The Thermal Infrared Sensor (TIRS) instruments on board Landsat 8 and Landsat 9 provide routine thermal band image measurements of the Earth for the Landsat program. Although these observatories are specifically designed for mapping the Earth’s surface from their 705-km altitude orbits, they were recently utilized to image the Moon during the total lunar eclipse of May 2022. The full Moon is frequently used as a calibration target for Landsat. However, the imaging of the lunar eclipse provided a unique opportunity to gather accurate temporal thermal band data over the full lunar disc as solar illumination is removed. This campaign required a large effort by the Landsat Flight Operations teams to coordinate acquisitions and technical constraints on both observatories to capture the long temporal extent of the eclipse. The result of this effort was a series of resolved thermal images of the Moon at discrete times as the Earth’s shadow swept across the lunar surface through the start, partial, and total phases of the eclipse. This sequence of images showed an overall drop in surface temperature from approximately 370 K to 180 K in about 300 minutes as solar insolation was removed. Furthermore, the spatial distribution of cooling rates from this unique event provided information about different material properties (density and thermal inertia) across the lunar surface and showed a clear distinction among mare, highlands, and impact craters.
The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) operates over the ∼0.4- to 4.3-μm wavelength range. Radiometric calibration over this broad range requires the use of multiple calibration sources. Initial OVIRS in-flight calibration coefficients were previously computed using ground calibration from visible integrating sphere and IR blackbody sources, cross-calibrated with Earth-observing satellites for visible wavelengths, and adjusted using the spectrum of the OSIRIS-REx mission’s target body, asteroid (101955) Bennu. As part of the final in-flight calibration, we determined that the best calibration method removes out-of-band IR signal leakage prior to radiometric calibration and updated the calibration coefficients accordingly. These final calibration coefficients work well for data where the field of view is filled, and we document the possible artifacts in underfilled spots.
The Thermal Infrared Sensor-2 (TIRS-2) aboard Landsat 9 will continue Landsat’s four decade-long legacy of providing moderate resolution thermal imagery from low earth orbit (at 705 km) for environmental applications. Like the Thermal Infrared Sensor aboard Landsat 8, it is a pushbroom sensor with a cross-track field of view of 15° and provides two spectral channels at 10.8 and 12 μm. To ensure radiometric, spatial, and spectral performance, a comprehensive pre-launch testing program is being conducted at NASA Goddard Space Flight Center at the component, subsystem, and instrument level. This paper will focus on the results from the subsystem level testing where the instrument is almost completely assembled. This phase of testing is specifically designed to assess imaging performance including focus and stray light rejection, but is also used to provide a preliminary assessments of spatial and spectral performance. The calibration ground support equipment provides a flexible blackbody illumination source and optics to conduct these tests. The spectral response test setup has its own illumination source outside the chamber that propagates through the calibration ground support equipment in an optical configuration designed for this purpose. This test configuration with the calibration ground support equipment and TIRS-2 subsystem in the thermal vacuum chamber enables a large range of illumination angles for stray light measurements. The results show that TIRS-2 performance is expected to meet all of its performance requirements with few waivers and deviations.
The Ralph instrument on the New Horizons mission consists of a telescope that feeds two focal planes: the Multi-spectral Visible Imaging Camera (MVIC), a visible, near-IR imager and the Linear Etalon Imaging Spectral Array (LEISA), a short-wavelength IR spectral imager. During the encounter with the Pluto system in 2015, Ralph operated as expected collecting numerous high spatial resolution images of the main components of the system, Pluto and Charon, as well as the four much smaller objects Hydra, Kerberos, Nix and Styx. New Horizons, launched on January 19, 2006, is the first mission to explore Kuiper Belt Objects (KBOs).
Lunar Ice Cube, a science requirements-driven deep space exploration 6U cubesat mission was select-ed for a NASA HEOMD NextSTEP slot on the EM1 launch. We are developing a compact broadband IR instrument for a high priority science application: un-derstanding volatile origin, distribution, and ongoing processes in the inner solar system. JPL’s Lunar Flash-light, and Arizona State University’s LunaH-Map, both also EM1 lunar orbiters, will provide complimentary observations to be used in understanding volatile dynamics on the Moon.
