Energy deposition and Infrasonic measurement of Bolides P. Brown Dept of Physics and Astronomy,...
-
Upload
maryann-rogers -
Category
Documents
-
view
213 -
download
0
Transcript of Energy deposition and Infrasonic measurement of Bolides P. Brown Dept of Physics and Astronomy,...
Energy deposition and Infrasonic measurement of
Bolides
P. BrownDept of Physics and Astronomy, Western University, London CANADA
Work sponsored by:NASA Meteoroid Environment Office (MEO)
Impact Frequency
2
Meter-sized Impactors@ 20 km/s (0.08 kT)@ 11 km/s (0.03 kT)@ 30 km/s (0.2 kT)Mass ~2 T
One such event globally every~week – ten days
Any one optical site on Earth can “see” a meter-sized impact once every ~two decades
Some large (D>5 m) impacts over the last two decades (having speed
and peak height)
3
Date Location a e inc q Q Energy D V HPeak
(AU) degs (AU) (AU) (kT) (m) km/s (km)
20130215 Chelyabinsk, Russia 1.71 0.56 4.1 0.753 2.67 500 19 19.0 29.5
20101225 Pacific Ocean (Japan) 1.01 0.39 16.4 0.611 1.40 33 7.5 18.5 26.0
20040903 Southern Ocean (Antarctica)0.86 0.18 12.2 0.710 1.02 13 6.9 13.0 25.0
20130430 Mid-Atlantic Ocean 1.07 0.12 7.2 0.936 1.20 10 6.6 12.3 21.2
19940201 S. Pacific (Kosrae Islands) 2.1 0.74 2.0 0.546 3.65 31 6.2 25.0 24.0
19990114S. Pacific Ocean 1.90 0.49 14.0 0.969 2.83 10 5.7 15.0 35.0
20091121 Botswana 0.84 0.59 56.4 0.346 1.33 18 5.2 32.0 38.0
20091008Indonesia (South Sulawesi) Gulf of Boni
1.20 0.55 14.1 0.541 1.85 33 5.2 22.0 19.1
20140823 Southern Ocean (Antarctica) 1.35 0.34 20.7 0.894 1.80 8 5.0 17.6 22.2
Observational data for meter-sized impactors
• Three Sources:– Ground-based fireball networks (European
Network, Prairie Network, MORP)• [6 meter-sized events]
– Fireball producing meteorites [23 to date] with instrumental flight data• [10 produced by >1m diameter]
– US Government (USG) sensor data • [>50 with speed and energy]
http://neo.jpl.nasa.gov/fireball/4
Impact Statistics
• SpeedMean = 18.5 ± 0.7 km/sMedian = 17.9 km/s
• Entry angle = 46◦ ± 3◦
• Mean height of peak brightness 33 km >90% lie between 20 – 40 km
5Height at peak brightness
20 30 40 50 60 70
Count
0
2
4
6
8
10
12
14
16
18
Orbital Characteristics:Meter-sized impactors
6
Semi-Major Axis (AU)
0.0
0
0.2
5
0.5
0
0.7
5
1.0
0
1.2
5
1.5
0
1.7
5
2.0
0
2.2
5
2.5
0
2.7
5
3.0
0
3.2
5
3.5
0
3.7
5
4.0
0
4.2
5
4.5
0
4.7
5
5.0
0
5.2
5
5.5
0
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
Eccentricity0.0 0.2 0.4 0.6 0.8 1.0
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
Inclination0 10 20 30 40 50 60
Fra
ction
0.0
0.1
0.2
0.3
0.4
0.5
Fra
ction
Fra
ction
Semi-Major axis (AU)1 2 3 4
Eccen
tricity 0.0
0.2
0.4
0.6
0.8
1.0
Semi-Major axis (AU)
1 2 3 4
Inclin
ation
(deg
rees)
0
10
20
30
40
50
60
T=3
T=2
q=1.017
Q=0.983
q=
0.9
q=
0.5
Impact Statistics - II • Orbital origins
Source population mainly from ν6 (inner main-belt)
• 7% Halley Type Comet (HTC) orbits; similar fraction Jupiter-family comet (JFC) origin
• No trend in strength with size/energy
7
Log M(kg)
3.00 4.00 5.00 6.00 7.00 8.00
Hp
eak Pressu
re (MP
a)
0.01
0.10
1.00
10.00
100.00
