Atmospheric Humidity
Measurement Types
Atmospheric humidity is the amount of water vapour or moisture in the air, and is vital for weather forecasting due to its impact on clouds, rainfall, storms, and atmospheric movement. Space-based platforms can observe near-surface humidity, vertical humidity profiles, total water vapour columns, and water vapour imagery.
Humidity describes the amount of moisture, or water vapour, in the air. Because warm air can hold more water vapour than cold air, humidity is closely linked to temperature and atmospheric stability. It can be assessed using several measures: 1) 2) 3) 4)
- Relative humidity (RH) - measure of how close the air is to saturation at a given temperature
- Specific humidity - the mass of water vapour relative to the total mass of air
- Mixing ratio - ratio of the mass of water vapour to the mass of dry air
- Dew point - the temperature at which air becomes saturated and water vapour begins to condense
- Wet-bulb temperature - measure of cooling caused by evaporation.
Water vapour in the air also plays an important role in Earth’s energy balance by trapping heat and transferring energy through the atmosphere. As warm, moist air rises, it expands and cools; when it reaches the dew point, condensation forms cloud droplets and releases latent heat. This added energy can strengthen rising air, support cloud development, and intensify storms, particularly thunderstorms and tropical systems.
Ground-based instruments, such as psychrometers and capacitive humidity sensors, can be used to measure atmospheric humidity. Psychrometers use wet-bulb and dry-bulb thermometers to calculate relative humidity from evaporative cooling, while capacitive humidity sensors sense the changes in capacitance of a polymer as it absorbs or releases water vapour. 5)
Satellites can measure atmospheric humidity by detecting how water vapour absorbs and emits electromagnetic (EM) radiation at specific wavelengths. Water vapour has a distinct “spectral fingerprint”, and satellite instruments can observe radiation in microwave and infrared (IR) bands where moisture-related absorption or emission is expected. Microwave sensors are particularly useful because they can detect atmospheric moisture and penetrate cloud cover, while IR sensors often provide higher spatial resolution but are more sensitive to cloud and weather conditions. Each measurement channel records spectral radiance, commonly expressed as brightness temperature, which represents the blackbody temperature that would produce the same radiance at that frequency. Retrieval algorithms then convert these observations into estimates of atmospheric humidity, including humidity profiles and total column water vapour. 6)
Example Products
NASA CLIMCAPS Water Vapour Profiles
CLIMCAPS (Community Long-term Infrared Microwave Combined Atmospheric Processing System is derived from IR measurements by the Atmospheric Infrared Sounder (AIRS, onboard Aqua) and Cross-track Infrared Sounder (CrIS, onboard Suomi NPP/JPSS), and microwave measurements from the Advanced Microwave Sounding Unit (AMSU, onboard Aqua) and Advanced Technology Microwave Sounder (ATMS, onboard Suomi NPP/JPSS). For water vapour retrievals, the IR channel set is centred on water-vapour lines in the 3.7, 6.6, and 12 µm spectral regions. The microwave channel set uses the 89 GHz band for AMSU, and the 165.5 GHz and 183.31 GHz bands for ATMS. The retrieval uses a sequential optimal estimation approach that combines selected infrared and microwave channels, weights them by scene-dependent information content, and retrieves atmospheric variables on standard vertical layers. The record spans 2002 to the present and supports atmospheric sounding applications, with Level-3 outputs provided on a 1° × 1° grid as daily or monthly gridded summaries. 7) 8)
IASI All-Sky Temperature and Humidity Profiles
The EUMETSAT Infrared Atmospheric Sounding Interferometer (IASI) All-Sky Temperature and Humidity Profiles climate data record is derived from IASI observations on the MetOp series, combined with collocated inputs from the Advanced Microwave Sounding Unit-A (AMSU-A) and Microwave Humidity Sounder (MHS), also aboard MetOp, using the Piece-Wise Linear Regression-cube (PWLR3) statistical retrieval.
