Thursday, January 24, 2013

Ship Tracks 3

Cliff Mass posted some ship tracks pictures in Strange lines over the northeast pacific.  He showed examples from the GOES (the G stands for geostationary) satellite, which flies over the equator.  The imagery at high latitudes can be distorted. I was surprised at the lack of distortion at Seattle's latitude.
He also showed a swath image from MODIS instrument on the polar-orbiting Terra satellite at 20:05 UT.  Below that, you can see the next granule* in the satellite data stream, off the coast of California, at 20:10 UT.

The ship track region is more centered in this granule from the MODIS instrument on Terra's twin, Aqua.
I'm so grateful that professor Mass kept NASA's name for the image files when he uploaded them on his blog.  That made it easy for me to find the date and time of the files.

For instance, the filename
says the image was taken off Terra in 2013 on Julian Day 015 at 20:05 to 20:10 UT. It's the 2 km resolution file. To look at it in higher resolution, set your browser to
and then use the pulldown menu to toggle to January 15.  Visit that link to see the images in fantastic 250 meter resolution.

BTW, days are numbered sequentially from 1 to 365 in a Julian calendar.  It's much easier than keeping track of months and dates in software.  January is easy because the Julian day is just the date.  But, for subsequent months, this Julian day calendar comes in handy.

* NASA downloads and processes satellite data in chunks they call granules.  Whenever you shoot a continuous movie, you have to chunk it down somehow, and granule is a good, descriptive name.


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