and at + or – 90°.
Depending on the orientation, we get RCP or LCP. If
the phase is not exactly correct then the distance
between the two dipoles can be adjusted. It is goodpractice to match the dipoles to 100 Ω and feed them inparallel from a 50 Ω source.
The set-up illustrated in figure 8 makes themeasurement symmetric for RCP and LCP. It will beclear that if we want to measure small LCP
contributions to a dominant RCP sensitivity, that thecircular polarisation of the transmitting antenna has
to be more precise than that.
We mounted the RQHA-12 and made AZ-scans at threedifferent EL-angles. One scan was made with the axesof the transmitting and receiving antennas in line,
corresponding with the situation of a satellite
overhead. A second AZ-scan was made at an angle of
45° between the two axes, corresponding with asatellite at an EL of 45°. The third AZ-scan was madewith the axes at 90°, corresponding with a satellite at
the horizon. The EL-scan was made in two steps. First,
the EL-rotor tilted the RQHA-12 from axes in line andantennas facing each other over 180° till the RQHA
was irradiated from the rear; then the AZ-angle waschanged by 180° and the same EL-tilt was performed
to produce the second half of the full EL-scan. Results
are shown in figure 9 and have to be compared with thetheoretical pattern of figure 3.

Figure 8 - Set-up for circular polarisation measurements using
two transmitting dipoles at 90° and a quarter wavelength apart. The phase of the feed is indicated with+ and - signs. The change from RCP to LCP is
obtained by reversing the phase of one dipole (180°rotation) or, as shown in the figure, by a 90° rotationof both dipoles.

Measurements
For our experiments we choose a site with two hills
about 100 yards apart, one for the transmitter and one
for the antenna under test (AUT) (figure 11). First we
tested the effect of the circular polarisation of thetransmitting antenna with a receiving antennaconsisting of a simple dipole. A variation of 5.6 dB was
found by an AZ-scan when the antennas were in line.
The use of a reflector reduced this variation to 2.8 dB.
We concluded that the reception of the dipole isseriously influenced by the material at the rear of theantenna; in our case a rather massive piece of metalfrom the rotors. At the transmitting side a crossed
dipole without reflectors was used. There we did nothave any metal in the vicinity, except for the feed
cable. The circular polarisation is probably not perfect,
but good enough for the measurement of the radiation
pattern. For a cross-polarisation measurement, to bedone in a later trial, we have to use pure LCP and RCP
fields.
Page 30

Analysis
The dB values in figure 9 (vertical scale) are relative to
1 µV at the input of the receiver, from which the gainof the antenna amplifier should be subtracted to get
the antenna signal. However this time we wereinterested in the patterns and less in the gain. The
constant sensitivity at all AZ-angles is remarkable,
although it was meant to be so. Also the EL-scan isvery symmetric and close to what it should be , asillustrated in figure 10.
The ratio of diameter over axial length of 0.444 wasselected according to Wang [3] to get a decrease of about
6 dB at the horizon (I live in the city and wanted some
reduced sensitivity at the horizon to avoid terrestrial
interference) and we indeed find a reduction of 7 dB.
Even the lobe at the bottom, which should not be there,
is identical with that also found by Kilgus [2] on his
antennas 35 years ago.
In figure 10, the calculated and measured results areshown for the elevation scan—the most interesting
feature. It is clear that the RCP-part of the radiation
pattern in the upper hemisphere is well described by
the calculations. The lobe in the lower hemisphere is
probably due to LCP-contamination of the transmitted
field.

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August/September 2004

Group for Earth Observation

GEO Quarterly No 3

Figure 9 - Measured sensitivity patterns of my RQHA with a D/L ratio of 0.444. At the top-left an AZ-scan is shown where the RQHA
axis is pointing toward the transmitter (should be insensitive to the small linear polarisation component of the transmitting
dipole). At the top-right an AZ-scan is shown at an elevation of 45 degrees, showing a deviation of ± 0.2 dB fromperfect constant sensitivity. At the bottom-left an AZ-scan is shown for an elevation of zero degrees (at the horizon),showing a deviation of ± 0.5 dB. At the bottom-right an elevation scan is shown (the pattern is independent of the azimuth
angle!). Note that the vertical dB-scale of the figure at the bottom-left is different!

Conclusions
Although expectations were high, we are astonished by the results. It seems that all the care in making theconstruction pays off. From the electrical measurements it was already clear, that the phasing of the RQHA, withan inductive and a capacitive loop, is almost perfect. Now it is also clear that the radiation pattern is close toperfect. We conclude that the RQHA is not only in theory an ideal antenna for the reception of polar orbiting
satellites, but that the RQHA can also be an ideal antenna in practice when properly made.

References
1 J.D. Jackson, Classical Electrodynamics, 2nd ed. John Wiley & Sons, 1975.
2 C.C. Kilgus, Resonant Quadrafilar Helix, IEEE Transactions on Antennas and Propagation,
Vol. AP-17, May 1969, pp 349-351.
3 H.S.C. Wang, Theoretical design and predictions of volute antenna performance, IEEE Transactions on Antennas
and Propagation, Vol. AP-39, No.8, August 1991, pp 1227-1230.
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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Figure 4 - Maximum field strength as a function of the diameterover length ratio (number of turns as parameter).
The maximum field strength for a dipole is 0.694
and for a crossed dipole 0.909 in the same arbitrary
units (a.u.).

Figure 5 - Full beam width as a function of the diameterover length ratio (number of turns as parameter).

Figure 6 - Sensitivity drop at the horizon as a function of
the diameter over length ratio (number of turns
as parameter) relative to the maximal sensitivity.

Figure 7 - Percentage of circular polarisation at the horizon
as a function of the diameter over length ratio(number of turns as parameter). The polarisation
upwards is 100% RCP.

Figure 10 - Comparison of the calculated (blue for RCP
and red for LCP) and the measured (black)radiation pattern of my RQHA. A (notperfect) RCP transmitting antenna (crossed
dipoles with phase loop) was used. The
vertical scale is in dB (see text).
Page 32

Figure 11 - The RQHA-12 under test
(notice the weight to balance the set-up)
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August/September 2004

Group for Earth Observation

GEO Quarterly No 3

John Tellick
One thing I forgot to mention in my article on LNBs in
GEO Q2 was that the poor LNB has to withstandfreezing in the winter and being baked in the summer
sun. The LO frequencies must remain within quite
tight tolerances, typically ± 2-3 MHz over thetemperature range –40°C to +60°C and any drift of theLO will of course alter the frequency of the block
downloaded IF band in sympathy.
If you are using an 85 cm offset dish for EUMETCast(as recommended by EUMETSAT), you can use thesame dish for the reception of other satellites byplacing additional LNBs on a dual or multi-feedbracket.
My original set up (figure 1) was a dish and LNB
centred on 13°E for Hot Bird-6 EUMETCast receptionwithanother
LNB
mounted slightly to theleft (looking at the dish)for reception (slightly offbeam) of the Astracluster at 19.2°E forsatellite TV.
Since the EUTELSATERP is lower than that ofAstra the dish and Hot
Bird LNB is centred on
13°E
for
maximumsignal. Owing to thestronger ERP of Astra,
one can afford to beslightly off beam andreceive a slightly lower
signal.

