AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation...

32
AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang Xu Department of Earth and Atmospheric Sciences University of Nebraska – Lincoln Robert Spurr RT Solutions, Inc. Xiong Liu The Harvard Smithsonian Center for Astrophysics Michael Mishchenko, Brent Holben, Aliaksandr Sinyuk NASA Goddard Space Flight Center Qingyuan Han University of Alabama - Huntsville

Transcript of AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation...

Page 1: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of

APS/RSP Aerosol Products

Jun WangJing Zeng, Xiaoguang Xu

Department of Earth and Atmospheric SciencesUniversity of Nebraska – Lincoln

Robert SpurrRT Solutions, Inc.

Xiong LiuThe Harvard Smithsonian Center for Astrophysics

Michael Mishchenko, Brent Holben, Aliaksandr Sinyuk NASA Goddard Space Flight Center

Qingyuan HanUniversity of Alabama - Huntsville

Page 2: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Motivation

The 1991 eruption of Mount Pinatubo, photo from USGS

The validation of APS aerosol product has two major challenges (Mishchenko et al., BAMS, 2007): (1)the expected accuracy … is unlikely to be matched by most ground-based and in situ instruments; (2) the lack of cross-track converge …

Physically consistent Validation: reff, veff, mr, mi , ε,

of fine & coarse aerosol

multi-angle multi-radiance + polarization

RSP algorithm

AERONET retrieval algorithm

Page 3: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Current AERONET retrieval algorithm

Dubovik and King (2000): designed a flexible inversion algorithms and original Nakajima and King’s algorithm was replaced.

Dubovik et al. (2000): accuracy assessment of the new algorithmDubovik et al. (2006): Spheroid consideration in the retrieval…

• Limited use of Polarization; not used in the operational retrieval • While AERONET inversion products significantly advanced our understanding

of aerosol properties, they, similar as any other retrievals, have limitations:• the inversion of aerosol refractive indices and single scattering albedo is only

reliable in conditions of high AOT (>0.4 at 0.4μm) and at high solar zenith angle (>50º).

• most products are reported at the 68% confidence level; • single scattering albedos for both the fine and coarse modes are estimated, but

they are not advised for use, since the inversion algorithms assume the same complex refractive indices for all particle size;

• this refractive index limitation can lead to large errors in retrieval of size distributions when the refractive indices for fine mode and coarse mode aerosols have large difference; and

• Other inconsistence with RPS• size distribution: bin (AERONET) vs. log-normal (RPS)

Page 4: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

“A preliminary analysis shows that adding polarization in the inversion can reduce possible errors (notably for about 30% of our field cases) in the fine mode size distribution, real part of refractive index and particle shape parameter retrievals, especially for small particles.”

• A theoretical framework to study and retrieve the aerosol information content from ground-based polarimetric instrument is highly needed.

• AERONET collects polarization data at 870nm over many stations (primarily in Europe) since its inception in 1990s.

Page 5: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

HITRAN &LBLRTM

GEOS-chemAtm

ospheric

Profile

LMIELTmatrix

Reff , v

eff , mr , m

i , ε, of fine

& coarse aerosol

VLIDORT

Gas Absorption

&Rayleigh

Scattering

Single scattering properties & their

Jacobian to reff, veff, mr, mi ε

M, ρ of fine & coarse aerosol

Sky radiances and polarization & their Jacobians w.r.t. reff, veff, mr, mi , , ε

AERONET sun + sky radiance & polarization

VLIDORT

flow chart of this study

Inversion(Optimal Estimation

Module)

reff, veff, mr, mi ε, of fine & coarse aerosol

Page 6: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Forward Model Structure

User’s Setting Inputs

- Via a simple namelist

User’s Setting Inputs

- Via a simple namelist

Load Atmospheric Profiles

- Z; P; T- Air & trace gas density

Load Atmospheric Profiles

- Z; P; T- Air & trace gas density

Trace Gas Module

- HITRAN 2008- Raman

Trace Gas Module

- HITRAN 2008- Raman

Diagnostic Module

- Output to netCDF

Diagnostic Module

- Output to netCDF

Aerosol Module

- Linearized Mie- Scale height

Aerosol Module

- Linearized Mie- Scale height

Rayleigh Module

-Bodhaine (1999)

Rayleigh Module

-Bodhaine (1999)

VLIDORT Module

- Prepare VLIDORT IOP- VLIDORT: RTM solution

VLIDORT Module

- Prepare VLIDORT IOP- VLIDORT: RTM solution An undergraduate can

play with it easily.

