AMSU

AMSU
Name	Advanced Microwave Sounding Unit
Acronym	AMSU
Manufacturer	NASA / NOAA contractors
Country	United States
Applications	Atmospheric sounding, weather forecasting, climate monitoring
Launched	1998–2010 (series)
Status	Operational/legacy

AMSU is a series of spaceborne microwave radiometers developed to measure atmospheric temperature and humidity profiles from Low Earth Orbiting satellites. The instruments provided multispectral microwave observations that supported numerical weather prediction from platforms operated by NOAA, EUMETSAT, NASA, and partner agencies such as JAXA and CNSA. AMSU data contributed to operational forecasting, climate records, and research programs involving organizations like ECMWF, UK Met Office, GMAO, and JMA.

Overview

AMSU instruments followed heritage from microwave sounding systems including the SSM/T, MSU, and HIRS, extending capabilities developed under programs led by NOAA, NASA and contractors such as Ball Aerospace and Honeywell. They flew on polar-orbiting platforms coordinated via the World Meteorological Organization and assimilated by centers such as NCEP, JMA, Met Office, Météo-France, and DWD. AMSU supported initiatives like the Global Climate Observing System, GCOS, WMO Integrated Global Observing System, and contributed to datasets used in the IPCC assessments and studies by teams at CIRES and NCAR.

Instrument Design and Specifications

The AMSU design comprised two main units often referred to as microwave sounders and imagers, developed in the context of engineering advances from contractors including Honeywell, TRW Inc., and ITT Corporation. The radiometer arrays covered frequency bands near oxygen and water-vapor absorption lines and interfaced with satellite bus systems from manufacturers such as Lockheed Martin and Northrop Grumman. Key specifications included nadir spatial resolution, channel center frequencies, antenna beamwidth, and noise-equivalent delta temperature derived through calibration methods pioneered at NASA Goddard Space Flight Center and NOAA/NESDIS. Instrument subsystems used components from suppliers like RCA and Raytheon, with thermal control designs similar to those on TIROS-N and POES series platforms. AMSU channels were designed for vertical weighting functions that aligned with retrieval algorithms produced by teams at ECMWF, NOAA GFDL, and NASA JPL.

Flight History and Platforms

AMSU units flew on polar-orbiting satellites in sun-synchronous orbits built by spacecraft programs including NOAA-KLM series, MetOp-A, EOS Aqua derivatives, and missions coordinated with EUMETSAT and NASA. Launch vehicles delivering these platforms included Delta II, Ariane 5, Atlas V, and sometimes Pegasus air-launched vehicles. Flight operations coordinated with ground segments such as EUMETCast, HRPT, and DMSP relay networks, and mission planning involved agencies like USAF Space Command and ESA. The series succeeded the MSU instruments and preceded instruments such as the ATMS, preserving continuity across satellite programs managed by NOAA and partners like CIRA.

Data Processing and Applications

Data from AMSU were processed through operational pipelines at NOAA/NESDIS, research centers including ECMWF, CMA, and university groups like University of Wisconsin-Madison and Colorado State University. Algorithms produced geophysical products—temperature profiles, humidity profiles, and cloud liquid water—used in numerical weather prediction systems at NCEP, Met Office Unified Model, and ECMWF Integrated Forecasting System. Reanalysis projects such as ERA-Interim, ERA5, MERRA, and CFSR ingested AMSU radiances, which were also exploited in climate trend analyses by NOAA ESRL, NASA GISS, and institutions like Princeton University and Columbia University's Lamont–Doherty Earth Observatory. Applications extended to tropical cyclone studies conducted by JTWC and NHC, precipitation retrievals used by TRMM and GPM investigators, and assimilation research at UCAR and NCAR.

Calibration and Validation

Calibration schemes for AMSU used onboard blackbody references and cold-space views, building on techniques developed at NASA Goddard and validated via field campaigns by groups such as ARM and SPARC. Inter-satellite calibration efforts involved cross-comparisons with instruments like SSM/I, ATMS, and AMSR-E, coordinated by agencies including GSICS and WMO. Validation campaigns compared AMSU retrievals to radiosonde networks maintained by IGRA, RAOB stations, and targeted campaigns by NOAA Air Resources Laboratory and research consortia at Leipzig University and University of Tokyo. Long-term stability assessments informed climate monitoring by IPCC authors and groups such as Hadley Centre.

Limitations and Challenges

AMSU faced challenges such as calibration drift, footprint-size limitations, and sensitivity to cloud and surface emissivity that complicated retrievals over heterogeneous terrain including Sahara Desert, Amazon Rainforest, and polar regions like Antarctica and Greenland. Interference issues included radio-frequency interference monitored by ITU and mitigation strategies developed with partners such as ESA and EUMETSAT. Integration into multi-sensor frameworks required harmonization with datasets from MODIS, AVHRR, CrIS, and microwave imagers like AMSR2, managed through initiatives at NOAA and NASA to ensure consistent climate records used by IPCC and national meteorological services.

Category:Remote sensing instruments Category:Weather satellites