Effect of NO 2 on Geostationary Satellite Chlorophyll Retrieval In Coastal Water: False Diurnal...

Effect of NO2 on Geostationary Satellite Chlorophyll Retrieval In

Coastal Water:False Diurnal VariationJay Herman & Maria Tzortziou

Annual Average NO2 Climatology from OMI

OMI

Examples of NO2 Diurnal Variation

OMI observed pixel NO2 variability for Sept. 30, 2005 over eastern and central US with clouds. Areas covered with clouds have no current NO2 information.

Ad =17.1O

40ONSZA

~4.5O

~35.5O

0.5*12756

~36000 + 0.5*12756

Angular Diameter = Ad = 2 arctan (0.5*12756/(36000 + 0.5*12756)) = 17.1 deg

Geostationary Ray Path Geometry

350 400 450 500 550 600 6500.044

0.046

0.048

0.050

0.052

0.054

0.056

0.058

0.060

Ref

lect

ivit

y

Wavelength (nm)

Measured Reflectivity for Chesapeake Bay

Tzortziou et al. [2007]

Input to Radiative Transfer Equation

Measured Reflectivity of Chesapeake Bay[Tzortziou et al., 2007]Including Chlorophyll and CDOM

300 350 400 450 500 550

0

5

10

15

300 350 400 450 500 550-5

0

5

10

15

20

25

30

35

40

45

300 350 400 450 500 550-5

0

5

10

15

20

25

30

0 - 20

30

40

50

60

70

SZA = 80 O3 = 330 DU

R = 0.05NO2 from 0 to 2 km

Percent Error in nLw per DU of NO2

Per

cen

t E

rro

r


0 - 20

30

40

50

60

70

SZA = 80 O3 = 330 DU


Wavelength (nm)


0 - 20

3040

50

60

70

SZA = 80

O3 = 330 DU


Per

cen

t E

rro

r

Wavelength (nm)

The Effect of NO2 Altitude Distribution

Use 0 - 3 km CaseIn following slides

0–2 km 0–4 km

0–3 km

300 350 400 450 500 550-5

0

5

10

15

20

25

30

35

40

45

50

0

50

60

70

Wavelength Dependent Reflectivity

Per

cen

t E

rro

r

Wavelength (nm)

0 10 20 30 40 50 60 70 80

SZAeff

80

Output from Radiative Transfer Equation

Reflectivity Change per DU of NO2

dR/R = -0.01*(3.84243 + 0.08821*exp(SzaEff/14.91337)) Wvl=490 nm

dR/R = -0.01*(7.42119 + 0.40409*dexp(SzaEff/18.29943)) Wvl=443 nm

0 20 40 60 80

68

10121416182022242628303234363840

y0= 7.42119A1=0.40409t1=18.29943

y = A1*exp(SZA/t1) + y0

Per

cen

t E

rro

r

SZA

443 nm Error vs szs R=Maria variable vs wvl NO2=1DU 0-3km

0 20 40 60 802

4

6

8

10

12

14

16

18

20

22

24

490 nm Error vs szs R=Maria variable vs wvl NO2=1DU 0-3km

y0= 3.84243A1=0.08821t1=14.91337

y = A1*exp(SZA/t1) + y0

Per

cen

t E

rro

r

SZA

490 nm

443 nm

-10 0 10 20 30 40 50 60 70 80 90

-60

-40

-20

0

20

40

60

80

100

120

140 R = 0.03

dR

/R*1

00

d

P/P

*100

SZA

Coastal

R = 0.05

Percent Change in Pigment per DU of NO2

dP/P = -3.03552 dR/R Coastal (Hydrolight)

dP/P = -2.35105 dR/R Open Ocean (Mobley)

0 5 10

0

2

4

6

8

Pig

men

t =

CA

(R)

R = R443/R550

Ca = 2.5104 R-3.03552

R = ratio of Blue to Green

Chlorophyll Blue/Green Ratio From MODIS Website data a0,a1,a2,a3,a4/ 0.3660,-3.0670, 1.9300, 0.6490,-1.5320/ x = log10( ratio(i)) x2 = x*x; x3 = x2*x; x4 = x3*x Ca(i) = 10**( a0 + a1*x + a2*x2 + a3*x3 + a4*x4 )

Retrieval Error per DU of NO2

P = Ca = A R –N

dP/P = -N dR/R * [NO2]

The Power Coefficient N is the key to the magnitude of the NO2 false diurnal variation effect on retrieved chlorophyll values

Case 1

Case 3

Case 2

Measured NO2 Amounts vs Time of Day

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

0

5

10

15

20

25

30d

P/P

(P

erce

nt)

Time (hours)

Percent Error in Chlorophyll RetrievalLat = 40 Look angle = 4.5 Ray_angle = 35.5

for R443/R550 and R490/R550

Case 1

NO2ref = 0.3 DU

0.0

0.1

0.2

0.3

0.4

0.5

0.6

dN

O2

(DU

)

dNO2

dP/P

Case 1: An Example of False Diurnal Variation in Chlorophyll

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

10

20

30

40

50

60

dNO2

dP/P

dP

/P (

Per

cen

t)

Time (hours)

-0.5

0.0

0.5

1.0

1.5

NO2ref = 0.3 DU


for R443/R550 and R490/R550

dN

O2

(DU

)

Case 2


4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

-20

-10

0

10

20

30

40

50

60

OMI NO2ref = 0.75 DU


for R443/R550 and R490/R550

dP/P

dNO2

dP

/P (

Per

cen

t)

Time (hours)Case 3

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

dN

O2

(DU

)


4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19-5-4-3-2-10123456789

10111213

Case 3

OMI NO2ref = 0.75 DU

Percent Error in Acdom RetrievalLat = 40 Look angle = 4.5 Ray_angle = 35.5

for R490/R550

d(A

cdo

m)

Acd

om

Time

dNO2

d(Acdom) Acdom

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

dN

O2

(DU

)

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 192

4

6

8

10

12

14

16

Case 2

d(A

cdo

m)

Acd

om

Time

-0.5

0.0

0.5

1.0

1.5

NO2ref = 0.3 DU

Percent Error in Acdom RetrievalLat = 40 Look angle = 4.5 Ray_angle = 35.5

for R490/R550

dNO2

d(Acdom) Acdom

dN

O2

(DU

)

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

0

1

2

3

4

5

6

7 Percent Error in Acdom Retrieval

Lat = 40 Look angle = 4.5 Ray_angle = 35.5for R490/R550

dNO2

d(Acdom) Acdom

d(A

cdo

m)

Acd

om

Time

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Case 1

NO2ref = 0.3 DU

dN

O2

(DU

)

Case 1,2,3: An Example of False Diurnal Variation in Acdom

Since Acdom, depends R490,the percent error per DU of NO2is reduced compared to retrievals based on R443

Summary

• NO2 can be highly variable throughout the day.

• Using an incorrect assumed value of NO2 affects the retrieved water leaving radiance nLw and can be interpreted incorrectly as chlorophyll absorption.

• Chlorophyll retrievals errors can be over 50% based on using an assumed NO2 amount from another instrument or climatology.

• NO2 should be measured at the same time that coastal ocean water leaving radiances are measured.

Effect of NO 2 on Geostationary Satellite Chlorophyll Retrieval In Coastal Water: False Diurnal...

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