scholarly journals Using Two-Stream Theory to Capture Fluctuations of Satellite-Perceived TOA SW Radiances Reflected from Clouds over Ocean

2020 ◽  
Author(s):  
Florian Tornow ◽  
Carlos Domenech ◽  
Howard W. Barker ◽  
René Preusker ◽  
Jürgen Fischer
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Cloud Water ◽  
Effective Radius ◽  
Distribution Models ◽  
New Approach ◽  
Cloud Albedo ◽  
Cloud Parameters

Abstract. Shortwave (SW) fluxes estimated from broadband radiometry rely on empirically gathered and hemispherically resolved fields of outgoing top-of-atmosphere (TOA) radiances. This study aims to provide more accurate and precise fields of TOA SW radiances reflected from clouds over ocean by introducing a novel semi-physical model predicting radiances per narrow sun-observer geometry. Like previous approaches, this model was trained using CERES-measured radiances paired with MODIS-retrieved cloud parameters as well as reanalysis-based geophysical parameters. By using radiative transfer approximations as a framework to ingest above parameters, the new approach incorporates cloud-top effective radius and above-cloud water vapor in addition to traditionally used cloud optical depth, cloud fraction, cloud phase, and surface wind speed. A two-stream cloud albedo – serving as a function of cloud optical thickness and cloud-top effective radius – and Cox-Munk ocean reflectance were used to describe an albedo over each CERES footprint. A simple equation of radiative transfer, with this albedo and attenuating above-cloud water vapor as inputs, was used in its log-linear form to allow for statistical optimization. We identified the two-stream cloud albedo that minimized radiance residuals and outperformed the state-of-the-art approach for most observer-geometries and solar zenith angles between 20° and 70°, reducing median standard deviations of radiance residuals per solar geometry by up to 13.2 % for liquid clouds, 1.9 % for ice clouds, and 35.8 % for footprints containing both cloud phases. Tested for a variety of scenes, we further demonstrated the plausibility of scene-wise predicted radiance fields. This new approach may prove useful when employed in Angular Distribution Models and may result in improved flux estimates, in particular dealing with clouds characterized by small or large droplet/crystal sizes.

scholarly journals Using two-stream theory to capture fluctuations of satellite-perceived TOA SW radiances reflected from clouds over ocean

2020 ◽  
Vol 13 (7) ◽  
pp. 3909-3922
Author(s):  
Florian Tornow ◽  
Carlos Domenech ◽  
Howard W. Barker ◽  
René Preusker ◽  
Jürgen Fischer
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
State Of The Art ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Cloud Water ◽  
Effective Radius ◽  
The State ◽  
Distribution Models ◽  
New Approach

Abstract. Shortwave (SW) fluxes estimated from broadband radiometry rely on empirically gathered and hemispherically resolved fields of outgoing top-of-atmosphere (TOA) radiances. This study aims to provide more accurate and precise fields of TOA SW radiances reflected from clouds over ocean by introducing a novel semiphysical model predicting radiances per narrow sun-observer geometry. This model was statistically trained using CERES-measured radiances paired with MODIS-retrieved cloud parameters as well as reanalysis-based geophysical parameters. By using radiative transfer approximations as a framework to ingest the above parameters, the new approach incorporates cloud-top effective radius and above-cloud water vapor in addition to traditionally used cloud optical depth, cloud fraction, cloud phase, and surface wind speed. A two-stream cloud albedo – serving to statistically incorporate cloud optical thickness and cloud-top effective radius – and Cox–Munk ocean reflectance were used to describe an albedo over each CERES footprint. Effective-radius-dependent asymmetry parameters were obtained empirically and separately for each viewing-illumination geometry. A simple equation of radiative transfer, with this albedo and attenuating above-cloud water vapor as inputs, was used in its log-linear form to allow for statistical optimization. We identified the two-stream functional form that minimized radiance residuals calculated against CERES observations and outperformed the state-of-the-art approach for most observer geometries outside the sun-glint and solar zenith angles between 20 and 70∘, reducing the median SD of radiance residuals per solar geometry by up to 13.2 % for liquid clouds, 1.9 % for ice clouds, and 35.8 % for footprints containing both cloud phases. Geometries affected by sun glint (constituting between 10 % and 1 % of the discretized upward hemisphere for solar zenith angles of 20 and 70∘, respectively), however, often showed weaker performance when handled with the new approach and had increased residuals by as much as 60 % compared to the state-of-the-art approach. Overall, uncertainties were reduced for liquid-phase and mixed-phase footprints by 5.76 % and 10.81 %, respectively, while uncertainties for ice-phase footprints increased by 0.34 %. Tested for a variety of scenes, we further demonstrated the plausibility of scene-wise predicted radiance fields. This new approach may prove useful when employed in angular distribution models and may result in improved flux estimates, in particular dealing with clouds characterized by small or large droplet/crystal sizes.

