Some Practical Considerations for the GEO-CAPE Mission

Sensitivity, Saturation, Sun glint, Cloud cover, etc

Chuanmin Hu, Zhongping Lee, Keping Du, Antonio Mannino

NASA GEO-CAPE Science Working Group Meeting11-13 May 2011, Boulder, Colorado

Some practical considerations for the GEO-CAPE mission

Sensitivity, Saturation, Sun glint, Cloud cover, etc

ObjectivesHelp define sensor constraints

Help implement measurement plans

NASA GEO-CAPE Science Working Group Meeting11-13 May 2011, Boulder, Colorado

SeaWiFS Florida Strait

MODIS/Aqua Florida Strait

Sensitivity versus Saturation

MODIS RGB (land bands) MODIS FLH (ocean bands)

Sensitivity versus Saturation

Lt_555Lt_859

Lt_551Lt_667Lt_678Lt_748Lt_869

0.0

5.0

10.0

15.0

Lt (

mW

cm

-2

m-1

sr-1

)

100 110 120 130 140 150

Pixel # (1 km per pixel)

Land Water

Problem with Low Saturation

Lt_555Lt_670Lt_765Lt_865

Lt_412Lt_443Lt_490Lt_510

0.0

10.0

20.0

30.0

40.0

50.0

Lt (

mW

cm

-2m

-1 s

r-1)

200 300 400 500 600 700 800 900 1000

Lt (DN)

SeaWiFS Bi-linear Gains

SeaWiFS Solution

Knee Values

551 (555) 667 (670) 748 (765) 869 (865)

MODIS Saturation

6.96 3.50 2.23 1.30

SeaWiFS Knee

6.00 3.35 2.46 2.03

MODIS versus SeaWiFS

Units: mWcm-2m-1sr-1

How Precise are MODIS Chl?

Month in 20031 2 3 4 5 6 7 8 9 10 11 12 13

Chl

(mg

m-3

)

0.00

0.02

0.04

0.06

0.08

28oS, 105oW

5-10% RMS speckle noise. Resolves to <0.005 mg m-3 at low concentrations

MODIS Fluorescence Sensitivity

MODIS/Aqua Chl, Sargasso Sea MODIS FLH

Not sufficient to resolve Chl < 0.1 mg m-3

Then, how do we choose the trade between sensitivity and dynamic range (saturation)?

MODIS versus SeaWiFS

Radiance (L) units: mWcm-2m-1sr-1. Numbers in () are for SeaWiFS

1 DN of MODIS 678 band is corresponding to 0.1 – 0.2 mg m-3 Chl

Band

(nm) Res. L (1 DN) NEL

1 620-670 250 m 0.0217 0.01702 841-876 250 m 0.0083 0.01233 459-479 500 m 0.0167 0.01454 545-565 500 m 0.0145 0.0127

438-448 1 km 0.0039 (0.0136) 0.0050 (0.0130)

546-556 1 km 0.0018 (0.0076) 0.0028 (0.0080)

673-683 1 km 0.0007 (0.0042) 0.0008 (0.0056)

From Xing et al. (2007, Ocean Science Journal)

MODIS 665.1 (10) 676.7 (10) 746.4 (10)MERIS 665.0 (10) 681.3 (7.5) 709.0 (9)GLI 666.7 (10) 679.9 (10) 710.5 (10)GOCI 660.0 (20) 680.0 (10) 745.0 (20)

MODIS 0.0008 0.0007 0.0009MERIS 0.0013 0.0014 0.0011GLI 0.0015 0.0014 0.0012GOCI 0.0032 0.0031 0.0020

NEL (mWcm-2m-1sr-1)

Band Center (Bandwidth)

MODIS versus Others

MODIS/Aqua Lt (typical)

0 = 75o

0 = 70o

0 = 65o

0 = 45o

0 = 30o

MODIS/Aqua data

500 1000 1500 2000

(nm)

10-2

10-1

100

101

MO

DIS

Lt (

mW

cm

-2m

sr-1

)

