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Summary of the Ninth DSCOVR EPIC and NISTAR Science Team Meeting

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Summary of the Ninth DSCOVR EPIC and NISTAR Science Team Meeting

Introduction

The ninth Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Camera (EPIC) and National Institute of Standards and Technology (NIST) Advanced Radiometer [NISTAR] Science Team Meeting (STM) was held virtually October 16–17, 2023. Over 35 scientists attended, most of whom were from NASA’s Goddard Space Flight Center (GSFC), with several participating from other NASA field centers, U.S. universities, and U.S. Department of Energy laboratories. One international participant joined the meeting from Estonia. A full overview of DSCOVR’s Earth-observing instruments was printed in a previous article in The Earth Observer and will not be repeated here. This article provides the highlights of the 2023 meeting. The meeting agenda and full presentations can be downloaded from GSFC’s Aura Validation Data Center.

Opening Presentations

The opening session consisted of a series of presentations from DSCOVR mission leaders and representatives from GSFC and NASA Headquarters (HQ), who gave updates on the mission and the two Earth-viewing science instruments on board. Alexander Marshak [GSFC—DSCOVR Deputy Project Scientist] opened the meeting. He discussed the agenda for the meeting and mentioned that both Earth science instruments on DSCOVR are functioning normally – see Figure 1. At this time, more than 115 papers related to DSCOVR are listed on the EPIC website. Marshak emphasized the importance of making the Earth Science community more aware of the availability of the various EPIC and NISTAR science data products.

DSCVR figure 1
Figure 1. Sun-Earth-Vehicle (SEV) angle (red curve) and the distance between Earth and the DSCOVR satellite (blue curve) versus time starting from the DSCOVR launch on February 15, 2015 to April 1, 2024. These two measurements are used to track the location and orientation, respectively, of DSCOVR. The spacecraft changes its location by about 200,000 km (~124,274 mi) over about a 3-month period, and its SEV gets close to zero (which would correspond to perfect backscattering). The gap around the year 2020 was when DSCOVR was in Safe Mode for an extended period.
Figure credit: Adam Szabo (Original figure by Alexander Marshak, with data provided by Joe Park/NOAA)

Adam Szabo [GSFC—DSCOVR Project Scientist] welcomed the STM participants and briefly reported that the spacecraft, located at “L1” – the first of five Lagrange points in the Sun-Earth system – was still in “good health.” The EPIC and NISTAR instruments on DSCOVR continue to return their full science observations. Szabo gave an update on the 2023 Earth Science Senior Review, which DSCOVR successfully passed with overall science scores of ‘Excellent/Very Good.’ The Senior Review Panel unanimously supported the continuation of DSCOVR for the 2024–2026 period.

Thomas Neumann [GSFC, Earth Sciences Division (ESD)—Deputy Director] welcomed meeting participants on behalf of the ESD. Neumann noted the impressive engineering that has led to 8.5 years of operations and counting. He also commended the team on the continued production of important science results from these instruments – with nearly 110 papers in the peer-reviewed literature.

Following Neumann’s remarks, Steve Platnick [GSFC, Earth Sciences Division—Deputy Director for Atmospheres] welcomed the members of the DSCOVR ST as well as users of EPIC and NISTAR observations. He thanked NASA HQ for its continued strong interest in the mission. Platnick also expressed his appreciation for the mission team members who have worked hard to maintain operation of the DSCOVR satellite and instruments during this challenging time.

Richard Eckman [NASA HQ, Earth Science Division—DSCOVR EPIC/NISTAR Program Scientist] noted that a new call for proposals will be in ROSES-2025 and looks forward to learning about recent accomplishments by ST members, which will be essential in assessing the mission’s performance.

Jack Kaye [NASA HQ, Earth Science Division—Associate Director for Research] discussed the NASA research program that studies the Earth, using satellites, aircraft, surface-based measurements, and computer models. The two Earth science instruments on DSCOVR (EPIC and NISTAR) play an important role in the program. He highlighted the uniqueness of the DSCOVR observations from the Sun–Earth “L1” point providing context for other missions and the ability to discern diurnal variations.

Updates on DSCOVR Operations

The DSCOVR mission components continue to function nominally, with progress on several fronts, including data acquisition, processing, archiving, and release of new versions of several data products. The number of people using the content continues to increase, with a new Science Outreach Team having been put in place to aid users in several aspects of data discovery, access, and user friendliness.

Hazem Mahmoud [NASA’s Langley Research Center (LaRC)] discussed the new tools in the Atmospheric Science Data Center (ASDC). He reported on DSCOVR metrics since 2015 and mentioned the significant increase in using ozone (O3) products. He also announced that ASDC is moving to the Amazon Web Services (AWS) cloud.

Karin Blank [GSFC] covered the EPIC geolocation algorithm, including the general algorithm framework. She highlighted additional problems that needed to be resolved and detailed the various stages to refine the algorithm, emphasizing the enhancements made to improve geolocation accuracy.

