This work develops a framework for the development of an SI-traceable model of lunar irradiance over the visible-to-near-infrared (VNIR) spectral region and provides an estimate of the uncertainties in the disseminated scale. The lunar model, called the common lunar model—robotic lunar observatory (ROLO) (CLM-R), is based on revisions to the ROLO model of lunar reflectance developed by the United States Geological Survey. Inputs from several different instruments are included in its development; SI-traceable lunar measurements by the airborne-lunar spectral irradiance (air-LUSI) instrument are used to establish the absolute scale and give an estimate of the phase correction to ROLO and residual corrections to the ROLO model for lunar libration angles. Uncertainties in a disseminated lunar irradiance scale are developed using long-term lunar datasets from Moderate Resolution Imaging Spectrometers (MODISs) on NASA’s Terra and Aqua satellites. Based on lunar measurements by MODIS and the visible and infrared imaging radiometer (VIIRS) on NOAA’s Suomi National Polar-orbiting Partnership and NOAA-20 satellites, a combined standard uncertainty of less than 1% for lunar-based calibrations of satellite sensors may be achievable.

The first two Visible Infrared Imaging Radiometer Suite (VIIRS) instruments, on-board the Suomi National Polar-orbiting Partnership (SNPP) and the NOAA-20 (N20) satellites, have been operating for over 11 and 5 years since their launches on 28 October 2011 and 18 November 2017 respectively. The day-night band (DNB) onboard VIIRS is a panchromatic visible/near-infrared (Vis/NIR) channel designed to detect radiance from the brightest daytime scenes down to very dim nighttime scenes illuminated by a quarter moon. In this paper, we present the SNPP and N20 VIIRS DNB calibration results performed by the NASA VIIRS Characterization Support Team (VCST) to generate the calibration coefficient look up tables (LUTs) for the latest NASA Level 1B Collection 2 products. The differing DNB straylight contamination between VIIRS instruments is discussed along with the correction methodology and performance.

Launched on November 10, 2022, the NOAA-21 (N-21) VIIRS has successfully completed its initial post-launch testing (PLT) and intensive calibration and validation (ICV) activities. It is now operated in its nominal configuration and characterized using measurements from its on-board calibrators (OBC) and lunar observations. In this paper, we provide a brief description of N-21 VIIRS on-orbit operation and calibration activities and present results derived from its early mission performance assessments, including examples of its OBC performance, spectral band responses, as well as detector signal to noise characteristics. As shown in this paper, the overall performance of N-21 VIIRS is better than that of its predecessor currently operated on the S-NPP and comparable to the one onboard the N-20, with an exception of relatively large changes in its SWIR band responses.

The NOAA-20 (N20) satellite was launched on November 18, 2017 carrying the second Visible Infrared Imaging Radiometer Suite (VIIRS) instrument. Immediately following the launch, the VIIRS passed a series of intensive calibration and validation tests, after which regular calibration and operation activities have continued successfully for more than three years. The production of NASA Collection 2 Level 1B (C2 L1B) for N20 VIIRS began in summer 2019. In this article, we evaluate the early mission performance of the N20 VIIRS reflective solar bands (RSB) covering the first three full years of operation. The calibrated RSB gains are calculated primarily from the onboard solar diffuser (SD) and used in generating the C2 L1B reflectance and radiance products. We also show the on-orbit performance of the instrument noise, signal-to-noise ratio (SNR), and a reflectance uncertainty assessment. Comparisons are made to the first three years of operation of the first VIIRS instrument, aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite. We evaluate the long-term stability of the calibrated N20 RSB reflectance product by looking at the long-term trends of lunar observations and data from the pseudo-invariant Libya 4 desert site. The N20 RSB have had excellent early mission performance, with changes in the gain of less than 0.5% in the first three years across all detectors, stable L1B reflectance, and very stable values of detector SNR and reflectance uncertainty.

The Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-orbiting Partnership (SNPP) satellite has been on orbit for more than eight years since its launch on October 28, 2011. The VIIRS has 22 spectral bands, among which 14 are reflective solar bands (RSBs) covering a spectral range from 0.41 to 2.25 μm. The VIIRS RSBs are primarily calibrated on-orbit by an on board solar diffuser (SD) panel and an SD stability monitor (SDSM). Besides the SD and SDSM calibration, the RSBs are scheduled to view the Moon approximately monthly through the instrument's space view (SV). The lunar observations have also been used to calibrate the RSBs on-orbit since early mission. Due to the nonuniformity of the SD degradation, the calibration coefficients that are derived from the SD/SDSM calibration have long-term biases, especially at short wavelengths. In addition, the SDSM has no capability to monitor the SD degradation beyond 0.935 μm, resulting in long-term bias in the short-wave infrared bands, about 0.72% for band M8 ( 1.238 μm). These biases induce significant errors and long-term drifts in the VIIRS sensor data records (SDRs) and consequently in the environmental data records (EDRs). Unlike the SD, the Moon is a known stable target and any temporal drifts observed while viewing the Moon can be attributed to the sensor's degradation. Thus, the VIIRS lunar calibration is used to track the RSB on-orbit changes, especially to provide an accurate long-term baseline. Due to the nonuniformity of the lunar surface, the lunar irradiance, instead of the lunar radiance, is used to calibrate the RSBs. The lunar irradiance strongly depends on lunar view geometry and it is still a challenge to accurately characterize the geometric effects associated with the lunar measurements and any residual errors can induce seasonal oscillations in the derived calibration coefficients. The errors of the geometric dependence correction induce seasonal oscillations in the derived RSB lunar calibration coefficients. In this article, the algorithms for the view geometric effect correction are significantly improved, resulting in a significant reduction in the seasonal oscillations observed in the calibration coefficient time series. The lunar and SD/SDSM calibration results are properly incorporated to generate a set of hybrid calibration coefficients and implementation of these coefficients is shown to significantly improve the long-term stability of the VIIRS SDR. This is of fundamental importance in making accurate Earth observations from which reliable and high-quality science products are generated. The consequent improvements in Suomi National Polar-orbiting Partnership (SNPP) VIIRS RSB SDRs and EDRs are shown and discussed. The lunar calibration methodology can be directly applied to follow-on VIIRS instruments.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on board the Terra and Aqua spacecrafts were launched on December 18, 1999, and May 4, 2002, respectively. One of the features of the MODIS instruments is the ability to perform observations of the lunar surface from its space view (SV) port. This event is scheduled approximately once a month via a spacecraft roll maneuver, which enables the lunar phase to be confined to within 1° for each instrument. The Moon is considered to be an extremely stable reference to monitor the long-term radiometric stability of the reflective solar bands (RSB). Each MODIS instrument can also view the Moon for about four months in a year without a roll maneuver. This is caused by the intrusion of the Moon in the SV. The lunar phase angles of these unscheduled lunar observations are distributed over a wide range varying from approximately 50° to 80° for Terra MODIS and from about -80° to -50° for Aqua MODIS, where the positive phase angle refers to a waning Moon, while the negative phase angle corresponds to a waxing Moon. Together, the scheduled and unscheduled lunar observations are used to monitor the long-term radiometric stability of the RSB. Of the several challenges involved in the modeling of the lunar optical properties, such as its absolute brightness, a number of optical and view geometry effects need to be considered. These effects are much easier to characterize for the scheduled observations due to confinement of the lunar phase angles compared to those for the unscheduled intrusions of the Moon in the SV. Nevertheless, it is still a challenge to remove the view geometry effect in the calibration coefficients derived from the scheduled lunar observations and even more challenging for the unscheduled lunar intrusions. In this work, the lunar absolute irradiance is modeled using known attributes and from the lunar observations by the two MODIS instruments from the time period between the years 2005 and 2012. The model developed here attempts to mitigate for the deficiencies in the lunar irradiance measurements by the RObotic Lunar Observatory (ROLO) model, developed by the United States Geological Survey. Overall, the relative uncertainty of the ROLO model for MODIS calibration has been assessed to be about 4% for the shortest wavelength (a center wavelength of 412 nm) in the phase angle range mentioned above. With our new established lunar model, the calibration coefficients derived from the lunar observations, especially those from the unscheduled lunar observations, for the RSB of the two MODIS instruments are significantly improved for the entire mission. A good agreement is observed between the calibration coefficients derived from the scheduled and unscheduled lunar observations. Both the absolute uncertainty of the new lunar irradiance model and its relative uncertainty due to view geometry variation are much smaller than those of the current ROLO model which has been widely used for most remote sensors' lunar calibrations. Our newly developed lunar irradiance model can be applied to other remote sensors for their lunar calibrations as well. Finally, the significant improvement in the measurement of the lunar irradiance led to a polarization effect in the Moon response for MODIS to be identified. In this article, the impact of the polarization of the moonlight for the MODIS RSB is quantified. This is extremely vital as polarization effect for remote sensors such as MODIS and the follow-on suite of the Joint Polar Satellite System Visible Infrared Imaging Radiometer Suite has been found to significantly increase the calibration uncertainty, especially at short wavelengths.

Crosstalk contamination in the Moderate Resolution Imaging Spectroradiometer (MODIS) thermal emissive bands (TEBs) has been a known issue since prelaunch, that has amplified on-orbit for some of bands. A linear algorithm has been developed and successfully applied to mitigate the crosstalk effect and restore the quality and accuracy of the MODIS L1B products. Significant crosstalk effect has also been found and characterized in TEBs of the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (SNPP). NOAA-20 VIIRS, a follow-on instrument to SNPP VIIRS, was launched on November 18, 2017. In this report, it is shown that there are nonnegligible crosstalk contaminations among the TEBs of NOAA-20 VIIRS as well. They are characterized using the scheduled lunar observations and compared with those in SNPP VIIRS.

The NOAA-20 Visible Infrared Imaging Radiometer Suite (VIIRS) has been in orbit for more than two and a half years. VIIRS has 22 bands, among which 14 are reflective solar bands (RSBs) covering a spectral range from 0.41 to 2.25 μm. The RSBs are calibrated on-orbit using an onboard solar diffuser (SD), on-orbit degradation of which is tracked by an onboard SD stability monitor (SDSM). NOAA-20 VIIRS is also scheduled to view the Moon approximately monthly and the lunar observations are used to track the RSB on-orbit changes as well. Both SD and lunar calibration results for the RSBs are shown and it is demonstrated that the two sets of the calibration coefficients diverge with time, especially at short wavelengths. The divergence is due to the non-uniformity of the SD degradation, which results in a long-term bias in the calibration coefficients derived from the SD calibration. A hybrid method, which properly combines the SD and lunar calibration results, is applied to generate the RSB calibration coefficients as has been done for SNPP VIIRS RSBs. The hybrid results have both the accuracy and frequency and ensure the high quality of the VIIRS sensor data records (SDR).

We provide an overview of the progress on producing accurate global ocean color products from the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) and NOAA-20 satellites. VIIRS global ocean color products include normalized water-leaving radiance spectra nLw(l) at VIIRS five spectral bands, chlorophyll-a (Chl-a) concentration, water diffuse attenuation coefficients at 490 nm, Kd(490), and at the domain of photosynthetically available radiation (PAR), Kd(PAR). However, VIIRS-derived daily ocean color images on either SNPP or NOAA-20 have some limitations in ocean coverage due to its swath width, high sensor-zenith angle, sun glint, and cloud, etc. Merging VIIRS ocean color products derived from the SNPP and NOAA-20 significantly increases the spatial coverage of daily data images. The two VIIRS sensors on SNPP and NOAA-20 have similar sensor characteristics, and ocean color products are derived using the same Multi-Sensor Level-1 to Level2 (MSL12) ocean color data processing system. Therefore, the merged VIIRS ocean color data from the two sensors have high data quality with consistent statistical property and accuracy globally. We describe an approach to remove data gaps of missing pixels from the SNPP and NOAA-20 merged global ocean color data. Some applications using the new complete global data coverage of daily ocean color product are also presented and discussed.

