Optical Techniques

Scientific Objectives

• The measurement of trace gases in the troposphere to middle stratosphere; interactions of chemistry and dynamics and troposphere - stratosphere exchange.
• Studies of the chemistry and dynamics of the polar stratosphere, observing annual cycles of ozone including springtime losses and longer term recovery; the trace species effecting ozone chemistry; including the nature of PSCs and their effects on ozone.
• Determination of long term changes in the chemistry of the troposphere and stratosphere; the effects of changing halogen inputs in the post Montreal Protocol era; changes in ozone precursors and climate change forcers; changes in anthropogenic sourced species.
• Promote the improvement of long term ground-based remote sensing measurements world wide via the Network for the Detection of Atmospheric Composition Change (NDACC) and in particular the NDACC Infrared Working Group (IRWG).

Ongoing Observation Program

• Deployment and long term operation of high resolution solar viewing spectrometer at Thule, Greenland (76ºN); analysis of change in the amounts and vertical distribution of trace gases over time scales from days to decades.
• Deployment and long term operation an identical high resolution spectrometer at Mauna Loa Observatory, Hawaii (20ºN).
• We maintain a third high resolution spectrometer at our Boulder, Colorado, Lab (39ºN) for both atmospheric and laboratory studies.

Field Campaigns

• A month-long deployment (March 2006) to a surface site near Mexico City to measure throughout the day a number of gases important to the tropospheric chemistry of the region in connection with the MIRAGE field program.
• Participation in the Polar Aura Validation Experiment (PAVE) in January- February 2005, to measure, from an aircraft platform, column amounts and profiles of upper tropospheric and lower stratospheric gases coincident with observations by the four remote sounding experiments aboard the NASA Aura spacecraft.
• Participation in TOPSE on the C-130 (spring 2000) to measure CO in the springtime free troposphere and help determine its sources, transport, and oxidation; use of N₂O concentration for diagnostics of winter and springtime intrusion of stratospheric ozone into the free troposphere.
• Participation in SOLVE airborne polar mission (winter 1999-2000) to measure the infrared extinction spectra of stratospheric aerosols and PSCs to deduce the physical and chemical nature of the particles and to measure columns of trace gases to determine the effect of the aerosols on the trace gas chemistry.

Community Support

• With international colleagues we develop and maintain the widely distributed spectral analysis package SFIT4.

Atlas Spectra

• In cooperation with colleagues we maintain the most recent atlas of balloon borne solar infrared spectra.  These spectra can be viewed and downloaded here.

SFIT Development

Along with our international colleagues and collaborators we maintain SFIT4 retrieval code.  This code employs an atmospheric transmission and radiative transfer forward model paired with an implementation of the Optimal Estimation algorithm to retrieve trace gas constituents from infrared spectra.  The code is used by more then 50 groups around the world to retrieve gases from ground-based, airborne solar and emission spectra.  More can be learned at the SFIT4 wiki. The code is freely available.