Birdies

In general, a "birdie" is an artificial signal added to the input of a signal-processing system to verify that the system works correctly.

We use this idea in the SETI@home back end. Our birdies are simulated ET signals: beacons with fixed sky position and frequency. For each one, we generate a set of SETI@home signals (currently just spikes) that mimics as closely as possible what we'd expect to detect from the birdie. We add these to the signal database at the start of the Nebula pipeline, before RFI removal.

These birdies serve several purposes:

Birdie parameters

Each birdie has several parameters:

Generating birdie signals

We generate signals for a given birdie by scanning the pointing history of each beam (we have this history with a time resolution of about 1 second). When the beam is close to the birdie position, we consider generating spikes of the different FFT lengths. The power of each potential spike is a function of

If the result is above the power threshold for spikes, we create a signal. We limit the time spacing of these signals to reflect the fact that each FFT can produce at most one spike of a given frequency. The detection frequency and chirp rate of the signal are calculated in a way that reflects both the birdie parameters and the receiver velocity and acceleration.

Code

The code for birdie generation is here.


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©2018 University of California
 
SETI@home and Astropulse are funded by grants from the National Science Foundation, NASA, and donations from SETI@home volunteers. AstroPulse is funded in part by the NSF through grant AST-0307956.