Aqua (2002-now)

NASA, Sun-synchronous, near polar orbit, afternoon (1:30 pm) ascending node, altitude 705 km

The NASA EOS-Aqua platform (Source:

The NASA EOS-Aqua is a science multi-purpose satellite mission collecting information about the Earth’s water cycle, including evaporation from the oceans, water vapor in the atmosphere, clouds, precipitation, soil moisture, sea ice, land ice, and snow cover on the land and ice. Additional variables also being measured by Aqua include radiative energy fluxes, aerosols, vegetation cover on the land, phytoplankton and dissolved organic matter in the oceans, and air, land, and water temperatures. Its polar orbit delivers repeat coverage viewing the entire Earth’s surface every 1 to 2 days. Aqua was originally developed for a six-year design life but has now far exceeded that original goal. It continues transmitting high-quality data from four of its six instruments:

  • Atmospheric InfraRed Sounder (AIRS)
  • Advanced Microwave Sounding Unit (AMSU-A)
  • Clouds and Earth’s Radiant Energy System (CERES): 2 identical CERES instruments aboard Terra providing cloud property estimates. 1 instrument operates in a cross-track scan mode and the other in a biaxial scan mode. Twins of CERES aboard NASA Terra.
  • Humidity Sounder for Brazil (HSB)
  • Advanced Microwave Scanning Radiometer for EOS (AMSR-E)
  • Moderate-Resolution Imaging Spectroradiometer (MODIS): passive sensor, atmosphere (aerosols, clouds, CO – Carbon monoxide), surface, fire. Swath 2,330-km-wide viewing swath, 1-2 days global coverage in 36 discrete spectral bands. Twins of MODIS aboard NASA Terra.

Aura, NASA (2004-now)

The NASA EOS-Aura (“breeze” in Latin) satellite is focussed on observing atmospheric chemistry, in order to contribute to address major environmental questions related to the O3 – Ozone layer, the sources – chemical transformation and transport of tropospheric pollutants and the Earth’s climate. It consist of 4 instruments:

  • High Resolution Dynamics Limb Sounder (HIRDLS)
  • Microwave Limb Sounder (MLS)
  • Tropospheric Emission Spectrometer (TES)
  • Ozone Monitoring Instrument (OMI): Dutch-Finnish passive sensor, air quality purpose, designed for trace gas pollutants and aerosols

CALIPSO (2006-now)

Joint NASA and CNES

The Delta II rocket with CALIPSO and CloudSat (Source:
  • Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP): active sensor (lidar), high-resolution vertical profiles of aerosols and clouds.
  • Imaging Infrared Radiometer (IIR): cirrus cloud emissivity and particle size.
  • Wide Field Camera (WFC): a modified version of the commercial off-the-shelf Ball Aerospace CT-633 star tracker camera.

Greenhouse gases Observing SATellite “IBUKI” (GOSAT) (2009-now)

GOSAT satellite, artist view and lift off. Credit JAXA (Source:

Joint effort of the Japan Ministry of the Environment (MOE), the Japan National Institute for Environmental Studies (NIES), and the Japan Aerospace Exploration Agency (JAXA), GOSAT is the 1st worldwide satellite mission specifically designed to observe the concentrations of CO2 – Carbon dioxide & CH4 – Methane, the two major greenhouse gases, from space and to estimate related fluxes on a subcontinental scale (several thousand km2). The spacecraft was launched successfully on January 23, 2009, and has been operating properly since then at the altitude of 666 km. The observation instrument on-board the satellite is the Thermal And Near-infrared Sensor for carbon Observation (TANSO), which is composed of two subunits:

  • Fourier Transform Spectrometer (FTS): passive sensor measuring backscattered sunlight in the shortwave and thermal infrared, spatial resolution 10.5 km, climate purpose, designed for green-house gases (including CO2 – Carbon dioxide & CH4 – Methane) and aerosols
  • Cloud and Aerosol Imager (CAI): cloud characteristics and aerosol amounts in the visible, near, and shortwave infrared, 500 m spatial resolution.

MetOp A (2006-now), B (2012-now) & C (expected 2018)

The MetOp satellites are the first European polar-orbiting missions dedicated to operational meteorology, and lead by EUMETSAT. They carry a set of state-of-the-art sounding and imaging instruments that offer improved remote sensing capabilities to both meteorologists and climatologists. The Metop series is part of the Initial Joint Polar-Orbiting Operational Satellite System (IJPS) constellation, along with the NOAA-18 and NOAA-19 satellites.

