Within the NASA GSFC Code 618 Calibration Laboratory, the Radiometric Calibration Lab (RCL) is focused on maintaining National Institute of Standards and Technology (NIST) traceable calibrated sources and detectors to calibrate, characterize, and monitor remote sensing instrumentation throughout NASA and the larger scientific community.
Among these RCL sources, the Grande broadband source, a 9-lamp 1m diameter integrating sphere with a 25.4cm aperture and PTFE coating housed in a Class 10,000 cleanroom environment, is the workhorse for providing regular NIST traceable calibration services to ground, flight, and remote sensing missions on a consistent basis.
As part of an initiative to improve the Grande calibration uncertainty budget, monitoring spectrometers were recently installed on Grande to provide continuous spectral radiance measurements of the integrating sphere source whenever Grande is in use. This monitoring data is used to characterize Grande’s ramp up stabilization and nominal operation process. Over multiple calibration sessions with Grande, we can observe long term source behavioral changes as the lamps age.
Having continuous monitoring allows us to validate Grande’s stability during remote sensing calibration sessions. As stability data is accumulated and analyzed it results in updated and improved uncertainty budget for calibrations using Grande.
The NASA GSFC Code 618 Calibration Laboratory maintains instruments and National Institute of Standards and Technology (NIST) traceable calibrated sources and detectors to calibrate, characterize, and monitor remote sensing instrumentation throughout NASA and the larger scientific community. Under the Calibration Laboratory umbrella, we operate the Radiometric Calibration Lab (RCL) focused on calibrating instrument radiometers, the Diffuser Calibration Lab (DCL) specializing in NIST traceable calibration of reflective and transmissive space diffusers. The RCL uses broadband sources as well as an array of options for monochromatic spectral calibration to provide regular NIST traceable calibration services to ground, flight, and remote sensing missions at NASA GSFC. The DCL uses scatterometers to measure the Bidirectional Reflectance and Transmittance Distribution Functions (BRDF & BTDF) of flight diffusers and witness samples. As we look to the future, the Calibration Laboratory will be automating routine processes throughout the facility and updating our online data collection and distribution capabilities. We are adding monitoring radiometers to our Grande calibration sphere to improve NIST traceability. Hardware updates to our scatterometers will keep us aligned with the diffuser calibration capabilities being developed at NIST.
The Goddard Laser for Absolute Measurement of Radiance (GLAMR) is a mobile spectral and radiometric sensor characterization facility based at NASA/Goddard Space Flight Center. Based on NIST’s traveling Spectral Irradiance and Radiance Calibration using Uniform Sources (SIRCUS), GLAMR consists of a system of tunable lasers to generate quasi-monochromatic energy between 310 and 2500nm, a large integrating sphere to provide a full aperture uniform source, a control system to automate operations and a data system to record and serve telemetry. GLAMR was used to characterize the Ocean Color Instrument (OCI) to be launched aboard the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission. The test of the OCI flight instrument took place in October 2022. GLAMR will be used to characterize the CLARREO Pathfinder (CPF) instrument in September 2023. Both programs had stringent calibration requirements on GLAMR, necessitating additional characterization of GLAMR radiometric uncertainty and improvements in the NIST traceability. This paper will discuss the improvement in the GLAMR uncertainty budget and the performance of GLAMR for the OCI instrument as well as the upcoming test for CPF.
The Goddard Laser for Absolute Measurement of Radiance (GLAMR) is a transportable calibration facility that provides characterization of spectral and radiometric response of airborne and satellite-based instruments operating in the solarreflective spectral region. In this work, the time resolved output of GLAMR’s integrating sphere coupled with a modelocked source was measured. The 76-cm diameter sphere with 30-cm output aperture was illuminated using a modelocked pulse train at 76 MHz, with single pulse durations of 12 ps. The time constant of the sphere was found to be 36 ns, and the resultant temporal averaging of pulses produced a maximum time varying irradiance at the output of 20% of the mean. A comparison of instrument calibration data generated with this integrating sphere using both a mode-locked source and a continuous-wave source is also given.
The Climate Absolute Refractivity and Reflectance Observatory (CLARREO) Pathfinder (CPF) mission is being developed to demonstrate SI-traceable retrievals of reflectance at unprecedented accuracies for global satellite observations. An Independent Calibration of the CPF sensor using the Goddard Laser for Absolute Measurement of Radiance (GLAMR) is planned to allow validation of CPF accuracies. GLAMR is a detector-based calibration system relies on a set of NIST-calibrated transfer radiometers to assess the spectral radiance from the GLAMR sphere source to better than 0.3 % (k=2). The current work describes the calibration of the Solar, Lunar Absolute Reflectance Imaging Spectroradiometer (SOLARIS) that was originally developed as a calibration demonstration system for the CLARREO mission and is now being used to assess the independent calibration being developed for CPF. The methodology for the radiometric calibration of SOLARIS is presented as well as results from the GLAMR-based calibration of SOLARIS. The portability of SOLARIS makes it capable of collecting field measurements of earth scenes and direct solar and lunar irradiance similar to those expected during the on-orbit operation of the CPF sensor. Results of SOLARIS field measurements are presented. The use of SOLARIS in this effort also allows the testing protocols for GLAMR to be improved and the field measurements by SOLARIS build confidence in the error budget for GLAMR calibrations. Results are compared to accepted solar irradiance models to demonstrate accuracy values giving confidence in the error budget for the CLARREO reflectance retrieval.
