Radio Occultation in NASA Earth Science Programs

Jack A. Kaye(1), Tsengdar Lee(1), Gail Skofronick-Jackson(1), Gerald Bawden(1), Charles Webb(1), Will McCarty(2), Tony Mannucci(3), Bill Schreiner(4), and Maudood Khan(5) (1) NASA Earth Science Division, (2) NASA/GSFC/GMAO, (3) NASA/JPL, (4) UCAR, (5) Booz Allen Hamilton 1 October 22, 2020 1 Outline of Talk • Support for algorithm development and research that enhances the capability of GNSS-RO • Providing instruments that have flown or will fly on NASA and partner satellites (including GPS/MET, CHAMP, SAC-C, GRACE, GRACE-FO, Sentinel-6 Michael Freilich) • Supporting a competitively selected science team to use data from the Global Navigation Satellite System (GNSS) –including both radio occultation and reflection • Consideration of role of GNSS-RO in Incubation Activity for Planetary Boundary Layer • Purchasing, evaluating and sharing data from Spire Global, Inc. with the NASA research community. SWOT (CNES) NASA EARTH FLEET LANDSAT-9 (USGS) SENTINEL-6 Michael Freilich/B (ESA) OPERATING & FUTURE THROUGH 2023 TROPICS (6) GEOCARB NISAR (ISRO) MAIA TSIS-2 TEMPO PREFIRE (2) PACE (NSO) INVEST/CUBESATS GLIMR ICESAT-2 RainCube GRACE-FO (2) (GFZ) CSIM-FD CYGNSS (8) HARP NISTAR, EPIC (DSCOVR/NOAA) TEMPEST-D CIRiS ISS INSTRUMENTS CLOUDSAT (CSA) CTIM EMIT TERRA (JAXA, CSA) HyTI CLARREO-PF AQUA (JAXA, AEB) SNoOPI GEDI AURA (NSO, FMI, UKSA) NACHOS OCO-3 TSIS-1 CALIPSO (CNES) ECOSTRESS GPM (JAXA) LIS LANDSAT 7 (USGS) SAGE III LANDSAT 8 (USGS) JPSS-2, 3 & 4 INSTRUMENTS OCO-2 (PRE) FORMULATION SMAP OMPS-Limb IMPLEMENTATON LIBERA SUOMI NPP (NOAA) PRIMARY OPS 09.23.20 EXTENDED OPS 3 SWOT (CNES) NASA EARTH FLEET LANDSAT-9 (USGS) SENTINEL-6 Michael Freilich/B (ESA) OPERATING & FUTURE THROUGH 2023 TROPICS (6) GEOCARB NISAR (ISRO) MAIA TSIS-2 TEMPO PREFIRE (2) PACE (NSO) INVEST/CUBESATS GLIMR ICESAT-2 RainCube GRACE-FO (2) (GFZ) CSIM-FD CYGNSS (8) HARP NISTAR, EPIC (DSCOVR/NOAA) TEMPEST-D CIRiS ISS INSTRUMENTS CLOUDSAT (CSA) CTIM EMIT TERRA (JAXA, CSA) HyTI CLARREO-PF AQUA (JAXA, AEB) SNoOPI GEDI AURA (NSO, FMI, UKSA) NACHOS OCO-3 TSIS-1 CALIPSO (CNES) ECOSTRESS GPM (JAXA) LIS LANDSAT 7 (USGS) SAGE III LANDSAT 8 (USGS) JPSS-2, 3 & 4 INSTRUMENTS OCO-2 (PRE) FORMULATION SMAP OMPS-Limb IMPLEMENTATON LIBERA SUOMI NPP (NOAA) PRIMARY OPS 09.23.20 EXTENDED OPS 4 Support for Algorithm Development and Research that Enhances the Capability of GNSS-RO

• NASA provides directed support to JPL and UCAR for provision of GNSS-RO data to the research community, including algorithm development and improvement • UCAR support is provided as part of interagency agreement with US National Science Foundation • Continuing effort serves to improve quality of retrievals, especially to look to increase penetration to lower altitudes • Products are shared with broader national and international user community GNSS Satellite Instrument Provision