Marshall Sutton [GSFC] reported on the DSCOVR Science Operations Center (DSOC) and Level-2 (L2) processing. DSOC is operating nominally. EPIC L1A, L1B, and NISTAR data files are produced daily. EPIC L1 products are processed into L2 science products using the computing power of the NASA Center for Climate Simulations (NCCS). Products include daily data images, including a cloud fraction map, aerosol map, and the anticipated aerosol height image. In addition, Sutton reported that the DSCOVR spacecraft has enough fuel to remain in operation until 2033.

EPIC Calibration

Alexander Cede [SciGlob] and Ragi Rajagopalan [LiftBlick OG] reported on the latest EPIC calibration version (V23) that includes the new flat field corrections based on the lunar observations from 2023 and an update to the dark count model. The EPIC instrument remains healthy and shows no change in parameters, e.g., read noise, enhanced or saturated pixels, or hot or warm pixels. The current operational dark count model still describes the dark count in a satisfactory way.

Liang-Kang Huang [Science Systems and Applications, Inc. (SSAI)] reported on EPIC’s July 2023 lunar measurements, which filled in the area near diagonal lines of the charged coupled device (CCD) not covered by 2021 and 2022 lunar data. With six short wavelength channels ranging from 317 to 551 nm, the two sets of lunar data are consistent with each other. For the macroscopic flat field corrections, he recommended the six fitted sensitivity change functions of radius and polar angle. 

Igor Geogdzhaev [NASA’s Goddard Institute for Space Studies (GISS)/Columbia University] reported how continuous EPIC observations provide stable visible and near infrared (NIR) channels compared to the contemporaneous data from Visible Infrared Imaging Radiometer Suite (VIIRS) on NASA’s Suomi National Polar-orbiting Partnership (Suomi NPP) and the NASA–National Oceanic and Atmospheric Administration (NOAA) Joint Polar Satellite System (JPSS) missions. (To date, two JPSS missions have launched, JPSS-1, which is now known as NOAA-20, and JPSS-2, which is now known as NOAA-21.) Analysis of near simultaneous data from EPIC and from the Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellite–R (GOES R) platforms showed a high correlation coefficient, good agreement between dark and bright pixels, and small regression zero intercepts. EPIC moon views were used to derive oxygen (O2) channel reflectance by interpolation of the calibrated non-absorbing channels.

Conor Haney [LaRC] reported that the EPIC sensor was intercalibrated against measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua platforms as well as from VIIRS on Suomi NPP and NOAA-20, using ray-matched pair radiances, and was found to be radiometrically stable when tested against two invariant calibration targets: over deep convective clouds over the tropical Pacific (dark target) and over the Libya-4 site located in the Libyan desert in Africa (bright target). The ray-matched and Earth target EPIC gain trends were found to be consistent within 1.1%, and the EPIC sensor degradation was found to be less than 1% over the seven-year record. Preliminary results intercalibrating EPIC with the Advanced Himawari Imager (AHI) on the Japan Aerospace Exploration Agency’s (JAXA) “Himawari–8” Geostationary Meteorological Satellite were also promising when both subsatellite positions were close—i.e., during equinox.

NISTAR Status and Science with Its Observations

The NISTAR instrument remains fully functional and continues its uninterrupted data record. The presentations here include more details on specific topics related to NISTAR as well as on efforts to combine information from both EPIC and NISTAR.

Steven Lorentz [L-1 Standards and Technology, Inc.] reported that NISTAR has been measuring the irradiance from the Sun-lit Earth in three bands for more than eight years. The bands measure the outgo­ing reflected solar and total radiation from Earth at a limited range of solar angles. These measurements assist researchers in answering questions addressing Earth radiation imbalance and predicting future climate change. NISTAR continues to operate nominally, and the team is monitoring any in-orbit degradation. Lorentz explained the evolution of the NISTAR view angle over time. He also provided NISTAR shortwave (SW) and photodiode (PD) intercomparison. NISTAR has proven itself to be an extremely stable instrument – although measurements of the offsets have measurement errors. A relative comparison with the scaled-PD channel implies long-term agreement below a percent with a constant background.

Clark Weaver [University of Maryland, College Park (UMD)] discussed updates to a new reflected- SW energy estimate from EPIC. This new product uses generic Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) aircraft observations over homogeneous scenes to spectrally interpolate between the coarse EPIC channels. This approach assumes the spectra from an EPIC pixel is a weighted combination of a solid cloud scene and the underlying (cloud-free) surface. Weaver and his team used a vector discrete ordinate radiative transfer model with a full linearization facility, called VLIDORT, to account for the different viewing/illumination geometry of the sensors. Each pixel residual between EPIC observations at six different wavelengths (between 340 and 780 nm) and the composite high-resolution spectrum from AVIRIS has been reduced by about 50%, since the last report. While the total reflected energy for a single EPIC image can be about 15 W/m2 different than the NISTAR measurement, by 2017 the offset bias was, on average, about 1 W/m2. 

Andrew Lacis [GISS] said that DSCOVR measurements of Earth’s reflected solar radiation from the “L1” position offer a unique perspective for the continuous monitoring of Earth’s sunlit hemisphere. Six years of EPIC data show the seasonal and diurnal variability of Earth’s planetary albedo – but with no discernible trend. Planetary scale variability, driven by changing patterns in cloud distribution, is seen to occur at all longitudes over a broad range of time scales. The planetary albedo variability is strongly correlated at neighboring longitudes but shows strongly anticorrelated behavior at diametrically distant longitudes.

