Yellapragada Bhavani Kumar
@narl.gov.in
Scientist and Boundary Layer Lidar
Dr. Bhavani Kumar Yellapragada presently works as Scientist SG at the National Atmospheric Research Laboratory (NARL), a unit of the Indian Space Research Organization (ISRO), India. Dr. Kumar has made significant technical contributions to laser remote sensing instrumentation for environmental research in India. Some of these technologies have been transferred to Indian industries for commercialization. These technologies have been employed to remote-sense atmospheric boundary layer, aerosol, clouds, water vapor, winds, and mesospheric Sodium. His works were recognized by ISRO and conferred with ISRO's prestigious Merit Award in 2017. Dr. Kumar has published 104 publications. He has two IPRs granted with patent status listed under ISRO. Currently, he is listed as an expert member under VIDWAN, an MHRD initiative of the Government of India. Dr Kumar is a recognized Mentor of SRF programme of three national science Academies of India. Under this program he mentored 16 M.Tech students an
EDUCATION
M.Sc, PhD
RESEARCH, TEACHING, or OTHER INTERESTS
Earth and Planetary Sciences, Multidisciplinary, Environmental Science, Atmospheric Science
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Vishnu Rajendra Kumar, Richard L. Collins, and Bhavani Kumar Yellapragada
Elsevier BV
Kamana Mishra and Bhavani Kumar Yellapragada
Wiley
G. Kumar, B. L. Madhavan, L. K. Sahu, Y. B. Kumar, J.‐P. Vernier, H. Liu, B. Zhang, A. K. Pandit, R. K. Manchanda, V. K. Dadhwal,et al.
American Geophysical Union (AGU)
AbstractThe 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 (βext), 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 βext with significant differences in magnitude below 4 km; however, it fails to reproduce EALs for all seasons and regions during the study period.
Kamana Mishra and Bhavani K. Yellapragada
SPIE
The mixing of air layers, wind shear components, mountain waves, aerosol particles, and other pollutants causes rotational turbulence that affects the lowest and densest layer of the earth’s surface troposphere. This turbulence results in a significant change in the height of the Convective Boundary Layer (CBLH) over a day. To analyze the behavior of the convective boundary layer, a statistical technique is used to observe the variation in peak positions of Light Detection and Ranging (LiDAR) back-scatter signals. Furthermore, a statistical method is provided to obtain the best-fit distribution to demonstrate how the result leads to the physical observation of the data. This method involves selecting a suitable distribution for the dataset and defining the percentile bins to use a specific range of the data. The observed frequencies and expected frequencies are then calculated to formulate the chi-square statistics, which are used to determine the fitness of the distribution. Finally, a histogram with the best-fit distribution curve is plotted to examine whether the formulation of the function is appropriate. This approach provides a comprehensive understanding of the behavior of the entire boundary layer and can be used to inform further analysis and interpretation of the data.
Kamana Mishra and Bhavani Kumar Yellapragada
IEEE
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.
Y. Bhavani, K. Praveen Kumar, K. Dharmateja, P. Pranathi, and R. Sowmya
IEEE
In Distributed Database System (DBS) and multitasking system, the occurrence of deadlocks is one of the most serious problems. If a site request for a resource that is already in the another site which is waiting for another resource then the scenario is called as distributed deadlock. Different distributed environments require a suitable deadlock detection algorithm to detect deadlocks. Different distributed environments needs to maintain their platforms by avoiding deadlocks. To achieve this environment, it is required to fed with optimized deadlock detection and avoidance algorithms. In this article, different deadlock detection algorithms that uses Wait For Graph and resolution algorithms to trace out deadlocks were discussed. An optimization technique is used for resolving deadlock in an efficient manner. A comparison between different deadlock detection algorithms based on different parameters like, delay time, message size, number of messages and whether the algorithm detects false deadlocks or not were performed. Based on the comparisons, a few deadlock detection algorithms were suggested for the distributed environment.
R. Vishnu, Y. Bhavani Kumar, and Anish Kumar M. Nair
Springer Science and Business Media LLC
Natarajan Sangeetha Kalaivasan
SPIE-Intl Soc Optical Eng
Abstract. 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.
Mercy Varghese, Thara V. Prabha, P. Murugavel, A.S. Anu, E.A. Resmi, G. Dinesh, Y. Jaya Rao, Baban Nagare, P.D. Safai, Sathy Nair,et al.
Elsevier BV
Mohammed Sharukh, Bhavani Kumar Yellapragada, and Rafiq Ayub
SPIE
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.
Y. Meenakshi and Yellapragada Bhavani Kumar
Springer International Publishing
Sangeetha N., Bhavani Kumar Y., and Sivabalan S.
Elsevier BV
R. Vishnu, Y. Bhavani Kumar, P. R. Sinha, T. Narayana Rao, E. James Jebaseelan Samuel, and P. Kumar
Informa UK Limited
ABSTRACT 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.
