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All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

The Algorithm for MODIS Wavelength On-Orbit Calibration using the SRCA

The Spectro-Radiometric Calibration Assembly (SRCA) provides on-orbit spectral calibration of the MODerate resolution Imaging Spectroradiometer (MODIS) reflected solar bands and this paper describes how it is accomplished. The SRCA has two adjacent exit slits: 1) Main slit and 2) Calibration slit. The output from the main slit is measured by a reference silicon photo-diode (SIPD) and then passes through the MODIS. The output from the calibration slit passes through a piece of didymium transmission glass and then it is measured by a calibration SIPD. The centroids of the sharp spectral peaks of a didyrnium glass are utilized as wavelength standards. After normalization using the reference SIPD signal to eliminate the effects of the illuminating source spectra, the calibration SIPD establishes the relationship between the peaks of the didymium spectra and the grating angle; this is accomplished through the grating equation. In the grating equation the monochromator parameters, beta (half angle between the incident and diffractive beams) and theta(sub ff) (offset angle of the grating motor) are determined by matching, in a least square sense, the known centroid wavelengths of the didymium peaks and the calculated centroid grating angles from the calibration SIPD signals for the peaks. A displacement between the calibration SIPD and the reference SIPD complicates the signal processing. The response of the MODIS bands to the SRCA output is also normalized by the reference SIPD signal to eliminate the effect of the source spectrum. That response differs from what is measured by MODIS using the Spectral Measurements Assembly (SpMA), a laboratory double-monochromator, due to the wider slit width of the SRCA. The SRCA slit function, calculated using measurements by the SPMA and the SRCA at the same MODIS temperature, will be used to recover the MODIS spectral response using the SRCA data measured on-orbit.

Montgomery, Harry↗
DOE OSTI2024

Epitaxially Grown Single-Crystalline SrTiO 3 Membranes Using a Solution-Processed, Amorphous SrCa 2 Al 2 O 6 Sacrificial Layer

Water-soluble sacrificial layers based on epitaxially-grown, single crystalline (Ca, Sr, Ba) 3 Al 2 O 6 layer are widely used for creating free-standing perovskite oxide membranes. However, obtaining these sacrificial layers with intricate stoichiometry remains a challenge, especially for molecular beam epitaxy (MBE). In this study, we demonstrate the hybrid MBE growth of epitaxial, single crystalline SrTiO 3 films using a solution processed, amorphous SrCa 2 Al 2 O 6 sacrificial layer onto SrTiO 3 (001) substrates. Prior to the growth, the oxygen plasma exposure was used to first create the crystalline SrCa 2 Al 2 O 6 layer with well-defined surface crystallinity. Utilizing reflection high energy electron diffraction, x-ray diffraction, and atomic force microscopy, we observe an atomic layer-by-layer growth of epitaxial, single crystalline SrTiO 3 film on the SrCa 2 Al 2 O 6 layer with atomically smooth surfaces. The SrCa 2 Al 2 O6 layer was subsequently dissolved in de-ionized water to create free-standing SrTiO3 membranes that were transferred onto a metal-coated Si wafer. Membranes created with Sr-deficiency revealed ferroelectric-like behavior measured using piezo force microscopy whereas stoichiometric films remained paraelectric-like. Furthermore, these findings underscore the viability of using ex-situ deposited amorphous SrCa2Al2O6 for epitaxial, single crystalline growth, as well as the importance of point defects in determining the ferroic properties in membranes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