• NASA has history of providing GNSS-RO instruments for partners satellites. • Currently a GNSS-RO instrument is flying as part of the GRACE FO satellite (a partnership between NASA and Germany/GFZ). This picks up from the earlier GRACE (2002-2017) partnership between NASA, DLR, and GFZ. • The TriG instrument developed at NASA is flying aboard COSMIC-2/FORMOSAT-7. • A GNSS-RO instrument (TriG) will be launched aboard the forthcoming (10 November planned launch date) Sentinel 6 Michael Freilich satellite (note partnership with European Commission, ESA, EUMETSAT, NOAA, and CNES). GRACE-FO Radio Occultation Status o GF1 rising RO has been enabled since June 2019 o ~280 rising RO per day (~180 passed QC) o GF2 setting RO remains disabled o Expect GF2 RO to be switched on in early 2021 o Preliminary results with first RO retrieval with GPS L5 signal in space o L5 RO processing is still being optimized o V4.3 SW upload to GF1 resolved issue with GPS PRN 32 L1CA/L5 RO Profile vs. NCEP L2C RO that improves RO quality o ~78.2% RO with L1CA/L2C passed QC (17 PRNs) o ~51.7% RO with L1CA/L2P passed QC (12 PRNs) o ~65.3% RO with L1CA/L5 passed QC (2 PRNs) o SW team is testing SW update to output the first three frequency RO (GPS L1/L2/L5) o The measurements will be useful in providing the dataset for assessing and reducing the Residual Ionosphere Error in GNSS-RO retrievals Sentinel-6 Michael Freilich o Sentinel-6 Michael Freilich will provide radio occultation data beginning in 2021 using two different POD Antenna spacecraft. The satellites will launch in November (on Spine) 2020 and in 2025. GNSS-RO o The GNSS-RO instrument is based on the COSMIC-2 Fore Antenna o Payload from NASA/JPL for measuring bending angles of GNSS signals occulted by Earth’s atmosphere includes: o GNSS receiver (TriG) o Two Radio Occultation antennas o One POD antenna o Bandpass filter / low-noise amplifiers (BPF/LNAs) o Data processing GNSS-RO o Near Real Time products will be generated by JPL and Aft Antenna GNSS-RO (on Bottom) distributed by NOAA on the GTS for weather Receiver & BPF/LNAs forecasting (Inside S/C Structure) o Non Time Critical data products will be generated by EUMETSAT & JPL and available for climate studies Orbit Altitude 1330 km and research using improved orbit and clock data Inclination Angle 66 Mission Life 5.5-7.5 Years 116 GNSS Science Team • NASA has been funding a competitively selected GNSS Science Team since 2007 o September 2007 – selected 7 proposals, $1M/year o July 2012 – selected 9 proposals, $1.5M/year o July 2015 – selected 10 proposals, $1.7M/year o August 2020 – selected 11 proposals, ~$1.9M/year NOAA also selected 1 additional proposal • Over time, GNSS team has grown to include more work on reflection (not just RO!) • GNSS-related proposals could be selected under any relevant solicitation as well! Global Navigation Satellite System Research 2020 Selected Teams • Chi Ao/Jet Propulsion Laboratory - High-Resolution Characterization of the Planetary Boundary Layer Using GNSS- RO, Ground GNSS, and Passive Satellite Observations • Donald Argus/Jet Propulsion Laboratory - Improving the Accuracy of GNSS Positions and the Terrestrial Reference Frame Using GNSS, SLR, and GRACE Observations • Manuel de la Torre Juarez/Jet Propulsion Laboratory - Using Polarimetric Signatures of GNSS Signals for the Remote Sensing Characterization of the Vertical Structures of Heavy Precipitation and Water Vapor in Clouds • Scott Gleason/University Corporation For Atmospheric Research - Exploring GNSS Remote Sensing Applications in Geosynchronous Orbit Using GOES GPS Receivers • Attila Komjathy/Jet Propulsion Laboratory - Ionospheric Gravity Wave Decoupling from Tsunamis and Applications • Kristine Larson/University of Colorado, Boulder - Open Source GNSS Reflectometry Code for the Geoscience Community • Angelyn Moore/Jet Propulsion Laboratory - Multi-Constellation GNSS Processing for Transient Identification • Jeffrey Ouellette/Naval Research Laboratory - Studies of Off-Specular Bistatic Sea Surface Scattering for GNSS and Geostationary Satellite Emissions • Matthew Siegfried/Colorado School of Mines - Constraining West Antarctic Snow Accumulation and Firn Densification Processes with GNSS Reflectometry • Dong Wu/NASA Goddard Space Flight Center - Marine Atmospheric Boundary Layer (MABL) Water Vapor from GPSRO Diffraction Signals • Johnathan York/University of Texas, Austin - Towards MM-Level Direct Ties via Integrated GNSS and VLBI Interferometric Measurements Earth System Science Research Advanced by Use of RO data

