Martin de Graaf

Koninklijk Nederlands Meteorologisch Instituut | KNMI

The purpose of this study is to investigate the ability of the Sentinel-5P TROPOspheric Monitoring Instrument (TROPOMI) to derive accurate geometrical features of lofted aerosol layers on a continental scale. Comparisons with ground-based correlative measurements constitute a key component in the validation of passive satellite aerosol products. Fo...

Constraint of the vertical distribution of aerosol particles is crucial for the study of aerosol plume structure, aerosol radiative effects, and ultimately monitoring surface air pollution. We developed an algorithm to retrieve the aerosol optical central height (AOCH) of absorbing aerosols by using, for the first time, the oxygen (O2) A and B abso...

The representations of clouds, aerosols, and cloud–aerosol–radiation impacts remain some of the largest uncertainties in climate change, limiting our ability to accurately reconstruct past climate and predict future climate. The south-east Atlantic is a region where high atmospheric aerosol loadings and semi-permanent stratocumulus clouds are co-lo...

The ultraviolet (UV) Absorbing Aerosol Index (AAI) is widely used as an indicator for the presence of absorbing aerosols in the atmosphere. Here we consider the TROPOMI AAI based on the 340 nm/380 nm wavelength pair. We investigate the effects of clouds on the AAI observed at small and large scales. The large-scale effects are studied using an aggr...

The representation of clouds, aerosols and cloud-aerosol-radiation impacts remain some of the largest uncertainties in climate change, limiting our ability to accurately reconstruct and predict future climate. The south-east Atlantic is a region where high atmospheric aerosol loadings and semi-permanent stratocumulus clouds are co-located, providin...

The representation of clouds, aerosols and cloud-aerosol-radiation impacts remain some of the largest uncertainties in climate change, limiting our ability to accurately reconstruct and predict future climate. The south-east Atlantic is a region where high atmospheric aerosol loadings and semi-permanent stratocumulus clouds are co-located, providin...

The goal of the study described in this paper is to determine the accuracy of the radiometric calibration of the TROPOMI instrument in flight, using its Earth radiance and solar irradiance measurements, from which the Earth reflectance is determined. The Earth reflectances are compared to radiative transfer calculations. We restrict ourselves to cl...

The TROPOspheric Monitoring Instrument (TROPOMI) level-2 aerosol layer height (ALH) product has now been released to the general public. This product is retrieved using TROPOMI's measurements of the oxygen A-band, radiative transfer model (RTM) calculations augmented by neural networks and an iterative optimal estimation technique. The TROPOMI ALH...

The direct radiative effect (DRE) of aerosols above clouds has been found to be significant over the south-east Atlantic Ocean during the African biomass burning season due to elevated smoke layers absorbing radiation above the cloud deck. So far, global climate models have been unsuccessful in reproducing the high DRE values measured by various sa...

Abstract. The ultraviolet (UV) Absorbing Aerosol Index (AAI) is widely used as an indicator for the presence of absorbing aerosols in the atmosphere. Here we consider the TROPOMI AAI based on the 340/380 nm wavelength pair. We investigate the effects of clouds on the AAI observed at small and large scales. The large scale effects are studied using...

Abstract. The goal of the study described in this paper is to determine the accuracy of the radiometric calibration of the TROPOMI instrument in-flight, using its Earth radiance and solar irradiance measurements, from which the Earth reflectance is determined. The Earth reflectances are compared to radiative transfer calculations. We restrict ourse...

Before the launch of the TROPOspheric Monitoring Instrument (TROPOMI), only two other satellite instruments were able to observe aerosol plume heights globally, the Multi-angle Imaging SpectroRadiometer (MISR) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). The TROPOMI aerosol layer height is a potential game changer, since it has da...

To retrieve aerosol properties from satellite measurements of the oxygen A-band in the near-infrared, a line-by-line radiative transfer model implementation requires a large number of calculations. These calculations severely restrict a retrieval algorithm's operational capability as it can take several minutes to retrieve the aerosol layer height...

Abstract. Before the launch of TROPOMI, only two other satellite instruments were able to observe aerosol plume heights globally, MISR and CALIOP. The TROPOMI aerosol layer height is a potential game changer, since it has daily global coverage and the aerosol layer height retrieval is available in near-real time. The aerosol layer height can be use...

The Tropospheric Monitoring Instrument's (TROPOMI) level-2 aerosol layer height (ALH) product has now been released to the general public. This product is retrieved using TROPOMI's measurements of the oxygen A-band, radiative transfer model (RTM) calculations augmented by neural networks and an iterative optimal estimation technique. The TROPOMI AL...

The retrieval of geophysical parameters is increasingly dependent on synergistic use of satellite instruments. More sophisticated parameters can be retrieved and the accuracy of retrievals can be increased when more information is combined. In this paper, a synergistic application of Ozone Monitoring Instrument (OMI), on the Aura platform, and Mode...

