Retrieval of Cloud Properties Using CALIPSO Imaging Infrared Radiometer. Part I: Effective Emissivity and Optical Depth

AbstractThe paper describes the operational analysis of the Imaging Infrared Radiometer (IIR) data, which have been collected in the framework of the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission for the purpose of retrieving high-altitude (above 7 km) cloud effective emissivity and optical depth that can be used in synergy with the vertically resolved Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) collocated observations. After an IIR scene classification is built under the CALIOP track, the analysis is applied to features detected by CALIOP when found alone in the atmospheric column or when CALIOP identifies an opaque layer underneath. The fast-calculation radiative transfer (FASRAD) model fed by ancillary meteorological and surface data is used to compute the different components involved in the effective emissivity retrievals under the CALIOP track. The track analysis is extended to the IIR swath using homogeneity criteria that are based on radiative equivalence. The effective optical depth at 12.05 μm is shown to be a good proxy for about one-half of the cloud optical depth, allowing direct comparisons with other databases in the visible spectrum. A step-by-step quantitative sensitivity and performance analysis is provided. The method is validated through comparisons of collocated IIR and CALIOP optical depths for elevated single-layered semitransparent cirrus clouds, showing excellent agreement (within 20%) for values ranging from 1 down to 0.05. Uncertainties have been determined from the identified error sources. The optical depth distribution of semitransparent clouds is found to have a nearly exponential shape with a mean value of about 0.5–0.6.

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The interdependence of continental warm cloud properties derived from unexploited solar background signals in ground-based lidar measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-8389-2014 ◽

2014 ◽

Vol 14 (16) ◽

pp. 8389-8401 ◽

Cited By ~ 7

Author(s):

J. C. Chiu ◽

J. A. Holmes ◽

R. J. Hogan ◽

E. J. O'Connor

Keyword(s):

Optical Depth ◽

Effective Radius ◽

Liquid Water Path ◽

Cloud Optical Depth ◽

Cloud Properties ◽

Warm Cloud ◽

Lidar Measurements ◽

Atmospheric Radiation Measurement ◽

Ground Based Lidar ◽

Geometric Thickness

Abstract. We have extensively analysed the interdependence between cloud optical depth, droplet effective radius, liquid water path (LWP) and geometric thickness for stratiform warm clouds using ground-based observations. In particular, this analysis uses cloud optical depths retrieved from untapped solar background signals that are previously unwanted and need to be removed in most lidar applications. Combining these new optical depth retrievals with radar and microwave observations at the Atmospheric Radiation Measurement (ARM) Climate Research Facility in Oklahoma during 2005–2007, we have found that LWP and geometric thickness increase and follow a power-law relationship with cloud optical depth regardless of the presence of drizzle; LWP and geometric thickness in drizzling clouds can be generally 20–40% and at least 10% higher than those in non-drizzling clouds, respectively. In contrast, droplet effective radius shows a negative correlation with optical depth in drizzling clouds and a positive correlation in non-drizzling clouds, where, for large optical depths, it asymptotes to 10 μm. This asymptotic behaviour in non-drizzling clouds is found in both the droplet effective radius and optical depth, making it possible to use simple thresholds of optical depth, droplet size, or a combination of these two variables for drizzle delineation. This paper demonstrates a new way to enhance ground-based cloud observations and drizzle delineations using existing lidar networks.

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The interdependence of continental warm cloud properties derived from unexploited solar background signal in ground-based lidar measurements

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-8963-2014 ◽

2014 ◽

Vol 14 (7) ◽

pp. 8963-8996

Author(s):

J. C. Chiu ◽

J. A. Holmes ◽

R. J. Hogan ◽

E. J. O'Connor

Keyword(s):

Optical Depth ◽

Effective Radius ◽

Liquid Water Path ◽

Background Signal ◽

Cloud Optical Depth ◽

Cloud Properties ◽

Lidar Measurements ◽

Atmospheric Radiation Measurement ◽

Ground Based Lidar ◽

Geometric Thickness

Abstract. We have extensively analysed the interdependence between cloud optical depth, droplet effective radius, liquid water path (LWP) and geometric thickness for stratiform warm clouds using ground-based observations. In particular, this analysis uses cloud optical depths retrieved from untapped solar background signal that is previously unwanted and needs to be removed in most lidar applications. Combining these new optical depth retrievals with radar and microwave observations at the Atmospheric Radiation Measurement (ARM) Climate Research Facility in Oklahoma during 2005–2007, we have found that LWP and geometric thickness increase and follow a power-law relationship with cloud optical depth regardless of the presence of drizzle; LWP and geometric thickness in drizzling clouds can be generally 20–40% and at least 10% higher than those in non-drizzling clouds, respectively. In contrast, droplet effective radius shows a negative correlation with optical depth in drizzling clouds, while it increases with optical depth and reaches an asymptote of 10 μm in non-drizzling clouds. This asymptotic behaviour in non-drizzling clouds is found in both droplet effective radius and optical depth, making it possible to use simple thresholds of optical depth, droplet size, or a combination of these two variables for drizzle delineation. This paper demonstrates a new way to enhance ground-based cloud observations and drizzle delineations using existing lidar networks.