Measuring Crosstalk in MODIS Spectral Bands On-orbit Using the SRCA

Near-identical MODIS instruments launched on-board the Terra and Aqua spacecraft in 1999 and 2002, respectively. Each MODIS instrument has36 spectral bands covering 0.41 to 14.2μm mounted among four focal plane assemblies, along with a series of on-board calibrators (OBCs) used to characterize the instrument performance on-orbit. One such OBC is the Spectro-radiometric Calibration Assembly (SRCA), which is a multi-function calibrator, able to provide calibration sources to measure spatial, spectral, or radiometric properties of the MODIS bands depending on its configuration. The MODIS instrument performance, including measurements of the signal cross-contamination (crosstalk) between bands, was measured on-orbit during early-mission characterization for both instruments. This crosstalk test used the SRCA in its spatial mode while utilizing the thin slit, which is normally used for spectral calibrations. A similar crosstalk test was recently performed for Terra MODIS. Since the Terra safe mode event in 2016, the PVLWIR bands specifically (6.7-9.7μm) have shown increased influence from crosstalk. The process involved in preparing and performing this crosstalk test is included in this work, as well as the findings from the recent and previous SRCA-based crosstalk characterizations.

MODIS↗
DOE OSTI2025

The development and application of the stirred‐reactor coupon analysis (SRCA) test method

A new technique, termed the stirred‐reactor coupon analysis (SRCA) method, has been developed to measure the rate of glass dissolution in forward‐rate conditions. Monolithic glass coupons are partially masked with an inert material before placement in a large volume of well‐mixed solution with known chemistry and temperature for a predetermined duration. After the test, the mask is removed, and the difference in step height between the protected area and the exposed corroded portions of the sample coupon is measured to determine the extent of glass dissolution. The step height is converted to a rate measurement using the test duration and glass density. Test parameters such as sample surface preparation and test duration were evaluated to determine their effects on the measured rates. Additionally, results from an interlaboratory study (ILS) consisting of 12 laboratories from 11 different institutions are presented, where each laboratory performed 12 independent tests. When removing experimental outlier data, the 95% reproducibility limits for the SRCA method has no statistical difference with previously published standardized test methods used to determine the forward rate of glass dissolution. Overall, this paper describes steps necessary to perform the test method and provides the statistical calculations to evaluate test accuracy.

chemical durability↗
NASA NTRS1998

The Algorithm for MODIS Wavelength On-Orbit Calibration Using the SRCA

The Spectro-Radiometric Calibration Assembly (SRCA) provides on-orbit spectral calibration of the MODerate resolution Imaging Spectroradiometer (MODIS) reflected solar bands and this paper describes how it is accomplished. The SRCA has two adjacent exit slits: 1) Main slit and 2) Calibration slit. The output from the main slit is measured by a reference silicon photo-diode (SIPD) and then passes through the MODIS. The output from the calibration slit passes through a piece of didymium transmission glass and then it is measured by a calibration SIPD. The centroids of the sharp spectral peaks of a didymium glass are utilized as wavelength standards. After normalization using the reference SIPD signal to eliminate the effects of the illuminating source spectra, the calibration SIPD establishes the relationship between the peaks of the didymium spectra and the grating angle; this is accomplished through the grating equation. In the grating equation the monochromator parameters, Beta (half angle between the incident and diffractive beams) and Theta(sub off) (offset angle of the grating motor) are determined by matching, in a least square sense, the known centroid wavelengths of the didymium peaks and the calculated centroid grating angles from the calibration SIPD signals for the peaks. A displacement between the calibration SIPD and the reference SIPD complicates the signal processing.

Montgomery, Harry↗
DOE OSTI2020

Materials Data on SrCa(CO3)2 by Materials Project

SrCa(CO3)2 crystallizes in the orthorhombic Pmc2_1 space group. The structure is three-dimensional. Sr2+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of Sr–O bond distances ranging from 2.60–2.80 Å. Ca2+ is bonded to seven O2- atoms to form distorted edge-sharing CaO7 pentagonal bipyramids. There are a spread of Ca–O bond distances ranging from 2.40–2.50 Å. There are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.29 Å) and two longer (1.30 Å) C–O bond length. In the second C4+ site, C4+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.27 Å) and two longer (1.31 Å) C–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to one Sr2+, two equivalent Ca2+, and one C4+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Sr2+, one Ca2+, and one C4+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Sr2+ and one C4+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Sr2+, one Ca2+, and one C4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrCa(CoO3)2 by Materials Project

