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IN DEPTH ON LIGHTING TECHNOLOGY

In this article ,late us discuss some charactertics of signal of lighting detection .early, when stereoscopes was introduced in 1970’s and evolved from WX7A up through WX-R ,later ,know as series I .after later improved version was series (II) WX1000 system. It made things more easy .while developing WX1000 system ,a ground based triangulating sensor system in florida which monitored while flight testing was progress. This made easy where area of interest and also to better analyze and validate the flight results.

Weather mapping system is used to detect lighting discharges and then graphically displayed to pilot. Late us see how the phenomena of lighting produces by electromagnetic atom in air .when study have been made that lighting produces electromagnetic (em) field by stripping electrons from atom in the air. In this process, it emits a broad spectrum of electromagnetic energy as well as great deal of light and sound. It starts when transient collisions of ice crystals with rimina graupel peven,thus transferring charges within the maturing cloud as heavier particles falls; which results in vertical electric field. The net effect of this self-propagating lighting is transfer of negative charges from atmosphere to earth. i.e, from cloud towards grounds.

When stepped leader hits the ground ,the return stroke is triggered, producing a sharp voltage rise.this specific signature distinguishes a cloud -to- ground stroke from other electromagnetic noise.this radiated field of lighting stroke will induce some current in crossed loop portion of antenna horizontal field and sense antenna willrecognize the generated vertical field ,which is electric field.

When we study the things in depth,we see that lighting strikes are unique and so some question arise when ,we study the things ,some point came in our mind that how do we plot these unique events? We shall see in later study.

As mentioned in above,the spectrum that is a result of lighting strike contains a broad range of frequencies with very fast rise time .evaluating ,these type of ranges selectivity play important role .it is impartical to attempt to observe the broad spectrum in one channel,the bandwidth must be narrow enough to minimizethe effect of interfering signals & yrt must be wide enough to pressure the amplitude and duration of wanted signal.

In pratical there are several frequency bands we want to specify. The first group is centered around 50khz and then a wider band of 1 to 250 khz , which dictates why skin mapping is so very important when installing these system. Last group is from 1 to 15 khz ,but it is not so important.

Some theory have define lighting strike as series of low frequency( 1 to 100 khz) Strokes super-imposed with high freg component (100khz to 5mhz) sub-pulsed and this being preceded by leader discharge of 5 to 15 mhz .the rise time of strike are less then 5 microsecounds with s zero crossing accurrence in range of 50 microsecounds.

Normally EM field have tendency to dominate at one distance from the radiation source while different behavior can be dominated at another.there are three types of Field which are so far define as near-field. If field extending towards two-wavelenth away from radiating source is far –field.. mid-field is region that is existing between near –field and far-field, it is mid-field.signal strength depends upon the amplitude or the medium over which their propagate away from the source . EM waves and its energy is speard out at very larger areas because the radius increases from source ,so it will decreased signal strength at any one point.it happen because the total energy radiated remains constant while strength of wave or amplitude of signal decreases the futher out from source it gets.


CALIBRATION OF LIGHTING STRIKE.

We can calibrate the lighting strike by specific formulas which represent near-field,mid-field and far-field. Let us proceed futher ,we know that surface area of sphere is 4pir*r ,here area can be increases which is proportional to r*r,and energy if equally spread cut is inversely proportional to r*r what we call inverse-square law, which states that signal strength decreases as square of distance from the source.it is seen that ,narrow pulse in a period of approximately 10 microsecounds are generated by intra-cloud lighting discharger,the cloud to ground discharge generates fewer pulses out a larger period in 20 to 50 microseccounds time frame ,which is know as zero crossing point. Sense portion of antenna is vertically polarized ,because clouds to ground strike is vertical polarized.

SIGNAL PROCESSING

Let us see ,how signal is generates and proceed, when there is strike occurs then first the sense propagation of antenna will receive the “E”field while loop portion senses the bi-directional “h” field filtering has to be done within the receiver in order to be captured several frequency. mode I have seen reflect a 50-100 microseconds of time ,which is depends upon types of signal field that is received. In order to capture adequate signal the sampling time of either is compatible is double. When we qualified the freq,the rate and duration of this signal what does it mean?first the far-field,which is influential overtime,but futher it is send through bandpass filter,while mid-field could be in wide-bandpassfilter . In aircraft the lighting detection is in cloud-ground strikes so sense portion of the antenna is vertical polarized ,while synchronous detection of crossed loop signal are critical and so the sense channel signal is filter and coincides and proceed loop signal must than be level compared to reference voltage.if the threshold is exceeds by signal them it is in 20nm listening area.

Aircraft nose with quadrant placement should be determined ,the direction and distance of strike is determine from hx and hy loop amplitude . synchrous detection again is used to resolve 180 degree ambiguity.this process generates two component value .if a specific range equation is assigned to each based on inverse square law,then we can refine the unit accuracy and determine the distance between them. It is them converted a/d by software then the digital portion and pattern of processor and its is software can futhr magnitude to properly place the strike based on a specific strike “mode” contained in it memory.

When the process is completion the strike which in turn placed into video logic memory for futher hadling by video logic and finally transmittyed into display for representation to the pilot. A lighting detection system have proud the help pilot in circumnavigate there hazards.