Date post: | 19-Jan-2016 |
Category: |
Documents |
Upload: | brianna-dixon |
View: | 214 times |
Download: | 2 times |
Weighting functions (Box AMFs) for Limb measurements of stratospheric trace species
using 3D Monte Carlo RTMChristoph v. Friedeburg, A. Butz, F. Weidner, S. Sanghavi, K. Pfeilsticker, U. Platt and T. Wagner
•Box AMF and profile retrieval
•3D Monte Carlo RTM „AMFTRAC“
•AMF investigation example
•Balloon-borne limb geometry
•Outlook
IUP University of Heidelberg
Box AMF and profile retrieval
•Discretization of atmosphere into boxes i=1,..,n
•SCD box-wise
•AMF box-wise: A(i)
•Weighting Function
•S(i) = c(i) * d(i)
•V(i) = c(i) * v(i)
•S(i) = V(i) * A(i)
•SCD = Σ S(i)
•SCD = Σ c(i) * v(i)* A (i)
•=> into equation system C [cm-3]
Altd [m]
v(i)
•SCD and AMF do not tell us where along the light path the trace gas is located
•But this is what we’d like to know.
d(i) c(i),σ(c,i)
Box AMF and profile retrieval
C [cm-3]
Altd [m]
v(i)
d(i) c(i),σ(c,i)
Box AMF defined as:
•sum over all intensity having traversed the layer/cell
•divided by total intensity received by detector
•divided by layer‘s/cell‘s vertical extension
Box AMF and profile retrieval
θ
ε
•Multiple scattering increases retrieval difficulty since
•geometrical approximations/estimations not valid and misleading
•AMF and A(i) must be modelled with RTM
•Behaviour of A(i) with relevant parameters must be investigated & understood
3D Monte Carlo RTM „AMFTRAC“ (working title)e.g. v. Friedeburg EGS 2002
di
ai
detector
features
•spherical 3D geometry
•supports arbitrary platform positions and viewing geometries
•full MS by Rayleigh, aerosols, clouds, albedo
•refraction, polarization and solar CLD (limb)
principle
•backward Monte Carlo technique
•N photon launched out of telescope
•random numbers, scatt. centre ND & c/s govern light path => establish path sun->detector
•molecular absorption calculated analytically
•AMF computed from modelled av. intensity with/without absorber
vv,i
3D Monte Carlo RTM „AMFTRAC“
output
•SCDs, SODs, AMFs, Box AMFs (A(i)) for a specified set of boxes/layers
•abs. radiances
•geometrical path length, traversed air column, O4
•number of Rayleigh, Mie and albedo scattering events
•altitudes of first and last scattering event, distance detector-last scattering event
•entry angle of light into atmosphere, first scattering angle
•Solar CLD effect parameter, polarization (under testing)
•parameters as intensity weighted means
•errors as intensity weighted std dev.
3D Monte Carlo RTM „AMFTRAC“
radiance validation
•In addition to validation against AMF by other RTMs:
•validation against measurements with calibrated spectro-radiometer
60 65 70 75 80 85 900.0
1.0x10-8
2.0x10-8
3.0x10-8
4.0x10-8
5.0x10-8
6.0x10-8
7.0x10-8
Radia
nce
[W
cm-2nm
-1sr
-1]
SZA [°]
Radiance 22.2.2003 roof IUP Heidelbergfrom 5° around zenith
measured 420 nm modelled 420 nm measured 350 nm modelled 350 nm
AMF investigation example
ground based MAX DOAS scenario•λ = 352 nm
•atmosphere: 1 km vertical discret., 0-70 km
•ε = 2°, 5°, 10°, 20°, 45°, 90°;
•azimuth α to sun 90°, aperture 0.1°
•albedo values 0%, 30%, 50%, 70%
•standard aerosol scenario
•BrO near ground: 3 profiles
0
1
2
3
4
5
0.0 2.0x108 4.0x108 6.0x108 8.0x108 1.0x109
[BrO] [cm-3]
Altd
[km
]
P1 P2 P3
investigation of total AMFs in relation to scattering parameters
AMF investigation example
BrO AMF
0 20 40 60 80 1000
2
4
6
8
10
12
14
AM
F [
]
Elev. [°]
Albedo 0 % P1 P2 P3
0 20 40 60 80 1000
2
4
6
8
10
12
14
Elev. [°]
AM
F []
Albedo 30 % P1 P2 P3
0 20 40 60 80 1000
2
4
6
8
10
12
14
AM
F [
]
Elev. [°]
Albedo 50 % P1 P2 P3
0 20 40 60 80 1000
2
4
6
8
10
12
14
Elev. [°]
AM
F []
Albedo 70 % P1 P2 P3
P1,P2: AMF highest for 2° elev.