SrCa(CoO3)2 is (Cubic) Perovskite-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are three inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent CaO12 cuboctahedra, corners with eight SrO12 cuboctahedra, faces with two equivalent SrO12 cuboctahedra, faces with four CaO12 cuboctahedra, and faces with eight equivalent CoO6 octahedra. There are eight shorter (2.71 Å) and four longer (2.72 Å) Sr–O bond lengths. In the second Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with twelve CaO12 cuboctahedra, faces with two equivalent CaO12 cuboctahedra, faces with four equivalent SrO12 cuboctahedra, and faces with eight equivalent CoO6 octahedra. All Sr–O bond lengths are 2.72 Å. In the third Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent CaO12 cuboctahedra, corners with eight equivalent SrO12 cuboctahedra, faces with six CaO12 cuboctahedra, and faces with eight equivalent CoO6 octahedra. There are eight shorter (2.71 Å) and four longer (2.72 Å) Sr–O bond lengths. There are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to twelve O2- atoms to form CaO12 cuboctahedra that share corners with four equivalent SrO12 cuboctahedra, corners with eight CaO12 cuboctahedra, faces with two equivalent CaO12 cuboctahedra, faces with four SrO12 cuboctahedra, and faces with eight equivalent CoO6 octahedra. There are four shorter (2.69 Å) and eight longer (2.71 Å) Ca–O bond lengths. In the second Ca2+ site, Ca2+ is bonded to twelve O2- atoms to form CaO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with two equivalent SrO12 cuboctahedra, faces with four equivalent CaO12 cuboctahedra, and faces with eight equivalent CoO6 octahedra. All Ca–O bond lengths are 2.69 Å. In the third Ca2+ site, Ca2+ is bonded to twelve O2- atoms to form CaO12 cuboctahedra that share corners with four equivalent SrO12 cuboctahedra, corners with eight equivalent CaO12 cuboctahedra, faces with six SrO12 cuboctahedra, and faces with eight equivalent CoO6 octahedra. There are four shorter (2.69 Å) and eight longer (2.71 Å) Ca–O bond lengths. Co4+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with six equivalent CoO6 octahedra, faces with four SrO12 cuboctahedra, and faces with four CaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–1°. There is five shorter (1.91 Å) and one longer (1.92 Å) Co–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to two Sr2+, two Ca2+, and two equivalent Co4+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to two Sr2+, two Ca2+, and two equivalent Co4+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to three Sr2+, one Ca2+, and two equivalent Co4+ atoms. In the fourth O2- site, O2- is bonded in a distorted linear geometry to one Sr2+, three Ca2+, and two equivalent Co4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrCa by Materials Project

SrCa crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Sr is bonded to six equivalent Sr and six equivalent Ca atoms to form SrSr6Ca6 cuboctahedra that share corners with eighteen equivalent SrSr6Ca6 cuboctahedra, edges with six equivalent SrSr6Ca6 cuboctahedra, edges with twelve equivalent CaSr6Ca6 cuboctahedra, faces with eight equivalent SrSr6Ca6 cuboctahedra, and faces with twelve equivalent CaSr6Ca6 cuboctahedra. All Sr–Sr bond lengths are 4.12 Å. All Sr–Ca bond lengths are 4.06 Å. Ca is bonded to six equivalent Sr and six equivalent Ca atoms to form CaSr6Ca6 cuboctahedra that share corners with eighteen equivalent CaSr6Ca6 cuboctahedra, edges with six equivalent CaSr6Ca6 cuboctahedra, edges with twelve equivalent SrSr6Ca6 cuboctahedra, faces with eight equivalent CaSr6Ca6 cuboctahedra, and faces with twelve equivalent SrSr6Ca6 cuboctahedra. All Ca–Ca bond lengths are 4.12 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrCa by Materials Project

