. The mission of the Earth cloud, aerosol and radiation explorer (EarthCARE) mission to observe c... more . The mission of the Earth cloud, aerosol and radiation explorer (EarthCARE) mission to observe cloud, aerosol, precipitation and radiation using four complementary instruments requires the development of many single-instrument and synergistic algorithms for the retrieval of geophysical quantities. The retrieval products employ one or more of the cloud profiling radar (CPR), atmospheric lidar (ATLID) and multispectral imager (MSI), while the broadband radiometer (BBR) places the retrieved quantities in the context of the atmospheric radiation budget. To facilitate the development and evaluation of the ESA EarthCARE production model prior to launch, sophisticated instrument simulators have been developed to produce realistic synthetic EarthCARE measurements from the output of cloud-resolving model simulations. While acknowledging that the physical and radiative representation of cloud, aerosol and precipitation in the test scenes are based on numerical models, the opportunity to perform a detailed evaluation wherein the model ``truth'' is known has provided rare insights into the performance of EarthCARE's instruments and retrieval algorithms. This level of omniscience will not be available for the evaluation of in-flight EarthCARE retrieval products, even during validation activities coordinated with ground-based and airborne measurements. In this study we intercompare EarthCARE retrieval products from within the ESA production model both statistically across all simulated EarthCARE granules, and using timeseries of data from an individual scene. The comparison between the retrieved quantities helps to illustrate the strengths and limitations of the single-instrument retrievals, and the degrees to which the synergistic retrieval and composite products can represent the entire atmosphere of clouds, aerosols and precipitation. We show that radar-lidar synergy has the greatest impact in ice clouds; when compared with single-instrument radar and lidar retrievals, the synergistic ATLID-CPR-MSI cloud, aerosols, and precipitation (ACM-CAP) product accurately retrieves profiles of both ice water content and effective radius. While liquid cloud is difficult to detect directly from spaceborne remote sensors, especially in complex and layered scenes, the synergistic retrieval benefits from combined constraints from lidar backscatter, solar radiances and radar path-integrated attenuation, but still exhibits a high degree of random error. For precipitation retrievals, the CPR cloud and precipitation product (C-CLD) and ACM-CAP have similar performance when well-constrained by CPR measurements. The greatest differences are in coverage, with ACM-CAP reporting retrievals in the melting layer, and in heavy precipitation where the radar is dominated by multiple scattering and attenuation). Aerosol retrievals from ATLID compensate for a high degree of measurement noise in a number of ways, with the ATLID extinction, backscatter and depolarization (A-EBD) product and ACM-CAP demonstrating similar performance in the test scenes. The multispectral imager (MSI) cloud optical properties (M-COP) product performs very well in unambiguous cloud layers; similarly, the MSI aerosol optical thickness (M-AOT) product performs well where the possibility of contamination by cloud signal is very low. A summary of the performance of all retrieval products is provided, and may help to inform the selection of EarthCARE data products by future users.
. The Earth Clouds and Radiation Explorer mission (EarthCARE) is a multi-instrument cloud-aerosol... more . The Earth Clouds and Radiation Explorer mission (EarthCARE) is a multi-instrument cloud-aerosol-radiation process study oriented mission embarking a high spectral resolution lidar, a cloud profiling radar, a multi-spectral imager and a three-view broad-band radiometer. An important aspect of the EarthCARE mission is its focus on instrument synergy. Many L2 products are the result of L1 inputs from one or more instruments. Since no existing complete observational proxy-data sets comprised of co-located and co-temporal "EarthCARE-like" data exists, it has been necessary to create synthetic data sets for the testing and development of various retrieval algorithms as well as the data processing chain. Given the synergistic nature of the processing chain, it is important that the test data are physically consistent across the various instruments. Within the EarthCARE project, a version of the EarthCARE simulator multi-instrument framework (ECSIM) has been used to create unified realistic test data frames. These simulations have been driven using high resolution atmospheric model data (described in a companion paper). In this paper, the methods used to create the test data scenes are described. As well, the simulated L1 data corresponding to each scene is presented and discussed.
