The Experimental Cloud Lidar Pilot Study (ECLIPS) for Cloud—Radiation Research

Platt, C. M. R.; Young, Stuart A.; Carswell, A. I.; Pal, S. R.; McCormick, M. P.; Winker, David M.; DelGuasta, M.; Stefanutti, L.; Eberhard, Wynn L.; Hardesty, M.; Flamant, Pierre H.; Valentin, R.; Forgan, Bruce; Gimmestad, Gary G.; Jäger, H.; Khmelevtsov, S. S.; Kolev, Ivan; Kaprieolev, B.; Lü, Daren; Sassen, Kenneth; Shamanaev, Vitalii S.; Uchino, Osamu; Mizuno, Yumiko; Wandinger, Ulla; Weitkamp, C.; Ansmann, Albert; Wooldridge, C. E.

doi:10.1175/1520-0477(1994)075<1635:teclps>2.0.co;2

Cited by 75 publications

(48 citation statements)

References 22 publications

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“…Cloud top can be determined by calculating the standard deviation of noise above cloud top, and moving downward in altitude from maximum range. This method was proposed by Platt et al (1994). Accordingly, the mid-cloud height is defined as the geometric center of the cirrus cloud.…”

Section: Methodsmentioning

confidence: 99%

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Giannakaki¹,

Balis²,

Amiridis

et al. 2007

Atmos. Chem. Phys.

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Abstract. Optical and geometrical characteristics of cirrus clouds over Thessaloniki, Greece (40.6 • N, 22.9 • E) have been determined from the analysis of lidar and radiosonde measurements performed during the period from 2000 to 2006. Cirrus clouds are generally observed in a mid-altitude region ranging from 8.6 to 13 km, with mid-cloud temperatures in the range from −65 • to −38 • C. The cloud thickness generally ranges from 1 to 5 km and 38% of the cases studied have thickness between 2 and 3 km. The retrieval of optical depth and lidar ratio of cirrus clouds is performed using three different methods, taking into account multiple scattering effect. The mean optical depth is found to be 0.31±0.24 and the corresponding mean lidar ratio is 30±17 sr following the scheme of Klett-Fernald method. Sub-visual, thin and opaque cirrus clouds are observed at 3%, 57% and 40% of the measured cases, respectively. A comparison of the results obtained between the three methods shows good agreement. The multiple scattering errors of the measured effective extinction coefficients range from 20 to 60%, depending on cloud optical depth. The temperature and thickness dependencies on optical properties have also been studied in detail. A maximum mid-cloud depth of ∼3.5 km is found at temperatures around ∼−47.5 • C, while there is an indication that optical depth and mean extinction coefficient increases with increasing mid-cloud temperature. A correlation between optical depth and thickness was also found. However, no clear dependence of the lidar ratio values on the cloud temperature and thickness was found.

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Section: Methodsmentioning

confidence: 99%

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Giannakaki¹,

Balis²,

Amiridis

et al. 2007

Atmos. Chem. Phys.

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“…Following Platt et al (1994), who used a threshold method to detect cloud bases, the PT algorithm is also using a threshold approach. Platt et al (1994) used a multiple of the standard deviation of the background fluctuations as a threshold to be exceeded by the attenuated backscatter signal as one of the conditions for cloud-base detection.…”

Section: Threshold Approachmentioning

confidence: 99%

“…Platt et al (1994) used a multiple of the standard deviation of the background fluctuations as a threshold to be exceeded by the attenuated backscatter signal as one of the conditions for cloud-base detection. This approach is similar to the definition of the SNR that is used in this study, with the value of the SNR threshold determining which data points remain for possible cloud-base detection by the PT algorithm.…”

Section: Threshold Approachmentioning

confidence: 99%

“…3.1, the background signal of clear polar air is extremely small. As noise levels are lowest near the surface, the standard deviation of this background signal near the surface is accordingly extremely small, which is problematic for using the method by Platt et al (1994) that is based only on this standard deviation. This is conceptually visualized in Fig.…”

