Blog

Retrieving aerosol height and tropospheric NO2 from OMI – Ebook Thesis online!

PhDBook
Research Thesis book cover – Julien Chimot – July 2018

Almost 3 months ago, on 2018.10.10, I had the privilege to defend my research thesis at Delft University Of Technology. A big moment after 4 years of intensive collaboration with my colleagues of Geoscience & Remote Sensing Department and KNMI and in the presence of several friends and relatives. An very strict protocol to follow according to the Dutch rules and tradition.

My thesis book is now available online as an Ebook here! Feel free to have a look if you are interested by aerosol layer height retrieval, UV-Vis satellite measurements such as OMI, tropospheric NO2, air quality and climate observations. My main papers are concatenated there.

Enjoy the reading!

Seeing electricity energy through night-time pictures

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Night-time pictures of of 2018.10.07 observed by the NASA SUOMI NPP VIIRS sensor. Credit NASA Worldview Earthdata

I am never tired of watching at night-time pictures from NASA SUOMI satellite worldview. We can directly observe how much our western societies depend on electricity.

While the last Intergovernmental Panel on Climate Change (IPPC) report just got released, and stresses the urgency to act extremely quickly for limiting the global warming close to 1.5 deg, one should keep in mind that the worldwide electricity sector is one of the highest source of CO2  – Carbon dioxide released in the atmosphere. Do we want to keep our lights on? Let’s ban then coal gas & use electricity sources with low CO2  – Carbon dioxide emissions (including nuclear!).

 

More information?

  • The last IPCC report here
  • NASA-NOAA Satellite Reveals New Views of Earth at Night here

More than 20 years of satellite NO2 observations!

More than 20 years of Tropospheric NO2 satellite observations that we have now thanks to the great investments of Europe and all scientists. An example with the month of March GOME on ERS-2 (from the European Space Agency ESA) in 1998 & TROPOMI on Sentinel 5-Precursor (from Copernicus) in 2018. Maps are from TEMIS website.

Analyses of the trends is possible but overall a challenging and sensitive task. Over 20 years, very different sensor techniques, instrument specificities & degradations, variable pixel sizes, cloud detection possibilities etc… A lot of works to harmonise these data!

 

More information?

  • TEMIS website here
  • The European Copernicus program here
  • The European Space Agency here
  • NO2 – Nitrogen Dioxide WebPage here

Just another Day on Aerosol Earth by NASA – A well-done picture highlighting the very diverse aerosol types and their heterogeneous distributions!

Just Another Day on Aerosol Earth
NASA Earth Observatory images by Joshua Stevens, using GEOS data from the Global Modeling and Assimilation Office at NASA’s Goddard Space Flight Center (Credit NASA, https://earthobservatory.nasa.gov/images/92654/just-another-day-on-aerosol-earth).

 

Have you seen this very recent visualisation aerosol mapping, released by NASA and made by Joshua Stevens? This visualisation very nicely highlights the different aerosol types and their complex distribution on Earth for a single day, 23rd August 2018, based on the GEOS FP model output. Some satellite observations were assimilated to constrain the modelling of atmospheric transport and physical processes.

Atmospheric aerosol are particles suspended in the air. Their sources are very mixed. Aerosol can be man-made or natural: e.g. smoke, desert dust, sea spray, nitrates and sulfates. The aerosol effects on the sunlight modify the shortwave radiation field in the atmosphere. This directly impacts the climate and the satellite observations devoted to ocean surface, land surface, vegetation, and atmospheric gases. Furthermore, heavy load of aerosols affects our air quality.

In spite of many progresses during the last 10-20 years, aerosol observations from space-borne instruments remain incredibly complex. One of the main reasons is their heterogeneity: aerosols are everywhere, but with very variable quantities  spatially (horizontally and vertically!), and temporally. And, as highlighted by this NASA picture, aerosol types are also very heterogeneous! Retrieving all these parameters from single satellite measurements, without ambiguity with respect to surface characteristics and clouds, is the difficult task of the scientists working with atmospheric satellite measurements. Many works to continue to do…

 

More information

  • NASA WebPage “Just another Day on Aerosol Earth” here
  • Aerosol WebPage here

A new paper submitted – Minimizing aerosol effects on the OMI tropospheric NO2 retrieval – An improved use of the 477 nm O2-O2 band and an estimation of the aerosol correction uncertainty

We recently submitted a new paper in the Atmospheric Measurement Techniques (AMT) journal. This work relies on the activities achieved during the last months with my colleagues of the Geoscience and Remote Sensing (GRS) department of TU Delft and KNMI: Dr. J. Pepijn Veefkind, Dr. Johan de Haan, Dr. Piet Stammess, and Prof. Dr. Pieternel  F. Levelt.

This paper is based on the last developments we published during 2016, 2017, and 2018. During these years, not only the OMI cloud algorithm was improved (Veefkind et al., 2016), but also an OMI aerosol layer height (and optical thickness) neural network algorithm was developed (Chimot et al., 2017, 2018). This time, we directly evaluate the impacts of these developments to correct of aerosol absorption and scattering effects in the visible spectral range in view of retrieving tropospheric NO2, an important trace gas affecting air quality in urban and industrialised areas.

Gotten curious? See more information here.

I greatly thank my co-authors from the Netherlands for this very interesting work! This paper closes the loop of my whole research work achieved during the last 4 years with the Geoscience and Remote Sensing (GRS) department of TU Delft and KNMI.

All_NO2Diffs_OMCLDONew
Statistics of relative tropospheric NO2 VCD changes in (%) in 2006-2007, due to differences between the different explicit aerosol corrections and the implicit aerosol correction based on OMCLDO2-New: (a), and (b): China summertime (June-July-August), (c), and (d): China wintertime (December-January-February), (e), and (f): South America biomass burning season (August-September).

Sentinel-3 B launch in live from EUMETSAT

We attended the launch of the second satellite platform of the Sentinel-3 mission. An event in live was organised at EUMETSAT, and what a blast!

Check the pictures here.

As part of the Copernicus programme, Sentinel-3 is a very important mission for ocean colour, sea and land surface, fire, atmosphere and climate purposes. With the two platforms, Sentinel-3 A and B, an optimal global coverage will be now obtained. The next observations and related products are promising!

More information?

  • Check the diverse pictures of this fantastic launch via the Twitter accounts of EUMETSAT and ESA
  • Sentinel-3 satellite mission here
  • The current Sentinel-3 services provided by EUMETSAT here

And watch below the movie from EUMETSAT in live in the Sentinel-3 control centre “Sentinel-3: Operating satellites” with Hillary Wilson, EUMETSAT’s Sentinel-3 manager, and Kevin Marston, EUMETSAT’s System operation manager.

A new paper published on OMI aerosol layer height retrieval from the O2-O2 visible band and neural networks – Comparison with CALIOP aerosol spatial patterns

I am very glad to have a new paper recently published in the Atmospheric Measurement Techniques (AMT) journal. This paper relies on a research work achieved during the last months with my colleagues of the Geoscience and Remote Sensing (GRS) department of TU Delft and KNMI: Dr. J. Pepijn Veefkind, Dr. Tim Vlemmix, and Prof. Dr. Pieternel  F. Levelt.

This paper is based on the work of 2017, in which a neural network algorithm was developed for retrieving aerosol layer height (ALH) from the OMI O2-O2 visible measurements. This time, we directly compare our retrievals with CALIOP aerosol observations and evaluate the spatial patterns on several remarkable case studies including urban pollution, biomass burning events and a Saharan dust outbreak!

Gotten curious? See more information here.

I greatly thank my co-authors from the Netherlands for this very interesting work!