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See Inside August 2006

Weather Gets Personal

New devices can make forecasts for your own backyard
AMATEUR METEOROLOGISTS



JOHN FRASER
My mother loves watching the weather news on television. When I was a kid, she insisted on total silence during the five minutes near the end of the evening broadcast when the meteorologist stood in front of a map of New York City and pointed at the various temperature readings. Her face rapt, she gazed at the radar images of storm clouds sweeping through the tristate area. I asked her once why she loved the weather news so much, and she said with a shrug, "I want to know what to wear tomorrow." But this explanation never satisfied me. Her obsession seemed to go way beyond a simple desire to know whether to put on a coat or carry an umbrella the next morning.

Although I don't watch much television nowadays, I've inherited my mother's fascination with weather. When I read the New York Times, the first thing I turn to is the newspaper's weather report, specifically the graph that shows how the recorded and forecasted temperatures compare with the normal highs and lows for the week. So I was intrigued when I learned that Davis Instruments, a company based in Hayward, Calif., had introduced a personal weather station that could wirelessly send me continual updates on the conditions outside, even in the crowded canyons of Manhattan. Although similar devices have become quite common among weather hobbyists, the Vantage Pro2 is the first to combine powerful transmission capabilities with proprietary software than can make accurate forecasts for the microclimate around your home.

The weather station has two parts, an integrated sensor suite that can be installed on your roof or in your backyard, and a display console that can be placed on a desk or mounted on a wall for easy viewing. The sensor suite includes an anemometer--the familiar pinwheel of cups that measures wind speed--as well as a wind vane, a rain collector, a thermometer and a humidity gauge. (The barometer is in the console.) The thermometer and humidity sensor are housed in a slotted plastic chamber that lets air in but shades the instruments from sunlight; for even more accurate measurements, some models come with a fan that circulates air within the chamber. (The Vantage Pro2 costs $495 for the cabled station and $595 for the wireless version; the fan adds another $200.)

As I assembled the sensor suite, I took a special interest in the rain collector, which funnels the drops into a mechanism called a tipping bucket. This ingenious little gadget looks like a seesaw with a scoop at each end. First, the water collects in the upraised scoop until one hundredth of an inch of rain has fallen. Then the full scoop tips downward, spilling its water to the ground and raising the other scoop, which begins to fill with rain. Each time the device seesaws, a magnet hanging from the middle of the lever swings by a switch that records the event, adding another 0.01 inch to the rainfall tally.

The power for the sensor suite comes from a small solar panel, which generates enough electricity to charge a capacitor that keeps the device running at night. (A lithium battery provides backup power for weather stations located in especially dark places, such as Alaska during the winter.) The wireless transmitter that sends the weather data to the display console consumes about eight milliwatts. Although this amount doesn't sound like a lot of juice, it is significantly more than that used by previous models, which were constrained by Federal Communications Commission regulations that limit the power of radio signals sent on a single frequency.

The Vantage Pro2 avoids those limits by transmitting spread-spectrum signals that hop from one frequency to another. (Believe it or not, movie star Hedy Lamarr co-invented the technique during World War II as a way to prevent the jamming of radio-guided torpedoes.) As a result, the sensor suite can send data easily through windows and walls; the transmission range is at least 1,000 feet when there is an open line of sight to the display console. I tested the device in the headquarters of Scientific American by hauling the sensor suite into an office on the other side of the floor. The signal successfully traversed doors, corridors and all kinds of partitions to arrive at the console sitting on my desk. Then I took the weather station downstairs in the elevator and set it up on the opposite side of Madison Avenue, where it continued to send data to the 12th floor.

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