(nm)500 1000 1500 2000

MO

DIS

Lt_

max

from

clo

uds

0

10

20

30

40

50

0 = 70o

0 = 25o

Lt maximum, mW cm-2 m-1 sr-1

MODIS/Aqua Lt (max)

Lt Dynamic Range

70deg SZA 0.33* Lmax(Barnes) 0.7* Lmax(Barnes)ACE GEO GEO ~45SZA 70 deg SZA ACE reduced 70 deg SZA ACE

Band Center1

Minimum SNR Ltyp(Hu)2,3

Lmax (Barnes)1,3

ACE Ltyp(Ahmad)1,

3 Lmax(70) LmaxDYNAMI C

RANGEDYNAMI C

RANGE350 500 39.26 356.0 74.60 117.48 249.2 2.99 3.34360 500 38.00 376.0 72.20 124.08 263.2 3.27 3.65385 1000 32.16 381.0 61.10 125.73 266.7 3.91 4.36412 1000 41.77 602.0 78.60 198.66 421.4 4.76 5.36425 1000 40.63 585.0 69.50 193.05 409.5 4.75 5.89443 1000 37.51 664.0 70.20 219.12 464.8 5.84 6.62460 1000 33.14 724.0 68.30 238.92 506.8 7.21 7.42475 1000 30.25 722.0 61.90 238.26 505.4 7.88 8.16490 1000 29.25 686.0 53.10 226.38 480.2 7.74 9.04510 1000 24.23 663.0 45.80 218.79 464.1 9.03 10.13532 1000 20.09 651.0 39.20 214.83 455.7 10.69 11.63555 1000 16.11 643.0 33.90 212.19 450.1 13.17 13.28583 1000 14.56 624.0 28.10 205.92 436.8 14.14 15.54617 1000 11.25 582.0 21.90 192.06 407.4 17.07 18.60640 1000 9.39 564.0 19.00 186.12 394.8 19.82 20.78655 1000 8.33 535.0 16.70 176.55 374.5 21.20 22.43665 1000 7.83 536.0 16.00 176.88 375.2 22.59 23.45678 1000 7.37 519.0 14.50 171.27 363.3 23.24 25.06710 1000 5.36 489.0 11.90 161.37 342.3 30.10 28.76748 600 4.89 447.0 9.30 147.51 312.9 30.17 33.65765 600 3.62 430.0 8.30 141.90 301 39.18 36.27820 600 2.82 393.0 5.90 129.69 275.1 46.04 46.63865 600 2.54 333.0 4.50 109.89 233.1 43.26 51.801245 300 0.560 158.0 0.88 52.14 110.6 93.11 125.681640 250 0.280 82.0 0.29 27.06 57.4 96.64 197.932135 100 0.060 22.0 0.08 7.26 15.4 121.00 192.50

Question

With these MODIS-based settings, can GEO-CAPE differentiate fluorescence quantum

efficience changes at large solar zenith angles?

Chlorophyll fluorescence quantum yield

Morrison (2003, L&O)

Decreased

Photochemical

QuenchingIncreased N

on-

Photochemical

Quenching

Qua

ntum

Yie

ld

PAR ( molem-2s-1)1 10 100 1000

0= 60o

0= 70o

0= 80o

Surface PAR Dec. 22June 22

GMT: 18:30Longitude: 95oW

-80

-60

-40

-20

0

20

40

Lat

itude

(deg

ress

)60

80

0 500 1000 1500 2000 2500

Surface PAR ( mole m-2 s-1)

Hours from Sunrise and Sunset

June 22

Solar zenith = 60o

Solar zenith = 70o

Solar zenith = 80o

-60 -40 -20 0 20 40 60

Latitude (degrees)

0.0

1.0

2.0

3.0

4.0

5.0H

ours

from

sunr

ise

and

suns

et

PAR ~

970

PAR ~ 60

0

PAR ~ 250

Solar zenith = 60o

Solar zenith = 70o

Solar zenith = 80o

December 22

-60 -40 -20 0 20 40 60

Latitude (degrees)

