Seeing into the Future

Seeing into the Future

Seeing into the Future

Radar reveals only what a storm is. Vertical Profile reveals what it will soon be.

Illustration from the Dr. Kenneth Wilk study of 45 years ago on the growth of various storm types. He found that the echo of a general “Popcorn” storm begins as a weak echo at 20,000 to 30,000 feet. The first red appears at about 22,000 feet, after rain begins to fall.

Instantly after radar engineers discovered how to convert millevolts, ohms and dBs into digital code, they begin adding dozens of high-tech features to airborne radars. The digital revolution brought on such things as color displays, turbulence detection, auto tilt, extended STC, REACT, digitized signal generators, and on and on. None of these technologies add to the two basic things a pilot needs to know to conduct a safe, comfortable flight: “Where is it?” and “What’s a safe path for avoiding its hazards?”

In truth, there have been only two advances in radar engineering of help to pilots in thunderstorm see-and-avoid since that first system designed by George Lucchi of RCA 60 years ago. First was the so-called “flat plate” antenna that came to airborne radars near 50 years ago. Before that, the radiation pattern from our small parabolic antennas was so scattered, half the echoes displayed were false side-lobe returns. The phased array antenna rounded them up into a much cleaner beam.

Second of the only two meaningful advances in radar engineering was the addition of Vertical Profile 30 years ago. That was an innovation by engineers at King Radio just after it was acquired by AlliedSignal. A new general manager at the King Division floated the idea by engineering and, since it was simple to do, it quickly became an added feature to the Bendix RDS 81/82 systems.

VP: A Simple Add-On

Echoes most likely to grow into hazardous
Supercells tend to begin as a weak echo at a much higher 25,000 to 40,000 feet and develop a red core at about 35,000 feet.

Creating the feature required only a simple software addition. Antenna stabilization, which has been a common feature of airborne radar since the beginning, requires that the antenna be articulated to swing 30-degree up and down as the antenna sweeps back and forth horizontally to detect weather and terrain ahead from top to bottom. But to accommodate maneuvers of aircraft in both pitch and roll the TILT limits must be about 15 degrees.

Therefore, to create VP it was only necessary to create digital software to stop the side-to-side swing of the antenna at some position and direct it to commence running the antenna vertically through the natural up-and-down, 30-degree limits at that position. Voila! A Vertical Profile feature! A VP 30-degree up-and-down scan. (It was limited to 25 degrees on early systems and 30 degrees on later ones.) Also, later, more software was added to allow pilot selection of which azimuth position VP would scan up and down. Of course, it wasn’t quite that simple, but almost.

Amid that development, Bendix was acquired by AlliedSignal as was the Bendix/King line of avionics. When the Bendix/King RDR 2000 was next added to the Allied radar lineup, that radar also had the VP feature. Later Allied/Bendix/King was scooped up by Honeywell and the Bendix/King RDR 2000 then became a division of Honeywell, where it remains today.

Next, when Garmin decided to expand into airborne radar products with the GWX 68, Vertical Profile was one of several features copied from those earlier Bendix/King radars. That was followed by the GWX 70, also with VP. Today only those three have it: RDR 2000, GWX 68 and 70. (The top-to-bottom scan of certain other “high-tech” radars isn’t true VP, but a limited, mixed horizontal/vertical scan.)

Why VP is Important to Flying

Why hasn’t it become a feature of other radars? Because radar engineers know so little about convective meteorology they don’t know what it’s good for. After inventing it, Bendix/King had no idea of what value it was except as another gadget for radar salesmen and ladies to brag on. Their early RDR 2000 POG reflects that lack of understanding.

Why VP is extremely useful for flight safety is not a deep mystery; it’s been known for 45 years. A study by Dr. Kenneth Wilk at the NOAA National Severe Storms Laboratory published an illustrated report about it that long ago. Fact is, his report revealed, typically thunderstorms do not grow from the ground up, they grow from precipitation that forms aloft and then propagates downward. Furthermore – and this is a critical fact – common air mass “popcorn” thunderstorms tend to begin at 15,000 to 25,000 feet then grow down to the surface. But severe, extremely dangerous supercells tend to begin much higher, way up around 25,000 to 35,000 feet and then rapidly descend to the surface.

