Tag: ionospheric disturbance

Nowcasting the ionosphere: Evaluating GloTEC for real-time GNSS corrections
One of the most persistent sources of GNSS error — ionospheric delay — has been challenging to correct in real time, especially for mass-market devices. While dual-frequency receivers and commercial correction services can mostly mitigate this issue, they remain too costly and impractical for the billions of smartphones and IoT devices that rely on single-frequency GNSS. Even for dual-frequency systems, the commonly used ionosphere-free linear combination amplifies multipath and receiver errors and reduces data redundancy — yielding only two usable combinations from four original measurements.

This landscape may be shifting with the introduction of GloTEC, a real-time global Total Electron Content (TEC) map from NOAA’s Space Weather Prediction Center (SWPC), released in February 2025. GloTEC assimilates both ground- and space-based observations to provide real-time global ionospheric corrections without relying on error-prone linear combinations.

Unlike coarse models such as the broadcast Klobuchar algorithm or forecast-only products such as the predicted IGS Global Ionosphere Maps, GloTEC updates every 10 minutes using real-time measurements. This high refresh rate establishes a new benchmark for open-access ionospheric nowcasting in GNSS applications.

Originally designed to monitor and mitigate space weather impacts on aviation and communications, GloTEC may also deliver a broader benefit: enabling precise, scalable GNSS corrections for low-cost, single-frequency devices, making high-accuracy positioning more accessible and democratic.

Why Nowcasting Matters for GNSS

The GNSS community has long had to choose between accuracy and latency. Predictive models, such as those from NASA CEDIS or CODETEC, can offer reasonable approximations but may fall short when real-time corrections are required, particularly in the context of navigation, asset tracking or autonomous systems.

Post-processed products (such as rapid/final IGS GIMs) provide excellent fidelity but are typically delayed by hours, days, or even weeks. This makes them useful for research or auditing, but not for real-time navigation needs.

Commercial correction services, such as Trimble RTX and Hexagon’s TerraStar, have filled the gap for high-value applications. These systems interpolate ionospheric corrections in real time, but at a significant cost and they typically require specialized GNSS receivers.

GloTEC bridges this gap by delivering a publicly accessible, high-refresh ionospheric product that can support near real-time corrections. Updated every 10 minutes with a 2.5° latitude and 5° longitude spatial resolution, GloTEC represents a major step forward for public sector GNSS capability, particularly in contexts where accuracy, reliability and scale are all crucial. The data has also been supporting the United States Space Force and is accessible through their Unified Data Library (UDL).

Technical Approach: Adapting GloTEC for Practical Use

While the potential of GloTEC is exciting, turning it into usable corrections for consumer-grade devices isn’t straightforward. TEC maps represent volumetric electron density, while most mass-market GNSS chipsets, especially in smartphones, expect simplified models, such as the eight-parameter Klobuchar model broadcast by GPS satellites. GloTEC is a three-dimensional data assimilation system that uses a Gauss-Markov Kalman Filter to estimate electron density in the ionosphere. It ingests slant TEC measurements from ground-based GNSS receivers and space-based radio occultation data, using the IRI-2016 model as its background state.

To bridge this mismatch, Zephr’s team has been exploring regional fitting techniques, whereby a local subset of GloTEC data is used to generate custom Klobuchar coefficients. These can be transmitted to devices via standardized protocols, such as the LTE Positioning Protocol (LPP), enabling improved ionospheric delay estimation with minimal changes to device-side computation. Even with a regionalized Klobuchar fit and LPP encoding, there is still the problem of accessing the GNSS chip to apply the corrections. To solve this problem, Zephr has created a virtualized positioning engine that takes the raw GNSS measurements from the chip and provides a purely software-based solver. This approach allows the team to implement a variety of more advanced positioning techniques using commodity hardware such as smartphones.

Field Testing: A Quantitative Step Forward

To evaluate the efficacy of GloTEC in improving GNSS accuracy, engineers at Zephr used the virtualized positioning engine to conduct 51 real-world campaigns across various conditions – including urban, suburban, static, walking, and driving – using a Pixel 8 smartphone and an RTK unit for ground truth.

