The Extreme Low Frequency Observatory operate in the
frequency range from (close to) 0 Hz to 15360 Hz. The ELFO is located
in the AMS in Hessdalen. All strong
electromagnetical (EM) signals are detected. The threshold level can be adjusted. Each day,
the previous day and night detected
EM signals, is converted to pictures, and transmittet to this page.
More details can be found in the studentreport,
and at the bottom of this page.
#!/usr/bin/perl
#
#Copyright (C) 2003 Christian A. Br�the
#Developted for Jan Steinar Kvilesj�, Christian A. Br�the, Lars Martin Dobbe
#Changed 2007 by Erling Strand
#
sub print_http_header
{
print "Content-type: text/shtml\n\n";
}
sub list_folders
{
$where_to_read = "../italia/images";
opendir(DIR,$where_to_read);
@files = readdir(DIR);
@reversedFiles;
@sortedFiles;
foreach(@files)
{
next if ($_ eq '.' || $_ eq '..'); # skip this and up dirs
($day, $month, $year ) = split("_",$_,3);
$day_new= $day;
$month_new= $month;
if ($day < 10 )
{
$day= "0" . $day;};
if ($month < 10 )
{ $month = "0" . $month;};
$reversed = $year . "_" . $month . "_" . $day;
push(@reversedFiles,$reversed);
}
closedir(DIR);
@sortedFiles = sort { ($da = lc $a) =~ s/[\W_]+//g;
($db = lc $b) =~ s/[\W_]+//g;
$db cmp $da;
} @reversedFiles;
print " ";
print "";
print "| Choose a folder for a specific day: | ";
print " ";
print "";
$counter = 0;
$newyear = 0;
foreach(@sortedFiles)
{
($year, $month, $day) = split("_",$_,3);
$month_new = $month;
if ($month < 10) { $month = $month & 15; };
$day_new = $day;
if ($day < 10) { $day = $day & 15; };
$linkName = "showDir1.cgi?dirName=" . $day . "_" . $month . "_" . $year;
$printing = "Elfo - ". $day_new . "." . $month_new . "." . $year;
if ($newyear != $year)
{
print " Year:
$year | ";
print "";
$counter = 0;
}
if( $counter == 4 )
{
print "| $printing | ";
print " ";
print "";
$counter = 0;
}
else
{
print "| $printing | ";
$counter++;
}
$newyear = $year;
}
print " ";
}
print_http_header();
list_folders();
exit(0);
Thanks to Jader Monari for this info:
The file is stored only when some signal in spectra domain within 0 up to 15360Hz hits a particular
threshold set remotely by hands (0dBm).
The average of the receiver+atmospheric spectral noise in Hessdalen is -40dBm/Hz.
In general, the signals that hit the threshold are strong statics or man-made.
The files are represented in JTFA (Join Time Frequency Analysis) format.
The colours represent the strength or intensity of the signal. The dynamic range
is from -80dBm up to 10dBm. These amplitudes are compared with 16581375 different numbers
(representing all possible colours in RGB using hex values.). Each one of those values is spitted into three
different values representing the RED component, the GREEN component and the
BLUE component.
The x axis is the frequency from 0 up to 15360Hz. The resolution is 15Hz
The y axis is the time in seconds.
You may read more about natural low frequency EM signals at
http://www.vlf.it/regularsig/regularsignals.htm and
http://www.vlf.it/nrs/nrs.htm
|
