# Poseidon-4 SAR Altimeter
*component . products*

Ku/C-band nadir-pointing SAR radar altimeter for Sentinel-6 sea-surface height and inland-water measurements. Stored as component candidate because current D1 SAR sensor spec lacks Ku-band/radar-altimeter support.

## Specifications
- **manufacturer**: esa
- **deployment context**: orbital
- **entity type**: component
- **last verified date**: 2026-06-16
- **verified by**: agency-doc
- **claim status**: agency-sourced
- **provider**: esa
- **attributes**: {"kind":"component","manufacturer":"esa","deployment_context":"orbital","description":"Ku/C-band nadir-pointing SAR radar altimeter for Sentinel-6 sea-surface height and inland-water measurements. Stored as component candidate because current D1 SAR sensor spec lacks Ku-band/radar-altimeter support."}
- **relevance**: in-scope

## Editorial
Poseidon-4 is the primary nadir-pointing dual-frequency SAR radar altimeter for the Copernicus Sentinel-6 mission.[^copernicus-s6-payload][^esa-s6-how-it-works][^wmo-poseidon-4] It flies on Sentinel-6A Michael Freilich and Sentinel-6B, with WMO listing Sentinel-6A for 2021-2027 service and Sentinel-6B for 2026-2032 service.[^wmo-poseidon-4] The main surface-height channel is Ku band at 13.575 GHz with 320 MHz bandwidth, paired with a 5.41 GHz C-band channel with 320 MHz bandwidth for dual-frequency ionospheric correction.[^copernicus-s6-payload][^wmo-poseidon-4] Poseidon-4 uses interleaved operation to collect SAR high-resolution and pulse-limited low-resolution measurements, maintaining continuity with Jason-series altimetry while improving Sentinel-6 measurement detail.[^esa-s6-how-it-works][^wmo-poseidon-4] Its supported measurements include sea-surface height, significant wave height, wind speed, ice topography, and ionospheric correction support from the second frequency.[^copernicus-s6-payload][^wmo-poseidon-4][^esa-s6-how-it-works]

## Compositional position
- sentinel-6b (missions) --[mission_payloads]--> Poseidon-4 SAR Altimeter
- sentinel-6a (missions) --[mission_payloads]--> Poseidon-4 SAR Altimeter

## Sources
- [copernicus-s6-payload] | Sentinel-6 instrument payload, Copernicus Sentinel Online | https://sentinels.copernicus.eu/missions/sentinel-6/instrument-payload | tier=agency-doc | accessed=2026-06-16
- [esa-s6-how-it-works] | How Sentinel-6 Poseidon-4 works, ESA | https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-6/How_it_works | tier=agency-doc | accessed=2026-06-16
- [wmo-poseidon-4] | WMO OSCAR instrument record: Poseidon-4 | https://space.oscar.wmo.int/instruments/view/poseidon_4 | tier=agency-doc | accessed=2026-06-16

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Source: https://eo-atlas.org/products/component/poseidon-4
Maintainer: SpectraWorks B.V. (CC-BY 4.0)