It can be tracked by way of its model number:
flightaware.com/live/aircrafttype/U2
Today I see it in flight as flight number NASA908:
flightaware.com/live/flight/NASA809
The call sign for this aircraft is always NASA809. NASA uses the aircraft number and the acronym “NASA” for all of its flights. So, if you know the aircraft number (ignore the letters at the end and beginning) then you know the call sign.
Interesting pattern over Oklahoma? Wonder what that’s all about? 
It looks like a typical mapping flight to me.
[quote=“damiross”]
Sounds like a good explanation. But why the northeast and southwest directions? Why not straight north-south or east-west? And I thought satellites provided the map images…
After reading your question, Needlenose, I thought of something else it might be. It could be air sampling. Why the sampling/mapping/whatever isn’t done along N-S or E-W lines, I don’t know.
If it is sampling, they could be following the direction of the winds aloft.
Having a business in Oklahoma, I have asked around about this. I have been told that NASA and the State of Oklahoma are mapping vis-a-vis water table and ag. interests (at least I think that is what I remember hearing). I guess it is something that the U2 can do well at that Satellites aren’t as good at.
Haven’t seen one as yet, but at FL280, I don’t think I am gonna!
Long Live the Starship!
Chris
NC-29/N8244L