KEYWORDS: Sensors, Calibration, Signal detection, Landsat, Temperature metrology, Quantum well infrared photodetectors, Infrared sensors, Black bodies, Space telescopes, Earth observing sensors
The Thermal Infrared Sensor (TIRS) on board Landsat 8 continues thermal band measurements of the Earth for the Landsat program. TIRS improves on previous Landsat designs by making use of a pushbroom sensor layout to collect data from the Earth in two spectral channels. The radiometric performance requirements of each detector were set to ensure the proper radiometric integrity of the instrument. The performance of TIRS was characterized during pre-flight thermal-vacuum testing. Calibration methods and algorithms were developed to translate the raw signal from the detectors into an accurate at-aperture spectral radiance. The TIRS instrument has the ability to view an on-board variable-temperature blackbody and a deep space view port for calibration purposes while operating on-orbit.
After TIRS was successfully activated on-orbit, checks were performed on the instrument data to determine its image quality. These checkouts included an assessment of the on-board blackbody and deep space views as well as normal Earth scene collects. The calibration parameters that were determined pre-launch were updated by utilizing data from these preliminary on-orbit assessments. The TIRS on-orbit radiometric performance was then characterized using the updated calibration parameters. Although the characterization of the instrument is continually assessed over the lifetime of the mission, the preliminary results indicate that TIRS is meeting the noise and stability requirements while the pixel-to-pixel uniformity performance and the absolute radiometric performance require further study.
The Landsat Data Continuity Mission (LDCM) will have two pushbroom Earth-imaging sensors: the Operational Land
Imager (OLI) and the Thermal InfraRed Sensor (TIRS). The OLI has the reflective 30-meter and panchromatic 15-meter
ETM+ bands plus additional 30-meter bands at 443 nm and 1375 nm. The TIRS has two 100-meter bands that spectrally
split the ETM+ thermal band. OLI has completed performance testing and is scheduled for a late summer 2011 delivery
to the spacecraft. OLI radiometric performance has shown that polarization sensitivity is 1-2%; Signal-to-Noise Ratios at
signal levels about 5-10% of full scale are between 6-12 times better than ETM+, e.g., 250 versus 30; radiometric
stability over 16 days is better than 0.5% (2-sigma); coherent noise is not visible; detector operability is 100% (no dead
or inoperable detectors), absolute radiance calibration uncertainty is ~4%, reflectance calibration uncertainty is ~2.5%
and detector-to-detector radiometric uniformity is generally better than 0.5%. TIRS completed initial performance
testing in March 2011 and in August 2011 will be entering its primary thermal vacuum performance testing with the
integrated instrument. At this point indications are that the TIRS instrument will have noise levels roughly ¼ of the
ETM+ bands and detector-to-detector radiometric uniformity of better than 0.5%.
The Landsat Data Continuity Mission consists of a two-sensor platform with the Operational Land Imager and Thermal
Infrared Sensor (TIRS). Much of the success of the Landsat program is the emphasis placed on knowledge of the
calibration of the sensors relying on a combination of laboratory, onboard, and vicarious calibration methods. Rigorous
attention to NIST-traceability of the radiometric calibration, knowledge of out-of-band spectral response, and
characterizing and minimizing stray light should provide sensors that meet the quality of Landsat heritage. Described
here are the methods and facilities planned for the calibration of TIRS which is a pushbroom sensor with two spectral
bands (10.8 and 12 micrometer) and the spatial resolution 100 m with 185-km swath width. Testing takes place in a
vacuum test chamber at NASA GSFC using a recently-developed calibration system based on a 16-aperture black body
source to simulate spatial and radiometric sources. A two-axis steering mirror moves the source across the TIRS field
while filling the aperture. A flood source fills the full field without requiring movement of beam providing a means to
evaluate detector-to-detector response effects. Spectral response of the sensor will be determined using a monochromator
source coupled to the calibration system. Knowledge of the source output will be through NIST-traceable thermometers
integrated to the blackbody. The description of the calibration system, calibration methodology, and the error budget for
the calibration system shows that the required 2% radiometric accuracy for scene temperatures between 260 and 330 K
is well within the capabilities of the system.
The Landsat Data Continuity Mission (LDCM), a partnership between the National Aeronautics and Space Administration
(NASA) and the Department of Interior (DOI) / United States Geological Survey (USGS), is scheduled for launch in
December, 2012. It will be the eighth mission in the Landsat series. The LDCM instrument payload will consist of the
Operational Land Imager (OLI), provided by Ball Aerospace and Technology Corporation (BATC) under contract to NASA
and the Thermal Infrared Sensor (TIRS), provided by NASA's Goddard Space Flight Center (GSFC). This paper outlines the
present development status of the two instruments.
