Don’t miss #GRS_TROPOMI event, a series of post on “why are we excited this week about #TROPOMI #Sentinel5P launch?!”


Why are we (I and my colleagues) that excited this week? Why is TROPOMI so much important for the new coming era in air quality & climate satellite era?

Throughout the week, we will post more information on our GRS TU Delft website and also be using the #GRS_TROPOMI on social media (Twitter and Instagram) as we explain more about the mission, its goals, and how it all works in relation to the goals and work being done in our department. The week will culminate with the Sentinel-5P launch event taking place at the Space Expo in Noordwijk.


More information?


20th OMI Science Meeting at NASA Goddard Space Institute

During 3 days, from 12 to 14 September 2017, I had the pleasure to attend, with my KNMI colleagues from the R&D satellite department, the 20th OMI Science Team Meeting hosted by NASA Goddard Space Institute in Greenbelt MD (close to Washington DC) in the USA.

Group picture at NASA, Goddard Space Institute, Greenbelt MD, Virginia, USA, 2017.09.13 in front the morning and A-Train satellite constellation, with all our OMI colleagues.

Despite its quite advance age for a satellite mission (13 years old!), OMI is still delivering remarkable measurements about our atmospheric composition and air quality. So many talks and discussions on the aerosol global record over cloud-free scenes and above clouds, decade global volcanic SO2 – Sulfur dioxide missions, the use of OMI data by air quality model simulations to inform air quality policy, the case studies on emissions monitoring and to support authorities and clean-tech industry, the new generation of the Quality Assurance For Essential Climate Variables (QA4ECV), the evolution in the ozone trends and related mechanisms, and of course the future with the forthcoming TROPOMI (Sentinel-5 Precursor) mission, TEMPO (NASA Geostationary) and TROPOLITE.

I was honoured to present the status of our work on the retrieval of aerosol layer height from the OMI visible band using machine learning technique, and the results with single day CALIOP aerosol along-track observations.

Chimot J., Veefkind P., van Ouwerkerk G., Vlemmix T., Levelt P., Aerosol layer height retrieval from OMI and neural network- Possibility for a 13-year time series?, 20th OMI Science Team Meeting, NASA Goddard, Greenbelt MD, Virginia, USA, 2017.09.12 (Source:

Several nice social moments accompanied us during these 3 days:

  • The Nationals baseball game on Wednesday 13th September evening in Washington DC
  • The guided tour by NASA during lunch break, a great opportunity to see the control rooms of the Aura (OMI spacecraft!!), Aqua and Landsat missions!


I am very grateful to all the organizers for this inspiring meeting, and my current promotors (Dr. Pepijn Veefkind, Prof. Dr. Pieternel Levelt & Dr. Tim Vlemmix)!

In spite of being glad of having been part of this adventure, I cannot stop myself thinking this may have been my very last OMI conference, before finishing my current research project and starting new professional & personal adventures (still in satellite & atmospheric community of course!). But this last point will be specifically mentioned later in future weeks. Stay tuned!


More information?

Preparing TROPOMI to join OMI in space in Autumn 2017

Loading Sentinel-5P (Source:
S5P leaves UK
Moving Sentinel-5P on its way from Airbus Defence & Space in Stevenage, UK, to Standsted airport (Source:

Finally, that’s official! TROPOMI, on-board Sentinel-5 Precursor, the 1st European operational satellite mission devoted to air quality, ozone & climate monitoring, should be launched within the next weeks. And this looks very impressive!

What are the new signs? The Sentinel-5P campaign kicked off, the satellite left UK to Russia some days ago, and several media allow to follow it (through ESA blogs and Twitter accounts). All of these new elements have appeared just some days before our very soon 20th OMI Science Team Meeting focused on the last 13-year developments and data sets.

Let’s keep the fingers crossed that OMI can continue to fly and acquire new observations together with its successor TROPOMI. Autumn 2017 promises to be a very exciting season for our community!

More information?