The results were promising, as shown in Figure 1:

Figure 1: GloTEC vs. CODETEC vs. Android Native across multiple scenarios. (All figures provided by author)

We can break down these results using detailed graphs for each scenario as examples. This will provide a more in-depth look at the positioning for specific traces through the outlined scenarios in Figure 2, Figure 3 and Figure 4:

Figure 2: GloTEC vs. CODETEC vs. Android Native for an open sky walking scenario

Figure 3: GloTEC vs. CODETEC vs. Android Native for a suburban downtown walking scenario.

Figure 4: GloTEC vs. CODETEC vs. Android Native for a mixed sky driving test.

Across all categories, the GloTEC-based regional fitting approach significantly outperformed both the default GNSS solution (which uses broadcast data plus a Klobuchar mode) and the competing IGS products. Accuracy improved by up to 69% in driving scenarios and 46% in walking scenarios, compared to standard smartphone GPS.

While the Pixel 8 used in testing supports dual-frequency GNSS, smartphones face several practical limitations that hinder effective use of ionosphere-free dual-frequency combinations. These include limited signal availability (due to antenna constraints, L1/L5 support gaps, and partial constellation coverage), elevated multipath and noise (especially from omnidirectional antennas in dynamic conditions), and unstable clock biases that complicate error modeling. In fact, iono-free combinations can amplify multipath effects, potentially degrading accuracy in some conditions.

Despite these constraints, the results show that meaningful improvements in positioning are possible using a software-based approach with publicly available corrections. GloTEC, when paired with cooperative or cloud-based GNSS engines, offers a substantial step forward without requiring expensive commercial correction services or specialized hardware.

Broader Implications and Next Steps

While these results are promising, several challenges remain before GloTEC-based corrections can be broadly deployed:
- Connectivity Requirements: Real-time access to GloTEC requires periodic downloads over cellular or Wi-Fi connections, raising questions about reliability in low-bandwidth or disconnected environments.
- Global Calibration: The accuracy of regional fitting depends on local coverage density and VTEC variability. Further tuning may be needed in equatorial or polar regions, where ionospheric behavior is more volatile.
Nevertheless, the availability of GloTEC marks a significant milestone. For the first time, a free, real-time, high-resolution ionospheric correction product is accessible to developers, researchers, and engineers seeking to improve GNSS accuracy at scale. NOAA SWPC has plans to integrate more low-latency space-based and ground-based data into GloTEC in the near future. The new version of the model outputs will be released to the public once the results are validated. As techniques for applying it to mobile and IoT devices mature, the GNSS community may see a broad shift toward more precise, resilient, and cost-effective positioning systems.

GloTEC may have been designed to help forecasters monitor the response of the ionosphere due to space weather events, but its potential to provide an advanced tool for positioning on Earth is just beginning to be understood. In a world where nearly every mobile application depends on location, and where the cost of poor accuracy is rising (from package delivery failures to navigation errors), this kind of public infrastructure is invaluable.

Researchers and industry developers alike should explore how this NOAA capability can be integrated into their positioning systems. If properly supported, GloTEC could become one of the most impactful GNSS innovations of the decade.
July 14, 2025
Seen & Heard: Moscow taxis hacked, Norway turns to radar

“Seen & Heard” is a monthly feature of GPS World magazine, traveling the world to capture interesting and unusual news stories involving the GNSS/PNT industry.

Photo: Space Norway

Norway to get radar assist

Norway’s sea areas are seven times larger than its land area. Now the country is creating a radar satellite system to surveil and locate ships in waters of interest, including the High North. On Aug. 25, Space Norway signed contracts with vendors to build the MicroSAR system, which will launch in 2025. Plans are to make a constellation of radar satellites that can detect small vessels in a large area simultaneously. While the system will use GNSS for orbit tracking, the radar function is independent of GNSS during acquisition. This will solve a flaw in the Automatic Identification System (AIS) now used for maritime surveillance — estimates are that 5% of vessels either do not send out AIS information or are transmitting false information.

Photo: Yandex

Russia’s driverless autos hit the brakes

Russian driverless projects are facing hurdles following the invasion of Ukraine, reports TU-Automotive. For instance, Russian IT giant Yandex had hoped to launch robo-taxis in the United States but has suspended street tests and robotic delivery pilots and laid off employees in its U.S. office. Russian freight carriers are experiencing a shortage of new vehicles and spare parts from Western trade sanctions and countermeasures by the Russian government. Meanwhile, Russia’s pilot tests of connected road infrastructure are still taking place, according to V2X vendor Sreda Software Solutions.