Changes in TOA SW Fluxes over Marine Clouds When Estimated via Semi-Physical Angular Distribution Models

2021 ◽  
Author(s):  
F. Tornow ◽  
C. Domenech ◽  
J. N. S. Cole ◽  
N. Madenach ◽  
J. Fischer
Keyword(s):  
Angular Distribution ◽  
Optical Depth ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Cloud Water ◽  
Effective Radius ◽  
Distribution Models ◽  
Radiative Fluxes ◽  
Cloud Optical Depth ◽  
Aerosol Indirect Effects

AbstractTop-of-atmosphere (TOA) shortwave (SW) angular distribution models (ADMs) approximate – per angular direction of an imagined upward hemisphere – the intensity of sunlight scattered back from a specific Earth-atmosphere scene. ADMs are, thus, critical when converting satellite-borne broadband radiometry into estimated radiative fluxes. This paper applies a set of newly developed ADMs with a more refined scene definition and demonstrates tenable changes in estimated fluxes compared to currently operational ADMs. Newly developed ADMs use a semi-physical framework to consider cloud-top effective radius, , and above-cloud water vapor, ACWV, in addition to accounting for surface wind speed and clouds’ phase, fraction, and optical depth. In effect, instantaneous TOA SWfluxes for marine liquid-phase clouds had the largest flux differences (of up to 25 W m−2) for lower solar zenith angles and cloud optical depth greater than 10 due to extremes in or ACWV. In regions where clouds had persistently extreme levels of (here mostly for <7μm and >15μm) or ACWV, instantaneous fluxes estimated from Aqua, Terra, and Meteosat 8 and 9 satellites using the two ADMs differed systematically, resulting in significant deviations in daily mean fluxes (up to ±10 W m−2) and monthly mean fluxes (up to ±5 W m−2). Flux estimates using newly developed, semi-physical ADMs may contribute to a better understanding of solar fluxes over low-level clouds. It remains to be seen whether aerosol indirect effects are impacted by these updates.

scholarly journals Deuterium excess in marine water vapor: Dependency on relative humidity and surface wind speed during evaporation

2014 ◽  
Vol 119 (2) ◽  
pp. 584-593 ◽  
Author(s):  
Marion Benetti ◽  
Gilles Reverdin ◽  
Catherine Pierre ◽  
Liliane Merlivat ◽  
Camille Risi ◽  
...  
Keyword(s):  
Water Vapor ◽  
Wind Speed ◽  
Relative Humidity ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Marine Water ◽  
Deuterium Excess

scholarly journals Maritime-Continental Contrasts in the Properties of Low-Level Clouds: A Case Study of the Summer of the 2003 Yamase, Japan, Cloud Event

2014 ◽  
Vol 2014 ◽  
pp. 1-16 ◽  
Author(s):  
Nawo Eguchi ◽  
Tadahiro Hayasaka ◽  
Masahiro Sawada
Keyword(s):  
Cloud Water ◽  
Effective Radius ◽  
Mountainous Terrain ◽  
Combined Effects ◽  
Low Level ◽  
Stratus Clouds ◽  
Cloud Parameters ◽  
Cloud Water Path ◽  
The Relationship