  • TROPOMI WebPage here
  • OMI WebPage here
  • Sentinel-5P launch campaign kicks off on ESA blog here
  • Farewell to Sentinel-5P on ESA blog here
  • The 20th OMI Science Team Meeting WebPage announcement here


Neural Network, NO2 and aerosol height retrievals at the next 20th OMI Science Team Meeting at NASA, USA

© Rendering of Ozone Monitoring Instrument (OMI) on board of AURA in flight (Source:

The 20th OMI Science Team Meeting will be held at NASA Goddard in Greenbelt MD, USA from Tuesday September 12 through Thursday September 14, 2017. With nearly 14 years of data and the impending launch of TROPOMI on board-Sentinel-5 Precursor, there is much to discuss within the OMI (& TROPOMI) team and user community regarding the current state of OMI, trends and longer-terms records, comparisons with (satellite) data sets, and the validation of OMI data. This meeting will highlight recent OMI results as well as address research plans and program goals for the coming year.

On Tuesday afternoon, at 14:00 during the aerosol – cloud session, I will have the great opportunity to present the status of our activities. In particular, focus will be on the development, application and validation of the OMI aerosol layer height retrieval based on a neural network (i.e. machine learning) approach, and the correction of aerosol radiation effects in the OMI tropospheric NO2 observations.

Gotten curious? See you there then!


More information?

Measuring CO2, temperature and humidity in our office



Since beginning summer, tests and works have been undertaken at our office at the Geoscience & Remote Sensing (GRS) department of TU Delft to improve temperature conditions while working. In order to support these tests, some measurements have been acquired.

And it is still very interesting to observe not only the temporal variability of temperature, CO2 – Carbon dioxide concentrations and relative humidity but also the apparent nice correlations between them! Especially, CO2 in our office and temperature seem to follow similar diurnal variation. Of course, these variables, at a such local scale, are also strongly dependent on external parameters such as wind transport, the number of people present in the room, whether the windows are open etc…


More information?

  • CO2 – Carbon dioxide, an important greenhouse gas and its impacts on our changing climate here


“Our house is burning and we are looking somewhere else” said French president Jacques Chirac in 2002 – Fires from Canada to Greenland in 2017

“Our house is burning and we are looking somewhere else. Nature mutilated, overexploited is not able to recover and we refuse to admit it. From North to South, it suffers from ill-development, and we are indifferent. Earth and humanity are in great peril and we are accountable” (from my own English translation).

Those were the words pronounced by our former French president in 2002 in Johannesburg (South-Africa) in 2002 during the Earth summit. The real French words pronounced were the following: “Notre maison brûle et nous regardons ailleurs. La nature, mutilée, surexploitée, ne parvient plus à se reconstituer et nous refusons de l’admettre. L’humanité souffre. Elle souffre de mal-développement, au nord comme au sud, et nous sommes indifférents. La terre et l’humanité sont en péril et nous en sommes tous responsables.”

Jacques Chirac, former French president of the Republic (1995-2007), at the Earth summit in Johannesburg in 2002 pronouncing the famous statement “Our house is burning and we are looking somewhere else”.

At that time, large wildfires were ravaging Australia and societies were debating on the responsibility of climate change. 15 years later, 2017, these words are somehow ringing a bell to me. When looking at all the twitter posts during the last 2 months, we quickly get the feeling that Earth is on fire.

Not only, British Colombia (Western Canada) is facing one of its worst wildfire season, France and other European countries (Portugal, Greece, Croatia) have been victims of raging forest fires this Summer, wildfire episodes are increasing in eastern Russia, but also a fire sparked in Greenland the last weeks, an odd occurrence for this island more known for ice.

