National Aeronautics and Space Administration

Lessons Learned from EO-1 Calibration Activities

Advanced Land Imager (ALI) band misregistration impact on spectral indices

Radiometric stability of lunar test sites based on Hyperion observations

Ungar, Stephen a,b, Ong, Lawrence c, and Thome, Kurtis a

a NASA/Goddard Space Flight Center (GSFC), Greenbelt, MD 20771, USA b Universities Space Research Assoc. (USRA), Columbia, MD 21044, USA c Science Systems and Applications, Inc. (SSAI), Lanham, MD 20706, USA

IGARSS 2014 Quebec, Canada July 16,2014

CONCLUSIONS! • Push broom observing systems of the ALI variety can not

produce inherently (band-to band) co-aligned measurements. This is not a design flaw, but rather a “feature” designed to produce higher SNR.

• This “”feature” does not necessarily hamper uses of the data in a variety of applications. However, it does introduce significant uncertainty in determining vegetation indices.

• The moon serves as a solar diffuser monitor for several orbiting missions. The EO-1 CalVal Team, in collaboration with EO-1 Operations, is refining strategies to use specific “vicarious calibration sites” on the lunar surface, enhancing use of orbiting imaging spectrometer missions to serve as transfer radiometers for other passive optical missions.

Lets cut to the chase and get directly to the bottom line

Wavelength

Cross Track Sample (Pixel)

Depiction -Grids represent the detectors

-Spots represent the IFOV centers

-Colors represent the wavelengths

Pushbroom Observing System Sensor Chip Array (SCA) “cartoon”

Pushbroom Observing System

Pushbroom systems come in two flavors

Pushbroom Observing System

Areas viewed simultaneously by each band

Pushbroom Observing System

Areas viewed simultaneously by each band

Pushbroom Observing System

Areas viewed simultaneously by each band

Pushbroom Observing System

Areas viewed sequentially by each band

Pushbroom Observing System

Areas viewed sequentially by each band

Pushbroom Observing System

Areas viewed sequentially by each band

Pushbroom Observing System

Areas viewed sequentially by each band

Pushbroom Observing System

Areas viewed sequentially by each band

E

S

E

Adjusting Attitude and Frame Rate to Ensure Band-to-Band Co-registration

• The ground sampling distance (GSD) is a function of the sub-satellite “ground” speed and detector sampling rate.

• Pixel “size” is a function of the detector angular field of view (IFOV), integration time, range (distance) to target, and ground “velocity”.

• EO-1’s strategy to ensure inherent band-to-band registration for the Advanced Land Imager (ALI) is to: – Align the ALI sensor chip array (SCA) with the ground velocity

vector direction by yawing the spacecraft; – Adjust sampling rate, based on ground speed, such that an

integral number (N) of GSD’s exactly equal the projected ground distance between simultaneously collected bands.

How ALI Achieves Inherent Band-to-Band Coregistration

Adjusted (ALI) Sampling Rate

Fixed (L8/OLI) Sampling Rate ~236 frames/sec

Adjusting Attitude and Frame Rate to Ensure Band-to-Band Co-registration

• The EO-1 approach uses a fixed value of N which is based on maintaining a GSD equal to the nominal pixel size. However, any integer value of N ensures band-to-band co-registration.

• Lowering the value on N leads to under-sampling and decrease in data volume, while increasing N results in oversampling, increased data volume, and possible reduction in SNR.

Further Considerations

Adjusting Frame Rate to Ensure Band-to-Band Co-registration

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All you need to know about spectral/spatial alignment impact on derived-parameter uncertainty in 10 minutes

Steve Ungar – NASA/GSFC Scientist Emeritus HyspIRI Science Symposium – NASA GSFC – May 4, 2010

This initial characterization of a synthetic scene, composed of two landscape components, represents a landscape- based radiometric parameterization which is independent of any specific remotely–sensed (pixel-oriented) observation strategy. This is followed by characterizations of the same scene which are based on (pixel-oriented) observation strategies.

