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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Integrated Aerosol Extinction Profiles from Ceilometer and Sunphotometer Combination against Sunphotometer Measurements at Various Heights
摘要： The aerosol extinction profiles at Granada (Spain) have been obtained combining ceilometer and sun/sky measurements in the GRASP code. In order to see the goodness of these retrieved profiles, three photometers at different altitudes have been used. The aerosol optical depth (AOD) at different height layers have been calculated with these photometers and it has been compared against the integrated retrieved extinction at the same layers. The obtained AOD (from GRASP and from photometers at different altitudes) correlates well, showing the most of r2 values above 0.6. The differences between both AOD values indicates that the retrieved aerosol extinction profiles are within the uncertainty of the photometers but this method overestimates the extinction at low levels and underestimates at high levels.
关键词： Validation,GRASP,Aerosol Optical Depth,Aerosol Extinction,Ceilometer
更新于2025-09-23 15:21:21
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Evaluation of cloud base height measurements from Ceilometer CL31 and MODIS satellite over Ahmedabad, India
摘要： Clouds play a tangible role in the Earth’s atmosphere and in particular, the cloud base height (CBH), which is linked to cloud type, is one of the most important characteristics to describe the influence of clouds on the environment. In the present study, CBH observations from Ceilometer CL31 were extensively studied during May 2013 to January 2015 over Ahmedabad (23.03? N, 72.54? E), India. A detailed comparison has been performed with the use of ground-based CBH measurements from Ceilometer CL31 and CBH retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) onboard Aqua and Terra satellite. CBH retrieved from MODIS is ～ 1.955 and ～ 1.093 km on 25 July 2014 and 1 January 2015 respectively, which matches well with ceilometer-measured CBH (～ 1.92 and ～ 1.097 km). Some interesting features of cloud dynamics viz. strong downdraft and updraft have been observed over Ahmedabad which revealed different cloud characteristics during monsoon and post-monsoon periods. CBH shows seasonal variation during the Indian summer monsoon and post-monsoon period. Results indicate that the ceilometer is an excellent instrument to precisely detect low- and mid-level clouds, and the MODIS satellite provides accurate retrieval of high-level clouds over this region. The CBH algorithm used for the MODIS satellite is also able to capture the low-level clouds.
关键词： monsoon,satellite,MODIS,post-monsoon,cloud dynamics,cloud base height,ceilometer
更新于2025-09-23 15:21:21
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A comparison between laser ceilometers at Hong Kong International Airport
摘要： The Vaisala LD12 ceilometer has been in use at the meteorological garden at Hong Kong International Airport (HKIA) since its opening in mid-1998. Another model, the LD40, was installed at the airport in the early 2000s. These instruments are mainly used for providing cloud base height measurements for reference in aviation weather reporting. The data are available on several platforms, including the aerodrome meteorological observing system and a web-based self-briefing system for pilots. Technical support for the LD12 and LD40 models is no longer provided by the manufacturer, and they are due to be replaced at HKIA by a new model with the latest laser ceilometer technology, such as the CL31. To assure continuity of cloud base height measurement, a field comparison between the LD12 and the CL31 was conducted at the meteorological garden at HKIA between July 2010 and June 2011. Another field comparison was performed between the LD40 and the CL31 over a period of 2 years from January 2016 to December 2017. In each comparison, the two ceilometers were separated by about 10m and were pointing vertically upwards without mutual interference. Photographs of the ceilometer field comparison setups are shown in Figure 1. This paper describes the analysis of the ceilometer data for the assurance of continuity of cloud base height measurements following the equipment change. It is hoped that the findings presented here might provide a useful reference for other airports implementing similar equipment replacements.
关键词： ceilometer,CL31,LD40,Hong Kong International Airport,aviation meteorology,cloud base height,LD12
更新于2025-09-11 14:15:04
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An improved algorithm for polar cloud-base detection by ceilometer over the ice sheets
摘要： 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.
关键词： optically thin ice clouds,cloud-base detection,polar regions,mixed-phase clouds,ceilometer
更新于2025-09-10 09:29:36
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Accuracy Analysis of the Aerosol Backscatter Coefficient Profiles Derived from the CYY-2B Ceilometer
摘要： Ceilometers are originally designed for cloud base height monitoring. Since a few years, the number of ceilometers available worldwide is rapidly increasing, and these simple backscatter lidars are investigated to be used for aerosol research. This study presents an assessment of the potential of CYY-2B ceilometer for the quantitative retrieval of aerosol properties. The signal-to-noise ratio of the ceilometer is calculated, and the e?ective height of inversion is determined. It is shown that the e?ective height of the ceilometer for backscatter coe?cient pro?le inversion is 3-4 km at night and about 1.5–2 km during the day, which is lower than that of the micropulse lidar (MPL) system. The accuracy of the backscatter coe?cient pro?les derived from the CYY-2B ceilometer is analyzed by using the Vaisala CL51 ceilometer, MPL, forward scatter visibility instrument, and aerosol optical depth (AOD) dataset from aerosol robotic network (AERONET). Spectral conversions of the ceilometer’s and lidar’s data are performed using the ?Angstr¨om exponent estimated by AERONET measurements. A good agreement is found between two ceilometers and the MPL lidar in backscatter coe?cient pro?les inversion. The AODs agree well with the AERONET AODs during the observation period of small AODs. However, for the period of large AODs, the results are approximately 50%–60% of AERONET AODs. The limited range of extinction integration is the main cause of this problem.
