Satellites & instruments

Visible and infrared imagers were among the first spaceborne instrument ever flown. After tests with these type of instruments in the 1950s the advent of operational observations from visible and infrared imagers for weather monitoring started in the 1960s. These type of instruments capture images of visible reflected sunlight and emitted infrared radiation. Meteorological imagers are flow in polar orbits, circling the earth from pole-to-pole at an altitude of about 800 km, and in geostationary orbits, positioned over a fixed position of the equator at an altitude of about 36000 km. Depending on orbit and specifications, these satellites capture imagery at 5x5km to about 0.5x0.5 km spatial, and hourly to 5-minute temporal sampling, respectively.

The data are used by EUMETSAT to generate a multitude of climate data records such as the cloud, radiation, land and sea surface temperature and Atmospheric Motion Vectors products. The latter and the radiances themselves are also used for the assimilation into global reanalysis. EUMETSAT is recovering, recalibrating and reprocessing observations from many past and present visible and infrared imagers and prepares on future imagers on MTG and EPS-SG missions with the objective to provide best possible quality long time-series for climate analysis.

AVHRR on NOAA and Metop

With more than 40 years of operation the Advanced Very High Resolution Radiometer (AVHRR) is one of the oldest instruments, carried on-board the National Oceanic and Atmospheric Administration (NOAA) series starting in 1979 with TIROS-N and still operating in 2020 on EUMETSAT’s Metop satellite series. The AVHRRs measure the reflectance from Earth in three (first generation) to five (third generation) spectral bands, ranging from the visible to infrared wavelengths. Although AVHRR was designed for meteorological purposes, it proved very valuable observing global climate variability of land, ocean, and atmosphere.

MVIRI on Meteosat First Generation

The Meteosat Visible Infra-Red Imager (MVIRI) is a three-channel imager collecting measurements at visible, infrared, and water vapour wavelengths. It was designed to scan the part of the Earth from a geostationary orbit every 30 minutes at a 5x5 km spatial sampling. MVIRI was operated on-board Europe’s first series of meteorological satellites, Meteosat-1 to -7 operated from 1977 to 2017.

SEVIRI on Meteosat Second Generation

The successor of MVIRI is called Spinning Enhanced Visible and InfraRed Imager (SEVIRI) . Similar to MVIRI instrument it collects measurements at visible, infrared and water vapour wavelengths, but over more channels (12), and with a better temporal (15-minutes) and spatial (3x3km) sampling. SEVIRI is being operated on-board Europe’s second series of meteorological satellites, Meteosat-8 to -11 from 2004 to present day.

Visible and Infrared Imagers on JMAs Geostationary Satellites

In collaboration with the Japanese Meteorological Agency (JMA), EUMETSAT developed methods to recalibrate the infrared and water vapour channels of these satellites and to detect image anomalies in all channels of JMA’s geostationary satellites, GMS to GMS-5, MTSAT-1R, and MTSAT-2..

The Visible and Infrared Spin Scan Radiometer (VISSR) was operated on-board the Geostationary Meterological Satellites (GMSs) of the Japanese Meteorological Agency (JMA). The VISSR instruments on the first four GMS satellites, were two-channel imagers collecting measurements at visible and infrared wavelengths. VISSR on GMS-5 and GOES-9, a NOAA satellite that took over operations from JMA during 2003–2005, collected measurements at one visible, one infrared, and one water vapour wavelength. The GMS’s were spin-stabilized satellites that were positioned at a sub-satellite longitude of 140° E. They scanned the complete Earth disk every 3 hours before 1989, and every 30 minutes after 1989. VISSR was operated on-board GMS to GMS-5 from 1978 to 2003.

The JAMI instrument on-board the Multi-functional Transport Satellite-1R (MTSAT-1R) is the successor of the JMA’s first series of GMS geostationary satellites. MTSAT-1R is a three-axis stabilised satellite and was positioned at a sub-satellite longitude of 140° E. Compared to the VISSR instrument, the JAMI instrument carried more channels, i.e., one visible and four infrared channels, and collected data at a higher spatial resolution. It scanned the complete Earth disk every 30 minutes and was operated from 2005 to 2014.

The IMAGER instrument on-board the Multi-functional Transport Satellite-2 (MTSAT-2) is the successor of the JMA’s MTSAT-1R geostationary satellite. MTSAT-2 is a three-axis stabilised satellite that was positioned at a sub-satellite longitude of 145° E and was operated from 2007 to 2016. The IMAGER instrument is very similar to JAMI, it also carried one visible and four infrared channels and scanned the complete Earth disk every 30 minutes.