Figure 1 - The original setup

Later, I wanted to receive the South East regional
programmes from BBC TV, which are transmitted
DVB via Astra at 28.2°E. for the Kent/Sussex coastal
weather forecasts. With my dish centred on 13°E.,
28.2°E. is quite a split, but the Astra satellites at that

Figure 2 - Lining up the LNB with a Technisat ‘Satfinder’ meter

location have an ERP to work into a 45 cm dish.I foundthat by placing a third LNB to the left of the ‘offset’
19.2° LNB—which would be even more ‘offset’—thesignal from 28.2°E came romping in with no problem at
all and at a high level.
As you will see, my dish ison the ground on a ‘nonpiercing roof mount’ standwhich allows endless easy
adjustment
andexperimentation which I’d
not be happy doing ‘up aladder.’ It also allows me toconnect the receiver andTV adjacent to the dish in
order
to
allow
easy
identificationofthesatellite.
Having said that, you willfindtheTechniSat‘SatFinder’ level meter
invaluable if you plan toexperiment with multi-feed
reception from one dishand I can thoroughly
recommend it.

Figure 3
Temporary installation for the
reception of Astra 28.2°E(using a camera tripod).
Note the slightly higher LNB
position due to the lower
satellite elevation.

The LNB will require adjusting for polarisation offset(‘skew’). That means that the further around thegeostationary arc the satellite is, the more it appears totilt in relation to the horizon; this twists the verticaland horizontal polarised signals out of alignment. For
satellites to the west of 0°. the LNB needs to be skewed
to the right (looking south) and for satellites east of 0°,
the LNB needs to be skewed to the left. Linear
polarised signals from a satellite at 0° should be
perfectly horizontal and vertical without any skew.
The further a satellite is around the arc, away from 0°,
the more the skew. This is important for two reasons.
One is to obtain maximum signal from the channel you
actually want and the other is to minimisecross-channel polarisation from signals of the opposite
polarisation.
To squeeze all the channels transmitted into the
bandwidth available on the satellite, the vertical andhorizontal channels overlap one another slightly(figure 4): described as the frequency offset. So, if your
LNB is not properly aligned (polarisation offset) you
will pick up a little bit of the polarisation you don’t
want whilst reducing the polarisation you do want,
which will cause some interference. Professionals line
up LNBs with a spectrum analyser which shows the

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Figure 4 - Hot Bird-6 downlink frequency plan.Note the overlap between H and V channels

power level relationship between the two polarisation
bands and allows accurate skewing for maximum levelat one polarisation and minimum on the other.
If you want the ultimate in multi-feed reception then
you want the Wave Frontier dish—up to 16 LNBs on
one dish. WOW!

The toroidal design and sub-reflector allow every LNB
to be at a ‘proper’ focal point (and therefore at its
optimal position, along the line of the LNB bracket)
across an arc of some 40 degrees. An LNB mounted
away from the centre point of an ordinary offset dish isa bit of a compromise—but it works.

Figure 5
The ‘Wave Frontier’ dish with 10 LNB’s

Figure 6
The ‘Wave Frontier’ dish installed and in action

Weather Satellite Frequencies
Frequencies (MHz)
APT

HRPT

Geostationary
Satellites

137.501698.0GOES-ENOAA-14-1707.0NOAA-15137.501702.5

NOAA-16-

NOAA-17

Polar Orbiting Satellites
NOAA-12Feng Yun 1C, 1D

Location

Frequencies
WEFAX (MHz)

USA

75°W

1691.0GOES-W

USA

135°W

1691.0

Meteosat-5

INDOEX

63°E

1691.01698.0

Meteosat-6

Europe10°E

1691.0137.621707.0

Meteosat-7

Europe0°1691.0, 1694.5-

1700.4

Meteosat-8

Europe0°

D VB

Download NASA 2-line Elements
Satellite tracking programs require regular updates of the NASA 2-line element sets that are essential for calculating the positionsof Earth-orbiting satellites. One of the best Internet sources for these files is Celestrak at: http://www.celestrak.com
Elements for many groups of satellites are updated daily. Particularly useful are:http://celestrak.com/NORAD/elements/weather.txt (most weather sats)
http://www.celestrak.com/NORAD/elements/stations.txt (ISS)
Page 34

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August/September 2004

Group for Earth Observation

GEO Quarterly No 3

Mike Stevens (G4CFZ) e-mail: mikeg4cfz@tiscali.co.uk
I became interested in all types of radio reception someyears ago when I first started listening to Short Wave.
This prompted me to try for the Radio Amateur Exam,which I passed, then subsequently the Morse Test.
After purchasing my first HF rig and going ‘on air’ withthat brand new call sign I soon discovered there was a
new world at my fingertips: so I worked the world andenjoyed every moment of it. My best DX contact was
Pitcairn Island from an early morning CQ call—I shallnever forget that one.
But it was some time before I discovered that weather
satellites were within my reach. One day at work I justhappened to read a scientific paper which mentioned
weather reception by amateurs and came completewith a picture. As I worked for a large corporatecompany with a good network system it was easy to
put out a question about the subject. This I did; just a
simple ‘anybody know anything about satellites forweather and how you receive them’ question.

the equipment to arrive, it was all delivered safely andundamaged a few days later—so assembly began.
The Antenna was very simple to assemble but to those
who are new to this game, do please read the
instructions fully before starting. One of the mostimportant points is to make sure the elements areplaced correctly on the pole and that you ensure thelower elements are in line with the top ones. Once you
are happy with that you can connect the co-ax cable.
You must take care to connect the short length of co-ax(the phasing harness) correctly otherwise this willcause the antenna to be out of phase and result insignal loss.

Within a quarter of an hour, back came a reply fromMichael, a friend of mine who worked on a site about
10 miles away. His reply came with two programs, one
called Wxsat, the other Wxtrack. Well! This was abonus as you can imagine, and as soon as I started toopen Wxtrack I was amazed at the picture before me.
There and then I suddenly realised that this was thehobby for me.
I installed both of the programs and started to learn
how to use them. It was fantastic! Here I had all theinformation I required. I had the frequency thesatellites transmitted on, I knew when they passed
over or near to my location. All that I needed now wasa suitable receiver and antenna.
Then I had a look at Wxsat. That took a bit more timeto understand and even to this day I am still
experimenting with the settings to get the best images.
But we do have a Wxsat expert in the group: Les
Hamilton has written an article [1] on the subject and it
is very informative, any newcomer would do well toread it. He has also produced a step by step guidewhich can be accessed on the GEO website at:
http://www.geo-web.org.uk/process.html

So to the equipment. My initial choice was theTimestep Proscan Weather Satellite Receiver with aTurnstile Antenna and Pre-amp. Also, for back-up, I
purchased an RX2 Kit (as yet unbuilt). The cheques
were posted off, and after waiting very impatiently for

A typical NOAA image

There has been an excellent article in GEO recently by
Arne van Belle [2], regarding the use of Satellite TV
co-ax cable with a weather satellite antenna. I havebeen using this for some time and have found it to be
extremely good for this type of application. It has low
loss, matches well and is weather-proof—important
where I live on the Dorset coast due to salt water
corrosion.

