Ronald Carlson

Thermal and Chemical Structure Variations in Titan's Stratosphere during the Cassini Mission

We have developed a line-by-line Atmospheric Radiative Transfer for Titan code that includes the most recent laboratory spectroscopic data and haze descriptions relative to Titans stratosphere. We use this code to model Cassini Composite Infrared Spectrometer data taken during the numerous Titan flybys from 2006 to 2012 at surface-intercepting geometry in the 600-1500 cm–1 range for latitudes from 50°S to 50°N. We report variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE). We find indication for a weakening of the temperature gradient with warming of the stratosphere and cooling of the lower mesosphere. In addition, we infer precise concentrations for the trace gases and their main isotopologues and find that the chemical composition in Titans stratosphere varies significantly with latitude during the 6 years investigated here, with increased mixing ratios toward the northern latitudes. In particular, we monitor and quantify the amplitude of a maximum enhancement of several gases observed at northern latitudes up to 50°N around mid-2009, at the time of the NSE. We find that this rise is followed by a rapid decrease in chemical inventory in 2010 probably due to a weakening north polar vortex with reduced lateral mixing across the vortex boundary.

Infrared spectroscopic remote sensing from the Cassini orbiter

An infrared spectroscopy instrument for infrared remote sensing from the Cassini orbiter is being breadboarded in the laboratory. The Composite Infrared Spectrometer (CIRS) consists of a pair of Fourier Transform Spectrometers (FTS) which together cover the range from 10 - 1400/cm with a spectral resolution up to 0.5/cm. The far-infrared FTS is a polarizing interferometer covering the 10 - 300/cm range. The mid-infrared FTS is a conventional Michelson FTS covering 200 - 1400/cm in three spectral channels. CIRS will retrieve information on the atmospheres of Titan and Saturn with good vertical resolution, from deep in their tropospheres to high in their stratospheres, and into the upper few centimeters of the regoliths of icy objects. The science objectives and design of CIRS are discussed.

Thermal Infrared Spectroscopy of Saturn and Titan from Cassini

The Cassini spacecraft completed its nominal mission at Saturn and Titan in 2008 and began its extended mission. Cassini carries the Composite Infrared Spectrometer that measures composition, thermal structure and dynamics.

Infrared Observations of Saturn and Titan from Cassini

The Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft has been orbiting Saturn for 2-1/2 years. CIRS is a Fourier transform spectrometer that measures atmospheric thermal structure and dynamics, and atmospheric composition, of Saturn and Titan. CIRS also maps the temperatures and dynamical processes of the rings and icy moons.

Wavelength Calibration of the Cassini Composite Infrared Spectrometer (CIRS) Using Spectrum De-Stretching

A new wavelength calibration of the Cassini Composite Infrared Spectrometer (CIRS) based upon spectrum de-stretching is described. The calibration accurately predicts the wavenumbers of spectral features for all 21 CIRS far- and mid-IR detectors.

Vector Radiometric Calibration Model for the Cassini Composite Infrared Spectrometer (CIRS)

The radiometric calibration of the Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft is described. CIRS is a dual-temperature FTS with absorbing beam splitters. It was therefore necessary to develop a vector radiometric calibration model.