Satellite data were used to investigate maritime-continental differences in the characteristics of the low-level cloud (the Yamase cloud) that covered northeast Japan during the summer of 2003. The features of the Yamase cloud were found to be almost the same as those of general stratus clouds but with a smaller effective radius (re) and a greater optical thickness (τ) over land, as compared with general stratus clouds. The values ofreover land (average, 11.8 μm) were smaller than those over the ocean (13.5 μm), and the values ofτand the cloud water path over land (20 and 145 gm−2, resp.) showed larger spatial variances than those over the ocean (10 and 86 gm−2, resp.), although the cloud top altitude was nearly the same over both ocean and land (1–3 km). We suggest that this maritime-continental contrast is a result of the combined effects of topography and aerosols characteristics. The Yamase wind blowing from the ocean is forced upwards in coastal regions by the steep mountainous terrain. The updraft drives the inhomogeneity in cloud parameters, and a convective-like cloud develops without precipitation. The relationship betweenreandτsuggests high aerosol concentrations and unstable conditions over land.

scholarly journals Validation of the Hurricane Imaging Radiometer Forward Radiative Transfer Model for a Convective Rain Event

2019 ◽  
Vol 11 (22) ◽  
pp. 2650
Author(s):  
Abdusalam Alasgah ◽  
Maria Jacob ◽  
Linwood Jones ◽  
Larry Schneider
Keyword(s):  
Radiative Transfer ◽  
Brightness Temperature ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Temperature Measurements ◽  
Radiative Transfer Model ◽  
Squall Line ◽  
Transfer Model ◽  
Rain Event ◽  
Brightness Temperatures

The airborne Hurricane Imaging Radiometer (HIRAD) was developed to remotely sense hurricane surface wind speed (WS) and rain rate (RR) from a high-altitude aircraft. The approach was to obtain simultaneous brightness temperature measurements over a wide frequency range to independently retrieve the WS and RR. In the absence of rain, the WS retrieval has been robust; however, for moderate to high rain rates, the joint WS/RR retrieval has not been successful. The objective of this paper was to resolve this issue by developing an improved forward radiative transfer model (RTM) for the HIRAD cross-track viewing geometry, with separated upwelling and specularly reflected downwelling atmospheric paths. Furthermore, this paper presents empirical results from an unplanned opportunity that occurred when HIRAD measured brightness temperatures over an intense tropical squall line, which was simultaneously observed by a ground based NEXRAD (Next Generation Weather Radar) radar. The independently derived NEXRAD RR created the simultaneous 3D rain field “surface truth”, which was used as an input to the RTM to generate HIRAD modeled brightness temperatures. This paper presents favorable results of comparisons of theoretical and the simultaneous, collocated HIRAD brightness temperature measurements that validate the accuracy of this new HIRAD RTM.

Direct Assimilation of AMSR-E Brightness Temperatures for Estimating Sea Ice Concentration

2012 ◽  
Vol 140 (3) ◽  
pp. 997-1013 ◽  
Author(s):  
K. Andrea Scott ◽  
Mark Buehner ◽  
Alain Caya ◽  
Tom Carrieres
Keyword(s):  
Radiative Transfer ◽  
Sea Ice ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Ocean Model ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Sea Ice Concentration ◽  
Brightness Temperatures ◽  
Ice Concentration

Abstract In this paper a method to directly assimilate brightness temperatures from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) to produce ice concentration analyses within a three-dimensional variational data assimilation system is investigated. To assimilate the brightness temperatures a simple radiative transfer model is used as the forward model that maps the state vector to the observation space. This allows brightness temperatures to be modeled for all channels as a function of the total ice concentration, surface wind speed, sea surface temperature, ice temperature, vertically integrated water vapor, and vertically integrated cloud liquid water. The brightness temperatures estimated by the radiative transfer model are sensitive to the specified values for the sea ice emissivity. In this paper, two methods of specifying the sea ice emissivity are compared. The first uses a constant value for each polarization and frequency, while the second uses a simple emissivity parameterization. The emissivity parameterization is found to significantly improve the fit to the observations, reducing both the bias and the standard deviation. Results from the assimilation of brightness temperatures are compared with those from assimilating a retrieved ice concentration in the context of initializing a coupled ice–ocean model for an area along the east coast of Canada. It is found that with the emissivity parameterization the assimilation of brightness temperatures produces ice concentration analyses that are in slightly better agreement with operational ice charts than when assimilating an ice concentration retrieval, with the most significant improvements during the melt season.