A methodological variant of the standard on-orbit calibration of reflective solar bands (RSBs) is presented for the Visible Imaging Infrared Radiometer Suite (VIIRS) housed in the Suomi National Polar-orbiting Partnership (SNPP) satellite. The new variant uses the full profile of direct solar illumination of the solar diffuser (SD), including both full and partial illuminations, to characterize the on-orbit gain change of the RSBs, differing from the standard approach that uses a smaller “sweet spot” subinterval within the full-illumination stage. The extended incident angular range of the solar light requires a new characterization analysis of the impact of the transmission function of the SD screen, SD bidirectional reflectance factor (BRF), and other affected calibration steps. Instead of the standard a priori derivation of the known characterization functions for the wider range, this analysis directly characterizes their manifested impact in the instrument data through a step-by-step extraction from a selected three-year period to build up a series of intermediate functions that are applicable mission-long. This newly adopted procedure presents a significant simplification as well as more clarity of the characterization analysis. The new RSB calibration coefficient of the full-profile approach is extracted for all 14 RSBs of SNPP VIIRS and is shown to be stable and smooth at the level of 0.1%. For bands M5 and above, the full-profile result achieves excellent agreement with the standard result, whereas results for bands M1-M4 diverge, in particular up to 2% for band M1, the shortest wavelength RSB at 410 nm. The finding elucidates a key challenge of the on-orbit RSB calibration arising from the nontrivial angular dependence of the on-orbit degradation of SD that introduces calibration error into any SD-based approach, such that the on-orbit RSB calibration result is not stable with different choices of the angular range of incident and outgoing light with respect to the SD. A detailed discussion of the nontrivial angular dependence in SD degradation is provided in the context of the known on-orbit RSB calibration results and recent findings, including discrepancy with the lunar-based calibration for bands M1-M4.

In this paper, we provide an overview of the progress on producing accurate global ocean color products from the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) and NOAA-20 satellites. SNPP and NOAA-20 were launched on October 28, 2011 and November 18, 2017, respectively. VIIRS global ocean color products include normalized water-leaving radiance spectra nLw(λ) at VIIRS five spectral bands, chlorophyll-a (Chl-a) concentration, water diffuse attenuation coefficients at the wavelength of 490 nm, Kd(490), and at the domain of photosynthetically available radiation (PAR), Kd (PAR). In addition, new products of nLw(λ) at VIIRS I-band (638 nm for SNPP and 642 nm for NOAA-20) and quality assurance (QA) score are now included. VIIRS global ocean color products are being routinely produced using the Multi-Sensor Level-l to Level-2 (MSL12) ocean color data processing system. Specifically, we describe our effort for the improvements of MSL12, particularly over coastal and inland waters, as well as some evaluations with in situ data from the Marine Optical Buoy (MOBY). Furthermore, we provide VIIRS ocean color data from both SNPP and NOAA-20, as well as from merged global Chl-a data from two VIIRS sensors, showing significantly improved data coverage. Some examples from the recently developed data gap-filling technique for VIIRS-SNPP are also presented and discussed.

In this paper, we provide an overview of the progress on producing accurate and consistent ocean color products from the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP). To meet requirements from broad users (e.g., operational, research, modeling, etc.), we have proposed and now been routinely producing two VIIRS ocean color data streams, i.e., the near-real-time (NRT) and delayed science quality ocean color product data. The implementation details for the two data streams will be discussed. In addition, with significantly improved satellite data processing algorithms, as well as considerably improved sensor on-orbit radiometer calibration using both solar and lunar methods, VIIRS mission-long ocean color data have been successfully reprocessed using the Multi-Sensor Level-1 to Level-2 (MSL12) ocean color data processing system. VIIRS ocean color data have been significantly improved over the global open ocean, as well as turbid coastal and inland waters. In particular, VIIRS-derived water property data over global high altitude lakes (e.g., Lake Victoria in South Africa) are now very much improved, providing a significant progress for satellite remote sensing of inland water properties. Some detailed evaluation of VIIRS ocean color products, as well as sensor performance, will be discussed. Results show that VIIRS can provide high-quality global ocean color products in support of the science researches and operational applications.

In this paper, we provide overview of the progress on the evaluations of the Visible Infrared Imaging Radiometer Suite (VIIRS) ocean color products with long-term time series and more in situ data for matchup analysis. Specifically, VIIRS ocean color products include normalized water-leaving radiance spectra nLw(λ) at VIIRS five spectral bands, chlorophyll-a concentration (Chl-a), water diffuse attenuation coefficients at the wavelength of 490 nm, Kd(490), and at the domain of photosynthetically available radiation (PAR), Kd(PAR). VIIRS ocean color products derived from the NOAA Multi-Sensor Level-1 to Level-2 (MSL12) ocean color data processing system are evaluated and compared routinely with in situ data from the Marine Optical Buoy (MOBY) and several AERONET-OC sites. In order to meet requirements from all users, we propose to routinely produce two ocean color data streams, i.e., the near-real-time (NRT) data and delayed science quality data. The NRT ocean color data stream has the advantage of quick data turn around with data latency −12–24 hours, while the science quality data stream has high consistence (with the mission-long data reprocessing) and accuracy of ocean color products. In addition, we have significantly improved on-orbit sensor calibration by combining the lunar calibration into the current solar calibration method. Our results show that VIIRS is now providing high-quality global ocean color products in support of the scientific research and operational applications.

