Ionospheric sounding — the systematic measurement of the ionosphere’s structure, density, height and dynamics by probing it with radio waves — has been a core discipline of upper-atmospheric physics since Edward Appleton’s first vertical-incidence sounding experiments in 1924. For most of the next ninety years it was practised with bespoke government and university hardware: vertical-incidence Digisonde ionosondes (consolidated from the 1990s onward into the Global Ionospheric Radio Observatory network at the University of Massachusetts Lowell, now numbering roughly 80 active stations worldwide); the Super Dual Auroral Radar Network (SuperDARN), a global array of HF coherent backscatter systems mapping plasma drift velocities across the auroral and polar ionosphere; oblique sounders; and incoherent-scatter radars at a handful of high-cost facilities — Jicamarca, Millstone Hill, EISCAT in Scandinavia, and until its catastrophic structural collapse in December 2020, the 305-metre dish at Arecibo. From the 1990s onward, GNSS-derived total-electron-content (TEC) maps added a further global layer. Through all of this, the professional network maintained very thin coverage across the open oceans, the Southern Hemisphere, and the equatorial belt, leaving enormous regions where the ionosphere’s state could only be inferred, never observed directly.
The SDR Revolution in Ionospheric Monitoring
The arrival of software-defined radio and weak-signal digital modes changed that picture fundamentally. A 1990s superheterodyne ham receiver could spot one signal on one band at a time; a single modern KiwiSDR running WSPRdaemon now decodes 14 HF bands simultaneously, 24 hours a day, with GPS-disciplined timing accurate to the microsecond, posting tens of thousands of conditioned spots per day from a single unattended site. The RX888 brought direct-RF-sampling 16-bit ADCs into the same price bracket and pushed the noise floor further still. WSJT-X and its FST4W, FT8, FT4 and JS8 modes — developed at Princeton by Nobel laureate Joe Taylor K1JT — moved the receive-sensitivity threshold down by roughly 20 dB beyond what conventional CW could achieve, decoding signals at –28 dB SNR in a 2.5 kHz bandwidth. Multiply those per-station gains across hundreds of operating sites worldwide and feed them into existing aggregation infrastructure — the Reverse Beacon Network for CW and digital skimmer reports, WSPRNet for the billions of weak-signal spots accumulated since 2008, PSKReporter for FT8/FT4/JS8 reception, and the KiwiSDR public network of over 700 openly-shared HF receivers — and the amateur community ends up producing a parallel ionospheric dataset that dwarfs the professional network in scale, geographic breadth and frequency diversity. Every spot is tagged with call sign, Maidenhead grid, frequency, SNR and microsecond-accurate timestamp; the data are open, free and continuous; and they fill enormous coverage holes across the Southern Ocean, the Antarctic margin and the equatorial Pacific that have never had a professional ionosonde within range.
National Programs and Their SDR Connection
The national programs underpinning this work span every inhabited continent and include some of the world’s longest-running atmospheric research traditions. Australia operates one of the Southern Hemisphere’s most important ionosonde networks through the Bureau of Meteorology’s Space Weather Services branch, with Digisonde stations at Darwin, Townsville, Learmonth, Canberra and Hobart feeding data into the GIRO global repository. The University of Adelaide’s Buckland Park radar facility — approximately 40 kilometres north of the conference venue — is a key Southern Hemisphere HF atmospheric radar research site; the SuperDARN TIGER system (Bruny Island, Tasmania, La Trobe University) extends high-latitude ionospheric coverage into the sub-Antarctic approaches. Most significantly for the Defence portion of this conference’s audience, DSTG’s sustained HF propagation research programme in support of the Jindalee Operational Radar Network (JORN) — which must model the ionospheric channel accurately in real time to place its over-the-horizon detections correctly — gives Australian defence science a sovereign operational stake in ionospheric accuracy that few other nations replicate. An active VK amateur community contributes WSPR and FT8 spots continuously, and HamSCI’s GRAPE receiver platform has been adopted by Australian amateurs as part of the broader global calibrated monitoring effort. New Zealand’s contribution to ionospheric science is disproportionate to its size: GNS Science operates ionosondes at Christchurch and the Chatham Islands; the SuperDARN Unwin Radar in Southland (University of Otago) extends the global SuperDARN map into the Southern Ocean sector; and — most consequentially for this conference’s technical audience — KiwiSDR itself was designed and built in New Zealand by John Seamons, making an instrument now used by hundreds of stations worldwide a direct New Zealand contribution to global ionospheric science. In the United States, the HamSCI programme — funded by NSF and NASA and anchored at NJIT, Case Western Reserve University and MIT Haystack Observatory — has formalised the amateur contribution into