Section: Threshold Approachmentioning

confidence: 99%

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An improved algorithm for polar cloud-base detection by ceilometer over the ice sheets

et al. 2014

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Abstract.Optically thin ice and mixed-phase clouds play an important role in polar regions due to their effect on cloud radiative impact and precipitation. Cloud-base heights can be detected by ceilometers, low-power backscatter lidars that run continuously and therefore have the potential to provide basic cloud statistics including cloud frequency, base height and vertical structure. The standard cloud-base detection algorithms of ceilometers are designed to detect optically thick liquid-containing clouds, while the detection of thin ice clouds requires an alternative approach. This paper presents the polar threshold (PT) algorithm that was developed to be sensitive to optically thin hydrometeor layers (minimum optical depth τ ≥ 0.01). The PT algorithm detects the first hydrometeor layer in a vertical attenuated backscatter profile exceeding a predefined threshold in combination with noise reduction and averaging procedures. The optimal backscatter threshold of 3 × 10 −4 km −1 sr −1 for cloud-base detection near the surface was derived based on a sensitivity analysis using data from Princess Elisabeth, Antarctica and Summit, Greenland. At higher altitudes where the average noise level is higher than the backscatter threshold, the PT algorithm becomes signal-to-noise ratio driven. The algorithm defines cloudy conditions as any atmospheric profile containing a hydrometeor layer at least 90 m thick. A comparison with relative humidity measurements from radiosondes at Summit illustrates the algorithm's ability to significantly discriminate between clear-sky and cloudy conditions. Analysis of the cloud statistics derived from the PT algorithm indicates a year-round monthly mean cloud cover fraction of 72 % (±10 %) at Summit without a seasonal cycle. The occurrence of optically thick layers, indicating the presence of supercooled liquid water droplets, shows a seasonal cycle at Summit with a monthly mean summer peak of 40 % (±4 %). The monthly mean cloud occurrence frequency in summer at Princess Elisabeth is 46 % (±5 %), which reduces to 12 % (±2.5 %) for supercooled liquid cloud layers. Our analyses furthermore illustrate the importance of optically thin hydrometeor layers located near the surface for both sites, with 87 % of all detections below 500 m for Summit and 80 % below 2 km for Princess Elisabeth. These results have implications for using satellite-based remotely sensed cloud observations, like CloudSat that may be insensitive for hydrometeors near the surface. The decrease of sensitivity with height, which is an inherent limitation of the ceilometer, does not have a significant impact on our results. This study highlights the potential of the PT algorithm to extract information in polar regions from various hydrometeor layers using measurements by the robust and relatively low-cost ceilometer instrument.

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“…The first step of the methodology is to identify the presence of cirrus clouds, by using the method proposed by Platt et al, (1994) [2] . Hence the following geometrical properties are found: cloud base altitude, cloud top altitude and geometrical thickness.…”

Section: Methodology Basic Descriptionmentioning

confidence: 99%

Comparison of Cirrus Cloud Characteristics as Estimated by A Micropulse Ground-Based Lidar and A Spaceborne Lidar CALIOP Datasets Over Lille, France (50.60 °N, 3.14 ° E)

Nohra¹,

Parol²,

Dubuisson³

2016

EPJ Web of Conferences

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Our goal is to establish a climatology of cirrus cloud properties over Lille, France (50.60°N, 3.14 °E) using a ground-based lidar. A statistical analysis of mid-latitude cirrus clouds from lidar data in Lille over the period 2008-2013 is presented and discussed. The macrophysical properties (cloud base altitude, cloud top altitude, geometrical thickness, mid-cloud temperature) and optical properties (cloud optical thickness and lidar ratio) are evaluated and compared between the ground-based and the spaceborne lidar CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) measurements for the period 2008-2013. We found similar results of macrophysical properties derived from both lidars. In addition a difference in the optical properties results is due to the multiple scattering and the heterogeneity of the observed scenes.

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The Experimental Cloud Lidar Pilot Study (ECLIPS) for Cloud—Radiation Research

Cited by 75 publications

References 22 publications

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

An improved algorithm for polar cloud-base detection by ceilometer over the ice sheets

Comparison of Cirrus Cloud Characteristics as Estimated by A Micropulse Ground-Based Lidar and A Spaceborne Lidar CALIOP Datasets Over Lille, France (50.60 °N, 3.14 ° E)

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