Update on EPIC Products and Science Results

EPIC has a suite of data products available. The following subsections summarize content during the DSCOVR STM related to these products. They provide updates on several of the data products and on related algorithm improvements. 

Total Column Ozone

Natalya Kramarova [GSFC] reported on the status of the EPIC total O3 using the V3 algorithm. The absolute calibrations are updated every year using collocated observations from the Ozone Mapping and Profiling Suite (OMPS) on Suomi NPP. EPIC total O3 measurements are routinely compared with independent satellite and ground-based measurements. Retrieved EPIC O3 columns agree within ±5–7 Dobson Units (DU, or 1.5–2.5%) with independent observations, including those from satellites [e.g., Suomi NPP/OMPS, NASA’s Aura/Ozone Monitoring Instrument (OMI), European Union’s (EU) Copernicus Sentinel-5 Precursor/TROPOspheric Monitoring Instrument (TROPOMI)], sondes, and ground-based Brewer and Dobson spectrophotometers. The EPIC O3 record is stable and shows no substantial drifts with respect to OMPS. In the future, the EPIC O3 team plans to compare EPIC time resolved O3 measurements with observations from NASA’s Tropospheric Emissions Monitoring of Pollution (TEMPO) and the South Korean Geostationary Environment Monitoring Spectrometer (GEMS) – both in geostationary orbit. (Along with the EU’s Copernicus Sentinel-4 mission, expected to launch in 2024, these three missions form a global geostationary constellation for monitoring air quality on spatial and temporal scales that will help scientists better understand the causes, movement, and effects of air pollution across some of the world’s most populated areas.) 

Jerrald Ziemke [Morgan State University] explained that tropospheric column O3 is measured over the disk of Earth every 1–2 hours. These measurements are derived by combining EPIC observations with Modern-Era Retrospective Analysis for Research and Applications (MERRA2) assimilated O3 and tropopause fields. These hourly maps are available to the public from the Langley ASDC and extend over eight years from June 2015 to present. The EPIC tropospheric O3 is now indicating post-COVID anomalous decreases of ~3 DU in the Northern Hemisphere for three consecutive years (2020–2022). Similar decreases are present in other satellite tropospheric O3 products as well as OMI tropospheric nitrogen dioxide (NO2), a tropospheric O3 precursor.

Algorithm Improvement for Ozone and Sulfur Dioxide Products

Kai Yang [UMD] presented the algorithm for retrieving tropospheric O3 from EPIC by estimating the stratosphere–troposphere separation of retrieved O3 profiles. This approach contrasts with the traditional residual method, which relies on the stratospheric O3 fields from independent sources. Validated against the near-coincident O3 sonde measurements, EPIC data biased low by a few DU (up to 5 DU), consistent with EPIC’s reduced sensitivity to O3 in the troposphere. Comparisons with seasonal means of TROPOMI tropospheric O3 show consistent spatial and temporal distributions, with lows and highs from atmospheric motion, pollution, lightning, and biomass burning. Yang also showed EPIC measurements of sulfur dioxide (SO2) from recent volcanic eruptions, including Mauna Loa and Kilauea (Hawaii, U.S., 2022–2023), Sheveluch (Kamchatka, Russia, 2023), Etna (Italy, 2023), Fuego (Guatemala, 2023), Popocatépetl (Mexico, 2023), and Pavlof and Shishaldin (Aleutian Islands, U.S., 2023). Yang reported the maximum SO2 mass loadings detected by EPIC are 430 kt from the 2022 Mauna Loa and Kilauea eruptions and 351 kt from the 2023 Sheveluch eruption.

Simon Carn [University of Michigan] showed EPIC observations of major volcanic eruptions in 2022–2023 using the EPIC L2 volcanic SO2 and UV Aerosol Index (UVAI) products to track SO2 and ash emissions. EPIC SO2 and UVAI measurements during the 2023 Sheveluch eruption show the coincident transport of volcanic SO2, ash, and Asian dust across the North Pacific. The high-cadence EPIC UVAI can be used to track the fallout of volcanic ash from eruption clouds, with implications for volcanic hazards. EPIC SO2 measurements during the November 2022 eruption of Mauna Loa volcano are being analyzed in collaboration with the U.S. Geological Survey, who monitored SO2 emissions using ground-based instruments during the eruption. Carn finished by mentioning that EPIC volcanic SO2 algorithm developments are underway including the simultaneous retrieval of volcanic SO2 and ash.

Aerosols

Myungje Choi [UMD, Baltimore County (UMBC)] presented an update on the EPIC V3 Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm to optimize smoke aerosol models and the inversion process. The retrieved smoke/dust properties showed an improved agreement with long-term, ground-based Aerosol Robotic Network (AERONET) measurements of solar spectral absorption (SSA) and with aerosol layer height (ALH) measurements from the Cloud–Aerosol Lidar with Orthogonal Projection (CALIOP) on the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) mission. (Update: As of the publication of this summary, both CALIPSO and CloudSat have ended operations.) Choi reported that between 60–90% of EPIC SSA retrievals are within ±0.03 of AERONET SSA measurements, and between 56–88% of EPIC ALH retrievals are within ±1km of CALIOP ALH retrievals. He explained that the improved algorithm effectively captures distinct smoke characteristics, e.g., the higher brown carbon (BrC) fraction from Canadian wildfires in 2023 and the higher black carbon (BC) fraction from agricultural fires over Mexico in June 2023.

