Retrieval of atmospheric ozone profiles from an infrared quantum cascade laser heterodyne radiometer: results and analysis

Abstract

Following the recent development of a ground-based prototype quantum cascade laser heterodyne radiometer operating in the midinfrared, atmospheric ozone profile retrievals from a solar occultation measurement campaign performed at the Rutherford Appleton Laboratory on 21 September 2006 are presented. Retrieval is based on the optimal estimation method. High resolution (0.0073 cm(-1)) atmospheric spectra recorded by the laser heterodyne radiometer and covering a microwindow (1033.8-1034.5 cm(-1)) optimized for atmospheric ozone measurements were used as measurement vectors. As part of the evaluation of this novel instrument, a comprehensive analysis of the retrievals is presented, demonstrating the high potential of quantum cascade laser heterodyne radiometry for atmospheric sounding. Vertical resolutions of 2 km near the ground and about 3 km in the stratosphere were obtained. The information content of the retrieval was found to be up to 48 bits, which is much higher than any other passive ground-based instrument. Frequency mismatches of several absorption peaks between the forward model and experimental spectra have been observed and significantly contribute to the retrieval noise error in the upper-troposphere lower-stratosphere region. Retrieved ozone vertical profiles were compared to ozonesonde data recorded at similar latitudes. The agreement is generally excellent except for the 20 to 25 km peak in ozone concentration, where ozonesonde data were found to be 20% lower than the amount retrieved from the laser heterodyne radiometer spectra. Quantum cascade laser based heterodyne radiometry in the midinfrared has been demonstrated to provide high spectral resolution and unprecedented vertical resolution for a passive sounder in a highly compact and mechanically simple package.

High sensitivity stand-off detection and quantification of chemical mixtures using an active coherent laser spectrometer (ACLaS)

“…The end result is a concentration measurement accompanied by robust metrics describing the level of confidence that can be placed in the measurement. The approach we retain is based on optimal estimation (OE) used in atmospheric data retrieval from space-borne spectrometers 21 . It has been mathematically formalized in a comprehensive and consistent way by C. Rogers 23 .…”

Evaluation of laser heterodyne radiometry for numerical weather prediction applications

“…QCL‐based LHR technology has advanced rapidly in the last decade, initially for trace‐gas detection in Earth observation and planetary applications (Weidmann et al, ). Atmospheric science applications have included ozone profiling (Weidmann et al, ), multi‐constituent profiling (Weidmann et al, ; Tsai et al, ), and most recently atmospheric CO 2 measurements (Hoffmann et al, ). Developments are currently underway to miniaturize the LHRs using optical integration technologies (Weidmann et al, ) and make them suitable for small satellite applications (Weidmann et al, ).…”

Atmospheric vertical profiles of O3, N2O, CH4, CCl2F2, and H2O retrieved from external-cavity quantum-cascade laser heterodyne radiometer measurements

“…Thermal infrared spectral sounding in the 3-5 and 8-12 μm atmospheric windows, where atmospheric trace gases exhibit strong fundamental rovibrational bands, is an effective method already widely used in currently operating passive remote sounding instruments [1]. Quantum-cascade laser heterodyne radiometry (QC-LHR) offers the potential for the development of extremely compact and lightweight thermal infrared sounders that combine high spectral resolution (<100 MHz or 0.003 cm −1 ), high spatial resolution due to coherent field of view (FOV), and high sensitivity (ideally close to shot-noise-limited operation) [2,3].…”