Now primarily focus on the shortwave spectrum

Page 7: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer), Ricchiazzi,P., 1988, BAMS. It uses LOWTRAN with spectral resolution about 5 nm in uv-visible spectrum.

Gas Absorption Lines

Page 8: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

- Evans and Stephens (1991)

o τ = 1.0

o Upwelling at TOA

o surface ρ = 0.25

o cosθ0 = 0.8

o 8 difference θ

Average Error

I Q U

Evans and Stephens 2.1E-4 9E-5 7E-5

This Model 1.9E-4 2E-5 4E-5

Relative Error(This model) 0.05% 0.14% 0.03%

Compare with Coulson et al (1960)

I UQ

Validation: Pure Rayleigh Atmosphere

Page 9: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

- Red: positive values- Green: Negative values

Validation: VLIDORT Jacobians w.r.t. AOT

Input parameter:

mid-latitude summerτ = 1.0 scale height: 2.0 kmλ: 550nmΘ0=30°, 45°Θ: 10°-80° with 10° intervalϕ: 90°m = 1.53 + 0.001 i

Log-normal size distributionRg = 0.1 μmσg = 1.6 μm

Page 10: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

- Jacobian of Stokes parameters with respect to aerosol single scattering albedo (ω)

- Red: positive values- Green: Negative values

Validation: VLIDORT Jacobians w.r.t. ω

Page 11: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Validation: Jacobians of Stokes parameters w.r.t. real part of refractive index

I

U

Q

V

Page 12: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Validation: Jacobians of Stokes parameters w.r.t. imaginary part of refractive index

I

U

Q

V

Page 13: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Validation: Jacobians of Stokes parameters w.r.t. geometric mean radius

I

U

Q

V

Page 14: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Validation: Sensitivity of Stokes parameters w.r.t. geometric standard deviation

I

U

Q

V

Page 15: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Linear Tmatrix

Page 16: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

LINEARIZED T-MATRIX CODE

Robert SpurrRT Solutions, Inc.Cambridge, MA 02138, USA

Jun Wang, Jing ZengUniversity of Nebraska, Lincoln, NE, 68588, USA

Michael MishchenkoNASA GISS, 2880 Broadway, New York, NY 10025, USA

GLORY STM, 10-12 August 2011, NASA-GISS

Page 17: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Linearized T-matrix code• Mie code was linearized several years ago by 3 groups including RT Solutions.• Macroscopic optical properties: Extinction and scattering coefficients Cext and

Csca, scattering matrix expansion coefficients k (k=1,…6) and F-matrix F()• Linearized Mie code Analytic derivatives of optical properties with respect

to r and i (refractive index components)• Also Analytic derivatives of polydispersed properties w.r.t PSD parameters

such as mode radius rg and standard deviation sg for Lognormal• From polarization measurements, you can retrieve microscopic aerosol

properties {r, i, rg, sg} instead of specifying macroscopic optical properties• Butz et al. (2009) did study for OCO measuring XCO2, much better able to

characterize aerosols in the retrieval using combination of linearized Mie code and linearized Vector RT model.

• We have developed combined Mie/VLIDORT tool for looking at ground-based Aeronet data as part of our participation in the GLORY Science Team.

• Extension to T-matrix capability has potential to extend the reach of Mie-based applications.

