National Aeronautics and
Space Administration

CLARREO Pathfinder
Mission Overview and Status
Yolanda L. Shea1, Rajendra Bhatt1
And CPF Project Team1,2,3
1
2

NASA Langley Research Center

Laboratory for Atmospheric and Space Physics
3

NASA Goddard Space Flight Center

1

CLARREO Pathfinder: Mission Summary
Climate Absolute Radiance and Refractivity Observatory
• Core Mission Objectives: Take climate-critical high
accuracy measurements of Earth reflectance and intercalibrate with CERES (broadband) & VIIRS (multi-spectral)
• LASP-Led Payload & Reflected Solar Spectrometer (350 –
2300 nm)
• Hosted on International Space Station
• Nominal 1-year mission operations + 1-year science data
analysis

Spectrally-Resolved Earth
Reflectance

• But wait there will hopefully be more! On ISS schedule through end
of ISS life (2030)!

• Launch: December 2023

https://clarreo-pathfinder.larc.nasa.gov/

2

CPF Science Objectives
Objective #1: High Accuracy SI-Traceable
Reflectance Measurements

Objective #2: Inter-Calibration Capabilities
Transfer
calibration
accuracy to other
key RS satellite
sensors by intercalibrating with
CERES & VIIRS.

Conduct on-orbit
calibration to achieve
reflectance
uncertainty a factor of
5-10 times better
than the best
operational sensors
on orbit.
Objective #1

Objective #2

Uncertainty

Spectrally-resolved & broadband reflectance: ≤0.3% (1σ)

Data Product

Level 1A: Highest accuracy, best for inter-cal, lunar obs
Level 1B: Approx. consistent spectral & spatial sampling, best
for science studies using nadir spectra

Intercalibration Methodology Uncertainty: ≤0.3% (1σ)
Level 4: One each for CPF-VIIRS & CPF-CERES inter-cal.
Merged data products including all required info for intercal analysis

https://clarreo-pathfinder.larc.nasa.gov/ 3

CPRS Payload: LASP Leadership
HYSICS: Hyperspectral Imager for Climate Science

Radiometric Uncertainty
Spectral Range
Spectral Resolution
Swath Width

0.3% (1-sigma)
350 nm – 2300 nm
6 nm
10° (70 km nadir)

Spatial Resolution

0.5 km

Sampling Rate

15 Hz

4

Calibration & Measurement Approach
Earth Viewing

Solar Viewing

 Earth reflectance will be obtained using a
band-ratioing approach

 CPF will view both Sun & Earth with similar
optical paths using

 Aperture attenuation
 Over 3 orders of magnitude (20 mm to 0.5 mm)
 Integration time attenuation
 Over 2 orders of magnitude (66 ms to 1.17 ms)

 Solar measurements & on-orbit calibration
 Cross-slit scan
 Flat fielding for both apertures – along-slit scan
 Pen-ray lamp measurement

Input Aperture

Hyperspectral
Imager
Exposure time

Integration
Time

FPA
time

P. Smith (LASP)

Hyperspectral
Imager
FPA

Exposure time

time
5

5

Instrument Cradle

Yoke Assembly
Pedestal Assembly

Star Tracker

Main Baseplate

HPS Controller

Launch Locks (x3)
Kinematic Flexures (x4)

HySICS Pointing System (HPS) – the primary structure and two-axis pointing system of the CLARREO Pathfinder payload.
The HySICS instrument and associated electronics reside within the tan-colored instrument cradle. The kinematic flexures
serve as the payload attachment to the ISS-provided ExPRESS Pallet Adapter (ExPA) (ExPA not pictured).
6

4MA Telescope
Aperture Wheel
Offner Mirrors (with GSE covers)
Spectrometer Grating
(with GSE cover)

Spectrometer Section

Detector Port

Internal view of the HyperSpectral Imager for Climate Science (HySICS) Instrument – the heart of the CLARREO
Pathfinder Payload. Visible are the Aperture Wheel; 4-Mirror Anastigmat (4MA) Telescope; and spectrometer section
with Offner mirrors and spectroscopic grating (with protective GSE covers installed); detector port.
7