Nathaniel Frissell and team. (Photo: University of Scranton)

Bunches of grapes

A University of Scranton collaborative research project will use daily Doppler shift receiver measurements to study how dawn, dusk and solar eclipses affect the ionosphere. The team, led by Nathaniel Frissell, will use a network of GNSS-stabilized and synchronized high-frequency receivers known as Grapes, developed as part of another National Science Foundation project in 2019. The last solar eclipses to traverse the continental United States until 2044 will occur Oct. 14, 2023 and April 8, 2024. “This project takes advantage of the unprecedented opportunity to study the ionospheric impacts of the 2023 and 2024 solar eclipses and the daily ionospheric variability associated with dawn/dusk transitions,” Frissell said. A better understanding of the effects of ionospheric disturbances is imperative, because the changes affect GNSS navigation and communications systems.

Screenshot: Anonymous TV

Moscow navigation fail

The hacker collective Anonymous managed to disrupt Yandex’s Moscow taxi fleet on Sept. 1, sending dozens of taxis to an address on Kutuzovsky Prospekt. The hacking caused a two-hour traffic jam in the center of Moscow near the Stalinist-era building Hotel Ukraina (Hotel Ukraine), now a Radisson. Hackers likely bypassed Yandex’s safety measures, creating multiple fake orders that prompted drivers to simultaneously go to the same location.

September 21, 2022
Joint NASA-Brazil CubeSat mission will unlock equatorial phenomena that affect GPS

NASA and a team of Brazilian space researchers have announced a joint CubeSat mission to study phenomena in Earth’s upper atmosphere — a region of charged particles called the ionosphere — capable of disrupting communications and navigation systems on the ground and potentially impacting satellites and human explorers in space.

Two phenomena in the ionosphere — equatorial plasma bubbles and scintillation — have impacted GPS signals, radio communication systems and satellite technologies for decades, said Jim Spann, chief scientist for the Science and Technology Directorate at NASA’s Marshall Space Flight Center in Huntsville, Alabama.

Equatorial plasma bubbles are regions of comparatively low density which may elongate into towering plumes during high-intensity periods.

Scintillation is a unique type of atmospheric fluctuation that can interrupt radio frequencies, much like the “twinkling” effect seen in starlight when optical frequencies are disrupted.

The Scintillation Prediction Observations Research Task (SPORT) mission, funded by NASA’s Science Mission Directorate in Washington, will observe these peculiar structures in order to understand what causes them, determine how to predict their behavior and assess ways to mitigate their effects.

The joint U.S.-Brazilian team, led by Spann as principal investigator, will design and launch SPORT as a CubeSat, a compact satellite about the size of two loaves of bread. It will be launched in 2019 to an Earth orbit 217-248 miles high (350-400 km). Its operational phase is expected to last at least a year.

“Degraded communications and GPS signals are known to be closely linked to these phenomena,” Spann said. It’s his goal to shed new light on these phenomena and inspire new operational solutions to contend with the disturbed conditions.

Protecting Brazil’s aviation, agriculture

The Brazilian SPORT team seeks targeted solutions as well. Otavio Durão, project manager for the team at Instituto Nacional de Pesquisas Espaciais (INPE) in São Jose dos Campos, a São Paulo municipality, said ionospheric responses to a space phenomenon called the South Atlantic Anomaly or the South American Magnetic Anomaly — where space radiation dips close to Earth — negatively impacts Brazil’s busy airports.

“Our country is interested in refining GPS signal processing, making takeoffs and landings safer and more precise,” he said. “Because so many international flights come to and through Brazil, this should be a matter of concern for all countries.”

Brazil’s strong agricultural industry also is concerned about the anomaly’s effects on GPS, said Durão’s colleague Luís Loures, the SPORT spacecraft manager at the Instituto Tecnológico da Aeronáutica in São Jose dos Campos.

“Our agribusiness is always trying to increase crop productivity,” he said. “One way to accomplish this is by using automated tools. But being able to precisely position those automated tractors and field sprayers, without disruption from solar phenomena, is crucial.”

“As society becomes more dependent every day on space-based technology — cell phones, self-driving cars, secure military communications — it’s critically important we first understand the environment in which our technology resides, then learn how to operate through and preserve it from potentially disruptive or damaging interference,” Spann said.

