Download - OMI UV spectral irradiance: comparison with ground based measurements in an urban environment

21.04.23

OMI UV spectral irradiance: comparison with ground based measurements in an urban environment

Stelios KazadzisA. Bais, A. Arola

OMI science team meeting Helsinki, June 2008

Finnish Meteorological InstituteLaboratory of Atmospheric Physics, Thessaloniki, Greece

21.04.23Stelios Kazadzis, OMI science team meeting Helsinki, June 2008 2

Outline

• OMI – ground based UV spectral irradiance comparison – statistics

• Aerosol absorption – post correction approaches

• Campaign: Spacial and temporal UV variability within an OMI grid


• The problem - absorbing aerosolsCurrent OMI UV algorithm does not account for absorbing aerosols

(e.g. organic carbon, smoke, dust )

OMI – GB UV comparison – statistics

Tanskannen et al., JGR 2007

Tokyo: +32%


Thessaloniki Area


forest

agricu lture

w etlands

grasslands

other

Thessaloniki

Longitude (degrees)

Latit

ude

(deg

rees

)

-High aerosol load

- Aerosol transport Sahara dust intrusions Biomass burning from NE

- Very high PM10 conc.

Sahara - Dream model

Fire hot spots - summer


Instrumentation - comparisonOMI – GB UV comparison – statistics

Rooftop of the School of Natural Sciences

Brewer instrumentBrewer instrument(spectral-calibrated, wavelength shift corrected)(spectral-calibrated, wavelength shift corrected)

UV irradiance at 305, 324, 380 nm and CIEUV irradiance at 305, 324, 380 nm and CIETotal column ozoneTotal column ozonespectral AOD at UV wavelengths spectral AOD at UV wavelengths

CIMELCIMELAOD (340nm) , SSA(440nm), ..AOD (340nm) , SSA(440nm), ..

NILU-UV NILU-UV 305nm, 324nm, 340nm, 380nm305nm, 324nm, 340nm, 380nm

Cloud – cloudless case separationCloud – cloudless case separationPyranometer, observations, sky cameraPyranometer, observations, sky camera pix pix

Daily OMI overpass time (mean over Daily OMI overpass time (mean over ±±15 minutes)15 minutes)

Thessaloniki September 2004-December 2007Thessaloniki September 2004-December 2007


Results

0 20 40 60 80OMI

0

20

40

60

80

Bre

wer

305 nm

0 100 200 300 400 500OMI

0

100

200

300

400

500

Bre

wer

324 nm


305nm OMI +30% 324nm OMI +17%


Results

0 1 2 3OMI - GB ratio

0.0

0.1

0.2

0.3

ΔΝ

/Ν

380 nm

Days

cloud free

cloudy


0 1 2 3OMI - GB ratio

0.0

0.1

0.2

0.3

ΔΝ

/Ν

C IED

Days

cloud free

cloudy

380nm OMI +11% CIED OMI +20%


Results - statistics

Wavel.(nm)

All data cloudless

m R2 W10 W20 m R2 W10 W20

305 1.30 0.94 43.3 68.2 1.27 0.95 64.8 87.6

324 1.17 0.89 51.3 73.1 1.15 0.91 76.9 92.4

380 1.13 0.89 47.2 70.7 1.11 0.91 71.8 89.7

CIED 1.20 0.93 51.5 75.4 1.19 0.95 75.0 91.9



Post correction methods

Krotkov et al., OE 2004Krotkov et al., OE 2004

)(1

)()(

abs

ac b

EE

Post correction methods - TOMS experience

Arola et al., JGR 2005

Cloudless cases: Ta(Cloudless cases: Ta(λλ) = AOD() = AOD(λλ) * [1 - SSA() * [1 - SSA(λλ)])]


UV attenuation – Thessaloniki, cloudless casesPost correction methods

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonths

-35

-30

-25

-20

-15

-10

-5

0

% U

V a

tten

uat

ion

du

e to

aer

oso

l at

(324

nm

)

UV attenuation OMI-Ground based % bias

77% of cases


Post correction : method 1

0.00 0.02 0.04 0.06 0.08 0.10 0.12Absorption optical depth

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Irra

dia

nce

rat

io O

MI /

Bre

wer

at

324

nm

Slope = 1.5 per unit of absorption optical depthIntercept = 1.10

ssa >0.98

ssa= [0.94, 0.98]

ssa= [0.88, 0.94]

ssa < 0.88

Ta (Ta (λλ) = AOD() = AOD(λλ) * [1 - SSA(440nm)]) * [1 - SSA(440nm)]

