This paper reports the results of a study related to the optical and physical characteristics of columnar aerosols and variation in total column ozone (TCO) and precipitable water content (PWC) over Gadanki (13.45°N, 79.18°E), a tropical station in peninsular India, for the first time, using MICROTOPS-II (Microprocessor-based Total Ozone Portable Spectrometer), comprising of both sun photometer and ozonometer. Results show wavelength dependence of AOD, having mean value of ~0.4 (± 0.09) at 500 nm optical channel. Daily mean aerosol size spectra shows, most of the time, power-law distribution. However, its diurnal variations show significant changes in aerosol size spectra modulated by a combination of both power-law and bi-modal distributions. To characterize AOD, the Ångström parameters (i.e., α and β) were used. The day-to-day variations in TCO were found to be in fair agreement with that derived from TOMS satellite data for all the experimental days, having mean observed value of ~253 (± 8) DU over the station. Interestingly, an inverse relationship between TCO and AOD or PWC was observed over the station, on some times of the day, which could be attributed to the mixing of significant fraction of ozone with aerosol and water vapor-rich air mass. However, a significant positive correlation was observed between AOD and PWC.

This study presents the daily and seasonal variation of the atmospheric mixing layer height (MLH) over Gadanki, India (13.45(degrees)N, 79.18(degrees)E), a tropical rural location based on polarization lidar observations. The observations spanned the years 2009-2014, encompassing 303 instances, and coinciding with radiosonde and surface weather station measurements. The MLH was determined through the analysis of aerosol profiles and confirmed with the MLH values derived from radiosonde data. The lidar depolarization ratio was employed to characterize aerosol shape. This study aims to establish a connection between aerosol backscatter and its shape through lidar observations, considering diurnal and seasonal variations, while also identifying the influencing factors. This study illustrates four distinct case studies conducted during different seasons to depict aerosol behavior in both convectively active and non-active periods. These case studies unveil the influence of aerosol shape on water intake and subsequent residual layer and cloud formation. The observed fluctuations in MLH and aerosol shape suggest a dynamic relationship between local meteorology and long-range aerosol transport.

The vertical distribution of aerosols in the lower troposphere is critically important for assessing their impact on Earth's radiation budget and modulation of cloud microphysics. This study analyzed cloud‐free aerosol extinction coefficient ( β ext ), aerosol subtypes, and particulate depolarization ratios obtained from CALIOP (Cloud‐Aerosol Lidar with Orthogonal Polarization) over the six regions of India during 2008–2018. We investigated unprecedented climatology of the physical and optical characteristics of elevated aerosol layers (EALs) along with their source and formation mechanism. The key findings include: (a) EALs over the Indian region were persistent between 4 and 6 km during all seasons, (b) geometrical layer thickness of EALs increased up to 36.7% and 25% from the annual mean during summer and fall seasons, respectively, compared to that of spring and winter, (c) dust and polluted dust accounted for up to 50%–80% from near‐surface to 6 km and up to 80%–90% of the EALs between 4 and 6 km, respectively for all the seasons and regions, (d) we anticipated that locally confined recirculation coupled with stratified stable layer capped within turbulent layers could be a possible mechanism of formation of stratified EALs between 4 and 6 km during winter‐spring‐fall, while in summer, vertical transport of pollutants from the PBL to mid‐troposphere due to enhanced deep convection served as a key formation mechanism of the EALs, (e) the second Modern‐Era Retrospective analysis for Research and Applications Global Modeling Initiative model reasonably simulated the shape and vertical gradient of β ext with significant differences in magnitude below 4 km; however, it fails to reproduce EALs for all seasons and regions during the study period.