Jupiter Family Comet (JFC)Outer Main-Belt (OB)3:1 MMR with Jupiter (P_31)Intermediate Mars Crossers (P_IMC)ν6 secular resonance (P_Nu6 )
Bottke et al (2002) Source Regions:
Meter-class impactors : Physical Characteristics
• Median energy = 0.4 kT
• Triggered Progressive Fragmentation Model (TPFM) [ReVelle 2005] used for comparison
8
Fireball Class
FragPres (Mpa)
ΔHfrag-peak
(km)
I 0.7 10-14
II 0.2 14-17
IIIa 0.01 17-19
IIIb 0.001 19-24 Velocity (km/s)
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Height of P
eak Brightness (km
)
10
20
30
40
50
60
70
80Tj > 3
MeteoritesNetworks2<Tj<3
Tj<2
0.01 MPa
0.2 MPa
Type I
Type II
Type IIIa
Type IIIb
SM
M
B
PFBC
TL
KAS
C
0.7 MPa
AS – Almahata Sitta (Ure-Anom)K – Kosice (H5)TL – Tagish Lake (C2 ung)
BC– Buzzard Coulee (H4)C - Chelyabinsk (LL5)PF – Park Forest (L5)
B – Benesov (LL3.5, H5,Primitive Achondrite)SM – Sutter’s Mill (CM2)M – Mariboo (CM2)
Meteorites – individual symbols:
Energy Deposition
• Light curve ~ energy deposition
• Caveat: τ(m,h,v,comp)• Of 5m class events with
speeds LC only available for Chelyabinsk (top) and Feb 1, 1994 (bottom)
9
Height (km)
20253035404550
kt / k
m(h
eig
ht)
0
20
40
60
80
100
Brown et al (2013)
Tagliaferri et al (1995))
dtdV
MVdt
dM2
VI
2
W/s
ter
Detailed data (Borovicka and Spurny 1996) including light curve, fragmentation behavior, precise astrometry and spectra
Benesov meteorites recovered 2011 (Spurny et al 2014) – mixture of OC types?
Detailed model comparisons to Benesov observations by Borovicka and Popova (1998)
Benesov:V =21 km/s; Imax~ -19.5mag
Hpeak~24 kmMass estimates:3000-4000 kg (Borovicka et al.,1998) (ReVelle&Ceplecha, 2002)D ~ 1.3mE = 0.20 kT
Benesov (EN 070591) & Sumava (EN 041274)
Sumava:V =27 km/s; Imax~ -21.5mag
Hpeak~67 kmMass estimates:5000 kg (Borovicka& Spurny,1996) D ~ 3mE = 0.4 kT
Benesov spectra of final flares
Borovicka and Spurny (1996)
One model interpretation (Borovicka et al., 2013): Earliest fragmentation at ~45 km
altitude at P = 0.7 MPa Large scale disruption at 30 – 37 km
height with P= 1 – 5 MPa By 29 km object was ~20 boulders of
1-2m sizes based on changes in lightcurve
These boulders break again at 26 km under P~10 MPa
Lateral fragment speeds ~400 m/s
Another (bottom by Popova et al (2013))
Based on a number of plausible simulation realizations to encompass large parameter space of fragmentation behavior (in particular)
11
Chelyabinsk - Fragmentation
Borovicka et al (2013)
Popova et al (2013)
12
Kosice (H5)Fell Feb 28, 2010 – producing 11 kg of H5
meteorites in 200+ fragmentsDetailed data (Borovicka et al 2015)
including light curve, fragmentation behavior, precise astrometry
Very weak meteoroid – fragmented under < 0.1 MPa
Catastrophic disintegration at P ~ 1 MPa Infrasound constrained energy from I43
RU @ 1400 km range: Kosice:V =15 km/s; Imax~ -18mag
Hpeak~36 kmMass estimates:3500 kg (Borovicka et al.,2015D ~ 1.2mE=0.1- 0.2 kT
Pre
ssure
(Pa
)A
rriv
al A
zim
uth
Height (km)
57
39
29
22
V
c
MS
1sin
13Extreme meteoroid velocities between ~Mach 30 – 240 produce long, narrow shocks over very short time scales.
