Replacement For Aging Doppler Radar Being Tested

longacre writes "Due to its limited range and slow scan times, the backbone of weather prediction in the US since the early 1990s, the NEXRAD radar system, is deeply flawed in the eyes of meteorologists. A new system being tested by researchers at the NOAA and four universities called the Collaborative Adaptive Sensing of the Atmosphere (CASA) network aims to fill the holes left by NEXRAD, using radar nodes piggybacked onto existing infrastructure, such as rooftops and cell towers. From the article: 'Based on faster and more comprehensive data collection, [Distributed Collaborative Adaptive Sensing] processing can refocus the CASA radars on a particularly interesting part of a storm (like an area that looks like it might develop a tornado) without losing track of an entire storm cell. "The system is continuously diagnosing the atmosphere and reallocating resources using wireless Internet as a backbone," says [the CASA team director].' Testing has begun in Oklahoma, Houston, and Puerto Rico, and initial installations could begin in 5 years."

Stealth hunter?

[AHuxley]

In many parts of the world this would be cover for a new passive radar system :-)
http://www.globalsecurity.org/org/news/2001/e20010619stealths.htm [globalsecurity.org]

Outdated information

[lpangelrob]

From the article...

Under the current NEXRAD Doppler system, a warning could be statewide, leading to false alarms for most of its residents.

No, not so much. The National Weather Service has started issuing storm-based (polygon-area based) warnings since August 2007. Prior to that, they were county-based warnings, which were a problem (Cook County, IL being about 50 miles tall by 40 miles wide, while average tornado widths are about 100 yards) but nowhere near the "statewide warning" the article claims.

Awful FAQ here: http://www.nws.noaa.gov/sbwarnings/FAQ/engage.html [noaa.gov]

Re:Slow

[MichaelSmith]

Suppose that doppler radar is slow, and that it takes 5 seconds for it to do a 360 degree sweep. Is a faster system going to improve the generally rubbish weather forecasts of "it might rain today"?

If anything the slow rotation rate radar might be better for this application. Radars with short rotation periods are used in military applications where you need to see what is happening from second to second, and are increasingly being used in ATC applications.

But those radars need special software and hardware to deal with the fact that the returning signal is going to be coming from a significantly different azimuth (relative to the radar head) from where it was transmitted.

It is a lot of needless complexity and I really don't see why weather should need radars which rotate that fast.

Re:Slow

[oodaloop]

I think we'll see what's going on now with more fidelity, but weather prediction is still limited by chaos. Weather is sensitive to initial starting conditions, so no matter how well we know those starting conditions (today's weather), we will not be able to predict future weather more than about 10 days out with any kind of fidelity. We've also noticed that some weather patterns are more chaotic than others. You may notice sometimes they say stuff like, "The hurricane will make landfall tomorrow morning at 2am here." And sometimes they say, "We really don't know what this storm is going to do. It could land tonight or blow north. We'll have to see." What they do is run several simulations using variables a few decimal places off. Sometimes they all do the same thing, sometimes they vary so much there's no way to know what's going to happen. Adding new radar will not change the fact that weather is inherently chaotic and unpredictable.

Re:Slow

[TigerPlish]

Is a faster system going to improve the generally rubbish weather forecasts of "it might rain today"

No, nothing can help that. It's really tea-leaf reading.

What a faster system with a finer resolution will do is help better tell if that big nasty storm moving into your part of town will be an F1, or an F5 Magic Eraser.

It also will help stretch the warning leadtime. It's still not good enough.

Nexrad took the warning from pretty much after-the-fact to about +15 minutes these days. Nexrad, compared to the old-school FPS-77 and the like, is pixie dust.

The real clincher, not mentioned in TFA?

They're working on a phased-array replacement for Nexrad. Hit multiple individual cells at once. http://www.nssl.noaa.gov/research/radar/par.php [noaa.gov]

Title is misleading

[hcdejong]

because it suggests they'll use some new radar technology to replace doppler radar. In fact, they'll just install lots more radars (which can be cheap, short-range items) to improve coverage. According to the CASA site, they'll use modified marine navigation radars, ie the cheapest type of radar available, and these invariably are doppler radars.

