Retrieval of mixed layer height (MLH) from lidar using analytical methods and estimation of MLH growth rates over a tropical site Gadanki
05 May 2016-Vol. 9879, pp 155-168
TL;DR: In this paper, a single channel elastic-backscatter lidar system was developed in-house at National Atmospheric Research Laboratory, an institution under Department of Space and Government of India, for studies on boundary layer dynamics during convective periods.
Abstract: A single channel elastic-backscatter lidar system was developed in-house at National Atmospheric Research Laboratory, an institution under Department of Space and Government of India, for studies on boundary layer dynamics during convective periods. The developed lidar system operates at the second harmonic wavelength of Nd: YAG laser and uses biaxial configuration. The lidar system utilizes a mini PMT for detecting laser returns from the atmosphere and operates in the analogue mode of data acquisition. The analogue recorder operates at 20 MHz sampling and uses a 12 bit A to D converter. The lidar system capable to operate at a maximum vertical resolution 7.5 m and 1-sec time sampling. However, in the present study, the lidar was operated with 30 m vertical resolution and 30-sec time sampling to understand the boundary layer dynamics during convective periods. The lidar measurements conducted between January and March 2014 were used in the present study. The laser backscatters obtained at 532 nm wavelength were corrected for noise and range before application of above mentioned analytical methods. This study presents evaluation of mixed layer height (MLH) from lidar using different analytical methods such as gradient, variance and wavelet techniques and presentation of inter-comparison between methods to achieve suitable method for assessment of MLH. The estimated MLH is then compared with the simultaneous radiosonde observations and empirical model values. We computed the MLH growth rates and observed that a significant enhancement was seen during the transition from winter to pre-monsoon period which could be attributed to increased convective activity over the tropical site. We present the lidar measurements and discuss the MLH retrieval and growth rates over Gadanki using lidar measurements.
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TL;DR: In this paper, a signal processing methodology using different analytical techniques such as Gradient, IPM, LGM, Variance and Wavelet as its modules to derive the height of ABL on an automatic basis.
Abstract: The atmospheric boundary layer (ABL), the lowest layer of the atmosphere, is a highly dynamic layer that is influenced byseveral parameters such as surface heating, turbulence, moisture transport etc.,. The detection of the height of ABL plays a crucial role in aviation, pollution monitoring,meteorology and agriculture sectors. At present, several methods are available to identify the height of the boundary layer (BL), however with coarse temporal and spatial resolutions. LIDAR offers high resolution measurements oncontinuous basis. LIDAR is one of the active remote sensors of atmosphere works on the principle of radar but employs laser with fine pulse widths. LIDAR technique has been employed to study the altitude profiles of aerosols, clouds, winds,temperature and humidity layers in the atmosphere. In this paper, we show a signal processing methodology to derive the ABL height from LIDAR signals. The signal processing methodology uses different analytical techniques such as Gradient, IPM, LGM, Variance and Wavelet as its modules to derive the height of ABL on an automatic basis. The automatic detection of ABL height from LIDAR signals employs an algorithm that employs a correlation process that works on inter-comparison results between different analytical methods. All these processes undergo in a systematic manner to present the ABL height detection automatically over a period of time frame set. The minimum time period required for detection of ABL height on automatic basis needs half-hour time period. In this presentation, we show the results of LIDAR measurements corresponds to convective period and present the detection of ABL height using the above signal processing algorithm. Keywords-Atmosphere, ABL, Remote sensing, aerosols, LIDAR
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TL;DR: In this paper, the authors present a review of the literature on the analysis of profile measurements and the use of parameterisations and simple models, and suggest for the preprocessor development and for future research activities.
898 citations
"Retrieval of mixed layer height (ML..." refers background or methods in this paper
...This method uses the gradient of the described atmospheric parameter to detect the boundary for the MLH [6]....
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...The most conventional method uses radiosonde measured profiles of wind, temperature, and relative humidity (RH) [6]....
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...Several instrumentation techniques and analytical methods have been utilized for the study of the structural evolution of mixed layer height but they vary considerably due to their own constraints, and are dependent on the availability and resolution of vertical profile data [6]....
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...PC Computer system capable of providing continuous measurements of the key variables of the atmosphere with high spatial and temporal resolution leading to better sampling statistics of the instantaneous MLH [6]....
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TL;DR: In this paper, a new analytic solution to the lidar equation is presented, which realistically considers the scattering properties of the aerosols and the molecular atmosphere individually, and it is shown that accurate vertical profiles of the volume extinction cross section can be obtained with an uncalibrated lidar, provided that the total transmittance of the atmospheric layer being investigated is known.
Abstract: A new analytic solution to the lidar equation is presented, which realistically considers the scattering properties of the aerosols and the molecular atmosphere individually. With this solution, it is shown, in turbid atmospheres where the aerosols dominate the scattering properties, that accurate vertical profiles of the volume extinction cross section can be obtained with an uncalibrated lidar, provided that the total transmittance of the atmospheric layer being investigated is known. This solution is applied to data samples collected under very clear and under very dusty conditions.
427 citations
"Retrieval of mixed layer height (ML..." refers background in this paper
...For CBL LIDAR system, O(R) is 1 for heights more than 360 m above ground level [12]....
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...The lidar signal is usually background noise corrected and transformed into a variable that removes the range square [1/R(2)] dependence X(R) or its logarithm, S(R) [12], [ ]R P R P R X b − = ) ( ) ( (2) [ ] ) ( ln ) ( R X R S = (3) Where X(R) is called range corrected signal (RCS)....
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...The expression that relates laser energy output E0 and the backscattered signal P(R), in the case of a biaxial lidar configuration, is given by [12]...