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GEO Quarterly No 3Group for Earth Observation

I next connected the pre-amp to the other shortlength of cable. You have several choices; you cansolder direct as I did or you can use F-connectors
with the pre-amp mounted into a waterproof box. I
actually used a combination of both. As I stated
before I live near the sea and in winter we get lotsof storms with high winds and spray resulting in avery corrosive atmosphere. So I needed to make allconnections waterproof and secure. I soldered themain co-ax cable from the antenna to the pre-amp
and the outgoing connections to an F-socket withplug, all inside a waterproof box. It is still goingstrong to this day.
The Timestep receiver is an excellent item. It’s acase of ‘out the box, plug in and use’. All theconnections are clearly marked and it can be used
manually or under computer control. The 12-volt
supply required by the pre-amp is fed from theantenna socket and is adequate for the unit.
Once all the connections were complete it was timeto switch on and listen for a satellite with Wxtrack
running to track it and Wxsat set to record. My firstsatellite was NOAA 12 and as it entered my signal
area that familiar ‘tick tock’ sound started.
Suddenly a picture was starting to build up before
me, in colour, but dark. I increased the gain control
which improved it and further adjustments weremade until the quality of the picture was good.
Amazing! I had my first colour weather picturefrom a live satellite.
The next satellite pass was to be NOAA 15 and I
tweaked Wxsat ready for this pass. Again the
picture started to build and this time it was perfect;
the colour was good and the contrast, visibility anddetail were excellent. I was hooked! My next
satellite was Meteor 3-05 and although it was inblack and white the details were outstanding. How
we miss this satellite these days.
It was at this point that John, another friend, who
unbeknown to me was also interested in weather
satellite reception, advised me to download a copyof WxtoImg, an extremely versatile satellite
software program.
For those who have not seen this software in action
take it from me it is excellent, I have recently
purchased the upgrade and the 3-D effect it createsis stunning. I also find that the precipitation mode
provides one with an accurate picture as to thelocation of heavy rain and storms. It is well worth
the cost which supports Craig Anderson for updating the software. My thanks to our friends in
New Zealand for this excellent offering.
With APT Polar Orbiting transmission reception
sorted I now wanted to copy data from Meteosat-7.
This looked to be a challenging project but as John
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August/September 2004

was moving on to Meteosat-8, I was lucky—he sold me
his old kit comprising a Timestep down converter with
LNB and dish. The dish was an ex analogue satellite
unit, so a bit of work was required to change over the
LNB and make a bracket to attach the dish to a mast.
Again I used satellite TV co-ax cable for the feed fromthe converter to the receiver which works fine.
Assembly was completed by fitting the dish to themast, attaching the LNB to the down-converter andconnecting the power supply.
I had a rough idea of the location of the Geostationary
Satellite Meteosat-7 and upon switch on I heard asignal from the speaker. I had already installed the
JVComm 32 software which I loaded up. Sure enough.
There was a picture coming in. I checked the exact
location of Meteosat-7 using Wxtrack, which from mylocation it is azimuth 177.21°, elevation 32.34°. A
magnetic compass was used to orientate the dishprecisely, taking into consideration magnetic
variation, which at that time was 3.25°.
On completion of the operation I switched on thesystem and there it was—a perfect Meteosat-7 picture.
The image of the south Atlantic cyclone reproduced on
page 46 of GEO Q2 was one of those created using thisvery system.
So where to go next? Will it be HRPT? Or Meteosat-8?
I have applied for my licence from EUMETSAT but todate nothing has been heard. Apparently there is aproblem in the system between our Met Office and
EUMETSAT but I have been assured this will besorted out in time. Incidentally I have to say that thehelp and advice I have received from EUMETSAT on
this matter has been excellent. I have not found afriendlier organisation to deal with—most polite andhelpful.
I would love to tackle HRPT but the set up is expensive
so I will look for someone ready to sell a set-up then try
it, as I still consider that the polar orbiting satellites
can and do produce some excellent pictures and each
one is so different in detail.
I hope this article has been of help to some of you.
Everything is described just as it happened and theresults are there to be seen. This is one of those hobbies
where you have to persevere until you get the results
you want. If at first you fail then try again. Also, there
are websites that will help you get all the information
you require—and we now have the experts within GEO
who will assist where they can. So keep on trying. It’s
fun, and rewarding when it all goes well.

References
1 First Steps in Setting up an APT Ground Station
Les Hamilton - GEO Q1 - page 42
2 Using Satellite TV Co-axial Cable
Arne van Belle - GEO Q2 - page 14

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August/September 2004

Group for Earth Observation

GEO Quarterly No 3

Mike Stevens obtained this NOAA 17 image at 11:43 UT on May 1, 2004. Processed using WXtoImg in MSA mode.

Two further NOAA 17 images
from Mike Stevens illustrating theMSA (multispectral analysis)mode of WXtoImg with additional
precipitation overlays.

Left: NOAA 17 at 11:10 UT on
March 21, 2004.
Right: NOAA 17 at 11:50 UT on
March 6, 2004.

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Douglas Deans - douglas@dsdeans.freeserve.co.uk
With all the excitement generated by the wonderful images andscience being returned from the Mars Exploration Rovers, Spirit
and Opportunity, I thought this would be an appropriate time tohave a look at the updated 3DEM program which offers theopportunity (excuse the pun) not only to make 3 dimensional
images of the surface of the earth but other planets such as
Mars. 3DEM works on all Windows platforms and will produce
three dimensional terrain scenes and flyby animations from awide variety of freely available data sources. Those include
•
•
•
•
•
•
•
•

USGS Digital Elevation Model (ASCII DEM) files.
USGS Spatial Data Transfer Standard (SDTS DEM) files.
USGS National Elevation Dataset (NED) files.
USGS Global 30 Arc Second Elevation Data Set(GTOPO30 DEM) files.
NOAA Global Land One-km Base Elevation (GLOBE
DEM) files.
NASA Shuttle Radar Topography Mission (SRTM) files.
NASA Mars Orbiter Laser Altimeter (MOLA) files.
NASA Mars Viking Orbiter Digital Topographic Map (DTM)
files.

3DEM allows low resolution flyby of DEM landscapes using
OpenGL. The path through space is recorded in memory during
flight, allowing subsequent creation of a full resolution mpeg
animation along the flight path. Real-time flyby animations canbe created in AVI or MPEG format. A sample flyby is provided on
the CD.
The program has now been updated to version 18.8 andincludes a number of improvements. These are too numerous tolist in full and many are probably of little interest for amateur
use, but two which do seem worth mentioning are improved
red/blue 3D anaglyph images and better support for the
GTOPO30 and GLOBE terrain models. One noticeable change
is that the program can no longer deal with the original Mars
MOLA files and now requires the 64 or 128 pixels per degree
data. Even compressed the 64 data comprises four files
constituting over 500 Mb of download, and so can really only beconsidered by those with a broadband connection.
In order to provide a useful step by step guide for producing
wonderful images, and to alleviate lengthy data downloads,
Software Showcase has allocated a complete CD (GS3)comprising a package full of useful guides, help and prepareddata.
Let me explain what is on the CD and how best to use it. Unlike
the other CDs in the showcase, GS3 sets out not just to provide
programs and data but to be a complete learning tool for
producing first class 3D images and flybys. Firstly and mostimportantly I recommend you read the three published articles
by Ed Murashie and Les Hamilton both experienced users of thesoftware and data, and now included with the CD. The articles
make reference to some of David Taylor’s programs which canbe downloaded from his web site at www.satsignal.net, but arealso available in CD GS1 from the Showcase Library.

