LIGHTNING DETECTION SYSTEM.pdf

83 and proactive action for replacement of the exhausted batteries. This record comprises the batteries issued to Met Section for various types of UPS issued to Met Section by Central Met Stores. LIGHTNING DETECTION SYSTEM Intro...

83 and proactive action for replacement of the exhausted batteries. This record comprises the batteries issued to Met Section for various types of UPS issued to Met Section by Central Met Stores. LIGHTNING DETECTION SYSTEM Introduction 97. Atmospheric Lightning refers to electrical discharges within a cloud and cloud to ground, known as IC (Intra-Cloud) and CG (Cloud to Ground) respectively. Lightning occurs when electrical fields within a cloud intensify as particles of opposite polarity collect at differing regions. Below the negatively charged thunderstorm cloud base, positive charges begin to gather on the ground. A cloud to ground lightning strike begins as an invisible channel of electrically charged air moving from cloud to ground called a stepped leader as it moves in steps in nanoseconds. When this initial electrical breakdown pulse approaches an object on the ground, a powerful surge of electricity from the ground moves upwards to the cloud (called leader channel) and produces the visible lightning strike. This type of lightning is called negative lightning because negative charges are moving from cloud to ground. Similarly, when lightning occurs from positive charges located at top portion of the cloud, it is called positive lightning. Positive lightning when strikes ground is extremely dangerous as it has exceptionally high current and voltage to make its way from top of the cloud towards the ground. Positive lightning amounts to just 5% of the total lightning strikes. 98. Lightning detection has great value for real time storm tracking, warning, and now casting as well as estimating rainfall. In remote regions where conventional data sources are not available, tracking of thunderstorms and assessing their intensification / track are important challenges in weather prediction. These potentially deadly weather events often occur within 5 to 30 minutes of Intra-Cloud (IC) flash initiation. The lightning sensors installed at various locations detect millions of flashes each day, utilizing time-of-arrival methodology over a broad frequency range of 1 Hz to 12 MHz and employing adaptive digital filtering. The system provides the highest levels of detection efficiency in real time. It has ability to significantly improve severe weather warning times over radar and other technologies, incorporating highly advanced predictive capabilities that are crucial for characterizing severe storm precursors, improving severe storm warning lead times, and comprehensive weather management planning. Working Principle & Components 99. An overview of LDS is illustrated below: -  84 Fig. 2.41 - An overview of LDS Working Principle 100. ensor location is shown in Fig.2.41 Waveform data indicative of lightning activity is received by a waveform sensor from one or more signal converters. The waveform data comprises a group of electromagnetic waveforms. This data is filtered by a processor to remove noise frequencies. One or more uncompressed portions of the waveform data are transmitted to processing servers, collectively called Central Processing and Management System (CPMS). One or more unnecessary frequencies are again removed from the waveform data by spectral analysis techniques resulting into a compressed waveform. The compressed waveform data from the one or more sensors is aligned based on time of arrivals at sensors locations. CPMS determines location, amplitude (vertical extent), peak current (in kilo ampere), polarity and type of stroke (IC or CG) based on compressed waveform data using Time Of-Arrival principle.  85 Fig. 2.42 - Lightning Detection at a remote lightning sensor location Time of Arrival Principle 101. Systems that measure the arrival times of waveform can locate the signals in 2- or 3dimentional space and time. Among other things, this approach forms the basis for the Global Positing System (GPS) that is providing revolutionary technological, societal, and scientific developments. Time-Of-Arrival (TOA) measurements are also used in locating cell phones and for seismological studies. 