The Landsat-9 satellite will carry the Operational Land Imager-2 (OLI-2) as one of its payloads. This instrument is a clone of the Landsat-8 OLI and its mission is to continue the operational land imaging of the Landsat program. The OLI-2 will continue to populate an archive of Landsat earth images that dates back to 1972. The OLI-2 instrument is not significantly different from OLI though the instrument-level pre-launch spectral characterization process was much improved. While OLI was characterized by a double monochromator system, the OLI2 spectral characterization made use of the Goddard Laser for Absolute Measurement of Radiance (GLAMR), a system of tunable lasers that cover 350-2500nm which are fiber-coupled to a 30-in integrating sphere and is monitored by NISTtraceable radiometers. GLAMR allowed the spectral characterization of every detector of the OLI-2 focal plane in nominal imaging conditions. The in-band relative spectral responses were sampled at 1 or 2nm wavelength increments and the out-of-band responses at 10 or 20nm wavelength increments (increment is dependent on spectral band/region). The final relative spectral responses (RSRs) represent the best characterization any Landsat instrument spectral response. This paper will cover the results of the instrument-level spectral characterization, including in-band response, out-of-band response, spectral cross-talk and spectral uniformity.
The Landsat-9 Operational Land Imager 2 (OLI-2) instrument, currently under development for launch in late 2020, is a clone of the Landsat-8 OLI instrument, which was launched in 2013. Ball Aerospace built and rigorously characterized the Landsat-8 OLI and is repeating the process for the Landsat-9 OLI-2. A major difference between the testing for OLI and OLI-2 will be spectral test equipment. The instrument-level spectral test for OLI made use of a double monochromator; the OLI-2 test will use of Goddard Laser for the Absolute Measurement of Radiance (GLAMR). The GLAMR system is a set of lasers, which collectively cover the entire spectral range of the OLI-2 spectral bands. The laser outputs are fed to a 30” integrating sphere via fiber optic cables, which OLI-2 can view from its position inside the thermal vacuum chamber. The laser-based spectral characterization offers several major advantages over the monochromator-based methods: (1) higher signal levels as compared to the lamp in the double monochromator providing better signal to noise and capabilities to measure out of band response, (2) full aperture illumination and flood illumination of multiple focal plane modules so that all detectors are tested and crosstalk effects can be observed, as opposed to the approximately 60 detectors illuminated by the slit image of the monochromator (3) an absolute spectral response characterization as opposed to relative spectral response. OLI-2 spectral testing with GLAMR should begin in late 2018. This work describes the spectral-radiometric test plan, test requirements, and GLAMR performance demonstrated prior to OLI-2 characterization.
The polarization sensitivity of the Visible/NearIR (VISNIR) bands in the Joint Polar Satellite Sensor 1 (J1) Visible Infrared Imaging Radiometer Suite (VIIRS) instrument was measured using a broadband source. While polarization sensitivity for bands M5-M7, I1, and I2 was less than 2.5 %, the maximum polarization sensitivity for bands M1, M2, M3, and M4 was measured to be 6.4 %, 4.4 %, 3.1 %, and 4.3 %, respectively with a polarization characterization uncertainty of less than 0.38%. A detailed polarization model indicated that the large polarization sensitivity observed in the M1 to M4 bands is mainly due to the large polarization sensitivity introduced at the leading and trailing edges of the newly manufactured VISNIR bandpass focal plane filters installed in front of the VISNIR detectors. This was confirmed by polarization measurements of bands M1 and M4 bands using monochromatic light. Discussed are the activities leading up to and including the two polarization tests, some discussion of the polarization model and the model results, the role of the focal plane filters, the polarization testing of the Aft-Optics-Assembly, the testing of the polarizers at the National Aeronautics and Space Administration’s (NASA) Goddard center and at the National Institute of Science and Technology (NIST) facility and the use of NIST’s Traveling Spectral Irradiance and Radiance responsivity Calibrations using Uniform Sources (T-SIRCUS) for polarization testing and associated analyses and results.