Page 38

By following the articles and using both the data and thespecially prepared files on the CD it should be possible toproduce fascinating 3D images of anywhere on Earth andselected areas of Mars (see offer below). In addition to help withproducing first class images from your own or downloaded
HRPT data, a selection of HRPT images remapped in
GroundMap for use in the 3DEM program and alreadyaccompanied by their own georeferencing files has been
included.
It has only been possible to include a quarter of the Mars MOLA
64 data on the CD, due to the size of the files. But for readers
who may want the full set of Mars MOLA 64 data, but do nothave broadband, I would be happy to provide a CD, at cost, withthe full set. Please contact me, by e-mail, mail or telephone(01786 822828) to arrange this.
I would also like to thank Ed Murashie and Les Hamilton forallowing their articles to be included on the CD and a special
thanks to Les who provided many of the prepared data files for
the HRPT options.
In the hope of encouraging readers to try this, I haveproduced a coloured 3D image of the Sharonov Crater
on Mars. This was prepared using the 64 data and isreproduced on the inside front cover of this issue..
All the above and more is available on GS3. The 3DEM program
can be downloaded fromhttp://www.visualizationsoftware.com/3dem.html
with lots of other information, images and excellent flybys.

How to Purchase CDs
Simply write to the address below requesting GS1,
GS2, GS3 or GS4. Prices are £5 for any single CD,
2 for £8, 3 for £11 or all 4 for £14. Please enclose
cash or cheque (made payable to Douglas Deans
not GEO) for the appropriate amount. Nothingelse is required.
The cost includes the CD, packaging and posting,a small donation towards the cost of overheads,
the cost of overseas orders and the search for new
or updated software. No fee is asked from overseas
members although an exchange of software orinteresting satellite images is always welcome.
Orders are normally dispatched on the day ofreceipt.
Order your CDs from:
Douglas Deans, 17 Montrose Way,
Dunblane, Perthshire FK15 9JL, Scotland.

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August/September 2004

Group for Earth Observation

GS1 A l l D a vi d Ta yl o r ' s w e a t he r s a t e l l i t e p r o g r a m s a ndli b ra ri e s , i nc lud i ng the c urre nt re le a s e s o f W X tra c k ,S atsi gnal, HRP T Reader, GeoS atsi gnal, GroundMap,
RX2 PassControl and many other program extras. This
disc also contains a large quantity of samp[le files, manyof high-resolution data, for use with these programs.
WXtrack
Satellite Tracking Program v 3.4.2
Creates images from
SatSignal
v 4.0.8
wave files
Converts raw HRPT data
HRPT Reader
v 2.5.2
files into images
Manipulates geostationary v 4.1.0
GeoSatsignal
weather satellite images
GroundMap

Rescales satellite images

v 1.3.8

RX2 PassControl

Computer control program
for the RX2 receiverv 2.2.8

GS2 A wi d e r a ng e o f s o ftwa r e fo r a ll a s p e c ts o f we a the rs a t e l l i t e r e c e p t i o n, i nc l ud i ng t r a c k i ng , r e c e i vi ng ,monitoring and image manipulation. Content is detailedb e l o w b u t m a n y o t h e r e x t r a s a r e p r o v i d e d . Ti t l e s
correspond with folder names. * implies a DOS program.
Recall (wave file recorder), PaletteCollection D02(modifies Wxsat colour palettes).
Scanner recorder v 1.8 (wave filerecorder), *NOAA95/*FENG99
Collection D03(software for the NOAA 95 HRPT
project)
Wxsat v 2.59 (wave file
Collection D04
recorder/decoder), Satmon (wavefile recorder).
AGSatTrack
Satellite tracking program v 1.33
Documents for the Cirkit Wxsat
Cirkitreceiver and the UOSat receiver(PDF format)
Downloads current weather
e-weatherman
conditions from the Internet direct toyour computer
Element Manager 2-line element manager v 1.58
Footprint
Satellite tracking program v 2.10
Irfan View
Image/slideshow viewer v 3.80
Evaluation version
JVcomm32(APT/FAX/SSTV decoder)Macintosh kepler Edits verbose AMSAT format
editorelements. Mac OS X and OS9 only.
Image processing program
NeoPaint(30 day evaluation)
Image processing program
Paintshop Pro(30-day evaluation)
Satellite tracker and wave file
Satscape
recorder v 2.00
Utility program for splitting andSplitterreuniting large files
WAV file recording and decoding
WXtoImg
program with many options. v 2.5.10

GS3 3DEM Package for 3D Terrain Visualisation
This CD includes the full set of GLOBE Tiles to allow you
to p r o d uc e e xc e lle nt i m a g e s a nd flyb ys fr o m HRP T
inages. Also included is a selection of Mars MOLA files,
sample images and helpful guides by Ed Murashie.
GS4 Image CD
A wide selection of high-resolution remote images froma range of satellites, including stunning imagery from theSpace Shuttle missions. A full description and source ifprovided for each image.

GEO Quarterly No 3

Douglas Deans, who will be familiar to our readers
through his Software Showcase column, has offered to
put himself forward as GEO’s first helpline member
Douglas was one of the first enthusiasts to embrace the
new DVB technology now in use to disseminate
Meteosat-8 imagery, and he will be delighted to pass
on his experience to help others who are just starting
to set up their equipment (or who are still at the stageof just thinking about it).
Contact Douglas at:• telephone:(01786) 82 28 28• e-mail:douglas@dsdeans.freeserve.co.uk
Douglas adds that he is also happy to help with
queries on other aspects of the weather satellite
scene, such as APT and HRPT.

Extending the GEO Helplines
Douglas has set the ball rolling by kindly offering his
services. But of course, any GEO reader who is of amind to help others with their hobby is welcome to add
his name to the list. If you would like to do so, please
send a brief note to the editor, stating your name andcontact details, and the specific area in which you feel
you can be of help. Contact details for the editor appear
in the right-hand panel on page 1.
To date, two other GEO subscribers have added theirnames to GEO’s Helpline Service:

John Tellick
John has been involved in extensive dialogue withEUMETSAT for many years, and is the man to contact
with queries about registering for Meteosat-8 andthe EUMETCast dissemination system. John is also
happy to field any more general queries about weather
satellites.
Contact John at:• telephone: (0208) 390 3315
• e-mail: info@geo-web.org.uk

Keith Holland
Keith has been imaging from the APT polar orbiting
weather satellites on the 137 MHz frequency as well as
the geostationary Meteosat-7 (Wefax). Keith will bepleased to hear from readers requiring assistance inthese areas.
Contact Keith at:• e-mail: geo@koholland.plus.com
E-mail contact can of course be made at any time, but
we would ask you to restrict telephone contact to theperiod 7.00-9.00 pm in the evenings.

