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Research paper thumbnail of Removing the thermal component of the NOAA-AVHRR Channel 3 in cloudy conditions

IGARSS '98. Sensing and Managing the Environment. 1998 IEEE International Geoscience and Remote Sensing. Symposium Proceedings. (Cat. No.98CH36174), 1998

Abstract.- In this paper, an operational method for the extraction of solar component from the AV... more Abstract.- In this paper, an operational method for the extraction of solar component from the AVHRR-Channel 3 radiance, is addressed. This is based on the implementation of a simple radiative transfer model that explains the radiative behavior of each pixel in the image. ...

Research paper thumbnail of <title>Discretization of effective droplet radius in order to extract stratocumulus cloud parameters from NOAA-AVHRR channel 3</title>

Satellite Remote Sensing of Clouds and the Atmosphere III, 1998

ABSTRACT In this work, a method for the retrieval of droplet radius, temperature and optical thic... more ABSTRACT In this work, a method for the retrieval of droplet radius, temperature and optical thickness of oceanic stratocumulus is developed.It is based on night imagery obtained from the NOAA-AVHRR IR channels and an atmospheric radiative transfer model that makes use of the discrete ordinate method called DISORT. Using this mode, we have simulated the theoretical radiance that reaches the satellite supposing a planar homogeneous cloud layer. The stratocumulus clouds are assumed to be composed by spherical water droplets with a gamma size distribution that provides a particular effective radius. The single scattering parameters are deduced from Mie&#39;s theory. Once evaluated the model behavior, we must invert a non lineal system of three equations to obtain the cloud parameters from the channels, 3,4 and 5 brightness temperatures. The main problem is the behavior of the radiative parameters when the effective radius is varied, because exist several values that provide the same temperatures. That implies that the systems have not a unique solution and, in order to avoid this problem we propose an optimal radii discretization on the basis of the above-mentioned microphysical features.

Research paper thumbnail of Method to estimate the emissivity from NOAA-AVHRR channel 3 in order to extract a distribution of effective droplet radius of stratocumulus clouds

Satellite Remote Sensing of Clouds and the Atmosphere III, 1998

In this work, a method to estimate the emissivity distribution is developed for stratocumulus clo... more In this work, a method to estimate the emissivity distribution is developed for stratocumulus clouds paying special attention to water vapor over these clouds. The main aim is to obtain an approximate distribution of effective radius for optically thick stratocumulus clouds. This method is based on night imagery obtained from the NOAA-AVHRR IR channels, and an atmospheric radiative transfer model that makes use of the discrete ordinate method called DISORT. We have solved the problem of the local estimation, for the Canary Islands, of the influence of the water vapor over the stratocumulus level. Finally we associate the emissivity distribution with the distribution of the droplet effective radius. This allows us to estimate a unique effective radius for the cloud taking advantage of statistic in the image in order to avoid the non-monotonous behavior of emissivity with the droplet effective radius in the 3.7 micrometers band. The results are compared with satellite data from NOAA-14.

Research paper thumbnail of Stratocumulus parameter retrieval using MODIS nighttime imagery: a theoretical approach

Remote Sensing of Clouds and the Atmosphere V, 2001

This work is a preliminary study of the viability of retrieving macro physical and micro physical... more This work is a preliminary study of the viability of retrieving macro physical and micro physical cloud parameters from nighttime radiances provided by MODIS sensor, onboard Terra spacecraft. It is based on the analysis of the sensitivity of every MODIS IR band to each of ...

