UMD AOSC Seminar

Ozone Profile and Tropospheric Ozone Retrievals from Hyperspectral Backscattered Ultraviolet Measurements

Dr. Xiong Liu

Goddard Earth Sciences & Technology Center, University of Maryland, Baltimore County
Harvard-Smithsonian Center for Astrophysics
NASA Goddard Space Flight Center

Ozone profiles have been retrieved from backscattered ultraviolet radiances measured by Nimbus-4 BUV, Numbus-7 SBUV, and a series of SBUV/2 instruments since 1970. Because measurements are taken sequentially at 12 discrete wavelengths, vertical ozone profile information is limited to 1-20 hPa (20 hPa-surface ozone column and total ozone column are well retrieved). To retrieve tropospheric ozone, various techniques have been developed since 1990 to extract Tropospheric Ozone Column (TOC) using residual-based techniques, subtracting measured/derived Stratospheric Ozone Column (SOC) from the TOMS Total OZone column (TOZ). Due to poor spatiotemporal resolution/coverage or inadequate accuracy in SOC data, most of the TOC products (priori to the AURA launch) are monthly mean in the tropics.

Since 1995, hyperspectral instruments (e.g., GOME, SCIAMACHY, OMI, GOME-2) have been flown to measure backscattered ultraviolet radiances. The moderate spectral resolution and high signal to noise ratio make it possible to extend the ozone profile information to the troposphere. We have developed an algorithm to retrieve ozone profile (including tropospheric ozone) as well as a number of trace gases (e.g., BrO, SO2) from GOME and OMI measurements using the optimal estimation technique. Due to detailed radiometric and wavelength calibrations and accurate forward model simulations, radiances in the Huggins bands can be fitted to the 0.1% level so that weak tropospheric ozone information can be extracted. The retrievals provide more accurate estimates of stratospheric ozone compared to SBUV retrievals. In addition, the retrievals have sufficient accuracy in the troposphere to see ozone perturbations caused by convection, biomass burning, anthropogenic pollution, stratosphere intrusion, and track their transport spatiotemporally. TOZ, SOC, and TOC can be retrieved with retrieval errors typically in the few Dobson unit range at solar zenith angles less than 80. SOC can be retrieved accurately with errors smaller than those from current limb instruments. This algorithm will be used as the basis for the version 9 algorithm to retrieve total ozone, ozone profiles, SO2, from TOMS, SBUV and future hyperspectral backscattered ultraviolet measurements.

In this presentation, I will give a brief introduction to this retrieval algorithm and retrieval characteristics (e.g., retrieval averaging kernels, retrieval errors), and show retrievals from GOME and OMI, validation against other correlative measurements, and evaluation of chemical transport models. Finally, future work will be discussed.

September 3, 2009, Thurday

Seminar: 3:30-4:30pm

Computer and Space Sciences (CSS) Building, Auditorium (Room 2400)
Refreshment is served at 3:00pm in the adjoining Atrium

[Contact: Russ Dickerson]
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