102. TOA measures the time difference of similar waveforms received by remote sensors. TOA systems basically solve the D=V.t equation where D is the distance, V is the speed and t is the time, or more specifically, , where is the difference between the arrival time at location i and source time t, and is the distance between the measurement location , , and source location x,y,z. This is TOA principle involving linear equations (equations of first order). TOA lightning flash. In this case, the hyperbola is the set of points at a constant range difference from two foci and each sensor pair gives a hyperbola on which the location lightning flash lies. Then location of lightning flash is the intersection of all hyperbolae. Large number of sensors achieve high accuracy and performance for location estimation with more complexity of calculations. IAF Total Lightning System uses TOA involving linear equations to solve the problem of a lightning flash location.  86 Components of LDS 103. The various components of Lightning Detection System are as follows: - (a) Lightning Antenna and GPS. The Lightning antenna senses lightning. It is fitted outdoor onto a steel mast having clear view of sky and far from local noise sources. GPS antenna senses satellites and provides (coupled inside data logger). The GPS has 2 nanosecond timing accuracy (b) Earth Networks Digital Signal Processor (ENDSP). Earth Network Digital Signal Processor is a data logger, also called Grey Box. It receives the lightning waveform sensed by antenna. The data, along with GPS timestamp, is forwarded to Red Box through a data cable. Fig. 2.43 - Hardware components of a remote lightning sensor location (c) Data Cable. Data cable is a 60 meter 8 core cable with 24 American Wire Gauge (AWG) specifications. It is used to connect Grey Box with Red Box. (d) Earth Networks Network Appliance (ENNA). Commonly known as Red Box because of its obvious colour, this indoor equipment mainly serves as an interface between lightning data and network through which data is communicated to CPMS. The data received from the antenna and GPS in data logger is sent to CPMS through AFNET. Data is also stored locally in Red Box if there is no connectivity. The Red Box occasionally calls home the server (CPMS) to communicate its status. (e) Central Processing and Management System (CPMS). Central Processing and Management System are two sets of rack servers installed at AFCNWP. CPMS consists of several software components that are responsible for processing the raw electromagnetic waveforms and timing data from remote Air Force lightning sensors and determining the location,  87 amplitude and type of detected lightning flash. This is also used for achieving raw waveform data, lightning stroke location data and gathering system statistics and performance over time. Some important software components of CPMS are described below: - (i) Spectral Analysis Filter (SAF). It is responsible for spectrally analysing waveform data, generating digital filter data and updating the sensor configuration database. The digital filters notch-out local sources of electromagnetic radiation such as power lines or radio transmission. Fig. 2.44 - Central Processing Management Server (ii) Configuration Server (CS). A lightning sensor is registered with configuration server when powered up for the first time. Response from CS controls Lightning Data Receiver (LDR) to take lightning waveforms from the sensor. The lightning sensor is assigned both a primary and secondary LDR server. In case primary LDR is not accessible, sensor attempts a connection to the redundant (secondary) LDR.  88 (iii) Lightning Data Receiver (LDR). It gathers waveform data from multiple sensors in memory and aligns the waveform in time before forwarding to Lightning Location Processor (LLP). Each flash is rated with a confidence factor based upon how many sensors saw the flash, among other factors. (iv) Lightning Location Processor (LLP). It is the main processing software responsible for determining flash location, amplitude, and classification (IC vs. CG). (v) Sensor Calibrator. It is responsible for gathering waveform and location data over time for sensor calibration use. (vi) Lightning Manager Post-Processor (LMPP). It receives the flash data and location confidence statistics from LLP. The lightning flash is subjected to several post processing tests and if successful flash data is forwarded to Lightning Data Feeder (LDF). (vii) Lightning Data Feeder (LDF). It is responsible for distributing the lightning flash data to multiple consumer applications via binary transport. (viii) Lightning Database (LDB). It is a long-term disk used for archiving both raw waveform as well as lightning flash locations. (ix) Sensor Monitoring and Statistics (SMS) Server. This server gathers and compiles various sensor statistics and generates historical performance graphs for operational monitoring and management of the processing system. (x) Indian Air Force Total Lightning Viewer (IAFTLV). Indian Air Force