Research paper thumbnail of Retrieval of Marine Stratus Cloud Droplet Size from NOAA–AVHRR Nighttime Imagery

Remote Sensing of Environment, 2000

A method for retrieval of the droplet radius and temscopic, including water content, droplet size... more A method for retrieval of the droplet radius and temscopic, including water content, droplet size, and its phase. In turn, the sizes and number of droplets are reperature of oceanic stratocumulus is presented. It is lated with the cloud condensation nuclei (CCN) concenbased on night imagery obtained from the infrared chantration present during the cloud formation (Twomey, nels of NOAA-AVHRR and an atmospheric radiative 1977; Twomey et al., 1984). In recent years, data from transfer model that makes use of the discrete ordinate multispectral radiometers have been used to extract method DISORT. It uses the observed satellite brightness these parameters, especially data provided by the Adtemperature differences (BTD) between channels 4 and 5 vanced Very High Resolution Radiometer (AVHRR) on to obtain the cloud temperature and between channels 3 board National Oceanic and Atmospheric Administration and 4 to extract the effective radius of the cloud droplets. (NOAA) operational satellites. We also studied the peculiarities of the method, taking Numerous studies have addressed getting the painto account the behavior of the single scattering paramerameters that characterize clouds of very different naters, deduced from Mie theory, with droplet size. Results ture, from fog (Wetzel et al., 1996) to cirrus (Ou et al., obtained are compared with in situ data collected at the 1993), including midlevel and low clouds, such as strato-Canary Islands (Spain) during summer 1996. ©Elsevier cumulus, and even overlapping clouds at different Science Inc., 2000 heights (Baum et al., 1994). Relationships between the different satellite channels are used in both the visible and the infrared regions, to obtain the microscopic and

Research paper thumbnail of Chemical and microphysical properties of marine stratiform cloud in the North Atlantic

Journal of Geophysical Research: Atmospheres, 1998

The chemical and microphysical properties of marine stratiform cloud were measured at a ridgetop ... more The chemical and microphysical properties of marine stratiform cloud were measured at a ridgetop elevation of 992 m above mean sea level (AMSL) on Tenerife in the Canary Islands in the eastern North Atlantic during the summers of 1995 and 1996. The results show an inverse relationship between hourly-averaged cloud droplet diameter and droplet number concentration, which ranged from 116 to 1355 cm-3. Strong relationships were observed between droplet number and equivalent clear air concentrations of non-sea-salt sulfate, nitrate, and elemental carbon in the droplets. Droplet sizes inferred from radiances measured by satellite for clouds offshore and upwind agreed with droplet sizes derived for clouds over the mountain sampling site, and also with those measured in cloud 4-5 hours later. Estimated cloud shortwave radiative forcing was enhanced by 8% in radiative model studies of polluted versus clean clouds with droplet concentrations of 786 and 127 cm a and droplet effective radii of 6 and 10 [tm, respectively. 1. Introduction Clouds play an important role in regulating global climate through heat and water transfer and by interacting with shortwave and longwave radiation. A crucial aspect of global climate change is the potential effect of anthropogenic aerosols on clouds. Twomey [1977] and Twomey et al. [1984] suggested that increases in anthropogenic or natural cloud condensation nuclei (CCN) would increase cloud droplet numbers, decrease droplet size, and increase cloud optical depth and albedo. This is the so-called "Twomey effect", and it may be similar in magnitude but opposite in sign to the "greenhouse effect", such that the reduction in the net flux of solar energy reaching the surface (a negative radiative forcing) due to increased globally averaged cloud albedo could counterbalance the atmospheric warming caused by greenhouse gases. Numerous estimates of changes in cloud radiative forcing due to the influence of anthropogenic aerosols have been made [e.g., Charlson et al., 1992; Jones et al., 1994; Boucher and Lohmann, 1995]. Chuang et al.[1997] estimated the average annual global cloud radiative forcing due to anthropogenic aerosol sulfate to be-0.6 to-1.6 W m '2. The greatest uncertainty in the global radiation balance equation is our knowledge of the magnitude of the indirect effect of aerosols on clouds [Schwartz and Andreae, 1996].

Research paper thumbnail of Stratocumulus properties retrieval method from NOAA-AVHRR data based on the discretization of cloud parameters

International Journal of Remote Sensing, 2002

A method is presented for determining the optical thickness, effective droplet radius and tempera... more A method is presented for determining the optical thickness, effective droplet radius and temperature of oceanic stratocumulus clouds from NOAA-AVHRR infrared channels. The satellite data used in the present study correspond to night-time images in which large-...