MetOp (Source:
  • Advanced Data collection System-2 (A-DCS): UHF receiver (401.65 MHz) and signal processor for locating and/or collecting meteorological data from remote fixed and free floating terrestrial and atmospheric platforms
  • Advanced Microwave Sounding unit A1 & A2 (AMSU-A): microwave sounder temperature clear & overcast conditions,
  • Advanced Very High Resolution Radiometer (AVHRR): passive imaging radiometer, cloud cover, sea surface temperature, ice, snow and vegetation cover
  • Advanced SCATterometer (ASCAT): pulsed radar C-band, global sea surface wind
  • Global navigation satellite system Receiver for Atmospheric Sounding (GRAS): Radio occultation, atmospheric temperature and humidity
  • Global Ozone Monitoring Experiment-2 (GOME-2): passive sensor, air quality purpose, trace gases (pollutants) & aerosols
  • High resolution Infrared Radiation Sounder (HIRS): atmospheric sounder, temperature, humidity, surface temperature, cloud & O3 – Ozone
  • InfraRed Atmospheric Sounding Interferometer (IASI): passive sensor, meteorology purpose (temperature, H2O – Water vapour), chemistry interest (trace gases)
  • Microwave Humidity Sounder (MHS): microwave radiometer, atmospheric H2O – water vapour
  • Search And Rescue SATellite (SARSAT) aided tracking system: VHF/UHF transponder and signal processor for locating and collecting information from remote distress platforms such as Emergency Locator Transmitters (ELTs), and Emergency Position Indicating Radio Beacons (EPIRBs)
  • Space Environment Monitor (SEM): VHF/UHF transponder and signal processor for locating and collecting information from remote distress platforms such as Emergency Locator Transmitters (ELTs), and Emergency Position Indicating Radio Beacons (EPIRBs)

 Orbiting Carbon Observatory-2 (OCO-2) (2014-now)

OCO-2. Credit Jet Propulsion Laboratory (JPL) California Institute of Technology (Source:

The NASA Jet Propulsion Laboratory (JPL) OCO-2 Project primary science objective is to collect the first space-based measurements of atmospheric CO2 – Carbon dioxide with the precision, resolution and coverage needed to characterize its sources and sinks and quantify their variability over the seasonal cycle. OCO-2 flies in a sun-synchronous, near-polar orbit with a group of Earth-orbiting satellites with synergistic science objectives whose ascending node crosses the equator near 13:30 hours Mean Local Time (MLT). Near-global coverage of the sunlit portion of Earth is provided in this orbit over a 16-day (233-revolution) repeat cycle. OCO-2’s single instrument incorporates three high-resolution grating spectrometers, designed to measure the near-infrared absorption of reflected sunlight by CO2 and molecular oxygen. OCO-2 is based on the previously launched Orbiting Carbon Observatory (OCO) satellite that unfortunately failed in 2009 (see in Media).

Sentinel-3 A (2016-now), B (2018-now)

Sentinel-3 A. Left: Artist view of Sentinel-3 and its solar array (Source: Right: Sentinel-3 A lift off on 16th February 2016 (Source: Credit ESA.

The ESA and EUMETSAT Sentinel-3 mission is based on two identical satellites orbiting in constellation for optimum global coverage and data delivery. As part of the Copernicus programme, it observes Earth’s oceans, land, ice and atmosphere to monitor large-scale global dynamics. This includes temperature, colour and height of the sea surface as well as the thickness of sea ice, changes in sea level, marine pollution and biological productivity, monitoring wildfires, mapping the way land is used, provide indices of vegetation state and measure the height of rivers and lakes – complementing the high-resolution measurements of its sister mission Sentinel-2. ESA processes land products and Eumetsat the marine products for application through the Copernicus services. Sentinel-3 carries 4 instruments working in synergy:

