The source level for surface generated noise and discrete sources is by default assumed to be constant in frequency. Although this is a reasonable assumption for surface generated noise over reasonably wide frequency bands, it is usually unrealistic for discrete sources which will be characterized by distinct frequency lines in their source spectrum. Therefore the source spectra can optionally be specified in ASCII files which will be read by OASN if the source levels are specified as negative, in which case the value is interpreted as the negative of the logical unit corresponding to the file. Therefore, the file should either be assigned to the environmental variable FORxxx or the file should have the name fort.xxx, where xxx is the absolute value of the number specified for SNLEV or DNLEV .
A particular source file (and logical unit) can be shared by any number of sources.
The format of the file is a follows:
NFREQ FREQ1 FREQ2
dB(FREQ1)
dB(FREQ1+DELFRQ)
:
:
:
dB(FREQ2)
The first line specifies the frequency sampling of the source levels, and it must be consistent with the sampling specified in Block III of the input file. The following lines simply states the source level in dB at each frequency value.