SrCa is alpha La-derived structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Sr sites. In the first Sr site, Sr is bonded to six equivalent Sr and six Ca atoms to form SrSr6Ca6 cuboctahedra that share corners with twelve SrSr6Ca6 cuboctahedra, edges with twelve SrSr6Ca6 cuboctahedra, edges with twelve CaSr6Ca6 cuboctahedra, faces with six equivalent SrSr6Ca6 cuboctahedra, and faces with twelve CaSr6Ca6 cuboctahedra. All Sr–Sr bond lengths are 4.08 Å. All Sr–Ca bond lengths are 4.08 Å. In the second Sr site, Sr is bonded to ten equivalent Sr and six Ca atoms to form SrSr10Ca6 cuboctahedra that share corners with ten CaSr6Ca6 cuboctahedra, corners with twelve SrSr6Ca6 cuboctahedra, edges with eight CaSr6Ca6 cuboctahedra, edges with sixteen SrSr6Ca6 cuboctahedra, faces with sixteen equivalent SrSr10Ca6 cuboctahedra, and faces with eighteen CaSr6Ca6 cuboctahedra. There are a spread of Sr–Sr bond distances ranging from 4.08–8.17 Å. All Sr–Ca bond lengths are 4.08 Å. There are three inequivalent Ca sites. In the first Ca site, Ca is bonded to six equivalent Sr and six equivalent Ca atoms to form CaSr6Ca6 cuboctahedra that share corners with twelve CaSr6Ca6 cuboctahedra, edges with twelve equivalent SrSr6Ca6 cuboctahedra, edges with twelve CaSr6Ca6 cuboctahedra, faces with six equivalent CaSr6Ca6 cuboctahedra, and faces with twelve equivalent SrSr6Ca6 cuboctahedra. All Ca–Ca bond lengths are 4.08 Å. In the second Ca site, Ca is bonded to six Sr and six equivalent Ca atoms to form CaSr6Ca6 cuboctahedra that share corners with five equivalent SrSr10Ca6 cuboctahedra, corners with twelve CaSr6Ca6 cuboctahedra, edges with ten SrSr6Ca6 cuboctahedra, edges with twelve CaSr6Ca6 cuboctahedra, faces with six equivalent CaSr6Ca6 cuboctahedra, and faces with fifteen SrSr6Ca6 cuboctahedra. All Ca–Sr bond lengths are 4.08 Å. All Ca–Ca bond lengths are 4.08 Å. In the third Ca site, Ca is bonded to six Sr and six equivalent Ca atoms to form CaSr6Ca6 cuboctahedra that share corners with five equivalent SrSr10Ca6 cuboctahedra, corners with twelve CaSr6Ca6 cuboctahedra, edges with ten SrSr6Ca6 cuboctahedra, edges with twelve CaSr6Ca6 cuboctahedra, faces with six equivalent CaSr6Ca6 cuboctahedra, and faces with fifteen SrSr6Ca6 cuboctahedra. All Ca–Ca bond lengths are 4.08 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrCa by Materials Project

SrCa is beta-prime cadmium gold-like structured and crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. Sr is bonded in a distorted body-centered cubic geometry to four equivalent Sr and four equivalent Ca atoms. All Sr–Sr bond lengths are 3.98 Å. All Sr–Ca bond lengths are 3.93 Å. Ca is bonded in a distorted body-centered cubic geometry to four equivalent Sr and four equivalent Ca atoms. All Ca–Ca bond lengths are 3.98 Å.

36 MATERIALS SCIENCE↗
NASA NTRS2013

On-Orbit Lunar Modulation Transfer Function Measurements for the Moderate Resolution Imaging Spectroradiometer