P3:?
Results: AMF
AMF->f(Albedo), O4 AMF
0 20 40 60 80 100
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
AM
F [
]
Elev. [°]
AMF P3Albedo
0 % 30 % 50 % 70 %
0 20 40 60 80 1002
3
4
5
6
AM
F [
]
Elev. [°]
O4 AMF
Albedo 0 % 30 % 50 % 70 %
•P3: AMF increases with albedo, but behaviour pertains:
•AMF for smallest elevations not highest
•same effect for O4 - looks like P1 & 2, but higher proportion (~3/4) located above 1 km.
AMF investigation example
Number of scatterings
0 20 40 60 80 1000.0
0.5
1.0
1.5
2.0
2.5
3.0
Num
ber
Elev. [°]
NO of Rayleigh scatteringsAlbedo
0 % 30 % 50 % 70 %
NO of Aerosol scatteringsAlbedo
0 % 30 % 50 % 70 %
•Single scattering approx. („1/sin(τ)“, „1/cos(θ)“) heavily limited
•similar investigations for higher wavelengths useful
AMF investigation example
Last Scattering Altitude LSA
0 20 40 60 80 100102
103
104
LSA
[m]
Elev. [°]
Last Scattering Altitude 0 % 30 % 50 % 70 %
LSA
•LSA for small elevations between 300 and 400 m
=>decreases light path within lowest boxes as comp. to 1/sin(ε)
AMF investigation example
LSA -> AMF(i)
LSA
•LSA for small elevations < 1 km
•A(i) for boxes above 1 km decrease for low elevations
0
2
4
6
8
10
2 4 6 8 10 12 14AMF(i)
Altd
(i) [k
m]
2 ° Elev. 10 ° Elev.
error ~5%
Balloon-borne limb geometry
•relevant to SCIAVAL balloon operations
•SCIAMACHY limb mode
SZA (at altd 0 below instrument position): 70°
atmosph. discret. 1 km
Variation of
•altitude
•elevation angle
•azimuth angle
•aperture angle
•cloud cover
Balloon-borne limb geometry
Error investigation
0 2000 4000 6000 8000 100000.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
BO
X A
MF
re
l err
or
PU modelled
0-1 km 9-10 km 10-11 km 19-20 km 29-30 km 39-40 km 49-50 km 59-60 km 69-70 km
Box AMF error’s absolute value depends on:Number of pathslayer’s/grid cell’s shape & extensionlayer’s/grid cell’s distances from the instrument
influence of multiple scattering on the way to & within the layerincl. albedo, clouds
2000 PU was used for the calculations to follow.
Balloon-borne limb geometry
Altitude variationLine Of Sight Parameters:-4° elevation, 90° azimuth, 0.5° aperture, 30% albedo
above instrument: Box AMF governed by SZA
below instrument: Box AMF increases due to LOS geometry,at altd<25 km LOS hits ground
below altitude of highest Box AMF: fall-off depends on aperture (see aperture var.)
near ground AMFs dependent on multiple scattering
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30 35 40 45 50
Box AMF
Altd
[km
]
floating altd 10 km 15 km 20 km 25 km 30 km 35 km 40 km
Balloon-borne limb geometry
Altitude variation: scattering parameters
NRS (MS importance) decreases with increasing altitude
Last Scattering Distance (LSD) affected by MS
LSA complies well with altitude of highest Box AMF
10000 15000 20000 25000 30000 35000 400001.35
1.40
1.45
1.50
1.55
1.60
1.65
1.70
1.75
1.80
Altd [km]
NRS
05000
100001500020000
25000
100000
200000
300000
400000
LSA
[m]
LS
D [m
]
NR
S
LSD LSA
(last sctrg distance)
Balloon-borne limb geometry
Elevation variationLOS Parameters:90° azimuth, 0.5° aperture, altitudes 10 and 30 km
strong variation in sensitivity for tangent altitude
tangent altitude moves upwards
important for limb scanning geometry - total Box AMF as weighted average
below tangent altitude Box AMF largely unaffected
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30 60 80 100Box AMF
Altd
[km
]
fltg altd 30 km -4° elev. -2° elev. 0° elev. +2° elev. +4° elev.