Research paper thumbnail of Removing the thermal component of the NOAA-AVHRR Channel 3 in cloudy conditions

IGARSS '98. Sensing and Managing the Environment. 1998 IEEE International Geoscience and Remote Sensing. Symposium Proceedings. (Cat. No.98CH36174), 1998

Abstract.- In this paper, an operational method for the extraction of solar component from the AV... more Abstract.- In this paper, an operational method for the extraction of solar component from the AVHRR-Channel 3 radiance, is addressed. This is based on the implementation of a simple radiative transfer model that explains the radiative behavior of each pixel in the image. ...

Research paper thumbnail of <title>Discretization of effective droplet radius in order to extract stratocumulus cloud parameters from NOAA-AVHRR channel 3</title>

Satellite Remote Sensing of Clouds and the Atmosphere III, 1998

ABSTRACT In this work, a method for the retrieval of droplet radius, temperature and optical thic... more ABSTRACT In this work, a method for the retrieval of droplet radius, temperature and optical thickness of oceanic stratocumulus is developed.It is based on night imagery obtained from the NOAA-AVHRR IR channels and an atmospheric radiative transfer model that makes use of the discrete ordinate method called DISORT. Using this mode, we have simulated the theoretical radiance that reaches the satellite supposing a planar homogeneous cloud layer. The stratocumulus clouds are assumed to be composed by spherical water droplets with a gamma size distribution that provides a particular effective radius. The single scattering parameters are deduced from Mie&#39;s theory. Once evaluated the model behavior, we must invert a non lineal system of three equations to obtain the cloud parameters from the channels, 3,4 and 5 brightness temperatures. The main problem is the behavior of the radiative parameters when the effective radius is varied, because exist several values that provide the same temperatures. That implies that the systems have not a unique solution and, in order to avoid this problem we propose an optimal radii discretization on the basis of the above-mentioned microphysical features.

Research paper thumbnail of Method to estimate the emissivity from NOAA-AVHRR channel 3 in order to extract a distribution of effective droplet radius of stratocumulus clouds

Satellite Remote Sensing of Clouds and the Atmosphere III, 1998

In this work, a method to estimate the emissivity distribution is developed for stratocumulus clo... more In this work, a method to estimate the emissivity distribution is developed for stratocumulus clouds paying special attention to water vapor over these clouds. The main aim is to obtain an approximate distribution of effective radius for optically thick stratocumulus clouds. This method is based on night imagery obtained from the NOAA-AVHRR IR channels, and an atmospheric radiative transfer model that makes use of the discrete ordinate method called DISORT. We have solved the problem of the local estimation, for the Canary Islands, of the influence of the water vapor over the stratocumulus level. Finally we associate the emissivity distribution with the distribution of the droplet effective radius. This allows us to estimate a unique effective radius for the cloud taking advantage of statistic in the image in order to avoid the non-monotonous behavior of emissivity with the droplet effective radius in the 3.7 micrometers band. The results are compared with satellite data from NOAA-14.

Research paper thumbnail of Stratocumulus parameter retrieval using MODIS nighttime imagery: a theoretical approach

Remote Sensing of Clouds and the Atmosphere V, 2001

This work is a preliminary study of the viability of retrieving macro physical and micro physical... more This work is a preliminary study of the viability of retrieving macro physical and micro physical cloud parameters from nighttime radiances provided by MODIS sensor, onboard Terra spacecraft. It is based on the analysis of the sensitivity of every MODIS IR band to each of ...