<p>The Aeolus mission offers unique opportunities for lidar surface returns... more <p>The Aeolus mission offers unique opportunities for lidar surface returns (LSR) applications considering its incidence angle (~37.5<sup>o</sup>) and the operated wavelength (~355 nm). Previous Aeolus-oriented studies have indicated that the contrast between LSR over dark and bright surfaces is expected to be particularly pronounced at 355 nm. We evaluated this surmise by comparing new LSR estimates from novel Aeolus prototype processor (using an optimal estimation approach) with various types of land for the Intensive Observation Period of Aeolus (September 2019) and an additional period during the same year. We discerned a very clear LSR gradient between the signal from water (mostly weak, but variable) and the signal from land (mostly strong), whereas the strongest LSR was found over white surfaces (ice or snow). Moreover, the sensitivity of LSR to the type of surface was also identified as the gradient between the brightest surfaces (snow/ice, sparse vegetation) and the dark surfaces (herbaceous forest, mangrove, wetland) was significant. Specifically, besides Antarctica and Greenland, the strongest returns over land were reported over the snow-covered areas of Tibet and Andes, followed by the arid areas of Northern America, Northern Africa and Middle East. Notably, the LSR from water was not always low as the average LSR estimate over water exhibited the strongest variability (~0.001 – 0.042 sr<sup>-1</sup>) and yielded most statistical outliers. The application of sea ice mask from MERRA-2 model revealed that most strong LSR cases over water were associated with the undetected ice. The masking of detected ice has resulted in the dramatic reduction of the average LSR over water. As a result, the related LSR variability over water was dwindled by the factor of ~10 down to ~0.001 – 0.004 sr<sup>-1 </sup>and >95% of outliers disappeared. Our findings about the sensitivity of Aeolus surface returns to the type of surface are beneficial because statistically robust LSR estimates over ocean lay the foundation for the Aeolus LSR-based Aerosol Optical Depth (AOD) retrieval over ocean. This retrieval can be established based on the fundamental link between LSR, near-surface wind speed and AOD over sea surface.</p>
The CLAAS-2.1 record provides cloud properties derived from the SEVIRI sensor onboard METEOSAT se... more The CLAAS-2.1 record provides cloud properties derived from the SEVIRI sensor onboard METEOSAT second generation (MSG) satellites. This first update of the second edition (Benas et al., 2017; CLAAS-2 DOI:10.5676/EUM_SAF_CM/CLAAS/V002; see also Stengel et al., 2014) features a temporal extension by two years (the record is now covering 2004-2017) and a bugfix for the monthly CTO products. As for previous editions of CLAAS, the solar SEVIRI channels of MSG-1, MSG-2 and MSG-3 were intercalibrated with MODIS Aqua (following Meirink et al., 2013) before applying the cloud retrievals. CLAAS-2.1 features the following cloud properties: cloud mask/type, cloud top temperature/pressure/height, cloud phase as well as cloud microphysical properties such as optical thickness, effective droplet radius and cloud water path. The data are available on native SEVIRI resolution, i.e. 15 minutes repeat cycle and 3km (nadir) to 11km (edge of the field of view) spatial resolution. In addition, spatio-tem...
The CLARA-A2 record provides cloud properties, surface albedo and surface radiation parameters de... more The CLARA-A2 record provides cloud properties, surface albedo and surface radiation parameters derived from the AVHRR sensor onboard polar orbiting NOAA and METOP satellites. This second edition is the improved and extended follow-up of the first version of the record (Karlsson et al., 2013; CLARA-A1 DOI: 10.5676/EUM_SAF_CM/CLARA_AVHRR/V001) which now covers a 34 year time period (1982-2015). Original visible radiances were inter-calibrated and homogenised, using MODIS data as a reference, before applying the various parameter retrievals. The inter-calibration was based on an original method introduced by Heidinger et al. (2010) which now has been updated (MODIS Collection 6) and extended (six years have been added). CLARA-A2 features a range of cloud products: cloud mask, cloud top temperature/pressure/height, cloud thermodynamic phase, and (for liquid and ice clouds separately) cloud optical thickness, particle effective radius and cloud water path. Cloud products are available as...