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Page 39

Summer arrives early in Great Britain - Fantastic cloud formations off north-west Scotland - NOAA 17 at 11:41 UT on May 16, 2004
Image: NOAA Satellite Active Archive (www.saa.noaa.gov)

Processing: HRPT Reader (vegetation mode)August/September 2004

Group for Earth Observation

GEO Quarterly No 3

Digital Weather Satellites and DVB... continued from page 25

GEO has its own private and moderated on-line
discussion forum on Yahoo!®Groups.
It is called GEO-Subscribers
The aim of this Group is to provide a means for
efficient on-line communication between GEO
Quarterly subscribers.
GEO-Subscribers allows you to share information,
ask questions and receive speedy responses, mostparticularly from those involved in the day-to-day
running of GEO. For example, if you are having
problems with your NOAA or Meteosat hardware
or software, post details of your problem on GEOSubscribers and tap into the combined experienceand expertise of the Group’s 200 members. If
someone has the answer to your problem, you can
expect a reply within 24 hours (often much less).
Many of our readers have already benefited fromthis service—so can you!
To sign up with GEO-Subscribers, either• send an e-mail asking to be placed on the listto:

• FEC - Forward Error Correction - a way of protecting thedata stream against errors during transmission. The
greater the expected losses, the higher the proportion oferror correction added.
• QPSK - Quasi Phase Shift Keying – a method of placing
the data stream on to a suitable RF frequency carrier wave.
The information modulates the RF carrier wave bychanging the phase of the carrier.
• DVB-S - The satellite digital standard for DVB
transmissions in Europe and a growing number of othercountries.
• Virtual Container (VC) - the data stream provided for DVB
transmission is cut up into packets. Other information isadded to identify and time-stamp it. The data packet that
results is sometimes referred to as a ‘virtual container’.
• Symbol Rate - the rate of change of the modulated RF
carrier produces differing ‘states’ that can be detected by asuitable receiver. These ‘states’ are called ‘symbols’ andcan be attributed a binary value, e.g. 00, 01, 10, 11 etc. The
symbol rate is the number of possible detectable ‘symbols’
per second.
• EUMETCast - EUMETSAT’s data distribution system.
• Tellicast - a registered name (T-Systems Germany). The
data stream management component of the EUMETCast
system.
• Multiplexer - a device for ‘slicing up’ a number of data
sources to produce a single data stream.

Many thanks to John Tellick and David Taylor for
their assistance during the writing of this article.
More information about DVB can be aquired from:

GEO-Subscribers-subscribe@yahoogroups.com• or visit the GEO website at

http://www.dvb.org

Further information on the MSG programme:

http://www.geo-web.org.uk/about.html

http://www.eumetsat.deand type your e-mail address into the YAHOO‘send’ window at the foot of that page. Thenclick on the Yahoo!Groups logo to submit yourrequest.

Please note
Since GEO was established early in 2004, a
number of other individuals have set up Internet
discussion/news groups under the ‘GEO’ banner.
But there is only one official Group run under the
auspices of GEO itself—GEO-Subscribers. If you
wish to be kept up to date with the latest news
from GEO, or to bring your queries to the notice ofmembers of the GEO Management Team, this is
the Group to which you must subscribe.
The GEO Management Team cannot be
guaranteed to monitor, or respond to queries
placed on any of the other Internet Newsgroups.

Please Keep Your e-mailAddress up to Date
Many thanks to all those readers who submitted their e-mailaddresses to GEO when they subscribed.
However, we are all well aware just how easy it is to lose touch
when an e-mail address changes after switching to a new ISP or
upgrading to Broadband etc. We also sometimes experienceproblems simply because a handwritten e-mail address provesdifficult to read.
If your e-mail address has changed since you first subscribed
to GEO, please take a moment to inform the Membership
Secretary, Nigel Evans, so that your contact details can be
updated. Needless to say, he would also appreciate hearing if
you have recently moved house.
The Membership Secretary can be contacted at:members@geo-web.org.uk

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Robert Moore
I operate a small amateur weather station in North
Wales. This consists of a standard instrument shelterwith dry and wet-bulb, maximum and minimum
thermometers and an electronic rain gauge on theworkshop roof. Earth and grass temperatures arerecorded on the lawn. The barograph is kept indoors.
Because of the hill and deep tree-cover to the south of
the house I can not record sunshine or wind but I do
have a fine view to the north and north-west whichenables me to see weather developing from those
directions. I write a quarterly weather report for themagazine produced by our community council—now
nearly always containing either an HRPT or MSG-1
image. HRPT coverage is restricted by the roof of myhouse to the east and, because of surrounding trees, I
can see no further south than latitude 40°N. Whilst
HRPT North Atlantic coverage is excellent, MSG-1 fills
a very important southerly gap for me.
I am essentially an amateur: my naval training inmeteorology dates from pre-satellite days andconcentrated on oceanic weather, basically the Atlantic
depression and the tropical storm. Later, as a shortwave listener, I developed an interest in radio
propagation which rekindled my interest in theweather. In my retirement I intended to learn a bit
more about the Atlantic weather when it reaches thecoast. Terrain effects are a particular interest of mine,
having lived in two rain shadows (the Grampians in
Aberdeen and now Snowdonia in North Wales). I now
live close to the ‘Welsh Riviera’, renowned for its
sunshine. On one day last year Capel Curig had theheaviest rainfall in the UK whilst Prestatyn, a mere
43 kilometres away, recorded the most sunshine.

Figure 1 - Straight line in the clouds over Liverpool Bay

animation showed a continuous stream of cloud fromthe north-west dissipating along the line—presumably
the effect of the warm sea on the cloud. The cloud ‘line’is also visible in the MSG-1 image (figure 2).
Satellite imagery has thus offered me a good
opportunity to indulge my interests in radio, space andcomputing alongside my interest in weather. For the
future I have two tasks. One is to bring myself up to
speed and learn more meteorology. This has been goingwell and I am learning a lot from reading some of themany excellent books available—a selection of which I
have listed at the end of this article. TORRO (Tornado
and Storm Research Organisation) web-based
discussions are invaluable. One thing is clear—I am
never going to understand numerical analysis—thevery thought of it induces an urgent need to lie down ina darkened room.

It is also very noticeable how our weather often differsfrom the remainder of the UK. Furthermore, I candrive to Queensferry or Liverpool, or over the Clwydian
hills (journeys of 15, 25 and 12 km respectively) andencounter radically different conditions from home interms of temperature, precipitation, fog, visibility etc. I
suspect that the relatively shallow parts of the Irish
Sea warm up and cool fairly quickly and influence theweather in North Wales.
Winter images from HRPT have shown that there canbe a very steep temperature gradient from the warm
middle regions of the Irish Sea towards cooler inshoreand estuary waters and finally very cold land surfaces.
Figure 1 shows a straight line in the clouds over
Liverpool Bay, a line that persisted all day. The MSG-1
Page 42

Figure 2 - The straight line in the clouds over Liverpool Bay as
shown by MSG-1 (March 28, 2004)
Image: © EUMETSAT 2004 - Processing: GeoSatsignal

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August/September 2004

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GEO Quarterly No 3

Secondly I have to learn to interpret satellite data for
micro-scale weather. MSG-1 offers so much more than
HRPT in terms of seeing the dynamics of weather (forexample clouds at different levels travelling in opposite
directions) and it is continuous, 24 hours a day. I must
confess to still being at the stage where I find myself
just gazing at some of the jaw-dropping imagery fromthe UK and beyond. I guess many of us are still at thatstage—just looking at the images of our world in
wonder and apprehension. That we can do this isthanks not only to EUMETSAT but to David Taylor
and others who can work magic with computers.

