VI-5475(SamCalValNotes) 1

SAM (Sun and Aureole Measurement)

Calibration

Prepared for MODIS/VIIRS Science Team Meeting

Dennis Villanucci, Andrew LePage

John DeVore, A.T. Stair

January 2010

10+4

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Angle f rom Sun Center

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Please open in “Notes” mode to see the notes.

VI-5475(SamCalValNotes) 2

1. Introduction

• SAM radiance measurements

- Solar disk and aureole profiles At 670 +/- 5 nm

- Lab calibration NIST traceable

- Field verification using AERONET for low ODs

- Radiometric accuracy: Disk radiance <1%, if OD<~0.6 Disk radiance <~10%, otherwise Aureole radiance ~15%

- Aureole profile precision (gradient): Pixel-to-Pixel Stnd Dev <0.5%

VI-5475(SamCalValNotes) 3

2. SAM Lab CalibrationNIST Standard Practice

Parameter Solar Disk Camera

Aureole Camera

Multiple Exposures: Duration

Relative to 40 ms standard

Relative to 40 ms standard

Radiometric (NIST Traceable Sphere (Absolute: 2%)

Absolute: <1% for ODs <~0.6

(AERONET ref); Otherwise <~10%

Absolute: ~15%

Flat-Field Not Needed See Panel 4

Linearity (Radiance)

See Panel 5 See Panel 5

Temperature Drift

-6ºC to 44ºC Not Needed

Internal

Scattering

Not Needed End-to-end, optics in place

Neutral

Density Filter

Independent Measurement

Not Applicable

Pixel Scale (deg/pixel)

Lab Measurement

Lab Measurement

VI-5475(SamCalValNotes) 4

3. SAM/AERONET Radiance Statistics

• RMS difference < 0.7% (~1000 values)

VI-5475(SamCalValNotes) 5

4. Flat Fielding (Aureole Camera)

Before FlatFielding

Af ter FlatFielding

NI ST Source Flat to 0.5%

Before FlatFielding

Af ter FlatFielding

NI ST Source Flat to 0.5%

VI-5475(SamCalValNotes) 6

5. Linearity (Typical Camera)

Polynomial: y = 6.615E-12 x3 - 1.348E-9 x2 + 1.633E-6 x1

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

3.5E-04

4.0E-04

0 50 100 150 200 250

Pixel Value Above Bkgnd

Rad

ian

ce (

W/c

m2/s

r)

1000 ms

Linear

Poly. (1000 ms)

S/ N 300

Linearity of camera response with scene

brightness at one exposure and

temperature. Similar measurements

are made at other exposure durations, and

for each of the cameras used

in the SAM sensor.

VI-5475(SamCalValNotes) 7

6. Aureole FPA Trace Definitions

Up

Down

RightLef t

Average

Up

Down

RightLef t

Average

VI-5475(SamCalValNotes) 8

7. Typical Uniform Cloud Data Traces

• Demonstrates precision of profile

1.E-02

1.E-01

1.E+00

1.E+01

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0.01 0.1 1 10

Angle From Sun Center (deg)

Radia

nce

(W

/cm2/s

r/um

)

Average

Right

Lef t

Up

Down

SAM #300 - GSFC

17 J AN 09 ~ 18.5308 UT

I nstrumentalData Gap

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0.01 0.1 1 10

Angle From Sun Center (deg)

Radia

nce

(W

/cm2/s

r/um

)

Average

Right

Lef t

Up

Down

SAM #300 - GSFC

17 J AN 09 ~ 18.5308 UT

I nstrumentalData Gap

VI-5475(SamCalValNotes) 9

8. Radial Average, Std Dev of Traces

• Demonstrates precision of profile

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0.01 0.1 1 10

Angle From Sun Center (deg)

Rad

ian

ce (

W/c

m2/s

r/u

m)

Average

SAM #300 - GSFC

17 J AN 09 ~ 18.5308 UT

I nstrumentalData Gap

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0.01 0.1 1 10

Angle From Sun Center (deg)

Rad

ian

ce (

W/c

m2/s

r/u

m)

Average

SAM #300 - GSFC

17 J AN 09 ~ 18.5308 UT

I nstrumentalData Gap

VI-5475(SamCalValNotes) 10

9. Non-uniform Cloud Example

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0.01 0.1 1 10

Angle From Sun Center (deg)

Radia

nce

(W

/cm2

/sr/

um

)

Average

Right

Lef t

Up

Down

SAM #300 - GSFC

17 J AN 09 ~ 18.5867 UT

I nstrumentalData Gap

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0.01 0.1 1 10

Angle From Sun Center (deg)

Radia

nce

(W

/cm2

/sr/

um

)

Average

Right

Lef t

Up

Down

SAM #300 - GSFC

17 J AN 09 ~ 18.5867 UT

I nstrumentalData Gap

• Cloud non-unformity is detectable

VI-5475(SamCalValNotes) 11

10. Moderately Thick Cloud Example

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0.01 0.1 1 10

Angle From Sun Center (deg)

Radia

nce

(W

/cm2

/sr/

um

)

Average

Right

Lef t

Up

Down

SAM #300 - GSFC

17 J AN 09 ~ 19.0753 UT

Solar Disk Camera

AureoleCamera

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

0.01 0.1 1 10

Angle From Sun Center (deg)

Radia

nce

(W

/cm2

/sr/

um

)

Average

Right

Lef t

Up

Down

SAM #300 - GSFC

17 J AN 09 ~ 19.0753 UT

Solar Disk Camera

AureoleCamera

• Demonstrates accuracy (2 cameras) and precision of profile (gradient)

VI-5475(SamCalValNotes) 12

11. Field Calibration Verification

• For absolute radiometric calibration of cameras; verified for solar disk radiance with thousands of measurements next to AERONET sensors

• For flat fielding of aureole pixel-to-pixel response, e.g. “gradient” correction; verified with hundreds of measurements of uniform clouds

VI-5475(SamCalValNotes) 13

SAM-AERONET Comparison

Quantity AERONET SAMScatterer Aerosols Clouds

(and aerosols)Size range (radius) ~ 0.1 – ~ 1

m~ 2.5 – ~ 25 m

OD range(high precision)

0 to ~ 1 0 to ~ 5 (ice)0 to ~ 10 (water)

Minimum aureole angle from disk edge

~ 2.25º ~ 0.25º

Measurement sampling

~ 10 min (typical)

~ 12 sec (adjustable)

Field of View or Regard

~ 120º(Scan FOR)

+/- ~ 8º (FOV)and ~ 6º to 50º

Pixel IFOV 1.2º 0.015º(1024 x 1280)

OD measurement accuracy (absolute)

0.01 to 0.02 < ~ 0.03

OD measurement precision (relative)

< 0.005 < 0.005

VI-5475(SamCalValNotes) 14

SAM Applications

• Climate (cloud) monitoring

• Cloud physics research

• Satellite algorithm cal/val

• Circumsolar radiation

Dennis Villanucci 781-272-1220 villa@visidyne.comAndrew LePage 781-272-1220 lepage@visidyne.com

Contacts: