Comparison of MISR and MODIS cloud-top heights in the presence of cloud overlap

CIMSS, University of Wisconsin–Madison, Madison, WI 53706, United States
Remote Sensing of Environment (Impact Factor: 6.39). 03/2007; 107(1):200-210. DOI: 10.1016/j.rse.2006.09.030


Coincident MISR and MODIS cloud-top heights retrieved above two vertically pointing radar sites (ARM-SGP and UK-CFARR) are compared for 54 scenes between March 2000 and October 2003. The difference between MODIS and MISR cloud-top heights is assessed in situations where multiple cloud layers are present in a vertical column (i.e., cloud overlap or multilayered cloud). MISR stereo cloud-top heights are known to be sensitive to low-level clouds of high contrast (between two camera views) even if high clouds with a wide range of optical thicknesses are also present in the scene. MODIS retrieved cloud-top heights do not experience this problem as long as the highest cloud layer has a visible optical thickness greater than approximately 1. Consequently, the difference in cloud-top heights between MODIS and MISR is often large and positive in cloud overlap conditions. In cloud overlap conditions, small differences between MODIS and MISR cloud-top heights can be found where both instruments detect the highest cloud layer or, on the contrary, where they both fail to detect the highest cloud but instead detect some lower level cloud. The comparison with radar cloud-top heights on a 21-scene subset confirmed that large differences are associated with cloud overlap, but also showed that small differences can be found in similar situations if the highest layer is of large contrast (both instruments detect the highest cloud layer) or of extremely small optical thickness (both instruments fail to detect the highest cloud layer). With the use of a cloud-typing technique applied to MODIS data that can also identify areas containing cloud overlap, small differences were found to occur for 60–70% of all overlap pixels examined here, highlighting the weakness of using the MODIS-MISR cloud-top height differences as a sole indicator for automated cloud overlap detection. While the accuracy of the MODIS cloud-top pressure/height algorithm decreases as the cirrus optical thickness becomes less than 1, the MISR approach may still be able to infer an accurate cloud-top height depending on the cloud contrast between two view angles. However, synergy between the difference in MODIS-MISR cloud-top height analysis and the MODIS cloud-typing method could improve overlap detection for thin cirrus over low cloud situations and provide additional information on the cloud-top height of two distinct layers.

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Available from: Catherine Naud
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    • "As a result, the accurate estimation of Cloud Top Height (CTH) is appropriate in order to calculate and eliminate the parallax effect and it can provide the real location of the convective systems above the Earth's surface, more accurately. There are several studies that propose different approaches and methodologies to estimate the geometric CTH but they are mainly lacking in high accuracy or usually refer to small geographic areas [9] [10] [11] [12]. Our effort is to propose a robust, generalized and accurate methodology to estimate the geometrical height of different cloud features (especially convective ones) at a broad range of latitudes and longitudes. "
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    ABSTRACT: This study investigates the cloud top height estimation using nonlinear methods to Meteosat imagery. The suggested approach aims to develop an integrated statistical methodology to estimate the cloud top height on a pixel basis using Meteosat Second Generation water vapor imagery. Radiosonde measurements are used as reference dataset and a spatio-temporal correlation with Meteosat images is performed in order to collect a representative sample for the statistical analysis. Here, we apply Multi Layer Perceptron (MLP) and Support Vector Machines (SVM) and we compare the results to the Linear Regression model. The best results are achieved using SVM for regression. The proposed approach is very promising as it can be used for future in-depth analysis so as to develop a robust approach for geometrical height estimation on a pixel basis of the operational data of Meteosat imagery. It is noted that an accurate estimation of cloud top height can help to eliminate geometric restrictions (e.g. Parallax phenomenon) of the Meteosat satellite imagery, improving its usefulness in a wide area of applications and especially in satellite-based weather forecast.
    Full-text · Conference Paper · Apr 2013
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    • "[3] Multi‐layer cloud information cannot be retrieved from passive sensor data except when a thin layer overlaps optically thick warm clouds [e.g., Chang and Li, 2005] or a moderately thick ice clouds occurs over a water cloud over a water surface [Minnis et al., 2007]. In addition, multi‐layer clouds sometimes cause a cloud height retrieval error that depends on specific algorithm and cloud properties [Naud et al., 2007]. Additionally, retrievals of total cloud water path tend to be biased when an ice cloud overlaps a liquid water cloud [Minnis et al., 2007]. "
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    ABSTRACT: 1] A cloud frequency of occurrence matrix is generated using merged cloud vertical profiles derived from the satelliteborne CloudAerosol Lidar with Orthogonal Polarization (CALIOP) and cloud profiling radar. The matrix contains vertical profiles of cloud occurrence frequency as a function of the uppermost cloud top. It is shown that the cloud fraction and uppermost cloud top vertical profiles can be related by a cloud overlap matrix when the correlation length of cloud occurrence, which is interpreted as an effective cloud thickness, is introduced. The underlying assumption in establishing the above relation is that cloud overlap approaches random overlap with increasing distance separating cloud layers and that the probability of deviating from random overlap decreases exponentially with distance. One month of CloudAerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat data (July 2006) support these assumptions, although the correlation length sometimes increases with separation distance when the cloud top height is large. The data also show that the correlation length depends on cloud top hight and the maximum occurs when the cloud top height is 8 to 10 km. The cloud correlation length is equivalent to the decorrelation distance introduced by Hogan and Illingworth (2000) when cloud fractions of both layers in a twocloud layer system are the same. The simple relationships derived in this study can be used to estimate the topofatmosphere irradiance difference caused by cloud fraction, uppermost cloud top, and cloud thickness vertical profile differences.
    Full-text · Article · Jul 2010 · Journal of Geophysical Research Atmospheres
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    • "Almost all of the collocations found using this method with a MISR CTH of one to three kilometers and a Meteosat-9 CTH of three to five kilometers, were found in the South Atlantic Ocean between 40 • S and 60 • S. Visual analysis confirmed, that multilayer or broken cloud fields were often present in this area. As referenced in Naud et al. [4], MISR is more sensitive to low-level clouds of high contrast, and even if high cirrus clouds are present,it tends to track the more optically thick low-level clouds. Therefore, these collocations most likely corresponded to cases where Meteosat- 9 tracked high-level clouds while MISR tracked low-level clouds. "

    Preview · Thesis · Mar 2010
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