Sujung Go [UMBC] presented a global climatology analysis of major absorbing aerosol species, represented by BC and BrC in biomass burning smoke as well as hematite and goethite in mineral dust. The analysis is based on the V3 MAIAC EPIC dataset. Observed regional differences in BC vs. BrC concentrations have strong associations with known distributions of fuels and types of biomass burning (e.g., forest wildfire vs. agricultural burning) and with ALH retrievals linking injection heights with fire radiative power. Regional distributions of the mineral dust components have strong seasonality and agree well with known dust properties from published ground soil samples.

Omar Torres [GSFC] reported on the upgrades of the EPIC near-UV aerosol (EPICAERUV) algorithm. The EPICAERUV algorithm’s diurnal cycle of aerosol optical depth compared to the time and space collocated AERONET observations at multiple sites around the world. The analysis shows remarkably close agreement between the two datasets. In addition, Torres presented the first results of an improved UV-VIS inversion algorithm that simultaneously retrieves aerosol layer height, optical depth, and single scattering albedo.

Hiren Jethva [Morgan State University] discussed the unique product of absorbing aerosols above clouds (AAC) retrieved from EPIC near-UV observations between 340 and 388 nm. The validation analysis of the retrieved aerosol optical depth over clouds against airborne direct measurements from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) campaign revealed a robust agreement. EPIC’s unique capability of providing near-hourly observations offered an insight into the diurnal variations of regional cloud fraction and AAC over “hotspot” regions. A new and simple method of estimating direct radiative effects of absorbing aerosols above clouds provided a multiyear timeseries dataset, which is consistent with similar estimations from Aura–OMI.

Jun Wang [University of Iowa] reported on the development and status of V1 of the L2 EPIC aerosol optical centroid height (AOCH) product – which is now publicly available through ASDC – and on improvements to the AOCH algorithm – which focus on the treatment of surface reflectance and aerosols models. He presented applications of this data product for both climate studies of Sahara dust layer height and air quality studies of surface particulate matter with diameter of 2.5 µm or less (PM2.5). In addition, Wang showed the comparisons of EPIC AOCH data product with those retrieved from TROPOMI and GEMS and discussed ongoing progress to reduce the AOCH data uncertainty that is estimated to be 0.5 km (0.3 mi) over the ocean and 0.8 km (0.5 mi) over land.

Clouds

Yuekui Yang [GSFC] explained the physical meaning of EPIC cloud effective pressure (CEP) in an “apples-to-apples” comparison with CEP measurements from the Global Ozone Monitoring Experiment 2 (GOME-2) on the European Operational Meteorology (MetOp) satellites. The results showed that the two products agreed well.

Yaping Zhou [UMBC] showed how current EPIC O2 A-band and B-band use Moon calibrations due to lack of in-flight calibration and other comparable in-space instruments for absolute calibration. This approach is ineffective at detecting small changes in instrument response function (IRF). This study examined the O2 band’s calibration and stability using a unique South Pole location and Radiative Transfer Model (RTM) simulations with in situ soundings and surface spectral albedo and bidirectional reflectance distribution function (BRDF) measurements as input. The results indicate EPIC simulations are within 1% of observations for non-absorption bands, but large discrepancies exist for the O2 A-band (15.63%) and O2 B-band (5.76%). Sensitivity studies show the large discrepancies are unlikely caused by uncertainties in various input, but a small shift (-0.2–0.3 nm) of IRF could account for the model observation discrepancy. On the other hand, observed multiyear trends in O2 band ratios in the South Pole can be explained with orbital shift – which means the instrument is stable.

Alfonso Delgado Bonal [UMBC] used the EPIC L2 cloud data to characterize the diurnal cycles of cloud optical thickness. To fully exploit the uniqueness of DSCOVR data, all clouds were separated in three groups depending on their optical thickness: thin (0–3), medium (3–10), and thick (3–25). Bonal explained that there is a predictable pattern for different latitudinal zones that reaches a maximum around noon local time – see Figure 2. It was also shown that that the median is a better measure of central tendency when describing cloud optical thickness.

DSCVR Figure 2
Figure 2. Daytime variability of the median liquid cloud optical thickness over the ocean for different seasons of the year derived using EPIC L2 data. The various colored curves represent data collected in different seasons of the year. The black curve represents the annual average – which is most useful for calculations of cloud optical thickness.
Figure credit: Alfonso Delgado Bonal

Elizabeth Berry [Atmospheric and Environmental Research (AER)] reported on how coincident observations from EPIC and the Cloud Profiling Radar (CPR) on CloudSat have been used to train a machine learning model to predict cloud vertical structure. A XGBoost decision tree model used input (e.g., EPIC L1B reflectance, L2 Cloud products, and background meteorology) to predict a binary cloud mask on 25 vertical levels. Berry discussed model performance, feature importance, and future improvements.