0.0

1.0

2.0

3.0

4.0

5.0H

ours

from

sunr

ise

and

suns

et

PAR ~ 970PAR ~ 600PAR ~ 250

Hours from Sunrise and Sunset

Sensitivity of Lw685 to solar/viewing geometry

[0 - 70o], [0 - 180o]

L w68

5 (m

W c

m-2

m

-1 s

r-1)

0.00

0.01

0.02

0.03

0.04

0.05

0 = 40o

Chl = 0.5 mg m-3, fluorescence efficiency = 2%

0 = 60o

0 = 70o

0 = 80o

Sensitivity of fluorescence (Lw685 and FLH) to solar/viewing geometry

MODIS NEL (678 nm) ~ 0.001 mWcm-2m-1sr-1

0 [0 - 80o]20 40 60 80

L w68

5 an

d FL

H (m

W c

m-2

m

-1 s

r-1)

0.0001

0.001

0.01

0.1

Empty: Lw685; Solid: FLHFLH wavelengths: 665, 685, 750 nm

Chl = 0.1 0.5 1.0 5.0

Fluorescence efficiency = 2%

(PAR ~ 250)(970)(600)

Chlorophyll fluorescence quantum yield

Morrison (2003, L&O)

Decreased

Photochemical

QuenchingIncreased N

on-

Photochemical

Quenching

Qua

ntum

Yie

ld

PAR ( molem-2s-1)1 10 100 1000

0= 60o

0= 70o

0= 80o

Sensitivity of fluorescence (Lw685 and FLH) to solar/viewing geometry

MODIS NEL (678 nm) ~ 0.001 mWcm-2m-1sr-1

Assuming MODIS sensitivity on GEO-CAPE and a constant fluorescence efficiency (quantum yield) of 2%, for Chl = 0.5, FLH decreased by 0.002 mWcm-2m-1sr-1 (nearly halved) from 0=60o to 70o.

Quantum efficiency nearly doubled from 0=60o to 70o, resulting in similar FLH changes if everything else remains the same.

Conclusion: With MODIS sensitivity on GEO-CAPE, it is possible to derive fluorescence quantum efficiency changes in the non-photochemical regime for Chl ~> 0.5 mg m-3

June 22. # of hourly observations with non-photochemical quenching (100 < PAR < 1000)

Dec. 22. # of hourly observations with non-photochemical quenching (100 < PAR < 1000)

Summary on Sensitivity

MODIS sensitivity can serve as a good template

Sufficient to resolve fluorescence quantum efficiency changes between 0=60o to 80o for Chl ~ 0.5 or higher

Saturation radiance determined from MODIS measurements (together with ACE missions). May need adjustment when global dataset is considered.

Twice/day versus once/dayTwice/day versus once/day

Cloud-free percentage from daily MODIS and SeaWiFS data from 1 June to 15 October 2003. Zero value means no data collection.Area: 22 to 31oN, 91 to 79oW

MODIS Daily Average: 48.88%SeaWiFS Daily Average: 25.72%

0 20 40 60 80 100

MODIS percentage of cloud-free pixels (daily)

0

20

40

60

80

100

SeaW

iFS

perc

enta

ge o

f clo

ud-f

ree

pixe

ls (d

aily

)

Cloud Avoidance - TBD

June 22. # of hourly observations with o< 80o

June 22. # of hourly observations with sun glint (wind = 6 m/s)

Sun Glint Considerations

Dec. 22. # of hourly observations with o< 80o

Dec. 22. # of hourly observations with sun glint (wind = 6 m/s)

Sun Glint Considerations

Sun Glint Is Not Always A Bad Thing

% of days showing surface oil presence, April 22 – July 31, 2010

Makes it easier to detect oil spills

Cyanobacteria (Trichodesmium erythraeum) blooms observed by GOES and MODIS

What Time Is Desirable to Capture Diurnal Changes?

WFS

5/22/2004

Conclusions- MODIS sensitivity can be followed- Saturation radiance may need

adjustment- Need to implement a data acquisition

matrix to optimize performance for science needs

- Timing and frequency of measurements- Synoptic or targeted mode, where/when- Clouds and glint considerations

NASA GEO-CAPE Science Working Group Meeting11-13 May 2011, Boulder, Colorado