Characteristics (period and amplitude) of the shock wave are related to meteoroid energy deposition
Meteor generated infrasound provides another means of determining meteoroid MASS & KINETIC ENERGY
@ M = 30, β = 1.9° @ M = 240, β = 0.2°
β
2
1
)/
(o
O p
dLdER
R O
• Meteors (bolides/airbursts) produce low frequency sound when they detonate in the atmosphere
• Detectable at infrasound arrays at long distances due to low attenuation of sound and natural sound waveguides in atmosphere
MET
EORS!
Gra
vity
Waves
Infra
sou
nd
Au
dib
le
14
• Blast Radius dictates the frequency at which a meteor will produce its sound
• Small Ro: High Frequency / Large Ro: Low Frequency
• cm – m size objects Infrasound: 0.1 – 10 Hz• >10 m size (eg Chelyabinsk): < 0.1 Hz • As Frequency ↓ Attenuation ↓• Large, energetic sources produce IS which goes
further– Lower frequencies, lots of energy
Bolide Infrasound
15
o
Sm R
Cf
81.2(ReVelle 1974/1976)
Ground-level overpressure from cylindrical line source theory
• Numerical implementation of ReVelle (1974) meteor shock theory and comparison to observations of cm-sized meteoroids by Silber et al (2015)– Main finding – weak-shock to linear transition distance from source is
larger than originally assumed
• Crude rule of thumb – ΔP at the ground scales as ~E1/216
Application to Chelyabinsk• At Chelyabinsk, nuclear
airblast relations (Glasstone and Dolan, 1977) predict 5 – 10 kPa overpressure (0.5-1 MT)
• Cylindrical weak-shock theory predicts ~ 2-3 kPa
• Need more instrumental records of ground-level overpressure from large bolides
Cylindrical theory using lightcurve
1 MT Nuclear
0.5 MT Nuclear
International Monitoring System• 45/60 Stations Complete
(75%)• Stations are arrays
composed of 4 – 12 microbarometers
• Signals found through cross-correlation
• Arrival direction and steepness directly measureable
• Local wind noise and stratospheric wind system determines detection efficiency
• Varies with geography and time of year
181 km
IMS Bolide events : 2010 – mid 2014Removed auto detected IS events correlated with mining, rocket launches, volcanoes,
repeating sources etc. – Total events examined: 1462– Total number of potential airbursts : 69 (4% of 1462)– Expected number of meter-sized impacts from Brown et al (2002) : 29/yr (130 vs 69)– Expected number of kiloton (~2 m) class airbursts : 4/yr (18 vs 69)
2014 IMS event also detected by USG sensors
IMS bolide detection efficiency – Cued vs. “survey”
• Based on 2014 cued search with USG Sensors:– IMS identifies ~1/4 of all meter-sized
impacts– Approximately 3/4 of all such impacts
are detectable infrasonically– Cuing important!
• IMS raw (survey) detections (~15 /yr)
Implications • As a stand alone system, current IMS
system identifies minority (<0.5) of all meter-sized impactors
• Cued impacts from next Gen asteroid surveys (eg. ATLAS) should expect most impacts to be detectable by IMS– Will give an estimate of total energy and
geolocation
21
Airburst Energy Estimation : Period – Yield
• Source energy estimates based on periods/amplitudes calibrated to explosive sources
• Small events at short ranges usually better estimated with amplitudes (but need to include winds)
• Larger events show good agreement with ground-truth/USG energies (Ens et al., 2012) particularly by averaging periods across many stations
USG
Example: Regional Infrasound for the Chatham Island AirburstMay 16, 2014 @1242 UT (0.8 kT)
PaUSG Measurements:Energy = 0.8 kTMass ~ 25 TDiameter 2.5 – 3 mV = 16.5 km/sBurst altitude = 44 kmEntry Angle = 66 degs
Time (Sec) from12:45:15 UT May 16, 2014
20 40 60 80 100
Arrival A
zimuth
0
100
200
300
20 40 60 80 100
Arrival A
ngle (degrees)
0
10
20
30
40
50
60
70
Infra Measurements:End Height ~ 33 kmBegin Height ~ 69 kmBurst Height ~ 47 km
Infrasound cross-correlation in 15 sec windows with 80% overlap
12
3
4
1 2 3 4
Bolide Infrasound measurements
Pilger et al (2015)Chelyabinsk
Infrasound only estimated terminal burst altitude = 20 ± 4 km
Energy ~ 50 kt
Line source
Point source
US Government Sensor data (2014):Terminal burst altitude = 19 km
Energy ~ 33 kt
Silber et al (2011)Oct 8, 2009 - Indonesia
Future Research• Luminous efficiency – calibrate from different
techniques• Infrasound models for validation of cylindrical line
source overpressure estimates at the ground (particularly amplitude model constraints)– (Silber et al., 2015) applied to cm-sized meteoroids,
need to expand to meter-sizes– Search IMS for regional IS airburst detection and
apply/modify model– Adapt Whitham weak-shock theory to cylindrical
hypersonic sources (eg. Haynes and Millet, 2013)
24
General Observations• Meter-sized impactors begin fragmentation under 0.1 – 1
MPa ram pressure (Popova et al 2011)– peak luminosity is reached 1-2 scale heights lower
• Fragmentation is complex• Lightcurves are crucial to constraining atmospheric energy
deposition in individual cases– Not enough meter-class LCs available to make any generalizations
about fragmentation behavior
• Spectra very helpful, but rare• Recovered meteorites provide ground-truth• Multi-instrumental observations critical – each measurement
technique suffers different systematic biases
25
Need for Model validationModels have now incorporated very elaborate physics
BUT we have few constraints from observations to guide choices in a very large parameter space (Fragmentation!).