04/20/23 17GLORY STM, NASA-GISS, 10-12

August 2011

Page 18: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Linearized T-matrix code• Maxwell’s theory is linear! Should be analytically differentiable• Electromagnetic Field, vector spherical function expansion:

• T-matrix, linear relation between incident and scattered fields

where and

max

1

)()()(n

n

n

nmmnmnmnmninc kRgbkRga RNRMRE

max

1

)()()(n

n

n

nmmnmnmnmnpar kRgdkRgc RNRMRE

max

1

)()()(n

n

n

nmmnmnmnmnsca kqkp RNRMRE

1Rg QQT

b

a

TT

TT

b

aT

q

p2221

1211

d

c

QQ

QQ

b

a2221

1211

d

c

QQ

QQ

q

p2221

1211

RgRg

RgRg

04/20/23 18GLORY STM, NASA-GISS, 10-12

August 2011

Page 19: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Linearized T-matrix code

Linearization:

Already have T and Q from T-matrix evaluation, just need to calculate derivatives of Rg Q and Q; y is one of {r, i, }

Rg Q and Q made up of products of vector spherical functions

Here, x is particle size parameter kR, hn(x) are Hankel (Bessel) functions depend on radius R() which is function of

For internal field, argument is kR ( is the complex refractive index) need complex Bessel functions, depending on {r, i, }

C, P, B are angular functions related to Wigner spherical functions, not dependent on {r, i, }, no need to differentiate.

1][][Rg

QQ

TQT

yyy

04/20/23 19GLORY STM, NASA-GISS, 10-12

August 2011

)exp()()()1()( )1( imxhdkR mnnnm

mn CM

)exp()()(1

)()()1(

)1()( )1()1( imxxhxx

xhkR

nndkR mnnmnnn

mmn

BPN

Page 20: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Linearized T-matrix code• Bessel functions developed by simple recursion relations, easy to

differentiate. Applies equally to Mie and T-matrix.• Surface area integration (T-matrix). r = r Expressions such as

• Integrals of following type (no , as axially symmetric)

• Done by quadrature sums. E.g. for spheroids

• Through-differentiation / with respect to .• R~() is equivalent sphere (ES) radius (constant for volumes)

04/20/23GLORY STM, NASA-GISS, 10-12

August 201120

S nmmn

mmnnm krkrRgrdST ),,(),,()(ˆ)1(11 MMn

0

2

0

dsin),(;dsin),( rr

rGJrrFJ r

222

2

222 cossin

cossin)1()(1;

cossin

)(~

)(21

31

r

r

Rr

Page 21: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Linearized T-matrix code• ESAS representation (equivalent surface-area sphere)

• E. g. Prolate spheroids (a/b = < 1)

• Just need to work through the differentiation / • So far, monodisperse. For polydisperse, need only to

differentiate PSD functions n(r) with respect to their parameters such as rg and sg for Lognormal.

• Through-differentiate the PSD numerical integration. Applies equally to Mie and T-matrix.

04/20/23GLORY STM, NASA-GISS, 10-12

August 201121

213

1

4

)()(;

)()(;

)(

)(~)(

~)(

~

3400

A

EV

EE

ERSRR AV

A

V

21

31

2)(;1

1arcsin122)(;

3

4)(

2

222

2

HSaHaA

baV

Page 22: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Linearized T-matrix code

• Start with GISS F77 T-matrix code. Keep this. Original commentary regarding convergence issues and accuracy still applies.

• Convert to modular F90 code, implicit none, explicit Intent (in/out/inout) statements, no Common blocks or Equivalences.

• Additional PSD specifications from Meerhoff (Dutch) Mie code• Add linearization code. 2 “masters”, one just regular optical property

output, other with regular + additional linearized output.• Package has configuration-file input with new linearization flags and

additional control options (e.g. optional F-matrix).• Kept original names for the most part. Much of the original code still

intact and in use. Continue using LAPACK utility for Matrix inversion• Validation (1) optical properties against original F77 code; (2)

Jacobians by finite difference constructions.• Package (when finished) will be publicly available.

