COMPACT DUAL POLARIZATION LIDAR

Compact Dual Polarization Lidar The compact Dual Polarization Lidar (DPL) developed by ISRO provides an insight in locating the presence of aerosol particles and clouds in the atmosphere which plays a major role in regulating earth's climate and air quality. The lidar system uses a single wavelength laser for excitation of the atmosphere and performs polarization diversity measurement in receiver for detection and discrimination of various suspended particles / aerosols of interest. In the simpler form, a laser transmitter generates a monochromatic spectrum of light beam having a predetermined state of polarization. Light scattered from the lower atmospheric aerosol / particles is detected using a polarization sensitive receiver and thereby the degree of change in polarization of the scattered light is determined. The ratio of the depolarization at the exciting wavelength is then calculated and used to discriminate between the various particles / aerosols. Figure 1: Schematic Block Diagram – Compact Dual Polarization LIDAR The DPL is an independent lidar system that contains a pulsed laser transmitter, a receiver telescope, optics, dual detectors, signal digitizers, timing and power supply electronics and a computer for control and data recording. The lidar system employs biaxial configuration Sailent Features: a) DPL is a compact, Ethernet operated fully remote controlled system. b) If operated in shaded region, DPL system works both in day and night without pause. c) Data recording is done both in analog and photon counting mode. d) Range resolution is 7.5 m or in integer multiples of 7.5m. e) Lidar system operates in any elevation angle between 0 and 90 deg Application DPL an active LIDAR instrument with inbuilt polarization capability probes the properties of thin clouds and air borne particles in the atmosphere. The LIDAR vertical profiles provide detailed structure and content of aerosol particles, evolution of atmospheric boundary layer height, cloud height, identification of aerosol plumes in urban and industrial areas etc. Scientific Application a. Lidar data provides dynamical structure of the atmosphere, which can be used for real-time detection of atmospheric boundary layer height (ABL) and can provide continuous height information of planetary boundary layer. b. Lidar data provides valuable information on presence of dust in the atmosphere . This information is vital for air quality requirements. c. Time evolution of lidar data provides new insight in to the different types of cloud structure and its content. The CDPL is an independent lidar system that contains a pulsed laser transmitter, a receiver telescope, optics, dual detectors, signal digitizers, timing and power supply electronics and a computer for control and data recording. The lidar system employs biaxial configuration Sailent Features: a) DPL is a compact, Ethernet operated fully remote controlled system. b) If operated in shaded region, DPL system works both in day and night without pause. c) Data recording is done both in analog and photon counting mode. d) Range resolution is 7.5 m or in integer multiples of 7.5m. e) Lidar system operates in any elevation angle between 0 and 90 deg Application DPL an active LIDAR instrument with inbuilt polarization capability probes the properties of thin clouds and air borne particles in the atmosphere. The LIDAR vertical profiles provide detailed structure and content of aerosol particles, evolution of atmospheric boundary layer height, cloud height, identification of aerosol plumes in urban and industrial areas etc. Scientific Application a. Lidar data provides dynamical structure of the atmosphere, which can be used for real-time detection of atmospheric boundary layer height (ABL) and can provide continuous height information of planetary boundary layer. b. Lidar data provides valuable information on presence of dust in the atmosphere . This information is vital for air quality requirements. c. Time evolution of lidar data provides new insight in to the different types of cloud structure and its content.

INDIAN LIDAR NETWORK

Indian Lidar Network The present knowledge of the aerosol distribution is far from sufficient to estimate properly the role of aerosols in changes of the global and regional climate as well as environmental conditions that are important for the quality of life. It is particularly true for the vertical distribution of aerosols that is important for many of the processes in which aerosols are involved, e.g. governing their formation, transport, sedimentation, and their impact on atmospheric processes such as dynamics of boundary layer, modification of cloud microphysics, formation of fog and haze, and smoke/pollutant. To address this, a Network of Lidars is proposed to quantify the aerosol distribution and its variability in space and time, with specific attention given to vertical distribution. This lidar network will also monitor the boundary layer dynamics and is also useful in developing inverse algorithms and validation for satellite retrieval of aerosol concentrations. The principal objective of this network is to establish a comprehensive, quantitative, and statistically significant database for the aerosol distribution over India . Towards this, the technology of Boundary Layer Lidar (BLL), developed at the National Atmospheric Research Laboratory (NARL), has been transferred to the Indian Industry M/s General Optics (Asia) Limited, (GOAL),Pondicherry for development of industrial grade BLL systems. The industrial grade lidars are named as “Lidar for Atmospheric Measurement and Probing (LAMP)”. Based on the geographical distribution and the major two-wind system (SW and NE) over the country ten stations are selected for installation in the first phase of the network.

VHF ACTIVE ARRAY

VHF Active Array A pilot 53-MHz 133-element active phased array radar has been developed at National Atmospheric Research Laboratory (NARL) for probing the atmosphere upto troposphere. This radar is developed with an objective to validate the technology concepts like out-door installation of solid-state transmit-receive (TR) modules, beam steering, optical interface and control, fiber-based phase calibration etc. This array is developed as a precursor R&D activity for the ultimate up-gradation of the existing 1024-element main MST radar into a full-fledged active phased array system. The 133-element array is configured with seven segments each comprising a 19-element hexagonal sub-array employing equilateral triangle grid. Each element of the array is directly fed by dedicated 1-kW solid-state TR modules with a maximum duty ratio of 10%. A low power feed network distributes the radar exciter output to the TR modules and combines the the receive signals and delivers to the radar receiver. The received signal, after combining, is suitably amplified, band limited before feeding the digital receiver. Digital receiver performs the analog-to digital conversion, digital down conversion, pulse compression and coherent integration. The time domain data is uploaded into host PC for data processing to compute Doppler spectrum and spectral moments. Wind vector and turbulence are determined using the 2nd and 3rd moments respectively. The antenna array is located at about 140 m distance from the control room, where the Radar instrumentation and other subsystems are located. The communication between the TR modules and radar controller is implemented through optical Ethernet network using optical Ethernet switches. 19 TR modules of each group are connected to 19 ports of each 24 port switch. Optical Distribution and Calibration Switching Network receives the 16 MHz reference clock and reference IPP marker as inputs and distributes each of them, converts them into optical signal to feed the TR modules, which are located in the field. Figure-1 shows the pictures of the antenna array with TR modules (top panel), individual TR module (bottom-left) and control and instrumentation (bottom right). All the subsystems have been developed, installed and integrated. The system is being operated in Doppler beam swinging (DBS) regularly since August 2012 with typical height coverage upto 8-12km. About 300 hrs of data is collected. Figure-2 shows sample range-Doppler spectra obtained on March 07, 2013. The wind data measured agreeing well with the collocated GPS Sonde and MST radar. Figure-3 shows typical wind comparison scatter plots with GPS Sonde (top) and MST radar (bottom). This radar demonstrates the intended technology concepts like out-door installation of TR modules, beam steering, optical Ethernet-working, automatic Optical phase calibration. Details will be presented at the Symposium.

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© 2018 - DevExpress ASP.NET project copyright


© 2018 - DevExpress ASP.NET project copyright