The value of operational satellite systems for decadal climate trending can be greatly enhanced by implementing on-orbit transfer standards for testing and improving calibration accuracy. This concept is an important part of the Climate Absolute Radiance and Reflectivity Observatory (CLARREO) mission recommended as a Tier 1 mission in the 2007 Decadal Survey.
The Absolute Radiance Interferometer (ARI) was designed to measure absolute spectrally resolved infrared radiance (200 – 2700 cm-1 at 0.5 cm-1) with ultra-high accuracy (<0.1 K, k = 3 brightness temperature). A key feature of the ARI instrument is the On-orbit Verification and Test System (OVTS), which provides end-to-end calibration verification of the ARI measurements with direct on-orbit traceability to international standards (SI). The ARI instrument has demonstrated the required radiometric accuracy for CLARREO and has achieved NASA Technology Readiness Level 6.
The International Space Station (ISS) would provide an affordable opportunity to demonstrate this new capability. The ISS orbit gives good time of day coverage for latitudes below 52 degrees, and the natural precession of the ISS offers many orbit crossings for radiance intercomparisons with operational satellites in sun-synchronous orbits. Thus, the ARI could serve as an on-orbit reference calibration standard for the operational infrared sounders, and these sounders could in turn be used to create climate benchmark products at all latitudes. In this approach, an ARI mission on the ISS would leverage operational instruments to provide a demonstration of the new climate decadal trending capability offered by spectrally resolved radiances with high accuracy proven on-orbit.
Future NASA infrared remote sensing missions will require better absolute measurement accuracies than now available,
and will most certainly rely on the emerging capability to fly SI traceable standards that provide irrefutable absolute
measurement accuracy. To establish a CLARRREO-type climate benchmark, instrumentation will need to measure
spectrally resolved infrared radiances with an absolute brightness temperature error of better than 0.1 K, verified onorbit.
This will require an independent high-emissivity (<0.999) verification blackbody with an emissivity uncertainty of
better than 0.06%, an absolute temperature uncertainty of better than 0.045K (3 sigma), and the capability of operation
over a wide range of (Earth scene) temperatures. Key elements of an On-Orbit Absolute Radiance Standard (OARS)
meeting these stringent requirements have been demonstrated in the laboratory at the University of Wisconsin and have
undergone further refinement under funding from NASA’s Earth Science and Technology Office, culminating in an end-to-end demonstration under vacuum with a prototype climate benchmark instrument. We present the new technologies that underlie the OARS, and the results of testing that demonstrate the required accuracy is being met in a vacuum
environment. The underlying technologies include: on-orbit absolute temperature calibration using the transient melt
signatures of small quantities (<1g) of reference materials (gallium, water, and mercury) imbedded in the blackbody
cavity; and on-orbit cavity spectral emissivity measurement using a carefully baffled heated halo placed in front of the
OARS blackbody viewed by the infrared spectrometer system. Emissivity is calculated from the radiance measured
from the blackbody combined with the knowledge of key temperatures and radiometric view factors.
The GOSAT thermal infrared (TIR) band calibration is reviewed for the five-year time period from April 2009 through
March 2014. Pre-launch characterization has been augmented by post-launch analysis of on-orbit data and comparison
with coincident measurements from other satellite, airborne, and ground-based sensors. Successive refinements of the
TIR band ground-processing software have incorporated corrections for detector non-linearity and polarization.
Estimates of radiometric uncertainty have also been made. The comparison of GOSAT TIR band nadir and off-nadir
comparisons (SNOs and SONOs) provide a quantitative spectral assessment of the radiometric bias relative to the NASA
AIRS and EUMETSAT IASI sensors.
Spectrally resolved infrared (IR) and far infrared (FIR) radiances measured from orbit with extremely high absolute
accuracy are a critical observation for future climate benchmark missions. For the infrared radiance spectra, it has been
determined that a measurement accuracy, expressed as an equivalent brightness temperature error, of 0.1 K (k = 3)
confirmed on orbit is required for signal detection above natural variability for decadal climate signatures [1, 2].
The challenge in the sensor development for a climate benchmark measurement mission is to achieve ultra-high
accuracy with a design that can be flight qualified, has long design life, and is reasonably small, simple, and affordable.
The required simplicity is achievable due to the large differences in the sampling and noise requirements for the
benchmark climate measurement from those of the typical remote sensing infrared sounders for weather research or
operational weather prediction.
The University of Wisconsin Space Science and Engineering Center, with funding from the NASA Instrument Incubator
Program (IIP), developed the Absolute Radiance Interferometer (ARI), which is designed to meet the uncertainty
requirements needed to establish spectrally resolved thermal infrared climate benchmark measurements from space. The
ARI is a prototype instrument designed to have a short upgrade path to a spaceflight instrument.
Recent vacuum testing of the ARI, conducted under funding from the NASA Earth Science Technology Office, has
demonstrated the capability to meet the 0.1 K (k = 3) uncertainty requirement on-orbit. An overview of the instrument
design and summary of the radiometric performance verification of the UW-SSEC ARI will be presented.