Infrared sounding instruments were first operated in the 1970s. The term sounders refers to the fact that these type of instruments sense emitted thermal radiation coming from the Earth surface and from different heights in the atmosphere. Infrared sounders are capable to provide information on vertical profiles of temperature and water vapour from the Earth's surface to the top of the atmosphere. The assimilation of the data has been a significant step forward in the quality of global weather prediction and climate reanalysis. Infrared sounders sense in spectral wavelength between 3 and 15 micrometre. Early sounders, such as the High Resolution Infrared Radiation Sounder (HIRS), scanned the Earth in 20 spectral channels, whereas present day sounders, such as the Infrared Atmospheric Sounding Interferometer (IASI), scans the Earth in over 8000 spectral bands.

The assimilation of radiances into numerical prediction models for reanalysis and the retrieval of data records of Essential Climate Variables from these data, such as temperature and humidity profiles as well as cloud properties, atmospheric composition, and sea surface temperature are major applications for the data. In addition, these data serve as reference for the recalibration of heritage infrared imagers, such as MVIRI instrument in geostationary orbit. EUMETSAT is recovering and reprocessing observations from many past and present infrared sounders and plans the use of future sounders with the objective to extend time-series both back and forward in time up.

HIRS on NIMBUS

The HIRS instrument was first flown on board NIMBUS-6, which collected observations from June 1975 until May 1976. Although this instrument is inferior to the new multi-spectral instruments, such as AIRS and IASI, it is of sufficient accuracy to extend our infrared sounder climate data records back in time and provide over 40 years of global temperature and humidity profiles.

HIRS/2 on TOVS and NOAA-6 to -14

The TIROS Operational Vertical Sounder (TOVS) equipped aboard NOAA's Television Infrared Observation Satellite Program (TIROS) series is among the first polar orbiting satellites carrying sounding instruments that were capable to provide vertical profiles of temperature and water vapour from the Earth's surface to the top of the atmosphere. Among others, the TOVS operated the HIRS/2 instrument, which was a modified version of the HIRS instrument on NIMBUS. HIRS/2 operations were continued on the NOAA-6 to -14 satellites that were operated from 1983 to 2007.

HIRS/3 on NOAA-15 to -17

Further modified instrument compared to HIRS/2, of which the most important was the modification made to the spectral position and width of the 6 µm water vapour channel. This instrument was operated on NOAA-15 to -17 from 1998 to 2013.

HIRS/4 on Metop and NOAA-18 and -19

The HIRS/4 has an improved spatial resolution (10 km) compared to its predecessors (18 km) but is spectrally mostly unchanged to HIRS/3. The HIRS/4 instrument is operated since 2006 to the present day with the last instrument on the Metop-B satellite.

AIRS on AQUA

The launch of the Atmospheric Infrared Sounder (AIRS) in 2002 marked the start of a new era of infrared sounding. Apart from some pilot satellites, AIRS is the first hyper-spectral infrared radiometer designed to support the requirements for operational medium range weather forecasting during its nominal lifetime of at least seven years. The advantage of these hyper-spectral infrared radiometers over HIRS is their much finer spectral sampling allowing to measure atmospheric temperature and humidity profiles more accurate and with better vertical resolution. The AIRS is operational since 2002 to the present day.

IASI on Metop

The Infrared Atmospheric Sounding Interferometer (IASI) is the most advanced instrument carried on the Metop satellites. Its launch marked a significant technological step forward, by providing meteorologists with data of unprecedented accuracy and resolution on atmospheric temperature and humidity with which to improve weather prediction. This EUMETSAT instrument is also destined to provide a wealth of data on various components of the atmosphere to further our understanding of atmospheric processes and the interactions between atmospheric chemistry, climate and pollution. In addition, the IASI delivers data on land-surface emissivity and sea-surface temperature (in cloud free conditions). The Infrared Atmospheric Sounding Interferometer (IASI) was the first operational interferometer in space measuring the 3.5–16.4-μm (610–2825 cm−1) spectrum in 8461 spectral channels with a spectral resolution of 0.5 cm⁻¹ and a spectral sampling interval of 0.25 cm⁻¹. The IASI is operational since 2007 to the present day.

Microwave imaging and sounding instruments were first operated in the late 1970s. These instruments sense upwelling microwave radiation coming from the Earths’ surface and the atmosphere. Oxygen and humidity in the atmosphere, in different forms, attenuate the microwave radiation emitted from the surface of the Earth, cloud or raindrops. The different channels represent signals close to the surface and from different altitude ranges. Total column water vapour and cloud liquid water path, precipitation, as well as near surface wind speeds can be inferred from microwave imager observations over oceans. In addition, it is also possible to retrieve quantitatively reliable information on sea ice, land snow cover and over-land precipitation. whereas atmospheric temperature and humidity profiles can be derived from the observations of sounding channels, most often in combination with infrared sounder observations. Microwave imagers typically sense polarised radiation at frequencies between 18 and 90 GHz whereas sounders typically sense at frequencies between 19 and 183 GHz, where the frequencies around 60 and 183 GHz are used for temperature and humidity sounding.

