Quality of the official SCIAMACHY Absorbing

Aerosol Index (AAI) level-2 product

L.G. Tilstra and P. Stammes

Royal Netherlands Meteorological Institute (KNMI)

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (2)

Absorbing Aerosol Index: version 3.01 versus version 5.02WAbsorbing Aerosol Index: version 3.01 versus version 5.02W

– Totally new algorithm setup

– New look-up tables (pseudo

spherical atmosphere +

including polarisation)

– Better surface height database

– ...

Changes in L1–2 data processor:

version 5.02W is a huge

improvement on version 3.01

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (3)

Scientific product (SC-AAI)

Official product (L2-AAI v5.02W)

Scientific product SC-AAI versus L2-AAI v5.02WScientific product SC-AAI versus L2-AAI v5.02W (2003)(2003)

(grey = sun glint filtering)

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (4)

Scatter plot:

Scientific product SC-AAI versus L2-AAI v5.02WScientific product SC-AAI versus L2-AAI v5.02W (2003)(2003)

Good agreement (in the year 2003)

– Calibration correction SC-AAI

– Degradation correction SC-AAI

– Ozone dependence taken into

account in SC-AAI

– L2-AAI: measurements

“converted” to the (shorter)

integration time of cluster 26

(O2–A band)

Explanation for the differences:

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (5)

Scientific product (SC-AAI)

Official product (L2-AAI)

Scientific product SC-AAI versus L2-AAI v5.02WScientific product SC-AAI versus L2-AAI v5.02W (2011)(2011)

The official L2-AAI is suffering from

a scan-angle dependence

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (6)

Scatter plot:

Scientific product SC-AAI versus L2-AAI v5.02WScientific product SC-AAI versus L2-AAI v5.02W (2011)(2011)

Official product suffers from a strong scan-angle dependence in 2011

colours: scan mirror positions

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (7)

Influence of (scan-angle dependent) instrument degradation:Influence of (scan-angle dependent) instrument degradation:

Global mean reflectance

Global mean residue (AAI)

[no m-factors applied]

[Tilstra et al., JGR 117, 2012]

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (8)

M-factors applied in calculation of L2-AAI:M-factors applied in calculation of L2-AAI:

Global mean residue (AAI)

Current m-factor approach is scan-angle independent; the official L2-AAI product

therefore shows a scan-angle dependence.

Although v5.02W is a large improvement on the previous version, data after 2006

are not to be used without application of necessary corrections by the user.

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (9)

Conclusion:Conclusion:

– The official AAI product of level-2 version 5.02W is a large improvement w.r.t.

the previous version 3.01.

– Instrument degradation has a large impact on the residue. The use of the official

AAI product after 2006 is problematic.

– This is, however, a level-1 issue.

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (10)

Extra slidesExtra slides

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (11)

(A is assumed to be wavelength independent: A340 =

A380)

A. Definition of the residue:

where the surface albedo A for the simulations is such that:

Rayleighmeas

380

340 10

380

34010 log log 100 R

R

R

Rr

)(Rayleigh380

meas380 ARR

The AAI represents the scene colour in the UV

Introduction: Absorbing Aerosol Index (AAI)Introduction: Absorbing Aerosol Index (AAI)

B. Definition of the AAI:

AAI = residue > 0 (and the AAI is not defined where residue < 0)

The AAI can be retrieved over land and sea surfaces, even in the presence of clouds.

no clouds, no aerosols : r = 0

clouds, scattering aerosols : r < 0

absorbing aerosols : r > 0

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (12)

Example of global aerosol distribution recorded by SCIAMACHY:

The “Global Dust Belt”:

Desert Dust Aerosols (DDA)

(dust storms, all year)

AAI from other UV satellite instruments: TOMS, GOME-1, OMI, GOME-2. Combined with

SCIAMACHY there are more than three decades (1978–2012) of AAI data available for

studies of trends in desert dust and biomass burning aerosol.

Biomass Burning Aerosols (BBA)

(dry season, anthropogenic)

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (13)

The “Global Dust Belt”

SCIAVALIG workshop, KNMI, De Bilt, 30-11-2012 (14)

Wavelength Wavelength pair (nm)pair (nm)

Equator Equator crossing crossing

timetime

Pixel size Pixel size (km)(km)

Days needed Days needed for global for global coveragecoverage

Platform / Platform / Operation periodOperation period

GOME–1GOME–1 340 / 380340 / 380 10 : 30 LT10 : 30 LT 320 × 40320 × 40 33ERS-2ERS-2

(1995 – 2003*)(1995 – 2003*)

SCIAMACHYSCIAMACHY 340 / 380340 / 380 10 : 00 LT10 : 00 LT 60 × 3060 × 30 66EnvisatEnvisat

(2002 – 2012)(2002 – 2012)

GOME–2GOME–2 340 / 380340 / 380 09 : 30 LT09 : 30 LT 80 × 4080 × 40 1.51.5MetOp-AMetOp-A

(2006 – present)(2006 – present)

OMIOMI 354 / 388354 / 388 13 : 30 LT13 : 30 LT 13 × 2413 × 24 11AuraAura

(2004 – present)(2004 – present)

AAI products from GOME-1, SCIAMACHY, GOME-2, and OMI:

*GOME-1: loss of global coverage on 22 June 2003 ; instrument retired on 4 July 2011