Radio Telescope on Track

This post was originally published by Australia’s Science Channel on 29th July 2016 but was removed when the website was updated.

David Gozzard is a PhD student who has found himself on an interesting journey to remote Australia. In this blog, he shares some of the fun work he’s been up to!

When I started my PhD in experimental physics, I knew there would be a lot of travelling involved, mostly to conferences, meetings and workshops both in Australia and overseas. What I did not realize was how often I would find myself travelling to remote areas of Australia and South Africa to conduct field work. I’m not complaining. The field work is both challenging and rewarding, it gets me out of the lab, and it means I get to visit some of the world’s premier scientific facilities.

And that’s where I am now. After a four-hour flight from Perth to Sydney, a short hop from Sydney to Tamworth, and a two-hour drive from Tamworth to Narrabri (lugging two heavy cases full of scientific equipment), I find myself at the Paul Wild Observatory, home of CSIRO’s Australia Telescope Compact Array, the largest radio interferometer telescope in the southern hemisphere.


Antennas 1 – 5 of the Australia Telescope Compact Array.

Built in the 1980s, the Compact Array is a radio telescope comprising six 270-tonne
dish-antennas, five of which can be driven to various positions along a 3 km track in order to change their view of the sky. Although it’s not as famous as The Dish at Parkes, the Compact Array holds the distinction of being the most scientifically productive radio telescope in the southern hemisphere. In radio engineering, the plural of “antenna” is “antennas”. Biologists, calm down.


Me, driving antenna 3 during an array reconfiguration (see video below).

This is my 3rd trip to the Compact Array. I’m here to test equipment developed for the Square Kilometre Array (SKA) radio telescope. Radio telescope arrays like the Compact Array and the SKA need high-precision reference signals from atomic clocks to be transmitted to each antennas in order for the array to function properly. Over long transmission distances, the precision of these signals can become degraded and when that happens, the array fails.

On something the size of the Compact Array (6 km from one end to the other), this is not a problem; but for the SKA, which will have antennas located up to 150 km away from the centre of the site, signal degradation is a big problem. The equipment I have brought with me is designed to compensate for the degradation of the reference signal by measuring how the reference signal has been perturbed and modifying the transmission to compensate.


My signal stabilization test equipment setup at ATCA.

My supervisor and I have been developing this stabilization system over the past two years at The University of Western Australia, and we have tested its performance extensively in the laboratory. Now the time has come to plug it into a working radio telescope to confirm that it works in the real world!

Because this is a synthesis imaging telescope, every few weeks the antenna dishes are moved to different positions along a track to change how they image the sky. I was lucky enough to be allowed to take part in one of these array reconfigurations. Each of the six antennas weighs 270 tonnes and has a top speed of 4 km/h. Reconfiguration can take 1 – 2 hours depending on the extent of that day’s changes. Antenna 2 shown in the video was driven nearly 2 km in this reconfiguration job.

The Compact Array is the best facility to perform these tests because it was constructed with an almost unique receiver system that allows us to run the array using both its conventional reference distribution system and our stabilized reference system at the same time. Our system runs over an extra 77 km of fibre-optic cable to a communications hut and back. The telescope data from the conventional reference system can be compared directly with ours to see if the stabilization system is working as designed.

The Compact Array is the best facility to perform these tests because it was constructed with an almost unique receiver system that allows us to run the array using both its conventional reference distribution system and our stabilized reference system at the same time. Our system runs over an extra 77 km of fibre-optic cable to a communications hut and back. The telescope data from the conventional reference system can be compared directly with ours to see if the stabilization system is working as designed.


Me, sitting in the ATCA control room.

Working with the CSIRO team is an absolute pleasure. Everyone is very professional, they all know the systems they are responsible for insideout, and they are very helpful. The experiments that I have performed at the Compact Array would not have been possible without the efforts they made to accommodate my test schedule and the modifications I needed on some of the antennas.


This photo is the group of us who contributed to the work on this trip. The people in the photo are left-to-right: David Gozzard, Mike Hill, Sascha Schediwy, Peter Mirtschin, Jamie Stevens and Jock McFee (not pictured – Brett Lennon).

They also took a keen interest in the experiment itself. Many of the staff at the Compact Array reminisce about how it used to be, only a few years ago, when the site was buzzing with astronomers from Australia and around the world. Now, astronomers can operate the telescope remotely from Sydney or, in some cases, from the other side of the world. As a result, the onsite staff have seen their ranks halve as less support is needed. The engineers and other support staff miss being able to quiz astronomers about what they are using the telescope for, and what they are discovering.

