centralmass Posted February 11, 2011 Share Posted February 11, 2011 Radar was offline for a few hours today, now these lines are showing up. Any idea what's going on there? Link to comment Share on other sites More sharing options...
Cold Miser Posted February 11, 2011 Share Posted February 11, 2011 Looks like a sliver of moisture from central ct. into ny, as well a some, skinny bands moving along the ocean. Link to comment Share on other sites More sharing options...
radarman Posted February 11, 2011 Share Posted February 11, 2011 Very hard to say what's going on here without more info, but here are some possible clues. The radar appears to be working, mostly at least, since we see bits of ground clutter showing up in the clear region bounded by the 2 steady radials appearing at roughly 260 degrees and 140 degrees. Those radials show something that looks similar to raw reflectivity. What I mean is, the noise floor for reflectivity goes up as you get further away from the radar. At the end of it's range (~230KM away) you might well expect to see a 15 dbz return even in clear air. (not sure exactly what the number is but it's probably something like that) So if you were to plot the reflectivity radials exactly as they arrive you would always see blue concentric rings, darker as you get further away. (imagine if the whole picture was full of radials like the ones appearing). Because blue rings don't make for good pictures, especially when overlaid on top of maps, generally a filter is applied so that the raw values are not plotted unless there is something real there. How you decide if it's real could include a number of factors, including solving the radar equation and thresholding on signal to noise ratio, estimating the noise floor, looking at the velocity return for correlation (velocity in clear air is a random number somewhere in the range of plus/minus the nyquist, and thus spatial correlation of values is a sign of a "real" signal), etc. It appears what might be occurring is that in certain places the filter is failing and the radial's raw value is being plotted. Looking at the velocity you see not random numbers as you'd expect to see, but UNK values. The power values are not UNK values. The fact that the radials are always appearing in exactly the same places leads me to believe it's not something like a busted oscillator. Maybe there's some sidelobe contamination in certain spots? Or a thin trickle of ice on the radome could be skewing the phase in places? I'm out on a limb here.... Link to comment Share on other sites More sharing options...
HoarfrostHubb Posted February 11, 2011 Share Posted February 11, 2011 Very hard to say what's going on here without more info, but here are some possible clues. The radar that appears to be working, mostly at least, since we see bits of ground clutter showing up in the clear region bounded by the 2 steady radials appearing at roughly 260 degrees and 140 degrees. Those radials show something that looks similar to raw reflectivity. What I mean is, the noise floor for reflectivity goes up as you get further away from the radar. At the end of it's range (~230KM away) you might well expect to see a 15 dbz return even in clear air. (not sure exactly what the number is but it's probably something like that) So if you were to plot the reflectivity radials exactly as they arrive you would always see blue concentric rings, darker as you get further away. (imagine if the whole picture was full of radials like the ones appearing). Because blue rings don't make for good pictures, especially when overlaid on top of maps, generally a filter is applied so that the raw values are not plotted unless there is something real there. How you decide if it's real could include a number of factors, including solving the radar equation and thresholding on signal to noise ratio, estimating the noise floor, looking at the velocity return for correlation (velocity in clear air is a random number somewhere in the range of plus/minus the nyquist, and thus spatial correlation of values is a sign of a "real" signal), etc. It appears what might be occurring is that in certain places the filter is failing and the radial's raw value is being plotted. Looking at the velocity you see not random numbers as you'd expect to see, but UNK values. The power values are not UNK values. The fact that the radials are always appearing in exactly the same places leads me to believe it's not something like a busted oscillator. Maybe there's some sidelobe contamination in certain spots? Or a thin trickle of ice on the radome could be skewing the phase in places? I'm out on a limb here.... Big bird poops Link to comment Share on other sites More sharing options...
Turtle Posted February 11, 2011 Share Posted February 11, 2011 Hi gang! Yes, there is an issue with the radar. I just came in at 730 PM, but was informed that the radar was down for a while today (as you already know). There does seem to be occasional problems with some of the signal from the radar. It appears that, for the most part, it's working except for some radial issues. I'm sure that our electronics staff will work on this again tomorrow. --Turtle Link to comment Share on other sites More sharing options...
HoarfrostHubb Posted February 11, 2011 Share Posted February 11, 2011 Hi gang! Yes, there is an issue with the radar. I just came in at 730 PM, but was informed that the radar was down for a while today (as you already know). There does seem to be occasional problems with some of the signal from the radar. It appears that, for the most part, it's working except for some radial issues. I'm sure that our electronics staff will work on this again tomorrow. --Turtle If they scrub off the bird poop, it should be fine And can you NWS folks make some snow happen? Link to comment Share on other sites More sharing options...
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