<p>LIDAR is an optical profiler that generally works during clear sky periods.  Lidars operation during disturbed weather conditions is rare [1]. An Infrared lidar sensor was developed indigenously at NARL site to profile clouds and rain during thunderstorm periods. The lidar operates in slant mode through a window and make measurements continuously during cloudburst periods. The developed lidar employs a Nd:YAG laser that operates at its fundamental spectrum in the Infrared band and works in pulsed mode. A spare optical tube assembly (OTA) is employed in the experimental work for collecting the backscattered infrared photons. A high degree of alignment made between laser and OTA units to collect light photons from far ranges. An adjustable conical pin-hole system is employed in the present work, which permitted lidar to function in daylight period. A silicon avalanche photodiode (APD) is used in the demonstration work for optical sensing and signal conditioning. Thin-film interference (IF) filter doublet and a peltier cooled APD supported the lidar measurements at room temperature conditions. An Ethernet interfaced single channel transient recorder unit employed in the receiver measurements, which digitizes signal at 40 MHz rate. The experimental data were recorded at one-second sampling with 7.5 m range resolution. The pump laser uses an in-line optical attenuator that switches at 20 pulses per second. The laser radar probes the atmosphere at a slant angle through a window of the lidar room. The lidar first measurement during thunder clouds and rain is shown in Figure 1. Figure 1 contains two panels. The first panel illustrates the range time intensity map generated using the lidar data that collected between 1200 and 1300 Hrs LT on November 2018 at NARL site. The data plotted in Figure 1 correspond to 7.5 m range resolution at one second time sampling. The other panel of Figure 1 indicates the height profile of lidar range corrected signal (RCS) that obtained at 1203 Hrs LT, which has been shown indicate the lidar signal strength during cloud conditions.  One can notice from Figure 1 the downward movement of thunderstorm cloud deck with time, which further leads fall of rain over land.  One can see rainfall as varying streaks of intensity with range. Different color bands shown in Figure 1 indicate the variations in the intensity of lidar RCS. The red color band indicates the peak value that represents the thunderstorm cloud base. The yellow-orange represents heavy rain events, whereas the shades of green and blue color indicate light rain. The lidar signal overlap occurs at a range of around 100 m, which is 50 m above ground level.</p> <p><img src="" alt="" width="777" height="365" /></p> <p>Figure 1. Infrared lidar measurements of cloud and rain during thunderstorm period over NARL site through a window.</p> <p> </p> <p>References</p> <p> </p> <p>[1]. R. Vishnu, Y. Bhavani Kumar, T. Narayana Rao, Anish Kumar M. Nair, A. Jayaraman , “Development of lidar sensor for cloud-based measurements during convective conditions,”, Proc. SPIE. 9876, Remote Sensing of the Atmosphere, Clouds, and Precipitation VI</p> <p> </p>

The rotational turbulence caused by mixing the layers of air, wind shear components, mountain waves, aerosol particles, and other pollutants affects the lowest and densest layer of the earth's surface troposphere. Due to the turbulence, the height of the convective boundary layer (CBLH) changes over the day dramatically. We observe the variation in peak positions of lidar backscatter signals by performing a statistical technique for analyzing the behavior of the convective boundary layer (CBL). After that, to examine the behavior of the whole boundary layer, a distribution method and histogram plots will be used. We provide the statistical method for getting the best fit distribution to show how the result leads to the physical observation of data.

The turbulence caused by vertical and horizontal components of wind shear, the presence of aerosol particles, and other pollutants affects the closest layer to the earth's surface i.e., the troposphere. Due to the turbulence, the height of the convective boundary layer (CBLH) changes over the day dramatically. To observe these changes in-depth, peaks of Lidar backscatter signals will be detected using a statistical technique. After that, a statistical technique to find the best fit distribution will be used to examine the behavior of the whole boundary layer.

We conducted laser radar measurements of the atmosphere during a strong thunderstorm condition over a tropical site in India. The laser radar was operated in the slant direction and has detected variability in precipitation in spatial direction.

Polarization lidar observations were made to study the transport of an elevated aerosol layer over Gadanki, India (13.45° N, 79.17° E) during the pre-monsoon period of the year 2009. Observations show significant aerosol layering within and above the boundary layer. Coordinated observations with radiosondes were carried out from 2 to 10 April 2009. Temporal and spatial variations of the parameters are studied for the boundary layer (≈ 2.5 km) and up to 5 km. The backscattering coefficient and the depolarization ratio are observed to increase and decrease with an increase in humidity, respectively. Clouds are not formed, indicating less efficiency of the aerosol in acting as condensation nuclei. The transport of the elevated aerosol layer is investigated using a back-trajectory analysis, revealing that the transported layer originating from the central Indian region has a depolarization ratio of at least 0.05. From model analysis and satellite fire-count data, it is inferred that the source of the aerosol layer is wildfire events over the central Indian region. The elevated smoke-aerosol layer (not mixing with the boundary layer) has implications for the altering of the temperature profile of the atmosphere and the suppression of cloud formation.