28

Synthetic Scene Composition

0102030405060

0,4 0,6 0,8 1,0

Ref

lect

ance

(%)

Wavelength (μm)

Vegetation Bright "Soil"

.3 .3 .5 .5

.3 .3 .5 .5

.5 .3 .3 .5

.5 .3 .3 .5

NIR Reflectance

.3 .3 .1 .1

.3 .3 .1 .1

.1 .3 .3 .1

.1 .3 .3 .1

VIS Reflectance

Landscape Reflectance Values Synthetic Scene Scenario

29

30

Landscape Reflectance Ratios Synthetic Scene Scenario

NIR Reflectance (RNIR)

.3 .3 .5 .5

.3 .3 .5 .5

.5 .3 .3 .5

.5 .3 .3 .5

.3 .3 .1 .1

.3 .3 .1 .1

.1 .3 .3 .1

.1 .3 .3 .1

=

1 1 5 5

1 1 5 5

5 1 1 5

5 1 1 5

= VI RNIR

RVIS

VIS Reflectance (RVIS)

.5 .5 ..5

.5 .5 .5

.5 .5 .5

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.5 .5 .5

.5 .5 .5

.5 .5 .5

.5 .5 ..5

.5 .5 .5

.5 .5 .5

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.5 .5 .5

.5 .5 .5

.5 .5 .5

.5 .5 ..5

.5 .5 .5

.5 .5 .5

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.5 .5 .5

.5 .5 .5

.5 .5 .5

.5 .5 ..5

.5 .5 .5

.5 .5 .5

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.5 .5 .5

.5 .5 .5

.5 .5 .5

.1 .1 .1

.1 .1 .1

.1 .1 .1

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.1 .1 .1

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.1 .1 .1

.1 .1 .1

.1 .1 .1

31

Nominal Position VIS Band Nominal Position NIR Band

Pixel Reflectance Values Aligned Bands Scenario

.5 .5 ..5

.5 .5 .5

.5 .5 .5

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.5 .5 .5

.5 .5 .5

.5 .5 .5

.5 .5 ..5

.5 .5 .5

.5 .5 .5

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.5 .5 .5

.5 .5 .5

.5 .5 .5

.5 .5 ..5

.5 .5 .5

.5 .5 .5

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.5 .5 .5

.5 .5 .5

.5 .5 .5

.5 .5 ..5

.5 .5 .5

.5 .5 .5

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.3 .3 .3

.5 .5 .5

.5 .5 .5

.5 .5 .5

Nominal Position NIR Band

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.1 .2 .1

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

.3 .2 .3

“Half-pixel” Shift VIS Band

Pixel Reflectance Values Misaligned Bands Scenario

32

Results of half pixel misalignment and correction through linear re-sampling

Scenario Category 1 Ratio Value

Category 1 Discrepancy

Category 2 Ratio Value

Category 2 Discrepancy

VIS and NIR co-aligned 1.00 0% 5.00 0%

VIS and NIR misaligned 1.17 +17% 4.17 -17%

VIS realigned by resampling 1.13 +13% 3.89 -22%

33

What’s missing from this picture? How we can provide consistent CalVal across Decadal Missions!

The Moon can serve as a virtual solar diffuser monitor to validate HyspIRI solar calibration!

Well characterized test sites facilitate further validation and transfer of calibration to other Decadal Survey and International Missions !

As explained in the following slides

How EO-1 uses Lunar Images • Lunar Calibration

– Calculate Lunar spectral irradiance (EM(λ)) – Compare to the USGS Robotic Lunar

Observatory (ROLO) lunar irradiance model

• Lunar Calibration Team – Jim Butler – Brian Markham – Lawrence Ong – Kurt Thome – Steve Ungar

-- Jack Xiong

Typical Lunation (aka Lunar Cycle)

1 total lunation takes ~29.5 days

ROLO Model USGS Robotic Lunar Observatory

EO-1 Lunar Cal/Val

kM

kk

N

1iki,pk

EΩIπA

LΩIp

⋅=

= ∑=

-6.0

-1.0

4.0

9.0

14.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0

Per

cent

Diff

eren

ce fr

om R

olo

Mission Year

426.82 508.22 599.80 803.30 1205.07 1497.63 2002.06 2254.22

Quasi-annual variations not understood but appears somewhat correlated with the Sun-Moon and Spacecraft-Moon selenographic coordinates.

Hyperion Lunar Trends Comparison of Hyperion integrated lunar responses with the

USGS Robotic Lunar Observatory (ROLO) model for selected bands.

