Ionospheric Remote Sensing at JPL

Welcome to ionospheric remote sensing research at NASA's Jet Propulsion Laboratory. We utilize L-Band radio frequency (RF) signals from Global Navigation Satellite Systems (GNSS) networks to estimate ionospheric density for various uses such as deep space navigation, aircraft positioning, natural hazard warning, and space weather monitoring.

• Anthony Mannucci
• Olga Verkhoglyadova
• Angelyn Moore
• Attila Komjathy
• Lawrence Sparks
• Panagiotis Vergados
• Robert Meyer
• Siddharth Krishnamoorthy
• Camille Martire

The JPL-GIM software developed at the Ionospheric and Atmospheric Remote Sensing (IARS) Group at JPL is the mainstay for the delivery of ionospheric calibrations to many customers. This software synthesizes global ionospheric maps using total electron content (TEC) measurement from hundreds of multi-constellation GNSS receivers around the world. More details about the JPL-GIM software and its products can be found in Martire et. al. (2024). See our publications section for more details.

We provide research-oriented products (JPLD and JPLI, described in Martire et. al. (2024) – see publications section) consisting of TEC maps provided in netCDF format. They can be found here. These maps are derived from GPS and Galileo data and are provided with a spatiotemporal resolution of 15 min (time) × 1° (longitude) × 1° (latitude). They are periodically generated every two months. The point of contact for GIM for research is Dr. Olga Verkhoglyadova.

We have been conducting research in space weather and several heliophysics areas. The main directions are: LEO satellite data analysis of ionosphere-thermosphere-plasmasphere dynamics, estimation of energy budget of the upper atmosphere during geomagnetic activity, ULF wave coupling of the magnetosphere with the upper atmosphere, TEC forecasting, space weather risks, solar energetic particles in the heliosphere and their effects on the Earth atmosphere, ionospheric scintillations, machine learning in space physics and GNSS data analysis. We utilized GITM (Global Ionosphere-Thermosphere Model) and developed High-latitude Input for Mesoscale Electrodynamics (HIME) modeling framework to incorporate high-latitude meso-scale ionosphere driving into GITM upper boundary conditions. Team members are involved in NASA missions Electrojet Zeeman Imaging Explorer (EZIE), Geospace Dynamics Constellation (GDC)) and DYNAMIC (Phase A) missions. The point of contact for space weather research is Dr. Olga Verkhoglyadova.

Phase delay in radio-frequency waves introduced by the Earth’s ionosphere is one of the largest sources of error in tracking deep space assets. The IARS group delivers daily Prompt and Final line-of-sight ionospheric and tropospheric time-delay calibrations to the Deep Space Network (DSN) to enable the accurate tracking of these assets. Global ionospheric maps that utilize global Galileo and GPS observations are used to extract ionospheric and tropospheric time delays along the line joining deep space assets to antennas at DSN sites at Goldstone, CA; Madrid, Spain; and Tidbinbilla, Australia. These delays can then be used to correct for the phase effects of the ionosphere during spacecraft tracking passes. Ongoing development enabled rapid calibrations for critical tracks leading to the successful landing of the Perseverance rover at Mars. The task lead for the DSN media modeling effort is Dr. Angelyn Moore.

We operationally compute daily estimates of the L1/L2 inter-frequency correction terms for all GPS satellites, also known as Timing Group Delay (TGD). These values are derived from ionospheric data analysis, and are regularly delivered to the US Space Force, which updates the GPS broadcast messages with the latest estimates. Since August 2024, we also compute estimates of the E1/E5a correction term for all Galileo satellites. The TGDs are crucial correction terms for GPS and Galileo users constrained to perform single-frequency point positioning. Beside factory calibrations, estimates such as JPL's are the only way to obtain up-to-date approximations of the necessary corrections. The task lead for TGD operations is Dr. Panagiotis Vergados.

