Satellite oberservations

Satellite observations

Satellite based atmospheric observations have many applications in the areas of weather prediction, climate research, air quality monitoring and security.

R&D Satellite Observations

The Satellite observation department at KNMI studies the composition and dynamics of the global atmosphere using satellite observations of trace gases, aerosols, clouds, and winds. Satellite instruments used within our department include OMI, GOME-2, SCIAMACHY, SEVIRI and ASCAT. We are also performing work in in preparation for the upcoming TROPOMI, ADM-Aeolus and EarthCARE missions.

We prepare new satellite missions, develop calibration and retrieval algorithms, and process and distribute data products to users via the TEMIS, MSGCPP, and Scatterometer data portals. Our data products are used for weather forecasting, climate analysis, environmental monitoring as well as many other atmospheric research studies. To evaluate satellite observations we also operate ground-based instruments and have organized specific campaigns in cooperation with other KNMI departments and numerous external partners (for example the CINDI-2 campaign held at the Cabauw measurement site).

Our division holds the Principal Investigatorship for OMI, launched in 2004 on NASA's EOS-Aura satellite, and for TROPOMI, to be launched in 2017 on ESA's Sentinel-5 Precursor satellite. We also perform work in preparation of the new atmospheric composition satellite missions Sentinel-4 and Sentinel-5. Our projects are often conducted in collaboration with various national and international partners, and are funded by both national and international agencies, including NSO, EUMETSAT, ESA, and the EU.

More information can be found in the department brochure. The older atmospheric composition department web portal can be found here.

The group
The people behind the science.
Air quality and Ozone
Left: OMI global Nitrogen dioxide measurements. Right: Gome-2 Ozone measurements.
Winds and cloud observations.
Left: Scatterrometer derived surface winds. Right: SEVIRI cloud products.

Themes

Air quality and emissions

Air quality is determined by the presence of short-lived trace gases, mainly O3 and NO2, and aerosols, which affect human health and climate. We perform retrievals of tropospheric NO2 from OMI and GOME-2, which are assimilated in global and regional air quality forecast systems. NO2 and CH4 satellite data are also used to determine the sources and strengths of emissions in a top-down approach.

Clouds, aerosols, and radiation

Clouds are strong regulators of the Earth's radiative balance, and play a key role in the hydrologic cycle by determining precipitation and evaporation. We determine cloud physical properties and solar radiation using the CPP algorithm from SEVIRI and AVHRR for nowcasting, climate monitoring, and model evaluation. For cloud correction of trace gas retrievals, we determine cloud height from O2 A-band spectra using the FRESCO algorithm applied to GOMEGOME-2, SCIAMACHY and plan for its application to TROPOMI data.

Aerosols are an important component of air pollution and affect the radiative balance of the Earth. For aviation, volcanic ash is an important threat. We monitor absorbing aerosols, like volcanic ash, desert dust and smoke using UV, visible and IR radiation. In cooperation with other KNMI departments, the group operates a UV-polarization lidar at Cabauw which has proved to be useful for the detection and quantification of profiles of ash mass concentrations. KNMI also operates an advanced multiwavelength Raman Lidar for cloud and aerosol studies.

Active remote sensing is needed to determine the vertical structure of clouds and aerosols. For ESA’s EarthCARE mission (launch 2018) we are developing lidar algorithms and developing high-quality synthetic data for EarthCARE L2 algorithm development and testing.

Ozone and UV

Ozone in the stratosphere is the Earth's natural shield for the damaging UV radiation from the sun. However, ozone is also an air pollutant when it is close to the surface (smog) and an important greenhouse gas when it is around the tropopause. We measure ozone using UV satellite measurements and make global ozone data products: total ozone, ozone profiles, and assimilated total ozone. On the basis of satellite ozone measurements we provide UV forecasts. Data can be found on the TEMIS website.

Winds measured from space

Winds can be measured from space by several types of active remote sensing instruments, for example by Wind Scatterometers (radar) or by Wind Lidars (laser). The R&D Satellite Observations department at KNMI is involved in many projects involving wind retrievals.

A wind scatterometer is a radar instrument mounted on a weather or research satellite which emits pulses of energy (centimeter radio waves) to the sea surface and then measures the energy scattered by centimeter waves on the sea surface. Wind speed and direction can be derived from this backscatter signal. We provide scatterometer ocean wind vector products operationally in near-real time (i.e., winds are computed and distributed as soon as the raw satellite data are received) and as climate data records. For the latter, special attention is paid to the temporal stability and uniform calibration of data from different instruments. For more information and an overview of our activities on wind scatterometry.

A Doppler Wind Lidar emits a laser beam into the atmosphere and detects the reflection from molecules, aerosols and cloud droplets, depending on laser wavelength. The frequency of the reflected light will be slightly shifted due to the movement of the particles, the so-called Doppler shift. The frequency shift is a measure for the particle speed and hence for the ambient wind speed. The time delay between emitted and received laser light allows the retrieval of wind profiles using this technique. ESA's Core Earth Explorer Atmospheric Dynamics Mission (ADM-Aeolus) will be the first instrument to provide a three-dimensional global coverage of wind observations.

Climate and atmospheric composition

It has been established by the IPCC that it is extremely likely that more than half the observed increase in global average surface temperature from 1951 to 2010 was caused by anthropogenic factors. The most important of these influences is the change in the chemical composition of the atmosphere due to anthropogenic emissions of greenhouse gases like CO2 and CH4. Anthropogenic emission of short-lived trace gases, like NO2 and HCHO, lead to a change in heating rate of the atmosphere via tropospheric ozone formation. Anthropogenic emission of aerosols can either cool or heat the atmosphere. Clouds are an important natural feedback factor, since clouds mostly cool the surface. Our satellite data products contribute to climate monitoring.

Ground-based Measurements

Ground-based measurements are performed to compliment and evaluate satellite-based measurements.

  • Brewer Spectrometer: The Brewer spectrophotometer measures ultraviolet sunlight at 6 wavelengths between 302 and 320 nm. The extinction of sunlight by ozone varies hugely with wavelength in this part of the spectrum. From these measurements the total ozone content of the atmosphere above De Bilt is computed.   Another Brewer whose data is processed by KNMI is installed at Paramaribo (Surinam).
  • Ozone sonde: An ozone sonde is a balloon borne instrument that measures ozone concentration in situ between the ground and 32 km altitude.  Ozone sondes are launched at least once a week. Additional sondes are also launched for satellite validation. Weekly ozone sondes are also launched in Paramaribo.
  • NO2 sonde: For tropospheric NO2 validation an NO2 sonde has been developed at KNMI . This sonde is a balloon borne NO2 sensor, which measures the vertical distribution of NO2. The NO2 sonde is used extensively during validation campaigns, like CINDI, PEGASOS, DISCOVER-AQ, AROMAT, and CINDI-2.
  • MAX-DOAS: We perform MAX-DOAS measurements to measure the tropospheric NO2 column from the surface. Recently, a Pandora instrument was installed, and used for the first time during the CINDI-2 campaign.
  • Lidars: In cooperation with other departments a cloud/aerosol UV-polarization lidar and the Caeli (CESAR Water Vapour, Aerosol and Cloud Lidar) Raman lidar are operated at Cabauw.

 

Basic Research

In addition to the work described above, the group conducts supporting but more general research in the areas of:
  • Radiative transfer modelling.
  • Cloud-aerosol interaction studies.
  • Retrieval algorithm development.
  • Transport modelling.

 

 

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