omicron_virgo.md

@@ -76,7 +76,20 @@ At Cascina, Omicron triggers are centralized (see [Omicron triggers](omicron_vir
 <a href="https://git.ligo.org/virgo/virgoapp/Omicron/-/raw/master/doc/images/plot_V1-LSC_DARM-1217376018-187200_rate.png"><img src="https://git.ligo.org/virgo/virgoapp/Omicron/-/raw/master/doc/images/plot_V1-LSC_DARM-1217376018-187200_rate.png"  width="300"></a>
 <a href="https://git.ligo.org/virgo/virgoapp/Omicron/-/raw/master/doc/images/plot_V1-LSC_DARM-1217376018-187200_snr.png"><img src="https://git.ligo.org/virgo/virgoapp/Omicron/-/raw/master/doc/images/plot_V1-LSC_DARM-1217376018-187200_snr.png"  width="300"></a>
 
+## Scans of multiple channels
 
+Omicron offers display methods. They can be used to scan many channels around a given time. The typical output is a web page displaying Omicron maps for a long list of channels. Running an Omicron scan is an easy thing to do providing you have a valid [parameter file](omicron_virgo#configurations).
+
+Running an omicron scan on a given GPS time is simple. For example:
+```
+omicron 1111824671.5625 ./parameters.txt
+```
+Omicron can only run with a single frequency range for all channels. This can be a constraint to process channels with different sampling frequencies. For example, if you want to explore frequencies above 500Hz, you can only use channels sampled at more than 1000Hz. Because of this constraints, you might need to run several scans over different frequency regions. Moreover, Omicron is designed to only work with sampling frequencies of any given power of 2. This is a constraint to process Virgo channels. For example, channels sampled at 2000 Hz will be first down-sampled at 1024 Hz and the maximum Fourier frequency is 512 Hz (Nyquist). 
+
+For a complete documentation to run omicron, see [the omicron documentation](https://virgo.docs.ligo.org/virgoapp/Omicron/omicron_8cc.html#details)
+
+<a href="https://git.ligo.org/virgo/virgoapp/Omicron/-/raw/master/doc/images/gw170817_spectro.png"><img src="https://git.ligo.org/virgo/virgoapp/Omicron/-/raw/master/doc/images/gw170817_spectro.png"></a>
+ The most basic plot produced by a scan is a SNR spectrogram. Omicron offers additional plots: amplitude spectrogram, raw time series, time series after whitening, PSD, ASD...
  
 ## Other applications