Figure 4 - The ‘thundersnow’ front on January 28
Image: © EUMETSAT 2003

channels) for one week so that anyone in the TORRO
organisation who is investigating severe weather can
ask me for images; I have had two calls so far andapparently the material was very useful.
So, in summary, how is this amateur using MSG-1? I’mlearning from it and planning some systematic
observation on my local micro-climate and I’m
supporting colleagues interested in weather. I should
point out that I am also reading, researching andwriting in my own professional field—thus ensuring avery active retirement.
Figure 3 - The November 13, 2003 storm over the UK
Image: © EUMETSAT 2003

So now I’m teaching myself how to interpret theimages. I am using the learning aids provided by
EUMETSAT and the CDs produced by the Dutch andFinnish Meteorological Institutes and the Central
Institute for Meteorology and Geodynamics (supported
by EUMETSAT). In addition, I use radar imagery tomonitor local precipitation (rain shadow effects arequite clear). An HF whip aerial on my chimney brings
in radio-fax weather charts and I also make use of the
web-based weather maps that many of us accessthrough GeoSatSignal and Autoget. At present I’m stillat the stage of studying MSG-1 imagery and tying it inwith the MSLP charts and local observations—but theupper air now beckons, especially with the MSG-1
animations.
With HRPT, I used to keep the best image near to noon
and the noon MSLP chart in an archive. I was planning
to archive my MSG-1 images by keeping, say the noon
visible, the midnight IR image and the two charts—
plus, of course, animations of anything especiallyinteresting. But with so much archived data alreadyavailable I may spare myself the effort for the routine
data. I am currently keeping all my HRIT images (allMemorable Moments
There have been some memorable weather images forme during this first year with MSG-1 (I suppose wereally should call it Meteosat-8 now). Figure 3 shows
the centre of an Atlantic depression which passed up
Ireland on November 13, 2003. It stopped over Donegal
before turning sharply east and crossing the Irish Sea(rattling my dish on the way) then disappearing off
southern Norway on the 15th. Why did it turn so
sharply?
A tongue of extremely cold Arctic air crossed thecountry on January 28. This was closely monitored by
local observers throughout the UK and was thus well
documented right across the country. It was
accompanied by very unusual ‘thundersnow’ events—that is, snow with thunder and lightning. My
animation tracked the cold tongue across the UK andright down into Europe. The HRV close-up in figure 4

www.geo-web.org.uk

Figure 5 - The ground view on January 28
Page 43

GEO Quarterly No 3Group for Earth Observationshows the point at which the front crossed mystation—the clouds appear to lag behind the front
because the cold air was cutting under them. Figure 5
shows the view at ground level at the same time. An
hour later I could pick out details on Cumbrianhillsides, 70 miles away through the crystal-clear
arctic air.
My piece de resistance so far has been to spot a‘rope cloud’ running from St David's Head to Finisterre(figure 6). Rope cloud is a thin line of convective cloudcaused by cold air sinking from a decaying cold front.

August/September 2004

Bader, M J et al
Images in Weather Forecasting, Cambridge University Press,
1995
This volume should be the satellite observer’s bible. It has
everything as of 1995 including extremely detailed discussionsof the interpretation of satellite imagery (including radar
imagery). Ideal for observers in the UK.
Unfortunately this book is out of print and will be neither revised
nor reprinted. Inter-library loan is probably the only way to get it.
If you are lucky enough to find one second-hand expect to pay
a good price for it—if I’m not there first!
Conway, E D and the Maryland Space Grant Consortium
An Introduction to Satellite Imagery Interpretation - Johns
Hopkins University Press, 1997
Comes with a CD. This is almost certainly the best readily
available book on interpreting satellite images Although
USA-oriented, it is full of interesting and useful material which isrelevant on this side of the Atlantic.
Dunlop, S
Weather - Harper Collins, 1999
A short and useful book with plenty of illustrations that will fit into
your shirt pocket.
Dunlop, S
How to Identify Weather - Collins 2002
This should really be called ‘how to identify clouds’ and as suchit is an absolutely essential handbook for the amateur observer.
File, D
Weather Facts - Oxford University Press, 1990

Figure 6 - ‘Rope cloud’

In this case there was precipitation associated with therope cloud because ice crystals from high level cloud
were seeding the rain. Ton Lindeman is writing this up
for publication. We hope this will be a significant
contribution to theoretical debates in meteorology.
This may be typical of the sort of contribution thatamateurs can make; few professionals will have thetime to browse around every image—they will beworking on research programmes, forecasting
deadlines or specific highly focused projects. This
leaves room for the amateur observer to contribute hisor her three ha’porth. For myself, I hope to understandthe weather in this corner of North Wales better in a
few years’ time.
(Robert Moore is Emeritus Professor of Sociology. He has held
Chairs in the Universities of Aberdeen and Liverpool - Ed)

Some Useful Titles
Ahrens, D C: Meteorology Today
An Introduction to Weather, Climate and the Environment, West
Publishing Company (Minneapolis/St Paul) 1994
This is an excellent student text book complete with casestudies and test-yourself exercises. It is very well illustrated andcarefully explained throughout.
Whilst an extremely useful and handsomely presented volume itis oriented to North America. Why can’t we have a European
equivalent?
Page 44

How to understand the weather and climate and their impact oncommerce and society—an interesting book but perhaps not
ideal for our purposes.
Hardy, R
Teach Yourself Weather - Hodder and Stoughton, 1998
Just that – a useful first book on the weather.
Reynolds, R
Philip’s Guide to Weather - George Philips, 2000
A well-illustrated guide-book with discussions of local weather
observation and, briefly, the use of satellites in meteorology.
Watts, A
The Weather Handbook - Waterline Books, 1999
This was the introductory text that taught me the most –excellent on weather systems and how they ‘work’,interpretation of weather charts and elementary interpretation of
weather satellite imagery. The book tells you what to look for on
the charts, in the sky and on your screen.
The CD set
Manual of Synoptic Satellite Meteorology Conceptual Models
This CD, produced by the Royal Netherlands and Finnish
Meteorological Institutes and the Central Institute for
Meteorology and Geodynamics (supported by EUMETSAT), is
an invaluable tool. It will probably take most of us more than ayear to work through. The higher your level of science education(especially physics) the more you will get out of it, but everyone
will learn from and enjoy this—and it’s free.

www.geo-web.org.uk

August/September 2004

Hi Les,I like GEO and I am looking forward forNo.2. I think the way you write about
technical stuff is quite good, toencourage other people with a different
view on our Earth, and I think that GEO
is an enrichment...
So go on....
Kindest regards,
Klaus Bolst, Bochum.
Dear Editor,
Perhaps you would allow me to ask aquestion of your membership.
Recently I have taken an interest in our
Earth’s fluid environments: our oceans
and atmosphere. Now I don’t likecoincidences, that is the juxtaposition of
two seemingly unrelated events. I know
they happens but I still don’t like them.
I have noticed that the volume of the
Earth’s atmosphere as measured at sea
level pressure is the same as thevolume of the Earth’s oceans.
The question is this: “Is this acoincidence or an equilibrium”? And,do I
have to wait a billion years to find out?
As usual I have my own view which isexpressed above but I don’t understandthe dynamics; hence the request forhelp from your membership.Consider
Mars!
Francis BellHi John
I would like to thank all of the
management team for the symposium.
Thank you for your very hard work to
make it happen and to Nadine Bell for
getting roped in too.
I really enjoyed the first magazine whichrekindled my interest. The speakers
were really interesting and there wassomething for everyone.
I have registered for my licence for
MSG with Eumetsat and I am looking to
get the system up and running.
Again thank you all for Saturday.
Best regards
Pete
Hi LesPlease find a letter for inclusion in GEO.
Its’ by a friend of mine, Joe Loy, towhom I loaned GEO Q2 for a read. I am
trying to entice him into GEO.
Best Wishes
Brian Walker

