As part of our testing process of different potential locations for receiving signals, we decided to again try to monitor a pass of the LES-1 from the grounds of LACMA — specifically, from the roof of the Pavilion for Japanese Art. We had two passes that we wanted to try to be able to monitor — one starting at 7.31am, and the other starting at 10.13am. So, another early morning, but at least this meant that we got to take a look at Los Angeles during one of its strange spring morning mists.
Later the same day, we met up with Stephan Esterhuizen, Engineer at NASA’s Jet Propulsion Laboratory, to talk about signals. Stephan spends a lot of time dealing with weak and far-flung signals, and was part of the team that received and processed signals for the ExoMars mission, among many other projects.
Stephan had plenty of advice to give about our setup, and possible future changes to it. After monitoring the pass, we talked through our plans with him, and gave him the big I/Q data files that we had from the process of monitoring the LES-1 last September, in Stolzenhagen in Germany.
These big I/Q files were the ones that we used to derive our existing audio excerpts of the signal from the satellite. One of the problems that we have with the signals in this data is that they have a quite pronounced doppler shift, meaning that, when played as audio, they shift lower in pitch over time. This will be the same for all of the signals that we record (because they all come from the same satellite, which is moving very fast…), but this data is the cleanest and ‘neatest’ that we have so far, so we were eager to potentially try to get versions of the audio derived from the data for which a doppler-shift compensation process has been applied.
Stephan was able to modify his ExoMars landing detection code to use it to remove the doppler shift from our data, through manually specifying a few dopplers (as observed in the waterfall plot), and then allowing the software to interpolate between these points and ‘blindly’ remove the doppler, thus ‘straightening out’ the audio.
The result, ‘tuned’ to 500hz, looks and sounds something like this: