A Near-Global Climatology of Single-Layer and Overlapped Clouds and Their Optical Properties Retrieved from Terra/MODIS Data Using a New Algorithm

2005 ◽  
Vol 18 (22) ◽  
pp. 4752-4771 ◽  
Author(s):  
Fu-Lung Chang ◽  
Zhanqing Li
Keyword(s):  
Optical Properties ◽  
Optical Depth ◽  
Single Layer ◽  
Cloud Amount ◽  
Bimodal Distribution ◽  
Cirrus Clouds ◽  
Modis Data ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Terra Modis ◽  
High Clouds

Abstract Cloud overlapping has been a major issue in climate studies owing to a lack of reliable information available over both oceans and land. This study presents the first near-global retrieval and analysis of single-layer and overlapped cloud vertical structures and their optical properties retrieved by applying a new method to the Moderate Resolution Imaging Spectroradiometer (MODIS) data. Taking full advantage of the MODIS multiple channels, the method can differentiate cirrus overlapping lower water clouds from single-layer clouds. Based on newly retrieved cloud products using daytime Terra/MODIS 5-km overcast measurements sampled in January, April, July, and October 2001, global statistics of the frequency of occurrence, cloud-top pressure/temperature (Pc/Tc), visible optical depth (τVIS), and infrared emissivity (ɛ) are presented and discussed. Of all overcast scenes identified over land (ocean), the MODIS data show 61% (52%) high clouds (Pc < 500 hPa), 39% (48%) lower clouds (Pc > 500 hPa), and an extremely low occurrence (<4%) of Pc between 500 and 600 hPa. A distinct bimodal distribution of Pc is found and peaks at ∼275 and ∼725 hPa for high and low clouds, thus leaving a minimum in cloud in the middle troposphere. Out of the 61% (52%) of high clouds identified by MODIS, retrievals reveal that 41% (35%) are thin cirrus clouds (ɛ < 0.85 and Pc < 500 hPa) and the remaining 20% (17%) are thick high clouds (ɛ ≥ 0.85). Out of the 41% (35%) of thin cirrus, 29% (27%) are found to overlap with lower water clouds and 12% (8%) are single-layer cirrus. Total low-cloud amount (single-layer plus overlapped) out of all overcast scenes is thus 68% (39% + 29%) over land and 75% (48% + 27%) over ocean, which is greater than the cloud amounts reported by the MODIS and the International Satellite Cloud Climatology Project (ISCCP). Both retrieved overlapping and nonoverlapping cirrus clouds show similar mean τVIS of ∼1.5 and mean ɛ of ∼0.5. The optical properties of single-layer cirrus and single-layer water clouds agree well with the MODIS standard retrievals. Because the MODIS retrievals do not differentiate between cirrus and lower water clouds in overlap situations, large discrepancies are found for emissivity, cloud-top height, and optical depth for high cirrus overlapping lower water clouds.

scholarly journals Total and partial cloud amount detection during summermonths 2005 at Westerland (Sylt, Germany)

2008 ◽  
Vol 8 (4) ◽  
pp. 13479-13505 ◽  
Author(s):  
N. H. Schade ◽  
A. Macke ◽  
H. Sandmann ◽  
C. Stick
Keyword(s):  
Cloud Cover ◽  
Cloud Amount ◽  
Cirrus Clouds ◽  
Total Cloud Amount ◽  
The North ◽  
Seaside Resort ◽  
The North Sea ◽  
Sky Imager ◽  
Downward Radiation ◽  
High Clouds

Abstract. The detection of cloudiness is investigated by means of partial and total cloud amount estimations from pyrgeometer radiation measurements and all-sky imager observations. The measurements have been performed in Westerland, a seaside resort on the North Sea island of Sylt, Germany, during summer 2005. An improvement to previous studies on this subject results from the fact that for the first time partial cloud amount (PCA), defined as total cloud amounts without high clouds, calculations from longwave downward radiation (LDR) according to the APCADA-Algorithm (Dürr and Philipona, 2004) are validated against both human observations from the German Weather Service DWD at the nearby airport of Sylt and digital all-sky imaging. Differences between the resulting total cloud amounts (TCA's), defined as total cloud amount for all-cloud situations, derived from the camera images and from human observations are within ±1 octa in 72% and within ±2 octa in 85% of the cases. Compared to human observations PCA measurements according to APCADA underestimate the observed cloud cover in 47% of all cases and the differences are within ±1 octa in 60% and ±2 octa in 74% of all cases. Since high cirrus clouds can not be derived from LDR, separate comparisons for all cases without high clouds have been performed showing an agreement within ±1(2) octa in 73(90)% for PCA and also for camera derived TCA. For this coastal mid-latitude site under investigation we find similar though slightly smaller agreements to human observations as reported in Dürr and Philipona (2004). Though limited to day-time the cloud cover retrievals from the sky imager are not much affected by cirrus clouds and provide a more reliable cloud climatology for all-cloud conditions than APCADA.

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

2019 ◽  
Vol 12 (3) ◽  
pp. 1717-1737 ◽  
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.

scholarly journals Satellite Observations of Cloud-Related Variations in Aerosol Properties

Atmosphere ◽  
2018 ◽  
Vol 9 (11) ◽  
pp. 430 ◽  
Author(s):  
Tamás Várnai ◽  
Alexander Marshak
Keyword(s):  
Particle Size ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Cloud Amount ◽  
Orthogonal Polarization ◽  
Radiative Processes ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Aerosol Properties

This paper presents an overview of our efforts to characterize and better understand cloud-related changes in aerosol properties. These efforts primarily involved the statistical analysis of global or regional datasets of Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol and cloud observations. The results show that in oceanic regions, more than half of all aerosol measurements by passive satellite instruments come from near-cloud areas, where clouds and cloud-related processes may significantly modify aerosol optical depth and particle size. Aerosol optical depth is also shown to increase systematically with regional cloud amount throughout the Earth. In contrast, it is shown that effective particle size can either increase or decrease with increasing cloud cover. In bimodal aerosol populations, the sign of changes depends on whether coarse mode or small mode aerosols are most affected by clouds. The results also indicate that over large parts of Earth, undetected cloud particles are not the dominant reason for the satellite-observed changes with cloud amount, and that 3D radiative processes contribute about 30% of the observed near-cloud changes. The findings underline the need for improving our ability to accurately measure aerosols near clouds.

scholarly journals Total and partial cloud amount detection during summer 2005 at Westerland (Sylt, Germany)

2009 ◽  
Vol 9 (4) ◽  
pp. 1143-1150 ◽  
Author(s):  
N. H. Schade ◽  
A. Macke ◽  
H. Sandmann ◽  
C. Stick
Keyword(s):  
Cloud Cover ◽  
Cloud Amount ◽  
Cirrus Clouds ◽  
Total Cloud Amount ◽  
The North ◽  
Seaside Resort ◽  
The North Sea ◽  
Sky Imager ◽  
Downward Radiation ◽  
High Clouds

Abstract. The detection of cloudiness is investigated by means of partial and total cloud amount estimations from pyrgeometer radiation measurements and visible all-sky imager observations. The measurements have been performed in Westerland, a seaside resort on the North Sea island of Sylt, Germany, during summer 2005. An improvement to previous studies on this subject resulting in the first time partial cloud amounts (PCAs), defined as cloud amounts without high clouds calculated from longwave downward radiation (LDR) according to the APCADA algorithm (Dürr and Philipona, 2004), are validated against both human observations from the National Meteorological Servive DWD at the nearby airport of Sylt and digital all-sky imaging. The aim is to establish the APCADA scheme at a coastal midlatitude site for longterm observations of cloud cover and to quantify errors resulting from the different methods of detecting cloudiness. Differences between the resulting total cloud amounts (TCAs), defined as cloud amount for all-cloud situations, derived from the camera images and from human observations are within ±1 octa in 72% and within ±2 octa in 85% of the cases. Compared to human observations, PCA measurements, according to APCADA, underestimate the observed cloud cover in 47% of all cases and the differences are within ±1 octa in 60% and ±2 octa in 74% of all cases. Since high cirrus clouds can not be derived from LDR, separate comparisons for all cases without high clouds have been performed showing an agreement within ±1(2) octa in 73(90)% for PCA and also for camera-derived TCA. For this coastal mid-latitude site under investigation, we find similar though slightly smaller agreements to human observations as reported by Dürr and Philipona (2004). Though limited to daytime, the cloud cover retrievals from the sky imager are not really affected by cirrus clouds and provide a more reliable cloud climatology for all-cloud conditions than APCADA.

scholarly journals Simultaneous Determination of Aerosol and Thin Cirrus Optical Depths over Oceans from MODIS Data: Some Case Studies

2006 ◽  
Vol 63 (9) ◽  
pp. 2307-2323 ◽  
Author(s):  
J. K. Roskovensky ◽  
K. N. Liou
Keyword(s):  
Optical Depth ◽  
Crystal Size ◽  
A Priori ◽  
Lookup Table ◽  
Ice Crystal ◽  
Radiative Forcings ◽  
Modis Data ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Ice Crystal Size

Abstract The importance of separating thin cirrus and aerosols from satellite remote sensing to produce broader and more accurate fields for the determination of respective radiative forcings is highlighted. This has been accomplished through the development of a new methodology for retrieving both thin cirrus and aerosol optical depths simultaneously over oceans from the Moderate Resolution Imaging Spectroradiometer (MODIS) data. This method employs a procedure to quantify and remove the thin cirrus contribution to the observed reflectance through a correlation of visible and 1.38-μm reflectances so that the aerosol signal can be extracted. Aerosol optical depths are then retrieved through comparisons with the simulated reflectances created a priori. Using the aerosol optical depth along with the specific viewing geometry and surface reflectance as pointers to locations in a lookup table of modeled reflectances, cirrus optical depth and an effective ice crystal size can be retrieved. An iterative scheme has been created that uses the retrieved effective cirrus ice crystal size to account for the effect that the particle size distribution has on the correlation of visible and 1.38-μm reflectance. Retrievals of both aerosol and thin cirrus optical depths over the Atmospheric Radiation Measurement (ARM) Tropical Western Pacific (TWP) site of Nauru performed on a limited number of cases have proven to be consistent with values determined from ground measurements. Also, comparisons with the MODIS aerosol retrievals over a broad area of ocean have highlighted the potential usefulness of this procedure in increasing the amount of potential aerosol information recovered and removing the ever-present thin cirrus contamination.

scholarly journals Validation of MODIS 3 km land aerosol optical depth from NASA's EOS Terra and Aqua missions

2018 ◽  
Vol 11 (5) ◽  
pp. 3145-3159 ◽  
Author(s):  
Pawan Gupta ◽  
Lorraine A. Remer ◽  
Robert C. Levy ◽  
Shana Mattoo
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Data Sets ◽  
Global Land ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Sensor Degradation ◽  
Terra Modis ◽  
Over Time

Abstract. In addition to the standard resolution product (10 km), the MODerate resolution Imaging Spectroradiometer (MODIS) Collection 6 (C006) data release included a higher resolution (3 km). Other than accommodations for the two different resolutions, the 10 and 3 km Dark Target (DT) algorithms are basically the same. In this study, we perform global validation of the higher-resolution aerosol optical depth (AOD) over global land by comparing against AErosol RObotic NETwork (AERONET) measurements. The MODIS–AERONET collocated data sets consist of 161 410 high-confidence AOD pairs from 2000 to 2015 for Terra MODIS and 2003 to 2015 for Aqua MODIS. We find that 62.5 and 68.4 % of AODs retrieved from Terra MODIS and Aqua MODIS, respectively, fall within previously published expected error bounds of ±(0.05 + 0.2 × AOD), with a high correlation (R= 0.87). The scatter is not random, but exhibits a mean positive bias of ∼ 0.06 for Terra and ∼ 0.03 for Aqua. These biases for the 3 km product are approximately 0.03 larger than the biases found in similar validations of the 10 km product. The validation results for the 3 km product did not have a relationship to aerosol loading (i.e., true AOD), but did exhibit dependence on quality flags, region, viewing geometry, and aerosol spatial variability. Time series of global MODIS–AERONET differences show that validation is not static, but has changed over the course of both sensors' lifetimes, with Terra MODIS showing more change over time. The likely cause of the change of validation over time is sensor degradation, but changes in the distribution of AERONET stations and differences in the global aerosol system itself could be contributing to the temporal variability of validation.