The Thermal Infrared Sensor (TIRS) on board the Landsat Data Continuity Mission (LDCM) is a two-channel,
push-broom imager that will continue Landsat thermal band measurements of the Earth. The core of the instrument
consists of three Quantum Well Infrared Photodetector (QWIP) arrays whose data are combined to
effectively produce a linear array of 1850 pixels for each band with a spatial resolution of approximately 100
meters and a swath width of 185 kilometers. In this push-broom configuration, each pixel may have a slightly
different band shape. An on-board blackbody calibrator is used to correct each pixel. However, depending
on the scene being observed, striping and other artifacts may still be present in the final data product. The
science-focused mission of LDCM requires that these residual effects be understood.
The analysis presented here assisted in the selection of the three flight QWIP arrays. Each pixel was scrutinized
in terms of its compliance with TIRS spectral requirements. This investigation utilized laboratory spectral measurements
of the arrays and filters along with radiometric modeling of the TIRS instrument and environment.
These models included standard radiometry equations along with complex physics-based models such as the
MODerate spectral resolution TRANsmittance (MODTRAN) and Digital Imaging and Remote Sensing Image
Generation (DIRSIG) tools. The laboratory measurements and physics models were used to determine the extent
of striping and other spectral artifacts that might be present in the final TIRS data product. The results
demonstrate that artifacts caused by the residual pixel-to-pixel spectral non-uniformity are small enough that
the data can be expected to meet the TIRS radiometric and image quality requirements.
The Thermal Infrared Sensor (TIRS) is a QWIP based instrument intended to supplement the Operational Land Imager
(OLI) for the Landsat Data Continuity Mission (LDCM) [1]. The TIRS instrument is a dual channel far infrared imager
with the two bands centered at 10.8μm and 12.0μm. The focal plane assembly (FPA) consists of three 640x512 GaAs
Quantum Well Infrared Photodetector (QWIP) arrays precisely mounted to a silicon carrier substrate that is mounted on
an invar baseplate. The two spectral bands are defined by bandpass filters mounted in close proximity to the detector
surfaces. The focal plane operating temperature is 43K. The QWIP arrays are hybridized to Indigo ISC9803 readout
integrated circuits (ROICs). Two varieties of QWIP detector arrays are being developed for this project, a corrugated
surface structure QWIP and a grating surface structure QWIP. This paper will describe the TIRS system noise
equivalent temperature difference sensitivity as it affects the QWIP focal plane performance requirements: spectral
response, dark current, conversion efficiency, read noise, temperature stability, pixel uniformity, optical crosstalk and
pixel yield. Additional mechanical constraints as well as qualification through Technology Readiness Level 6 (TRL 6)
will also be discussed.
The instrument named Ralph is a visible/NIR imager and IR hyperspectral imager that would fly as one of the core instruments on New Horizons, NASA's mission to the Pluto/Charon system and the Kuiper Belt. It is a compact, power efficient, and robust instrument with excellent imaging characteristics and sensitivity, and is well suited to this longduration flyby reconnaissance mission.
In this presentation we describe flight results for an airborne IR hyperspectral imager used as a test bed for LEISA, a compact spaceborne wedged filter spectrometer. The moderate spectral resolution Linear Etalon Imaging Spectral Array (LEISA) is a low-mass, low-power, low-cost infrared spectral imager for spacecraft applications. LEISA uses a state-of-the- art wedged infrared filter (a linear variable etalon, LVE) in conjunction with a detector array to obtain hyperspectral image cubes. The LEISA concept has been described previously in Reuter et al., 1997, SPIE Vol. 2957, pp 154 - 161, 'EUROPTO Conference on: Advanced and Next-Generation Satellites II.,' 23 - 26 September, 1996, Taormina, Italy. A LEISA type instrument, the Atmospheric Corrector (LAC), will fly on NASA's EO-1 spacecraft to be launched in Dec. 1999. The airborne version of LEISA covers the spectral region from 1.0 to 2.5 microns at a constant resolving power ((lambda) /(Delta) (lambda) ) of approximately 250 (i.e. 4 nm 1.0 microns and 10 nm 2.5 microns). The single pixel spatial resolution is 2 milliradians. This corresponds to 2 meters 1 km altitude and 20 meters 10 km. The instrument has been operated throughout this altitude range. The instrument has a swath width of approximately 29 degrees. A 256 X 256 element NICMOS (Near Infrared Camera Multi-Object Spectrometer) HgCdTe detector array is used as the focal plane. The focal plane is enclosed in a small cryogenic dewar at liquid Nitrogen temperature. Results will be presented for three series of airplane flights: Lubbock Texas (USA) June - September 1997, Lubbock Texas (USA) July - September 1998, Bethlehem Orange Free State (South Africa) March 1999. Issues to be discussed include pre-, and post-flight calibration, image registration and spectral image reconstruction. The relationship of these measurements to future spaceborne hyperspectral imagers will also be discussed.