1. Compare various models (particularly fragmentation characteristics) to existing published/detailed large bolide measurements (Chelyabinsk, Benesov, Sumava, Moravka, Kosice)
2. Apply models to USG data for statistical studies
3. Process/extract existing but unpublished precise large fireball data and apply models (EN – eg. EN 171101)
26
Modeling Capabilities• FM ablation model (theoretical and observational fit to bolide
data) [Ceplecha and ReVelle 2005]• Triggered Progressive Fragmentation ablation model (TPFM)
[ReVelle 2007a]• Acoustic Gravity Wave production from bolides [ReVelle
2007b]• Numerical Bolide - cylindrical line source weak shock model
[Edwards et al., 2007]• Seismic hypocenter geolocation of bolide airbursts [Edwards
et al. 2004]• Infrasound bolide airwave measurement and empirical energy
estimation [Ens et al., 2012]• Monte Carlo Dark Flight model of meteorite fall ellipse
production [Brown et al., 2011]27
28
The End
Backup
The Cylindrical Blast Radius
30
R O
V
po
dE/dL
Meteor is effectively an oriented cylindrical line source. Shock propagation is approximately perpendicular from trajectory
Atmospheric pressure = Meteor energy loss/length
31
• IMS Network requires 1kt globally
• thresholds vary primarily with stratospheric seasonal wind pattern.
• NH Winter– Westerly NH– Easterly SH
• NH Summer– Easterly NH– Westerly SH
(Le Pichon 2009)
Source Energy Estimation• Source energy estimates for bolides from IS has much
interstation variability due to:– Unique characteristics: Line source + quasi-Point source– Wide range of source altitudes detected at different stations– Compounded by numerous phases & extreme distance
• Two approaches:
1. First principles: Weak shock model (Revelle, 1976) – works at short ranges (<250 km)
2. Empirical Energy/Attenuation Relations– Signal Periods, Amplitudes + USG data.– Now calibrated by multi-instrumental, well-characterized events
(Ens et al (2012)– Use existing explosion relations (eg. Clauter and Blandford
1998).