Ajay Kumar Patel, Bhavani Kumar Yellapragada, R. Vishnu, M. V. R. Murti, and James Jebaseelan Samuel
Current Science Association
CURRENT SCIENCE, VOL. 113, NO. 6, 25 SEPTEMBER 2017 1134 *For correspondence. (e-mail: ypbk@narl.gov.in) 10. Burgoyne, L. N., Flynn, S. O. and Boylan, G. B., Undergraduate medical research: the student perspective. Med. Educ. Online, 2010, 15; doi:10.3402/meo.v15i0.5212. 11. Houlden, R. L., Raja, J. B., Collier, C. P., Clark, A. F. and Waugh, J. M., Medical students’ perceptions of an undergraduate research elective. Med. Teach., 2004, 26(7), 659–661; doi:10.1080/ 01421590400019542. 12. Oliveira, C. C., De Souza, R. C., Sassaki Abe, E. H., Silva Maz, L. E., de Carvalho, L. R. and Domingues, M. A. C., Undergraduate research in medical education: a descriptive study of students’ views. BMC Med. Educ., 2013, 14(51), 5–8; http://www. biomedcentral.com/1472-6920/14/51. 13. Khan, H., Khawaja, M. R., Waheed, A., Rauf, M. A. and Fatmi, Z., Knowledge and attitudes about health research amongst a group of Pakistani medical students. BMC Med. Educ., 2006, 6, 54; doi:10.1186/1472-6920-6-54. 14. Al-Hilali, S. M., Al-Khatani, E. A., Zaman, B., Khandekar, R., Al-Shahri, A. and Edward, D. P., Attitudes of Saudi Arabia undergraduate medical students towards health research. Sultan Qaboos Univ. Med. J., 2016; doi:10.18295/SQUMJ.2016.16.01.012. 15. Silcox, L. C., Ashbury, T. L., Van DenKerkhof, E. G. and Milne, B., Residents’ and program director’s attitudes toward research during anesthesiology training: a Canadian perspective. Anesth. Analg., 2006, 102, 859–864. 16. McKinnon, G., But I just want to be a good clinician, research in Canadian surgical training programs. Ann. R. Coll. Physicians Surg. Can., 2002, 35, 203–206. 17. Unnikrishanan, B. et al., Medical students’ research – facilitators and barriers. J. Clin. Diagn. Res., 2014, 8(12), XD01–XC04.
Bhavani Kumar Yellapragada
SPIE
The National Atmospheric Research Laboratory (NARL), a unit of Department of Space (DOS), located at Gadanki village (13.5°N, 79.2°E, 370 m AMSL) in India, is involved in the development of lidar remote sensing technologies for atmospheric research. Several advanced lidar technologies employing micropulse, polarization, Raman and scanning have been developed at this site and demonstrated for atmospheric studies during the period between 2008 and 2015. The technology of micropulse lidar, operates at 532 nm wavelength, was successfully transferred to an industry and the commercial version has been identified for Indian Lidar network (I-LINK) programme. Under this lidar network activity, several lidar units were installed at different locations in India to study tropospheric aerosols and clouds. The polarization sensitive lidar technology was realized using a set of mini photomultiplier tube (PMT) units and has the capability to operate during day and night without a pause. The lidar technology uses a compact flashlamp pumped Qswitched laser and employs biaxial configuration between the transmitter and receiver units. The lidar technology has been utilized for understanding the polarization characteristics of boundary layer aerosols during the mixed layer development. The demonstrated Raman lidar technology, uses the third harmonic wavelength of Nd:YAG laser, provides the altitude profiles of aerosol backscattering, extinction and water vapor covering the boundary layer range and allows operation during nocturnal periods. The Raman lidar derived height profiles of aerosol backscattering and extinction coefficient, lidar ratio, and watervapor mixing ratio inform the tropical boundary layer aerosol characteristics. The scanning lidar technology uses a near infrared laser wavelength for probing the lower atmosphere and has been utilized for high resolution cloud profiling during convective periods. The lidar technology is also used for rain rate measurement during small scale rain periods over the tropical station, Gadanki. This paper describes the lidar technologies developed and observations conducted using the technologies demonstrated.
Vishnu R., Bhavani Kumar Y., P. R. Sinha, Narayana Rao T., and James Jebaseelan Samuel E.
SPIE
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.
Vishnu R., Y. Bhavani Kumar, and E. James Jebaseelan Samuel
SPIE
This paper describes the measurements carried out on shape and size information of boundary layer aerosol particles using a lidar system developed at NARL, Gadanki. The lidar system profiles the boundary layer at 1064 and 532 nm wavelengths, which are fundamental and second harmonic components of Nd:YAG laser. However, the polarization measurements are conducted at 532 nm only. Using an external dichroic mirror in the laser path, the Nd:YAG laser output is separated into its harmonics. The fundamental harmonic of Nd:YAG laser is steered into atmosphere using a hard coated mirror and the atmospheric returns at 1064 and 532 nm are collected using two independent telescopes. The laser backscatter corresponding to 1064 nm is detected using an Avalanche photodiode; whereas the co and cross polarized signals returns corresponding to 532 nm laser are detected using a set of mini-PMT units. A three channel transient recorder unit is employed for recording the signals utilizing the analog and photon counting electronics. The lidar system is possible to operate in daylight period and can provide information on scattering properties of boundary layer aerosols. In the present study, measurements during long range transport events were performed at NARL, Gadanki during the year 2012. We proposed to present two case studies on long range transport that occurred during the year 2012. We present the results in terms of aerosol backscattering coefficient, depolarization ratio and color ratio with support of back trajectory analysis.