Re:Slow

[hcdejong]

When TFA says "slow", it's talking about 5 minutes, not 5 seconds. IDK why the update time is this slow, since 5 seconds is feasible even for a long-range radar (ie. 400 km).

Consumers need education on Doppler

[Anonymous Coward]

Hey It's cloudy outside I cant see the sun , that stupid Doppler radar doesn't show the clouds say many people Maybe this data is wrong or old
No it inst

  Doppler radar detects motion and in this case rain. The clouds simply have no falling rain in them.
You'll be surprised how many people don't know that Doppler radar does Not show clouds , it shows falling Rain ,
Maybe the weather service needs to educate he public better ?

Re:Outdated information

[morgan_greywolf]

At present USA is the only country in the world where planes have better Met radar capability and a better idea of what goes on in the atmosphere than ground staff even at some of the major airports.

In many areas of the USA, radar is currently being updated and upgraded. One of the most crucial technologies they are adding is

http://www.nssl.noaa.gov/research/radar/dualpol.php

, which bounces both horizontal and vertical waves simultaneously. Such radars can distinguish between a plane, a flock of birds and rain. Some say they are so accurate, they can actually measure a single drop of rain.

One TV news organization in our area already has one, and all of the NEXRADs that NWS uses are supposed to be replaced by like 2010.

Re:Slow

[DarthBart]

The radars take several scans of the sky per "update".

They take scans at .5 degrees of dish elevation, 1.45 degrees, 2.4 degrees and 3.35 degrees. Those scans dissect the storm and look for rotation and intensity in different parts of the storm.

  Then the radars take an "echo tops" scan where the dish moves up and down to its limits while scanning horizontal. That lets the radars detect the total height of a storm, which gives another estimate of its strength.

So, its not just the dish spinning around in a single plane.

Summary wrong in pretty much every claim

[lakshmanok]

The summary statement gets things wrong in pretty much every respect, so this is mainly for those folks who read the summary and assume it's a fair reflection of the story.

(1) CASA is not designed to replace the existing NEXRAD network. It is designed to supplement it. NEXRADs are designed for long-range surveillance. CASA radars see "under" the NEXRAD umbrella, up to 3km in height. The article makes this clear.

(2) NEXRAD scans are not slow. The fastest volume coverage patterns (VCPs) in NEXRAD, used in severe weather, scan the atmosphere every 4 minutes. The only thing faster is phased array radar and it is still experimental (See: http://www.oar.noaa.gov/spotlite/ [noaa.gov]). CASA radars don't have volume scans, but their antennas are about the same speed as NEXRAD's.

(3) NEXRAD is not limited in range. It goes up to 460 km. A CASA radar's range is only 30 km. If any one thinks that NEXRAD is "deeply flawed" due to its limited range, they need to take it up with the Flat Earth Society (the range limitation is mostly because of the earth's curvature).

Please make sure you understand an article before sending it off to Slashdot!

Re:Slow

[DeadChobi]

Well, if you're an atmospheric scientist doing research into weather, a faster system gives you finer resolution for studying the kind of time-dependent systems that they're interested in. Don't assume that this system won't ever be used to collect scientific data to analyze. One of the advantages of a faster sampling rate is that you can make better predictions based on your data. Essentially, you have a better idea of where some deterministic system has been, and so if you have a pretty good idea of the principles under which it works you can then get a better idea of where it's going. Hell, even if we don't have a technique for making better extrapolations in the face of higher resolution data, someone somewhere will come up with a way.

The other useful thing about this kind of data collection ability is that it can also be used to improve models, especially if it has a better resolution for storm cells than the current doppler system.

Re:Slow

[afidel]

If you don't know why weather radar needs to be faster then you have never been watching during an active thunderstorm. Sweep periods are quite slow in high resolution mode, they can speed things up but it costs significant resolution loss. What is needed is synthetic aperture radar where you can point a small array of antennas at the storm and get multiple different elevation readings simultaneously. We've had the technology for quite some time but it's just now coming down in price to where we can think of using it broadly for weather stations.

