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Using the Spectrometer with Spectrum . 51
Atmospheric (CO
2
/H
2
O) Suppression
Atmospheric suppression can be selected in the Setup Instrument Advanced tab (Figure 19).
Figure 19 Setup Instrument Advanced tab in Spectrum
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 20 Correction of an MIR spectrum at 4 cm
−1
resolution