• Atmospheric Boundary Layer • Tropopause Structure • Gravity Waves • Equatorial Waves • Inter-Seasonal Variability • Climate Monitoring Research under the NASA Earth Science US Participating Investigator (ESUSPI) o The Spanish PAZ-ROHP (Radio Occultations Through Heavy Precipitation) mission has demonstrated the sensitivity to liquid and frozen precipitations using the novel technique of polarimetric radio occultation and CloudSat radar profile data have been instrumental for simulation, validation, and furthering science investigations related to cloud convective processes. o This work has been greatly enhanced by NASA support through the Earth Science U.S. Participating Investigator (ESUSPI) program and the NASA Postdoctoral Program.

PAZ obs GNSS Radio Occultations Rain simulation OIceb +s Reainr vsimautlaiotionn

Simulations

Precipitation structure from GPM

https://paz.ice.csic.es/ Research at the NASA Jet Propulsion Lab (1)

Characterizing the Vertical Stratification of the Earth’s Planetary Boundary Layer with GNSS RO o GNSS-RO can profile moisture within the PBL, despite current retrieval uncertainty. o The vertical stratification of the PBL characterized here with the decoupling parameter (DCP), defined as the specific humidity difference between the bottom layer and the top layer of the PBL. o DCP obtained from RO are validated with radiosondes over the Pacific Ocean. o The observed PBLH and DCP can be used to assess climate models with different PBL parameterizations and resolutions

Source: Kuo-Nung Wang, Terry Kubar Radio Occultation Assimilation Research at GMAO (1) o NASA’s GMAO runs the GEOS Forward Processing (FP) atmospheric data assimilation system in real time: Background Departures vs. Height o GSI assimilation procedure, which is Normalized Bending Angle (O-B)/B co-developed with the NOAA NCEP o Hybrid 4D ensemble-variational analysis o Forecasts with the GEOS global Old H(x) model New H(x) o 12-km global resolution o Two key updates for assimilating radio occultation observations: o Improved forward operator: H(x) – more realistic use of the observations The updated forward operator (H(x)) adjusted the vertical interpolation (figure) scheme within the GSI, which reduced the systematic bias between the model state and the observations in the 5-10 km altitude range o New observing systems: COSMIC-2, KOMPSAT-5 – ~2-3 times more RO observations than used in GEOS-FP Radio Occultation Assimilation Research at GMAO (2) o Beneficial impacts: Forecast Skill Scorecard: Assessed against ECMWF Operations (12/1/2019-1/31/2020) o Upper troposphere: new forward operator for RO observations o Tropics: volume and quality of the COSMIC-2 observations o Improvements generally sustained through the forecast period o Next steps: o A GEOS-FP upgrade is planned for late 2020 o Undergoing GMAO’s parallel implementation and testing procedure o Incorporates these and other observing system-focused changes

The forecast skill scorecard shows large improvements (green) from using the new forward operator and the new RO observing systems in GEOS 2017 Decadal Survey Targeted Observables *ESD decided to only treat observable under the Explorer program element