Re:Slow

[afidel]

With the current density of information collecting stations anything past about 10 days is just an educated guess, seven day forecasts are pretty darn accurate (generally getting precipitation chance and high and low temperatures to within a percent or two) with an additional three days being fairly accurate.

Re:I just died a little inside...

[afidel]

Yeah I think they confused DS3 with E1 =)

Re:Slow

[tuxicle]

Surely you mean phased array radar, not synthetic aperture. The idea behind phased arrays is to improve overall volume scan times by allocating the limited energy budget of the radar as appropriate. Conventional radars, by design, will radiate an equal amount of energy over the entire scanned volume (over time). Phased arrays, given their ability to instantly (electronically) position the radar beam to any point in the sky, can allocate more energy to those areas that contain "interesting" targets (such as thunderstorms).

The DCAS part of CASA attempts to do this using multiple radars instead. So instead of each radar doing complete volume scans, a centralized system figures out where the "interesting" regions are, and directs the radars to scan only those sectors. The eventual plan is to use phased arrays at each radar node for even higher update rates.

Re:Slow

[tuxicle]

True, but only if you want to do target detection. If you want to make quantitative estimates about your target, you need to "dwell" longer, which pushes scan speeds up. Echoes from weather are generally weak, and weather radars need to estimate their properties. The slower you scan, the longer you dwell, and therefore, the estimates have lower variance. The trick is to get low variance as well as scan quickly.

Navigation Radars != Doppler Radars

[dunc78]

Most marine navigation radars (Furuno, etc.) are not doppler radars. They are simple single pulse systems that need to be able to detect stationary objects such as buoys.

Re:Summary wrong in pretty much every claim

[RudeDude]

Your comments are helpful, but still not 100% accurate.

The rotation rate of the radar is faster and the volume updates are faster as well. CASA currently operates on a one minute "heartbeat" where many scans at different elevations are completed which cover a large portion of the total reachable volume.

While CASA radar does not provide a traditional "full volume" scan this is by design. For the first time we are dealing with a weather sensor that reacts to the environment automatically adjusting it's scanning pattern to be appropriate to the weather and follow storm paths.

CASA is running on a range much shorter than Nexrad. The current testbed is actually at 40 km range. The primary flaw or gap we are filling is the lower atmosphere which, as you stated, is due to the Earth's curvature and therefore a short range is most desirable.

The CASA radars are indeed full Doppler (not just marine radar) with dual polarization as well. They are currently mechanically steered but the technology under research will adapt quite easily to electronically steered beams from phased array radar panels as well.

As a side note the Nexrad system is indeed being upgraded in place to handle dual polarization which should improve snow detection and precipitation estimation.

Also "Super-res" is being deployed. This is a software change that makes the radar appear to have greater resolution by changing the way the signal is processed into smaller "bins". Literature seems to indicate this will help the human observer of the radar, but with the increased visual noise the algorithms will not see a significant improvement.

Full disclosure: I am a graduate research assistant working on the project.

Re:Slow

[Kumba]

5 seconds? We had a tornado here in Omaha a couple weeks ago, and the sirens provided no warning because it hit during the 5 minute blind spot in the radar. On one pass it was a severe thunderstorm, on the next pass it was a tornado on the ground.

If they can't make the radar rotate faster, they should add more dishes to the same radar so it's looking in 2 or 3 directions at once.

The Radar, even if it lacked the blind spot, can't determine if there's a tornado on the ground or not. It can only detect if there's a significant amount of rotation that makes conditions favourable for tornado formation, and then issue a TVS, or Tornado Vortex Signature. The forecaster reviewing the data has to then decide if the radar's predictions are worth issuing a warning. They have to consider data not only from the radar, but current weather conditions and perhaps from the most important source, people on the ground who spot storms and report them in.

This is why the NWS runs the National Skywarn program to help educate everyday people like yourself on how to look for certain signs of damaging storms, including severe and tornadic storms, and report them in so that the forecasters have solid data on conditions on the ground (which the radar can't see!).

http://www.skywarn.org/