Group for Earth Observation

Joe Loy writes:Sir,
I read with some interest the article‘Death of a Planet’ by Francis Bell. I
take under consideration some of thepoints raised but really take exception
to a number of statements, because ofpractical experience, rather thanacademical knowledge.
The jumps back and forward ingeological time tended to break myconcentration and, may I say, were not
relevant to the subject and may be offputting to ordinary readers. Was it
necessary to introduce technical terms
unfamiliar to many readers, or was it aploy from an academic to impresslesser individuals? I say that because I
believe in facts: a theory still remains
such until proven. However, I
recognised both the terms and what
they are relative to, and say quite firmlythat it has nothing to do with the subject
in hand but to the environment to whichplants are exposed.
Let us first examine what ‘Global
Warming’ is. It is a theory, first proposedin the late sixties/early seventies andpresented to the Club of Rome as a factthat the planet was in danger from theburning of fossil fuels. It was
accompanied by a computer program
which purported to prove that the theory
was indeed fact. This idea was
debunked by a computer literate person
who showed that whatever was input,
including complete nonsense, the result
was always global warming!
As you may have guessed, my interest
is in the practical use of data available
on atmospheric gases. Having been
engaged in training and leading
personnel in the Mines Rescue Service,where correct identification of aparticular gas was vital because it may
have been the turning point for successor failure in terms of human life for boththemselves and others. The figure given
for the concentration of carbon dioxidein air is not as stated in the article but
was identified originally as 0.03%. It still
remains so, contrary to the efforts ofsome scientists to foist wrongly
obtained information on us in support ofdubious purposes.
A second point requiring reconsiderationis the stated nearly 6% for the carbon
dioxide level in the lungs. The norm forthis figure, allowing humans to breathe
at a rate and depth whilst resting, is 4%.
Increase of the level marginally above
this causes rate and depth to increase,www.geo-web.org.uk

GEO Quarterly No 3

whilst marginal decreases have theopposite effect. It is quite commonly
known that hyperventilation depletes thebasic level of CO2 in the lungs and can
reduce the triggering of the breathingreflex, often to a lethal extent. I havepractical knowledge of these facts fromstudying the results of tests performedon himself by Professor Haldane of
Edinburgh, in which he recorded
copious notes. I also experienced someof these things when I was a voluntary
patient in experiments at Edinburgh
Royal Victoria Hospital in the early ‘70’s.
Inclusion of material about evolution in
the animal kingdom and deprivation of
the planet of necessary carbon have no
relevance in relation to humanity. It
happened that way because the planetcreated the conditions suitable as eachnew species evolved and I suspect that
it was the change which created theevolution I am quite sure that, when all
ken of our generation and thosefollowing is forgotten, it is quite probablethat man will be replaced by somethingelse more fitted to the changes. It could
possibly be an improvement!
Those concerned about global warming,
climate change and greenhouse effectvary from politicians, bright-eyed
optimists who have found a cause andthe invariable silver tongued rogue out
to make a financial killing. My response
to all is a weary, knowing smile.
Joe Loy, Workington

Launch News
‘Aura’, the third and final memberof NASA’s first series of Earth
Observing flagships was finallylaunched from Vandenberg Air
Force Base, California at 3:01 PDT
on July 15 into its 705 kilometrehigh orbit.
Aura now joins Terra and Aqua on
NASA’s mission to understand andprotect the Earthy atmosphere.
The Aura mission has three key
aims: to investigate the recovery of
the ozone layer, determine theprocesses that control air quality
and investigate climate change.
The first scientific data from thesatellite are expected within 30 to
90 days. We hope to include anarticle about the new satellite in a
future issue of GEO Quarterly.
Page 45

GEO Quarterly No 3Group for Earth Observation

August/September 2004

Les Hamilton - lesw.hamilton@tiscali.co.uk
http://myweb.tiscali.co.uk/wxsatellite
Following our presentation in GEO Q1 describing how
to set up a basic APT weather satellite ground-station,
a number of readers have responded with requests forarticles which explain how they can improve their
NOAA APT images. In this issue we take you a stage
further as we explain how the same NOAA WAV files
you created with Wxsat can be processed by a moreversatile software application, SatSignal. SatSignal
not only converts WAV files into satellite images butallows the user to remove speckles and noisy imagelines as well as manipulate contrast, brightness andcolour rendition.

Satsignal takes much of the hassle out of APT image
processing by fully analysing each WAV file prior to
decoding and optimising basic decoding parameters
before creating the images. As a result, performance is
not hardware-related and anyone following themethods outlined below should obtain top quality
images. Satsignal simultaneously decodes each WAV
file into four separate images which can be viewed on
the four tabs on the main Satsignal screen as shown
below.

The development of SatSignal by David Taylor started
away back in 1999 and, following suggestions andfeedback from many enthusiasts around the world, it
has developed into the state-of-the-art program it istoday. It should be noted from the outset, however,that this software cannot itself capture the satellite
signals—you still require a program such as Wxsat tocreate the WAV files first.
SatSignal comes in two versions, unregistered andregistered. Many satellite imaging enthusiasts findthat even the free unregistered version offers all thefunctionality that they require—at least in their early
forays into satellite imaging. But to unlock the fullpower of the program, registration is required.
Installing SatSignal
To install SatSignal you require two items of software,
the Satsignal archive (satsignal4nn.zip) and the runtime library bundle (runtimes-setup-100.zip). Both areavailable from David Taylor’s website or from Software
Showcase [1]. Open the runtime bundle using Winzip
and double-click on the file runtimes-setup.exe to start
the installation. Once complete, create a new folder on
your computer called ‘Satsignal’ then open thesatsignal4nn.zip program file in Winzip and extract allits files into this folder. Finally, for convenience, createa Desktop shortcut by dragging the satsignal.exe iconfrom this folder on to your PC Desktop using the righthand mouse button and then clicking ‘Create shortcut
here’. You are now ready to start using SatSignal.

The Unregistered Version of Satsignal
Whilst Wxsat can produce excellent images from WAV
files, results do depend critically on the system used.
Both the wx-receiver output level and the type ofsoundcard utilised affect your results, and a set ofparameters that provides good images on one computeris unlikely to do so on another.
Page 46

Figure 1 - the Channel-A tab showing a visible image

The four tabs are:
• Main Image: a raw image consisting of the channel-2
visible image and the channel-4 infrared image side by side
• Channel-A: a modified channel-2 image• Channel-B: a modified channel-4 image• False colour: a colour composite image

Unless specified otherwise, all images shown in thisarticle were produced using a WAV file recorded fromthe 11:15 UT NOAA-17 pass on July 13, 2003, one of
the many wonderful sunny days experienced thatsummer. The colour version on the outer back cover
was created using a newly installed, unregistered copyof SatSignal, under the program’s default settings.
What you see is a screen dump of the Satsignal window
as it appears in Windows XP™, using a vertical screen
Decoding a WAV File
To use Satsignal you must already have available a
NOAA satellite WAV file that has been created using
Wxsat or WXtoImg. Load this into Satsignal by clicking<File> on the main menu-bar, selecting <Open>, thenwww.geo-web.org.uk

