Math, Doppler And The Missing Jetliner

mh370-tracksI just finished reading some technical data from Inmarsat and Ministry of Transport Malaysia concerning the analysis of satellite data transmissions from MH370. It’s this data that’s shifted the searchers from MH370’s planned route to a tract in the Southern Indian Ocean well west of Australia–nearly the opposite direction expected!

It is a brilliantly concocted method to get usable information from what should have been meaningless housekeeping transmissions.

Radio signals travel at the speed of light. If we know how long those signals take to go satellite-to-plane (or vice versa) we can start doing calculations and find the distance between the two.

Inmarsat was then able to calculate the range of the aircraft from the satellite, and the time it took the signal to be sent and received, to generate two arcs of possible positions – a northern and a southern corridor.

mh370 doppler shiftAs you probably know the northern track was thrown out. But why? That’s where the plane should have been flying. It was the most logical direction.

Enter Doppler!

Because the satellite and plane were both moving, their radio waves were subject to Doppler shift. This is an expected part of satellite work and equipment to compensate for it is built into the system.

The Inmarsat technique analysed the difference between the frequency that the ground station expected to receive and the one actually measured, known as the Burst Frequency Offset.

mh370 data versus tracksBecause the satellite wasn’t at the midpoint of the two project tracks, the expected northbound offset or shift was different than the southbound shift. What was actually seen only matched the southern track.

Depending on the plane’s speed the same Doppler shift could indicate slightly different positions. Unfortunately, that’s an unknown. It’s a good guess to estimate 400-450 knots. That’s why the area now being searched isn’t a single point, but a larger area.

Obviously, the plane hasn’t been found, there’s still no real explanation for what went wrong. However, this clever use of math helps bring those looking one step closer.

I know this is somewhat complex. I’m not 100% sure my explanation will be clear to everyone. Questions are welcome.

Like Paul Blart, Mall Cop


At 11:15 PM PST/2:15 AM EST

Observe and report. Like Paul Blart, Mall Cop, I’m observing and reporting.

First stop, radar. It’s active. Snow, identifiable by radar only recently, is the only precipitation being seen at the moment. It’s moving west-to-east.

Meteorologists call the radar’s targets, hydrometeors. Cool name.

We can detect rain, snow, hail, sleet, whatever. If a radar beam can bounce off it, it’s tracked.

Most times the radar is amazing. Not always. I’ve seen storms develop in an unusually bright patch of ground clutter. Surprise! Where did that come from? A once every few year event.

All my observing tonight is on the College of DuPage weather website. They carry nearly every product with well chosen color tables. Highly recommended.

The surface map shows the low pulling east, leaving New England. There’s more moisture following and colder temperatures. The snow isn’t quite finished.

Before ending this morning that additional snow will cover the slushy wet mess already on-the-ground. Up to a half foot more will fall in scattered sections of the Litchfield Hills all the way to the UCONN campus. Most areas a few inches less. Even less on the shoreline and near 395.

But still, look what it’s covering!

Oh–and windy and much colder.

The amount of forecast and observational data available is immense. New tools arrive all the time. For nerds like me, this is heaven. Forecasting in pajamas!

San Juan Radar’s Down


I can’t remember seeing this as a tropical system approached. The San Juan radar is down!

MESSAGE DATE: AUG 22 2011 03:26:00

There’s another radar at the airport. It’s not as good, but it’s on!

The Tragedy At The Indiana State Fair

It’s easy to look at the radar and think everything is obvious. It is not. That was proven this weekend in a tragic loss of life.

Like you I have been dumbfounded after seeing the video from the stage collapse this weekend at the Indiana State Fair. There is a blog with really excellent analysis of what happened, including a play-by-play of the radar imagery available.

If you’ve been watching Rachel and me on FoxCT you probably remember a storm last month where we pointed out exactly the same feature that caused the trouble in Indiana: a gust front.

These are easily visible on radar, but only if you know what you’re looking for!

After reading these storms were being monitored by a public safety officer on his smartphone Rob White, the blogger who did the analysis, added:

On his smartphone? Really, the Special Operations Commander and fair Executive Director were monitoring the potential for incoming severe weather on a smartphone? I’m sure many of the fans out in the crowd were as well, but most of them weren’t expecting to make a life or death decision on it.