The technique of integral projections is used to perform co- registration of data from a wedge spectrometer instrument that has been developed by NASA Goddard Space Flight Center. The spectrometer is currently being flown on a plane and operates in the 1 - 2.5 micron range. The technique involves a number of steps. First, an algorithm was developed to calculate the absorption bands that occur within the spectral region. At this point the method of Integral Projections is used to vectorize the image. The Integral Projections method performs a number of key functions in the registration process: increases SNR, reduces affects of spatial non-uniformities within the data, and results in a much faster algorithm since the operation is on vectors. The final step is to register the zero crossing of the second derivative of the vectors. Two issues encountered with co-registration is dealing with the absorption bands that occur within the spectral region of interest and the multiple problem of recognizing features that are not only shifting in x and y but also appear different at different wavelengths. Results will be presented in which the application of our algorithm obtains the appropriate x,y shifts necessary to reconstruct a registered data cube.
The Linear Etalon Imaging Spectral Array (LEISA) represents a new class of hyperspectral cameras which use non- dispersive thin film filters as wavelength selective elements. The simplicity and versatility of these instruments make them attractive for spaceflight use. LEISA currently operates in the shortwave IR spectral region, but the design is adaptable to operation at wavelengths from visible to longwave IR.
S. Alan Stern, David Slater, William Gibson, Harold Reitsema, Alan Delamere, Donald Jennings, Dennis Reuter, John Clarke, Carolyn Porco, Eugene Shoemaker, John Spencer
We describe the design concept for the highly integrated Pluto payload system (HIPPS): a highly integrated, low-cost, light-weight, low-power instrument payload designed to fly aboard the proposed NASA Pluto flyby spacecraft destined for the Pluto/Charon system. The HIPPS payload is designed to accomplish all of the Pluto flyby prime (IA) science objectives, except radio science, set forth by NASA's Outer Planets Science Working Group (OPSWG) and the Pluto Express Science Definition Team (SDT). HIPPS contains a complement of three instrument components within one common infrastructure; these are: (1) a visible/near UV CCD imaging camera; (2) an infrared spectrograph; and (3) an ultraviolet spectrograph. A detailed description of each instrument is presented along with how they will meet the IA science requirements.
Due to high launch vehicle costs, space instrumentation designers are constantly pressured to decrease weight and increase reliability of flight hardware. To meet these needs in a spectrometer, the infrared products team at Optical Coating Laboratory, Inc. (OCLI) and the NASA Goddard Space Flight Center (GSFC) have developed an infrared logarithmically variable filter for use in NASA's Pluto Fast Fly-by instrument. The filter and diode array combination replaces the multiple optical elements in conventional spectrometers, resulting in lower instrumentation weight and complexity with no moving parts. The choice of logarithmic rather than linear profile yields constant resolving power on every pixel of the array. Filters were produced in which the center wavelength varied from 1.0-1.581 micrometers , and 1.581-2.5 micrometers over a distance of 1.024 cm. Bandwidth was 0.3% FWHM and overall transmittance ranged from 30% to 50%. This paper discusses the major issues and tradeoffs in the design, manufacture, and testing of the filters. Measurement techniques are presented and comparisons are made between theoretical and measured performance of bandwidth, transmittance, and spectral profile.
A novel cryogenic grating spectrometer (FCAS) is being designed for observations of volatiles in cometary and planetary atmospheres, and in newly forming planetary systems. The instrument features two-dimensional detector arrays coupled to a high-dispersion echelle by infrared fibers, and will achieve a spectral resolving power of about 40,000. The primary observational platform for this instrument will be the Kuiper Airborne Observatory, but it will also be configured for use at ground-based observatories. Initially, the spectrometer will use a 58 x 62, 1- to 5-micron InSb array. Larger-format IR arrays and arrays of different composition, will later be incorporated as they become available. The instrument will be used in two modes. The first uses a large format IR array in the spectral image plane for the customary one-dimensional spectral-one-dimensional spatial coverage. In the second mode, a massive, coherent bundle of infrared transmitting ZrF4 fibers will be installed after the dispersive element, to reformat the two-dimensional array into an elongated one-dimensional array for wide spectral coverage, allowing multiple lines to be measured in a single integration with high sensitivity. The overall instrument design is discussed, and the system sensitivity is estimated.
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