The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission addresses the need to observe highaccuracy, long-term climate change trends and to use decadal change observations as a method to determine the accuracy of climate change. A CLARREO objective is to improve the accuracy of SI-traceable, absolute calibration at infrared and reflected solar wavelengths to reach on-orbit accuracies required to allow climate change observations to survive data gaps and observe climate change at the limit of natural variability. Such an effort will also demonstrate National Institute of Standards and Technology (NIST) approaches for use in future spaceborne instruments. The current work describes the results of laboratory and field measurements with the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. SOLARIS allows testing and evaluation of calibration approaches, alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a testbed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. Results of laboratory calibration measurements are provided to demonstrate key assumptions about instrument behavior that are needed to achieve CLARREO’s climate measurement requirements. Absolute radiometric response is determined using laser-based calibration sources and applied to direct solar views for comparison with accepted solar irradiance models to demonstrate accuracy values giving confidence in the error budget for the CLARREO reflectance retrieval.
A goal of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission is to observe highaccuracy, long-term climate change trends over decadal time scales. The key to such a goal is to improving the accuracy of SI traceable absolute calibration across infrared and reflected solar wavelengths allowing climate change to be separated from the limit of natural variability. The advances required to reach on-orbit absolute accuracy to allow climate change observations to survive data gaps exist at NIST in the laboratory, but still need demonstration that the advances can move successfully from to NASA and/or instrument vendor capabilities for spaceborne instruments. The current work describes the radiometric calibration error budget for the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. The goal of the CDS is to allow the testing and evaluation of calibration approaches, alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a test-bed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. The resulting SI-traceable error budget for reflectance retrieval using solar irradiance as a reference and methods for laboratory-based, absolute calibration suitable for climatequality data collections is given. Key components in the error budget are geometry differences between the solar and earth views, knowledge of attenuator behavior when viewing the sun, and sensor behavior such as detector linearity and noise behavior. Methods for demonstrating this error budget are also presented.
The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission addresses the need to observe highaccuracy, long-term climate change trends and to use decadal change observations as the most critical method to determine the accuracy of climate change. One of the major objectives of CLARREO is to advance the accuracy of SI traceable absolute calibration at infrared and reflected solar wavelengths. This advance is required to reach the on-orbit absolute accuracy required to allow climate change observations to survive data gaps while remaining sufficiently accurate to observe climate change to within the uncertainty of the limit of natural variability. While these capabilities exist at NIST in the laboratory, there is a need to demonstrate that it can move successfully from NIST to NASA and/or instrument vendor capabilities for future spaceborne instruments. The current work describes the test plan for the Solar, Lunar for Absolute Reflectance Imaging Spectroradiometer (SOLARIS) which is the calibration demonstration system (CDS) for the reflected solar portion of CLARREO. The goal of the CDS is to allow the testing and evaluation of calibration approaches, alternate design and/or implementation approaches and components for the CLARREO mission. SOLARIS also provides a test-bed for detector technologies, non-linearity determination and uncertainties, and application of future technology developments and suggested spacecraft instrument design modifications. The end result of efforts with the SOLARIS CDS will be an SI-traceable error budget for reflectance retrieval using solar irradiance as a reference and methods for laboratory-based, absolute calibration suitable for climate-quality data collections.
The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission key goals include enabling
observation of high accuracy long-term climate change trends, use of these observations to test and improve climate
forecasts, and calibration of operational and research sensors. The spaceborne instrument suites include a reflected solar
(RS) spectroradiometer, emitted infrared spectroradiometer, and radio occultation receivers. The requirement for the RS
instrument is that derived reflectance must be traceable to SI standards with an absolute uncertainty of <0.3% and the
error budget that achieves this requirement is described in previous work. This work describes the Solar/Lunar Absolute
Reflectance Imaging Spectroradiometer (SOLARIS), a calibration demonstration system for RS instrument, and presents
initial calibration and characterization methods and results. SOLARIS is an Offner spectrometer with two separate focal
planes each with its own entrance aperture and grating covering spectral ranges of 320-640, 600-2300 nm over a full
field-of-view of 10 degrees with 0.27 milliradian sampling. Results from laboratory measurements including use of
integrating spheres, transfer radiometers and spectral standards combined with field-based solar and lunar acquisitions
are presented.
The Ocean Radiometer for Carbon Assessment (ORCA), currently being developed at Goddard, is a hyperspectral
instrument with a spectral range extending from 350nm to 880nm in the UV and visible wavelength. Its radiometric
measurement accuracy will depend, in part, on the extent to which it is insensitive to linearly polarized light. A wedge
type depolarizer is used to reduce ORCA's polarization sensitivity over its entire spectral range. The choice for this
approach is driven by the large spectral range and to a certain extent is also influenced by the currently orbiting SeaWifs
instrument's use of a wedge depolarizer and its low polarization sensitivity. The wedge depolarizer's design, its modeled
and measured depolarization characteristics are presented.
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