Task 255

Advanced Retrieval of Ozone, Sulfur Dioxide, and Volcanic Ash from NASA A-Train Satellite Instruments

Principal Investigator(s):

Kai Yang (UMCP)


Nickolay A. Krotkov (GSFC/NASA)

Last Updated:

October 26, 2012 15:26:18

Description of Problem

Ozone (O3) and sulfur dioxide (SO2) are trace gases that have important effects on climate and air quality. The spatiotemporal distributions of these trace gases, which can be measured by space-borne ultraviolet (UV) instruments, provide essential information needed to monitor their changes over time and space, estimate their climate and pollution impacts, and understand the chemical and physical processes in the atmosphere. SO2 is also a unique marker of explosively injected volcanic plumes, which pose a significant threat to aircraft. Tracking volcanic plumes in near-real-time provides critical information for aviation hazard mitigation.

Scientific Objectives and Approach

The ESSIC investigator has developed and implemented a number of techniques for accurate retrievals of O3 and SO2 from UV measurements simultaneously and for near-real-time mapping and tracking of volcanic eruption clouds. The main objective of this research is to improve O3 and SO2 retrievals by taking full advantage of hyper-spectral backscattered UV radiance measurements.


In this year, considerable efforts are invested in the improvement and maintenance of the OMI data products. Specifically we have developed and implemented common approaches that can be applied to different OMI retrievals, including OMI ozone profiles and the direct spectral fitting (DSF) OMI SO2 product.

The first approach is the accurate accounting of the instrument degradation over time. Many OMI products, such as the ozone profile and the DSF SO2, are derived using a composite solar irradiance based on the OMI solar measurements in the first year of OMI operation. Doing so neglects the instrument degradation over time, resulting in bias in the products. To remove this bias, we have conducted a thorough analysis of the all the daily OMI measured irradiance since the start of its operation, and have derived the instrument degradation over time for all the wavelengths and all the cross-track positions.

The second approach to improve OMI product quality is the implementation of new Ring effect correction scheme based on Dr. Spurr’s LIDORT-RRS radiative transfer computation. Specifically using LIDORT-RRS, we have built a set of master tables and developed a set of Fortran 90 codes to efficiently use them to correct the Ring contributions to the measured radiance data from BUV instruments, such as OMI and OMPS. This approach can account for the Ring contributions more accurately under a diverse range conditions including variations in ozone amount, surface pressure, surface albedo, and viewing and illumination angles, leading to higher quality ozone and SO2 products.