Spatiotemporal variability of clouds is an important aspect of the climate system. Therefore clim... more Spatiotemporal variability of clouds is an important aspect of the climate system. Therefore climate data records of cloud properties are valuable to many researchers in the climate community. The passive SEVIRI imager onboard the geostationary Meteosat Second Generation satellites is well suited for the needs of cloud retrievals as it provides measurements in 12 spectral channels every 15 minutes and thus allows for capturing both the spatial and the temporal variability of clouds. However, requirements on climate data records are high in terms of record length and homogeneity, so that intercalibration and homogenization among the available SEVIRI instruments becomes a crucial factor.
We present the initial results of a deep ISO-SWS survey for the low J pure rotational emission li... more We present the initial results of a deep ISO-SWS survey for the low J pure rotational emission lines of H2 toward a number of Herbig Ae and T Tauri stars. The objects are selected to be as isolated as possible from molecular clouds, with a spectral energy distribution characteristic of a circumstellar disk. For most of them the presence of a disk has been established directly by millimeter interferometry. The S (1) line is detected in most sources with a peak flux of 0.3-1 Jy. The S(0) line is definitely seen in 2 objects: GG Tau and HD 163296. The observations suggest the presence of "warm" gas at T_(kin) ≈ 100 K with a mass of a few % of the total gas+ dust mass, derived assuming a gas-to-dust ratio of 100:1. The S(1) peak flux does not show a strong correlation with spectral type of the central star or continuum flux at 1.3 millimeter. Possible origins for the warm gas seen in H_2 are discussed, and comparisons with model calculations are made.
We introduce the development of EarthCARE Level 2 layer products derived from profile measurement... more We introduce the development of EarthCARE Level 2 layer products derived from profile measurements of the high-spectral-resolution lidar ATLID and column products obtained from combined information of ATLID and the Multi-Spectral Imager (MSI). Layer products include cloud top height as well as aerosol layer boundaries and mean optical properties along the satellite nadir track. Synergistic column products comprise cloud top height, Ångström exponent, and aerosol type both along-track and across the MSI swath.
The Earth Clouds and Radiation Explorer (EarthCARE) mission is a combined ESA, JAXA mission to be... more The Earth Clouds and Radiation Explorer (EarthCARE) mission is a combined ESA, JAXA mission to be flown in late 2015. It will be a polar sun-synchronous orbiting satellite with an orbit altitude of about 400 km and an equator crossing time of 13:45. EarthCARE's main focus is on providing data for better understanding the Earth's radiative balance. In order to do this, EarthCARE will carry four instruments: -A High Spectral resolution 355nm cloud/aerosol lidar(ATLID) -A 35 GHz cloud radar (CPR) -A multi-spectral imager (MSI) [0.67, 0.86, 1.65, 2.21, 8.8, 10.8, 12.0 um] -A long- and short-wave 3 view Broad-Band Radiometer (BBR) EarthCARE has been designed from the ground-up with the ideas of sensor-synergy playing a major role. For example, variational based retrievals are being developed which combine ATLID, CPR and MSI measurements in order to obtain `best-estimates' of 3-D cloud and aerosol properties on the 1-km scale. These fields will then be used as input to radiati...
Journal of Applied Meteorology and Climatology, 2008
Vertical profiles of ice water content (IWC) can now be derived globally from spaceborne cloud sa... more Vertical profiles of ice water content (IWC) can now be derived globally from spaceborne cloud satellite radar (CloudSat) data. Integrating these data with Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data may further increase accuracy. Evaluations of the accuracy of IWC retrieved from radar alone and together with other measurements are now essential. A forward model employing aircraft Lagrangian spiral descents through mid- and low-latitude ice clouds is used to estimate profiles of what a lidar and conventional and Doppler radar would sense. Radar reflectivity Ze and Doppler fall speed at multiple wavelengths and extinction in visible wavelengths were derived from particle size distributions and shape data, constrained by IWC that were measured directly in most instances. These data were provided to eight teams that together cover 10 retrieval methods. Almost 3400 vertically distributed points from 19 clouds were used. Approximate cloud optical dept...