Spatial quality of an imaging sensor can be estimated by evaluating its modulation transfer function (MTF) from many different sources such as a sharp edge, a pulse target, or bar patterns with different spatial frequencies. These well-defined targets are frequently used for prelaunch laboratory tests, providing very reliable and accurate MTF measurements. A laboratory-quality edge input source was included in the spatial-mode operation of the Spectroradiometric Calibration Assembly (SRCA), which is one of the onboard calibrators of the Moderate Resolution Imaging Spectroradiometer (MODIS). Since not all imaging satellites have such an instrument, SRCA MTF estimations can be used as a reference for an on-orbit lunar MTF algorithm and results. In this paper, the prelaunch spatial quality characterization process from the Integrated Alignment Collimator and SRCA is briefly discussed. Based on prelaunch MTF calibration using the SRCA, a lunar MTF algorithm is developed and applied to the lifetime on-orbit Terra and Aqua MODIS lunar collections. In each lunar collection, multiple scan-directionMoon-to-background transition profiles are aligned by the subpixel edge locations from a parametric Fermi function fit. Corresponding accumulated edge profiles are filtered and interpolated to obtain the edge spread function (ESF). The MTF is calculated by applying a Fourier transformation on the line spread function through a simple differentiation of the ESF. The lifetime lunar MTF results are analyzed and filtered by a relationship with the Sun-Earth-MODIS angle. Finally, the filtered lunarMTF values are compared to the SRCA MTF results. This comparison provides the level of accuracy for on-orbit MTF estimations validated through prelaunch SRCA measurements. The lunar MTF values had larger uncertainty than the SRCA MTF results; however, the ratio mean of lunarMTF fit and SRCA MTF values is within 2% in the 250- and 500-m bands. Based on the MTF measurement uncertainty range, the suggested lunar MTF algorithm can be applied to any on-orbit imaging sensor with lunar calibration capability.

Choi, Taeyong↗
NASA NTRS2008

Comparison of Terra and Aqua MODIS VIS Bands On-Orbit Response

The Moderate Resolution Imaging Spectroradiometer (MODIS) has 36 spectral bands with a total of 490 detectors, covering spectral regions in the visible (VIS), near-infrared (NIR), short-wave infrared (SWIR), mid-wave infrared (MWIR), and long-wave infrared (LWIR). MODIS is a cross-track scanning radiometer which collects data using a rotating scan mirror (both sides) over a wide range of scan angles. The VIS, NIR, and SWIR bands (bands 1-19 and 26) make measurements of daytime surface reflected radiances, thus are referred to as the reflective solar bands (RSB). MODIS was built with a complete set of on-board calibrators, capable of providing radiometric, spatial, and spectral calibration and characterization during its entire mission. The RSB on-orbit calibration is primarily provided using a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). The SD and SDSM calibration system is operated on a regular (weekly to bi-weekly) basis. The spectro-radiometric calibration assembly (SRCA) is another on-hoard calibrator that also provides RSB radiometric calibration support. For this purpose, the SRCA is operated in a radiometric mode on a monthly basis. A complete SRCA radiometric calibration is performed using different lamp configurations, or different radiance levels, to cover the range of RSB gain. Two additional SRCA modes with slightly different configurations are designed and operated for sensor on-orbit spectral and spatial characterization. In addition to its on-hoard calibrators, each MODIS makes monthly lunar observations to monitor RSB radiometric calibration stability. The MODIS lunar observations are made through its space view (SV) port at nearly the same lunar phase angles via spacecraft roll maneuvers. The SD, SRCA, and lunar measurements are made at different scan angles and data samples are collected for all spectral bands and detectors using both sides of the scan minor. Since launch, Terra and Aqua MODIS have operated successfully for more than 8 years and 6 years, respectively. Many SD/SDSM, SRCA, and lunar observations have been made by each instrument and used to derive RSB on-orbit calibration parameters, enabling corrections for sensor response changes and changes of the response versus scan angle (RVS). In general, the RSB calibration parameters are updated regularly into the MODIS Level 1B (LIB) code in support of continuous data processing for all MODIS science data products. This paper provides a brief description of MODIS RSB calibration methodologies and approaches, and summarizes on-orbit changes of their responses (gains), particularly for the VIS spectral bands.