scholarly journals Climatology Of Thin Cirrus Clouds at Gadanki (13.5°N, 79.2°E) Using Ground Based Lidar And Satellite Based Measurements

2014 ◽  
Vol XL-8 ◽  
pp. 283-286
Author(s):  
G. S. Motty ◽  
G. S. Jayeshlal ◽  
M. Satyanarayana
Keyword(s):  
Optical Properties ◽  
High Altitude ◽  
Optical Depth ◽  
Global Scale ◽  
Cirrus Clouds ◽  
Statistical Characteristics ◽  
Lidar System ◽  
Radiative Balance ◽  
Geometrical Properties ◽  
Ground Based Lidar

High altitude cirrus clouds play a significant role in the radiative balance of Earth atmosphere system. Information on cirrus occurrences and their optical properties is essential for climate modeling studies. The influence of high altitude thin cirrus clouds on the climate is important due to their optical and thermodynamic properties. In order to quantify their effect on atmosphere, the vertical structure and optical properties of these thin cirrus clouds are to be characterized. The Lidar technique has become a unique tool for detecting and characterizing cirrus clouds for their optical properties. Ground based LIDAR system offers an excellent way to obtain characteristic values on the cirrus formations, although the microphysical and optical properties of thin cirrus clouds can also obtained on global scale by the observations from Earth-orbiting Satellites .The ground-based lidar observations could provide more intensive measurements on continuous basis, compared to satellite observations. Utilising observations from both, the statistical characteristics, physical and optical properties of thin cirrus clouds can be retrieved more precisely. The present study is based on the ground based lidar measurements using the pulsed monostatic LIDAR system at the National Atmospheric Research Laboratory [NARL], Gadanki (13.5&deg; N, 79.2&deg; E), Andhra Pradesh, India. The data obtained in the altitude range of 8&minus;20 km are used for this study. Cirrus observations made using CALIPSO and MODIS satellites are compared with the ground based lidar data for systematic statistical study of cirrus climatology. Optically thin cirrus clouds (τ < 0.3) observed during 2009 are selected and their microphysical and geometrical properties are studied. The microphysical properties such as optical depth, lidar ratio and depolarisation ratio for cirrus clouds were obtained. It is observed that the variability in optical depth depends on the composition and thickness of the clouds. The relationships between various quantities were also processed. The study shows that the thin cirrus generally was present in higher altitudes and the optical properties show correlation with the height and the temperature.

scholarly journals Improvement of aerosol optical depth retrieval from MODIS spectral reflectance over the global ocean using new aerosol models archived from AERONET inversion data and tri-axial ellipsoidal dust database data