. The mission of the Earth cloud, aerosol and radiation explorer (EarthCARE) mission to observe c... more . The mission of the Earth cloud, aerosol and radiation explorer (EarthCARE) mission to observe cloud, aerosol, precipitation and radiation using four complementary instruments requires the development of many single-instrument and synergistic algorithms for the retrieval of geophysical quantities. The retrieval products employ one or more of the cloud profiling radar (CPR), atmospheric lidar (ATLID) and multispectral imager (MSI), while the broadband radiometer (BBR) places the retrieved quantities in the context of the atmospheric radiation budget. To facilitate the development and evaluation of the ESA EarthCARE production model prior to launch, sophisticated instrument simulators have been developed to produce realistic synthetic EarthCARE measurements from the output of cloud-resolving model simulations. While acknowledging that the physical and radiative representation of cloud, aerosol and precipitation in the test scenes are based on numerical models, the opportunity to perform a detailed evaluation wherein the model ``truth'' is known has provided rare insights into the performance of EarthCARE's instruments and retrieval algorithms. This level of omniscience will not be available for the evaluation of in-flight EarthCARE retrieval products, even during validation activities coordinated with ground-based and airborne measurements. In this study we intercompare EarthCARE retrieval products from within the ESA production model both statistically across all simulated EarthCARE granules, and using timeseries of data from an individual scene. The comparison between the retrieved quantities helps to illustrate the strengths and limitations of the single-instrument retrievals, and the degrees to which the synergistic retrieval and composite products can represent the entire atmosphere of clouds, aerosols and precipitation. We show that radar-lidar synergy has the greatest impact in ice clouds; when compared with single-instrument radar and lidar retrievals, the synergistic ATLID-CPR-MSI cloud, aerosols, and precipitation (ACM-CAP) product accurately retrieves profiles of both ice water content and effective radius. While liquid cloud is difficult to detect directly from spaceborne remote sensors, especially in complex and layered scenes, the synergistic retrieval benefits from combined constraints from lidar backscatter, solar radiances and radar path-integrated attenuation, but still exhibits a high degree of random error. For precipitation retrievals, the CPR cloud and precipitation product (C-CLD) and ACM-CAP have similar performance when well-constrained by CPR measurements. The greatest differences are in coverage, with ACM-CAP reporting retrievals in the melting layer, and in heavy precipitation where the radar is dominated by multiple scattering and attenuation). Aerosol retrievals from ATLID compensate for a high degree of measurement noise in a number of ways, with the ATLID extinction, backscatter and depolarization (A-EBD) product and ACM-CAP demonstrating similar performance in the test scenes. The multispectral imager (MSI) cloud optical properties (M-COP) product performs very well in unambiguous cloud layers; similarly, the MSI aerosol optical thickness (M-AOT) product performs well where the possibility of contamination by cloud signal is very low. A summary of the performance of all retrieval products is provided, and may help to inform the selection of EarthCARE data products by future users.
. The Earth Clouds and Radiation Explorer mission (EarthCARE) is a multi-instrument cloud-aerosol... more . The Earth Clouds and Radiation Explorer mission (EarthCARE) is a multi-instrument cloud-aerosol-radiation process study oriented mission embarking a high spectral resolution lidar, a cloud profiling radar, a multi-spectral imager and a three-view broad-band radiometer. An important aspect of the EarthCARE mission is its focus on instrument synergy. Many L2 products are the result of L1 inputs from one or more instruments. Since no existing complete observational proxy-data sets comprised of co-located and co-temporal "EarthCARE-like" data exists, it has been necessary to create synthetic data sets for the testing and development of various retrieval algorithms as well as the data processing chain. Given the synergistic nature of the processing chain, it is important that the test data are physically consistent across the various instruments. Within the EarthCARE project, a version of the EarthCARE simulator multi-instrument framework (ECSIM) has been used to create unified realistic test data frames. These simulations have been driven using high resolution atmospheric model data (described in a companion paper). In this paper, the methods used to create the test data scenes are described. As well, the simulated L1 data corresponding to each scene is presented and discussed.
