18.4 CONNOI and EVANOI, noise power spectral density

These two programs with the help of GMT allow to produce noise power spectral density (PSD) plots similar to the ones produced by the PQLX software. CONNOI is the tool that reads the continuous database and produces output files that are evaluated by EVANOI. The computation of the noise PSD follows the method described by McNamara and Buland (2004).

To run CONNOI on a SEISAN continuous database BER use for example:

connoi -start 20100501 -stop 20100502 -cbase BER

To run CONNOI on an archive structure BER use for example:

connoi -start 20100501 -stop 20100502 -arc BER

In both examples BER is the database, you can also specify 'def' and the program will take all default continuous databases or archives defined in SEISAN.DEF. The default output filename is connoi.out.

Example of output:

stat comp date and time       duration frequency noise PSD
----------------------------------------------------------
BER   HHZ 20100501 0000 0.00   3600.00  0.00200    -159.14
BER   HHZ 20100501 0000 0.00   3600.00  0.00204    -159.14
BER   HHZ 20100501 0000 0.00   3600.00  0.00209    -159.14
...

The output from CONNOI can then be used as input to EVANOI. You can enter station and component, give a time interval, select a time of day interval, and chose a reference station. EVANOI produces GMT plotting scripts files that are named after the station. Then simply run the script file to get a plot.

You can also output the data in a compact format using the -compact option. This output does not work with EVANOI, but it is fairly easy to read in your own scripts. An example output :

CONNOI: NF= 500 START=2008120101   STOP=2008120103   DURATION= 60.0min, SPACING= 50.%
STATN CMP yyyymmdd HHMMSS.FF   SPECLEN  -2.69897 -2.68955 -2.68014 ... 
BER   HHZ 20100501 0100 0.00   3600.00   -102.94  -102.94  -102.94 ... 
BER   HHN 20100501 0100 0.00   3600.00   -117.85  -117.85  -117.85 ... 
BER   HHE 20100501 0100 0.00   3600.00   -115.81  -115.81  -115.81 ...
VASAV BHZ 20100501 0100 0.00   3600.00   -134.16  -134.16  -134.16 ... 
VASAV BHN 20100501 0100 0.00   3600.00   -131.06  -131.06  -131.06 ... 
VASAV BHE 20100501 0100 0.00   3600.00   -124.60  -124.60  -124.60 ... 
...

By default, CONNOI calculates spectra every 30 minutes, with each spectra calculated over a 60-minute interval. You can change this using the -spectlen and -spectspace options, where -spectlen gives the interval over which to calculate the spectra (in minutes) and -spectspace gives the spacing between spectra with respect to -spectlen (1.0 for no overlap, 0.5 for 50% overlap, etc). For example:

connoi -start 20100501 -stop 20100502 -cbase BER -spectlen 60 -spectspace 1.

will calculate spectra over a 60-minute interval, spaced every 60 minutes (no overlap). Finally, you can calculate the spectra for a single channel of a single station using the -sgram option. This option always uses the -compact output format and sets spectspace to 1.0. For example:

connoi -start 20100501 -stop 20100502 -cbase BER -sgram TOTI BHZ

Figure 18.1: Example of plot created using CONNOI and EVANOI. The plot shows noise PDFs for station BER for three components in January 2015.