a recognised scientific network, deploying GRAPE receivers to monitor the 10 MHz WWV and WWVH reference signals with GPS-disciplined timing as a distributed real-time TEC measurement system, and developing the Personal Space Weather Station (PSWS) concept for standardised citizen-science HF monitoring. HAARP at Gakona, Alaska — now operated by the University of Alaska Fairbanks and open to scheduled scientific campaigns — broadcasts known HF transmissions receivable by SDR stations on any continent, serving as a controlled reference signal for ionospheric path-loss and reflection-height measurement. Millstone Hill’s incoherent scatter radar at MIT Haystack and the NOAA Space Weather Prediction Center’s ionosonde network anchor the professional tier. Canada contributes SuperDARN nodes operated by the University of Saskatchewan and University of Calgary, the CHAIN (Canadian High Arctic Ionospheric Network) GPS-TEC array across the Arctic Archipelago, and Defence Research and Development Canada’s sustained HF propagation research programme for military communications. The United Kingdom is the literal birthplace of the discipline: Appleton’s vertical-incidence soundings were made from Cambridge and the National Physical Laboratory, and RAL Space at Harwell continues a world-leading space-environment research tradition spanning nearly a century. The British Antarctic Survey operates ionosondes at Halley Bay and Rothera and a SuperDARN radar at the Falkland Islands, providing Southern Ocean high-latitude coverage no other national programme reaches; the UK is a founding member of EISCAT, whose incoherent scatter facilities at Tromsø and Longyearbyen now represent the world’s most powerful continuous ionospheric diagnostic capability following Arecibo’s loss. France leads through CNRS LPC2E at Orléans, the SuperDARN radar on the Kerguelen Islands, and continued CNES satellite ionospheric monitoring through the DORIS geodetic network and the heritage of the DEMETER space-environment mission. Germany contributes through DLR’s space weather monitoring operations, GFZ Potsdam’s global GNSS-based ionospheric TEC products, and the Max-Planck Institut für Sonnensystemforschung at Göttingen; Germany’s DARC amateur radio organisation runs one of Europe’s most active WSPR and FT8 monitoring networks, and Germany is a member of the EISCAT consortium alongside the UK, Norway, Sweden, Finland and Japan.
What the Data Is Enabling
The scientific output from this distributed network is already reshaping the field. Frissell’s 2014 Space Weather paper demonstrated that RBN data could resolve solar-flare-induced sudden ionospheric absorption in real time across a continental-scale distributed receiver array. The 2017 Great American Eclipse produced a Geophysical Research Letters paper — “Modeling Amateur Radio Soundings of the Ionospheric Response to the 2017 Great American Eclipse” — showing that amateur QSO patterns traced the F-region eclipse shadow at finer spatial and temporal resolution than any conventional instrument deployed for the event. Travelling ionospheric disturbances (medium-scale MSTIDs and large-scale LSTIDs) are now routinely extracted from WSPR and FT8 path-strength time series, including the acoustic-gravity wave signature of the January 2022 Hunga Tonga–Hunga Ha’apai eruption, which propagated around the planet and was captured by distributed HF receivers before most conventional instruments had processed their data streams. High-precision Doppler analysis of WSPR and FST4W traces yields F-layer reflection-height resolution at the kilometre level, previously requiring a purpose-built chain of ionosondes. Sporadic-E climatology has been extended retroactively into oceanic regions that historically had no direct measurements at all. NSF, NASA and ESA grants now routinely cite amateur datasets in funded proposals, URSI Commission G (Ionospheric Radio and Propagation) sessions regularly include amateur-radio-derived results, and the historic boundary between hobbyist measurement and academic ionospheric science has effectively dissolved at the HF propagation interface — which is one of the central themes this conference is designed to celebrate, examine, and accelerate.
SDR Conference 2026 is explicitly positioned to push this collaboration further. We welcome presentations spanning the full breadth of the field: ground-based ionosonde and SuperDARN observations and their operational applications; low-cost SDR receiver builds for GRAPE and Personal Space Weather Station (PSWS) class monitoring; WSPR, FST4W and FT8 propagation data analysis methods and results; HAARP reception campaigns and citizen-science coordination; ionospheric modelling validated against distributed amateur datasets; Australian HF propagation for defence and civil communications including JORN channel modelling; Southern Hemisphere coverage gaps and how SDR networks are closing them; and the policy and coordination questions raised by a global sensing network running almost entirely on volunteer infrastructure. If you have built a receiver, run a monitoring campaign, or published results from amateur-collected HF data, this is the conference where that work belongs.
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