Unique airborne observations made congruent to 330 km south of Mt. Everest during the Cloud-Aerosol Interaction Precipitation Enhancement EXperiment (CAIPEEX) 2014 are presented in this case study. These observations provide the vertical profile and elemental composition of aerosols from single particle analysis during the break period. An "aerosol dome" was also documented from the horizontal transect across the Varanasi city. The boundary layer was dominated by light scattering fine mode aerosols mainly a mixture of dust and pollution. The individual particle characterization revealed complex mixing states within the same aerosol aggregate. Externally mixed aerosols were present at the cloud bases. Elemental composition of aerosol particles collected from free atmosphere contained signatures of aged pollution with heavy metals, carbonaceous particles and radioactive elements. Cloud processed aerosols were also noted in the neighborhood of deep convective clouds. Shallow and deep cumulus clouds developing in the haze layer revealed distinct dropsize distributions. Shallow cumulus clouds embedded in the haze layer showed narrow droplet size distribution and were narrower than the ones observed for premonsoon conditions. Deep cumulus tops in the neighborhood of rapidly developing convection showed broad, bimodal droplet size distribution attributing to droplet evaporation and entrainment effects. Aerosol sampling near these cloud tops showed aggregates of particles that are internally mixed.

We constructed a polarization lidar system with single detector for atmospheric studies. The lidar employs a rotating polarizer in the optical part of the lidar receiver. The rotating polarizer contains a Glan Thomson prism which is used to separate the p- and s- components of incoming light. The rotation of polarizer is controlled through a stepper motor controller. The lidar contains a trigger unit, which is an integral part of lidar that controls the timing of rotation of polarizer and also the sequence of lidar signal acquisition. The integrated trigger unit is synchronized with laser Q– switch pulse and provides polarization discrimination in the incoming light with high degree angular alignment. The lidar uses an Nd:YAG pulsed laser for probing the atmosphere and is operated at low repetition rate to retrieve the coand cross polarized signal components from the single detector. Using the lidar setup, we derived the range resolved depolarization measurements of tropical cirrus at the second harmonic wavelength of Nd:YAG laser.

The ground-based lidar is an active remote sensing instrument to profile the lower atmosphere effectively. In general, a lidar receives an analog signal from a lower altitude, a photon count from a higher altitude, and glues them in order to profile the atmosphere effectively. We propose the Levinson recursion algorithm-based Wiener filter over an original lidar signal to convert an analog signal to virtual count. This count is further glued with photon counting through mean square error method, and the results are compared with the linear regression algorithm. It is found that the proposed algorithm enhances the scaled analog from 152 to 8780 MHz in 355 nm, 131 to 3591 MHz in 387 nm, and 79 to 2956 MHz in 408 nm wavelengths. Furthermore, the improvement in correlation coefficients is found to be 0.9899, 0.9942, and 0.9807 for 355, 387, and 408 nm wavelengths, respectively. The proposed algorithm can be applied to any ground-based lidar system for an accurate profiling of the lower atmospheric compositions. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)

In this paper, we propose an optical fiber design for a wide field of view (WFOV) lidar receiver. The proposed system intends to collect aerosol backscatter and aims to profile the lower atmosphere from 8 m onwards. We determined overlap function of lidar for various aperture stop diameters. As per our analysis, a fiber diameter of 21 mm is required at the focus point of telescope to obtain the full overlap at 8 m altitude. Since, it is impractical to realize such a large core diameter fiber of 21 mm, we propose a field lens to converge the blur disk to 3 mm spot size. To collect the focused beam, we propose to use a fused fiber bundle of 3.5 mm diameter. The fused fiber offers extraordinary capturing efficiency and projects an effective mode capturing area of 5 × 10−8 mm2. We present the fused fiber design details and compare its performance with hexagonal array fiber bundle.

