Tuesday, August 19, 2014

How Weather Radar Works and How It’s Getting Better

I don’t like thunderstorms. Oh sure, they’re fine if you’re on the ground, but ever since a particularly nasty encounter with windshear in a severe storm flying into Charlotte back in the early 1990s, flying around storms has made me anxious. So when I went to visit with Honeywell back in May, I was particularly interested in learning more about advances in weather radar. Unfortunately we didn’t get into much detail there, but I was able to schedule a follow up call. In short, weather radar is a whole lot better than it was back in the early 1990s, and there are a lot more cool things coming down the pipe.

[Disclosure: Honeywell paid for flights and hotel back in May]

The Basics
I suppose we should start with the basics. How does weather radar work? Well, take a look at that pretty rounded nosecone in the front of the airplane. Now imagine that popped right off. Underneath, you’ll find a big dish (Honeywell’s is 30 inches in diameter) that handles radar duty on every airplane. That’s right, the nosecone is really just an aerodynamic cover and nothing else.

That dish sends out pulses, and then it listens to hear when, or if, they come back. If something comes back, then the radar system figures out how far away it is. That paints a picture on the map of where there are objects. Here’s a basic look at how traditional radar works (all images via Honeywell):

Standard Radar

Of course, something like another airplane is an object that would create a return. Same goes for, oh, say, a mountain. That’s important for navigation, but it doesn’t help with weather. For weather, the returns come from water and ice in the atmosphere. And the size and intensity of the drops paints a picture on the screen for the pilots.

The pilots themselves have some control. As the image above shows, traditionally, they point the radar in the direction they want. If they’re flying straight, then they point it straight ahead. If they’re going to be descending, they might point it down. Or if they’re looking for other altitudes with a better ride, they could point it however they want.

The result is that you get a narrow view of precipitation, but it provides an important tool for pilots. The thing is, there’s a lot more that can be done with this data.

Cool New Stuff
From Honeywell’s perspective, the coolest thing their radar system can do (called IntuVue) is look at all altitudes from ground level to 60,000 feet without making an adjustment. It looks something like this in the cockpit:


The dashed lines in the main display show areas where there is weather outside of the current flight path. So if you need to change your path, then you’ll want to make sure to avoid those areas as well. But instead of manually searching, you can see the whole picture. Here’s another way to look at it on what looks to be a more advanced display:

IntuVue 3D

In this one you can see the whole cross-section at the bottom. This shows that 90 miles away, there is one ugly storm that you can’t fly above.

But there’s a lot more than just this. Radar manufacturers realized that they could measure the movement of the water droplets, and that can tell you all kinds of interesting information.

The most obvious is a turbulence predictor. Radar systems now can look 40 to 60 nautical miles ahead and measure how much the drops are moving. If they are moving a lot, then that means there’s likely going to be a lot of turbulence if an airplane flies through it. That looks like this:

A380 Turbulence Image

If I’m a pilot looking at this, I either need to climb to about 30,000 feet to get over this area of turbulence, or I need to go to the left to go around it.

You can imagine how this also lends itself to predicting windshear. Sudden changes in the direction of wind can easily be seen if there’s moisture in the air. If that happens on final approach, then pilots can be warned and you’ll probably be going around. In other words, what I flew through 20 years ago would not be flown through today.

Take this and combine it with temperature data and it can also help with predicting damaging weather events like lightning and hail. Honeywell said that with its tests, there was a 93 percent correlation between where Honeywell predicted there would be lightning and where it actually occurred. A lightning strike won’t usually cause much damage, but it still means a lengthy check after arriving. And of course, hail can cause serious damage.

Cool Stuff That’s Coming
As computing power increases in these systems, there’s a lot of cool stuff that can be done. Honeywell told me about two projects that are in progress now.

The first is working to create images that will show where a storm will be when the airplane gets there. Today, you see real-time weather images but the Honeywell system goes over 300 nautical miles out. So what they want is a system that will take into account movement of the storm to help pilots to know where the storm will be in 30 minutes when they get to that point. It can help pilots pick a better routing further in advance.

They are also working on modeling storm growth and decay. This is most important around nasty thunderstorms. You might be flying at 32,000 feet, and the storm ahead tops out at 30,000 feet. But what if it’s still growing and by the time you get there, you would be in the thick of it? Or what if there’s a storm ahead of you that’s collapsing? You might not have to change your routing because by the time you get there, it will be smooth sailing.

This is all pretty comforting stuff, but to me, the most interesting issue is one that is still pretty far off. Since radar requires something like a water droplet to create a return, it still can’t detect one of the bigger causes of injury – clear air turbulence (CAT).

The winds may be whipping around in crazy patterns that can shake an airplane severely but if there aren’t water droplets present, radar is useless. So weather radar manufacturers are working to figure out how they might be able to detect that.

The most promising method seems to be one that uses lidar. (Europe has been experimenting with this already.) Using lasers, they can get readings off the air molecules themselves. And if you can then measure the movement of those molecules, you can detect clear air turbulence.

This is still in the fairly early stages. I asked Honeywell if someone in their advanced technologies area could talk to me about this, but apparently it’s so early for them that they don’t really have anything to discuss. Once that actually happens, however, it would be a huge leap forward, and it’ll soothe the nerves of a lot of anxious travelers.

See other posts in my Honeywell series:
I Was on an Airplane That Nearly Crashed Into a Mountain (On Purpose)
What the F*&@ is an Auxiliary Power Unit?

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