Bendix/King’s RDR 2000 is one of the best-known examples of radar systems that provide vertical profile functionality.

Properly educated pilots have known that for 40 years. That’s the reason for the well-publicized “TUT” position of TILT, which is simply +10 degrees. When +10 degrees TILT is selected the height of storms is instantly revealed; the ratio is 1,000 feet per nautical mile. So, in operations below 20,000 feet, select TUT for several sweeps and any echoes detected at 10 nm are at minimum 10,000 feet above your current altitude; at 20 nm 20,000 feet above; at 30 nm 30,000 feet.

Thus, if a pilot climbing through 10,000 feet with TUT selected sees an echo at 10 nm he or she knows instantly that it’s a thunderstorm at minimum to 10,000 feet, plus the current aircraft altitude. So, it’s a thunderstorm. If there’s no red at +10 degrees,
run TILT on up several more degrees. If that echo now contains any red it’s most likely going to grow into a severe, hail-producing thunderstorm.

Wonderful! With TUT and TUT+altitude, a pilot can see into the future! Knowing that is a tremendous factor in conducting a safe, comfortable flight.

A problem arises, however, when the flight is down low, climbing through 3,000 or 4,000 feet and the growing, potentially severe, storm is only 5 or 6 nm distant. Max up TILT available without VP on other airborne radars is +15 degrees. At +15 degrees, the beam will not sweep high enough to detect any red that may exist at 25,000 to 35,000 feet when the aircraft is at lower altitudes.

Climbing out of New Orleans, noth­ing at my level, but VP reveals yel­low echo above me. In the near future that yellow may drop on me with most unpleasant results. I turned right to get out from under it. Note that the distance to the yellow is just 3.5 nm. Only a + 30 VP scan could detect it. The 15 degrees max of other radars will not reveal the impending danger above.

But with VP, the radar will see into the high aloft future, as it were, and the pilot will be alerted to echoes that will soon grow into very dangerous storms. That’s a capability other radars have but only with intelligent use of TILT, and to a limited degree. With VP, it’s only a button push away.

I flew one of the earliest VP radars from King extensively in my own aircraft while conducting thunderstorm research 30 years ago. One day I was climbing out of New Orleans, northbound, good visibility, no storms in sight, but under a high overcast. When I selected VP for several sweeps it revealed Level 1 and 2 echoes above me that had best be avoided. Otherwise, I was likely to have several tons of water drop on me. VP gave me a look into the future.

Another day I was doing thunderstorm research out of my home airport 50 nm south of DFW when my radar detected an echo ahead with another little echo directly behind it. No question the echo in the rear was more intense than depicted, but I needed to know how much more intense, so I selected VP. It revealed that the little echo was literally blowing its top. It was short but it had developed a totally detached wad of detectable precip above its top. I figured that was a weather system to stay far away from. Again, I had a look, not in the now, but into the potential future.

On that same flight, I encountered a vicious-looking storm with a smaller cell next to it. VP revealed that the large cell was very tall, the small one barely out of 15,000 feet. A wise convective storms research pilot, Jim Cook, had earlier warned me about just this situation. Often the larger storm will begin to drop its load of moisture and the smaller one will suck up that energy and explode upward. As I orbited at a safe distance and watched, sure enough in the next l0 minutes the large storm dissipated and the smaller one grew into a monster.

Again, VP revealed the future to me.

Why Not More VP?

VP revealing a small cell 32 nm ahead. Behind it a little bump that doesn’t appear to be anything, But look close and you’ll see it has some kind of top knot above it. In this area of obviously unsta­ble atmosphere that suggests an explosion is about to occur. It’s another look into the future only with VP.

The question that must be asked is why haven’t other radar development teams incorporated VP in their radars, only those three? Not even those automated radars manufactured by Collins and Honeywell have it, they scan only up to +15 degrees to create a top-to-bottom image of a storm. VP is to 30 degrees.

The answer to why other manufacturers haven’t offered VP is because their radar engineers have little-to-no knowledge of convective meteorology. Perhaps it should be a prerequisite to a degree in electrical engineering. 

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