04/20/23GLORY STM, NASA-GISS, 10-12

August 201122

Page 23: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Example 1

04/20/23GLORY STM, NASA-GISS, 10-12

August 201123

Page 24: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Example 2

04/20/23GLORY STM, NASA-GISS, 10-12

August 201124

Page 25: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

04/20/23GLORY STM, NASA-GISS, 10-12

August 201125

Bi-mode log normalSulfate (0.07, 1.8)Dust (0.4, 1.8) Fraction 0: all sulfateFraction 1: all dust

polarization is much more sensitive to the change of non-spherical large mode fraction than phase function F11, especially at 90..

Note the scale difference

Page 26: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Non-linear Optimal Estimation Theory

i: iteration time step; X: retrieved state vector; Xa: a priori vectorY: is the measurement vector; Ki is the Jacobian or weighting function matrix, defined as ∂F/∂Xi

Total error covariance matrix CT: = instrument + forward model error

Ca: A priori covariance matrix (Ca)

Similar as Waquet et al. (2010), we use OET by Rodgers (2000) and the cost function is:

Instrument Error Model Error

Sky radiance

5% relative error Holben et al., 1998

5% relative errorHalthore et al., 2005

LDOP 0.01 absolute errorDubovik et al., 2006

0.01 absolute error Zeng et al., 2008

the measured - the modeled difference with a priori

Page 27: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Non-linear Optimal Estimation Solutions

The optimal solution is:

Solution error covariance matrix for the retrieved parameters

We can also attribute the model and instrument errors to the error budget of retrieved parameters.

Page 28: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Theoretical retrieval of information content

In primarily plane, VZA=0, 10 at RAZ=0 and 180. Dust-like aerosols.3 wavelengths: 380, 470, and 670 nmtotal 8 retrieval parameters: rg, sigma_g, (mi, mr,) at 3 wavelengthsSurface is assumed to be well known; in this case, grassland surface.

With I only

With I, + Sunphometer tau

I, Q, U + Sunphometer tau

I, Q, U + Sunphometer tau + additional 2 angles

Adding polarization increases information content by 10%-40%, depending on SZA.

Page 29: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Theoretical retrieval of information content

In primarily plane, VZA=0, 10 at RAZ=0 and 180. Dust-like aerosols.Three wavelengths; total 8 retrieval parameters: rg, sigma_g, (mi, mr,) at 3 wavelengths

With I only

With I, + Sunphometer tau

I, Q, U + Sunphometer tau

I, Q, U + Sunphometer tau + additional 2 angles

The information content of refractive index, in particular, real part refractive index, can be better retrieved by adding polarization.

Page 30: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Theoretical retrieval of information content

In primarily plane, VZA=0, 10 at RAZ=0 and 180. Dust-like aerosols.Three wavelengths; total 8 retrieval parameters: rg, sigma_g, (mi, mr,) at 3 wavelengths

With I only

With I, + Sunphometer tau

I, Q, U + Sunphometer tau

I, Q, U + Sunphometer tau + additional 2 angles

The retrieval of refractive index, in particular, real part refractive index, can be significantly improved by adding polarization measurements at more angles.

Page 31: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.

Summary and next steps

• A modeling framework is developed to study the information content for aerosol retrievals using multispectral and multiangle sky radiance and polarization data (such as those collected by AERONET)

• A combination of VLIDORT with linearized Mie and Tmatrix codes will be a powerful tool for a formal inversion of aerosol parameters; it will be a useful tool for the retrieval community.

• Multi-angle polarization data are key for retrieval of refractive index, size, and shape of the particle.

• We plan to streamline the codes, and start the retrieval using AERONET data in fall, as well as any other sky radiance and polarization data collected from various field campaigns.

• Last but not least, we like to work with the Glory team’s research strategy (with RSP instrument) and plan well for our next steps.

Page 32: AERONET Skylight Retrievals Using Polarimetric Measurements: Toward Physically Consistent Validation of APS/RSP Aerosol Products Jun Wang Jing Zeng, Xiaoguang.