# Poseidon-3C Altimeter
*component . products*

Dual-frequency nadir radar altimeter on SWOT, collecting measurements in the gap between KaRIn swaths.

## Specifications
- **manufacturer**: cnes
- **deployment context**: orbital
- **entity type**: component
- **last verified date**: 2026-06-16
- **verified by**: agency-doc
- **claim status**: agency-sourced
- **provider**: cnes
- **attributes**: {"kind":"component","manufacturer":"cnes","deployment_context":"orbital","description":"Dual-frequency nadir radar altimeter on SWOT, collecting measurements in the gap between KaRIn swaths."}
- **relevance**: in-scope

## Editorial
Poseidon-3C is a nadir, dual-frequency Ku/C radar altimeter in the Poseidon and Jason heritage line, flown on SWOT rather than on Jason-3.[^poseidon-3c-assessment][^wmo-poseidon-3c][^aviso-poseidon-3c] The instrument operates around 13.575-13.6 GHz in Ku band and around 5.3 GHz in C band, giving SWOT a conventional nadir-altimetry channel alongside its wide-swath Ka-band interferometer.[^wmo-poseidon-3c][^aviso-poseidon-3c][^nasa-podaac-swot-nalt] Its measurements support sea-surface height, significant wave height, wind speed, ionospheric correction, KaRIn calibration, and continuity across the nadir gap between SWOT swaths.[^poseidon-3c-assessment][^nasa-podaac-swot-nalt][^aviso-poseidon-3c] Poseidon-3C is operational on SWOT, with WMO listing a 2023-2029 utilisation window and PO.DAAC distributing SWOT nadir-altimeter products from 2022-Dec-16 to present.[^wmo-poseidon-3c][^nasa-podaac-swot-nalt]

## Compositional position
- swot (missions) --[mission_payloads]--> Poseidon-3C Altimeter

## Sources
- [poseidon-3c-assessment] | Description and In-Flight Assessment of the POSEIDON-3C Altimeter of the SWOT Mission | https://www.mdpi.com/2072-4292/16/22/4183 | tier=peer-reviewed | accessed=2026-06-16 | author=Guerin et al. | published=2024-11-09
- [wmo-poseidon-3c] | WMO OSCAR instrument record: Poseidon-3C | https://space.oscar.wmo.int/instruments/view/poseidon_3c | tier=agency-doc | accessed=2026-06-16
- [aviso-poseidon-3c] | AVISO+ Poseidon-3C instrument page | https://www.aviso.altimetry.fr/en/missions/current-missions/swot/instruments/poseidon-3c.html | tier=agency-doc | accessed=2026-06-16
- [nasa-podaac-swot-nalt] | SWOT Level 2 Nadir Altimeter IGDR Version D, PO.DAAC | https://podaac.jpl.nasa.gov/dataset/SWOT_L2_NALT_IGDR_D | tier=agency-doc | accessed=2026-06-16

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Source: https://eo-atlas.org/products/component/poseidon-3c
Maintainer: SpectraWorks B.V. (CC-BY 4.0)