First antenna tested on site (June 13, 2025)
Overview and Status
Arizona State University is developing the Long Wavelength Array – Meteor Crater (LWA-MC) radio telescope research station just north of Meteor Crater, about 30 miles east of Flagstaff, Arizona. The telescope will consist of 64 tent-shaped antennas whose signals are combined digitally in computers to map the sky.
Upon completion in early 2026, the station will join a network of telescopes in the southwestern U.S. to help the Air Force study Earth’s ionosphere over 100 miles above. Eventually the station will join into a very long baseline array with other LWA stations, coordinated by the University of New Mexico, to provide new astronomical surveys of the low-frequency radio sky, help search for habitable exoplanets, and contribute to electromagnetic followup of LIGO events that could locate pairs of merging black holes that create gravitational waves rippling through the universe predicted by Einstein’s theory of general relativity.
The telescope will be built by undergraduate students and used for hands-on training in 21st-century skills, including artificial intelligence and machine learning, digital signal processing, and data science.
Ionospheric Science Background
Continuum radiation from the Sun ionizes the region of Earth’s atmosphere above ~60 km altitude, forming what is known as the ionosphere. Variations in the solar X-ray flux (on the 11-year solar cycle), diurnal variations of solar angle, tides and winds, and seasonal variations of solar elevation, atmospheric chemistry, and wind patterns act to create a highly dynamic ionosphere. Since the free electrons in the ionosphere interact with radio waves, the dynamics of the ionosphere can have a large impact on military and civilian radio systems used for positioning, navigation and timing (PNT) and communications. One of the biggest impacts in the High Frequency (HF; 3 – 30 MHz) and Very High Frequency (VHF; 30 – 300 MHz) bands is the phenomenon known as sporadic E (Es), which occurs in the E region of the ionosphere (~90 – 150 km altitude).
The ionospheric electron density generally increases with altitude until the peak frequency is reached in the F region, usually around ~200 km altitude. The height/density profile is usually relatively smooth and can be determined through HF radar techniques. While the E region is usually lower in density than the F region, Es is characterized by the formation of thin, high density patches of plasma that can far exceed the peak density of the F region. Es forms when ions get trapped in a thin layer due to interactions between mesospheric wind shears and the geomagnetic field.
Es, often observed at ~100 km altitude, acts as a mirror and prevents terrestrial radio waves from propagating up to the F region. Moreover, recent observations have also shown that sporadic E can cause scintillation on Global Positioning Satellite (GPS) and Global Navigation Satellite System (GNSS) signals. For these reasons it would be advantageous to be able to fully characterize the location, density, and movements of Es structures over a large region, but there are currently no facilities with all of these capabilities.
Most systems built to observe Es, do so by active means, where an intentionally generated radio signal is either reflected or scattered (radar) from Es or passes through it (e.g. GPS/GNSS). These techniques all have limitations, for instance while GPS/GNSS techniques as described in Maeda and Heki (2013, 2015) are capable of observing the position of Es structures, they do not provide enough information to ascertain the density of the Es structures. HF radars such as ionosondes on the other hand are capable of providing the electron density but can only do so for a single point along a propagation path. Therefore, in order to map the density structure of Es, a large number of HF transmitters and/or receivers would need to operate in an expansive, dense network, but no network currently exists.
Obenberger et al. 2020 showed that the density, location, velocity, and morphology of Es can be simultaneously measured passively with radio telescopes. This new method uses the unintentional emission from power lines and other anthropogenic sources as a broadband illumination source. Radio telescopes detect the intensity and spectral properties of this emission after it has been scattered by Es, enabling them to measure Es over a wide region. A collection of telescopes can use triangulation to track the movements of Es scatterers.
These capabilities were demonstrated by Obenberger et al. 2020 using existing Long Wavelength Array (LWA) radio telescope stations in New Mexico. ASU is adding an LWA mini-station near Meteor Crater to expand the coverage of the system, creating a “swarm” of instruments in the southwestern US that will be operated together as a pathfinder to further develop this new method for sporadic E measurement.
Figure 1. Map of the LWA Swarm station locations in the southwestern U.S.
About the Long Wavelength Array
The original Long Wavelength Array (LWA) radio telescope station is operated by the University of New Mexico (UNM) at the National Radio Astronomy Observatory’s Jansky Very Large Array (JVLA) facility in New Mexico. The LWA station consists of 256 dipole antennas arranged over an area 100 meters (about 300 feet) in diameter, similar to an American football field. It has two primary modes of operation: 1) beamforming with up to four simultaneous beams, each 20 MHz wide with dual polarization and two tunings; and 2) continuous all-sky imaging in a narrow bandwidth (100 kHz). U. New Mexico operates two additional LWA stations: 1) a full-size station with 256 antennas located at the Sevilleta National Wildlife Refuge in central New Mexico and 2) an LWA “mini-station” with 64 antennas at the north end of the JVLA. In addition, Caltech operates an extended LWA station (OVRO-LWA) in Owens Valley, California with over 300 antennas. ASU’s new LWA-MC station–and a matching new station operated by Texas Tech University in northern Texas–follow the “mini-station” design.
Mini-Station Design
The original LWA stations were designed for observations of faint astronomical sources. A full LWA station is more than necessary for sporadic E monitoring since the Es structures are usually the brightest signal in the sky when present. The LWA mini-station design is scaled to enable ionospheric science and create an array of LWA stations, dubbed the “LWA Swarm” that use very long baseline interferometer to open novel astronomical observations. The mini-station uses 64 dipoles instead of the full complement of 256 at the original LWA stations.
Each of the mini-stations follows the general design of a full-scale LWA station. The mini-station uses the same dipole antennas, analog electronics, and digital signal processing systems as a full LWA station. The antennas are dual-polarization broadband dipoles responsive from 10-90 MHz. They are connected directly to first-stage amplifiers and mounted on metal posts. A small wire mesh sheet is place on the ground directly below the antenna to improve its gain toward the sky and reduce sensitivity to soil conditions that change with weather. The antennas are located pseudo-randomly over an area 100 meters in diameter. This arrangement provides degree-scale azimuthal localization of Es scatterers. Two LMR-240 cables per antenna (one per polarization) carry the received signals to a central EMI-shielded cabinet that houses conditioning and processing electronics.
In the cabinet, signals are further amplified and low-pass filtering is applied to exclude strong transmitters including the FM and TV broadcast bands. They are then digitized, channelized, and routed through 40 GigE network switches to three GPU-augmented servers for pair-wise cross-correlation between antennas. Processing on computer servers combines the correlation products in real-time to image the full sky in all four pseudo-Stokes parameters every 5 seconds. Images are recorded to disk and asynchronously streamed off-site to UNM for aggregation with the other LWA Swarm measurements and further processing to identify and characterize Es. A separate monitor and control system oversees the mini-station health and activities.
The antennas, mounting hardware, and first-stage electronics are produced by industry partner, Burns Industries. The second-stage analog electronics and pre-configured digitization system is procured from the LWA Store at UNM. Commercial vendors are used for the servers, cabinet enclosure, and other supporting equipment. With regular maintenance, the mini-stations will have minimum usable lifetimes over 20 years.