This comes back to a point that I’ve tried to make many times on this blog. When it comes to severe weather safety and preparedness at a major public event, the organizers and/or managers of such an event need to leave it to a professional to monitor the weather for them – not a layman watching the weather on a smartphone (or even on a computer via the internet for that matter).

I couldn’t agree more. It’s easy to look at the radar and think everything is obvious. It is not. That was proven this weekend in a tragic loss of life.

This is the video of a tragic event. Lives were lost onscreen. You should consider this before clicking play.

When I Watch Radar Here’s What I Watch

He was an astronomer and mathematician. Today he’d be a nerd, but back then he was just crazy smart!

I’m hearing thunder in the distance so I fired my browser to take a look at the radar. NEXRAD, the Weather Service radar really is a marvel of technology. There’s a lot to see if you know what to look for.

A little background first. When I arrived in Connecticut there was a single radar available. It was a model WSR57. That stood for Weather Surveillance Radar 1957. Like most good government projects this 1957 radar didn’t become operational in most spots until the 1960s.

Hands up if you’re surprised?

As radars go the WSR57 up on Soapstone Mountain in Somers sucked! It was sited in a bad place for weather radar. Precipitation of the same intensity would produce different results depending on where it was. It was pretty much blind to snow. There was a huge area continually blocked by ground clutter. It was all we had.

Today’s NEXRAD radars are model WSR88D. The “D” stands for Doppler. It’s a big step up. NEXRAD is more powerful, more versatile and since much of what it does is software driven easily upgraded.

Radar is pretty simple. You bounce radio waves off hydrometeors (the official name we assign to the precipitation being measured). Since radio waves move at the speed of light if you measure the time it takes for the wave to return you can figure out the distance.

The intensity of that returned wave is the deciding factor for the colors you see. Stronger rain or hail or sleet produce stronger radar returns. Radar waves bouncing off light rain, drizzle or most snow are much weaker.

I’m looking at some rain south of Connecticut now which is really intense. The colors on the display are hot. The rain is coming down in buckets!

One of the things NEXRAD’s software makes possible is analyzing the radar returns to decide how much rain has actually fallen. It’s a neat trick involving math much more complex than you might expect. In potential flooding situations this ability is a life saver… literally! Some areas (mostly over the ocean at this moment) are seeing as much as 1.5″ of rain per hour!

All of this is geekily cool and we haven’t even touched Doppler!

Please note, it’s Doppler with a capital “D.” It’s someone’s name. Christian Doppler lived in the first half of the 19th Century. He was an astronomer and mathematician. Today he’d be a nerd, but back then he was just crazy smart!

Doppler postulated his principle (later coined the Doppler effect) that the observed frequency of a wave depends on the relative speed of the source and the observer, and he tried to use this concept for explaining the colour of binary stars. – Wikipedia

What works for stars seems to work for any wave. Take sound as an example. If you stand along a highway as cars approach the pitch of the sound of their engines rises until the car is upon you. As it moves away the pitch shifts downward. We call that Doppler shift.

As a hydrometeor being picked up on Doppler radar moves toward you the frequency of the radar wave bouncing off it shifts higher. If it’s moving away the radar frequency that returns is lower. NEXRADs software allows us to plot that.

What meteorologists look for are adjacent areas that show motion in opposite directions. That’s a signature found in tornadoes. There’s no way to see that without Christian Doppler’s work from the early 1840s!

Most of the time here in the Northeast that Doppler feature is unneeded and unused. However, when conditions warrant the WSR88D’s capability is nothing short of amazing.

Maybe I’ll Wait To Post

“You’d better get ready now,” she said. I am blessed with “Early Warning Pinpoint Wife.”

I wanted to post something this morning… OK, this afternoon. I wasn’t up this morning but you get the idea.

Then before I could fire up the blog Helaine pointed me to the radar. “You’d better get ready now,” she said. I am blessed with “Early Warning Pinpoint Wife.”

So a real post later. Right now my hands are full with radar returns in hot colors. This is a worrisome weather scenario.