关键词： ceilometer,AERONET,aerosol optical depth,aerosol backscatter coefficient,signal-to-noise ratio
更新于2025-09-10 09:29:36
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A comprehensive statistical study of cloud base height using ceilometer over western India
摘要： A comprehensive statistical analysis of the cloud base height (CBH) measured by ground-based Vaisala ceilometer (CL31) has been performed to study different layers of the cloud in the lower troposphere up to 7.5 km height over Ahmedabad, western India during 2014 and 2015. The total observations (≈69%) of cloud by using ceilometer show annual cloud occurrence frequency of around 64%. Seasonal variation of CBH and cloud occurrence frequency reveal that the maximum/minimum cloud cover is found during southwest (SW) Indian summer monsoon/pre-monsoon season. Three CBHs (CBH1, CBH2, and CBH3) are presented in monsoon period due to high cloud occurrence, and two CBHs (CBH1 and CBH2) are observed in other seasons due to low cloud occurrence by ceilometer over the observational site. The CBH1 (≈100–2000 m) and CBH2 (500–3000 m) are observed during SW monsoon and summer season, respectively. The CBH3 is occurred usually in SW monsoon season. Moreover, the cloud cover during the day and night time shows that the occurrence of cloud is more frequent in daytime than nighttime during pre-monsoon and post-monsoon season. The statistical analysis of cloud with ground-based observations is also performed in this study that may be useful for the development/improvement of regional weather and climate models to reduce the uncertainty in the prediction.
关键词： CBH,Occurrence frequency,Ceilometer,Indian Monsoon
更新于2025-09-09 09:28:46
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Assessment of mixed-layer height estimation from single-wavelength ceilometer profiles
摘要： Differing boundary/mixed-layer height measurement methods were assessed in moderately polluted and clean environments, with a focus on the Vaisala CL51 ceilometer. This intercomparison was performed as part of ongoing measurements at the Chemistry And Physics of the Atmospheric Boundary Layer Experiment (CAPABLE) site in Hampton, Virginia and during the 2014 Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field campaign that took place in and around Denver, Colorado. We analyzed CL51 data that were collected via two different methods (BLView software, which applied correction factors, and simple terminal emulation logging) to determine the impact of data collection methodology. Further, we evaluated the STRucture of the ATmosphere (STRAT) algorithm as an open-source alternative to BLView (note that the current work presents an evaluation of the BLView and STRAT algorithms and does not intend to act as a validation of either). Filtering criteria were defined according to the change in mixed-layer height (MLH) distributions for each instrument and algorithm and were applied throughout the analysis to remove high-frequency fluctuations from the MLH retrievals. Of primary interest was determining how the different data-collection methodologies and algorithms compare to each other and to radiosonde-derived boundary-layer heights when deployed as part of a larger instrument network. We determined that data-collection methodology is not as important as the processing algorithm and that much of the algorithm differences might be driven by impacts of local meteorology and precipitation events that pose algorithm difficulties. The results of this study show that a common processing algorithm is necessary for light detection and ranging (lidar)-based MLH intercomparisons and ceilometer-network operation, and that sonde-derived boundary layer heights are higher (10–15 % at midday) than lidar-derived mixed-layer heights. We show that averaging the retrieved MLH to 1 h resolution (an appropriate timescale for a priori data model initialization) significantly improved the correlation between differing instruments and differing algorithms.
关键词： boundary layer,radiosonde,ceilometer,lidar,mixed-layer height,air quality
更新于2025-09-09 09:28:46
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Recommendations for processing atmospheric attenuated backscatter profiles from Vaisala CL31 ceilometers
摘要： Ceilometer lidars are used for cloud base height detection, to probe aerosol layers in the atmosphere (e.g. detection of elevated layers of Saharan dust or volcanic ash), and to examine boundary layer dynamics. Sensor optics and acquisition algorithms can strongly influence the observed attenuated backscatter profiles; therefore, physical interpretation of the profiles requires careful application of corrections. This study addresses the widely deployed Vaisala CL31 ceilometer. Attenuated backscatter profiles are studied to evaluate the impact of both the hardware generation and firmware version. In response to this work and discussion within the CL31/TOPROF user community (TOPROF, European COST Action aiming to harmonise ground-based remote sensing networks across Europe), Vaisala released new firmware (versions 1.72 and 2.03) for the CL31 sensors. These firmware versions are tested against previous versions, showing that several artificial features introduced by the data processing have been removed. Hence, it is recommended to use this recent firmware for analysing attenuated backscatter profiles. To allow for consistent processing of historic data, correction procedures have been developed that account for artefacts detected in data collected with older firmware. Furthermore, a procedure is proposed to determine and account for the instrument-related background signal from electronic and optical components. This is necessary for using attenuated backscatter observations from any CL31 ceilometer. Recommendations are made for the processing of attenuated backscatter observed with Vaisala CL31 sensors, including the estimation of noise which is not provided in the standard CL31 output. After taking these aspects into account, attenuated backscatter profiles from Vaisala CL31 ceilometers are considered capable of providing valuable information for a range of applications including atmospheric boundary layer studies, detection of elevated aerosol layers, and model verification.
关键词： attenuated backscatter,aerosol layers,model verification,atmospheric boundary layer,ceilometer,Vaisala CL31,lidar
更新于2025-09-04 15:30:14