August/September 2004

Group for Earth Observation

GEO Quarterly No 3

navigating to the folder containing the WAV file itself.
Double-click on this WAV file to initiate processing (foryour first attempt, try to choose a good overhead passwithout any interference)
The WAV files from weather satellite APT are always
created with a nominal sample-rate of 11025 Hz. If
Satsignal finds this to be accurate, processing starts
immediately. However, if you are using a slow, older
computer, the sample-rate may differ slightly from thisfigure (even a 5 Hz deviation will make the decoded
images slant), and Satsignal will recommend a revised
value; if this is in the range 11,010 to 11,040Hz, accept
it. If the value suggested by SatSignal is outside thisrange, it is likely that there is something wrong withthe wave file or, less likely, with your soundcard.
If this still fails to provide straight (i.e. verticallyaligned) images, use the <Settings → Sample frequency →user> option which permits you to adjust the samplerate in single hertz increments. A good way todetermine the optimal value is to select a weak but‘clean’ signal, and set the sampling frequency mid-way
between the upper and lower values at which lock islost (i.e. the image just starts to slant). The new
sample-rate value will be stored for future use.
Decoding is highly processor-intensive and the time
taken to produce your images depends crucially on thespecification of your computer. Table 1 lists theprocessing times for the same WAV file on a variety ofcomputers. On a very basic 233 MHz Pentium-1 laptop
with 32 Mb RAM, image processing took (nearly)
forever—just four seconds less than ten minutes tocomplete the task. Increasing the available RAM has adramatic effect; 192 Mb reduced processing time by afactor of more than twenty, still with a very modest
processor. So the message is clear—the more RAM you
have the better. Faster processors help too, but theireffect is much less significant. Low specification
computers can take a very long time indeed, and theauthor recommends a minimum 64 Mb of RAM.

Figure 2 - the Channel-B tab showing an infrared image
Processor

Speed (MHz)RAM (Mb)

Processing Time

Pentium I
Pentium II

233

32

9 min 56 sec

366

192

2 7 se cPentium III

500

256

1 9 se cPentium IV

2800

1000

5 se cTable 1 - Processing times

Figure 3 - Gamma correction (channel-2 - visible)

Figure 4 - Gamma correction (channel-4 - infrared)

Optimising the Images
In line with their primary objective of helping toanalyse our planet’s weather, NOAA satellites havebeen designed mainly to image Earth’s cloud cover.
Clouds reflect brightly in sunlight, but land and sea
surfaces have a low albedo (reflectivity). This meansthat while cloud rendition is excellent, land regions
frequently show up very poorly by comparison. Twotools, ‘Equalise histogram’ and ‘Gamma correct’ will
frequently help to produce more pleasing results.

Figure 5 - Histogram equalisation
The right-hand image of each pair has been histogram
equalised: Channel-2 (left pair) and Channel-4 (right pair)Gamma Correction
Satellite APT produces images containing 256 greyscale tones, ranging from black through a range ofintermediate greys to white. A typical NOAA image
may emphasise the white and light greys (cloud),leaving the darker greys (land) at a very low level. The
gamma correction tool allows the intensities at the‘white’ end of the spectrum to be reduced while those at
the ‘black’ end are enhanced. No image information is
lost: intensities are simply redistributed so that they
produce a more aesthetically appealing result on the
PC screen. Satsignal offers five levels of gamma
correction from zero to 2.8. The default, which gives
good results for well-illuminated summertime passes

www.geo-web.org.uk

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GEO Quarterly No 3Group for Earth Observation

August/September 2004

Figure 6 - Histogram equalisation applied to the NOAA-15 image acquired at 07:13 UT on April 16, 2004

is 1.3. In an image where the land is particularly dark
and featureless try increasing the gamma. From themenu-bar click <Options → Gamma correct> and makeyour choice from the fly-out list (figure 2). Results ofdifferent gamma settings on a segment from the
Channel-2 visible/near-IR image are shown in figure 3.
Note how Scandinavia in particular benefits as the
gamma is progressively increased. On the other hand,cloud definition over the Atlantic Ocean deteriorates.
Figure 4 shows how the same range of gamma
adjustments affects the Channel-4 infrared image:again, land detail is progressively enhanced while
definition in the bright clouds suffers. Choose the
gamma setting that meets your requirements best.
Histogram Equalisation
This useful tool is found in the same menu under<Options → Equalise histogram> and may also be seen in
figure 2. Histogram equalisation redistributes thegreyscale intensities over the image so that each of the
256 levels in the image is distributed evenly across thebrightness range. This does not generally make much
impact with well-illuminated visible light images, but
often results in a startling improvement in infrared
images. Figure 5 illustrates the effects of histogram
equalisation, at the default gamma setting of 1.3.
Histogram equalisation may also prove advantageouswhen preparing images from morning satellite passes
when the sun is low in the sky and illumination is
uneven. Figure 6 shows just this situation with the
07:13 UT NOAA-15 pass from April 16: the sun is still
low in the eastern sky and the right-hand side of theimage is much more strongly illuminated than the left.
The upper row of images in figure 6 shows the effectsof gamma correction alone, which tends to result inrather ‘flat’ images with a restricted range of tones.
Application of histogram equalisation to each is shownin the lower rank of images. The actual choice ofparameters will be dictated by the particular part ofthe image that you are trying to enhance.
Page 48

Why Register?
On registering Satsignal, many worthwhile new
options present themselves. One of the most useful isthe Illumination adjust feature which compensates ina much more effective manner for the lateral lighting
imbalance present in images like figure 6. Figure 7
shows just how much detail can be preserved using thisoption. While cloud over the Atlantic is now nicely
rendered, the subtle light variations over the Baltic
Sea are retained—altogether a much more satisfying
result than any of the versions in figure 6.
If you look carefully at figure 7 you will also note thepresence of a toolbar above the image. This greatly
simplifies the use of the program by providing one-click
pathways to many of the most common options.
While the basic program offers just a single colour
scheme, registration opens the door for the use of
several predefined palettes and also allows you tocreate your own. The left-hand image in figure 8
employs a user-defined palette that adds blue to thesea surface while the right-hand image uses the
supplied ‘temperature’ palette. Additional palettes canbe created using a dedicated utility program called
LUT-Maker. Figure 8 also illustrates the addition of
automatic captions, gridding and country outlines tothe images.
A detailed appraisal of the registered version of
Satsignal is beyond the scope of this article. However,if past experience is anything to go by, most users will
be keen to register and experiment with the newfeatures for themselves.
Reference
1. Satsignal is available from Software Showcase. You canalso download it yourself from http://www.satsignal.net
on David Taylor’s website. You will find the link to
Satsignal under the ‘Satellite Tools’ section. The link to
the runtime library bundle is on the Satsignal page under
the section headed ‘Requirements’.

www.geo-web.org.uk

Figure 7 - The NOAA-15 image, processed using the registered version of Satsignal, and modified
by application of the strongest ‘NOAA illumination adjust‘ setting.

Figure 8 - The NOAA-17 image, processed using the registered version of Satsignal, displaying colour palettes, country outlines
and captions. The left-hand image uses a customised palette, that on the right shows the in-built ‘thermal’ palette.

A NOAA-17 image, processed in default mode using Satsignal
11:15 UT on July 13, 2003