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The FPICC (Fabry-Perot Interferometer for Column CO2) is a new instrument developed under the
Instrument Incubator Program that uses a novel technique for measuring the absorption of CO2 sunlight
reflected from the Earth. The optical setup consists of three channels. The first channel is built to measure
carbon dioxide by using a solid Fabry-Perot etalon to restrict the measurement to light in CO2 absorption
bands. The second and third channels focus on the O2 A band (759-771 nm) composed of about 300
absorption lines, which vary in strength and width according to pressure and temperature. We performed
measurements using solid Fabry-Perot etalons with different FSR and different pre-filters. We
demonstrated the instrument's significant capability to detect CO2 and O2 in laboratory, as well as in
ground based and airborne experiments. The initial tests indicate that when the instrument is used with a
sun tracker the sensitivity for CO2 detection is 2.1 ppm in one second average, and the sensitivity to the
oxygen column pressure changes is as low as 0.88 mbar. The reduced sensitivity for the airborne
experiments arises because the atmospheric scattering processes make the path length more variable and
uncertain. One solution to this problem is to use the glint reflection from water surfaces. For this purpose
we design and perform a theoretical study to build a different version of the FPICC instrument to be used
on a satellite orbiting the Earth and working in a glint mode.
This Fabry-Perot based technique is applicable to other species as well. For example one could use the
FPICC instrument for fractionations measurements of the stable carbon isotope (13C/12C). The instrument
can be used to study the atmosphere of Mars, which consists primarily of CO2. A theoretical study and
design of a version of the instrument for Mars for CO2 and CH4 measurements will be presented. We report
results on the recent calibration of the instrument, recent data from ground tests at Goddard, design
versions, and theoretical models for the Earth and Mars instruments.
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