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Marine liquid cloud geometric thickness retrieved from OCO-2's oxygen A-band spectrometer

Atmospheric Measurement Techniques ◽

10.5194/amt-12-1717-2019 ◽

2019 ◽

Vol 12 (3) ◽

pp. 1717-1737 ◽

Cited By ~ 5

Author(s):

Mark Richardson ◽

Jussi Leinonen ◽

Heather Q. Cronk ◽

James McDuffie ◽

Matthew D. Lebsock ◽

...

Keyword(s):

Optical Depth ◽

Single Layer ◽

Cloud Droplet ◽

Satellite Observation ◽

Cloud Optical Depth ◽

First Case ◽

Phase Classification ◽

Moderate Resolution Imaging Spectroradiometer ◽

Cloud Top Pressure ◽

Geometric Thickness

Abstract. This paper introduces the OCO2CLD-LIDAR-AUX product, which uses the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar and the Orbiting Carbon Observatory-2 (OCO-2) hyperspectral A-band spectrometer. CALIPSO provides a prior cloud top pressure (Ptop) for an OCO-2-based retrieval of cloud optical depth, Ptop and cloud geometric thickness expressed in hPa. Measurements are of single-layer liquid clouds over oceans from September 2014 to December 2016 when collocated data are available. Retrieval performance is best for solar zenith angles <45∘ and when the cloud phase classification, which also uses OCO-2's weak CO2 band, is more confident. The highest quality optical depth retrievals agree with those from the Moderate Resolution Imaging Spectroradiometer (MODIS) with discrepancies smaller than the MODIS-reported uncertainty. Retrieved thicknesses are consistent with a substantially subadiabatic structure over marine stratocumulus regions, in which extinction is weighted towards the cloud top. Cloud top pressure in these clouds shows a 4 hPa bias compared with CALIPSO which we attribute mainly to the assumed vertical structure of cloud extinction after showing little sensitivity to the presence of CALIPSO-identified aerosol layers or assumed cloud droplet effective radius. This is the first case of success in obtaining internal cloud structure from hyperspectral A-band measurements and exploits otherwise unused OCO-2 data. This retrieval approach should provide additional constraints on satellite-based estimates of cloud droplet number concentration from visible imagery, which rely on parameterization of the cloud thickness.

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Statistics of vertical backscatter profiles of cirrus clouds

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-12925-2011 ◽

2011 ◽

Vol 11 (24) ◽

pp. 12925-12943 ◽

Cited By ~ 7

Author(s):

P. Veglio ◽

T. Maestri

Keyword(s):

Optical Depth ◽

Satellite Observation ◽

Cirrus Clouds ◽

Cloud Base ◽

Physical Parameters ◽

Cloud Optical Depth ◽

Cloud Temperature ◽

The Mean ◽

Depth Increase ◽

The Impact

Abstract. A nearly global statistical analysis of vertical backscatter and extinction profiles of cirrus clouds collected by the CALIOP lidar, on-board of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, is presented. Statistics on frequency of occurrence and distribution of bulk properties of cirrus clouds in general and, for the first time, of horizontally homogeneous (on a 5-km field of view) cirrus clouds only are provided. Annual and seasonal backscatter profiles (BSP) are computed for the horizontally homogeneous cirri. Differences found in the day/night cases and for midlatitudes and tropics are studied in terms of the mean physical parameters of the clouds from which they are derived. The relationship between cloud physical parameters (optical depth, geometrical thickness and temperature) and the shape of the BSP is investigated. It is found that cloud geometrical thickness is the main parameter affecting the shape of the mean CALIOP BSP. Specifically, cirrus clouds with small geometrical thicknesses show a maximum in mean BSP curve located near cloud top. As the cloud geometrical thickness increases the BSP maximum shifts towards cloud base. Cloud optical depth and temperature have smaller effects on the shape of the CALIOP BSPs. In general a slight increase in the BSP maximum is observed as cloud temperature and optical depth increase. In order to fit mean BSPs, as functions of geometrical thickness and position within the cloud layer, polynomial functions are provided. The impact on satellite radiative transfer simulations in the infrared spectrum when using either a constant ice-content (IWC) along the cloud vertical dimension or an IWC profile derived from the BSP fitting functions is evaluated. It is, in fact, demonstrated that, under realistic hypotheses, the mean BSP is linearly proportional to the IWC profile.

