Parent Topic: <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/AVHRRAD|TEXT+SEGMENT+FORMAT">TEXT SEGMENT FORMAT</a><hr>
<H4>VISIBLE CHANNEL CALIBRATION</H4>
For visible channel calibration, AVHRRAD looks for text with the
following format in the text segment:
<P>
<PRE>
 SLOPES: 0.1020000 0.1030000 -0.0016797 -0.1581315 -0.1790746
 INTERCEPTS: -4.1300001 -4.2100000 1.6692461 157.2673558 178.9532614
</PRE>
The SLOPES line contains the slope coefficients for AVHRR channels 1
through 5. All five values must be specified if the SLOPES line is
present. These values are typically satellite dependent. The units
for these values are:
<P>
<PRE>
 Slope (channel 1)         percent reflectance/count
 Slope (channel 2)         percent reflectance/count
 Slope (channel 3)         milliWatts/m^2 sterad cm^-1/count 
 Slope (channel 4)         milliWatts/m^2 sterad cm^-1/count 
 Slope (channel 5)         milliWatts/m^2 sterad cm^-1/count
</PRE>
The INTERCEPTS line contains the intercept coefficients for AVHRR
channels 1 through 5. All five values must be specified if the
INTERCEPTS line is present. These values are typically satellite
dependent. The units for these values are:
<P>
<PRE>
 Intercept (channel 1)         percent reflectance
 Intercept (channel 2)         percent reflectance
 Intercept (channel 3)         milliWatts/m^2 sterad cm^-1
 Intercept (channel 4)         milliWatts/m^2 sterad cm^-1 
 Intercept (channel 5)         milliWatts/m^2 sterad cm^-1
</PRE>
The text segment generated when FIMPORT or MIAVHRR is used to read
in an AVHRR image may or may not contain a SLOPES and INTERCEPTS
line. Some AVHRR formats (such as Level 1b) contain this information
while others do not.<p>
If the SLOPES and INTERCEPTS lines are not present in the text
segment, then AVHRRAD will use default, pre-launch slope and
intercept values for AVHRR visible channels 1 and 2. These
pre-launch values are satellite dependent and can be found in the
NOAA Polar Orbiter Data Users Guide. AVHRRAD will look for a SATID
line in the text segment in order to acquire the satellite name.
Please see the section on radiometric correction for a description
of the format of the SATID line in the text segment.
<P>
<hr>
Parent Topic: <A href="http://www.pcigeomatics.com/cgi-bin/pcihlp/AVHRRAD|TEXT+SEGMENT+FORMAT">TEXT SEGMENT FORMAT</a><br>
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