Aerosol absorption CFAerosol absorption CF((λλ)) = 1.1 + 1.5 * Ta = 1.1 + 1.5 * Ta((λλ))


•no sza dependenceno sza dependence•SSA @ UV ?SSA @ UV ?•need of GB data need of GB data


Post correction: method 2Tas =Ta / cos(sza)

Aerosol absorption CFAerosol absorption CF((λλ)) = 1.07 + 1.8 * Tas = 1.07 + 1.8 * Tas((λλ))


•SSA @ UV ?SSA @ UV ?•need of GB data need of GB data

0.00 0.04 0.08 0.12slant column absorption optical depth

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

Irra

dia

nce

rat

io O

MI /

Bre

wer

at

324

nm

Slope = 1.8 per unit of slant absorption optical depthIntercept = 1.07

ssa >0.98

ssa= [0.94, 0.98]

ssa= [0.88, 0.94]

ssa < 0.88


Post correction: use of RT model

0 0.2 0.4 0.6 0.8 1 1.2 1.41

1.1

1.2

1.3

1.4

1.5

1.6

1.7

aerosol optical depth at 340 nm

corr

ecti

on

fo

r ir

rad

ian

ce a

t 32

4nm

sza=40

0.80.820.840.860.88 0.90.920.940.960.98 1

0.4 0.45 0.5 0.55 0.61.04

1.06

1.08

1.1

1.12

1.14

1.16

1.18

1.2

aerosol optical depth at 340 nm

corr

ecti

on

fo

r ir

rad

ian

ce a

t 32

4nm

sza=60

0.8

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1

ssa=0.88

ssa=1, no absorption

total correction

correction for scattering


S1: AOD and SSA synchronous measurementsS2: AOD and SSA@440 = constS3: AOD= const and SSA@340 = const

Abs + scat

scat


Overview of post corrections

6th Approach: CF(λ) = 1 + 3 * Ta(λ)

Table with all the results of the 6 approaches:

OMI/Brewer ratio [R]

Method 305 nm Mean (1σ)

324 nm Mean (1σ)

380 nm Mean (1σ)

Obs

Original No correction 1.27 (0.15) 1.15 (0.10) 1.11 (0.12) 267

S1 Apply Ta slope 1.17 (0.13) 1.07 (0.09) 1.05 (0.13) 135

S2 Apply Tas slope 1.18 (0.13) 1.09 (0.10) 1.05 (0.13) 135

M1 Model 1.13 (0.12) 1.04 (0.08) 1.01 (0.11) 135

M2 Model constant SSA 1.14 (0.13) 1.03 (0.09) 0.99 (0.10) 267

M3 Model const. SSA-AOD 1.12 (0.13) 1.02 (0.09) 0.98 (0.10) 267

S3 1 + 3 * Ta (λ) 1.11 (0.13) 1.03 (0.10) 1.01 (0.11) 135




6th Approach: CF = 1 + 3 * Ta(λ)




324 nm Mean (1σ)

380 nm Mean (1σ)

Obs


S1 Apply Ta slope 1.17 (0.13) 1.07 (0.09) 1.05 (0.13) 135

S2 Apply Tas slope 1.18 (0.13) 1.09 (0.10) 1.05 (0.13) 135

M1 Model 1.13 (0.12) 1.04 (0.08) 1.01 (0.11) 135



S3 1 + 3 * Ta (λ) 1.11 (0.13) 1.03 (0.10) 1.01 (0.11) 135








324 nm Mean (1σ)

380 nm Mean (1σ)

Obs


S1 Apply Ta slope 1.17 (0.13) 1.07 (0.09) 1.05 (0.13) 135

S2 Apply Tas slope 1.18 (0.13) 1.09 (0.10) 1.05 (0.13) 135

M1 Model 1.13 (0.12) 1.04 (0.08) 1.01 (0.11) 135



S3 1 + 3 * Ta (λ) 1.11 (0.13) 1.03 (0.10) 1.01 (0.11) 135



Correction results

0 10 20 30 40 50 60 70 800

10

20

30

40

50

60

70

80

OM

I ir

rad

ian

ce m

W/m

2n

m

Brewer irradiance mW/m2nm

305 nm

0 100 200 300 400 5000

100

200

300

400

500

OM

I ir

rad

ian

ce m

W/m

2n

m


324 nm

0 200 400 600 800 10000

200

400

600

800

1000

OM

I ir

rad

ian

ce m

W/m2n

m


380 nm


305nm +11%305nm +11%

380nm +0%380nm +0%

324nm +2%324nm +2%


Effects of sza, AOD, SSA, ozone, time on ratios

10 20 30 40 50 60 70 800.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Sza (deg)