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CORRECTION FOR THE CIRRUS CLOUD TOP HEIGHT OF MODIS BASED ON CALIPSO IN BEIJING-TIANJIN-HEBEI REGION

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xlii-3-w9-203-2019 ◽

2019 ◽

Vol XLII-3/W9 ◽

pp. 203-210

Author(s):

B. Y. Yang ◽

J. Liu ◽

X. Jia

Keyword(s):

Remote Sensing ◽

Satellite Observation ◽

Orthogonal Polarization ◽

Cirrus Cloud ◽

Weather System ◽

Cloud Optical Depth ◽

Lower Cloud ◽

Moderate Resolution ◽

Moderate Resolution Imaging Spectroradiometer ◽

The Difference

Abstract. Cirrus plays an important role in atmospheric radiation. It affects weather system and climate change. Satellite remote sensing is an important kind of observation for cloud. As a passive remote sensing instrument, large bias was found for thin cirrus cloud top height retrieval from MODIS (Moderate Resolution Imaging Spectroradiometer). Comparatively, CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) aboard CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) which is an active remote sensing instrument can acquire more accurate characteristics of thin cirrus cloud. In this study, CALIPSO cirrus cloud top height data was used to correct MODIS cirrus cloud top height. The data analysis area was selected in Beijing-Tianjin-Hebei region and data came from 2013 to 2017. Linear fitting method was selected based on cross-validation method between MODIS and CALIPSO data. The results shows that the difference between MODIS and CALIPSO changes from −3~2 km to −2.0~2.5 km, and the maximum difference changes from about −0.8 km to about 0.2 km. In the context of different vertical levels and cloud optical depth, MODIS cirrus cloud top height is improved after correcting, which is more obvious at lower cloud top height and optical thinner cirrus.

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Increasing the spatial resolution of cloud property retrievals from Meteosat SEVIRI by use of its high-resolution visible channel: implementation and examples

Atmospheric Measurement Techniques ◽

10.5194/amt-14-5107-2021 ◽

2021 ◽

Vol 14 (7) ◽

pp. 5107-5126

Author(s):

Hartwig Deneke ◽

Carola Barrientos-Velasco ◽

Sebastian Bley ◽

Anja Hünerbein ◽

Stephan Lenk ◽

...

Keyword(s):

High Resolution ◽

Optical Depth ◽

Spatial Resolution ◽

High Frequency ◽

Spatiotemporal Variability ◽

High Frequency Component ◽

Cloud Optical Depth ◽

Cloud Property ◽

Cloud Properties ◽

Narrowband Channels

Abstract. The modification of an existing cloud property retrieval scheme for the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument on board the geostationary Meteosat satellites is described to utilize its high-resolution visible (HRV) channel for increasing the spatial resolution of its physical outputs. This results in products with a nadir spatial resolution of 1×1 km2 compared to the standard 3×3 km2 resolution offered by the narrowband channels. This improvement thus greatly reduces the resolution gap between current geostationary and polar-orbiting meteorological satellite imagers. In the first processing step, cloudiness is determined from the HRV observations by a threshold-based cloud masking algorithm. Subsequently, a linear model that links the 0.6 µm, 0.8 µm, and HRV reflectances provides a physical constraint to incorporate the spatial high-frequency component of the HRV observations into the retrieval of cloud optical depth. The implementation of the method is described, including the ancillary datasets used. It is demonstrated that the omission of high-frequency variations in the cloud-absorbing 1.6 µm channel results in comparatively large uncertainties in the retrieved cloud effective radius, likely due to the mismatch in channel resolutions. A newly developed downscaling scheme for the 1.6 µm reflectance is therefore applied to mitigate the effects of this scale mismatch. Benefits of the increased spatial resolution of the resulting SEVIRI products are demonstrated for three example applications: (i) for a convective cloud field, it is shown that significantly better agreement between the distributions of cloud optical depth retrieved from SEVIRI and from collocated MODIS observations is achieved. (ii) The temporal evolution of cloud properties for a growing convective storm at standard and HRV spatial resolutions are compared, illustrating an improved contrast in growth signatures resulting from the use of the HRV channel. (iii) An example of surface solar irradiance, determined from the retrieved cloud properties, is shown, for which the HRV channel helps to better capture the large spatiotemporal variability induced by convective clouds. These results suggest that incorporating the HRV channel into the retrieval has potential for improving Meteosat-based cloud products for several application domains.