Xiong, Xiaoxiong↗
NASA NTRSDate not supplied

Twenty Years of Terra MODIS Spatial Performance Using the Spectro-Radiometric Calibration Assembly

The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on-board the NASA’s Earth Observing System Terra satellite has continued successful Earth-sensing operations for over 20 years. To aid in its mission in providing calibrated science data to the worldwide user community, the MODIS instrument is equipped with several on-board calibrators designed to measure changes in the instrument response over time. One such calibrator is the Spectro-Radiometric Calibration Assembly (SRCA), which can provide a source signal for radiometric, spectral, or spatial characterization. When commanded into its spatial calibration mode, the SRCA is able to produce light across the MODIS band spectral range (0.412μm to 14.2μm) at a variety of signal levels thanks to several internal halogen lamps, an IR glow bar, and a neutral density filter. This signal, used in combination with commanded sub-sample measurements of the MODIS detectors, provides a basis for determining changes in the spatial performance of the MODIS spectral bands. This work summarizes the spatial calibration process using the SRCA and presents 20 years of Terra MODIS spatial performance characterized through co-registration between MODIS bands, detectors, and focal plane assemblies. Results from pre-launch testing using the Integration and Alignment Collimator and the SRCA are incorporated in the history of the Terra MODIS mission-long spatial performance. We also note modifications to the spatial characterization methodology brought on by changes to the SRCA’s operational configuration and changes to the MODIS spectral band performance, particularly after the recovery from the safe-mode event in February 2016. Results are compared against the MODIS design specifications.

MODIS↗
NASA NTRS2010

Results and Lessons from a Decade of Terra MODIS On-Orbit Spectral Characterization

Since its launch in December 1999, the NASA EOS Terra MODIS has successfully operated for more than a decade. MODIS makes observations in 36 spectral bands from visible (VIS) to longwave infrared (LWIR) and at three nadir spatial resolutions: 250m (2 bands), 500m (5 bands), and 1km (29 bands). In addition to its on-board calibrators designed for the radiometric calibration, MODIS was built with a unique device, called the spectro-radiometric calibration assembly (SRCA). It can be configured in three different modes: radiometric, spatial, and spectral. When it is operated in the spectral modes, the SRCA can monitor changes in Sensor spectral performance for the VIS and near-infrared (NIR) spectral bands. For more than 10 years, the SRCA operation has continued to provide valuable information for MODIS on-orbit spectral performance. This paper briefly describes SRCA on-orbit operation and calibration activities; it presents decade-long spectral characterization results for Terra MODIS VIS and NIR spectral bands in terms of chances in their center wavelengths (CW) and bandwidths (BW). It is shown that the SRCA on-orbit wavelength calibration capability remains satisfactory. For most spectral bands, the changes in CW and BW are less than 0.5 and 1 nm, respectively. Results and lessons from Terra MODIS on-orbit spectral characterization have and will continue to benefit its successor, Aqua MODIS, and other future missions.

Xiong, X.↗
DOE OSTI2022

Stirred-Reactor Coupon Analysis: An International Round Robin Study

The objective of this task was to determine the precision of the SRCA technique when used to determine the dilute condition corrosion rate. To this end, an interlaboratory round robin study was conducted per the instructions in ASTM Practice E691 to measure the precision with which the SRCA test method can be conducted. Twelve independent labs from eleven different institutions each evaluated four glass compositions in three different conditions. The ASTM procedures recommend at least 6 labs participate in a round robin testing the same 3 materials in the same conditions to determine precision. In this case, 12 labs each performed 12 independent tests. This was only possible thanks to the multi-glass testing capability of the SRCA test. A total of 108 duplicate pairs were used to calculate the repeatability of the tests, with the same glass tested in the same vessel, producing as identical conditions as possible for the replicates. These test results were quite tightly clustered, with a median difference from the average value of the pair of only 2.9%. Based on the calculations outlined in ASTM E177-20 and a measured standard deviation of 4.74%, the intralaboratory repeatability limit (r) was calculated to be within 13.3% of the expected value with 95% confidence level. The reproducibility limit (R) of the test was examined using all 277 data points from the round robin. Because of the differences in dissolution rates due to pH variability and intrinsically for the 12 conditions tested, the reproducibility limits for each condition and overall were calculated from the percent relative residual value for each test. The SRCA test is expected to be reproducible within 64% of the expected value with a 95% confidence level.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2004

