Laboratory procedure for simulating nadir measurements with the ACE-FTS

Abstract

The Atmospheric Chemistry Experiment (ACE), or SCISAT mission, is a Canadian science satellite designed to investigate the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere. The ACE mission payload consists of two science instruments: a high-resolution infrared Fourier-Transform Spectrometer (FTS) and an ultraviolet/visible/near-infrared spectrometer. These instruments primarily function in occultation mode. However, during the dark portion of the orbit, the Earth passes between the Sun and the satellite. In this configuration, the ACE-FTS has the opportunity to acquire some nadir-view spectra of the Earth. Since the ACE-FTS was designed to view a hot source (i.e., the Sun) at high resolution using a single scan, it was necessary to determine if the ACE-FTS could also provide nadir spectra of the relatively cold atmosphere and surface with sufficient signal-to-noise ratio (SNR). As part of the pre-launch test program, laboratory measurements were performed to investigate this possibility. This paper reports the laboratory spectra of methane, ozone, and carbon monoxide gases measured with the ACE-FTS to determine the performance characteristics of the instrument when viewing a low-intensity blackbody source. From these results, it was shown that the ACE-FTS may be capable of measuring the column amounts of several abundant trace gases, such as methane, ozone, and nitrous oxide, in the atmosphere with sufficient SNR.