photo by Jessica Peacock
Your smartphone may be smarter than you think. At least, mine is.
If you have an iPhone 6, or a newer version of Apple’s device, your phone comes equipped with a barometer. A variety of non-Apple smartphones also have barometers built in. I have been a meteorology buff since I was a teenager, and I have had a barometer-equipped phone for years, but I never knew it until recently.
That’s because I don’t have any occasion to take weather observations from my phone. There’s an app for that if I change my mind. (Actually, there are quite a few.) But stupid smartphone tricks are not the main reason phone-makers would allocate precious space to a sensor to measure air pressure. Location – which can translate into marketing money as well as customer satisfaction – is.
Consider an airplane. When you’re flying in a jet cabin and your TV monitor tells you the plane is at 35,950 feet, you might assume the data is being pulled from the onboard GPS system. And today that is likely the case. But aircraft have had altimeters since long before GPS existed. Those altimeters work by measuring air pressure.
In other words, they are really just fancy and specialized barometers.
Imagine yourself standing on the ground. There is a column of air pressing down on you, starting at the top of your head and reaching to the edge of outer space where the atmosphere ends. The “standard” atmospheric pressure at sea level is 29.92 inches of mercury. (Pressure is measured this way, at least in meteorology, because that is how early barometers worked: by pushing mercury up a tube.) Of course, pressure varies as areas of high and low pressure in the atmosphere move around the globe. Cold, dry air is denser than moist, warm air, so the relative temperature and humidity all the way up the column affect the pressure at the surface. As these varying masses of air move around the globe, pressure changes.
But now, at the moment you are standing on the ground, imagine a bird flying 1,000 feet above you. The bird has the same column of air pressing on him, minus that lowest 1,000 feet. So the total air pressing on the bird is less. Even if you and the bird were carrying exactly the same model of barometer, the two readings would be different; the bird’s pressure reading would be lower than yours. The same would be true if you stood at the base of a steep cliff face and someone else stood atop the cliff, directly above you. The difference in the two readings can be used to compute altitude, but only if you know the pressure and elevation at the lower point.
Private pilots whose aircraft uses more basic altitude-measuring equipment periodically check radio broadcasts to get updated information about the pressure at the surface. They use that information in flight to update the calibration on their altimeters. Otherwise, flying through an area of low pressure might lead a pilot to believe she is higher than she actually is (since her altimeter would mistake the change in weather for an increase in altitude). This can be dangerous if you encounter something like a hill or a broadcast tower.
Of course, we don’t manually enter barometric information into our smartphones so that they can calibrate their barometers and use them as altimeters. But phones can still give an approximation of height by assuming average pressure. Or they can be even more precise by pulling local weather data from an internet connection.
An estimate of height above sea level (altitude when you’re flying, or elevation if you are on a mountain) could be a lifesaver if someone is lost or injured in the backcountry. Even in less remote locations, an estimated 80 percent of 911 calls are placed with a cellphone these days. Unlike calls from landlines, cellphone calls currently only give 911 operators a very general sense of a caller’s location. If phone-makers and wireless carriers are able to work together to get operators the precise location data a phone can register, thousands more lives could be saved every year. With enough sensitivity, elevation-sensitive phones might become precise enough lead rescuers to someone trapped high in a high-rise building during a fire or other emergency. There are probably infinite ways the information could be put to use.
One of those uses may even be weather forecasting. The more data that goes into a computer model, the more accurate the resulting forecast, all else being equal. Build a large enough network of smartphones monitoring the air around us, gather the data and run it through a powerful enough computer often enough to keep forecasts updated, and we might someday have a valuable tool to predict the development and path of weather systems more precisely or further out in time.
All that from the little device that keeps me abreast of my emails, my daughter’s tweets and the accomplishments of my friends’ grandchildren. Who knew?