<p>The Aeolus mission offers unique opportunities for lidar surface returns... more <p>The Aeolus mission offers unique opportunities for lidar surface returns (LSR) applications considering its incidence angle (~37.5<sup>o</sup>) and the operated wavelength (~355 nm). Previous Aeolus-oriented studies have indicated that the contrast between LSR over dark and bright surfaces is expected to be particularly pronounced at 355 nm. We evaluated this surmise by comparing new LSR estimates from novel Aeolus prototype processor (using an optimal estimation approach) with various types of land for the Intensive Observation Period of Aeolus (September 2019) and an additional period during the same year. We discerned a very clear LSR gradient between the signal from water (mostly weak, but variable) and the signal from land (mostly strong), whereas the strongest LSR was found over white surfaces (ice or snow). Moreover, the sensitivity of LSR to the type of surface was also identified as the gradient between the brightest surfaces (snow/ice, sparse vegetation) and the dark surfaces (herbaceous forest, mangrove, wetland) was significant. Specifically, besides Antarctica and Greenland, the strongest returns over land were reported over the snow-covered areas of Tibet and Andes, followed by the arid areas of Northern America, Northern Africa and Middle East. Notably, the LSR from water was not always low as the average LSR estimate over water exhibited the strongest variability (~0.001 – 0.042 sr<sup>-1</sup>) and yielded most statistical outliers. The application of sea ice mask from MERRA-2 model revealed that most strong LSR cases over water were associated with the undetected ice. The masking of detected ice has resulted in the dramatic reduction of the average LSR over water. As a result, the related LSR variability over water was dwindled by the factor of ~10 down to ~0.001 – 0.004 sr<sup>-1 </sup>and >95% of outliers disappeared. Our findings about the sensitivity of Aeolus surface returns to the type of surface are beneficial because statistically robust LSR estimates over ocean lay the foundation for the Aeolus LSR-based Aerosol Optical Depth (AOD) retrieval over ocean. This retrieval can be established based on the fundamental link between LSR, near-surface wind speed and AOD over sea surface.</p>
The CLAAS-2.1 record provides cloud properties derived from the SEVIRI sensor onboard METEOSAT se... more The CLAAS-2.1 record provides cloud properties derived from the SEVIRI sensor onboard METEOSAT second generation (MSG) satellites. This first update of the second edition (Benas et al., 2017; CLAAS-2 DOI:10.5676/EUM_SAF_CM/CLAAS/V002; see also Stengel et al., 2014) features a temporal extension by two years (the record is now covering 2004-2017) and a bugfix for the monthly CTO products. As for previous editions of CLAAS, the solar SEVIRI channels of MSG-1, MSG-2 and MSG-3 were intercalibrated with MODIS Aqua (following Meirink et al., 2013) before applying the cloud retrievals. CLAAS-2.1 features the following cloud properties: cloud mask/type, cloud top temperature/pressure/height, cloud phase as well as cloud microphysical properties such as optical thickness, effective droplet radius and cloud water path. The data are available on native SEVIRI resolution, i.e. 15 minutes repeat cycle and 3km (nadir) to 11km (edge of the field of view) spatial resolution. In addition, spatio-tem...
The CLARA-A2 record provides cloud properties, surface albedo and surface radiation parameters de... more The CLARA-A2 record provides cloud properties, surface albedo and surface radiation parameters derived from the AVHRR sensor onboard polar orbiting NOAA and METOP satellites. This second edition is the improved and extended follow-up of the first version of the record (Karlsson et al., 2013; CLARA-A1 DOI: 10.5676/EUM_SAF_CM/CLARA_AVHRR/V001) which now covers a 34 year time period (1982-2015). Original visible radiances were inter-calibrated and homogenised, using MODIS data as a reference, before applying the various parameter retrievals. The inter-calibration was based on an original method introduced by Heidinger et al. (2010) which now has been updated (MODIS Collection 6) and extended (six years have been added). CLARA-A2 features a range of cloud products: cloud mask, cloud top temperature/pressure/height, cloud thermodynamic phase, and (for liquid and ice clouds separately) cloud optical thickness, particle effective radius and cloud water path. Cloud products are available as...
