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PPK with free NOAA CORS data

Download free Base stationA GNSS receiver sitting still on a known spot. It figures out how wrong the satellite signals are right now and shares that as corrections.Full definition files from NOAANational Oceanic and Atmospheric Administration. The US agency that includes NGS and runs the CORS network.Full definition and use them to correct your drone or RoverThe receiver that moves around the job, like a survey pole or a drone. It uses the base's corrections to find its exact spot.Full definition data.

NOAA runs hundreds of permanent GPSThe US satellite navigation system. People often use "GPS" to mean all satellite positioning.Full definition base stations across the US. Together they are the NOAA CORSContinuously Operating Reference Station. A permanent GPS receiver that records satellite data all day, every day.Full definition Network (NCNThe NOAA CORS Network. NOAA's nationwide group of permanent base stations, with data free to download.Full definition). CORS means continuously operating reference station: a receiver bolted down in one spot that records satellite data all day, every day.

NOAA posts those recordings online for free in RINEXA standard file format for raw GPS data. Any brand of receiver or software can read it.Full definition, a standard file format any brand can read. You can use one as the base for PPKPost-processed kinematic. Like RTK, but the corrections are applied after the job using recorded data, so no live link is needed.Full definition.

After the flight. No live link needed.Drone or roverlogs raw GNSS dataand photo timesBase data (RINEX)from CORS or your own basePost-processEmlid Studio,RTKLIB or TerraCorrectedphoto positionsAfter the flight. No live link needed.Drone or roverlogs raw GNSSand photo timesBase dataRINEX from CORSor your own basePost-processEmlid Studio, RTKLIBor TerraCorrectedphoto positions
PPK using a CORS station as the base.
Illustrative diagram by FixFinder, not to scale.

1. Pick a station

Use the Nearest base station tool or the list on your state page (for example Pennsylvania). Closer is better. See baseline length.

2. Download the RINEX file (according to NGS)

  • NGSNational Geodetic Survey. The part of NOAA that runs the official US coordinate system, CORS and OPUS.Full definition says most data shows up within about an hour of being recorded.
  • Daily files live at https://geodesy.noaa.gov/corsdata/rinex/YYYY/DDD/ssss/. That's the year, the day of the year (1 to 366), and the station's 4-letter ID. The same files are also on Amazon's cloud (AWS) at noaa-cors-pds.
  • How often it records: after 30 days, NGS thins daily files down to one reading every 30 seconds. The full-rate data from 2004 on is available from NOAA NCEI CLASS, after a 30-day delay. You can ask for part of a day, several days joined, or thinned files through UFCORSA NOAA tool that lets you download CORS data for just the hours you need.Full definition.
  • Download the station's coordinates and antenna details too. Your PPK result can only be as good as the base's position.

3. Process it

  • Emlid Studio (free): load your rover file, the CORS RINEX file as the base, and the navigation file. Its drone workflow can also tag your photos with the corrected positions.
  • RTKLIB (free and open source): use RTKPOST in KinematicMeasuring while moving. The "K" in RTK and PPK.Full definition mode, and set the base position from the CORS coordinates.
  • DJI Terra: can do PPK for supported DJI drones. Check DJI's documents for which models and base file types work.
Keep your DatumThe starting point and ruler that coordinates are measured from. The same spot has different numbers in different datums.Full definition straight. NOAA publishes CORS coordinates in both ITRFInternational Terrestrial Reference Frame. A worldwide datum. In the US it's about a meter different from NAD 83.Full definition and NAD 83(2011)The official US datum for horizontal position right now. Most state networks give coordinates in it.Full definition. Process in the one your client needs (datums). Also, a far-away station recording only every 30 seconds works better for still (Static surveyRecording GPS data with the antenna sitting perfectly still for a while, which gives very precise results.Full definition) jobs than for fast drones. Use a closer station, or your own base recording more often, when you can.
Sources (checked Oct 16, 2026):NOAA CORS Network (NCN)NOAA NGS: CORS data accessNOAA NGS: UFCORSNCN on AWS (NOAA Open Data)Emlid Studio docsEmlid Studio: drone data processingRTKLIB (open source, T. Takasu)DJI TerraDiagrams are FixFinder illustrations. Always follow your equipment's current manual.

Related how-tos

Baseline length and accuracyHow-toFix: FIX, but your points are in the wrong placeHow-toDatums and geoid basics for drone mappingHow-toYour first NTRIP connection on a DJI controllerHow-toFix vs float, and why you lose a fixHow-toFree state network vs paid serviceHow-toNTRIP setup guides for drones and roversGuidesRTK glossaryReference

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