  • MicroWave Radiometer (MWR): supporting the SRAL by providing wet atmosphere correction, measure brightness temperature at 23.8 GHz and 36.5 GHz covering a bandwidth of 200 MHz in each channel. The lower frequency channel is mostly sensitive to atmospheric water vapour and the higher frequency channel to cloud liquid water.
  • Ocean and Land Colour Instrument (OLCI): push-broom imaging spectrometer, 21 distinct bands in the 0.4–1.02 μm spectral region tuned to specific ocean colour, vegetation and atmospheric correction measurement requirements, ocean ecosystems, support crop management and agriculture and provide estimates of atmospheric aerosol and clouds. Spatial resolution of 300 m and a swath width of 1270 km, overlapping the SLSTR swath.
  • Precise Orbit Determinaton (POD): package including a Global Navigation Satellite Systems (GNSS) instrument, a Doppler Orbit determination and Radio-positioning Integrated on Satellite (DORIS) instrument and a Laser Retro-Reflector (LRR).
  • Sea and Land Surface Temperature Radiometer (SLSTR):  dual view (near-nadir and backward views) conical imaging radiometer with a spatial resolution of 500 m for visible/near-infrared and short-wavelength infrared channels and 1 km for the thermal infrared channels. Focus on global sea- and land-surface temperatures every day to an accuracy of better than 0.3 K. In addition, 2 dedicated thermal infrared channels optimised for active fire detection and fire radiative power measurement.
  • SAR Radar Altimeter (SRAL): Ku/C Radar Altimeter comprising 1 nadir-looking antenna, externally mounted on the satellite’s +Zs Earth panel, and a central electronic chain composed of a Digital Processing Unit (DPU) and a Radio Frequency Unit (RFU). The main frequency is the Ku-band (13.575 GHz, bandwidth 350 MHz), while the C-band frequency (5.41 GHz, bandwidth 320 MHz) is used for ionospheric correction.

Sentinel-5 Precursor (2017-now)

Supported by ESA and with initiatives from the Netherlands, Sentinel-5 Precursor is part of the Copernicus programme and the first of the atmospheric composition Sentinels, launched in 2017 for an expected lifetime of seven years.. Low Earth Sun-Synchronous orbit, altitude 824 km, local observation time 1:30 pm, it includes only 1 instrument:

Terra (1999-now)

The NASA Terra platform. Credit NASA (Source:

The NASA Terra satellite was launched on 18th December 1999 as the first American space mission to look at Earth system science, collecting  multiple types of data dedicated to various areas of Earth science: e.g. atmospheric composition, carbon cycle and ecosystems, climate variability and changes, Earth’s surface and interior, water and energy cycle, and weather.  It flies in a circular sun-synchronous polar orbit that takes it from north to south (on the daylight side of the Earth) every 99 minutes.

  • Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER): high spatial resolution (15 to 90 m2 per pixel) images of the Earth in 14 different spectral wavelengths from visible to thermal infrared, stereoscopic images and detailed terrain height models. ASTER was built in Japan for the Ministry of Economy, Trade and Industry (METI). A joint United States/Japan Science Team is responsible for instrument design, calibration, and data validation.
  • Clouds and Earth’s Radiant Energy System (CERES): 2 identical CERES instruments aboard Terra providing cloud property estimates. 1 instrument operates in a cross-track scan mode and the other in a biaxial scan mode. Twins of CERES aboard NASA Aqua.
  • Multi-angle Imaging SpectroRadiometer (MISR): Cameras pointed at nine different angle: 1 toward nadir, and the others at the Earth’s surface, of 26.1°, 45.6°, 60.0°, and 70.5°. 4 spectral wavelengths (blue, green, red, and near-infrared). Distinction of types of clouds, aerosol particles, and surfaces.
  • Moderate-resolution Imaging Spectroradiometer (MODIS): passive sensor, atmosphere (aerosols, clouds, CO – Carbon monoxide), surface, fire.  Swath 2,330-km-wide viewing swath, 1-2 days global coverage in 36 discrete spectral bands.
  • Measurements of Pollution in the Troposphere (MOPITT): Focus on the lower atmosphere and the interactions with the land and ocean biospheres: e.g. distribution, transport, sources, and sinks of CO – Carbon monoxide in the troposphere. MOPITT employs the gas correlation spectroscopy by measuring emitted and reflected radiance from the Earth in three spectral bands. Spatial resolution of 22 km at nadir and a swath 640 km wide. Twins of MODIS aboard NASA Aqua.
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