ASCAT

ASCAT
Name	ASCAT
Operator	European Space Agency; EUMETSAT
Mission type	Scatterometer; Earth observation; Remote sensing
Spacecraft	Metop series
Launch	Metop-A; Metop-B; Metop-C
Orbit	Sun-synchronous low Earth orbit
Wavelength	C-band
Status	Operational

ASCAT is a C-band satellite scatterometer flown on the Metop series of polar-orbiting satellites, designed to measure near-surface wind vectors over the ocean and surface roughness over land and ice. It provides routine, all-weather, day-night measurements used by operational agencies such as EUMETSAT, European Centre for Medium-Range Weather Forecasts, and research organizations including National Oceanic and Atmospheric Administration, NASA, and numerous national meteorological services. ASCAT complements microwave sensors like QuikSCAT, SMAP, and Sentinel-1 to support global weather forecasting, oceanography, and cryospheric monitoring.

Overview

ASCAT operates as a wide-swath scatterometer providing backscatter coefficients used to infer surface vector winds and soil moisture proxies. The instrument supports operational forecasting centers such as Met Office, Deutscher Wetterdienst, and Météo-France as well as climate centers including Copernicus Climate Change Service and NOAA National Centers for Environmental Prediction. ASCAT data feed into assimilation systems at institutions like ECMWF, UK Met Office Unified Model, and US Navy NWP for improved cyclone tracking and medium-range forecasts. Its mission objectives align with programs such as Global Ocean Observing System and initiatives by World Meteorological Organization.

Instrumentation and Design

ASCAT is a real-aperture instrument derived from the heritage of scatterometers like ERS-1, ERS-2, and QuikSCAT. Mounted on Metop-A, Metop-B, and Metop-C, it employs multiple antenna beams to form three-antenna swaths that illuminate the surface at several incidence angles. The design includes C-band transmitters and receivers, digital processors, and calibration hardware developed by European contractors and agencies such as Airbus Defence and Space, Thales Alenia Space, and DLR. ASCAT's electronic subsystems interface with spacecraft buses provided by EUMETSAT and European Space Agency programs, while ground segment elements include processing chains at EUMETCast and national data centers.

Data Products and Processing

ASCAT generates calibrated normalized radar cross section (sigma0) measurements, surface wind vector retrievals, and quality flags. Processing levels include Level 1b radiometrically calibrated backscatter and Level 2 geophysical products such as 10 m wind vectors and sea ice extent indicators. Data processing pipelines are maintained by EUMETSAT and adopted by assimilation centers including ECMWF, Met Office, and NOAA NCEP, with ancillary products linked to databases like Global Telecommunication System and Copernicus Marine Service. Retrieval algorithms include variational methods, maximum likelihood estimators, and wind vector ambiguity removal schemes developed by teams at KNMI, Nansen Environmental and Remote Sensing Center, and University of Bremen.

Applications and Uses

ASCAT products serve a wide range of operational and scientific uses: improving numerical weather prediction at centers such as ECMWF and UK Met Office, enhancing tropical cyclone analysis at agencies like Joint Typhoon Warning Center and National Hurricane Center, contributing to ocean surface current estimation used by European Marine Observation and Data Network, and informing maritime safety through services run by International Maritime Organization partners. In cryospheric science, ASCAT backscatter aids studies by Norwegian Polar Institute and Scott Polar Research Institute for sea ice monitoring and glacier motion. Hydrology research groups at USGS, CNR, and CSIRO utilize land-surface roughness proxies from ASCAT for soil moisture and flood monitoring.

Performance and Validation

ASCAT performance is validated against in situ observations from moored buoys such as TAO/TRITON, PIRATA, and Argo float-derived products, and compared with airborne scatterometers and spaceborne instruments like QuikSCAT and Sentinel-1. Evaluation campaigns have involved institutions including WMO, EUMETSAT, NASA Jet Propulsion Laboratory, and NOAA/AOML. Metrics include wind vector accuracy, retrieval ambiguity rates, radiometric stability, and long-term calibration using corner reflectors and vicarious sites studied by Ifremer and Nansen Environmental and Remote Sensing Center.

History and Mission Operations

ASCAT's development built on scatterometer experience from missions such as ERS and QuikSCAT and was integrated into the EUMETSAT Polar System on the Metop platform. Operational control and product dissemination are managed by EUMETSAT in coordination with national meteorological services including Météo-France, Met Office, and Deutscher Wetterdienst. Successive satellites Metop-A, Metop-B, and Metop-C carried ASCAT to ensure continuity, with mission support from entities like ESA, EUMETCast broadcasters, and research partners at KNMI. ASCAT remains a cornerstone of modern scatterometry with ongoing upgrades to processing algorithms and incorporation in multi-sensor data records such as those curated by Copernicus programs.

Category:Satellite instruments Category:Remote sensing of the ocean Category:Earth observation satellites