The next generation of infrared remote sensing satellite instrumentation, including climate benchmark missions will
require better absolute measurement accuracy than now available, and will most certainly rely on the emerging capability
to fly SI traceable standards that provide irrefutable absolute measurement accuracy. As an example, instrumentation
designed to measure spectrally resolved infrared radiances with an absolute brightness temperature error of better than
0.1 K will require high-emissivity (<0.999) calibration blackbodies with emissivity uncertainty of better than 0.06%, and
absolute temperature uncertainties of better than 0.045K (k=3). Key elements of an On-Orbit Absolute Radiance
Standard (OARS) meeting these stringent requirements have been demonstrated in the laboratory at the University of
Wisconsin (UW) and refined under the NASA Instrument Incubator Program (IIP). This work recently culminated with
an integrated subsystem that was used in the laboratory to demonstrate end-to-end radiometric accuracy verification for
the UW Absolute Radiance Interferometer. Along with an overview of the design, we present details of a key underlying
technology of the OARS that provides on-orbit absolute temperature calibration using the transient melt signatures of
small quantities (<1g) of reference materials (gallium, water, and mercury) imbedded in the blackbody cavity. In
addition we present performance data from the laboratory testing of the OARS.
Spectrally resolved infrared (IR) and far infrared (FIR) radiances measured from orbit with extremely high absolute
accuracy (< 0.1 K, k = 3, brightness temperature at scene temperature) constitute a critical observation for future climate
benchmark missions.
The challenge in the IR/FIR Fourier Transform Spectrometer (FTS) sensor development for a climate benchmark
measurement mission is to achieve the required ultra-high accuracy with a design that can be flight qualified, has long
design life, and is reasonably small, simple, and affordable. In this area, our approach is to make use of components
with strong spaceflight heritage (direct analogs with high TRL) combined into a functional package for detailed
performance testing. The required simplicity is achievable due to the large differences in the sampling and noise
requirements for the benchmark climate measurement from those of the typical remote sensing infrared sounders for
weather research or operations.
A summary of the instrument design and development, and the radiometric performance of the Absolute Radiance
Interferometer (ARI) at the University of Wisconsin Space Science and Engineering Center (UW-SSEC) will be
presented.
Reliable calibration of high-accuracy spaceborne infrared spectrometers requires knowledge of both blackbody
temperature and emissivity on-orbit, as well as their uncertainties. The Heated Halo is a broadband thermal source that
provides a robust and compact method to measure emissivity. We present the results from the Heated Halo methodology
implemented with a new Absolute Radiance Interferometer (ARI), which is a prototype space-based infrared
spectrometer designed for climate benchmarking. We show the evolution of the technical readiness level of this
technology and we compare our findings to models and other experimental methods of emissivity determination.
The Climate Absolute Radiance and Refractivity Observatory is a satellite mission that will measure the Earth's
outgoing spectral radiance with accuracy better than 0.1 K in radiance temperature for climate benchmarking and
forecast testing. Part of the high-accuracy calibration system is the heated halo, which provides a robust and compact
method to measure the spectral emissivity of a blackbody. Measurement of the combined radiance of a blackbody, the
reflection from a thermal source, and knowledge of key temperatures and the viewing geometry allow the blackbody
spectral emissivity to be calculated. This allows the determination of blackbody radiance, and thus calibration of the
CLARREO instrument, with high accuracy.
A summary of the development of the Absolute Radiance Interferometer (ARI) at the University of Wisconsin Space
Science and Engineering Center (UW-SSEC) will be presented. At the heart of the sensor is the ABB CLARREO
Interferometer Test-Bed (CITB), based directly on the ABB Generic Flight Interferometer (GFI). This effort is funded
under the NASA Instrument Incubator Program (IIP).
We present a method to characterize the emissivity of a spaceborne blackbody and the instrument line-shape (ILS) of a
spectrometer using a quantum cascade laser (QCL) based reflectometer. QCLs allow the realization of on-orbit
reflectometry that directly observes blackbody surface properties. We present experimental data verifying that the QCL
reflected radiance signal can be measured by an Earth-observing spectrometer. The QCL can also be used to realize a
monochromatic, spatially uniform source of infrared radiation to measure the spectrometer's ILS, which can be inverted
to obtain diagnostic information about the integrity of the detector and nonlinearities in the detector signal-chain.
The scientific objectives of the CLimate Absolute Radiance and REfractivity Observatory
(CLARREO) new start recommended by the National Research Council Decadal Survey
prioritize high accuracy measurements of infrared spectra, tested for systematic error, tied
to international measurements standards, and suitable for testing long-term climate
forecasts (of 10 years or more). We present the results from a realistic proof-of-concept
study for this mission concept and examine the prospects of testing and improving long-term
climate forecasts from ensembles of coupled General Circulation Models (GCMs)
such as those participating in the Intergovernmental Panel on Climate Change 4th
Assessment Report (IPCC-4AR).
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.