The Suomi National Polar-orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) has successfully operated for more than three years since its launch in October 2011. Fifteen of the 22 VIIRS spectral bands are in the reflective solar spectral region, covering wavelengths from 0.41 to 2.3 μm. Similar to its heritage sensor, i.e., Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA Terra and Aqua spacecraft, the measurements of these spectral bands are routinely calibrated on orbit by a solar diffuser (SD) and an SD stability monitor (SDSM) system. In addition, lunar observations are regularly scheduled and implemented, allowing the reflective solar band (RSB) calibration stability to be independently monitored. This paper provides an overview of VIIRS RSB on-orbit calibration activities and methodologies, with a focus on the approaches and strategies developed for the lunar calibration. Results derived from VIIRS lunar observations are used to assess its RSB on-orbit performance and to compare with that derived from the SD measurements. Also discussed in this paper are issues identified since launch through comparisons of VIIRS SD and lunar calibration, remaining challenges, and future improvements. Specifically, potential impacts due to degradation caused by the telescope mirror coating contamination on both SD and lunar calibration are assessed. As demonstrated in this paper, VIIRS lunar calibration activities have been successfully planned and executed, in support of its RSB on-orbit calibration. Overall, the long-term response trending derived from lunar calibrations has been consistent with that derived from SD observations. In addition to small features in SD measurements, noticeable seasonal variations, on the order of 1%, between the lunar measurements and the model have been identified. These variations are likely due to the effect of different lunar viewing angles on the lunar irradiance reference model. Future improvements to the sensor's lunar response trending could be achieved with an improved lunar irradiance model.

The Visible Infrared Imager Radiometer Suite (VIIRS) has been on-orbit for more than three and half years. It has been scheduled to view the moon approximately monthly since its nadir door open on November 21, 2011. The scheduled lunar observations have been used to monitor the VIIRS reflective solar bands (RSB) on-orbit gain changes. The VIIRS RSB are primarily calibrated by an onboard Solar Diffuser (SD) panel and an accompanying Solar Diffuser Stability Monitor (SDSM). Due to non-uniformity of the SD degradation, the SD/SDSM calibration may have non-negligible errors, especially for the short wavelength bands. Since lunar surface is very stable, the Moon can be used to provide more reliable on-orbit long-term gain changes of the RSB. The RSB calibration coefficients derived from the lunar calibration are generally consistent with those derived from the SD/SDSM calibration, but clear differences in trend are seen, especially for the short wavelength bands.

The reflective solar bands (RSB) of the Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-orbiting Partnership (SNPP) satellite are primarily calibrated on-orbit by a solar diffuser (SD) panel whose performance is monitored by an accompanying solar diffuser stability monitor (SDSM). In this paper, the SD and SDSM calibration methodology is reviewed and the results from the analysis of the up-to-date three and half years of mission data are presented. With the newly derived product of the SD bidirectional reflectance factors, the vignetting functions for the screens in the SD/SDSM system and the carefully selected “sweet spots”, and the fully illumination region, the artificial seasonal patterns and noises in the derived SD degradation and the RSB calibration coefficients are removed or significantly reduced. The result shows that the SD degrades faster at short wavelengths while the RSB degrades in a much complex pattern.

In this paper, we provide evaluations and assessments of the Visible Infrared Imaging Radiometer Suite (VIIRS) ocean color products, including normalized water-leaving radiance spectra nLw(λ) at VIIRS five spectral bands, chlorophyll-a concentration (Chl-a), water diffuse attenuation coefficients at the wavelength of 490 nm, Kd(490), and at the domain of photosynthetically available radiation (PAR), Kd(PAR). Specifically, VIIRS ocean color products derived from the NOAA Multi-Sensor Level-1 to Level-2 (MSL12) ocean color data processing system are evaluated and compared with in situ data from the Marine Optical Buoy (MOBY) and measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS). In general, VIIRS ocean color products are matched well with MOBY in situ measurements, and are also consistent with those from MODIS-Aqua. Ocean color products were found to be highly sensitive to some operational sensor calibration issues. We have improved sensor calibration by combining the lunar calibration into the current calibration method. Here, the ocean color products based on the new sensor calibration are evaluated. Our results show that VIIRS is capable of providing high-quality global ocean color products in support of the scientific research and operational applications.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key instrument onboard the Suomi National Polar-orbiting Partnership (S-NPP) spacecraft that was launched on October 28, 2011. VIIRS is designed to provide top of the atmosphere radiometric measurements and imaging of the entire planet Earth twice daily. It is a wide-swath (3040 km) cross-track scanning radiometer with spatial resolutions of 375 and 750 m at nadir for imaging and moderate bands, respectively. It has 22 spectral bands covering the spectrum between 0.4 and 12.5 μm, including 15 reflective solar bands and 7 thermal emissive bands. VIIRS observations are used to generate 22 environmental data records used by various operational applications and for climate research. This paper describes the prelaunch radiometric calibration and characterization methodologies used by the NASA VIIRS Characterization Support Team, including performance assessments for the reflective and emissive band radiometric calibration, the signal-to-noise ratios, dual gain transition, and dynamic range. Other aspects of the sensor performance such as scattered light response, response versus scan angle, polarization sensitivity, relative spectral response, and crosstalk will also be briefly described. A comprehensive set of performance metrics generated during the prelaunch testing program will be compared to the sensor requirements, and a list of lessons learned will be presented to enhance testing and performance assessment for future Joint Polar-Orbiting Satellite System VIIRS sensors.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is a whisk broom scanning radiometer, which is onboard the Terra and Aqua spacecraft. Both MODIS instruments have successfully completed more than 12 years of on-orbit flight. The long-wave infrared (LWIR) photovoltaic bands (bands 27-30, 6.72-9.73 μm) on the LWIR focal plane assembly in Terra MODIS have contamination due to electronic crosstalk. In this paper, we examine Terra MODIS band 28 (7.33 μm) crosstalk effects, their impact, and mitigation. The crosstalk signal is identified and characterized using the regular lunar observations acquired by MODIS. It is evident from the derived crosstalk coefficients that the contamination was mainly from bands 27 (6.72 μm), 29 (8.55 μm), and 30 (9.73 μm). The crosstalk coefficients are generally a small positive quantity in the early to middle part of the mission with a few exceptions, and then changing directions. A linear correction algorithm is applied to both L1B calibration and retrieval to qualitatively and quantitatively assess the impact and improvements in this paper. It is shown that the crosstalk correction improved the imagery and radiometric fidelity of this band.