OM

I /

Bre

wer

rat

io a

t 32

4 n

m

original 1.15 (0.10)corr mod-c 1.03 (0.09)corr 1+1.5*Tabs 1.07 (0.09)corr 1+3*Tabs 1.03 (0.10)


10 20 30 40 50 60 70 800.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

solar zenith angle (deg)

OM

I / B

rew

er r

atio

305

nm

original

corrected-mod

corrected mod-c

corrected 1+3*Tabs

0 0.02 0.04 0.06 0.08 0.1 0.120.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Tabs

OM

I /

Bre

wer

rat

io 3

80n

m

originalcorrected-modcorrected mod-ccorrected 1+3*Tabs


Campaign: 1 to 30 October, 2007Spatial and temporal UV variability within an OMI grid

•3 sites

Each:NILU UV at 305, 324, 380nmCIMEL (AOD, SSA, ..) Pyranometer, sky camera

Main site+ Brewers Spectral UV, ozoneCCD (spectral AOD)

2 Lidars (City – Rural)


UV Measurements at the three sites

02-Oct 07-Oct 12-Oct 17-Oct 22-Oct 27-Oct 01-Nov0

50

100

150

200

250

300

350

Day of 2007

Irra

dia

nce

at

324

nm

(m

W m

-2 n

m-1

)

NILU-UV AUTHNILU-UV EPANOMINILU-UV SINDOSOMIBrewer cloudlessBrewer all

Spatial and temporal UV variability within an OMI grid


AOD variability in an OMI grid

30-Sep 3-Oct 6-Oct 9-Oct 12-Oct 15-Oct 18-Oct 21-Oct 24-Oct 27-Oct 30-Oct

Day of year - 2007

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

AO

D a

t 34

0 n

m

RAIN

Location

Epanomi / rural site

Sindos / industrial site

AUTH / urban site



UV differences in an OMI grid

14-Oct 15-Oct 16-Oct 17-Oct 18-Oct 19-Oct

Day of year 2007

0.0

0.1

0.2

0.3

0.4

0.5

0.6

AO

D a

t 34

0 n

m

AUTH

BREW ER AUTH

SINDOS

-20

0

20

40

% U

V Irrad

iance d

ifference

from

AU

TH

(380 nm

)

EPANOMI


+20%+20%

-20%-20%


Spatial UV variability at 3 stations (2 * sigma / mean)*100


270 275 280 285 290 295 300 3050

20

40

60

80

100

120

Days of 2007

10

0*[

2*S

D /

me

an

]

UV Variability at 324 nm

10

20

30

40

50

60

Integration Time

90% of cloudless cases

80% of cloudy cases


Temporal UV variability

270 275 280 285 290 295 300 3050

20

40

60

80

100

120

Days of 2007

10

0*[

2*S

D /

me

an

]

UV Variability at 324 nm

10

20

30

40

50

60

Integration Time

90% of cloudless cases

80% of cloudy cases

0 10 20 30 40 50 6020

21

22

23

24

25

26

27

28

29

30

Integration Time (min)

10

0*

[ 2

*SD

/ m

ea

n]

Average UV variability of October 2007 for OMi overpass time

324 nm


(2 * sigma / mean)*100


Conclusions•3.5 years of OMI and ground based at Thessaloniki, Greece: measurement comparison3.5 years of OMI and ground based at Thessaloniki, Greece: measurement comparison showed an OMI overestimation of UV irradiances. showed an OMI overestimation of UV irradiances. Cloudless cases: Main reason is the aerosol absorption. Cloudless cases: Main reason is the aerosol absorption. Higher deviations at lower Higher deviations at lower wavelengthswavelengths

•Possible methods to correct this effect: AOD and SSA measurements or/and an aerosol Possible methods to correct this effect: AOD and SSA measurements or/and an aerosol absorption climatology needed in a global scaleabsorption climatology needed in a global scale

•SSA in the UV: while mean SSA at 440 nm is 0.90 (Thessaloniki) an SSA of 0.82 is needed for SSA in the UV: while mean SSA at 440 nm is 0.90 (Thessaloniki) an SSA of 0.82 is needed for eliminating GB and OMI UV differences at 305nm. SSA at UV-B wavelengths needs further eliminating GB and OMI UV differences at 305nm. SSA at UV-B wavelengths needs further investigation. investigation.

•Simple public information (e.g. UVINDEX) retrieved from OMI at such populated-urban areas Simple public information (e.g. UVINDEX) retrieved from OMI at such populated-urban areas are affected from this bias. +20% on cloudless day. are affected from this bias. +20% on cloudless day.