Ocean

Robert Frouin [Scripps Institution of Oceanography, University of California] discussed ocean surface radiation products from EPIC data. He reported that surface radiation products were developed to address science questions pertaining to biogeochemical cycling of carbon, nutrients, and oxygen as well as mixed-layer dynamics and circulation. These products include daily averaged downward planar and scalar irradiance and average cosine for total light just below the surface in the EPIC spectral bands centered on 317.5, 325, 340, 388, 443, 551, and 680 nm and integrated values over the photosynthetically active radiation (PAR) and UV-A spectral ranges. The PAR-integrated quantities were evaluated against in situ data collected at sites in the North Atlantic Ocean and Mediterranean Sea. Frouin and his colleagues have also developed, tested, and evaluated an autonomous system for collecting and transmitting continuously spectral UV and visible downward fluxes. 

Vegetation

Yuri Knyazikhin [Boston University] reported on the status of the Vegetation Earth System Data Record (VESDR) and discussed science with vegetation parameters. A new version of the VESDR software was delivered to NCCS and implemented for operational generation of the VESDR product. The new version passed tests of physics (e.g., various relationships between vegetation indices and vegetation parameters derived from the VESDR) and follow regularities reported in literature. Analysis of hotspot signatures derived from EPIC and from the Multiangle Imaging Spectroradiometer (MISR) on Terra over forests in southeastern Democratic Republic of the Congo reaffirms that long-term precipitation decline has had minimal impact on leaf area and leaf optical properties.

Jan Pisek [University of Tartu/Tartu Observatory, Estonia] reported on the verification of the previously modeled link between the directional area scattering factor (DASF) from the EPIC VESDR product and foliage clumping with empirical data. The results suggest that DASF can be accurately derived from satellite observations and provide new evidence that the photon recollision probability theory concepts can be successfully applied even at a fairly coarse spatial resolution.

Sun Glint

Tamás Várnai [UMBC] discussed the EPIC Glint Product as well as impacts of sun glint off ice clouds on other EPIC data products – see Figure 3. The cloud glints come mostly from horizontally oriented ice crystals and have strong impact in EPIC cloud retrievals. Glints increase retrieved cloud fraction, the retrieved cloud optical depth, and cloud height. Várnai also reported that the EPIC glint product is now available at the ASDC. It is expected that glints yield additional new insights about the microphysical and radiative properties of ice clouds.

DSCVR figure 3
Figure 3. EPIC image taken over Mexico on July 4, 2018. The red, white and blue spot over central Mexico is the result of Sun glint reflecting off high clouds containing ice crystals. EPIC is particularly well suited for studies of ice clouds that cause Sun glint, because unlike most other instruments, it uses a filter wheel to take images at multiple wavelengths, which means the image for each wavelength is obtained at a slightly different time. For example, it takes four minutes to cycle from red to blue. During that time, Earth moves by ~100 km (~62 mi) meaning each image will capture a slightly different scene. Brightness contrasts between images can be used to identify glint signals.
Image credit: Tamas Vanai

Alexander Kostinski [Michigan Technology University] reported on long-term changes and semi-permanent features, e.g., ocean glitter. They introduced pixel-pinned temporally and conditionally averaged reflectance images, uniquely suited to the EPIC observational circumstances. The preliminary resulting images (maps), averaged over months and conditioned on cover type (land, ocean, or clouds), show seasonal dependence at a glance (e.g., by an apparent extent of polar caps).

More EPIC Science Results

Guoyong Wen [Morgan State University] discussed spectral properties of the EPIC observations near backscattering, including four cases when the scattering angle reaches about 178° (only 2° from perfect backscattering). The enhancement addresses changes in scattering angle observed in 2020. (Scattering angle is a function of wavelength, because according to Mie scattering theory, the cloud scattering phase function in the glory region is wavelength dependent.) Radiative transfer calculations showed that the change in scattering angles has the largest impact on reflectance in the red and NIR channels at 680 nm and 780 nm and the smallest influence on reflectance in the UV channel at 388 nm – consistent with EPIC observations. The change of global average cloud amount also plays an important role in the reflectance enhancement.

Nick Gorkavyi [SSAI] talked about future plans to deploy a wide-angle camera and a multislit spectrometer on the Moon’s surface for whole-Earth observations to complement EPIC observations. Gorkavyi explained that the apparent vibrational movement of Earth in the Moon’s sky complicates observations of Earth. This causes the center of Earth to move in the Moon’s sky in a rectangle, measuring 13.4° × 15.8° with a period of 6 years. 

Jay Herman [UMBC] reported on EPIC O3 and trends from combining Nimbus 7/Solar Backscatter Ultraviolet (SBUV), the SBUV-2 series, and OMPS–Nadir Mapper (NM) data. (OMPS is made up of three instruments: a Nadir Mapper (NM), Nadir Profiler, and Limb Profiler. OMPS NM is a total ozone sensor). Herman compared EPIC O3 data to OMPS NM data, which showed good agreement (especially summer values) for moderate solar zenith angle (SZA). Comparison with long-term O3 time series (1978–2021) revealed that there were trends and latitude dependent O3 turn-around dates (1994–1998). Herman emphasized that global O3 models do not show this effect but rather have only a single turn-around date around 2000.