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A novel method for estimating shortwave direct radiative effect of above-cloud aerosols using CALIOP and MODIS data

Atmospheric Measurement Techniques ◽

10.5194/amt-7-1777-2014 ◽

2014 ◽

Vol 7 (6) ◽

pp. 1777-1789 ◽

Cited By ~ 25

Author(s):

Z. Zhang ◽

K. Meyer ◽

S. Platnick ◽

L. Oreopoulos ◽

D. Lee ◽

...

Keyword(s):

Atlantic Ocean ◽

Optical Depth ◽

Radiative Forcing ◽

Orthogonal Polarization ◽

Radiative Effect ◽

Cloud Optical Depth ◽

Modis Data ◽

Joint Histogram ◽

The Impact ◽

Southeastern Atlantic

Abstract. This paper describes an efficient and unique method for computing the shortwave direct radiative effect (DRE) of aerosol residing above low-level liquid-phase clouds using CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) and MODIS (Moderate Resolution Imaging Spectroradiometer) data. It addresses the overlap of aerosol and cloud rigorously by utilizing the joint histogram of cloud optical depth and cloud top pressure while also accounting for subgrid-scale variations of aerosols. The method is computationally efficient because of its use of grid-level cloud and aerosol statistics, instead of pixel-level products, and a precomputed look-up table based on radiative transfer calculations. We verify that for smoke and polluted dust over the southeastern Atlantic Ocean the method yields a seasonal mean instantaneous (approximately 13:30 local time) shortwave DRE of above-cloud aerosol (ACA) that generally agrees with a more rigorous pixel-level computation within 4%. We also estimate the impact of potential CALIOP aerosol optical depth (AOD) retrieval bias of ACA on DRE. We find that the regional and seasonal mean instantaneous DRE of ACA over southeastern Atlantic Ocean would increase, from the original value of 6.4 W m−2 based on operational CALIOP AOD to 9.6 W m−2 if CALIOP AOD retrievals are biased low by a factor of 1.5 (Meyer et al., 2013) and further to 30.9 W m−2 if CALIOP AOD retrievals are biased low by a factor of 5 as suggested in Jethva et al. (2014). In contrast, the instantaneous ACA radiative forcing efficiency (RFE) remains relatively invariant in all cases at about 53 W m−2 AOD−1, suggesting a near-linear relation between the instantaneous RFE and AOD. We also compute the annual mean instantaneous shortwave DRE of light-absorbing aerosols (i.e., smoke and polluted dust) over global oceans based on 4 years of CALIOP and MODIS data. We find that given an above-cloud aerosol type the optical depth of the underlying clouds plays a larger role than above-cloud AOD in the variability of the annual mean shortwave DRE of above-cloud light-absorbing aerosol. While we demonstrate our method using CALIOP and MODIS data, it can also be extended to other satellite data sets.

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A climatology of dust episodes in the broader Mediterranean Basin using satellite MODIS C6.1 and OMI OMAERUV data

10.5194/egusphere-egu2020-20288 ◽

2020 ◽

Author(s):

Nikos Hatzianastassiou ◽

Maria Gavrouzou ◽

Antonis Gkikas ◽

Nikos Mihalopoulos

Keyword(s):