Apart from the Compact Array itself, the observatory is home to a lot of Australian science history. The array occupies a site formerly used by the Culgoora radioheliograph (pictured below), which CSIRO used from the mid-60s through to the mid-80s
to perform groundbreaking studies of radio emissions from the Sun and solar outbursts.


One dish of the Culgoora radioheliograph.

Most of the 96 dish-antennas from the radioheliograph still surround the site in a 3 km wide circle. Within that circle are also the Sydney University Stellar Interferometer, until recently used to make measurements of the size of distant stars; the CSIRO Applied Physics Solar Telescope, which studied the visible light from the Sun in conjunction with the radioheliograph; the Birmingham Solar Oscillations Network Telescope, used to study churning gas inside the Sun; and an IPS Radio and Space Services telescope, which monitors solar outbursts to forecast how they will affect space craft and radio communications.

As I write this, my time at the Compact Array is coming to an end. My experiments have worked, the stabilization system has performed well, and I am preparing to report the results to the SKA Office. And the results are looking good. The system reduces signal fluctuations to one part in ten trillion, over a 1-second period. If your wristwatch
was that stable, after 300,000 years it would be off by less than one second. This is more than 10 times better than the stability required by the SKA.

Now I just have to pack up my equipment and get ready for the journey home.

Further reading

Measuring Up for World Metrology Day

This post is a modified version of a World Metrology Day article I wrote for Australia’s Science Channel.

Saturday 20th May is World Metrology Day.

I’m not surprised if you hadn’t heard of it. I was three years in to a PhD in metrology before I found out we had a day for it.

Metrology is the science of measurement. It is an important foundation of other experimental sciences and is also a critical component of a nation’s ability to conduct business. Metrology considered to comprise three different fields:

Scientific metrology focusses on the definition of units of measurement (e.g. the kilogram, the metre, etc), how to actually make the measurements, and how to reliably trace a measurement back to an official reference.

Industrial metrology is about the application of measurement to manufacturing and other industrial and social applications. Industrial metrology is a very important factor in a nation’s engineering capability.

Legal metrology concerns the statutory requirements of measurement for trade, taxation, and protection of the public. Whenever farming produce is weighed, petrol is pumped, or shares are traded, the measurements (in these cases; weight, volume, and time) need to meet strict government controls on accuracy and precision.

Nearly every country has a metrology institute, involved in all of these important aspects of measurement. In Australia, we have the National Measurement Institute (NMI). America has the National Institute of Standards and Technology (NIST) and the UK have the National Physical Laboratory.

World Metrology Day is an international event commemorating the signing of the Metre Convention on 20th May 1875. The Metre Convention established international cooperation to develop the metric system and the International System of Units (SI).


Signatories of the Metre Convention. Technically, America uses the metric system. Somebody should probably tell them.

Measure for measure

For the past three-and-a-bit years I have been pursuing a PhD in optical metrology — I use light to measure stuff.

In particular, I work on the transmission of atomic clock signals for use by radio telescopes and other space science experiments. Over the years, atomic clocks have become more and more precise, and today we need new technologies in order to transmit the atomic clock signals to another location for use in scientific or industrial measurements.


My metrology lab.

Measuring up

The next few years hold some exciting developments for metrologists. We will soon re-define two of the most basic measurements we use every day, the kilogram, and the second.

The SI system has seven basic units of measurement. These are: the metre, the kilogram, the second, the ampere, the Kelvin, the mole, and the candela. All other units that we use to measure stuff, such as volts or kilowatts, a derived from these basic units.

The second is currently defined using caesium atomic clocks. The caesium within the atomic clock emits microwaves at around 9 GHz, and this frequency is used as the “tick” from which the second is defined.

As atomic clocks have got better, another type of atomic clock that uses atoms of ytterbium have proved to be more stable and precise than caesium-based clocks. These clocks emit light at a frequency around 518 THz, that is, they tick at around 518 trillion times per second. In a few years’ time, ytterbium clocks might become the new way to define time.

The second, and most of the other SI base units, are defined using physical constants. For example, the metre is defined as the distance light travels in 1/299792458th of a second. However, the kilogram is the only unit that is still defined by a physical object. A platinum-iridium ingot in a vault in France is defined to be the kilogram.


NIST’s copy of the kilogram.

Metrologists are working to find a better way to define the kilogram in terms of fundamental constants so that any metrology laboratory around the world can more easily make a precise and accurate measurement of the mass of the kilogram.

The leading contender is a device called a Watt balance that uses electromagnets to convert the mass of the kilogram into units of electrical power, Watts, which can be traced back to fundamental physical constants.