•Aerosol variation within an OMI satellite pixel can cause UV differences equal to a percentage Aerosol variation within an OMI satellite pixel can cause UV differences equal to a percentage (~18%) that 90% of cloudless comparison cases lie within. Statistical analysis limitations ?(~18%) that 90% of cloudless comparison cases lie within. Statistical analysis limitations ?

•Spatial and temporal UV variability has to be taken into account when comparing GB and Spatial and temporal UV variability has to be taken into account when comparing GB and satellite UV, especially at city areas.satellite UV, especially at city areas.

•Comparison under cloudy conditions requires more investigation as absolute differences are Comparison under cloudy conditions requires more investigation as absolute differences are large and spatial and temporal UV variability plays a very important role on single station – large and spatial and temporal UV variability plays a very important role on single station – satellite, comparison.satellite, comparison.


Thank you

Campaign acknowledgments:D. Balis, N. Kouremeti, V. Amiridis, M. Zebila,E. Giannakaki, J. Herman, AERONET


OMI – GB normalized biases 3 stations

27-Sep 2-Oct 7-Oct 12-Oct 17-Oct 22-Oct 27-Oct 1-Novday of Year 2007

-30

-20

-10

0

10

20

30

no

rmal

ized

OM

I - G

B %

dif

fere

nce

305 nm

380 nm

324 nm



Back up air masses 4 day back traj


Back up – Lidar 2 days

0

1

2

3

4

5

0 3 6 9 0 1 2 3 0 2 4 60

1

2

3

4

5

355 nm

BACKSC. COEF. [Mm-1sr-1]

HE

IGH

T, a

sl [

km]

06.10.2007 16.10.2007

532 nm

BACKSC. COEF. [Mm-1sr-1]

06.10.2007 16.10.2007

355 - 532 nm

COLOR INDEX

06.10.2007 16.10.2007


Back up TOMS and UVA correction

1996 1997 1998 1999 2000 2001 2002 2003 2004Year

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

To

ms

/ Bre

wer

at

324

nm

U se of additional U VA m easurem ents

No UVA m easurem ents

TOMS - BREW ER RATIO

original = 1.18 (0.13)

corrected = 1.01 (0.09)


Back up Brewer –MODIS (2000-2007)

0 0.4 0.8 1.2 1.6 2BREW ER AOD@355nm

0

0.4

0.8

1.2

1.6

2

MO

DIS

/T

err

a C

OR

RE

CT

ED

AO

D@

35

5n

m

MODI S/ Terra MEAN AOD v0.04

MODI S/ Terra MEAN AOD v0.05

MODI S/ Terra vs BREW ER 30 m inute coincidences

Equation Y = 0.8981 * X + 0.11322Num ber of data points used = 311

Average X = 0.395 & Y = 0.468R-squared = 0.576

Equation Y = 0.806 * X + 0.2059Num ber of data points used = 161

Average X = 0.353 & Y = 0.49R-squared = 0.453

21.04.23

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonths

0.00

0.20

0.40

0.60

0.80

Mea

n A

OD

at

340

nm

Clusters

#1 North W est (Atlantic)

#2 North

#3 W est

#4 East, North-East

#5 W estern, Local and Saharan dust

Mean AOD

Back up Brewer AOD (1996-2007)


Back up SSA Thessaloniki (1998-2005)


Back up SSA scout

195 196 197 198 199 200 201 202 203 204 205 206

D ay of year

0.75

0.8

0.85

0.9

0.95

1

Sin

gle

Sca

tter

ing

Alb

edo

B rew er (350nm )

C IM E L (440nm )

D U TH (550nm , average)

D U TH (550nm , average 0-1 km )

G round nephe lom eter (450nm )


Spectral measurements of direct and global UV irradiance at the surface were made with two Brewer spectroradiometers. In addition, global (diffuse plus direct) UV irradiance and photosynthetically active radiation (PAR) were measured, on a minute basis, at each of the three sites with three NILU-UV multi-channel radiometers. In-situ measurements of aerosol vertical profiles were derived from two Lidar systems operating at (AUTH) and the site of Epanomi.Total ozone column was derived from the Brewers and cloud observations and sky images at the AUTH site. Cloud observations were performed at all sites at a half hour basis.Sun and sky radiance measurements were conducted with three CIMEL automatic sun tracking photometers, each installed at one of the three sites. These data were used to derive aerosol optical properties such as the aerosol optical depth (AOD), the Angstrom exponent a (AEa) and the single scattering albedo (SSA).


Download - OMI UV spectral irradiance: comparison with ground based measurements in an urban environment

Top Related