September 18, 2014

The iPhone 6 has a barometer!

One of my major research projects has been to explore the potential for improving weather prediction using the pressure sensors in smartphones, something I have talked about in previous blogs.

A number of Android phones has decent barometers in them, including the highly popular Samsung Galaxy series.   A Windows-based phone, the Nokia 1020, also has a pressure sensor.   Amazingly, tens of millions of phones in North America have pressure sensors!

But we now have a major new addition to the pressure-enabled smartphone stable:  the new iPhone 6.
Both iPhone 6 models have a pressure sensor

According to online reports, the iPhone6 has a Bosch BMP280 sensor (see image), with fairly good numbers:  absolute accuracy of +-1 hPa and relative accuracy for pressure changes of +-.1 hPa (normal sea level pressure is roughly 1013 hPa).   To give you a better idea of the accuracy of this barometer, the average decrease in pressure with height near sea level is 1 hPa per 8 meters (26 ft) .

Bosch Pressure Sensor

So why am I so excited by smartphone atmospheric pressure sensors?  Why do I believe they have revolutionary potential for weather prediction?

Because they offer the chance to get a extraordinary density of pressure observations, which  provides the potential to describe small scale atmospheric structures.  Structures we need to knwo about if we are to predict key weather features like strong thunderstorms.

Let me illustrate how many surface pressure observations there are.  Currently, I am getting real time feeds from two small companies, Cumulonimbus, Inc, (with the Pressurenet app) and OpenSignal (with their WeatherSignal app).   Right now, there are about 115,000 pressure observations coming in per hour from these innovative firms, (90% of them coming from the PressureNet app).  Here is the map.
Amazing coverage from DC to Boston, and around other major cities.  But there is substantial density beyond, particular east of the Mississippi and along the West Coast.

 But keep in mind that this is less than one-hundredths of the smartphones with pressure sensors.  Yes, 1/100.  In a few years there will be at least 100 millions smartphones over North America with pressure sensors. So the additional of the iPhone 6 pressure sensors will only accelerate the growth, with Cumulonimbus, Inc already working on an appropriate iPhone pressure app.

If we could collect, say pressure from 1/10 of the phones with barometers, the eastern U.S. would be virtually covered and only few uninhabited western areas would have pressure observations.

So why would these pressure sensors be a boon for weather prediction?  Because the numerical weather prediction is now going to smaller and smaller scales, and meteorologist are trying to do much better in predicting  what will happen during the next few hours (called Nowcasting).

To forecast fine-scale weather features (like thunderstorms), you need a fine-scale description of the atmosphere, and the current observational network is often insufficient.  We need millions of observations per hour over the U.S. to do the job.  Same situation in China, Europe, and the rest of the world

And pressure is the perfect surface observation:  it reflects the deep structure of the atmosphere and has less exposure problems than temperature or wind.  Pressure can be measured inside our outside a building, in your pocket or hanging on your belt.  A number of number experiments have shown that  surface pressure measurements alone can produce a very good THREE-DIMENSIONAL description of the atmosphere.  Almost sounds like magic.

I believe that dense pressure observations could radically improve weather prediction, and early numerical experiment support this claim.

But the big promise will NOT be met until we find a way to collect a higher percentage of the smartphone pressures.

Google could obviously do this.  I have approached Google about capturing pressure observations on Android phones, but Google management does not seem interested (but a number of Google engineers have been very supportive).

Another approach would be for Samsung or Apple to preinstall the code for capturing and transmitting the pressure information

Or a group with a very popular app (like the WeatherChannel or the Weatherunderground) could include the relevant code .

Anyway, it is frustrating...a huge improvement in weather prediction is possible.  Their is no major technical hurdle.  The pressure sensors are in place.  And we have not put it together.   Maybe soon....


  1. Thankx for the heads up. We need to get these high density measurements (via smart phones) into the system. I'll try to do my part.

  2. For the Galaxy S4 users, here is a how to:

  3. Maybe there is reluctance for people's phones to be continuously broadcasting their GPS coordinates (along with the pressure reading) to a third party...

  4. Robert....I can understand that, but many people allow their coordinates to be used in other Google Maps. If those using google maps would also allow their pressures to be communicated...that would produce a huge increase. And the phone data could be made anonymous in the pressure data base....cliff

  5. Oh, I understand that the data could be made anonymous... butg how will you convince those millions of users, in this day of mistrust? Perhaps if the user got something out of it... Your mention of Google Maps brings to mind the question, can this be integrated with Google Maps?


  6. I run PressureNet on both of my devices and make sure that it's turned on especially when I travel. I'm glad to contribute a little bit to weather science.

    Devices are Samsung Galaxy S3 and Samsung Galaxy S4.

    With all the location and other data collected about us by our carriers and devices, the atmospheric pressure seems both non-identifying and benign. I wish they would collect it automatically from all devices.

  7. How does the climate control system in a building or vehicle impact the readings? Buildings are often pressurized as part of the HVAC system. When you roll the window down in your car while traveling down the highway you feel a pressure change.

    Wouldn't these situations provide false readings?

  8. My fitbit has recorded I've climbed up, or down, as many as forty flights of stairs in a storm, and I'd think that data would reflect a severe local event.

  9. just bought an s5. Will turn it on. By the way... bought your PNW weather book. Absolutely love it.

  10. Bricaud14, I often noticed that my readings vary drastically in the subway tunnel on the DC Metro from the measurements directly above me. Surely there are people -- or well-programmed computers -- that can "see" and judge these anomalies, either averaging them in (hope not), throwing them out (maybe), or marking them for what they are - anomalous readings. Cliff, do you know how they handle it? I doubt most HVAC systems make enough of a change (though a clean room would be a different story), but I have seen the subway tunnel drop it 20-30 in a few seconds.

  11. Bricaud14 & JewelyaZ,

    The most extreme positive pressure in a commercial HVAC system would only be 2 or 3 mm H2O, which works out to less than a millibar. This is within the margin of error of the sensor.

    I think the error generated by people taking their phones into clean rooms, Gamow bags, subway tunnels, etc. would be easily isolated as anomalies by any decent tracking software, and their data thrown out. If a 1 km radius has reported sea level pressures of 1013, 1014, 1013, 1013, 1015, and your phone reports 991, then that data point can be safely discarded.

  12. Cliff, do you feel there is any validity to this:

    Paul Nelson
    Seattle, WA

  13. This is a really great idea. I just wonder how altitude affects the readings. In an urban environment with many people in the same location several hundred feet up in skyscrapers could this have an impact on accuracy? Can the system correct for this somehow (maybe with a 3D location) or would the altitude be within the instrument's accuracy range? Thanks!

  14. Whoopty friggin' do. Androids have had a barometer for years - and the Samsung also has had a full thermister set for over a year (temp and RH).

    Apple puts an old idea into their latest offering, charges twice as much - and suddenly it competes with sliced bread for notoriety.

  15. We could use Google Earth and record pressure in that fashion. I used it with my high school English students to document where they found first person accounts of the Dust Bowl.

  16. One reason there is reluctance to start this sort of a program is due to the short battery life of smartphones.

    Currently smartphone batteries last barely a day. Sending atmospheric data in real time would require continuous data connectivity and would quickly drain the battery on the device.

    Until battery technology improves this isn't really feasible on a mass scale. That being said, I'm optimistic that within a few years battery technology will be where we need it to be.

  17. Please... not the weather channel though.

  18. It doesn't seem to be installed on my iPhone 6s Plus ( in this country? ) Is it not available...?

    I'm hoping now that Siri is available here for Apple TV... as of today?


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