Kalamos fires, in Greece, in August 2017 as seen by the COPERNICUS Sentinel-2 data (Source:

A series of blazes has burned in the vicinity of Kangerlussuaq, a small town that serves as a basecamp for researchers in the summer to access Greenland’s ice sheet and western glaciers. The largest fire has burned roughly 3,000 acres and sent smoke spiralling a mile into the sky, prompting hunting and hiking closures in the area, according to local news reports. There’s no denying that it’s weird to be talking about wildfires in Greenland because ice covers the majority of the island. Forests are basically non-existent and this fire appears to be burning through grasses, willows and other low-slung vegetation on the tundra that makes up the majority of the land not covered by ice.

Smoke from the Greenland fire seen in satellite images
copernicus sentinel -2b/pierre Markuse/ESA (Source:

Most of Greenland is covered by ice up to 3 kilometres thick but there is some tundra around the coastline. The wildfire is burning on tundra in the west of Greenland, near the small town of Sisimiut. The larger fire could be a result of melting permafrost, McCarty told Wildfire Today. As the once-frozen ground melts, the upper layers can dry out and become flammable if they are full of organic matter. Stef Lhermitte, a remote sensing expert at the Geoscience & Remote Sensing department (GRS) of Delft University of Technology (TU Delft) in the Netherlands, said there is evidence of fires burning in Greenland over the past 17 years of MODIS satellite records kept by NASA.

“It certainly is the biggest one in the satellite record,” says remote-sensing scientist Stef Lhermitte of Delft University of Technology in the Netherlands. That record only goes back to 2000, but it could well turn out to be the biggest wildfire in Greenland’s history. The fire, first spotted by a pilot on 31 July, has taken researchers by surprise.  His initial analysis of satellite observations suggests there have been a few small wildfires in Greenland since 2000 but that over the past three years there has been a huge increase in the area burning.

Smoke spotted over Greenland by plane (Source:


No doubt then that our house is burning. The question now is: where are we looking?


More information?

  • Canada wildfires from space and ground – Seeing beyond the flames: a series of observations here
  • Wildfires in French Mediterranean region observed from MODIS here
  • Stef Lhermite research: website & Twitter account
  • Video “Our home is burning” by former French President Jacques (subtitles in English) at the Earth summit in Johannesburg in 2002 here
  • Largest ever wildfire in Greenland seen burning from space here

  • There’s a Wildfire Burning in West Greenland Right Now, from Climate Central, here
  • Smoke and fire spotted spotted on 31st July 2017 by plane here

Canada wildfires from space and ground – Seeing beyond the flames: a series of observations

Since July, the province of British Columbia (BC), west coast of Canada, has been impacted by massive and violent wildfires. Such events are visually impressive. They can be a constructive force by maintaining the overall health and functioning of the forest ecosystem, but also a destructive force due to devastating impacts on the local population, soil and our atmosphere: e.g. visibility reduction, air quality deterioration caused by smoke fine particles (aerosols) that are harmful for health population and on a longer term, climate.

Left: the view over the Haro Strait on a typical summer’s day. (Source: Cordova Bay Golf Course) Right: the view on 4 August, 2017. (Photo: Alexander Izett)

These effects can easily be seen by different “eyes”. While BC is known for its clean, fresh air, the visibility reduction occurs as the increased concentration of smoke particles leads to more extinction of the sunlight passing through the atmosphere. This results in the formation of haze and the dark grey smoke that we see. The particles can also attract water, acting as condensation nuclei for droplet formation and a subsequent further reduction in visibility as fog and clouds form.

The Vancouver skyline and surrounding mountains obscured by haze, as seen from the Tsawwassen Ferry Terminal. (Photo: Jonathan Izett; 18 July, 2017)
Smoke accumulating in the Coastal Mountain range.        (Photo: Jonathan Izett; 1 August, 2017)
The sun through the smoke near Victoria, BC (Photo: Alexander Izett;              5 August, 2017)


Although the fires themselves are fairly localized in the interior of BC, their overall impact is not, with the smoke traveling far away from the source region – up to thousands of kilometers! Atmospheric and fire emission models are used to predict the amount and trajectory of smoke according to the prevailing circulation and dispersion patterns allowing for air quality forecasts and warnings, such as the Government of Canada’s wildfire smoke prediction system: FireWork.