Alexander Radkevich [LaRC] presented a poster that showed a comparative analysis of air quality monitoring by orbital and suborbital NASA missions using the DSCOVR EPIC O3 product as well as Pandora total O3 column retrievals. Comparison of the June 2023 total column O3 from EPIC data to the same periods in previous years revealed a significant – around 50 DU – increase of total O3 column in the areas impacted by the plume from 2023 Canadian wildfires.

Conclusion

At the end of the meeting Alexander Marshak, Jay Herman, and Adam Szabo discussed how to make the EPIC and NISTAR instruments more visible in the community. The EPIC website now allows visitors to observe daily fluctuations of aerosol index, cloud fraction, and the ocean surface – as observed from the “L1” point,  nearly one million miles away from Earth! More daily products, (e.g., cloud and aerosol height, total leaf area index, and sunlit leaf area index) will be added soon.

The 2023 DSCOVR EPIC and NISTAR Science Team Meeting provided an opportunity to learn the status of DSCOVR’s Earth-observing instruments, EPIC and NISTAR, the status of recently released L2 data products, and the science results being achieved from the “L1” point. As more people use DSCOVR data worldwide, the ST hopes to hear from users and team members at its next meeting. The latest updates from the mission are found on the EPIC website. (UPDATE: The next DSCOVR EPIC and NISTAR STM will be held on October 16–18, 2024. Check the website for more details as the date approaches.)

Alexander Marshak
NASA’s Goddard Space Flight Center
alexander.marshak@nasa.gov

Adam Szabo
NASA’s Goddard Space Flight Center
adam.szabo@nasa.gov

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      JAXA astronaut Satoshi Furukawa sets up hardware for the Fundamental Research on International Standard of Fire Safety in Space – Base for Safety of Future Manned Missions investigation. NASA/Jasmin MoghbeliView the full article
    • Space Force
      4 SOPS team goes the distance
      By Space Force
      A group of 18 personnel from the 4th Space Operations Squadron, a component of Delta 8, headquartered at Peterson Space Force Base, Colorado, recently traveled to Joint Base Pearl Harbor Hickam, Hawaii for a contingency operations exercise to test a highly technical piece of equipment known as a Mobile Constellation Control Station.