Research paper thumbnail of Retrieval of Marine Stratus Cloud Droplet Size from NOAA–AVHRR Nighttime Imagery

Remote Sensing of Environment, 2000

A method for retrieval of the droplet radius and temscopic, including water content, droplet size... more A method for retrieval of the droplet radius and temscopic, including water content, droplet size, and its phase. In turn, the sizes and number of droplets are reperature of oceanic stratocumulus is presented. It is lated with the cloud condensation nuclei (CCN) concenbased on night imagery obtained from the infrared chantration present during the cloud formation (Twomey, nels of NOAA-AVHRR and an atmospheric radiative 1977; Twomey et al., 1984). In recent years, data from transfer model that makes use of the discrete ordinate multispectral radiometers have been used to extract method DISORT. It uses the observed satellite brightness these parameters, especially data provided by the Adtemperature differences (BTD) between channels 4 and 5 vanced Very High Resolution Radiometer (AVHRR) on to obtain the cloud temperature and between channels 3 board National Oceanic and Atmospheric Administration and 4 to extract the effective radius of the cloud droplets. (NOAA) operational satellites. We also studied the peculiarities of the method, taking Numerous studies have addressed getting the painto account the behavior of the single scattering paramerameters that characterize clouds of very different naters, deduced from Mie theory, with droplet size. Results ture, from fog (Wetzel et al., 1996) to cirrus (Ou et al., obtained are compared with in situ data collected at the 1993), including midlevel and low clouds, such as strato-Canary Islands (Spain) during summer 1996. ©Elsevier cumulus, and even overlapping clouds at different Science Inc., 2000 heights (Baum et al., 1994). Relationships between the different satellite channels are used in both the visible and the infrared regions, to obtain the microscopic and

Research paper thumbnail of Chemical and microphysical properties of marine stratiform cloud in the North Atlantic

Journal of Geophysical Research: Atmospheres, 1998

The chemical and microphysical properties of marine stratiform cloud were measured at a ridgetop ... more The chemical and microphysical properties of marine stratiform cloud were measured at a ridgetop elevation of 992 m above mean sea level (AMSL) on Tenerife in the Canary Islands in the eastern North Atlantic during the summers of 1995 and 1996. The results show an inverse relationship between hourly-averaged cloud droplet diameter and droplet number concentration, which ranged from 116 to 1355 cm-3. Strong relationships were observed between droplet number and equivalent clear air concentrations of non-sea-salt sulfate, nitrate, and elemental carbon in the droplets. Droplet sizes inferred from radiances measured by satellite for clouds offshore and upwind agreed with droplet sizes derived for clouds over the mountain sampling site, and also with those measured in cloud 4-5 hours later. Estimated cloud shortwave radiative forcing was enhanced by 8% in radiative model studies of polluted versus clean clouds with droplet concentrations of 786 and 127 cm a and droplet effective radii of 6 and 10 [tm, respectively. 1. Introduction Clouds play an important role in regulating global climate through heat and water transfer and by interacting with shortwave and longwave radiation. A crucial aspect of global climate change is the potential effect of anthropogenic aerosols on clouds. Twomey [1977] and Twomey et al. [1984] suggested that increases in anthropogenic or natural cloud condensation nuclei (CCN) would increase cloud droplet numbers, decrease droplet size, and increase cloud optical depth and albedo. This is the so-called "Twomey effect", and it may be similar in magnitude but opposite in sign to the "greenhouse effect", such that the reduction in the net flux of solar energy reaching the surface (a negative radiative forcing) due to increased globally averaged cloud albedo could counterbalance the atmospheric warming caused by greenhouse gases. Numerous estimates of changes in cloud radiative forcing due to the influence of anthropogenic aerosols have been made [e.g., Charlson et al., 1992; Jones et al., 1994; Boucher and Lohmann, 1995]. Chuang et al.[1997] estimated the average annual global cloud radiative forcing due to anthropogenic aerosol sulfate to be-0.6 to-1.6 W m '2. The greatest uncertainty in the global radiation balance equation is our knowledge of the magnitude of the indirect effect of aerosols on clouds [Schwartz and Andreae, 1996].

Research paper thumbnail of Stratocumulus properties retrieval method from NOAA-AVHRR data based on the discretization of cloud parameters

International Journal of Remote Sensing, 2002

A method is presented for determining the optical thickness, effective droplet radius and tempera... more A method is presented for determining the optical thickness, effective droplet radius and temperature of oceanic stratocumulus clouds from NOAA-AVHRR infrared channels. The satellite data used in the present study correspond to night-time images in which large-...