32
Schematic: Bolide Entry IS Propagation
Weak Shock Theory (ReVelle, 1974)
x = R/R0
Weak shock regime
Linear regime
Applicable for direct arrivals – short (<200 km) range Can be used to estimate overpressure at the ground
34
http://neo.jpl.nasa.gov/fireballs/
Source Information from Observations
• Single Station– Alternative data source required! (Optical/radar/eyewitness etc.)– If trajectory information available
• Travel time/Arrival modelling (met.data required): Source Altitude
• Forward theoretical modelling energetics• Multiple stations
– 0th order: Intersection of observed back-azimuths– 1st improvement: Intersection + travel-time fit phase ID– 2nd improvement: Intersection + tt + wind correction + source model– Empirical attenuation & period relationships energetics
• NOTE: Energetics will often represent meteor at source position!• The more observations the better for energetics – large
variation! 36
Cylindrical Blastwave Theory (ReVelle 1974/1977)
• Propagation from source to observer goes through 2-3 stages – Nonlinear: very high
overpressures, strong attenuation– Weakly Non-linear: high
overpressures & attenuation, lengthening period
– Linear: low overpressure & attenuation, stable period
37
Bla
st R
adiu
s
Ro
Weakl
y N
on-l
inear
Pro
pagati
on
Δp ≤
po :
Incr
easi
ng P
eri
od
Non-l
inear
Pro
pagati
on
~1
0 R
o:
Δp >
> p
o10 Ro
Linear
Pro
pagati
on
Δp <
< p
o :
Peri
od S
table
d′ < dLinear Transition
002
1
p
pc
dt
d
38
Meteor Propagating Northward (red line)
Source Altitudes100 – 70 km
Radiant Altitude
7°
30°
50°
Radiant Altitude: 30°
Radiant Altitude: 50°
e.g. Grazers, Genesis, Stardust, Hayabusa
Most meteors fit in these
categories
Steeper is lost to atmosphere via
refraction
Fireball Infrasound Range Discriminators
39
Modeling of Bolides as Infrasonic Sources: Hypersonic Aerodynamics
• Line source blast wave analogy: Hypersonic flow– Ma >> 1 and dV/dt 0; Very narrow Mach cone Nearly
cylindrical source symmetry
• Line source energy deposition: Nonlinear blast wave relaxation radius: Ro– Ro Square root of energy deposited per length/pressure
Ro Mach no. diameter (No fragmentation assumed)
– Detectable Ro and source energy, Es, ranges from:• ~10 m to > 6 km (Tunguska)• ~10-5 kt to > 10 Mt (Tunguska)
– Wave period Ro/(local thermodynamic sound speed): Near-field weak shock wave valid for distances > ~10Ro
• Modified line source effects (fragmentation): Larger Ro at the same size and speed 40
Part III: Detailed numerical models
IDG group – SOVA 3D are only radiation hydrocode to date
Lack of good observations to calibrate the high fidelity in the models for large objects
Some USG lightcurves, but often lacking kinematic information or heights (or both)
41
Fragmentation - Assumptions• Most models assume that stagnation pressure =
material strength is trigger for breakup– ie. Breakup occurs when ρv2=strength
• Need to account for dust and macroscopic fragments – dust important in light production
• If time between successive fragmentation epochs is short compared to separation timescale (big objects, weak objects etc.) details of individual fragmentation can be ignored (large bodies) treat material as liquid-like object with no material strength (SL9 – like)
• Standard assumption in many models is interaction of individual fragment shocks produces pressure gradient produces lateral fragment speeds of order
• This gives fragment separatiuon speeds of a few tens of meters per second for meter-tens of meter sized bolides
Passey and Melosh (1980)42
Bolide Fragmentation Modeling• Break-up schemes: {A (drag) = A (heat transfer) for the single-body model}
– Baldwin and Sheaffer (1971): Frontal area, A (drag) N^1/3, where N = number of fragments produced during the gross-fragmentation process
– Petrov and Stulov (1975), Padavet (1973; 1977; 1978): A (heat transfer) >> A (drag) due to turbulent mixing of air/ablated vapor
– Liu (1978): A (heat transfer) >> A (drag) due to meteoroid porosity effects– Grigoryan (1977, 1979): “Pancake” break-up process (no ablation case)
• Once impactor is heavily fragmented the pressure difference between the front and back of the body compresses the impactor and it if forced to “flow” out the sides expanding in area at a rapid rate (pancaking)
– Bess (1979): Break-up: Progressive fragmentation process– Zahnle (1992), Hills and Goda (1993), Chyba et. al. (1993), Bronshten (1994; 1995
{after Grigoryan (1976; 1979) including ablation}, Svetsov (1995), Lyne, Tauber and Fought (1996), Nemtchinov et. al. (1995, 1997), Stulov (1997): Airburst, “Pancake” model development, tests and applications
