Lessons Learned from EO-1 Calibration Activities

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

a,b c a Ungar, Stephen , Ong, Lawrence , and Thome, Kurtis 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 Lets cut to the chase and get directlyCONCLUSIONS! to the bottom line • 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.

Pushbroom Observing System

Sensor Chip Array (SCA) “cartoon”

Depiction

Wavelength -Grids represent the detectors -Spots represent the IFOV centers -Colors represent the wavelengths

Cross Track Sample (Pixel) Pushbroom Observing System

Pushbroom systems come in two flavors 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

E S

AdjustingHow ALIAttitude Achieves and Frame Inherent Rate to EnsureBand Band-to-Band-to-Band Coregistration 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. Adjusted (ALI) Sampling Rate

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

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

Further Considerations

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

2 ROblateo ≡ EO −Earth1 orbital Approximation radius ' 2 2  RE cosθ + h  ω ≈ ω + ωE     R E ≡ mean Earth radius  RE + h  ω ' (R + h) h ≡ ΔR E + terrain altitude D = N E f θ ≡ ground target latitude = D ND0 ω ≡ angular orbital velocity ' ω (RE + h) f = ωE ≡ Earth rotational velocity D0 f ≡ EO -1 frame rate ω 'h f = f + h=0 ≡ D0 D0 GSD or pixel size/seperation

D0 = 30, N ≈ 23 D ≡ within frame band seperation ≈ ω ' ≈ −3 fh=0 227, 10 N ≡ frames till band coincidence h − f = 227 + ⇒ ∆D ≈ 10 3 ∆h ω’ < 3 10-3 ω 30,000 푎푎푎 ∆ 희 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 Synthetic Scene Composition

This60 initial characterization of a synthetic scene,50 composed of two landscape components,40 represents a landscape- based30 radiometric parameterization which20 is independent of any specific remotely (%) Reflectance 10 –sensed (pixel-oriented) observation0 strategy. 0,4 0,6 0,8 1,0 This is followed by characterizations of the same scene Wavelengthwhich are (μ m)based on (pixel-oriented)Vegetation observationBright strategies. "Soil"

28 Landscape Reflectance Values Synthetic Scene Scenario

.3 .1 .3 .1 .3 .5 .3 .5

.1 .3 .1 .3 .5 .3 .5 .3

.3 .1 .3 .1 .3 .5 .3 .5

.1 .3 .1 .3 .5 .3 .5 .3

VIS Reflectance NIR Reflectance 29 NIR Reflectance (RNIR)

.3 .5 .3 .5 Landscape Reflectance Ratios Synthetic Scene Scenario .5 .3 .5 .3

.3 .5 .3 .5 1 5 1 5

.5 .3 .5 .3 5 1 5 1 = VIS Reflectance (RVIS)

.3 .1 .3 .1 1 5 1 5

.1 .3 .1 .3 5 1 5 1

.3 .1 .3 .1

RNIR = VI .1 .3 .1 .3 RVIS 30 Pixel Reflectance Values Aligned Bands Scenario

.3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 ..5 .5 .3 .3 .3 .5 ..5 .5 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 ..5 .5 .3 .3 .3 .5 ..5 .5 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .1 .1 .1 .3 .3 .3 .1 .1 .1 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3

Nominal Position VIS Band Nominal Position NIR Band 31 Pixel Reflectance Values Misaligned Bands Scenario

.3 .3 .2 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .2 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .2 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .2 .5 ..5 .5 .3 .3 .3 .5 ..5 .5 .3 .3 .3 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .2 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .2 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .3 .3 .2 .1 .1 .2 .1 .1 .2 .1 .1 .2 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .2 .1 .1 .2 .1 .1 .2 .1 .1 .2 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .2 .1 .1 .2 .1 .1 .2 .1 .1 .2 .3 .3 .3 .5 .5 .5 .3 .3 .3 .5 .5 .5 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .2 .5 ..5 .5 .3 .3 .3 .5 ..5 .5 .3 .3 .3 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .2 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3 .1 .1 .2 .3 .3 .2 .1 .1 .2 .3 .3 .2 .5 .5 .5 .3 .3 .3 .5 .5 .5 .3 .3 .3

“Half-pixel” Shift VIS Band Nominal Position NIR Band 32 Results of half pixel misalignment and correction through linear re-sampling

Category 1 Category 1 Category 2 Category 2 Scenario Ratio Value Discrepancy Ratio Value 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’sHow we missing can provide from this consistent picture? CalVal across Decadal Missions!

As explained in the following slides

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 ! 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 EO-1 Lunar Cal/Val (aka Lunar Cycle) USGS Robotic Lunar Observatory ROLO Model

Np = Ik Ωp ∑Li,k i=1

π ⋅ Ik Ak = ΩM Ek 1 total lunation takes ~29.5 days Hyperion Lunar Trends Comparison of Hyperion integrated lunar responses with the USGS Robotic Lunar Observatory (ROLO) model for selected bands.

426.82 508.22 599.80 803.30 1205.07 1497.63 2002.06 2254.22

14.0

9.0

4.0

-1.0 Percent Difference from Rolo from Difference Percent -6.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 Quasi-annual variations not understood Mission Year but appears somewhat correlated with the Sun-Moon and Spacecraft-Moon selenographic coordinates. Hyperion Lunar Observations shows Spectral Variation with Phase Angles

Normalized with 7.434 Deg Phase Angle Phase Angles: -80.991 -53.679 -40.057 7.434 23.051 35.106 46.105 1.4

1.3

1.2

1.1

1 Normalized Response Normalized

0.9

0.8 400 900 1400 1900 2400

Wavelength [nm] Comparisons with RoLO at various Phase Angle

18 Some bands 15 show signs of

12 447.17 phase angle 487.87 dependencies, 9 569.27 eg 569, 660, 6 660.85 793, 864 and 793.13 1648 nm 3 864.35 1245.36 Difference from RoLO [%] RoLO from Difference 0 1648.91 -3 2213.93 -6 -85 -65 -45 -25 -5 15 35 Lunar Phase Angle [Degrees] 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. Future Use of EO-1 Lunar Images Hyperion Lunar Calibration Activities 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. 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 views the moon monthly

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

Mare Imbrium Mare Serenitatis Mare Mare Crisium Tranquilitatis

Full Moon USGS Lunar Map 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

1/01/10 4/28/10 6/27/10 12/21/10 Rotated Averaged (Aggregated) Oversampled Images

1/01/10 4/28/10 6/27/10 12/21/10 Mare Tranquilitatis Cal Site Preliminary

Date Mean S t d e v 2013027 35.72 2.18 2013086 42.32 8.35 2013145 59.09 11.08 2013204 36.24 3.30 2013292 39.29 2.47 2013322 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.