fltg altd 10 km -4° elev. -2° elev. 0° elev. +2° elev. +4° elev.
Balloon-borne limb geometry
Elevation variationLOS Parameters:90° azimuth, 0.5° aperture, altitudes 10 and 30 km
strong variation in sensitivity for tangent altitude
tangent altitude moves upwards
important for limb scanning geometry - total Box AMF as weighted average
below tangent altitude Box AMF largely unaffected
0
5
10
15
20
25
30
35
40
45
50
0 5 10 15 20 25 30 60 80 100Box AMF
Altd
[km
]
fltg altd 30 km -4° elev. -2° elev. 0° elev. +2° elev. +4° elev.
fltg altd 10 km -4° elev. -2° elev. 0° elev. +2° elev. +4° elev.
Balloon-borne limb geometry
Azimuth variationLOS Parameters:-4° elevation, 90° azimuth, 0.5° aperture, altitudes 10 and 30 km
impact small as compared to e.g. elevation influence
for az. 90° Box-AMF largest in tangent alt, above for az 180° “sun beam” has to travel longer distance to reach LOS intersection point
0
5
10
15
20
25
30
35
40
0 15 20 25 30 35
Box AMF
Altd
[km
]
fltg altd 30 km 0° az 20° az 45° az 90° az 180° az
fltg altd 10 km 0° az 20° az 45° az 90° az 180° az
Balloon-borne limb geometry
Aperture variationLOS Parameters:-4° elevation, 90° azimuth, 0.5° aperture, altitudes 10 km
fall-off below tangent altd influenced by aperture for geometrical reasons
for ap. angles <1° effect small but:
depends on chosen discretizationchanging elevation (scanning) equals a higher effective ap. angle
0
5
10
15
20
25
30
0 2 4 16 18 20
Altd
[km
]
Box AMF
fltg altd 10 km ap 0.2° ap 0.3° ap 0.4° ap 0.5° ap 1° ap 5°
Balloon-borne limb geometry
Cloud cover variationLOS Parameters:-4° elevation, 90° azimuth, 0.5° aperture, altitudes 10 and 30 km
cloud cover: 1. grid cell filled with Mie particles - high CPU time2. layer with altitude, coverage, albedo, transmission
multiple layers, vertical cloud surfaces easy to implementaccuracy depends on cloud effects impact on measurement
cloud layer altitude 5 km albedo 80%, transmission zero
0
2
4
6
8
10
12
20
30
0 5 10 15 20 25 30
Box AMF
Altd
[km
]
altd 30 km cloud cov 1 altd 10 km cloud cov 1 altd 10 km cloud cov 0.5 altd 10 km cloud cov 0.2 altd 10 km cloud cov 0
Balloon-borne limb geometry
Cloud cover variation: O4, radiance
LOS Parameters:-4° elevation, 90° azimuth, 0.5° aperture, altitude 10 km
radiance: smooth increase with cloud coverO4: decrease due to lower troposphere shielding
0.0 0.2 0.4 0.6 0.8 1.0
7.0x10-11
7.5x10-11
8.0x10-11
8.5x10-11
9.0x10-11
9.5x10-11
1.0x10-10
radi
ance
[W c
m-2
nm s
r-1
]
Cloud cover []
Rad
3.0
3.5
4.0
4.5
5.0
5.5
6.0
O4 A
MF
[]
O4AMF
Conclusion/Outlook
•AMFTRAC capable of handling limb geometry in relevant LOS parameters
•output parameters help understanding AMF‘s and A(i)‘s behaviour quantitatively
•Investigation of use of polarization and CLD effects
•Implementation of realistic clouds and aerosols
•Inclusion of basic LES-based retrieval module
MAX-DOAS, AMF and profile retrieval
•DOAS: Differential Optical Absorption Spectroscopy
•Measured quantity: optical density τ of trace gases investigated
•integrated over light path
•σ(λ) absorption cross section c(s) concentration
•along “slant” light path : Slant Column Density SCD = τ(λ) / σ(λ)
•along vertical path from location: Vertical Column Density VCD
•related by Air Mass Factor AMF
•VCD=SCD / AMF
•Measure of sensitivity
for the trace gas profile
dssc )()(
MAX-DOAS, AMF and profile retrieval
θ
ε
•Solar light enters atmosphere on straight path
•gets scattered by e.g. Rayleigh, Mie, albedo
•enters telescope => AMFs depend on:
•Solar Zenith Angle (SZA θ) and Solar Azimuth Angle
•scattering centre number density, cross section, phase fct.