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TL;DR: In this article, large-eddy simulation (LES) is used to investigate entrainment and structure of the inversion layer of a clear convectively driven planetary boundary layer (PBL) over a range of bulk Richardson numbers, Ri.
Abstract: The authors use large-eddy simulation (LES) to investigate entrainment and structure of the inversion layer of a clear convectively driven planetary boundary layer (PBL) over a range of bulk Richardson numbers, Ri. The LES code uses a nested grid technique to achieve fine resolution in all three directions in the inversion layer. Extensive flow visualization is used to examine the structure of the inversion layer and to illustrate the temporal and spatial interaction of a thermal plume and the overlying inversion. It is found that coherent structures in the convective PBL, that is, thermal plumes, are primary instigators of entrainment in the Ri range 13.6 # Ri # 43.8. At Ri 5 13.6, strong horizontal and downward velocities are generated near the inversion layer because of the plume‐interface interaction. This leads to folding of the interface and hence entrainment of warm inversion air at the plume’s edge. At Ri 5 34.5, the inversion’s strong stability prevents folding of the interface but strong horizontal and downward motions near the plume’s edge pull down pockets of warm air below the nominal inversion height. These pockets of warm air are then scoured off by turbulent motions and entrained into the PBL. The structure of the inversion interface from LES is in good visual agreement with lidar measurements in the PBL obtained during the Lidars in Flat Terrain field experiment. A quadrant analysis of the buoyancy flux shows that net entrainment flux (or average minimum buoyancy flux wu min) is identified with quadrant IV w2u1 , 0 motions, that is, warm air moving downward. Plumes generate both large negative quadrant II w1u2 , 0 and positive quadrant III w2u2 . 0 buoyancy fluxes that tend to cancel. The maximum vertical gradient in potential temperature at every (x, y) grid point is used to define a local PBL height, zi(x, y). A statistical analysis of zi shows that skewness of zi depends on the inversion strength. Spectra of zi exhibit a sensitivity to grid resolution. The normalized entrainment rate we/w * , where we and w * are entrainment and convective velocities, varies as ARi21 with A 0.2 in the range 13.6 # Ri # 43.8 and is in good agreement with convection tank measurements. For a clear convective PBL, the authors found that the finite thickness of the inversion layer needs to be considered in an entrainment rate parameterization derived from a jump condition.
378 citations
"Retrieval of mixed layer height (ML..." refers background in this paper
...The dynamics at the top of the ML has been shown to play a large role in the processes at the bottom of the boundary layer and thus becomes a major factor that governs pollutant concentrations and their transport [3]....
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...Furthermore, the entrainment near the top of the ABL is governed by complex dynamics and therefore, the ABL depth is variable on short time ranges [3][4]....
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TL;DR: This work presents methods suited for precise determination of the ABL structure's temporal evolution in a dynamic environment as complex as the Paris area and compares commonly used methods that permit ABL height retrievals from backscatter lidar signals under different meteorological conditions.
Abstract: The Paris area is strongly urbanized and is exposed to atmospheric
pollution events. To understand the chemical and physical processes
that are taking place in this area it is necessary to describe
correctly the atmospheric boundary-layer (ABL) dynamics and the ABL
height evolution. During the winter of 1994–1995, within the
framework of the Etude de la Couche Limite Atmospherique en
Agglomeration Parisienne (ECLAP) experiment, the vertical
structure of the ABL over Paris and its immediate suburbs was
extensively documented by means of lidar measurements. We present
methods suited for precise determination of the ABL structure’s
temporal evolution in a dynamic environment as complex as the Paris
area. The purpose is to identify a method that can be used on a
large set of lidar data. We compare commonly used methods that
permit ABL height retrievals from backscatter lidar signals under
different meteorological conditions. Incorrect tracking of the ABL
depth’s diurnal cycle caused by limitations in the methods is
analyzed. The study uses four days of the ECLAP experiment
characterized by different meteorological and synoptic
conditions.
327 citations
"Retrieval of mixed layer height (ML..." refers background or methods in this paper
...That can be considered as a gradient [8]....
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...Therefore, it is possible to use variance, σ2 of the range corrected backscattered signal to measure the Boundary Layer Height (BLH) [8]....
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...Therefore, it is possible to use variance, σ(2) of the range corrected backscattered signal to measure the Boundary Layer Height (BLH) [8]....
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...Generally lidar implements backscatter gradient and variance methods for identifying mixing layer height estimation studies [8]....
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...2 Double Gradient Method Double gradient method (DGM) uses minimum of the second order derivative of the range corrected signal, which is the location of the inflection point, as the height [8]....
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TL;DR: In this article, the Haar wavelet covariance transform was used to detect the boundary layer top from lidar backscatter profiles by locating the maximum in the covariance profiles.
Abstract: Several recent studies have utilized a Haar wavelet covariance transform to provide automated detection of the boundary layer top from lidar backscatter profiles by locating the maximum in the covariance profiles. This approach is effective where the vertical gradient in the backscatter is small within and above the boundary layer, and where the inversion is sharp and well defined. These near-ideal conditions are often not met, particularly under stable stratification where the inversion may be deep and is sometimes ill defined, and vertical gradients are common. Here the effects of vertical gradients and inversion depth on the covariance transform are examined. It is found that a significant dilation-dependent bias in the determination of the boundary layer top may result when using the published method. An alternative approach is developed utilizing multiple wavelet dilations, and is capable of identifying both the upper and lower limits of the backscatter transition zone associated with the inversion while remaining insensitive to mean vertical gradients in the background signal. This approach enables more detailed information on the small-scale structure of the inversion and entrainment zone to be retrieved than is possible using existing techniques.
267 citations