The Visible Infrared Imaging Radiometer Suite (VIIRS) Raw Data Records (or Level-0 data) are processed using the current standard Algorithm Development Library (ADL) to produce Sensor Data Records (SDR; or Level-1B data). The ocean color Environmental Data Records (EDR), one of the most important product sets derived from VIIRS, are processed from the SDR of the visible and near-infrared moderate resolution (M) bands. As the ocean color EDR are highly sensitive to the quality of the SDR, the bands from which the EDR data arise must be accurately calibrated. These bands are calibrated on-orbit using the onboard Solar Diffuser, and the derived calibration coefficients are called F-factors. The F-factors used in the forward operational process may have large uncertainty due to various reasons, and thus, to obtain high-quality ocean color EDR, the SDR needs to be regularly reprocessed with improved F-factors. The SDR reprocessing, however, requires tremendous computational power and storage space, which is about 27 TB for one year of ocean-color-related SDR data. In this letter, we present an efficient and robust method for reduction of the computational demand and storage requirement. The method is developed based on the linear relationship between the SDR radiance/reflectance and the F-factors. With this linear relationship, the new SDR radiance/reflectance can be calculated from the original SDR radiance/reflectance and the ratio of the updated and the original F-factors at approximately 100th or less of the original central processing unit requirement. The produced SDR with this new approach fully agrees with those generated using the ADL package. This new approach can also be implemented to directly update the SDR in the EDR data processing, which eliminates the hassle of a huge data storage requirement as well as that of intensive computational demand. This approach may also be applied to other remote sensors for data reprocessing from raw instrument data to science data.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments currently operate onboard the National Aeronautics and Space Administration (NASA's) Terra and Aqua spacecraft, launched on December 18, 1999 and May 4, 2002, respectively. MODIS has 36 spectral bands, among which 20 are reflective solar bands (RSBs) covering a spectral range from 0.412 to 2.13 μm. The RSBs are calibrated on orbit using a solar diffuser (SD) and an SD stability monitor and with additional measurements from lunar observations via a space view (SV) port. Selected pseudo-invariant desert sites are also used to track the RSB on-orbit gain change, particularly for short-wavelength bands. MODIS views the Earth surface, SV, and the onboard calibrators using a two-sided scan mirror. The response versus scan angle (RVS) of the scan mirror was characterized prior to launch, and its changes are tracked using observations made at different angles of incidence from onboard SD, lunar, and Earth view (EV) measurements. These observations show that the optical properties of the scan mirror have experienced large wavelength-dependent degradation in both the visible and near infrared spectral regions. Algorithms have been developed to track the on-orbit RVS change using the calibrators and the selected desert sites. These algorithms have been applied to both Terra and Aqua MODIS Level 1B (L1B) to improve the EV data accuracy since L1B Collection 4, refined in Collection 5, and further improved in the latest Collection 6 (C6). In C6, two approaches have been used to derive the time-dependent RVS for MODIS RSB. The first approach relies on data collected from sensor onboard calibrators and mirror side ratios from EV observations. The second approach uses onboard calibrators and EV response trending from selected desert sites. This approach is mainly used for the bands with much larger changes in their time-dependent RVS, such as the Terra MODIS bands 1-4, 8, and 9 and the Aqua MODIS bands 8 and 9. In this paper, the algorithms of these approaches are described, their performance is demonstrated, and their impact on L1B products is discussed. In general, the shorter wavelength bands have experienced a larger on-orbit RVS change, which, in general, are mirror side and detector dependent. The on-orbit RVS change due to the degradation of band 8 can be as large as 35% for Terra MODIS and 20% for Aqua MODIS. Vital to maintaining the accuracy of the MODIS L1B products is an accurate characterization of the on-orbit RVS change. The derived time-independent RVS, implemented in C6, makes an important improvement to the quality of the MODIS L1B products.

The MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands, covering a wavelength range from 0.4 to 14.4 μm. Terra MODIS band 27 (6.72 μm), a water vapor band, was found to have electronic crosstalk from other bands located on the same focal plane assembly, which causes surface feature contamination and pronounced detector level striping in the images. In a previous study, an algorithm using a linear approximation derived from on-orbit lunar observations was developed to correct the crosstalk effect. Results demonstrated that the correction substantially reduces the striping and removes the contaminated surface features. However, it was also demonstrated that the crosstalk effect might bring about a long-term increase in the brightness temperatures (BTs) in Terra band 27. In this paper, it is shown that there is a long-term drift (or decrease), which is strongly detector dependent, in the BT for the band induced by the crosstalk effect. It is also shown that the crosstalk correction with the linear algorithm substantially removes the detector-dependent long-term drift and greatly improves the radiometric accuracy of the band. The comparison between the BT of Terra band 27 in the most recent MODIS Level 1B (L1B) collection [Collection 6 (C6)] and those from the Infrared Atmospheric Sounding Interferometer using simultaneous-nadir-overpass observations shows that the detector-averaged long-term drift in the BT in Terra band 27 varies from approximately 1 K to 3 K. The detector difference can be as large as 9 K for a few detectors during the last five years in the northern and southern polar areas. With crosstalk correction applied, the long-term drift is reduced to be less than 0.5 K, and the detector difference is within 1 K. The crosstalk effect-induced detector-dependent long-term drift in Terra band 27 and the capability of the crosstalk correction algorithm to remove the drift are also assessed at three well-characterized sites with different radiance levels, namely, Dome Concordia (Dome C), Libya 1, and the Pacific Ocean at various radiometric levels. The long-term drift and the strong detector dependence of the drift are clearly observed at the three sites with the BT in the Terra band 27 C6 L1B products. The band-averaged BT drifts are about 0.8 K, 5 K, and 5.5 K, and the detector differences can be as large as 4 K, 12 K, and 15 K, respectively, for the three sites. With the crosstalk correction applied, the long-term drifts in the BT over the three sites are substantially removed, and the observed detector differences of Terra band 27 at the three sites are also significantly reduced. The crosstalk correction greatly improves the radiometric accuracy of the band as well as the image quality.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the National Aeronautics and Space Administration Earth observing system. The first MODIS instrument was launched in December, 1999 onboard the Terra spacecraft. MODIS has 36 bands, covering a wavelength range 0.4-14.4 μm. MODIS band 27 (6.72 μm) is a water vapor band, which is designed to be insensitive to Earth surface features. In recent Earth view images of Terra band 27, surface feature contamination is clearly seen with pronounced striping. In this paper, it is shown that these band-27 issues are caused by electronic crosstalk from bands 28-30. An algorithm using a linear approximation is developed to correct the crosstalk effect. The crosstalk coefficients are derived from Terra MODIS lunar observations. They show that the crosstalk is strongly detector-dependent and the crosstalk pattern has changed in a noticeable fashion since launch. The crosstalk contributions were positive to the instrument response of band 27 early in the mission but became negative and much larger in magnitude at later stages of the mission for most detectors of the band. The algorithms are applied to both the black body (BB) calibration and the MODIS L1B calibrated products. With the crosstalk effect significantly removed, the calibration coefficients of Terra MODIS band 27 derived from the BB show that the detector differences become smaller. With the algorithms applied to MODIS L1B products, the Earth surface features are significantly removed, thereby restoring the radiometric balance of the band and substantially reducing the striping features in the image.

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (S-NPP) spacecraft was launched on October 28, 2011. The S-NPP is orbiting the Earth in a sun-synchronous plane with nominal 13:30 local equatorial crossing time. The VIIRS nadir aperture door was opened on November 21, followed by cryo-cooler door opening on January 18, 2012. The NASA VCST team has carried out a series of VIIRS pre-launch and on-orbit calibration activities and analyses in support of the sensor data records validation and improvement. The sensor and its on-board calibrators have been successfully operated for more than one and a half years.

Since launch, Terra and Aqua MODIS have successfully operated for more than 13 and 11 years, respectively. MODIS observations, made in 36 spectral bands covering wavelengths from visible to long-wave infrared, have enabled a broad range of science and research activities and made significant contributions to the earth remote sensing applications. MODIS on-orbit calibration is performed by a set of on-board calibrators (OBC). In addition, lunar observations are made regularly to monitor sensor radiometric calibration stability. This paper provides an overview of the Terra and Aqua MODIS instrument operation and calibration activities, and summarizes their radiometric calibration performance. Also discussed in this paper are the latest changes made in MODIS L1B collection 6 (C6), remaining challenging issues, and future calibration effort.

As a key instrument for NASA's Earth Observing System (EOS), the Moderate Resolution Imaging Spectroradiometer (MODIS) has made significant contributions to the remote sensing community with its unprecedented amount of data products continuously generated from its observations and freely distributed to users worldwide. MODIS observations, covering spectral regions from visible (VIS) to long-wave infrared (LWIR), have enabled a broad range of research activities and applications for studies of the earth's interactive system of land, oceans, and atmosphere. In addition to extensive pre-launch measurements, developed to characterize sensor performance, MODIS carries a set of on-board calibrators (OBC) that can be used to track on-orbit changes of various sensor characteristics. Most importantly, dedicated and continuous calibration efforts have been made to maintain sensor data quality. This paper provides an overview of the MODIS calibration program, on-orbit calibration activities, methods, and performance. Key calibration results and lessons learned from the MODIS calibration effort are also presented in this paper.

Since launch, Terra and Aqua MODIS have successfully operated for more than 10 years and 8 years, respectively. Data products derived from MODIS observations have been widely distributed to the science and user community, enabling a broad range of applications. MODIS collects data in 36 spectral bands, covering wavelengths from visible (VIS) to long-wave infrared (LWIR). They are calibrated on-orbit by a set of on-board calibrators (OBC). This paper provides an overview of instrument operation, calibration, and performance, including lessons learned. Though having exceeded their design lifetime of 6 years, both Terra and Aqua MODIS continue to perform well, collect useful data, and support Earth remote sensing applications.

