NEW UNDERWOOD, S.D. – If you’ve ever driven east of Rapid City, or even just tuned into the weather, you’re probably aware of the National Weather Service doppler radar in New Underwood. It’s a NEXRAD, or Next Generation Radar, with radar being an abbreviated way of saying radio detection and ranging. There’s a lot more going on inside that “giant golf ball” than meets the eye.
“I’ve been working on radar for almost 40 years, so obviously it’s something I enjoy,” says Electronic Systems Analyst Pat Baye. “It’s a great challenge. You can come out and work on it one day and feel like a genius and come out the next day and it will humble you very quickly. So I like the challenge of it.”
It all starts in a tiny room, where the signal is first made.
“We generate our transmitted frequency and then we amplify that to 700,000 watts, and then we send it up the tower to our dome, and then we transmit that out into the atmosphere. And if there’s anything out there, a storm or anything like that…the RF [radio frequency] will bounce off of that and come back, and then we will pick that up and we will break that signal down and develop the picture that you see on your evening news,” Baye explains.
Basically, the radar emits energy strikes the water vapor, or even snow and hail, and then that energy bounces back to the radar, which provides a picture of what’s out there. The word doppler enters the doppler radar title because a principle known as doppler shift is utilized. By measuring how the received frequency has shifted from the transmitted frequency, the radar can calculate how fast and which way the targeted particles are moving.
The energy travels very fast: moving at 186,000 miles per second, or the speed of light. It’s also sent out almost constantly, as Baye depicts, “anywhere from 600 to 1,800 times a second.” Plus, for every hour that the radar operates, only one minute goes towards sending energy out. 59 minutes is spent listening for the energy to return.
The radar is also self-calibrating, which ensures that observations are accurate so that developing storms can be forecasted and warned with as much efficiency as possible.
“Between every volume coverage pattern, as the antenna comes back down to half a degree, the system calibrates itself. So it does that after every pattern, and then every 8 hours, it systematically parks the antenna, opens up the front end and listens to just RF out in the atmosphere and uses that to calibrate the radar from top to bottom,” says Baye.
Of course, there are also some challenges associated with all of the electronics, and even the topography of the landscape, which can’t exactly be changed. However, there are ways to work around these limitations.
“This is one of the reasons we moved the radar away from the Black Hills was to better see over the Black Hills…but the Black Hills do present some challenges down low. But because of the scan strategy, we scan up and angles we can see over the Black Hills a little bit,” explains Rapid City National Weather Service Meteorologist in Charge, Dave Hintz. “But one of the other limitations to the radar, and it’s nothing that really we can do about, is the earth curves away, and the radar beam curves up. So the further you get away from the radar, the more difficult it is to see things especially down low on the storm. And this is where our spotter network, emergency managers and everything else can be really helpful for us during convective season.”
On a clear day, you might think the radar just gets a break, but this actually isn’t the case. Instead, it focuses on winds and larger disturbances, like fronts that may not even have precipitation signatures. There are two different modes that the radar can operate in to favor forecasting of the current weather conditions.
“We can operate in precipitation mode and have clear mode. In precipitation mode, we will actually speed up the dish and how fast it rotates because obviously if we have convection going on, we want that data coming back to our forecasters as quick as possible so we can redo in five minutes an entire scan strategy,” says Hintz. “If we’re in clear mode, we’re more interested in wind shift patterns, perhaps fronts. So we’ll slow that down and maybe go through a complete scan strategy in eight minutes and we’ll go through the lower angles. We don’t need to go all the way up to our highest elevation cut because we’re not interested in that. There’s no convection going on, so we want to stay down low and see what’s going on down low with the fronts or wind shear patterns.”
There you have it – just a small glimpse into what’s happening inside that “giant golf ball” just off the interstate.
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