Assessment of the Quality of MODIS Cloud Products from Radiance Simulations

2009 ◽  
Vol 48 (8) ◽  
pp. 1591-1612 ◽  
Author(s):  
Seung-Hee Ham ◽  
Byung-Ju Sohn ◽  
Ping Yang ◽  
Bryan A. Baum
Keyword(s):  
Water Vapor ◽  
Radiative Transfer ◽  
Satellite Observation ◽  
Effective Radius ◽  
Radiative Transfer Model ◽  
Cloud Base ◽  
Transfer Model ◽  
Sufficient Information ◽  
Water Vapor Absorption ◽  
Absorption Bands

Abstract Observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS), the Atmospheric Infrared Sounder (AIRS), the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and CloudSat are synergistically used to evaluate the accuracy of theoretical simulations of the radiances at the top of the atmosphere (TOA). Specifically, TOA radiances of 15 MODIS bands are simulated for overcast, optically thick, and single-phase clouds only over the ocean from 60°N to 60°S, corresponding to about 12% of all the MODIS cloud observations. Plane parallel atmosphere is assumed in the simulation by restricting viewing/solar zenith angle to be less than 40°. Input data for the radiative transfer model (RTM) are obtained from the operational MODIS-retrieved cloud optical thickness, effective radius, and cloud-top pressure (converted to height) collocated with the AIRS-retrieved temperature and humidity profiles. In the RTM, ice cloud bulk scattering properties, based on theoretical scattering computations and in situ microphysical data, are used for the radiative transfer simulations. The results show that radiances for shortwave bands between 0.466 and 0.857 μm appear to be very accurate with errors on the order of 5%, implying that MODIS cloud parameters provide sufficient information for the radiance simulations. However, simulated radiances for the 1.24-, 1.63-, and 3.78-μm bands do not agree as well with the observed radiances as a result of the use of a single effective radius for a cloud layer that may be vertically inhomogeneous in reality. Furthermore, simulated radiances for the water vapor absorption bands located near 0.93 and 1.38 μm show positive biases, whereas the window bands from 8.5 to 12 μm show negative biases compared to observations, likely due to the less accurate estimate of cloud-top and cloud-base heights. It is further shown that the accuracies of the simulations for water vapor and window bands can be substantially improved by accounting for the vertical cloud distribution provided by the CALIPSO and CloudSat measurements.

scholarly journals Improvement of the detection of desert dust over the Sahel using METEOSAT IR imagery

2006 ◽  
Vol 24 (8) ◽  
pp. 2065-2073 ◽  
Author(s):  
G. Vergé-Dépré ◽  
M. Legrand ◽  
C. Moulin ◽  
A. Alias ◽  
P. François
Keyword(s):  
Radiative Transfer ◽  
Arid Regions ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Meteorological Conditions ◽  
Dust Layer ◽  
Desert Dust ◽  
Solar Elevation ◽  
The Arid Regions ◽  
Aerosol Properties

Abstract. Desert dust over the arid regions of Africa is detected using the Infrared Difference Dust Index (IDDI) derived from the thermal infrared (TIR) channel of METEOSAT. However, the comparison with photometric aerosol optical thickness (AOT) of this dust index reveals some discrepancies. Using an instrumented site in Sahel where aerosol properties and meteorological conditions were monitored daily during the dry season, we performed radiative transfer computations with the MODTRAN 4.1 code to develop a method to improve the IDDI usefulness. We found that discrepancies between AOT and IDDI variations mostly come from changes in the surface temperature (Ts), which is an important parameter for radiative transfer computations in the TIR. We show that this temperature varies from day to day with the surface wind speed and during the course of the season with the solar elevation, and that it is possible, for the site considered, to correct Ts from these combined effect using a simple parameterization. We also observe that the dust layer itself has an impact on Ts by reducing the amount of solar radiation at the surface, and that this phenomenon can also be accounted for by adding an AOT-dependence to the above parameterization of Ts. We show that this parameterization allows improving the agreement between the IDDI and the photometric AOT.

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