FireWork forecast of small particulate matters (PM2.5) concentration at the surface level from forest fire sources for 0000 UTC on 12 August, 2017. Notice the particles are carried far from their origin in central BC: to northern and central Canada; the US mid-west; and along the west coast of North America, all the way to Mexico (Source:

Satellite observations are vital to monitor such disasters. Not only do they provide an overview image from the top of the atmosphere of the raging fires, which already gives spectacular maps, they also allow detection of the substances released in the air by these episodes and follow their dispersion. This is vital for predicting the impact of air masses far away from the fire sources. Below are some illustrations of these satellite maps over the last 10 days.

Natural-color images from MODIS-Aqua sensor, over east Canada within the period of 2017.07.31-2017.08.08. Red points indicate actively burning areas identified from MODIS, on-board Terra and Aqua platforms. Smokes stretch very far away from these points  (Source:

Optical images like MODIS sensors (on-board Terra & Aqua platforms) capture the thick smokes directly linked to the fires: such plumes can extent to several hundreds thousands of kilometres. Moreover, measurements in thermal infrared spectrum allow detection of the actively burning areas.

Aerosol particles, suspended in air, monitored via MODIS-Aqua sensor, over east Canada within the period of 2017.07.31-2017.08.08. Here, the Aerosol Optical Depth (AOD) is plotted, a proxy of aerosol load or amount. Values are in the range of 0.5 (yellow-orange) – 2 (dark red – large amount of particles)  (Source:

The integrated amounts of aerosol particles that are suspended in the atmosphere can be quantified, and their horizontal distribution monitored. This is an important input for air quality models in charge of predicting the air quality for populations.

Some satellite sensors can distinguish some aerosol – particle – types. Here, the so-called UVAI index derived from the OMI-Aura sensor, over Canada within the period of 2017.07.31-2017.08.08, indicate in orange-red a large presence of very dark (i.e. absorbing) particles (UVAI values in the range of 2-5) (Source:

Knowing the type of these particles (i.e. whether they are dark or brighter) is of great importance for scientists and researchers. This directly gives insights on how these aerosols affect our atmosphere radiation, and consequently our climate on the long-term. Satellite sensors measuring light in the UV such as the Dutch-Finnish OMI mission, on-board the NASA Aura platform, provides with an important index (here named UV Absorbing Index or UVAI) to identify absorbing (i.e. very dark) aerosol particles on a daily-global coverage.

CO – Carbon monoxide total column from IASI sensor, on-board Metop-A, [1×10^18 molec/cm2] (Source:

Finally, wildfires do not only release smoke and particles, which already pose a problem for human respiratory health, but also a mix of toxic gases. One of the most important is CO – Carbon monoxide. Infrared sensors such as the European IASI mission, on-board Metop-A and B, quantify everyday the amount of CO present in the atmosphere. On some specific days in August, concentration values were comparable to those associated with African and South-American fires.

Many more compounds can be additionally measured over wildfires: CO2 – Carbon dioxide, NO2 – Nitrogen dioxide for some specific fire episodes etc…


This post was written by Julien Chimot and my colleague Jonathan Izett. Find more information on Jonathan via his Linkedin profile, and his website on his research work focused on the formation, evolution and prediction of fog in the atmospheric boundary layer.


More information?:

  • Government of Canada’s FireWork forecast here
  • BC Air Quality Health Risk here
  • NASA satellite images available on Worldview website here
  • IASI CO products available on the EUMETSAT Atmospheric COmposition Satelite Application Facilities (AC SAF) here
  • The UVAI index, identifying dark / absorbing particles, from OMI sensor here
  • OMI WebPage
  • Global news on British Columbia wildfires in Canada here
  • Aerosol particles WebPage
  • CO – Carbon monoxide WebPage
  • NO2 – Nitrogen Dioxide WebPage
  • Wildfires observed in France by MODIS WebPost