      View the full article
    • NASA
      Voyager 1 Team Accomplishes Tricky Thruster Swap
      By NASA
      5 min read
      Voyager 1 Team Accomplishes Tricky Thruster Swap
      A model of NASA’s Voyager spacecraft. The twin Voyagers have been flying since 1977 and are exploring the outer regions of our solar system. NASA/JPL-Caltech The spacecraft uses its thrusters to stay pointed at Earth, but after 47 years in space some of the fuel tubes have become clogged.
      Engineers working on NASA’s Voyager 1 probe have successfully mitigated an issue with the spacecraft’s thrusters, which keep the distant explorer pointed at Earth so that it can receive commands, send engineering data, and provide the unique science data it is gathering.
      After 47 years, a fuel tube inside the thrusters has become clogged with silicon dioxide, a byproduct that appears with age from a rubber diaphragm in the spacecraft’s fuel tank. The clogging reduces how efficiently the thrusters can generate force. After weeks of careful planning, the team switched the spacecraft to a different set of thrusters.
      The thrusters are fueled by liquid hydrazine, which is turned into gases and released in tens-of-milliseconds-long puffs to gently tilt the spacecraft’s antenna toward Earth. If the clogged thruster were healthy it would need to conduct about 40 of these short pulses per day.
      Both Voyager probes feature three sets, or branches, of thrusters: two sets of attitude propulsion thrusters and one set of trajectory correction maneuver thrusters. During the mission’s planetary flybys, both types of thrusters were used for different purposes. But as Voyager 1 travels on an unchanging path out of the solar system, its thruster needs are simpler, and either thruster branch can be used to point the spacecraft at Earth.
      In 2002 the mission’s engineering team, based at NASA’s Jet Propulsion Laboratory in Southern California, noticed some fuel tubes in the attitude propulsion thruster branch being used for pointing were clogging, so the team switched to the second branch. When that branch showed signs of clogging in 2018, the team switched to the trajectory correction maneuver thrusters and have been using that branch since then.
      Now those trajectory correction thruster tubes are even more clogged than the original branches were when the team swapped them in 2018. The clogged tubes are located inside the thrusters and direct fuel to the catalyst beds, where it is turned into gases. (These are different than the fuel tubes that send hydrazine to the thrusters.) Where the tube opening was originally only 0.01 inches (0.25 millimeters) in diameter, the clogging has reduced it to 0.0015 inches (0.035 mm), or about half the width of a human hair. As a result, the team needed to switch back to one of the attitude propulsion thruster branches.
      Warming Up the Thrusters
      Switching to different thrusters would have been a relatively simple operation for the mission in 1980 or even 2002. But the spacecraft’s age has introduced new challenges, primarily related to power supply and temperature. The mission has turned off all non-essential onboard systems, including some heaters, on both spacecraft to conserve their gradually shrinking electrical power supply, which is generated by decaying plutonium.
      While those steps have worked to reduce power, they have also led to the spacecraft growing colder, an effect compounded by the loss of other non-essential systems that produced heat. Consequently, the attitude propulsion thruster branches have grown cold, and turning them on in that state could damage them, making the thrusters unusable.
      The team determined that the best option would be to warm the thrusters before the switch by turning on what had been deemed non-essential heaters. However, as with so many challenges the Voyager team has faced, this presented a puzzle: The spacecraft’s power supply is so low that turning on non-essential heaters would require the mission to turn off something else to provide the heaters adequate electricity, and everything that’s currently operating is considered essential.
      Studying the issue, they ruled out turning off one of the still-operating science instruments for a limited time because there’s a risk that the instrument would not come back online. After additional study and planning, the engineering team determined they could safely turn off one of the spacecraft’s main heaters for up to an hour, freeing up enough power to turn on the thruster heaters.
      It worked. On Aug. 27, they confirmed that the needed thruster branch was back in action, helping point Voyager 1 toward Earth.
      “All the decisions we will have to make going forward are going to require a lot more analysis and caution than they once did,” said Suzanne Dodd, Voyager’s project manager at the Jet Propulsion Laboratory which manages Voyager for NASA.
      The spacecraft are exploring interstellar space, the region outside the bubble of particles and magnetic fields created by the Sun, where no other spacecraft are likely to visit for a long time. The mission science team is working to keep the Voyagers going for as long as possible, so they can continue to reveal what the interstellar environment is like.
      News Media Contact
      Calla Cofield
      Jet Propulsion Laboratory, Pasadena, Calif.
      626-808-2469
      calla.e.cofield@jpl.nasa.gov
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      Details
      Last Updated Sep 10, 2024 Related Terms
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      NASA Science for Your Classroom: Opportunities for Educators
      By NASA
      4 min read
      NASA Science for Your Classroom: Opportunities for Educators
      The summer season for educators can be a time of rest and rejuvenation, but it can also offer opportunities for professional learning with new colleagues beyond your own school. The following programs from NASA’s Science Activation Program offer end-of-summer/early-fall curricular resources and connections with other educators that can help you bring new science ideas and activities into your instructional practice.  
      Celebrating the Moon & Moon Rocks with NASA – A Webinar for Educators
      Join us, as the world awaits this year’s International Observe the Moon Night (InOMN on September 14, 2024), for this free NASA Astromaterials Research and Exploration Science (ARES) interactive webinar focusing on the Moon, Moon rocks, Apollo and future Artemis Missions! This session will be geared towards educators and their students (targeting grades 5-9 but other grade levels, college students, and individual educators are welcome to participate). Participants will interact with Dr. Juliane Gross, Artemis Curation Lead at the NASA Johnson Space Center in Houston, TX. The presentation will last approximately 45 minutes followed by an optional 15-30 minutes of Q&A. If you can’t participate live, feel free to register to receive an archived recording of the presentation. 
      When: September 11 at 1:00 – 2:15 p.m. EDT Learn more and register Infusing Space Rock Content and More into Learning Environments
      Join NASA Astromaterials Research and Exploration Science for an interactive webinar focusing on hands-on and digital Earth and Space Science resources appropriate for both formal and informal learning settings. This session, geared towards educators who work with grades 3 through HS or general audiences at public events, will prepare you to engage learners with content associated with Moon rocks, meteorites, samples from asteroids and more! Presentation will last approximately 50 minutes followed by an optional 10+ minutes of Q&A. Those who register below will receive an archived recording of the presentation. 
      When: September 17 at  8 p.m. EDT  Register now Spark Curiosity with Infiniscope’s Free Resources!
      Infiniscope is a NASA-funded project focused on sparking curiosity, fostering exploration, and delivering digital content and tools that transform the learning experience. NGSS-Designed digital learning experiences are just the beginning. Whether you want classroom-ready content or the tools and support to build your own, we’ve got you covered. 
      If you’re a middle school or highschool educator, join the webinars below and discover the incredible FREE resources waiting for you at Infiniscope.org. In this guided tour, you’ll learn how to: search for classroom-ready content on the website, find educator resources and detailed lesson information, enroll students in lessons and collections, sign up for future training events, access the virtual field trip creator, and get more information on our adaptive lesson builder. Learn more about Infiniscope.
      Intro to Infiniscope Registration – September 17 at 4 p.m. EDT Intro to Infiniscope Registration – October 22  at 6 p.m. EDT Take Your Learners Anywhere with Tour It!
      With Tour It, Infiniscope’s free virtual field trip creator, you can make place-based learning accessible to all your learners, boosting engagement and learning outcomes while enabling them to build personal connections. Tour It is your gateway to creating captivating virtual field trips! As a member of the Infiniscope teaching network, you’ll have exclusive access to this amazing tool that brings immersive learning experiences to life. Whether you’re a seasoned educator or just starting your journey, Tour It empowers you to craft engaging and interactive virtual tours that inspire learners and enable them to build personal connections to a place. Learn more about Tour it.
      Exploring Place-Based Learning Registration – September 17 at 4 p.m. EDT Planning Your Virtual Field Trip Registration – October 22 at 6 p.m. EDT Heliophysics Webinars for Educators: Physics in an Astronomy Context
      NASA’s Heliophysics Education Activation Team (HEAT) and the American Association of Physics Teachers (AAPT) have put together a free, monthly, virtual workshop series for teachers of astrophysics taught in the context of introductory and upper division physics and astronomy courses. While these workshops are intended for secondary- and tertiary-level teachers who teach in formal classroom contexts, other educators are also welcome if the content covered is appropriate to your teaching context. 
      These virtual gatherings of 25-50 teachers occur one Saturday per month and provide an astrophysics mini-lecture, a small group engagement with the core activity, and discussion time to connect with like-minded educators. 
      Dates and Topics: 
      September, 21, 2024 – Coronal Mass Ejection Science October 12, 2024 – Planetary Magnetism Science November 9, 2024 – Auroral Currents December 7, 2024 – Star Spectra Science Time: 1 – 2:30 p.m. EDT
      Register here 
      We hope these resources will help prepare you for a wonderful year of amazing science learning… and beyond!
      Share