Hyperion Lunar Observations shows Spectral Variation with Phase Angles

0.8

0.9

1

1.1

1.2

1.3

1.4

400 900 1400 1900 2400

Nor

mal

ized

Res

pons

e

Wavelength [nm]

Normalized with 7.434 Deg Phase Angle-80.991 -53.679 -40.057 7.434 23.051 35.106 46.105Phase Angles:

Comparisons with RoLO at various Phase Angle

-6

-3

0

3

6

9

12

15

18

-85 -65 -45 -25 -5 15 35

Diff

eren

ce fr

om R

oLO

[%]

Lunar Phase Angle [Degrees]

447.17487.87569.27660.85793.13864.351245.361648.912213.93

Some bands show signs of phase angle dependencies, eg 569, 660, 793, 864 and 1648 nm

Summary of ROLO Comparisons

• The ROLO model provides a convenient avenue to conduct overall trending of instrument performance.

• Unable to characterize individual detectors • Quasi-periodic trends observed – under investigation • Absolute calibration?

Hyperion Lunar Observations

• Hyperion Lunar observations are potentially highly valuable for the lunar calibration of instruments on both polar-orbiting and geostationary satellites.

• Lunar spectra can be convolved with the spectral response function of any given instrument.

• The relationship between moon phase angle and spectral changes for selected channels require further investigation.

Objective: develop a satellite-based lunar calibration strategy which will serve as the basis for cross calibrating space borne passive optical observing systems.

The EO-1 Hyperion imaging spectrometer will be used to develop an exo-atmospheric spectral radiometric database for a range of lunar phase angles surrounding the fully illuminated moon.

Initial studies will include a comprehensive analysis of the existing 12 year collection of monthly (plus some additional) lunar acquisitions.

Further studies will select specific lunar surface areas, such as lunar maria, and characterize their stability in the presence of lunar nutation and libration using a newly developed observing strategy to expand the EO-1 lunar dataset to include more phase angles during the next 2 years.

Future Use of EO-1 Lunar Images Hyperion Lunar Calibration Activities

Hyperion is now being used to slowly scan the lunar surface at a rate which results in a 32X oversampling to effectively increase the SNR. Several strategies, including comparison against the USGS RObotic Lunar Observatory (ROLO) model, will be employed to estimate the absolute and relative accuracy of the measurement set.

There is an existing need to resolve discrepancies as high as 10% between ROLO and solar based calibration of current NASA EOS assets. Analysis of this dataset will lead to the development of strategies to ensure more accurate cross calibrations when employing the more capable, future imaging spectrometers.

Hyperion Lunar Calibration Activities

Full Moon

(EO-1 ALI Pan band) (Selected sites)

Hyperion views the moon monthly

USGS Lunar Map

Mare Imbrium Mare

Serenitatis Mare Crisium Mare

Tranquilitatis

Hyperion Lunar Views Oversampled

by 8X

1/01/10 4/28/10 6/27/10 12/21/10

Hyperion Lunar Views

Averaged (Aggregated) Oversampled Images

Rotated Averaged (Aggregated) Oversampled Images

1/01/10 4/28/10 6/27/10 12/21/10

1/01/10 4/28/10 6/27/10 12/21/10

Mare Tranquilitatis Cal Site

Preliminary

Date Mean Stdev2013027 35.72 2.182013086 42.32 8.352013145 59.09 11.082013204 36.24 3.302013292 39.29 2.472013322 39.94 2.10

These values need adjustment for solar and selenographic ranges, nutation, libration, etc

CONCLUSIONS! • Push broom observing systems of the ALI variety can not

produce inherently (band-to band) co-aligned measurements. This is not a design flaw, but rather a “feature” designed to produce higher SNR.

• This “”feature” does not necessarily hamper uses of the data in a variety of applications. However, it does introduce significant uncertainty in determining vegetation indices.

• The moon serves as a solar diffuser monitor for several orbiting missions. The EO-1 CalVal Team, in collaboration with EO-1 Operations, is refining strategies to use specific “vicarious calibration sites” on the lunar surface, enhancing use of orbiting imaging spectrometer missions to serve as transfer radiometers for other passive optical missions.