Vertical profiles of ozone and trace UV/IR/microwave limb/nadir

i e Ozone & gases (including water vapor, CO, NO2,

r sounding and UV/IR solar/stellar TARGETED CANDIDATE MEASUREMENT a X

n l

SCIENCE/APPLICATIONS SUMMARY b g Trace Gases methane, and N2O) globally and with

p i occultation OBSERVABLE APPROACH u

E high spatial resolution

I D Snow Depth Snow depth and snow water equivalent Radar (Ka/Ku band) altimeter; or Aerosol properties, aerosol vertical Backscatter lidar and multi- & Snow including high spatial resolution in lidar** X profiles, and cloud properties to channel/multi- Water mountain areas Aerosols understand their direct and indirect angle/polarization imaging X Equivalent effects on climate and air quality radiometer flown together on 3D structure of terrestrial ecosystem Lidar** the same platform including forest canopy and above Terrestrial ground biomass and changes in above Clouds, Coupled cloud-precipitation state and Radar(s), with multi-frequency Ecosystem X Convection, dynamics for monitoring global passive microwave and sub-mm ground carbon stock from processes X Structure & hydrological cycle and understanding radiometer such as deforestation & forest contributing processes degradation Precipitation 3D winds in troposphere/PBL for Active sensing (lidar, radar, Large-scale Earth dynamics measured Spacecraft ranging transport of pollutants/carbon/aerosol scatterometer); passive imagery by the changing mass distribution within Atmospheric Mass Change measurement of gravity X and water vapor, wind energy, cloud or radiometry-based atmos. X X and between the Earth’s atmosphere, Winds dynamics and convection, and large- anomaly motion vectors (AMVs) tracking; oceans, ground water, and ice sheets scale circulation or lidar** Surface Earth surface geology and biology, Hyperspectral imagery in the ground/water temperature, snow visible and shortwave infrared, Diurnal 3D PBL thermodynamic Microwave, hyperspectral IR Biology & X reflectivity, active geologic processes, multi- or hyperspectral imagery properties and 2D PBL structure to sounder(s) (e.g., in geo or small Geology vegetation traits and algal biomass in the thermal IR understand the impact of PBL processes sat constellation), GPS radio Planetary on weather and AQ through high vertical occultation for diurnal PBL Surface Earth surface dynamics from Interferometric Synthetic Boundary X and temporal profiling of PBL temperature and humidity and Deformation earthquakes and landslides to ice sheets Aperture Radar (InSAR) with X Layer & Change and permafrost ionospheric correction temperature, moisture and heights. heights; water vapor profiling DIAL lidar; and lidar** for PBL CO2 and methane fluxes and trends, Multispectral short wave IR and height Greenhouse global and regional with quantification thermal IR sounders; or lidar** X High-resolution global topography Radar; or lidar** Gases of point sources and identification of Surface including bare surface land topography source types Topography X ice topography, vegetation structure, Global ice characterization including Lidar** & Vegetation and shallow water bathymetry elevation change of land ice to assess Ice Elevation sea level contributions and freeboard X ** Could potentially be addressed by a multi-function lidar designed to address two or more of the height of sea ice to assess sea Targeted Observables ice/ocean/atmosphere interaction Coincident high-accuracy currents and Radar scatterometer Other ESAS 2017 Targeted Observables, not Allocated to a Flight Program Element Ocean vector winds to assess air-sea Surface Aquatic Biogeochemistry Radiance Intercalibration momentum exchange and to infer X Winds & Magnetic Field Changes Sea Surface Salinity upwelling, upper ocean mixing, and sea- Currents ice drift. Ocean Ecosystem Structure Soil Moisture

16 Decadal Survey: Incubation Activity: Planetary Boundary Layer • The purpose of the incubation program element is to assemble two study teams (one each) for advancing (1) Planetary Boundary Layer (PBL) and (2) Surface Topography and Vegetation (STV) that will seek new capabilities addressing the Targeted Observables (TO) Program Goals outlined in the Decadal Survey: • National Academies of Sciences, Engineering and Medicine (NASEM) 2018 decadal survey, Thriving on Our Changing Planet: A Decadal Strategy for Earth Observation from Space (https://www.nap.edu/catalog/24938) • NASA solicited two teams to help advance planning for the Planetary Boundary Layer and Surface Topography and Vegetation Incubation Activity in Dec. 2019. • The main deliverable produced by each study team will be a white paper outlining potential future methods and activity areas, such as • modeling and Observing System Simulations Experiments (OSSEs); • field campaigns; and • a range of potential observing system architectures utilizing emerging sensor and information technologies. • Other deliverables include an interim report; presentations to NASA Headquarters; and a preliminary Science and Applications Traceability Matrix (SATM) that includes relevant societal or science questions, Earth science/application objectives, geophysical observables, and draft concepts of associated measurement approaches. Incubation PBL Team Members

• Chi Ao/Jet Propulsion Laboratory - Achieving PBL Science with Improved GNSS Radio Occultation Technology and Other Remote Sensing Techniques • Shuyi Chen/University of Washington, Seattle - Observing the Planetary Boundary Layer: A Vision to Fulfill an Unmet Challenge in Earth System Science and Global Weather-Climate Prediction • Carol Anne Clayson/Woods Hole Oceanographic Institution - Lessons Learned from Satellite-Derived Ocean Surface Flux Datasets • Ann Fridlind/Goddard Space Flight Center - Robustly Defining the Planetary Boundary Layer Within the Context of Common Atmospheric Inversions Globally • Matthew Lebsock/Jet Propulsion Laboratory - Planetary Boundary Layer Study Team Membership • Will McCarty/Goddard Space Flight Center - Contributions from the Global Modeling and Assimilation Office to the PBL Decadal Survey Incubation Study Team • Amin Nehrir*/Langley Research Center - Emerging Technologies and Measurement Synergies to Enable the Next Generation PBL Observing System • Jeffrey Piepmeier*/Goddard Space Flight Center - Planetary Boundary Layer Observation Architecture and Technology Strategy • Haydee Salmun/Hunter College - Using Global Ground-Based Measurements of Planetary Boundary Layer Height to Inform Incubation Study Team Strategies • Joseph Santanello/Goddard Space Flight Center - Addressing the Planetary Boundary Layer Gap Over Land and Importance of Improved Retrieval from Space • Joao Teixeira*/Jet Propulsion Laboratory - Planetary Boundary Layer from Space • David Turner/Office of Oceanic and Atmospheric Research, Boulder - Quantifying the Information Content and Theoretical Accuracy and Vertical Resolution of Retrieved Profiles in the Planetary Boundary Layer • Zhien Wang/University of Colorado, Boulder - A Proposal to Participate in the Decadal Survey Incubation Study Team of Planetary Boundary Layer • Xubin Zeng/University of Arizona - Preliminary Data Analysis for the Planetary Boundary Layer Incubation Study Team

* Team Leadership Roles NASA Incubation PBL Activity Information

• See web site: https://science.nasa.gov/earth- science/decadal-pbl • Overview • PBL Team • NASA PBL Study Team Charter • PBL Technology Survey - https://science.nasa.gov/earth- science/decadal-pbl/planetary-boundary-layer-incubation- study-technology-survey • Workshops – held over four days in May, 2020 NASA Commercial Smallsat Data Acquisition (CSDA) Program

• NASA has implemented program to purchase commercial data. Information may be found at https://earthdata.nasa.gov/esds/csdap. • NASA has put out two Requests for Information (RFIs) and used the first to purchase data from three companies (Planet, Digital Globe – now Maxar Technologies, and Spire Global) and then do evaluation of usefulness of data for helping to achieve NASA’s research and applications objectives. A report from the evaluation effort was made publicly available (see https://cdn.earthdata.nasa.gov/conduit/upload/14180/CSDAPEvaluation Report_Apr20.pdf). • NASA has entered into agreements for sustained purchase of data from both Planet and Spire Global, which are now available for use by NASA investigators. There are restrictions on use tied to the agreed upon End User License Agreement (EULA). • A research solicitation was put out allowing community to propose to use commercial data (also including ISS/DESIS instrument) for research and applications purposes. This closed on 1 September 2020. Commercial Smallsat Data Acquisition (CSDA) - Overview

NASA Earth Science Division augmented funds for research projects that could potentially benefit from the use of commercial RO data. The researchers were asked to evaluate the usefulness of data for their research work.

NASA acquired data and made them available for funded researchers in March 2019. Spire operates a constellation of satellites that, for the purpose of this study, measure Global Navigation Satellite Systems (GNSS) signals. Information of the earth system can be used inferred from these signals. Three specific applications of Spire data were : o Water (Sea surface height via GNSS-Reflectometry) o Atmosphere (vertical mass information via GNSS- Radio Occultation) o Space Weather (Thermospheric density via satellite Precise Orbit Determination) CSDA Spire Data Evaluation – Usefulness for Earth Science Research And Application o Spire Radio Occultation (RO) measurements were found to be of consistent quality to existing RO observing systems, and this was confirmed both through the Level 0 and Level 2 data o In the context of numerical weather prediction, they were seen to carry a similar weight per- observations in terms of their impact on short-term (24-hour) forecast error. o Spire were significant in count (~20-40% of total) but also complementary to the other GNSS-RO observing systems

Contribution of Spire, relative to the rest of the GNSS-RO observing system, to the reduction of 24 hour forecast error Distribution of the Spire data relative to the other RO observing systems illustrates that they are filling data (W. McCarty, NASA GSFC) voids (shown, observations at 00 UTC ± 3 hour) CSDA Spire Data Evaluation – Usefulness for Earth Science Research And Application (2)

o Spire RO observations were also found to be useful in delineating the height and temperature of the tropopause, though some extra care was noted by the fact that the constellation strategy results in varying spatial and temporal distributions. o They were also capable of detecting the top of the planetary boundary layer via sharp refractivity gradients. The penetration depths of the observations were noted to exceed those of previous observations. The varying spatial and temporal distributions may be a strength in this case.