Sangeetha N., Bhavani Kumar Yellapragada, and Venkata Rajanikanth Machavaram
SPIE
Water vapour profiling of surface layer, which constitutes the lowest hundred meters from earth’s surface, can aid in the understanding of spatial variability of atmospheric turbulence and the dynamics of boundary layer. In lidars, the effective area of an optical fiber-based receiver, also called the aperture stop diameter, controls the field of view of the telescope which in turn governs the overlap function. We determined overlap function vs altitude for different aperture stop diameters which showed that lower altitude profiling requires fibre receivers of larger effective area positioned at the location of blur disk or the position of maximum capture of back scattered light. We report on the design of a receiver which comprises of a converging lens system in conjunction with a commercially available fibre bundle of fused hexagonal shaped fibres of adequate numerical aperture and enhanced effective light capturing area. For a specified biaxial Raman lidar system with an excitation laser emitting at 532 nm, placing a one inch diameter lens at the plane of blur disk of diameter ~21 mm and the aforesaid fibre bundle of diameter 7.3 mm at the image plane of the blur disk was found to be suitable for relatively efficient light capture to enable profiling from an altitude of ~8m and above. The light capturing efficiency of the system was determined and compared with that of a conventional circular fibre-based bundle of same diameter. The proposed receiver design offers potential solution for low altitude profiling with reduced central obscuration.
Subhajit Roy, Bhavani Kumar Y., and M. V. R. Murti
SPIE
The clouds occur at high altitude have a significant impact on climate system. Much of the high altitude clouds generally occur in the tropical latitudes due to significant convective phenomena occurring in this region. 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. 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.
R. Vishnu, Y. Bhavani Kumar, T. Narayana Rao, Anish Kumar M. Nair, and A. Jayaraman
SPIE
Atmospheric convection is a natural phenomena associated with heat transport. Convection is strong during daylight periods and rigorous in summer months. Severe ground heating associated with strong winds experienced during these periods. Tropics are considered as the source regions for strong convection. Formation of thunder storm clouds is common during this period. Location of cloud base and its associated dynamics is important to understand the influence of convection on the atmosphere. Lidars are sensitive to Mie scattering and are the suitable instruments for locating clouds in the atmosphere than instruments utilizing the radio frequency spectrum. Thunder storm clouds are composed of hydrometers and strongly scatter the laser light. Recently, a lidar technique was developed at National Atmospheric Research Laboratory (NARL), a Department of Space (DOS) unit, located at Gadanki near Tirupati. The lidar technique employs slant path operation and provides high resolution measurements on cloud base location in real-time. The laser based remote sensing technique allows measurement of atmosphere for every second at 7.5 m range resolution. The high resolution data permits assessment of updrafts at the cloud base. The lidar also provides real-time convective boundary layer height using aerosols as the tracers of atmospheric dynamics. The developed lidar sensor is planned for up-gradation with scanning facility to understand the cloud dynamics in the spatial direction. In this presentation, we present the lidar sensor technology and utilization of its technology for high resolution cloud base measurements during convective conditions over lidar site, Gadanki.
R. Vishnu, Y. Bhavani Kumar, Y. Jaya Rao, E. James J. Samuel, P. Thara, and A. Jayaraman
SPIE
A compact dual polarization lidar (DPL) was designed and developed at National Atmospheric Research Laboratory (NARL) for daytime measurements of the boundary layer aerosol distribution and depolarization properties with very high vertical and temporal resolution. The lidar employs a compact flashlamp pumped Q-switched Nd:YAG laser and operates at 532 nm wavelength. The lidar system uses a stable biaxial configuration between transmitter and receiver units. The receiver utilizes a 150 mm Schmidt Cassegranin telescope for collecting laser returns from the atmosphere. The collected backscattered light is separated into co and cross-polarization signals using a polarization beam splitter cube. A set of mini-PMTs have been used for detection of light from atmosphere during daylight period. A two channel transient recorder system with built-in ADC has been employed for recording the detected light. The entire lidar system is housed in a compact cabinet which can be easily transported for field measurements. During 2014, the lidar system was installed at the Banaras Hindu University (BHU) campus, Varanasi (25.28° N, 82.96° E, 82 m AMSL) and operated for a period of three months in to support the cloud aerosol interaction and precipitation enhancement experiment (CAIPEEX) conducted by Indian Institute of tropical meteorology (IITM). During this campaign period, the lidar measurements were carried out in the vertical direction with spatial resolution of 7.5 m and time sampling of 30s. The lidar measurements revealed the occurrence of boundary layer growth during convective periods and also detected the long-range transport dust layers with significant depolarization. In the present paper, we present the lidar measurements obtained during the campaign period and discuss the observation of transport of dust layer over the experimental site with support of back trajectory analysis and satellite data. The Lidar observations were compared with the available satellite observations also presented here.