Understanding the phenomena

Building on decades of previous ground-based studies of plasma bubbles over equatorial regions, especially intensive research in Brazil and Peru, SPORT will help researchers determine what’s happening in the ionosphere to stir up the bubbles, why they form along the equator and what causes them to appear at night.

Plasma bubbles and scintillation are global equatorial and mid-latitude phenomena, made worse by the South American Magnetic Anomaly, where Earth’s magnetic equator dips close to Earth.

“Many of the discoveries to date have been confined to a limited number of longitudinal sectors,” Spann said. “SPORT will make a systematic study of the ionosphere at all longitudes around the planet, documenting the conditions that trigger formation of the bubbles, with particular focus on the South American sector.”

As multiple instruments on the ground also record data, Spann said, SPORT will probe the ionosphere from above. During subsequent passes, it will study specific sectors to identify conditions favorable for developing plasma bubbles and ionospheric scintillations.

These simultaneous satellite and ground-based studies will help researchers identify how the observations are related, providing a better understanding of the results at all longitudes.

The team is confident the findings will enable researchers to use physics-based models to determine the physics of plasma bubble triggers, and thus identify the resulting scintillation of radio signals that propagate throughout the turbulent region.

More about SPORT

SPORT science mission data will be distributed from and archived at the EMBRACE space-weather forecasting center in Brazil’s National Institute for Space Research (INPE) and mirrored at the Space Physics Data Facility at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The SPORT mission management team is led by Marshall alongside its international partners, the Brazilian Space Agency in Brasília, and the National Institute for Space Research and Technical Aeronautics Institute, both in São Jose dos Campos, São Paulo.

Spann’s team, which oversees the mission science, flight instruments and the CubeSat launch, includes researchers at Marshall; Goddard; Utah State University in Logan, Utah; The Aerospace Corporation in El Segundo, California; the University of Texas at Dallas; and the University of Alabama in Huntsville.

NASA’s Brazilian partners are overseeing the development of the spacecraft; integration and testing; mission operations; data management and dissemination; and the ground observation network. The science analysis will be conducted by the entire team.

SPORT is part of NASA’s Heliophysics Technology and Instrument Development for Science program. NASA’s heliophysics mission includes research into the effects of the sun on Earth, its atmosphere and the planets of our solar system.

August 15, 2017
NASA describes expected impact of total eclipse on GPS

NASA has issued a statement to let the GPS community know what to expect when the total solar eclipse takes place across America on Aug. 21.

On Aug. 21, the eclipse will cross all of North America. Anyone within the path of totality will see the moon completely cover the sun, and the sun’s tenuous atmosphere — the corona — can be seen.

Observers outside this path will still see a partial solar eclipse where the moon covers part of the sun’s disk.

A map of the United States showing the path of totality for the August 21, 2017 total solar eclipse. (Image: NASA)

For NASA, the eclipse provides a unique opportunity to study the sun, Earth, moon and their interaction because of the eclipse’s long path over land and coast to coast. Eleven NASA and NOAA satellites, as well as the International Space Station, more than 50 high-altitude balloons and hundreds of ground-based assets, will take advantage of this rare event over 90 minutes, sharing the science and the beauty of a total solar eclipse with all.

Via live streams and a NASA TV broadcast, NASA will bring the Aug. 21 eclipse live to viewers everywhere in the world.

Below is the statement from NASA regarding GPS.

NASA Note on the Aug. 21 Solar Eclipse and Its Effect on GPS Users

FOR THE GPS COMMUNITY

From ionospheric point of view, the expected effect of solar eclipse is a significant reduction in solar EUV ionization (solar EUV radiation is blocked) and thus in the amount of ionospheric total electron content (TEC) with respect to nominal conditions along the eclipse path.

Some observations also show wave-like TEC perturbations in small magnitude (~1 TECU) during eclipse as shown in the attached reference. The wave-like perturbations appear to be the effect of atmospheric gravity waves or traveling ionospheric disturbances (TIDs) that might be triggered during eclipse.

The TEC decrease would reduce ionospheric-induced delay of GPS signals. The small-magnitude TIDs won’t cause any major effects on GPS signals. These should not cause loss of GPS signals.

