locating initial breakdown pulses of lightning flashes · physics and astronomy - atmospheric...

Locating Initial Breakdown Pulsesof Lightning Flashes

Sumedhe Karunarathne

20th April 2010

Physics and Astronomy - Atmospheric Physics

1

Physics and Astronomy - Atmospheric Physics 2

Outline…

Background Sensors and sample data Time of arrival method Results, Comparison and Error results Future Plans.


Charge Structure of Thunder-Cloud

•Lower positive charge is not present always.•Two main charges produce a positive-dipole

BACKGROUND

Upper Positive(40-400C)

Main Negative(-40-400C)

Lower Positive (3 -30C)

+

-

+

~2km~7km~12km

4

Types of Lightning

(1) Downward Negative

(2) Upward Positive

(3) Downward Positive

(4) Upward Negative

BACKGROUND

90%

Less than 10%


Figure 4.3 of uman

Negative CG Flash

- Uman (1987 – 2001)


Video…

http://www.youtube.com/watch?v=djCdfSl-5o8&feature=related


Electric Field Change Meter~1.5ft

~1.5ft

Properties• Time Constant : 10s 1s 100us• Band Width : ~0Hz – 0.5Mhz• Sampling Rates: 1MHz triggered

100kHz Continuous•Resolution : 12bit

Block Diagram

Plate

Charge Amplifier

Follower

GPS

Battery Power (~11 hours)

10Ms/seconddigitizer

1s Time

Accuracy


2010 Summer data collection Kennedy Space Center (KSC)

•5 Stations•Each station have 3 sensors(10S, 1S and 100S antennas)

• Covered about 25x40km area roughly.

•Purpose-Study the beginning of the lightning flashes and lightning propagation

S1

S2

S3

Origin

S4

S5

~20km


What we see….

• Sensor sees the electric field change in the environment.• There are 3 major components we see as the field change

])/,(

.sin

)/,(.sin32

)/,(.sin32

[2

1),(

2

1

2

1

2

1

2

2

2

2

03

2

0

dzt

cRtzi

Rc

dzcRtzicR

dzdcRziR

tDE

H

H

H

H

tH

H

-Uman et al., 1975-Watson and Marshall , 2007

1. Electrostatic (1/R3) 2. Induction (1/R2)3. Radiation (1/R)


What we see at 2.8km…

For closer flashes we see,• More from electrostatic and induction

terms• Less from radiation field


What we see at 200km…

For far flashes we see,• Electrostatic and induction terms are negligible• Most of the filed change are represented by

radiation field


Sample Data – CG flash overall


Sample Data – CG flash Beginning


Time of arrival

v

Rtt i

i

||

(x,y,z,t)

ith sensor

ti

Ri

v

zzyyxxt

iii

222 )()()(

Excited time of a sensor due to pulse at the location (x,y,z),

•(xi,yi,zi,ti) known•(x,y,z,ti ) unknown•v speed of light in air - known

Assumption:Ignore the refractive index effect(EM wave travel in a straight line with a constant speed)Named PBFA (Position by Fast Antenna)

• 4 sensors are enough to find x,y,z and t.• 5th sensor can be use to validate the solution


LINET and LDAR2

S1S2

S3LDAR2 Origin

S4S5

L1

L2

L3

L6

L4

L5

L7

LINET LDAR2

LIghtning NETwork Lightning Detection And Ranging Array

VLF/LF Band (5-200kHz) VHF Narrow Band (64-66Mhz)

See long (~500 m) pulses well See short pulses (~5 m) well

Temporary mounted for 2010 summer Permanently working at KSC

7 stations 9 stations


Results

LINET


Results


Errors Summery•X,Y sigma ~ ±100- 500m•Z sigma ~ ±500m – 4km•t sigma ~ ±1s - 20s.

Critical Factors for betterTriangulations•Time resolution•Sensor placement•Flash location


Summery

• Finding pulse position using this method is strongly dependent onSensor Placement, Location of the flash, and Time resolution ofantenna.

• Since we have 5 sensors and only 4 sensors are needed to find thepulses location (x, y, x, t), the other sensor can be used to checkthe solution.

• Although the statistical error analysis gives relatively largestandard deviation, the results are reasonably consistent withLDAR2 and LINET data.

• Unlike LDAR and LINET, the PBFA method was able to find thelocation of the beginning pulses. We plan to use this informationto help determine the physics of initial lightning propagation.


Future Plans1. Improved sensors

2009/2010 sensors 2011 sensors

GPS time 1uS accuracy 5nS accuracy

Resolution 12-14bit 12bit

Sampling rate 1MHz 10MHz

Number of stations 5 (5 Calculations) 9 (126 calculations)

Downloading data Manually Automatically to a server at UOM

Position Finding Manual post process Automatic Real Time

2. 2011 Summer 1 data CollectionPlace – Rapid City – South Dakota Purpose – Study lightning from towers

compare with high speed video data

3. 2011 Summer 2 data collectionPlace – KSC - FloridaPurpose – Study the beginning pulses and structure of lightning

Compare with high-speed video data


Thank you!


Results

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