Total Lightning Viewer is a browser (Internet Explorer) based comprehensive lighting monitoring and display system that plots real- time lightning data on customizable and interactive maps. It is accessed by http://www.lds.iaf.in/iaf/index.php?id=LocationID. Visualization require a plugin Wx Internet Explorer. Any PC installed with WxScope plugin and access to MET_DATA VLAN can be used to visualize the lightning. IAFTLV is composed of the following key components: - (aa) Selection Interface. Product Selection Interface is located in the left panel; it allows selection of the products for viewing. (ab) Asset Monitoring Interface. Asset Monitoring Interface is located in the right panel, which provides automated assets monitoring.  89 (ac) Map (Plugin). Map is located in the center, the detailed map is used to monitor and view the most recent lightning activity. (ad) Full Screen. On clicking the Full screen option, a new browser window page opens with full screen display. (ae) User Options. do. (af) Page Selection. Page selection is used to view different web pages like Lightning, Radar, Satellite, Multi-Panesand Upload. Lightning page is the main page where lightning specific options, like Product Selection Interface, Asset Monitoring Interface, Map, etc. are available. Fig. 2.45 - Indian Air Force Total Lightning Visualisation (xi) Indian Air Force Total Lightning System (IAFTLS) Management Portal. The management portal is a page that allows to manage IAFTLS sensor locations and parameters, view current and historical statistics, view lightning waveforms, reconfigure sensors (if sensor IP addresses changes) and export lightning data. Access to Management Portal requires username and password. It is opened through http://www.lds.iaf.in/KenticoCMS/Sensor- Dashboard.aspx. IAFTLS is composed of the following three key menus:- (aa) Sensor Dashboard. The sensor dashboard is displayed automatically when you log on to the portal and click Sensor Dashboard. It allows interaction with the Configuration  90 Service to add or delete sensor sites, edit site details, edit site parameters and view waveforms for a selected site, besides some other functions. The sensor dashboard is color-coded to provide the current status of all of the sensors. There are five table: - Sensor Status Description The sensor packets count is lower that 75% (configurable) and the last call home is older than 2 hours. The sensor packets count is lower that 75%, but last call come is within the past 2 hours. The sensor's last call home is older than 2 hours, but packets counts is above 75% The sensor is running properly. The sensor never called home and never sent packets. This is the initial condition of all sensors prior to changing colors. Fig. 2.46 and Fig 2.47 - Sensor Dashboard (ab) Sensor Maps. Current state of Sensor Maps can be downloaded in KML format for viewing in Google Earth. Google Earth which does not require active internet connection during  91 usage, called offline Google Earth, is provided by Earth Networks for each workstation. The KML file contains five map layers namely Detection Efficiency: In-Cloud, Detection Efficiency: Cloud to Ground, Detection Efficiency: Total, Location Accuracy and Sensor Status. These are selectable and viewable in any KML viewer. Keyhole Markup Language (KML) is an XML notation for expressing geographic annotation and visualization within Internet-based, two-dimensional maps and three-dimensional Earth browsers. KML was originally developed for use with Google Earth originally named Keyhole Earth Viewer, created by Keyhole Inc., later this company was acquired by Google. Fig. 2.48 - Sensor Maps download screen (ac) Detection Report. Detection Report is used to query for lightning detections in a specific time range and area. You can download the report as either a KML or CSV file. The report can be created for lightning flashes or pulses that are IC, CG or both. Use detection report to create targeted reports about lightning occurrences of a specific type, time and location. Then save/download the report in a KML or CSV format. View the Comma / Character Separated Value (CSV) text) in plain text form. Plain text means that the file is a sequence of characters, with no data that has to be interpreted as binary numbers. A CSV file consists of a number of records, separated by line breaks of some kind; each record consists of fields, separated by some other character or string, most commonly a literal comma or tab. Usually, all records have an identical sequence of fields in a CSV file. These files can be opened in any spreadsheet like Microsoft Excel, Liber Office Spreadsheet, Open Office Spreadsheet, etc.