MODIS On-orbit Spectral Calibration for the Reflective Solar Bands

The Moderate Resolution Imaging Spectroradiometer (MODIS) makes observations in 36 spectral bands with wavelengths from 0.41 to 14.5 microns. The bands with center wavelengths below 2.2 microns are referred as the reflective solar bands (RSB) with their radiometric calibration performed by a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). This paper focuses on the MODIS spectral calibration performed by its unique on-board calibrator (OBC): the Spectro-Radiometric Calibration Assembly (SRCA). When operated in the spectral mode, the SRCA acts as a monochromator with internal spherical integration source (SIS) that measures the spectral responses for all the reflective solar bands. A wavelength calibrator, a didymium filter with known spectral profile, is utilized to calibrate the wavelength scale for the grating positions during each SRCA spectral calibration activity. The capability of self-wavelength calibration allows the SRCA to track the center wavelength shifts and to monitor the spectral response changes throughout the instruments lifetime. The MODIS spectral calibration, same for both Terra and Aqua missions, is performed every three months on-orbit. An overview of MODIS spectral characterization approach and a summary of the on-orbit results will be presented in this paper.

Xiong, X.↗
NASA NTRS2020

Twenty Years of Terra MODIS Spectral Performance using the Spectro-Radiometric Calibration Assembly

The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on-board the Terra spacecraft has provided valuable Earth data to the science community for the last 20 years. Equipped with several on-board calibrators (OBCs), MODIS has continued to operate nominally since its launch in December 1999. The Spectro-Radiometric Calibration Assembly (SRCA) is one such OBC that is able to provide on-orbit measurements of the MODIS reflective solar bands (RSBs) in radiometric, spatial and spectral modes. While the SRCA is operating in spectral mode, it is able to monitor the center wavelength (CW), bandwidth (BW) and in-band relative spectral response (RSR) of most RSBs. Prelaunch measurements of the CWs, BWs and RSRs of the RSBs were performed at the system level using the Spectral measurement Assembly (SpMA). Using both the prelaunch measurements and the measurements obtained on-orbit using the SRCA, the changes in the spectral response of the MODIS reflective bands can be monitored throughout the mission. This paper will provide a brief description of the spectral calibration approach and report on-orbit changes in these spectral performance parameters and their uncertainties over the last 20 years. It will also address changes to the SRCA operation on-orbit and their impact on measured spectral calibration results. Despite two decades in orbit, the spectral responses for most Terra MODIS reflective bands continue to remain within their design specifications.

MODIS↗
NASA NTRS2016

Status of MODIS Spatial and Spectral Characterization and Performance

Since launch, both Terra and Aqua MODIS instruments have continued to operate and make measurements of the earth's top of atmospheric (TOA) radiances and reflectance. MODIS collects data in 36 spectral bands covering wavelengths from 0.41 to 14.4 microns. These spectral bands and detectors are located on four focal plane assemblies (FPAs). MODIS on-board calibrators (OBC) include a spectro-radiometric calibration assembly (SRCA), which was designed to characterize and monitor sensor spatial and spectral performance, such as on-orbit changes in the band-to-band registration (BBR), modulation transfer function (MTF), spectral band center wavelengths (CW) and bandwidths (BW). In this paper, we provide a status update of MODIS spatial and spectral characterization and performance, following a brief description of SRCA functions and on-orbit calibration activities. Sensor spatial and spectral performance parameters derived from SRCA measurements are introduced and discussed. Results show that on-orbit spatial performance has been very stable for both Terra and Aqua MODIS instruments. The large BBR shifts in Aqua MODIS, an issue identified pre-launch, have remained the same over its entire mission. On-orbit changes in CW and BW are less than 0.5 nm and 1 nm, respectively, for most VIS/NIR spectral bands of both instruments.

Link, Daniel↗