HySICS Instrument: Light Path
Input Light

Aperture

Of
fn

1
Off

4MA

er

ner

Slit
Fol
d
M ir
ror

2

n
la
lP
ca
Fo rray
A
e

Zero-Order Trap
and Order Sorting
Filter

Laboratory for Atmospheric and Space Physics
University of Colorado, Boulder

8

9

Versatility in CPF Observations
Launch-Ready: Late 2023

Prime Mission Ops

Observation Type
On-orbit Instrument Calibration

Extended Mission Ops (TBD)

1-Year Prime Mission
Confirm success of calibration approach
over 1 year

2025—2030??
Confirm success of calibration approach
over longer period
•

Earth Reflectance and Radiance Nadir
Spectra

Will be used to confirm achieved
calibration, geolocation, etc requirements

LEO On-orbit Inter-calibration

Measurements and data analysis for
CERES and VIIRS Only

GEO On-orbit Inter-Calibration

Demonstration measurements with 1 GEO

Enhanced Land/DCC Pseudo-Invariant
Calibration Site (PICS) Characterization

Measurements over high priority PICS

Improved characterization of the Moon

Leveraging existing ops mode to cover
libration and phase angles available

Core Mission Objectives

Addl Capabilities

•
•

Develop partial (nearly-global) climate
benchmark prototype
Potential for overlap with TRUTHS
Additional opportunities for use in
science studies

•

Additional flexibility to inter-calibrate
other on-orbit LEO sensors (e.g.
PACE, Sentinel, Landsat, etc)

•

Expand GEO inter-calibration
measurements (e.g. TEMPO, GOES,
GERB, Himawari series, GeoCarb)

•

Additional PICS added with additional
viewing opportunities

•

Additional sampling within libration
and phase angles to further make
lunar models more robust

10

Nadir CPF Hyperspectral Measurements
High accuracy, information-packed measurements are critical for both detecting climate change and
identifying what is driving Earth’s changing climate (Shea et al., 2022 [In Press]).

B. Kindel

11

Leveraging the CPF Spectrum
Predecessor &
Complement to Several
Missions

Decadal Survey Missions
PACE
TRUTHS/Libra

Cloud, aerosol, water vapor, and surface remote
sensing studies and hyperspectral retrieval
algorithm development
Developing a Climate
Benchmark Prototype

Critical for monitoring
geophysical variable
changes to provide climate
model constraints

Development of Climate Change Attribution
Techniques
Evaluating temporal
variability of spectral
radiation

e.g. How has spectral
reflectance changed in past
20 years?

CPF Intercalibration Benefits
Core Mission Direct Targets (CERES
& VIIRS)

Earth Energy Imbalance
Spectral Response
Calibration evaluation across dynamic range

Independent Verification of Radiometric Consistency between multiple flight
models (e.g. CERES, VIIRS)
Climate Data Record Continued
Development, Improved Quality

MODIS-VIIRS Dark Target & Deep Blue Aerosol,
Cloud Continuity Products (20+ year records!)
Landsat/Land Imagers

Lunar Reflectance Characterization

Complement to ARCSTONE & airLUSI
Supplementing inputs to GIRO, ROLO, etc lunar
char. models

Pseudo-Invariant Earth Targets

Deep Convective Clouds
Hyperspectral, multi-angle land targets reflectance
Improved PICS uncertainty characterization

Augmenting Existing Intercalibration
Approaches

GSICS Standard?
e.g. All-sky tropical ray matching, Surface PICS,
DCCs, etc

Conclusions/Closing

• Science Education Opportunities Abound!
• CPF NPP Opportunity – please share
• CPF Internship Opportunities too

• Next CPF Science Workshop: ~Spring 2023
• Contact me if you’d like to be added to the participant list

• CLARREO Pathfinder scheduled to Launch on SpaceX Launch 29 –
December 2023
• CLARREO Pathfinder Science Team Solicitation anticipated in ROSES-24

https://clarreo-pathfinder.larc.nasa.gov/