The aim of this research is to investigate the ability of GOME-2 and TROPOMI instruments on board on the MetOp and Sentinel S5P satellite platforms, to deliver accurate geometrical features of lofted aerosol layers over the Europe. For this purpose, we use ground-based lidar data from Thessaloniki lidar station (THELISYS) belongs to EARLINET networ...

The Direct Radiative Effect (DRE) of aerosols above clouds has been found to be significant over the south-east Atlantic Ocean during the African biomass burning season due to elevated smoke layers absorbing radiation above the cloud deck. So far, global climate models have been unsuccessful in reproducing the high DRE values measured by various sa...

To retrieve aerosol properties from satellite measurements of the oxygen A-band in the near infrared, a line-by-line radiative transfer model implementation requires a large number of calculations. These calculations severely restrict a retrieval algorithm's operational capability as it can take several minutes to retrieve aerosol layer height for...

The retrieval of geophysical parameters is increasingly dependent on synergistic use of satellite instruments. More sophisticated parameters can be retrieved and the accuracy of retrievals can be increased when more information is combined. In this paper, a synergistic application of OMI/Aura and MODIS/Aqua Level 1B reflectances is described, enabl...

Operational monitoring of atmospheric gaseous and particular species of both tropospheric as well as stratospheric provenance sensed by satellite instruments are performed routinely in the Laboratory of Atmospheric Physics, Thessaloniki, Greece, using a suite of different ground based instruments. These include both a single and double Brewer spect...

The Sentinel-5 Precursor (S5P) mission, launched in October 2017, started the operational atmospheric composition measurements from space as part of the European Copernicus programme. The payload of the S5P mission is the TROPOspheric Monitoring Instrument (TROPOMI) that provides key information on air quality, climate and the ozone layer with high...

This paper presents a weighted least squares approach to retrieve aerosol layer height from top-of-atmosphere reflectance measurements in the oxygen A band (758–770 nm) over bright surfaces. A property of the measurement error covariance matrix is discussed, due to which photons travelling from the surface are given a higher preference over photons...

This overview paper highlights the successes of the Ozone Monitoring Instrument (OMI) on board the Aura satellite spanning a period of nearly 14 years. Data from OMI has been used in a wide range of applications and research resulting in many new findings. Due to its unprecedented spatial resolution, in combination with daily global coverage, OMI p...

This paper presents a weighted least squares approach to retrieve aerosol layer height from top-of-atmosphere reflectance measurements in the oxygen A band (758 nm - 770 nm) over bright surfaces. A property of the measurement error covariance matrix is discussed, due to which photons traveling from the surface are given a higher preference over pho...

Retrieving aerosol optical thickness and aerosol layer height over a bright surface from measured top-of-atmosphere reflectance spectrum in the oxygen A band is known to be challenging, often resulting in large errors. In certain atmospheric conditions and viewing geometries, a loss of sensitivity to aerosol optical thickness has been reported in t...

Marine stratocumulus clouds are important climate regulators, reflecting sunlight over a dark ocean background. A UV-depolarization lidar on Ascension, a small remote island in the south Atlantic, measured cloud droplet sizes and number concentration using an inversion method based on Monte Carlo (MC) modelling of multiple scattering in idealised s...

Short summary of the images in the video: top-left: original images top-right: FOV determined from MAX-DOAS data bottom-left: 0.1x0.1° FOV intensity data from image (synthetic test) bottom-right: 1x1° FOV intensity data from image (synthetic test) See also: https://vimeo.com/162520417

Retrieving aerosol optical thickness and aerosol layer height over a bright surface from measured top of atmosphere reflectance spectrum in the oxygen A-band is known to be challenging, often resulting in large errors. In certain atmospheric conditions and viewing geometries, a loss of sensitivity to aerosol optical thickness has been reported in l...

Global quantitative aerosol information has been derived from MODerate Resolution Imaging SpectroRadiometer (MODIS) observations for decades since early 2000, and widely used for air quality and climate change research. However, the operational MODIS Aerosol Optical Depth (AOD) products Collection 6 (C6) can still be biased, because of uncertainty...

This overview paper highlights the successes of the Ozone Monitoring Instrument (OMI) spanning more than 12 years of the OMI data record. Data from OMI has been used in a wide range of applications. Due to its unprecedented spatial resolution, in combination with daily global coverage, OMI plays a unique role in measuring trace gases important for...

Knowledge of the field of view (FOV) of a remote sensing instrument is particularly important when interpreting their data and merging them with other spatially referenced data. Especially for instruments in space, information on the actual FOV, which may change during operation, may be difficult to obtain. Also, the FOV of ground-based devices may...