•elevation ε, aperture angle,...
Investigation: Influence of aerosol
how to retrieve aerosol data - radiance?
•radiance series R(ε) : Spectrographs not usually absolutely calibrated
•dR/dε not significantly different to allow for concl. on aerosol
0 20 40 60 80 100
6.0x10-12
8.0x10-12
1.0x10-11
1.2x10-11
1.4x10-11
1.6x10-11
radi
ance
[Wcm
-2sr
-1]
Elev.[°]
no aerosols
aerosols 0.03 km-1 ext coeff 0 km
aerosols 0.05 km-1 ext coeff 0 km
0 20 40 60 80 1000.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Elev.[°]
rel.
radi
anc
e (
Ele
v. 9
0°
= 1
)
no aerosols
aerosols 0.03 km-1 ext coeff 0 km
aerosols 0.05 km-1 ext coeff 0 km
Investigation: Influence of aerosol
LSA
0 20 40 60 80 100100
1000
10000
LSA
[°]
Elev. [°]
aerosolsAlbedo
10 % 30 % 50 % 70 %
no aerosolsAlbedo
10 % 30 % 50 % 70 %
5 10
1000
Elev. [°]LS
A [°
]
aerosolsAlbedo
10 % 30 % 50 % 70 %
no aerosolsAlbedo
10 % 30 % 50 % 70 %
•without aerosol impact effect present, but much weaker
•aerosol scenario largely governs AMF -> f(ε)
•use of std. scen. Risky => need hard data on local aerosol
Investigation: Influence of aerosol
albedo in many cases known; aerosol load not.
investigation on AMF->f(aerosol) for albedo 30%
0 20 40 60 80 1000
2
4
6
8
10
12
14
16
18
AM
F []
Elev. [°]
aerosols P1 P2 P3
no aerosols P1 P2 P3
Investigation: Influence of aerosol
how to retrieve aerosol data - O4?
•But O4-AMF->f(ε) signif.tly different for large aerosol ld. differences
•parametrize the O4-AMF(ε) behaviour as f(aerosol ext. coeff.) => scale aerosol ext. coeff.
•uncertainties: effect of phase function ?
0 20 40 60 80 1002.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
O4
AM
F
Elev. [°]
no aerosols
aerosols 0.03 km-1 ext coeff 0 km
aerosols 0.05 km-1 ext coeff 0 km
MAX model scenario•aerosols:
•continental scenario (F. Hendrick, IASB, pers. comm.)
•ext. coeff. Value for 0 km varied for investigation
0
10
20
30
40
50
60
70
1E-7 1E-6 1E-5 1E-4 1E-3 0.01
Ext. Coeff. [km-1]
Altd
[km
]
Extinct. coeff Type1 Type2 Type3
0 20 40 60 80 100 120 140 160 1800.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Ph
ase
Fct
. V
alu
e (
a.u
.)
[°]
Phase function Type 1 Type 2 Type 3
Monte Carlo Approach for MS
• calculation of distance d to next voxel boundary
• extinctors (Rayleigh, Mie particles) yield probability p(x) for free passage up to x
• p(d)=p0 prob. of unscattered passage along d
• map random number p‘ to x by the inverse of function p(x):
• determines location of scattering event [0,d]
• use a second random number to decide between scatterers according to the relative probabilities
X d
p‘
1
d
p0