Monday, April 2, 2012

Four Decades of Ozone Measurement from Space


Maniac Talk by P.K. Bhartia -- March 28, 2012

A "story teller" is what I would call our Maniac talk speaker Dr P. K. Bhartia. Dr. Bhartia has been involved with the remote sensing of ozone for many years. In this exciting series of Maniac talks, Dr Bhartia's talk was yet another rare and complete story of its own kind. Woven together meticulously, he presented the history, science, and technicality behind satellite-based retrievals of total column ozone amount from the past 45 years. 

He began by introducing early ground-based measurements by Dobson based on the sun-photometry technique. Next he moved on to the theoretical work of Dave and others in the 1960s, which established the possibility of ozone remote sensing from space and introduced concepts such as Lambert-equivalent reflectivity, which are still in use today for applications not envisioned when they were created. From there he discussed the Total Ozone Monitoring Spectrometer (TOMS), which has flown on several satellites, and related instruments.

The last section of his talk concerned the discovery of the Antarctic ozone hole by Joe Farman and colleagues in the early 1980s, and the story of its confirmation and monitoring with the TOMS data, including the trials and tribulations which happened while trying to confirm whether or not this unexpected (at the time) phenomenon was real.

Dr. Bhartia offered a chance, probably the first for many in audience, to look through the lenses of a retrieval expert on how NASA both did and did not discover the famous Antarctic "Ozone Hole" from its satellite observations. It turns out that Dr Bhartia and his colleagues did see very low ozone values from the TOMS instrument in summer of 1984 when they processed the data from October 1983 (due to available computer power at the time, there was a considerable lag between data acquisition and processing). The data was quickly scrutinized and instrument, algorithm and satellite errors were ruled out. For the lack of agreement between ground based S. Pole data and the satellite observations, and the lack of a priori ozone profile for low ozone concentration (below 225 DU), the satellite algorithm flagged out the low Ozone retrievals!  In August of 1985, Dr Bhartia presented these results at the Symposium on Dynamics and Remote Sensing of the Middle Atmosphere held in Prague. However, the results were not published as they were thought to be a meteorological anomaly of some sort. This story behind the story of Ozone hole was a unique peek into a very interesting regional phenomenon that was discovered, recognized, and mitigated to avoid a global impact. The speaker, Dr Bhartia, very conscientiously made his point on how important it is for us to learn the lessons from history, and insure our future with regards to climate change!
by Falguni & Andy --- Edited by Pawan

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