Assimilation in global reanalysis and the derivation of wind, temperature and humidity data records are the main usages of microwave imager and sounder data in the context of climate monitoring. EUMETSAT reprocesses observations from many past and present microwave imager and sounder instruments, and prepares for future microwave sensors on EPS-SG with the objective to extend our time-series both back and forward in time.

SMMR on Nimbus-7

The Scanning Multi-channel Microwave Radiometer (SMMR) , carried on the Nimbus-7 satellite, was a ten-channel sensor that measured polarised radiation in five microwave frequencies: 6.6, 10.7, 18.0, 21.0, and 37.0 GHz. It was operated from late 1978 – 1987. Reprocessed SMMR radiances are available from the CM SAF and derived sea ice coverage data from the OSI SAF.

SSM/I on DMSP

The Special Sensor Microwave – Imager (SSM/I) on DMSP satellites was operated on DMSP-F08 to DMSP-F15 from 1987-2008. It was a seven channel passive microwave imaging radiometer that measured horizontal (H) and vertical polarization (V) at three frequencies (19, 37, and 85 GHz) and vertical polarization at 22 GHz. These measurements are provided at a sampling of 25 km for the 19, 37, and 22 GHz channels and a sampling of 15 km for the 85 GHz channel. CM SAF provides reprocessed SSM/I radiances and a big set of derived atmospheric variables over the ocean. OSI SAF uses the radiances for their long sea ice coverage data record.

SSM/T2 on DMSP

The Special Sensor Microwave – Humidity (SSM/T2) on NOAA’s Defense Meteorological Satellite Program (DMSP) is being operated on DMSP-F11 to DMSP-F15 since 1991-2005, with useful data starting in 1994. Reprocessed and uncertainty quantified radiances are provided by EUMETSAT to global reanalysis centres.

SSMIS on DMSP

The Special Sensor Microwave - Imager/Sounder (SSMIS) instrument was replacing and merging SSM/I, SSM/T and SSM/T-2 flown on DMSP up to the DMSP-F15 satellite. They are being operated on DMSP-F16 to DMSP-F19 from 2003 to present day. SSMIS operates almost identical imager channels as SSM/I, with the only exception being that the 85 GHz channels (SSM/I) were replaced 91 GHz channels. In addition, it operates sounding channels as on SSM/T and SSM/T2. SSMIS data are used to extend the long time series build with SMMR and SMM/I data in the CM SAF and OSI SAF.

AMSU-A on NOAA and Metop

The Advanced Microwave Sounding Unit - A (AMSU-A) is being operated on NOAA-15 to -19 since 1998 with the last one operating on NOAA-18 and on EUMETSAT Metop satellites since 2006. The data are used in combination with IASI data for a temperature and humidity profile data record.

AMSU-B on NOAA

The Advanced Microwave Sounding Unit - B (AMSU-B) was operated on NOAA-15 to -17 from 1998 to 2014. Reprocessed and uncertainty quantified radiances are provided by EUMETSAT to global reanalysis centres.

MHS on NOAA-18 and -19 and Metop

The Microwave Humidity Sounders (MHS) is a five-channel, total power, microwave radiometer designed to scan through the atmosphere to measure the apparent upwelling microwave radiation from the Earth at specific frequency bands. Since humidity in the atmosphere (ice, cloud cover, rain and snow) attenuate microwave radiation emitted from the surface of the Earth, it is possible, from the observations made by MHS, to derive a detailed picture of atmospheric humidity with the different channels relating to different altitudes. Temperature at the surface of the Earth can also be determined. The MHS instrument has been operated on NOAA (NOAA-18 and -19) and Metop (Metop-A (retired), Metop-B, and -C) since 2005 to the present day. Reprocessed and uncertainty quantified radiances are provided by EUMETSAT to global reanalysis centres. In addition, these data are also input the temperature and humidity profile data record derived with combined IASI data.

MWHS on Feng Yun

The Micro-Wave Humidity Sounder (MWHS) is an instrument operated by the Chinese Metrological Agency (CMA) since 2008 to the present day. Reprocessed and uncertainty quantified radiances are provided by EUMETSAT to global reanalysis centres.

ATMS on SNPP and NOAA-20

The Advanced Technology Microwave Sounder (ATMS) is an instrument operated on NOAA’s Suomi National Polar-orbiting Partnership and NOAA-20 satellites since 2011. Reprocessed and uncertainty quantified radiances are provided by EUMETSAT to global reanalysis centres.