Wildfires generate plumes of smoke which release toxic pollutants into the atmosphere and affect the surrounding air quality significantly. Smoke contains carbonous particles that influence the regional climate patterns. Wildfires sometimes generate thick smoke layers that cause poor visibility and accidents. Generally smoke tends to disperse in form of layers in the atmosphere. Aircraft measurements are performed to understand the dynamics of smoke plumes. However, these measurements involve cost and enormous amount of exercise. Significant amount of information is required for understanding the dissipation of smoke from wildfires. Occasionally, smoke generated from wildfires cross political boundaries and influence chemical composition of atmosphere. Recently, at a unit of Department of Space (DOS) located near Tirupati, a laser radar system was developed indigenously for remote sensing smoke layers in the atmosphere. The developed laser radar system uses a novel multi-angle method to track the smoke layers in the atmosphere. The LIDAR (Light Detection And Ranging) system uses visible wavelength for probing smoke layers. The system was operated during dry season to remote sense smoke layers produced by wildfires that occurred in the nearby reserve forest. During the observations, the LIDAR system was found suitable for tracking smoke plume boundaries, its top height, dispersion and change of its intensity with time.

There is no agreed reference method for accurately determination of mixing layer height (MLH) in the existing literature. In part, this is due to different definitions of the atmospheric boundary layer exist, depending on the quantities and the physical processes invoked. In addition, MLH during late afternoon transition period is highly challenging to determine and perform model simulations because of the rapid variations in turbulent kinetic energy. For the first time, MLH has been determined at remote tropical site of Gadanki, India (13.45°N, 79.17°E, 360 masl) using ground-based elastic backscatter LiDAR (EBL). This article focuses on the late afternoon transition period and compares it with MLH obtained from the EBL to concurrent radiosonde (RS) observations [MLH (RS)] and numerical models. Five different techniques have been applied to the EBL backscatter profiles for the determination of MLH. The mean of the five methods agreed to within 15% with the RS-derived MLH under various synoptic conditions at the site. This indicates the potential capability of continuous monitoring of MLH by our EBL system. However, MLH determined by Weather Research and Forecasting model and European Center for Medium-Range Weather Forecasts Re Analaysis (ERA)-interim reanalysis systematically underestimated of the MLH (LiDAR) by about 62% and 48%, respectively. The mean growth rate of diurnal evolution of MLH was found to about 120 and 200 m h−1 during winter and spring seasons, respectively.

We describe an indigenously developed dual polarization lidar (DPL) system for remote sensing of the rangeresolved properties of non-spherical nature of airborne and cloud particles. The DPL system probes the atmosphere using a linearly polarized second harmonic Nd : YAG laser. The design of receiver optics is such that it separates the collected backscattered light into parallel and perpendicular polarization components. The ratio of intensity of perpendicular to parallel signals is known as the depolarization ratio (DR), which is a gauge for non-spherical particle content in the atmosphere. The DPL employs an external irradiance standard to calibrate the depolarization measurements. Comparison of simultaneous measurements between DPL and a similar instrument validates the utility of the system for cloud and aerosol studies. The altitude profiles of DR derived from lidar signals potentially indicate the type of major particle layers in the atmosphere.

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.

The clouds occur at high altitude have a significant impact on climate system ([1]). Much of the high altitude clouds generally occur in the tropical latitudes due to significant convective phenomena occurring in this region ([2]). These clouds occur in different forms such as anvil and stratus trails and sometimes not visible to satellite based instruments. The only means to detect this type of cloud in the atmosphere is using the Light Detection and Ranging (LIDAR) Technique. At National Atmospheric Research Laboratory (NARL), a Department of space unit located at Gadanki near Tirupati in Andhra Pradesh a portable LIDAR was developed and has been made operational since 2005. The LIDAR system employs 532nm wavelength Light Amplification by Stimulated Emission of Radiation (LASER) and used for monitoring the high altitude clouds during Nocturnal Periods ([3]). In this paper, the occurrence of high altitude clouds during the monsoon period has been detected using Ground based LIDAR. Using this synergical instrumentation data the occurrence, transport phenomena, optical properties and dynamism of high altitude clouds have been explained over tropical site Gadanki.