A few weeks ago, the regular Melbourne metropolitan weather radar at Laverton was taken offline and the training system at Broadmeadows was made 'live' to cover the period while the Laverton station was upgraded.
From my location in the Dandenongs, Broadmeadows is 10kms closer than Laverton (40 kms vs 52 kms). The line-of-sight angle to Broadmeadows is also different, directed more towards me at sleep while the Laverton site is somewhat shielded by a brick wall.
Map showing location of weather radars and attitude to my house:
So the question arises - is my discomfort caused by the weather radars, and is it worse because of the passing storm?
Weather radar images of the storm passing through:
My thoughts
- The primary radar site covering the Melbourne metropolitan area is closer to my house and is more directly in line-of-sight as I sleep.
- Is the replacement radar system the same as the previous one or are there differences in the radiation profile, radiation strength?
- Was the replacement radar 'usually' working prior to the primary site being taken offline?
- We live on top of a hill, so a radar looking for rain activity will be directed upwards, potentially directly to where I live.
- Is it possible that a weather radar adapts it's signal profile if a rain event is passing through the area, potentially increasing signal strength to penetrate rain clouds better?
To try to get some answers, I put some questions in to the Bureau of Meteorology and was very pleased to get answers from Andrew Collins, Head of Radar. Here are the emails.
Terminology
C-band = microwave radiation, 4.0 - 8.0 GHz link
S-band = microwave radiation, 2-4 GHz link
Magnetron = a high powered microwave generator link
Klystron = a high powered microwave generator link
Dual polarisation = a microwave signal containing both horizontally and vertically polarised beams link
PRF = Pulse repetition frequency link
From Richard Cullen to BOM media relations
Hi Sally
Thanks for taking my call earlier.
I am interested to know some more about the weather radars that are active in the Melbourne area. I understand that the Laverton centre is being upgraded and that the Broadmeadows centre is the primary site at the moment. I found this 'explainer' video on Youtube https://www.youtube.com/watch?v=YeLRr56K7UA so perhaps Steven McGibbony is the right person to be in touch with?
My questions are of a technical nature about the radar systems that are active and which are being deployed, in particular some more in-depth information regarding the radar signals being generated by each centre and the radio-frequency emissions.
Specific questions include:
- what are the makes and models of the radar units? Are there specification sheets that can be provided?
- what are the power ratings of each unit, and under what conditions would power emissions be increased?
- what are the rates of rotation of each unit?
Many thanks
- Dr Richard Cullen
From Andrew Collins to Richard Cullen (12 October 2017)
Hi Richard,
The Bureau uses several types of radars. We operate both C-band and S-band. Magnetron transmitters at 250kW (C-band) and 850kW (S-band) and 750kW klystrons (Meteor 1700S radars).
Our scan rates vary as we generally do 14 elevations over a 6-minute or 10-minute scan strategy.
Buckland Park (Adelaide) for example - Long Range Scan: Single elevation angle (0.5º) at 400 Hz PRF. Maximum range of 375 km for extension of reflectivity products. Dual Polarisation mode: 14 elevation angle scans, 1000 Hz PRF, second-trip recovery. Maximum range up to 300 km, restricted to a maximum observed altitude of 20 km (i.e. maximum range decreases with increasing elevation angle).
Elevation angles scanned: 0.5º, 0.9º, 1.3º, 1.8º, 2.4º, 3.1º, 4.2º, 5.6º, 7.4º, 10.0º, 13.3º, 17.9º, 23.9º, 32.0º.
The hyperlinks below are our two current radar OEM with basic commercially available specifications.
http://www.eecweathertech.com/pdf/EEC-C-Band-Systems.pdf
http://www.de.selex-es.com/documents/16243296/30914095/Selex-ES-METEOR-1700S.pdf
If you need any other information please contact me directly.
Regards,
Andrew
Andrew Collins | Head of Radar
From Richard to Andrew (13 Oct 2017)
Thank you for getting back to me so promptly, Andrew. I very much appreciate the information.
My interest is particularly in the RF emissions from the radars deployed within the Melbourne area and in particular how the changes in the active sites and upgrades to existing sites (Laverton) can be expected to change the profile.
Specifically, the Laverton site was removed from operation and the Broadmeadows site made primary as the Laverton site gets upgraded. Were Laverton and Broadmeadows running the same systems or are their any differences? Can you share any information about the old-vs-new equipment being deployed into Laverton?
I also have a question regarding the operation of weather radars, particularly as storms come through. The challenge for a weather radar system is achieving range during storm activity, as the water in the clouds and rain absorb the signal. Therefore does the system adapt the strength of the transmission signal dependent on the conditions? i.e. if an accurate signal for distant locations can't be obtained due to clouds closer by, does the system increase transmission levels to compensate? And conversely, if conditions are favourable, does the system decrease transmission strength?
Many thanks
From Andrew to Richard (16 Oct 2017)
Hi Richard,
Broadmeadows radar is a C-band (5607MHz) 250kW magnetron running at 1000Hz PRF with a 1µS pulse.
Laverton radar is a S-band (2880MHz) 750kW klystron running at 1000Hz PRF with a 1µS pulse. Please bear in mind as this radar has recently undergone dual-polarisation upgrade, it will emit 375kW out of the vertical and horizontal channels respectively. Therefore, EIRP is reduced by 3dB. This is the only recent change. Whilst you may of never saw Broadmeadows on the web before it has been alive and kicking in a training role. It was made live to cover for the Laverton upgrade.
No, the output power remains constant in all conditions, obviously receiver gain varies with range. S-band have much better penetration and less rain attenuation than C-band but a little reduction in resolution.
Regards,
Andrew
From Richard to Andrew (16 Oct 2017
Thank you for the detailed update, Andrew.
>> it will emit 375kW out of the vertical and horizontal channels respectively
I presume simultaneously rather than in 2 separate passes?
Thanks
- Richard
From Andrew to Richard (17 Oct 2017)
That is correct, simultaneously.
Regards,
Andrew
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