Aqua MODIS has successfully operated on-orbit for more than six years since its launch in May 2002, continuously making global observations and improving studies of changes in the Earth's climate and environment. Twenty of the 36 MODIS spectral bands, covering wavelengths from 0.41 to 2.2 ?m, are the reflective solar bands (RSBs). They are calibrated on-orbit using an onboard solar diffuser (SD) and an SD stability monitor. In addition, regularly scheduled lunar observations are made to track the RSB calibration stability. This paper presents Aqua MODIS RSB on-orbit calibration and characterization activities, methodologies, and performance. Included in this paper are characterizations of detector signal-to-noise ratio, short-term stability, and long-term response change. Spectral-wavelength-dependent degradation of the SD bidirectional reflectance factor and scan mirror reflectance, which also varies with the angle of incidence, is examined. On-orbit results show that Aqua MODIS onboard calibrators have performed well, enabling accurate calibration coefficients to be derived and updated for the Level 1B production and assuring high-quality science data products to be continuously generated and distributed. Since launch, the short-term response, on a scan-by-scan basis, has remained extremely stable for most RSB detectors. With the exception of band 6, there have been no new RSB noisy or inoperable detectors. Like its predecessor, i.e., Terra MODIS, launched in December 1999, the Aqua MODIS visible spectral bands have experienced relatively large changes, with an annual response decrease (mirror side 1) of 3.6% for band 8 at 0.412 ?m, 2.3% for band 9 at 0.443 ?m, 1.6% for band 3 at 0.469 ?m, and 1.2% for band 10 at 0.488 ?m. For other RSB bands with wavelengths greater than 0.5 ?m, the annual response changes are typically less than 0.5%. In general, Aqua MODIS optics degradation is smaller than Terra MODIS, and the mirror-side differences are much smaller. Overall, Aqua MODIS RSB on-orbit performance is better than that of Terra MODIS.

MODIS reflective solar bands (RSB) cover the VIS, NIR, and SWIR spectral regions. They are calibrated by a set of on-board calibrators (OBC). The 7 VIS spectral bands are located on the same focal plane assembly (FPA), with wavelengths from 0.41 to 0.56 mum. On-orbit observations show that the changes in the VIS response have been relatively large compared to the other spectral bands. This paper provides a comprehensive study of changes in the VIS response for both Terra and Aqua MODIS. It examines the differences among individual detectors within the same spectral band and between the two mirror sides. Results derived from measurements made by the instrument OBC and regularly scheduled lunar observations show that Aqua MODIS has been more stable than Terra MODIS in the VIS spectral region, with small response changes and mirror side differences over time.

Two nearly identical Moderate Resolution Imaging Spectroradiometer (MODIS) sensors, one on the Terra and the other on the Aqua satellite, are currently operating in space, making continuous global observations in 36 spectral bands: 20 reflective solar bands (RSBs) and 16 thermal emissive bands. For MODIS RSB with wavelengths from 0.41 to 2.1 mum, the sensor-specified calibration-accuracy requirements are plusmn2% for reflectance and plusmn5% for radiance products. They are calibrated on-orbit by a solar diffuser (SD) and an SD stability monitor. In addition, lunar observations are scheduled regularly to monitor the RSB radiometric calibration stability. This letter describes an intercomparison method developed for evaluating the calibration consistency between Terra and Aqua MODIS RSBs and calibration differences among detectors in each spectral band. It presents intercomparison results derived from Terra and Aqua MODIS lunar observations made over their overlapped mission operation. This method uses predicted lunar irradiances derived from a lunar model to remove lunar-viewing-geometry differences among different observations made by each sensor. The results, excluding the bands which either have electronic crosstalk or saturate during lunar observations, show that the Terra and Aqua MODIS RSBs have been consistently calibrated to within plusmn1%. For the detectors within any one spectral band, the calibration differences are less than plusmn0.5%. The methodology developed here can be applied to other sensors for intercomparison studies.

The moderate resolution imaging spectroradiometer (MODIS) is one of the primary instruments in the Earth Observing System (EOS). Currently, MODIS instruments are onboard the NASA EOS Terra and Aqua spacecraft launched in December 1999 and May 2002, respectively. The MODIS reflective solar bands (RSBs) are sensitive to the polarization of incident light, particularly for the visible bands. To derive accurate top-of-the-atmosphere radiances, it is essential to know the polarization sensitivity, characterized by a polarization factor and phase angle, of the instruments. From prelaunch polarization sensitivity measurements, the polarization factors and phase angles for all visible and near-infrared bands of both instruments are derived, analyzed, and compared. The polarization factors are wavelength, angle of incidence on the MODIS scan mirror, and detector-dependent. For Terra MODIS, they are also mirrorside-dependent. The 412-nm band has the largest polarization factor, which is about 0.04 for both instruments. The polarization factors of all other bands are either smaller than or close to 0.02, which is the polarization requirement for the MODIS RSB whose wavelengths are longer than 412 nm. The unexpected one-, three-, and four-cycle anomalies observed in the measurements are analyzed. These anomalies are shown to be likely due to the nonuniformity of the light source and the retro-reflected light from the MODIS optical system. Their impacts on the derived polarization parameters are estimated and discussed.

The moderate resolution imaging spectroradiometer (MODIS) protoflight model on-board the Terra spacecraft and the MODIS flight model 1 on-board the Aqua spacecraft were launched on December 18, 1999 and May 4, 2002, respectively. They view the moon through the space view (SV) port approximately once a month to monitor the long-term radiometric stability of their reflective solar bands (RSBs). The lunar irradiance observed by MODIS depends on the viewing geometry. Algorithms were developed to select lunar views such that these geometric effects are minimized. In each MODIS lunar observation, the moon can be viewed in multiple scans. The lunar irradiance of a MODIS RSB can be derived from the response of all detectors of a spectral band in one scan which fully covers the moon, from that of one detector in multiple scans or from the response of all detectors in multiple scans. Based on lunar observations, a set of coefficients is defined and derived to trend MODIS system response degradation at the angle of incidence (AOI) of its SV port. It is shown that the degradation is both wavelength and mirror side dependent. Since launch, Terra and Aqua MODIS band 8 (412 nm) mirror side one have degraded 36% and 17%, respectively, at the AOI of the SV. A comparison between the lunar coefficients and those derived from the MODIS on-board solar diffuser (SD) calibrations shows that the response change of the MODIS RSB is both AOI and time dependent. Time-dependent response versus scan angle (RVS) lookup tables derived from lunar views, SD calibration, and Earth-view observations have been used to maintain the quality of the L1B data for both the Terra and Aqua MODIS RSB. The corrections provided by the RVS in the Terra and Aqua MODIS data from the 412-nm band are as large as 14% and 6.2%, respectively.