You can even download plans to build your own Watt balance. The US NIST released plans for a DIY Watt balance made out of LEGO. It’s millions of times less precise than NIST’s Watt balance, but about 10 to 100 times more precise than your kitchen scales (depending on how good your building skills are).


NIST’s LEGO Watt Balance

Metrology is an important part of our modern civilization. It is as fundamental to our way of life as electricity, or the internet. The progress of science and technology depends on the progress of our ability to make accurate and precise measurements.

Off their trolley problem

Why driverless cars don’t care about your ethical dilemmas

If you’ve been paying attention to the media stories about driverless cars, you will have heard the concerns about what driverless cars will do when faced with ethical dilemmas, scenarios in which the car’s computer program has to pick between different options of who to kill when faced with an impending collision. The problem is a variation of the famous, philosophical ‘trolley problem’.

The trolley problem is a thought experiment intended to discuss the ethics of action versus inaction in a no-win situation. The most common variant of the trolley problem goes:

A runaway trolley/train/tram is speeding down railway tracks. Ahead of it, five people are tied to the tracks and are unable to escape. The trolley will kill them. You are standing near a lever in the train yard. If you pull the lever, the trolley will be diverted down a separate track. However, there is also one person tied up and unable to escape on the diverting track. You have two options: do nothing and the trolley kills five people, or pull the lever and the trolley kills only one. What do you do?

There are many interesting variants of the trolley problem, including ones that require you to decide whether you would push a fat man off a bridge in the name of the greater good. (The kind of people who come up with these questions worry me…)

Pretty car

Tesla Model S — semi-autonomous, and, if it takes after the guy it’s named after, may develop an unhealthy attachment to pigeons

Various people have raised concerns that, under certain circumstances, a driverless car could be faced with a similar dilemma. In an impending, fatal crash, does the car swerve to avoid a pedestrian, thus killing the occupant of the car, or does the car stay on course and kill the pedestrian, allowing the occupant to survive? How do we program ethics into the car’s computer?

Like myself, most of the engineers that I posed this question to responded, “That’s a stupid question.”

The trolley problem is a highly contrived scenario that is so abstracted as to have lost all basis in reality. The problem is constructed such that you have no other options. There is no way to stop the trolley, there is no way to warn the people on the track or get them out of the way, the trolley cannot be derailed by pulling the leaver only half way… In real life, and thus, on the road, the trolley problem does not apply.

When this topic of conversation was brought up by some concerned acquaintances, the conversation went something as follows:

Them: What would you do if your car was going to crash and you had to decide between killing a cyclist or a little old lady?
Me: I’d put on the brakes.
Them: What if your brakes have failed?
Me: I’d put on the hand brake.
Them: Both sets of brakes have failed.
Me: Why would I be driving a car with no working brakes?
Them: It’s hypothetical. Let’s say you forgot to get it serviced.
Me: I’d cut the engine and use that to slow down.
Them: You can’t do that.
Me: Why not?
Them: You just can’t.
Me: And I really can’t steer between the granny and the cyclist?
Them: No. You’re between two walls.
Me: I’d steer the car so as to graze along the wall and let friction stop it.
Them: You can’t do that.
Me: Why not?
Them: You just can’t.
Me: Your question is stupid.

I have only been driving for around 10 years, but in that time I have never had to make an ethical decision about who to kill in what situation. No one else I have talked to has ever had to make a similar decision, and, I would be willing to bet, neither have you. If there was any real chance of us having to make ethical decisions about who to kill on the road, it would be part of drivers license exams. (For the love of God, please don’t mention this to the WA government. We don’t need an ethics test to go along with the road-law test, the practical exam, the driving-hours log book, the hazard perception test, the six-month curfew and the two-year probation.)

Like a human driver, the car should be working to avoid any sort of crash, and an autonomous car is likely to be a hell of a lot better at it than a human. With all-round sensors like having eyes in the back of your head, and reaction times that no human could ever hope to match, driverless cars are likely to make our roads far safer than they are now by removing the most failure-prone part of any vehicle, the squishy lump in the driver’s seat.

And how are the engineers working on Google’s self-driving car dealing with the trolley problem and ethical decisions? They are ignoring them, and are designing the car to avoid any crash as best it can. If the situation has developed such that the car has to choose who to run over, the car is so out of control that the question is rendered moot.

Whoever styled the Google cars should not be allowed to style cars.

“Here I am, brain the size of a planet, and they make me drive meatbags to work. Call that job satisfaction, ’cause I don’t.”

Driverless cars will not be infallible, no human-made system is. But they have the potential to make our roads safer, and our journeys far more pleasant. My only worry is that the car’s software will be vulnerable to hackers, and that one day, when deciding whether to hit the cyclist or the little old lady, my car attempts a 7-10 split.