Mean PBL height as detected directly from Spire data. It is noted that Spire’s penetration depth exceeds heritage, The Tropical Cold-Point Tropopause (CPT) mean height (left) making this measurement possible. and Temperature (right), as measured by Spire and other RO observations 23 (W. Schreiner, UCAR) Conclusion • NASA’s Earth Science Division has multiple ways to engage community in GNSS-RO related science, including helping to improve algorithms for data provided to community from past, current, and future satellites. • GNSS RO Data are provided from GRACE FO and will become available from the Sentinel-6 Michael Freilich satellite upon readiness after launch. • NASA offers competed opportunities for use of GNSS data (both radio occultation and reflection). • Decadal Survey Incubation Planetary Boundary Layer (PBL) activity is considering how GNSS-RO can contribute to PBL measurement in the future. • NASA is purchasing GNSS-RO data from Spire Global and making them available to the community. • NASA continues to engage with interagency and international partners, as well as related entities (e.g., CGMS IROWG) to facilitate coordination. Backup Research at the NASA Jet Propulsion Lab (3)

GNSS-RO on Upper Troposphere Amplification

Background: Discrepancies exist on the magnitude of the upper troposphere (UT) temperature trends and amplification between microwave sounders, radiosondes, and climate models. What do GNSS and AIRS observations reveal?

Result: CMIP6 AMIP models capture the same tropical upper tropospheric (UT) warming trend as GNSS-RO, AIRS v6, and ERA-Interim, and do not exaggerate UT warming as reported in IPCC AR5. GNSS-RO, CMIP6 AMIP, and AIRS v6 observations show excellent agreement, revealing that the tropical surface warming is amplified by 2x in UT.

Vergados, P., et al. (2020), Inferring the tropical upper troposphere amplification warming using radio occultations, Geophys. Res. Lett., 29 p. #2020GL0900742 (under revision) McKitrick, R., and J. Christy (2018), A test of the tropical 200-300 hPa warming rate in climate models, Earth and Space Science, 5, https://doi,org/10.1029/2018E000401 CSDAP Spire Data Evaluation – Usefulness for Earth Science Research And Application (1) o GNSS measurements that reflect off the ocean surface, or GNSS-Reflectometry, were used to retrieve Sea Surface Height (SSH) o The measurements, when inversion was possible, were estimated to have an accuracy of < 10 cm-1, and the precision was ~2.5 cm over 1 sec intervals. However, only a small percentage of observations (~4.3% over ocean) contained SNR and coherent signals needed for SSH retrieval. o The effort was a proof of concept and further work (both in terms of the retrieval and observation counts) could both improve the retrieval and better quantify its accuracy.

The retrieved (left, blue) and mean (left, red) sea surface height. The difference of the two (right, blue) illustrates the SSH variability seen in the observations

S. Nerem, University of Colorado CSDAP Spire Data Evaluation – Usefulness for Earth Science Research And Application (3)

o Spire POD measurements were capable of determining the day-to-day variability of thermospheric density at flight level. o By estimating drag coefficients from satellite CAD models and knowing the exact position of the satellites, the orbital drag can be inverted to measure flight-level density. For this, the constellation observing approach has substantial potential as the satellite is the observation itself. o Only sparse data was available outside of satellite RO operations. The ability to have high temporal fidelity outside of RO ops would improve this. CAD model of the Spire STRATOS satellite (inset) and the daily- effective density retrieved from the satellite POD for three different satellites as compared to the USAF HASDM model COSMIC-2 Status Update o All six flight Tri-Global Navigation Satellite System Radio Occultation Receiver’s (TGRS) are operating o FM1, FM2, FM3 and FM4 are at 540-550km mission orbit o FM5 Satellite is in orbit transfer to 550km orbit o FM6 Satellite expected to be lowered in late Dec o Consistently exceed 5000 neutral atm. RO when all six TGRS are ON o Neutral Atmosphere RO product was released since Dec 10, 2019 o Space Weather product was released since March 30, 2020 o Completed payload commissioning activities o Recent V4.3.5 SW update has significantly increased combined GPS and GLONASS Ionospheric limb and topside TEC o Preliminary assessment from JPL shows V4.3.5 TGRS SW is meeting Space Weather L1 requirements on the combined GPS and GLO Ionosphere limb TEC profiles and top TEC arc Post V4.3.5 SW upload results shows TGRS consistently exceeds L1 counts of 2000 per day-receiver combined TEC count requirement Research at the NASA Jet Propulsion Lab (3)