Terra Moderate Resolution Imaging Spectroradiometer (MODIS) has made continuous global observations for more than six years since its launch in December 1999. MODIS has 36 spectral bands: 20 reflective solar bands (RSBs) with wavelengths from 0.41-2.2 mum and 16 thermal emissive bands with wavelengths from 3.7-14.4 mum. It is a cross-track scanning radiometer that collects data at three nadir spatial resolutions: 0.25 km (2 bands), 0.5 km (5 bands), and 1 km (29 bands). An onboard solar diffuser (SD) and an SD stability monitor (SDSM) are used biweekly for RSB on-orbit radiometric calibration. Another onboard calibrator (OBC), a spectroradiometric calibration assembly, is used periodically to evaluate and monitor RSB spatial and spectral performance. In addition to measurements made using OBCs, lunar observations at nearly identical phase angles are used to track RSB calibration stability. This paper provides an overview of MODIS RSB on-orbit calibration algorithms and operational activities. It discusses sensor characteristics that could impact RSB calibration accuracy and data product quality, including degradation of the SD bidirectional reflectance factor (BRF), degradation of the scan mirror reflectance in the visible spectral region, and changes in operational configuration. The Terra MODIS OBCs have performed well in monitoring SD degradation and tracking changes in RSB response. Band 8 (0.41 mum) has experienced the largest response decrease with an approximate annual rate of 4.5% (mirror side 1). Band 9 (0.44 mum) has an annual response decrease of about 2.3% (mirror side 1). For most RSB bands with wavelengths greater than 0.5 mum, the annual response changes are generally less than 1.0%. Results from the SDSM on-orbit observations show that the SD BRF also has a similar wavelength-dependent degradation, with the largest degradation appearing at the shortest wavelengths. Among the 330 RSB detectors, there are no inoperable detectors, and only a few noisy detectors have appeared postlaunch

The first MODIS instrument was launched aboard NASA's EOS Terra spacecraft in December 1999. MODIS has 20 reflective solar bands (RSB) with wavelengths from 0.41 to 2.2 mum and nadir spatial resolutions of 0.25 km, 0.5 km, and 1.0 km. It also has 16 thermal emissive bands (TEB) with wavelengths from 3.7 to 14.4 mum, all with 1.0 km spatial resolution. MODIS RSB on- orbit calibration and characterization are performed periodically using a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). Another on-board calibrator, a spectro-radiometric calibration assembly (SRCA), is used for the sensor's spatial and spectral characterization. In addition to the SD/SDSM system, regularly scheduled lunar observations via spacecraft maneuvers are added to monitor RSB radiometric calibration stability. This paper provides an overview of Terra MODIS RSB calibration methodologies, operational activities, and on-orbit performance from its observations over 6 years. On-orbit results show that the Terra MODIS RSB calibrators have been performing well in tracking changes of detectors' responses and producing useful data sets to maintain RSB calibration and associated data product quality.

The Moderate Resolution Imaging Spectroradiometer (MODIS) makes observations using 36 spectral bands with wavelengths from 0.41 to 14.4 m and nadir spatial resolutions of 0.25km, 0.5km, and 1km. It is currently operating onboard the NASA Earth Observing System (EOS) Terra and Aqua satellites, launched in December 1999 and May 2002, respectively. The MODIS Level 1B (L1B) program converts the sensor's on-orbit responses in digital numbers to radiometrically calibrated and geo-located data products for the duration of each mission. Its primary data products are top of the atmosphere (TOA) reflectance factors for the sensor's reflective solar bands (RSB) and TOA spectral radiances for the thermal emissive bands (TEB). The L1B algorithms perform the TEB calibration on a scan-by-scan basis using the sensor's response to the on-board blackbody (BB) and other parameters which are stored in Lookup Tables (LUTs). The RSB calibration coefficients are processed offline and regularly updated through LUTs. In this paper we provide a brief description of the MODIS L1B calibration algorithms and associated LUTs with emphasis on their recent improvements and updates developed for the MODIS collection 5 processing. We will also discuss sensor on-orbit calibration and performance issues that are critical to maintaining L1B data product quality, such as changes in the sensor's response versus scan-angle.

The Moderate Resolution Imaging Spectroradiometer (MODIS) reflective solar bands (RSBs) are calibrated on-orbit using an onboard solar diffuser (SD) panel, made of Spectralon. An onboard Solar Diffuser Stability Monitor (SDSM) tracks the SDs degradation. The SDSM views the sun through a 1.44% attenuation screen during SD calibration. The observed SDSM sun view response has shown serious unexpected ripples that are as large as 10% of the averaged response and consequently disable the originally designed SD degradation tracking algorithms. In this report, a model based on geometric factors and design parameters is developed to simulate the SDSM sun view response. It is shown that the ripples are induced by erroneous design parameters and incorrect installation of the involved optical elements. The model could be used to improve the MODIS SD calibration and to provide helpful information for the design of future remote sensing systems.

Solar diffusers (SD) are frequently used for the on-orbit calibration of reflective solar bands in space-born remote sensing radiometers. To avoid sensor saturation due to viewing directly reflected sunlight on to the SD while keeping the same optical path and field of view as the scene observations, an attenuation screen, consisting of a two dimensional array of pinholes, is often used in front of the solar diffuser. The screen is either fixed or retractable. The illumination on the SD through the screen pinholes is not uniform due observation geometry and the moving spacecraft platform. We illustrate the effect of the SD screen on the sensor's radiometric calibration by examining the sensor's response variation using actual on-orbit observations taken from the NASA's EOS MODIS. Lessons learned from this analysis will undoubtedly benefit future design and applications.