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Feasibility of a Passive Weather Radar

Posted: Tue Apr 23, 2019 11:11 pm
by kuhny1
Just a quick question,
Would it be possible to use the passive radar capabilities to make a weather radar? I mean, the only reason I can't see it working is because of the relatively low frequencies you would need to work at. But if returns can he picked up from say, hail or very heavy rain, I could write a program that screen grabs the KSDR application window and then based off the direction the antenna used for receiving echos a RHI and PPI plot could be made as it is sweeped a across using steppers.

Of course there would be a dead spot in the direction of the transmitter though that dead spot could be narrowed with a calibration run on a clear day.

This would really be my only use for the PR system and my main reason for wanting the KSDR is for the direction finding.

Any thoughts?

Re: Feasibility of a Passive Weather Radar

Posted: Tue Apr 23, 2019 11:35 pm
by rtlsdrblog
Weather radar actually operates at 2-4 GHz, so outside the range of the RTL-SDR. Only these frequencies really reflect clouds and rain. Also the bandwidth is probably not large enough to get any sort of resolution.

That said, I have noticed that on windy days I can sometimes get patterns across the PR display. I believe this is coming from the wind and maybe rain rustling the trees. Using a DVB-T TV frequency at ~600 MHz.

Re: Feasibility of a Passive Weather Radar

Posted: Tue Apr 23, 2019 11:52 pm
by kb3cs

Re: Feasibility of a Passive Weather Radar

Posted: Wed Apr 24, 2019 2:33 am
by kuhny1
I knew that the WSRs used RF in the upper microwave range. That's why I said "relatively low frequencies".

The main thing that was pointed by out rtlsdrblog was that only those frequencies really reflect rain, and I guess that's kinda what I was asking. I couldn't seem to find anything on frequencies and their reflection/absorbtion to water.

Anyhow, I guess some testing with more severe storms that contain hail could be useful though it seems that, that isn't going to work either. As the only powerful transmission towers at a high frequency is Cell towers and that's at most 900MHz.

Maybe something can be used in regards to attenuation as a rain "core" comes between the receiver and the tower. To at least detect something.

Re: Feasibility of a Passive Weather Radar

Posted: Wed Apr 24, 2019 11:20 am
by kb3cs
the WSR specs are so you can see not only the frequency but the emitter power used to illuminate the weather stuff. your chances of -passive- weather radar are low, unless you just happen to live near a WSR installation. :-)

Re: Feasibility of a Passive Weather Radar

Posted: Sat May 18, 2019 1:44 pm
by snn47
Wx-RADAR come in different forms, e.g. not only (rain)clouds but also as windprofiler. While reflection come from from clouds it does not mean that the clouds produce rain. A L- band PSR will produce diffetent cloud formations compared to a S- or C-band PSR. Also polarosatiom will change echos received.
Min. useable frequencies vary with local weather like temperature and humidity, starting around 9xx in asia up to about 5000 MHz. Sensitivity varies with frequency.
Horizontally (360degree) rotating very high gain antennas with EIRP similar to other PSR are used by Wx RADAR, exception are windprofiler which radiate vertically and sometimes also have a loudspeaker array for modulation.
If you live close to a RADAR you might use their signals as reference to process echoes. Without a high gain beam you will only get a blurry teply and low range.

Re: Feasibility of a Passive Weather Radar

Posted: Fri Jun 07, 2019 10:51 pm
by gruene
It might be possible, to a point. Here's what I know about the WSR-88D radars. (ham that did P/T work at the local NWS.)

* Freq: 2880 mhz
* 1/2 million watts
* 1/2 degree beam with H & V.
* high PRF (pulse doppler)
* reasonably low turning rate, like 1 min per rev. (guess)
* raster scan, starts at the top, works it's way down, again a low rate. (guess)

It's like looking at the sky thru a soda straw. It's also why it take 5-6 min to build a single pic.
(meaning every pic you see is 5-6 min old...) But, you can "slice & dice" a storm, you should
see the "tools" the NWS uses, it does exactly just that.

When i get my board (July?), might give it a shot, but not much hope.

Re: Feasibility of a Passive Weather Radar

Posted: Fri Jun 07, 2019 10:59 pm
by gruene
oops, this board only works to 1.7 ghz, so WSR-88D's are out of the question without a mixer...

sorry, forgot the board freq limit.

Re: Feasibility of a Passive Weather Radar

Posted: Sat Jun 08, 2019 12:51 pm
by Username
Hack RF can get to higher Freq. :D

Re: Feasibility of a Passive Weather Radar

Posted: Mon Jun 10, 2019 7:33 pm
by snn47
For other RADARS look at radartutorial.eu and for the WSR-88D here:
http://www.radartutorial.eu/19.kartei/1 ... 11.en.html
https://www.weather.gov/iwx/wsr_88d