I have not seen any reports about ionospheric scintillation observations during eclipse (I might have missed them). It would be interesting to analyze GPS data along the path of upcoming August eclipse to see if any scintillation events could be triggered.

We have some GPS data processing tools at JPL and can contribute to this analysis.

FOR THE GENERAL PUBLIC

A solar eclipse occurs when the Moon passes between the Sun and the Earth, thereby totally or partly obscuring the image of the sun for a viewer on Earth. There is a region of Earth’s upper atmosphere, called the ionosphere which affects radio waves, including GPS.

The ionosphere consists of “ions,” a shell of electrons and electrically charged atoms and molecules. Because ions are created through sunlight interacting with the atoms and molecules in the very thin upper atmosphere, the density (thickness and consistency) of the ionosphere varies from day to night.

The ionosphere bends radio signals, similar to the way water will bend light signals. That is why you can hear AM radio broadcasts from far away at night. Also, ham radio operators rely on the ionosphere to bounce their signals from their station to the far reaches of the globe.

Since GPS is a radio signal, its measurements are slightly impacted by ionosphere changes, resulting in small increases in position error. For all except very precise GPS users, these changes are negligible.

Note that a total eclipse of the Sun is similar to our day-night cycle, only much faster. So, while the ionosphere will be more dynamic during an eclipse, it will not cause a loss of the GPS signal.

In summary, while any effects from the eclipse are of scientific interest, GPS service should not be adversely affected by the Aug. 21 solar eclipse.

Ionospheric effects should not be confused with those from solar flares (a brief eruption of intense high-energy radiation from the sun’s surface) that can cause significant electromagnetic disturbances on the earth, impacting radio frequency communications/transmissions (including GPS signals) and power line transmissions. Solar flares are not produced because of an eclipse.

NASA has funded 11 studies in a range of heliophysics disciplines; work at MIT Haystack Observatory and Virginia Tech will make extensive use of GPS receivers to study the effects of the total eclipse on the Earth’s ionosphere.

(NASA acknowledges the expertise of Larry Young and Xiaoqing Pi of NASA’s Jet Propulsion Laboratory for content, and AJ Oria of Overlook Systems Technologies for the coordination and editing of these statements.)

August 15, 2017
Research Online: Positioning with LTE signals

Rover positions obtained with 2D LTE versus GPS track.

Positioning with LTE Signals

An alternative to GNSS in urban canyons can be provided by signals from cellular base stations, particularly new signals from long-term evolution (LTE) networks, since LTE coverage will be high in cities. Wide LTE downlink bandwidth provides good resolution of multipath components, which also assists positioning.

A test used a universal software radio peripheral N210 synchronized to a GPS-locked Rubidium frequency standard. A personal computer stored LTE data samples together with GNSS sentences from a u-blox LEA-6T module. A Matlab-algorithm did the complete post-processing, extracting pseudoranges for the LTE base station and calculating the position solution.

Results of a car driven on an urban route show root-mean-square value of the absolute error using LTE compared to GPS position is 43 meters.

Positioning Using LTE Signals, by Fabian Knutti, Mischa Sabathy, Marco Driusso, Heinz Mathis, and Chris Marshall. Presented at the European Navigation Conference 2015.

Seamless Indoors

Sensor Augmented Indoor Navigation and Positioning, by M. Gemelli and Keith Nicholson, Bosch Sensortec. An overview of technologies that guide us indoors in a seamless and reliable manner, highlighting key requirements for motion and pressure sensing, low-power processing, efficient code design, wireless beaconing and map matching. Fusion software needs new data sources: Bluetooth low-energy, Wi-Fi fingerprinting, magnetic fingerprinting, ultrasound. Presented at ION GNSS+ 2015.

Disturbed Ionosphere

Mitigating satellite motion in GPS monitoring of traveling ionospheric disturbances (TIDs), by R.W. Penney and N.K. Jackson-Booth. Discusses the impact of satellite motion on the use of compact arrays of GPS receivers for estimating the velocity of travelling ionospheric disturbances (TIDs). It is shown that satellite motion has subtle effects upon standard techniques of waveform cross-correlation, or time-difference of arrival (TDOA), which can easily lead to spurious TID velocity estimates. In Radio Science, an AGU journal.

November 12, 2015
Septentrio Launches UAS Receiver, Software for Drone Market

The AsteRx-m UAS by Septentrio.

