Tuesday, March 26, 2013

Can a weather satellite read your license plate?

A question that I am often asked is:  what are the finest details observable from weather satellites?

Let me show you some examples.   Most of the weather satellite imagery you see on TV and the web is from the geostationary weather satellites, located over the equator at an altitude of 36,000 km.  In that orbit they remain over the same portion of the earth as the earth rotates during the day.  There are five of these satellites, two owned by the U.S.


The highest resolution imagery from those satellites are in the visible part of the spectrum (roughly .4 to .7 microns...millions of a meter), the wavelength your eyes are most sensitive.  The pixel size over the equator is roughly 1 km and that resolution degrades a bit as the satellite observes to the north and south.    Here is an example of a high-resolution visible image from one of these satellites (GOES-W, position at 135W) on March 23rd at 1 PM PDT.


And to illustrate what it can see better, let me show you a blow up over Puget Sound.

If you look carefully, Lake Washington and Lake Samamish are visible, as are the major river valleys in the Cascades.   No worries about license-plate reading!

But there is another class of satellite, called polar orbiters, that is positioned much closer to the surface (only about 800 km above) in orbits that allow them to see constantly changing swaths (often about 1000-2000 km wide) of the earth below.  I often show imagery from the MODIS polar orbiting satellites on this blog and they have pixel size of 250 meters.  Let me show you a sample of this for nearly the same time as the geostationary satellite image shown above, again for visible wavelengths.

You see the difference?   Much sharper.  And you can see the individual puffy cumulus clouds that were forming over land that day (as the land heated up the atmosphere destabilized, producing convection).  Look how well defined Seattle's harbor....Elliot Bay.. is!  You can even see the sand spit at Sequim.  One can learn a lot from such images.


Now there are other, non-meteorological, satellites that have much finer resolution.  For example, LANDSAT imagery has resolution of 15-30 meters.   Here is a sample:


And I assume that the CIA has satellite imagery capable of doing much better....

Want to look at the weather satellite imagery yourself?   A few good websites:

National Weather Service Western U.S. Products:  http://www.wrh.noaa.gov/satellite/?wfo=sew

NWS Aviation Weather Center Server:  http://aviationweather.gov/adds/satellite/

NCAR RAP Satellite Server: http://weather.rap.ucar.edu/satellite/



10 comments:

Nadine MacLane said...

When Nixon was meetiog with Leonid Brezhnev, there was a photo op on the steps of the Kremlin. One of the atendees took their picture using a CIA satellite, and yes, you could tell them apart. So I was talking one day, to a chap who used to be in imagery, so I asked what he was allowed to say. "I don'tknow what the declassified answer is, so I won't tell you that we can read the name on a golf ball" ??*?? Take it for what it's worth, but can we read eye color? He did say that its all in the enhancements. He was given a photo that he was told had an airplane in the corner, go read the wing number. the team started working, and got to where they could count rivits. You know, those little dot thingies that you see out on the wing... Or, look in your own back yard on google maps.

Mike said...

Also see this XKCD "what-if" for discussion of what it would be like to point Hubble down at us below.

Franz Amador said...

If I, a private citizen, want to see a satellite image of where the clouds are right now over the Seattle area, is there a way to do that, or is access to such photos restricted?

Jeremy Dyck said...

Pretty tough to get the right angle to read a vertical license plate from orbit, however! If your license plate is being spied, it ain't from orbit.

Tim said...

Google Maps and Bing use aerial photography for higher resolution

audioskeptic said...

Well, for Google Earth resolution for Redmond, wa, there appear to be about 40 pixels in the length of a Mazda 3. I'm not sure how long the car is, but that works out to something between 3" and 6".

In addition, the lens plus atmosphere effect on the MTF appears to be about 2 to 3 pixels, roughly Gaussian from the estimate I can make without more data.

p206.1981 said...

Drones under development are equipped with cameras that monitor an entire city simultaneously, with the ability to zoom all the way in to see your face in another window while continuing to monitor the rest of the city. The operator can open dozens of zoomed-in windows at once, meanwhile the rest of the city continues under surveillance.

iancruickshank said...

Is the MODIS visible imagery publicly available on the web anywhere?

Paul Henriksen said...

The assistant Harbormaster at a local Marina was talking to a Homeland security agent in San Diego.k The agent said he could tell her what color hat she was wearing.

beryllium10 said...

In response to a couple of the queries and comments here ...

Private companies like DigitalGlobe and Geoeye (recently merged) operate satellites with sub-meter imaging abilities and sell their products commercially. Publicly available satellite photos are limited to a best resolution of about 50 cm (see, for example this link on the Geoeye website), which is not sufficient to reveal number plates. In response to Mike - the resolving power of these satellites is quite similar to a downward-looking Hubble telescope. Anyone with enough money can buy high-resolution imagery, but you can also find it in abundance on Google Earth, Google Maps, Bing Maps, and elsewhere on the web. However, as pointed out by Tim, the highest resolution imagery in these mapping apps comes from good old aerial photography - you can count Priuses in the Google parking lot (at slightly sharper resolution than the current Google Earth view of Husky Stadium), but you still can't read their number plates. For a nice example of what polar scientists can do with high resolution satellite photos, google: "Counting penguins from space" (more detail here).