Spatiotemporal variability of clouds is an important aspect of the climate system. Therefore clim... more Spatiotemporal variability of clouds is an important aspect of the climate system. Therefore climate data records of cloud properties are valuable to many researchers in the climate community. The passive SEVIRI imager onboard the geostationary Meteosat Second Generation satellites is well suited for the needs of cloud retrievals as it provides measurements in 12 spectral channels every 15 minutes and thus allows for capturing both the spatial and the temporal variability of clouds. However, requirements on climate data records are high in terms of record length and homogeneity, so that intercalibration and homogenization among the available SEVIRI instruments becomes a crucial factor.
We present the initial results of a deep ISO-SWS survey for the low J pure rotational emission li... more We present the initial results of a deep ISO-SWS survey for the low J pure rotational emission lines of H2 toward a number of Herbig Ae and T Tauri stars. The objects are selected to be as isolated as possible from molecular clouds, with a spectral energy distribution characteristic of a circumstellar disk. For most of them the presence of a disk has been established directly by millimeter interferometry. The S (1) line is detected in most sources with a peak flux of 0.3-1 Jy. The S(0) line is definitely seen in 2 objects: GG Tau and HD 163296. The observations suggest the presence of "warm" gas at T_(kin) ≈ 100 K with a mass of a few % of the total gas+ dust mass, derived assuming a gas-to-dust ratio of 100:1. The S(1) peak flux does not show a strong correlation with spectral type of the central star or continuum flux at 1.3 millimeter. Possible origins for the warm gas seen in H_2 are discussed, and comparisons with model calculations are made.
We introduce the development of EarthCARE Level 2 layer products derived from profile measurement... more We introduce the development of EarthCARE Level 2 layer products derived from profile measurements of the high-spectral-resolution lidar ATLID and column products obtained from combined information of ATLID and the Multi-Spectral Imager (MSI). Layer products include cloud top height as well as aerosol layer boundaries and mean optical properties along the satellite nadir track. Synergistic column products comprise cloud top height, Ångström exponent, and aerosol type both along-track and across the MSI swath.
The Earth Clouds and Radiation Explorer (EarthCARE) mission is a combined ESA, JAXA mission to be... more The Earth Clouds and Radiation Explorer (EarthCARE) mission is a combined ESA, JAXA mission to be flown in late 2015. It will be a polar sun-synchronous orbiting satellite with an orbit altitude of about 400 km and an equator crossing time of 13:45. EarthCARE's main focus is on providing data for better understanding the Earth's radiative balance. In order to do this, EarthCARE will carry four instruments: -A High Spectral resolution 355nm cloud/aerosol lidar(ATLID) -A 35 GHz cloud radar (CPR) -A multi-spectral imager (MSI) [0.67, 0.86, 1.65, 2.21, 8.8, 10.8, 12.0 um] -A long- and short-wave 3 view Broad-Band Radiometer (BBR) EarthCARE has been designed from the ground-up with the ideas of sensor-synergy playing a major role. For example, variational based retrievals are being developed which combine ATLID, CPR and MSI measurements in order to obtain `best-estimates' of 3-D cloud and aerosol properties on the 1-km scale. These fields will then be used as input to radiati...
Journal of Applied Meteorology and Climatology, 2008
Vertical profiles of ice water content (IWC) can now be derived globally from spaceborne cloud sa... more Vertical profiles of ice water content (IWC) can now be derived globally from spaceborne cloud satellite radar (CloudSat) data. Integrating these data with Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data may further increase accuracy. Evaluations of the accuracy of IWC retrieved from radar alone and together with other measurements are now essential. A forward model employing aircraft Lagrangian spiral descents through mid- and low-latitude ice clouds is used to estimate profiles of what a lidar and conventional and Doppler radar would sense. Radar reflectivity Ze and Doppler fall speed at multiple wavelengths and extinction in visible wavelengths were derived from particle size distributions and shape data, constrained by IWC that were measured directly in most instances. These data were provided to eight teams that together cover 10 retrieval methods. Almost 3400 vertically distributed points from 19 clouds were used. Approximate cloud optical dept...
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