Septentrio has launched the AsteRx-m UAS, an RTK-accurate GNSS receiver solution specially designed for the drone market. The AsteRx-m UAS provides high-accuracy GNSS positioning with low power consumption, according to Septentrio.

The launch of the AsteRx-m UAS board is complemented by the release of GeoTagZ software suite. The GeoTagZ suite works with the UAS camera and image-processing solution to provide centimeter-accurate position tagging of images without the need for a real-time data link.

The AsteRx-m UAS will be on display at booth #635 during AUVSI’s Unmanned Systems 2015, held May 4-7 at the Georgia World Congress Center in Atlanta.

Despite being Septentrio’s smallest receiver, the AsteRx-m UAS provides consistent, robust and accurate positioning from to Septentrio’s in house GNSS+ algorithm technology. The receiver delivers cm-level accuracy at less than 600 mW with GPS and less than 700 mW with GLONASS. LOCK+ technology guarantees tracking under heavy usage and IONO+ guarantees no interference in challenging ionospheric conditions, Septentrio said.

Integration into Any UAS. One of the key characteristics of AsteRx-m UAS and GeoTagZ is the seamless integration into any UAS. AsteRx-m UAS features standard connection functionality that directly connects to a UAS autopilot, such as Pixhawk and Ardupilot. The power comes directly from a number of power sources, including micro USB, a 9-30V external power supply or the vehicle power bus. GeoTagZ is available as a library of software to integrate into an UAS image-processing tool chain.

“We want to make UAS-based data collection and processing extremely simple. AsteRx-m UAS and GeoTagZ do just that,” said Jan Leyssens, commercial product manager at Septentrio. “The GNSS board connects seamlessly to standard hardware and cameras used on a drone. Together with our software, we provide a data collection solution that provides cm-level accuracy without the need for ground control points or real-time data links, and that integrates effortlessly with an existing UAS image processing software solutions.”

May 4, 2015
GPS Data Show How Nepal Quake Disturbed Earth’s Upper Atmosphere

The April 25 magnitude 7.8 earthquake in Nepal created waves of energy that penetrated into Earth’s upper atmosphere in the vicinity of Nepal, disturbing the distribution of electrons in the ionosphere. These disturbances were monitored using GPS signals received by a science-quality GPS receiver in Tibet, a neighboring region to Nepal.

The data show that after the initial earthquake rupture (indicated by the vertical black line on the graphic), it took about 21 minutes for the earthquake-generated ionospheric disturbance to reach a GPS station (LHAZ) about 400 miles (640 kilometers) away from the epicenter in Lhasa, Tibet, China.

Image Credit: NASA/JPL/Ionosphere Natural Hazards Team

The disturbance measurements, known as vertical total electron content (VTEC) (depicted in blue in the upper panel), have been filtered using processing software developed by NASA’s Jet Propulsion Laboratory in Pasadena, Calif., to show wave-like disturbances (circled in red) in the distribution of electrons in the ionosphere. The waves have periods of between two and eight minutes in length. The disturbance measurements following the earthquake rupture are circled in black in the lower panel. The colors represent the relative strengths of the earthquake-induced ionospheric disturbances as captured by the GPS signals, with red being high and blue being low.

Attila Komjathy, a principal investigator of the Ionospheric and Atmospheric Remote Sensing group at JPL and adjunct professor at the University of New Brunswick, is leading this effort. Komjathy is also a GPS World annual award winner and named a Fellow of the Institute of Navigation in January.

The LHAZ GPS station is hosted at the Tibet Autonomous Regional Bureau of Surveying and Mapping Institute. The site collects both GPS and GLONASS (the Russian global navigation satellite system) data at a rate of 1 Hertz and is part of the International GPS Service (IGS).

Scientists study ionosphere-based measurements caused by natural hazards such as earthquakes, volcanic eruptions and tsunamis to better understand wave propagation in the upper atmosphere.The ionosphere is a region of Earth’s upper atmosphere located from about 37 miles (60 kilometers) to 621 miles (1,000 kilometers) above Earth’s surface.

The disturbances caused by earthquakes help scientists develop new first-principle-based wave propagation models. These models may become part of future early warning systems for tsunamis and other difficult-to-detect natural hazards.

The data is available on this FTP site.

May 2, 2015