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      Last Updated Sep 09, 2024 Related Terms
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    • NASA
      NASA Astronaut Don Pettit’s Science of Opportunity on Space Station
      By NASA
      3 min read
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      A fisheye lens attached to an electronic still camera was used to capture this image of NASA astronaut Don Pettit.NASA Science ideas are everywhere. Some of the greatest discoveries have come from tinkering and toying with new concepts and ideas. NASA astronaut Don Pettit is no stranger to inventing and discovering. During his previous missions, Pettit has contributed to advancements for human space exploration aboard the International Space Station resulting in several published scientific papers and breakthroughs.

      Pettit, accompanied by cosmonauts Alexey Ovchinin and Ivan Vagner, will launch to the orbiting laboratory in September 2024. In preparation for his fourth spaceflight, read about previous “science of opportunity” experiments Pettit performed during his free time with materials readily available to the crew or included in his personal kit.

      Freezing Ice in Space
      Thin ice under polarized light frozen aboard the International Space Station.NASA Have you ever noticed a white bubble inside the ice in your ice tray at home? This is trapped air that accumulates in one area due to gravity. Pettit took this knowledge, access to a -90° Celsius freezer aboard the space station, and an open weekend to figure out how water freezes in microgravity compared to on Earth. This photo uses polarized light to show thin frozen water and the visible differences from the ice we typically freeze here on Earth, providing more insight into physics concepts in microgravity.

      Space Cup
      NASA astronaut Don Pettit demonstrates how surface tension, wetting, and container shape hold coffee in the space cup.NASA Microgravity affects even the most mundane tasks, like sipping your morning tea. Typically, crews drink beverages from a specially sealed bag with a straw. Using an overhead transparency film, Pettit invented the prototype of the Capillary Beverage, or Space Cup. The cup uses surface tension, wetting, and container shape to mimic the role of gravity in drinking on Earth, making drinking beverages in space easier to consume and showing how discoveries aboard station can be used to design new systems.
      Planetary Formation
      To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video
      Astronaut Don Pettit demonstrates a mixture of coffee grounds and sugar sticking together in microgravity to understand planetary formation. NASA Using materials that break into very small particles, such as table salt, sugar, and coffee, Pettit experimented to understand planetary formation. A crucial early step in planet formation is the aggregation or clumping of tiny particles, but scientists do not fully understand this process. Pettit placed different particulate mixtures in plastic bags, filled them with air, thoroughly shook the bags, and observed that the particles clumped within seconds due to what appears to be an electrostatic process. Studying the behavior of tiny particles in microgravity may provide valuable insight into how material composition, density, and turbulence play a role in planetary formation.
      Orbital Motion
      Charged water particles orbit a knitting needle, showing electrostatic processes in space. NASA Knitting needles made of different materials arrived aboard station as personal crew items. Pettit electrically charged the needles by rubbing each one with paper. Then, he released charged water from a Teflon syringe and observed the water droplets orbit the knitting needle, demonstrating electrostatic orbits in microgravity. The study was later repeated in a simulation that included atmospheric drag, and the 3D motion accurately matched the orbits seen in the space station demonstration. These observations could be analogous to the behavior of charged particles in Earth’s magnetic field and prove useful in designing future spacecraft systems.
      Astrophotography
      Top: NASA astronaut Don Pettit photographed in the International Space Station cupola surrounded by cameras. Bottom: Star trails photographed by NASA astronaut Don Pettit in March of 2012.NASA An innovative photographer, Pettit has used time exposure, multiple cameras, infrared, and other techniques to contribute breathtaking images of Earth and star trails from the space station’s unique viewpoint. These photos contribute to a database researchers use to understand Earth’s changing landscapes, and this imagery can inspire the public’s interest in human spaceflight.

      Christine Giraldo
      International Space Station Research Communications Team
      NASA’s Johnson Space Center
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