• Break-up mechanisms:– Thermal effects: Very inefficient (too long of a time delay is necessary)– Mechanical effects: 1-D stagnation pressure exceeds the bolide’s “strength”
Pancake model : Predictions• The pancake model makes a number of
predictions/assumptions - cf. Grigoryan (1979), Melosh (1981), Zahnle(1992), Chyba et al (1993); Hills and Goda (1993;1998)); Korycansky et al (2002) Bland and Artemieva (2004)
– Most of the airburst energy is released as a nearly point source (assumption when used to calculate ground damage) (H&G, 1998)
– Lateral fragment speeds are a few tens of m/s (prediction)– Mass surviving to the ground as >100g fragments is ~50% of initial
mass (prediction) (B&A, 2006)
44
Collins et al., (2005)
Bolide masses
• Dynamic vs photometric mass• Long standing issue as photometric mass
10-100x larger than dynamic masses for bolides (Ceplecha et al 1980)
• Root cause – fragmentation (Ceplecha and ReVelle 2005)
• Luminous efficiency depends on velocity, mass (and maybe height and composition)
45
Panchromatic Luminous Efficiency:
Near the End of the Entry (TPFM)
46
Radiation Efficiencies• Panchromatic efficiencies calibrated using Lost City
– 6% at 13 km/s (Ceplecha, 1996)
• Large uncertainty in extrapolating results – camera network bolides much smaller than satellite
events
• Calibrate satellite energies by – cross-fusion with other sensors – either ground-truthing
or infrasound (Brown et al 2002)– Using hydrodynamic models which treat complete
radiative aspects of entry (Nemtchinov et al., 1997)47
Filled Circle – Meteorite events where energy is known well from many other techniques
Open Circles – Energy determined from infrasound observations alone
Brown et al (2002)
48
Numerical modeling results from Nemtchinovet al. (1997)
Graph shows result from entry model for pure Irons and H-Chondrites
Equation (14) is solid line in graphEquation (15) is dashed line in graph
Much spread, but average η close to empirical result found by Brown et al (2002) at smaller energies
49
Optical Energy (kT)
10-5 10-4 10-3 10-2 10-1 100 101 102
inte
gra
l (%
)
1
10
100
Integral Bolometric Efficiency Based on Calibrated Satellite – Sensor Events(Brown et al 2002)
50
Masses and Sizes• Total energy is determined by taking the observed
optical yield (Er) and dividing by efficiency (η)– Et=Er/ η
• With total yield (=energy = kinetic energy of impactor) known, mass is found from Et=1/2mv2
– Assumes velocity is known
• Size is found using mass and assuming a spherical shape and bulk density– Bulk density can be determined if meteorites are found51
Video Calibrations – Chelyabinsk Lightcurve• Uses indirect scattered
light and corrected for autogain
• Calibrated using meteorite-dropping fireball events and radiant intensity from US Gov Sensors
• Total deposited energy assuming η = 17% is >471 kT
52
Time [s]
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Ab
solu
te Mag
nitu
de
-29
-27
-25
-23
-21
-19
-28
-26
-24
-22
-20
-18
Height (km)
20253035404550
kt / k
m(h
eig
ht)
0
20
40
60
80
100
Brown et al (2013))
Chelyabinsk : Shock wave – Cylindrical or Spherical?
• Shock wave causing damage was cylindrical not spherical
• Ray tracing establishes origin height – arrivals are from various heights, not a single point
• Secondary, weaker shocks after main arrival are spherical - from discrete fragmentation 53
Top-down Modelling• Now find the blast radius from photometric measurements and entry model
run weak shock model to obtain the predicted signal amplitude and period
𝒅𝑬𝒅𝑳
=( 𝒗𝟐
𝟐𝒅𝒎𝒅𝑳
+𝒎𝒗𝒅𝒗𝒅𝑳 ) 𝑹𝟎=(𝒅𝑬 /𝒅𝑳
𝒑𝟎)𝟏/𝟐
1) Meteoroid intersects Earth and “collides”• Typical velocity ~20 km/s (11.7 – 73 km/s)• Meteoroid size: 0.1 – 10 m
2) Around 80 – 100 km Meteor becomes luminous
3) Meteoroid produces shock wave• Line source sound produced ┴ to trajectory
4) 15 – 40 km: Fragmentation• Point source sound produced
5) Direct Acoustic heard, Seismic Detections ? Meteorites ? 6) Ducted sound “heard”
at microbarometer array
7) Hydroacoustic in ocean (impact or airwave)
56
cS RER
Theoretical work has shown range scales with energy in
a power law (use USG sensor energy here)
Apply wind correction of form AA kv
w 10 Apply a multivariate linear least
squares regression in log-log space
RESULT:
cc
b
c
kva
ARE1
10
kvEcRbaA )log()log()log(
Airburst Energy Estimation : Amplitude – Yield
Depends on knowing the wind well
Lots of scatter Amplitude not very
reliable at large ranges