Guide

How to use the GNSS interference monitor

This site detects radio-frequency interference in GNSS signals recorded by NOAA CORS and IGS reference stations, and lets you explore it at every scale: the whole network on a map, one station's history, a single event down to each satellite, and patterns across many stations.

• Time slider — step through the record one UTC day at a time, drag to scrub, or press play (with loop). The map opens on the most recent day.
• Jump to date — a calendar picker limited to days that have data; it stays in sync while the slider plays.
• Reading the dots — light blue means healthy (no events) and grey means no data. Stations with events run from light green to dark red by their strongest detection, on the scale shown in the legend. Every dot is the same size.
• Station popups — click any dot for the station, date, status and number of events, with a link straight to its station page.
• Fast first view — the latest day draws first so the map is usable immediately, while the full history loads in the background.
• Fullscreen — expand the map to fill the screen.

• Search everywhere — the search box suggests stations as you type; an exact code jumps straight to that station's page.
• Browse by region — type a U.S. state (name or abbreviation) or a country (name or ISO code). Small typos are forgiven.
• Results by region — matching stations are grouped by state or country; click one to open it.
• Availability calendar — the calendar button next to a station shows which days have complete, partial or missing data. Click a day to open that month on the station page.

• C/N0 chart — one line per satellite, with the detection window shaded. Click an event to open it; it stays open until you close it (✕ or Esc).
• Bands & satellites — show L1, L2 or both, and pick exactly which satellites to plot.
• Scale — automatic y-axis, or set your own minimum and maximum.
• Skyplot — where each satellite sat in the sky at the start of the event, sized by how its signal compared with normal.
• Deep dive — the 🔬 button re-runs the detector second by second around the event: every satellite's signal against its model, where each one was in the sky, and why the detector fired.
• Downloads — save the timeline, C/N0 chart or skyplot as PNG, or the full event as JSON with raw C/N0 for each satellite, the expected values and the event record.
• Share an event — copy a link that opens this exact event for anyone, with a preview card when posted in chat or social apps.

• Model calendar — models are listed by training month; pick one to inspect it.
• Mean C/N0 vs elevation — the expected signal strength for each satellite as it rises, with an optional 1σ band. Click a satellite in the legend to isolate it with its overbound band and training points.
• Per-satellite fits — a small chart for each satellite with its fitted curve, its ±ζOB·σ overbound band and, where the model includes them, the training samples. Click one to isolate that satellite in the main chart.
• Model details — the training days and the overbound factor ζOB, with an explanation.
• Compare models — overlay another station's model (the nearest one by default), or compare two models of the same station.

• Year view — step between years; darker days mean a larger share of the selected stations had data.
• Filter — limit it to a country, a U.S. state, or a list of station codes.
• Day details — click any day to see which stations reported, each linking to its page.

• Headline numbers — detections and events (detections up to 30 s apart merged), rates per second processed, average lengths, station-days and sites.
• Breakdowns — a detection-length histogram, and tables by event type, by state or country, and by station.
• Detector view — show every number for all detectors, for the CN0 detectors together, or for Model or IUT alone.
• Exclude — leave a state or station out of every number on the page, instantly.
• Downloads — CSV tables by station, state or event type, the summary cards, or the full data as JSON.

• Guided start — a four-step guide and a one-click example that fills in a sensible state and date range.
• Flexible scope — any mix of states and stations, a date range, which detectors to include, and dates to exclude.
• Results timeline — every event coloured by station, with matches highlighted, plus per-station match counts and timing spread.
• Coincidence explorer — for same-second matches: filter by stations, minimum number of stations, strength, date and time of day; expand a match for exact times, distances between stations and a map.
• Side-by-side C/N0 — open every station's chart for one coincidence together, on a shared scale.
• Recent analyses — reopen recent runs made on the site, or reuse their settings.
• Shareable results — copy a link that reopens the run with your filters applied, with a preview card.

• Summary — total dropouts, seconds lost, days with data and satellites affected.
• Filters — date range, duration, elevation and satellite (PRN).
• Per-satellite chart — dropouts by PRN, by count or by seconds; click a bar to drill in.
• Calendar & daily trend — dropouts by time of day across dates, and a daily count.

• Map — zoom in to see the highways around each station, coloured by distance (red within ¼ mile, then orange, amber and green out to 1 mile). Stations whose roads have not been collected yet show none.
• Selected station — click a station marker to list its nearby highways and their distances.
• Download — a CSV of every highway distance collected so far.

• Charts, map or both — view the traces, a map of the stations, or both; each station links back to its event.
• Layout — stacked or grid, with the same band, satellite and scale controls as the station page.

• Write-ups with live panels — posts can embed interactive station, analysis, map, dropout and comparison panels, each with a link to open it full size.
• Documents — preview attached PDFs and open them full screen.
• Share a post — copy a link that scrolls straight to it.
• Publications — key papers with one-click citation and BibTeX, on the Contact page.

CORS

NOAA's Continuously Operating Reference Stations, mostly in the United States. Station codes are four characters.

IGS

International GNSS Service high-rate stations worldwide. Codes are nine characters and include the country. Support is currently marked experimental.

C/N0 (dB-Hz)

Carrier-to-noise density ratio, a direct measure of received signal quality. A drop below the expected level indicates possible interference.

C/N0 nominal model

A station's normal C/N0 for each satellite by elevation, fitted on a clean training day. Detection measures drops below it.

Model detector

Compares observed C/N0 with the nominal model, satellite by satellite, and flags significant drops.

IUT detector

An intersection–union test that flags a moment only when every visible satellite is below its own threshold at once.

Detection / event

A detection is one interval where a detector fired. Detections within 30 seconds of each other are grouped into one event.

Strength

How strongly the detector fired. An event's strength is its highest value; the mean is its average. Values above 1 exceed the detection threshold.

Station-day

One station on one processed calendar day.

Sidereal day

About 23 h 56 min. GPS satellite geometry repeats roughly 4 minutes earlier each UTC day.

PRN

A GPS satellite's identifying number, used on skyplots, dropout charts and the model charts.

L1 / L2

The GPS signal bands shown on the C/N0 chart.

ζOB

The overbound factor that widens the model's expected spread so normal variation is not flagged.

UTC

All times on the site are in Coordinated Universal Time.