Using the Spectrometer . 61
Atmospheric (CO
2
/H
2
O) Suppression
Atmospheric suppression can be set in the Advanced section on the Instrument tab of the
Scan and Instrument Setup dialog.
What is atmospheric suppression?
This is an atmospheric correction routine. This routine is more powerful than simple
subtraction, overcoming the following issues:
• Non-linearity due to resolution,
• The measured spectrum is temperature dependent,
• Lineshape and calibration are affected by J-stop and sample or accessory.
What does atmospheric suppression do?
When CO2/H2O is switched on, the software uses a single reference spectrum derived
from high resolution data and our understanding of the instrument to model the
lineshape, then finds the current real instrument parameters by least squares fitting to
the measured spectrum.
Figure 13 Correction of a mid infrared spectrum at 4 cm
-1
resolution
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