Radio Occultation Bias Correction Under Ducting Layer Using Surface-Reflection

Background: PBL refractivity and moisture profiles can be negatively biased under strong capping inversion that leads to a ducting layer. Result: A new technique has been developed where reflected RO signal is extracted from the RO measurement itself to constrain retrieved refractivity solution. This reconstruction method reduces the refractivity bias (N-bias) from 5~10% to less than 1% below the inversion. This study represents the first practical approach to remove the known RO bias without external information. Wang, K.-N.; Ao, C.O.; de la Torre Juárez, M. GNSS-RO Refractivity Bias Correction Under Ducting Layer Using Surface-Reflection Signal. Remote Sens. 2020, 12, 359, https://doi.org/10.3390/rs12030359 Earth System Science Research Advanced by Use of RO data (1)

• Atmospheric Boundary Layer: • ABL is the bottom turbulent layer of the atmosphere. It is characterized by large vertical gradients of temperature and water vapor. The depth of the ABL is an important parameter for NWP and climate models. • RO is the only remote sensing technique from space that can profile temperature and water vapor in the ABL. • RO data have been used to develop ABL climatology, such as the spatial and temporal variations of the ABL, and to evaluate GCMs with different ABL parameterizations and resolutions. • Tropopause Structure: • RO data offer a unique opportunity to observe tropopause structure and variability with accurate, high vertical resolution temperature soundings. • RO data have also been used study the tropopause inversion layer (Pilch Kedzierski et al., 2016), double tropopause (Rieckh et al., 2014), and revealed that the tropopause variability could be caused by different underlying physical processes. • Gravity Waves: • GW is an oscillation characterized by a restoring force by buoyancy. GWs are excited by a variety of mechanisms. They propagate upward, transporting energy and momentum upward, play an important role in driving the general atmospheric circulation in the middle atmosphere. • RO data enables us to investigate the previously unexplored global distribution of atmospheric GWs with high-vertical resolution temperature measurements. Earth System Science Research Advanced by Use of RO data (2) o Equatorial Waves: o Equatorial waves are dominant contribution to ULTS atmospheric variance. They are important to UTLS circulation, constituent transport and cloud formation. o Equatorial waves occurs with relatively small vertical scales, which are less well resolved in nadir- viewing satellite measurements or model (re)analyses. o Dense and accurate observations from C2 within the tropical UTLS offer a unique opportunity for evaluating wave variability across a broad spectrum. o Inter-seasonal Variability: o MJO is a dominant atmospheric oscillation pattern in thee tropics with a period of between 30-90 days. MJO involves the coupling between planetary scale waves and deep convection, propagating eastward slowly (5 m/s). MJO has a significant influence on various scales atmospheric variability. o RO data were composited to characterize the vertical moist thermodynamic structure and spatial- temporal evolution of the MJO. o Documenting the large-scale vertical moist thermodynamic structure of the MJO is very important for us to better understand the MJO dynamics and to improve the MJO simulation in global models. o Climate Monitoring: o RO data are well suited for establishing a stable, long-term record required for climate monitoring due to its low bias (< 0.5 K), and stability (< 0.05 K/decade) from mission to mission. o Beside RO temperature, RO moisture retrieval is also presented its long-term stability, which could be an excellent data source for studies of detecting climate change signals and understanding the processes underlying the atmospheric water cycle. Research at the NASA Jet Propulsion Lab (3)

Monthly mean gridded data products derived from multi-mission RO retrievals

Bayesian interpolation is used to create global 5°× 5°monthly gridded dataset 2002-2018 with full characterization of sampling errors.

Number of processed RO profiles from retrievals based on MERRA-2 at 200 hPa 70000

60000

50000

40000 Zonal variation of “tropical belts” 30000 derived from RO are used to assess 20000 the re-analyses [Luan et al. 2020]

10000

0 2002 2004 2006 2008 2010 2012 2014 2016 2018 Year Vertically-resolved, global, Utilizes consistently-processed CHAMP, COSMIC, GRACE, temperature trends from TerraSAR-X, and KOMPSAT-5 GPS-RO measurements. With RO (2003-2014) can be used support from NASA NDOA program to validate other datasets [Leroy et al. 2018]