We monitor the ionosphere in near-real-time using the GNSS-based Upper Atmospheric Realtime Disaster Information and Alert Network (GUARDIAN) system. GUARDIAN System is the first global, high-rate, multi-GNSS system for near-real-time (NRT) monitoring of the ionosphere for the acoustic or gravity wave signatures originating from natural hazard events on Earth's surface and due to solar-geomagnetic activity. GUARDIAN’s ultimate goal is to use NRT TEC time series to (1) allow users to explore ionospheric TEC perturbations due to natural hazards, (2) automatically detect those perturbations, and (3) characterize potential natural hazards. GUARDIAN estimates ionospheric TEC from approximately 350 stations around the globe focused on the Pacific Ring of Fire. NRT global ionospheric maps (NRTGIM) with a resolution of 15 min (time) × 1° (longitude) × 1° (latitude) derived from the GPS and Galileo are now also available on the GUARDIAN webpage. TEC data from GUARDIAN are delivered to NASA's Crustal Dynamics Data Information System (CDDIS) and can be accessed for free. More details can be found in Martire et. al. (2023). See our publications section for details. The points of contact for the GUARDIAN system are Dr. Siddharth Krishnamoorthy and Dr. Camille Martire. The point of contact for NRTGIM is Robert Meyer.

For more than twenty-five years, JPL has played a central role in the development of the Federal Aviation Administration’s (FAA) contribution to GNSS, namely, the WAAS, helping to render GPS safe and reliable for use in aircraft navigation over North America. We perform research on understanding ionospheric disturbances and mitigating their impact on the GNSS. In particular, we provide expertise concerning ionospheric phenomena that occur on different spatial scales: large, mesoscale disturbances that can adversely influence the accuracy of GNSS user position estimates, and small-scale irregularities that can cause scintillation and loss of signal, which in turn can result in an interruption of GNSS service. The evolution of WAAS methodology for mitigating threats to positioning accuracy posed by the ionosphere has been critically dependent upon IonoSTAGE (Ionospheric Slant TEC Analysis using GNSS-based Estimation), a software package developed at JPL that performs analysis and visualization of ionospheric slant TEC derived from GNSS measurements. IonoSTAGE is currently the primary code on which the FAA relies to construct its ionospheric threat model. This threat model contains tabulated corrections used to augment the confidence bounds of estimated vertical delays, broadcast at regularly-spaced points on an ionospheric grid over North America. These broadcast confidence bounds are used to calculate error bounds on a WAAS user’s position, thereby protecting the user from the worst-case threats posed by irregularities that escape detection by the system. In addition to generating each WAAS ionospheric threat model, IonoSTAGE has contributed to the development and implementation of the WAAS extreme and moderate storm detectors. The point of contact for WAAS support is Dr. Lawrence Sparks.

Ionospheric Measurements Based on GNSS Estimation for NISAR (IMAGEN) is a Python software package that generates ionospheric vertical total electron content data along Low Earth Orbit (LEO) spacecraft (such as NISAR) orbit tracks. To produce TEC data, IMAGEN collects and processes GPS data from hundreds of globally distributed GNSS stations and from a GNSS receiver onboard NISAR satellite. The TEC products include total TEC, measured from the ground to the GPS orbit altitude (~20,200 km), and topside TEC, measured from the LEO orbit altitude to the GPS orbit altitude. The products also allow the measurements of TEC below the satellite. Such TEC data has been used to remove ionospheric effects in precise coregistration or geolocation of InSAR images. IMAGEN will be operated by the JPL IARS group to support the NISAR mission for Earth remote sensing.

GAIM is developed jointly by scientists at JPL and University of Southern California. This model is based on physics principles of ionospheric plasma and dynamics. It is capable of assimilating ionospheric observations to bring the model results in line with ionospheric weather and to estimate the dynamical drivers. The GAIM model numerically solves for time evolution of 3-D volume densities of the major ion species, including O+, O2+, N2+, NO+, H+, He+, and electron density. GAIM has been assimilating GNSS-derived spaceborne and ground-based TEC, ionosonde data, etc. The model is validated through comparisons with independent measurements and has been applied to studies of ionospheric storms and assimilative modeling of the growth rate of plasma Rayleigh-Taylor instability.

We contribute Rapid and Final ionosphere maps to the IGS and participate in the Ionosphere Committee of the IGS. These products are combined with other Ionosphere Associate Analysis Centers’ solutions to form the IGS combination ionosphere products. The combination and JPL’s products are available from NASA's CDDIS. The JPL Rapid (latency 1 day) and Final (latency 3 days) products are GPS-only maps provided with a spatiotemporal resolution of 2h (time) × 5° (longitude) × 2.5° (latitude). The points of contact for these efforts are Dr. Panagiotis Vergados and Dr. Camille Martire.