Absorbing aerosols exert a warming or a cooling effect on the Earth’s system, depending on the circumstances. The direct radiative effect (DRE) of absorbing aerosols is negative (cooling) at the top-of-the-atmosphere (TOA) over a dark surface like the ocean, as the aerosols increase the planetary albedo, but it is positive (warming) over bright bac...

Aerosol optical depth (AOD) product retrieved from MODerate Resolution Imaging Spectroradiometer (MODIS) measurements has greatly benefited scientific research in climate change and air quality due to its high quality and large coverage over the globe. However, the current product (e.g., Collection 6) over land needs to be further improved. The is...

This study is to evaluate the sensitivity of Aerosol Optical Depth (AOD t) to aerosol vertical profile and type, using the Moderate Resolution Imaging Spectroradiometer (MODIS) collection 6 algorithm over land. Four experiments were performed, using different aerosol properties including 3 possible non-dust aerosol models and 14 vertical distributi...

The Ozone Monitoring Instrument (OMI) is a push-broom imaging spectrometer, observing solar radiation backscattered by the Earth's atmosphere and surface. The incoming radiation is detected using a static imaging CCD (charge-coupled device) detector array with no moving parts, as opposed to most of the previous satellite spectrometers, which used a...

Aerosol Optical Depth (AOD) retrieved from MOderate Resolution Imaging Spectroradiometer (MODIS) measurements over land, can be improved by taking into account the surface Bidirectional Reflectance Distribution Function (BRDF), as shown in a previous study (Wu et al., 2016). However, the relationship of the surface reflectance between visible and s...

The Ozone Monitoring Instrument (OMI) is a push-broom imaging spectrometer, observing solar radiation backscattered by the Earth's atmosphere and surface. The shape of an OMI pixel is not quadrangular, which is common for scanning instruments, but rather Gaussian-shaped as light from neighbouring pixels enters the Field of View (FoV). This has cons...

This paper introduces the recent EARLINET quality-assurance efforts at instrument level. Within two dedicated campaigns and five single-site intercomparison activities 21 EARLINET systems from 18 EARLINET stations were intercompared between 2009 and 2013. A comprehensive strategy for campaign setup and data evaluation has been established. Eleven s...

The aerosol direct radiative effect (DRE) of African smoke was analyzed in cloud scenes over the southeast Atlantic Ocean, using SCIAMACHY satellite observations and HadGEM2 climate model simulations. The observed mean DRE was about 30–35 Wm–2 in August and September 2006 – 2009. In some years, short episodes of high aerosol DRE can be observed, du...

The solar radiative absorption by smoke layers above clouds is quantified, using the unique broad spectral range of the space-borne spectrometer Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) from the ultraviolet (UV) to the shortwave infrared (SWIR). Aerosol radiative effects in the UV are separated from cloud r...

A method is introduced to derive integral properties of the aerosol size distribution, e.g., aerosol mass, from tropospheric multiwavelength Raman lidar aerosol extinction and backscatter data, using an adapted form of the principal component analysis (PCA) technique. Since the refractive index of general tropospheric aerosols is variable and aeros...

The retrieval of the aerosol direct radiative effect of smoke aerosols in cloudy scenes using space–borne spectrometers is described. The retrieval of aerosol parameters and radiative effects from satellite is often hampered by residual clouds in a scene. However, aerosols that absorb solar radiation in the ultraviolet (UV) reduce the reflectance i...

Cloud and aerosol information is needed in trace gas retrievals from satellite measurements. The Fast REtrieval Scheme for Clouds from the Oxygen A band (FRESCO) cloud algorithm employs reflectance spectra of the O₂ A band around 760 nm to derive cloud pressure and effective cloud fraction. In general, clouds contribute more to the O<sub...

The solar radiative absorption by an aerosol layer above clouds is quantified using passive satellite spectrometry from the ultraviolet (UV) to the shortwave infrared (SWIR). UV-absorbing aerosols have a strong signature that can be detected using UV reflectance measurements, even when above clouds. Since the aerosol extinction optical thickness de...

1] In this paper we study the close relationship between the radiometric calibration of a satellite instrument and the Absorbing Aerosol Index (AAI) derived from the observed Earth reflectance. Instrument degradation of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument in the ultraviolet wavelength ran...

The direct radiative effect of absorbing aerosols in cloudy scenes is currently not well constrained. The simultaneous observation of both clouds and aerosols is seriously limited due to their heterogeneous distribution in both space and time. Space-based observations have the potential of monitoring cloud and aerosol distributions on a daily basis...

Since August 2002 SCIAMACHY delivers a wealth of high-quality data permitting to study the status of the Earth’s atmosphere. Enhanced concentrations of greenhouse gases are identified as the major source of global warming and their atmospheric concentrations are increasing. SCIAMACHY monitors the most prominent species such as CO2, CH4 and water va...