Optical Depth ◽

Mediterranean Basin ◽

Cloud Condensation Nuclei ◽

Longwave Radiation ◽

Threshold Value ◽

Mean Value ◽

Dust Transport ◽

Cloud Properties ◽

The Mediterranean ◽

The Mediterranean Basin

Aerosols, due to their interaction primary with the shortwave, but also with the longwave radiation, constitute a significant climate component, and at the same time an important, but still uncertain, factor of the contemporary climatic change. Apart from radiation, aerosols also interact with clouds, acting as Cloud Condensation Nuclei (CCN) and/or Ice Nuclei (IN), modifying the cloud optical and physical properties like cloud albedo, extent, lifetime or precipitation producing ability. Hence, it is also expected that high loads of specific aerosol types, such as desert dust, can induce even stronger effects on the above mentioned cloud properties.More specifically, dust aerosols, which are inserted in the atmosphere mainly from the great world deserts, represent the major global aerosol component. These aerosols can remain suspended in the air and travel for several days, reaching areas far away from their sources. The Mediterranean Basin (MB), which is one of the most responsive regions to climate change, due to its location (nearby the Sahara desert in North Africa and the deserts of Middle East), is frequently affected from massive and extended dust transport. Because of the potentially significant role of these dust episodes, and their seasonal and inter-annual variability, they are worth to be studied and monitored through time.In the present study, a modified version of a satellite algorithm, which is fully described by Gavrouzou et al. in another study of this conference, is used for the determination of strong and extreme dust episodes in the Mediterranean Basin over the period 2005-2018. The algorithm, using MODIS C6.1 spectral Aerosol Optical Depth (AOD) and OMI OMAERUV Aerosol Index (AI) as input data, ran on a daily and an 1&#176;x1&#176; pixel level basis and determined the occurrence and intensity of dust episodes whenever the AI is greater than 1 and the Angstrom Exponent (AE), which is calculated from spectral AOD data, is lower than 0.4. Any day is characterized as an episodic one when the dust optical depth (DOD) exceeds a computed threshold value (mean value plus two or four standard deviations for strong and extreme episodes, respectively) on at least 30 pixels of the study area. According to the algorithm results, 148 dust episode days (104 strong and 44 extreme) are found during the 2005-2018 period in the Mediterranean Basin. Most of the episodes occur in July (27 strong- and 3 extreme-episode days) and April (25 strong- and 6 extreme-episode days) while dust episodes are not detected at all in November and December. It is also found that in April, March and May take place the highest number of extreme MB episodes (23 out of the total 44 ones).

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Observed Southern Ocean Cloud Properties and Shortwave Reflection. Part II: Phase Changes and Low Cloud Feedback*

Journal of Climate ◽

10.1175/jcli-d-14-00288.1 ◽

2014 ◽

Vol 27 (23) ◽

pp. 8858-8868 ◽

Cited By ~ 40

Author(s):

Daniel T. McCoy ◽

Dennis L. Hartmann ◽

Daniel P. Grosvenor

Keyword(s):

Solar Radiation ◽

Optical Depth ◽

Climate Models ◽

Phase Changes ◽

Shortwave Radiation ◽

Cloud Optical Depth ◽

Cloud Properties ◽

Low Cloud ◽

Model Transition ◽

Comparable Magnitude

Abstract Climate models produce an increase in cloud optical depth in midlatitudes associated with climate warming, but the magnitude of this increase and its impact on reflected solar radiation vary from model to model. Transition from ice to liquid in midlatitude clouds is thought to be one mechanism for producing increased cloud optical depth. Here observations of cloud properties are used from a suite of remote sensing instruments to estimate the effect of conversion of ice to liquid associated with warming on reflected solar radiation in the latitude band from 40° to 60°S. The calculated increase in upwelling shortwave radiation (SW↑) is found to be important and of comparable magnitude to the increase in SW↑ associated with warming-induced increases of optical depth in climate models. The region where the authors' estimate increases SW↑ extends farther equatorward than the region where optical depth increases with warming in models. This difference is likely caused by other mechanisms at work in the models but is also sensitive to the amount of ice present in climate models and its susceptibility to warming.

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Spectral invariant behavior of zenith radiance around cloud edges simulated by radiative transfer

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-14557-2010 ◽

2010 ◽

Vol 10 (6) ◽

pp. 14557-14581

Author(s):

J. C. Chiu ◽

A. Marshak ◽

Y. Knyazikhin ◽

W. J. Wiscombe

Keyword(s):

Radiative Transfer ◽

Optical Depth ◽

Cloud Optical Depth ◽

Cloud Properties ◽

Atmospheric Radiation Measurement ◽

Visible Wavelengths ◽

Thermodynamic Phase ◽

The Relationship ◽

Invariant Relationship ◽

Spectral Invariant

Abstract. A previous paper discovered a surprising spectral-invariant relationship in shortwave spectrometer observations taken by the Atmospheric Radiation Measurement (ARM) program. Here, using radiative transfer simulations, we study the sensitivity of this relationship to the properties of aerosols and clouds, to the underlying surface type, and to the finite field-of-view (FOV) of the spectrometer. Overall, the relationship is mostly sensitive to cloud properties and has little sensitivity to the other factors. At visible wavelengths, the relationship primarily depends on cloud optical depth regardless of cloud thermodynamic phase and drop size. At water-absorbing wavelengths, the slope of the spectral-invariant relationship depends primarily on cloud optical depth; the intercept, by contrast, depends primarily on cloud absorption properties, suggesting a new retrieval method for cloud drop effective radius. These results suggest that the spectral-invariant relationship can be used to infer cloud properties even with insufficient or no knowledge about spectral surface albedo and aerosol properties.

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