With the advent of Radio Occultation (RO) instruments in the 2000s, a ‘new’ Earth Observation technique for sounding the Earth’s atmosphere was born. These instruments receive radio signals that are continuously broadcasted by Global Positioning System (GPS) navigation satellites of the Global Navigation Satellite System (GNSS), and measure the time delay of the refracted GPS radio signals as the ray signal path skirts the Earth’s atmosphere on its way from the transmitting GPS to the Radio Occultation receiver. From RO measurements globally distributed and very precise vertical profiles of atmospheric parameters, such as temperature and water vapour in the stratosphere and troposphere, can be derived. These RO derived profiles complement those derived from infrared and microwave sounders. Their long-term stability, high accuracy, and high vertical resolution makes them very valuable for weather forecasting and climate monitoring.

Assimilation into global reanalysis models and the generation of climate data records of Essential Climate Variables, such as the temperature and humidity data records by the ROM SAF is the main usage of radio occultation data. EUMETSAT is reprocessing observations from past and present radio occultation instruments with the objective to deliver a as much as possible homogenous time-series that can be continued with future instrument data.

CHAMP

The German geoscience satellite Challenging Mini-Satellite Payload (CHAMP) carried a radio occultation device that was operated from 2000 to 2010.

GRACE

The Gravity Recovery and Climate Experiment (GRACE) is a joint NASA and Deutsches Zentrum

für Luft- und Raumfahrt (DLR) instrument that was operated from 2002 to 2008.

COSMIC-1

The joint Taiwanese and US Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites carrying radio occultation devices were operated from 2006 to 2020. A follow on COSMIC-2 constellation is evolving since 2019.

GRAS on Metop

The GNSS Receiver for Atmospheric Sounding (GRAS) is a Metop instrument that has been operated on on Metop-A (retired), –B, and -C since 2007 to the present day. It is the first operational system for weather prediction and climate research, and collects about 600 bending-angle profiles per day.

Although, tests with the first scatterometers in space were already made in 1970s, it was only in the early 1990s that measurements from a scatterometer in space became available with the SCAT instrument on ESAs ERS-1 satellite followed by several US research missions. Scatterometers are active instruments that emit radar waves towards the atmosphere and Earth and measure, after absorption or scattering, the back scattered radar waves. Over ocean changes in the backscatter power depends on the state of the sea surface from which wind speed and wind direction are inferred. Over land, scatterometer measurements are applied to the study vegetation, soil moisture, or polar ice. The method to derive land quantities, such as soil moisture, is complex because it needs to account for seasonal variations in vegetation growth, and for spatial variations in backscatter power of dry and saturated soil. Although scatterometer based products are relatively coarse resolution (25x25km), a huge advantage of these products is that they are available day and night and are independent of cloud cover. Both ocean surface wind vectors and soil moisture are essential variables of the climate system.

Assimilation in global reanalysis models and the generation of climate data records of ocean winds by the OSI SAF and soil moisture by H SAF are the main usages of the data in the context of climate monitoring. EUMETSAT provides recalibrated time series of observations from the Metop Advanced SCATterometer (ASCAT) instrument that has been operated on Metop-A (retired), –B, and -C since 2007 and prepares for the continuation of the time series with the EPS-SG scatterometer.

Spaceborne visible grating spectrometers were first operated in the 1990s. These spectrometers sense spectra of reflected solar irradiance coming from the Earth and the atmosphere in the ultraviole, visible, and near infrared spectral range (from ~200 nm to a maximum of ~2500 nm) distributed over more than 5000 narrow bands. Scientific analysis of these spectra allows for the retrieval of global maps of atmospheric ozone and trace gas concentrations, as well as ultraviolet radiation and aerosol properties from space.

The Global Ozone Monitoring Experiment- 2 (GOME-2) instrument is the successor of the first spaceborne visible grating spectrometers launched in 1995 (GOME). GOME-2 has been operated on Metop-A (retired), –B, and -C since 2007 to the present day. GOME-2 measures the earthshine radiance and the solar irradiance in the ultraviolet visible spectral range 240–790 nm at a moderate spectral resolution of 0.2–0.4 nm, and a coarse spatial resolution (40 x 80 km).

The data are used for the generation of climate data records of Essential Climate Variables, such as ozone, aerosol properties, or surface albedo products from the AC SAF. These data, in turn, are assimilated into global models for climate reanalysis. EUMETSAT is recalibrating and reprocessing observations from the GOME-2 visible spectrometer with the objective to provide a consistent time series that can be extended with measurements of the Copernicus Sentinel-5 instruments that will fly aboard the EPS-SG satellites.