# GNSS radio occultation
*sensing . methodologies*

Retrieves vertical profiles of atmospheric refractivity, temperature, pressure, humidity, and ionospheric electron density from direct GNSS signals refracted through the atmospheric limb.

## Specifications
- **family**: GNSS-RO
- **requirements envelope**: {"kind":"geometric","repeat_pass_geometry":false,"polarisation_modes":["L-band GNSS"]}
- **entity type**: methodology
- **last verified date**: 2026-06-08
- **verified by**: agency-doc
- **claim status**: unclaimed
- **subtype**: sensing
- **attributes**: {"family":"GNSS-RO","summary":"Retrieves vertical profiles of atmospheric refractivity, temperature, pressure, humidity, and ionospheric electron density from direct GNSS signals refracted through the atmospheric limb.","requirements_envelope":"{\"kind\":\"geometric\",\"repeat_pass_geometry\":false,\"polarisation_modes\":[\"L-band GNSS\"]}","kind":"sensing"}
- **technology**: gnss-signal-sensing
- **relevance**: in-scope

## Editorial
GNSS radio occultation uses a receiver on a low-Earth-orbit platform to track GNSS signals as they set or rise behind the atmospheric limb. Refraction along the limb path changes signal delay and bending angle; retrieval processing converts those measurements into refractivity and then into atmospheric temperature, humidity, pressure, and related profile products.[^ucar-gnss-ro][^ecmwf-gpsro]

This method is direct atmospheric and ionospheric sounding. It also supports space-weather profiling because the same occultation geometry can retrieve ionospheric electron density and total electron content products.[^ucar-gnss-ro][^noaa-ro-needs]

GNSS radio occultation is distinct from GNSS reflectometry. Radio occultation uses direct signals refracted through the limb for vertical atmospheric and ionospheric profiles. GNSS reflectometry uses reflected navigation signals from the surface to retrieve ocean wind, soil moisture, sea-ice, or roughness properties.

## Sources
- [ucar-gnss-ro] | GNSS Radio Occultation, UCAR COSMIC | https://www.cosmic.ucar.edu/what-we-do/gnss-radio-occultation | tier=operator-engineering | accessed=2026-06-08
- [ecmwf-gpsro] | GPSRO monitoring, ECMWF | https://www.ecmwf.int/en/forecasts/quality-our-forecasts/monitoring/gpsro-monitoring | tier=agency-doc | accessed=2026-06-08
- [noaa-ro-needs] | Assessment of Solution-Agnostic Observational Needs for GNSS-RO Data, NOAA NESDIS | https://www.star.nesdis.noaa.gov/sat/recommendationLibrary/SAT_Memo_Observational_Needs_for_Radio_Occultation_202306.pdf | tier=agency-doc | accessed=2026-06-08 | published=2023-06-14

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Source: https://eo-atlas.org/methodologies/gnss-radio-occultation
Maintainer: SpectraWorks B.V. (CC-BY 4.0)