Since August 2002 SCIAMACHY delivers a wealth of high-quality data permitting to study the status of the Earth’s atmosphere. Enhanced concentrations of greenhouse gases are identified as the major source of global warming and their atmospheric concentrations are increasing. SCIAMACHY monitors the most prominent species such as CO2, CH4 and water va...

Volcanic ash can be dangerous for aviation, when large amounts of ash are sucked into the engines. On 15 April 2010 the Eyjafjöll volcano in Iceland sent a huge ash cloud towards western Europe. Subsequently, the air space was closed over most parts of western Europe. After 5 days some air space corridors were opened, but a criterion to base the re...

a b s t r a c t The link between the African Monsoon systems and aerosol loading in Africa is studied using multi-year satellite observations of UV-absorbing aerosols and rain gauge measurements. The main aerosol types occurring over Africa are desert dust and biomass burning aerosols, which are UV-absorbing. The abundance of these aerosols over Af...

Aerosols affect the Earth's albedo and shortwave radiation balance by scattering and absorption of sunlight. It appears that the radiative effect of aerosols strongly depends on the underlying scene, whether it is dark or bright. For example, absorbing aerosols above a bright cloud can lower the albedo of the cloud and thereby perform a strong heat...

Absorbing aerosols, like smoke, can potentially have a large heating effect if they are situated above bright clouds. However, the detection of aerosols in the presence of clouds is not possible for satellite imagers operating in the visible. We use the Absorbing Aerosol Index (AAI) from OMI and SCIAMACHY ultraviolet radiances to detect aerosols in...

The inversion of optical Raman lidar data, to retrieve microphysical aerosol properties, is challenging, since solutions depend non-linearly on measurement errors. However, the retrieval of integral properties of the aerosol size distribution, such as total volume or sur-face area density, depend much less on measurement errors than the size distri...

We study the quality of the SCIAMACHY Absorbing Aerosol Index (AAI) product developed at our institutes. The AAI in general is determined from the reflectance at two wavelengths in the UV, and is highly sensitive to er-rors in the absolute radiometric calibration. We apply a degradation correction to the level-1 reflectance and test the temporal be...

In this paper we present the first results of long-term mon-itoring the Absorbing Aerosol Index (AAI) [1] measured by the satellite instrument SCIAMACHY [2]. We find a strong increase in the AAI with time, which is found to be caused completely by degradation of the optics. This we conclude from straightforward calculation of the effect of instrume...

Reflectance spectra from 280-1750 nm of typical desert dust aerosol (DDA) and biomass burning aerosol (BBA) scenes over oceans are presented, measured by the space-borne spectrometer Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). DDA and BBA are both UV-absorbing aerosols, but their effect on the top-of-atmospher...

Global Ozone Monitoring Experiment (GOME) Absorbing Aerosol Index (AAI) and AAI-related residue data were used to investigate areas with UV-absorbing aerosols. Time series of regionally averaged residues show the seasonal variation and trends of aerosols and clouds in climatologically important parts of the globe. GOME spectra were used to study sc...

The retrieval of column densities and concentration profiles of atmospheric trace gas species from satellites is sensitive to light scattered by clouds. The SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument on the Envisat satellite, principally designed to retrieve trace gases in the atmosphere, is also ca...

The validity of the Absorbing Aerosol Index (AAI) product from the SCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY (SCIAMACHY) is discussed. The operational SCIAMACHY AAI product suffers from calibration errors in the reflectance as measured by SCIAMACHY and neglect of polarisation effects in the AAI computational algorithm. Th...

The retrieval of column densities and concentration profiles of atmospheric trace gas species from satellites is sensitive to light scattered by clouds. The SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument on the Envisat satellite, principally designed to retrieve trace gases in the atmosphere, is also ca...

The retrieval of column densities and concentration profiles of atmospheric trace gas species from satellites is sensitive to light scattered by clouds. The SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument on the Envisat satellite, principally designed to retrieve trace gases in the atmosphere, is also ca...

The validity of the Absorbing Aerosol Index (AAI) product from the SCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY (SCIAMACHY) is discussed. The operational SCIAMACHY AAI product suffers from calibration errors in the reflectance as measured by SCIAMACHY and design errors. Therefore, the AAI product was recalculated, compensati...

A technique that has gained considerable interest over the last years to monitor aerosol distributions and characterise aerosol source regions has been the use of the absorbing aerosol index (AAI). It has been used extensively to monitor ultraviolet (UV) absorbing aerosols, mainly desert dust and biomass burning aerosols. The AAI is not an aerosol...

1] The Absorbing Aerosol Index (AAI) was investigated and used to analyze GOME data and compare it to TOMS data. The physical interpretation of the AAI was studied with an extensive theoretical sensitivity analysis. The dependence of the method on a number of atmospheric, surface, and aerosol properties was studied using a numerical radiative trans...