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Blog posts after 1 Feb 2018 about Steppe eagles tracked from Oman can be found at the Steppe eagle blog

Friday, August 21, 2015

Two satellite systems, more complete coverage

After spending some time last week around Bid Bid, the vulture we have been tracking has moved back east, and has been visiting the rubbish dump at Al Multaqua and the coast around Yiti.  These areas are where it has spent most of its time since being captured seven month ago.  Below are maps of the movement of the vulture over the last week.

In previous posts we explained that the technology we use to track the birds actually estimates locations in two ways, using two different satellite networks.  One is the GPS satellite network (green locations), in which the package attached to the bird listens for signals from geo-stationary satellites, then uses those signals to calculate the package's location on the earth.  That location is then uploaded via the Argos system of satellites and sent to us.  GPS locations are highly accurate, but can be expensive in terms of energy to acquire.  The second satellite network used to locate the package on the bird is the Argos system of satellites (red locations).  Argos system satellites are orbiting the earth, listening for signals from transmitters like the one on our vulture.  The transmitter is sending the GPS location via the Argos system, but also sends a stable signal, from which the orbiting Argos satellites can calculate the location of the package using the Doppler effect (the shift in frequency as a transmitter and receiver move relative to one another.).  Argos locations are generally less accurate than GPS, but require less energy.  The differences in the two maps arise not only from the different accuracies of the two systems, but also the different duty schedules of the two systems resulting from the need to manage power to acquire GPS locations.  So, while the Argos locations are generally less accurate than the GPS locations, they can be estimated more often and thereby fill in gaps in data collection time.
Locations of tracked vulture during 12-20 August 2015 as estimated by the GPS system of satellites. 

Locations of tracked vulture during 12-20 August 2015 as estimated by the Argos system of satellites. 
Generally speaking, vultures suffer from a poor public image.  Click on this link to view a page that discusses the truth about vultures and how they are important to human well-being.  http://www.bbc.com/earth/story/20150713-the-truth-about-vultures

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