2011 ◽  
Vol 11 (12) ◽  
pp. 33325-33355
Author(s):  
J. Lee ◽  
J. Kim ◽  
P. Yang
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Single Scattering ◽  
Lookup Table ◽  
Global Ocean ◽  
Dust Particles ◽  
Scattering Angle ◽  
Aerosol Model ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. New over-ocean aerosol models are developed by integrating extensive AERONET inversion data and a database of the optical properties of tri-axial ellipsoidal dust particles. These models allow more accurate retrieval of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) for high AOD cases. Spectral AOD, single scattering albedo (SSA), and phase function, which are used to calculate a lookup table (LUT), are archived by combining inversion data from Aerosol Robotic Network (AERONET) Sun/sky radiometers and single-scattering properties from the tri-axial ellipsoidal dust database. The aerosol models are categorized from the AERONET data using the fine-mode fraction (FMF) at 550 nm and the SSA at 440 nm to resolve a variety of aerosol types throughout the globe. For each aerosol model, the changes in aerosol optical properties (AOP) are included as functions of AOD. Comparisons of AODs between AERONET and MODIS for the period from 2003 to 2010 show that the new aerosol models improve correlation compared to the MODIS Collection 5 products with a Pearson coefficient of 0.93 and a regression slope of 0.99 compared to 0.92 and 0.85, respectively, for the MODIS operational algorithm. Moreover, use of the new algorithms increases the percentage of data within an expected error of ± (0.03 + 0.05 × AOD) from 62 to 64% overall and from 39 to 51% for high AOD cases (AOD > 0.3). Errors in the retrieved AOD are characterized further with respect to the Ångström exponent (AE), scattering angle (Θ), and air mass factor (AMF). Overall, the new aerosol models reduce systematic errors in AOD retrieval compared with the Collection 5 data due to realistic AOP assumptions. In particular, the scattering angle dependence of the retrieved AOD for dust cases is significantly mitigated due to improved treatment of the nonsphericity of dust particles by the new algorithm.

scholarly journals An improved cirrus detection algorithm MeCiDA2 for SEVIRI and its validation with MODIS

2012 ◽  
Vol 5 (4) ◽  
pp. 5271-5311 ◽  
Author(s):  
F. Ewald ◽  
L. Bugliaro ◽  
H. Mannstein ◽  
B. Mayer
Keyword(s):  
Optical Properties ◽  
Stratospheric Ozone ◽  
Detection Algorithm ◽  
Global Scale ◽  
Cirrus Clouds ◽  
Radiation Budget ◽  
High Temporal Resolution ◽  
Viewing Angle ◽  
Infrared Imager ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. The influence of cirrus clouds on the radiation budget of the Earth depends on their optical properties and their global coverage. The monitoring of cirrus coverage with instruments aboard geostationary satellites enables the investigation of cirrus clouds at the global scale as well as the identification of their diurnal variation. For instance, the Spinning Enhanced Visible and Infrared Imager (SEVIRI) aboard the Meteosat Second Generation (MSG) satellites provides data with high temporal resolution of 15 min and a spatial resolution of 3 km × 3 km at the sub-satellite point. In addition, the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the sun-synchronous platforms Terra and Aqua delivers at least one observation per day with a high spatial resolutions ranging from 250 m × 250 m to 1 km × 1 km. Since the infrared channels of the SEVIRI instrument are suitable for an observation which is independent from day-light, Krebs et al. (2007) developed a cirrus detection algorithm for SEVIRI (called MeCiDA), based solely on its thermal channels. Since MeCiDA was optimised for the area of Europe only, we present an improved version of the algorithm which allows application to the full Meteosat disc. Required changes include the consideration of the viewing angle dependency and of the sensitivity of the 9.7 μm channel to the ozone column. To this end, a correction is implemented that minimises the influence of the variability of the stratospheric ozone. The validation of the proposed improvements is carried out by using MeCiDA applied to MODIS data to address viewing angle-dependent cirrus detection and by additionally comparing it to the Cloud Optical Properties MOD06 cirrus product. The new MeCiDA version detects less cirrus than the original one for latitudes larger than 40° but almost the same amount elsewhere. MeCiDA's version for MODIS is more sensitive than that for SEVIRI with cirrus occurrences higher by 10%, and the new MeCiDA provides almost the same cirrus coverage (±0.1) as given by the Cloud Phase Optical Properties from MODIS for latitudes smaller than 50°. Finally, the influence of sub-pixel clouds on the SEVIRI cirrus detection has been examined: more than 60% of the undetected SEVIRI cirrus pixels have a cirrus coverage smaller than 0.5.

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