Geminids 2014

Geminids are one of the most known meteor showers with very high theoretical ZHR rate of around 120. Its maximum was calculated to be between 13th and 14th December. This time I rotated my Körner 19.3 antenna at north-eastern direction for an overnight recording. The results in evening were really encouraging with pings and bursts every few seconds! I added a preamp between XDR-F1HD and antenna and set the squelch few dBs over the noise floor. Tropospheric conditions were rather poor due to a cold front, so the VHF band was quiet and ready for MS reception. 

Here are some highlights that I have cut manually from a final video. As you can see I recorded most of pings on 89.9, one of my favorite MS frequencies. It was empty over entire night, however weak Eska Olsztyn (in opposite polarization) appeared in the morning with weak signal, so I tuned away to 100.7. The squelch function was extremely helpful for creating a video of all pings and bursts. I wrote a short bash script using ffmpeg’s silencedetect module. It seeks entire video, marks periods with audio amplitude less than -67dBFS, generates an EDL file and feeds it to mencoder, which drops silent parts of video:

#!/bin/bash
# 1. Upscale video to 480p (for YouTube…) and decompress audio - mencoder doesn't
# seem to work well together with EDL and OGG Vorbis audio
ffmpeg -i $1 -vf scale=-1:480 -vcodec libx264 -threads 4 -acodec pcm_s16le tmp.mkv
# 2. Get a silencedetect module output @ -67dBFS from the ffmpeg
ffmpeg -nostats -i tmp.mkv -af silencedetect=n=-67dB:d=0.1 -f null - 2> ff
# 3a. Generate an EDL - Edit Decision Lists file for mencoder
grep silence_end ff | awk '{print $5-$8 "\t" $5 "\t0"}' > edl
# 3b. Finish a silence range if it lasts to the end of a video
finish_silence=`grep silence ff | tail -n 1 | grep start`
if [ ! -z "$finish_silence" ]; then
echo $finish_silence | awk '{print $5 "\t999999999\t0"}' >> edl
fi
# 4. Use mencoder to transcode the video and drop silent parts
mencoder tmp.mkv -edl edl -ovc lavc -oac mp3lame -lameopts abr:br=256 -hr-edl-seek -o out.mkv
# 5. Remove all temporary files
rm ff edl tmp.mkv

Because of some problems with YouTube, I uploaded over 2 hours of pings and bursts to Vimeo instead. Anyway, it is not really suitable for watching and listening for more than few minutes… Mostly Kekc FM, Yle1, SR P1 (89.9) and Yle Puhe (100.7).