The dataset provides humidity profiles on European Centre for Medium-Range Weather Forecasts (ECMWF) 137 hybrid sigma levels, alongside 2-m humidity, Total Column Water Vapour (TCWV), and quality indicators. The current release has coverage extending from 10 July 2007 to 5 September 2021 for IASI-A, and from 20 February 2013 to 31 December 2023 for IASI-B. It provides global coverage at roughly 14 orbits per day and supports atmospheric profile analysis for weather, climate, and Numerical Weather Prediction (NWP). 9)
GOES-R Cloud and Moisture Imagery
GOES-R ABI Cloud and Moisture Imagery is derived from the Advanced Baseline Imager (ABI) aboard GOES-R series satellites, using measured reflectance and radiance to produce reflectance factors and top-of-atmosphere brightness temperatures across all 16 ABI bands. The 6.2, 6.95, and 7.34 μm emissive channels support water-vapour analysis. The archive runs from February 2017 to the present with continual updates, providing full-disk imagery every 10 minutes, continental US imagery every 5 minutes, and mesoscale imagery every 60 or 30 seconds. 10) 11)
Global Total Column Water Vapour (ESA CCI and EUMETSAT CM SAF)
The Total Column Water Vapour climate data record is a joint project by the ESA Climate Change Initiative (CCI) and EUMETSAT Satellite Applications Facility on Climate Monitoring (CM SAF). It combines near-infrared imager retrievals over land from the Medium Resolution Imaging Spectrometer (MERIS, onboard Envisat), Moderate Resolution Imaging Spectroradiometer (MODIS, onboard Terra & Aqua), and Ocean and Land Colour Instrument (OLCI, onboard Sentinel-3) with data from the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data (HOAPS) microwave total-column water vapour over open ocean project.
The dataset uses a merged land-ocean approach to provide a homogeneous global Total Column Water Vapour (TCWV) record on daily and monthly timescales. It covers 2002 to 2017 and supports climate-variability and trend analysis, model and reanalysis evaluation, and climate-service applications. 12) 13)
Related Missions
MetOp (Meteorological Operational Satellite Program of Europe)
MetOp is an ESA–EUMETSAT satellite programme supporting weather prediction and climate monitoring. The series provides key atmospheric data, especially temperature and humidity profiles, as well as ocean-surface wind information for numerical weather prediction (NWP).
The first satellite, MetOp-A, was launched in 2006 and each of the three satellites carries 11 instruments. The most relevant for atmospheric humidity are the Infrared Atmospheric Sounding Interferometer (IASI), which measures IR radiation to derive temperature and humidity profiles; the Microwave Humidity Sounder (MHS), which measures microwave radiation to observe humidity and precipitation-related conditions; and the Global Navigation Satellite System Receiver for Atmospheric Sounding (GRAS), which uses Global Navigation Satellite System (GNSS) radio occultation to provide atmospheric temperature and humidity soundings.
Meteosat Third Generation (MTG)
The Meteosat Third Generation (MTG) programme consists of four MTG-I imaging satellites and two MTG-S sounding satellites, with the first, MTG-I1, launched in December 2022. MTG will operate throughout the 2020s to 2040s, replacing the Meteosat Second Generation system. Each MTG-I satellite carries the Flexible Combined Imager (FCI), providing high-frequency visible and infrared imagery to derive Atmospheric Motion Vectors (AMVs) across Europe, Africa, and the surrounding oceans. Humidity sounding is provided by the Infrared Sounder (IRS) aboard the MTG-S satellites, with the prime objective of supporting atmospheric dynamics via tracking of vertical water vapour structures.
VIIRS
The Visible Infrared Imaging Radiometer Suite (VIIRS) is carried aboard the NASA and NOAA Suomi NPP satellite, launched in 2011, and the NOAA Joint Polar Satellite System (JPSS) satellites. Together, these polar-orbiting missions support weather forecasting, climate monitoring and environmental observation.
VIIRS provides global visible and infrared imagery used to observe clouds and atmospheric conditions. The satellites carry the Cross-track Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS), which provide global temperature and moisture profiles for numerical weather prediction.
Aqua
Aqua is a NASA-led Earth Observing System (EOS) satellite, jointly supported by NASA, the National Institute for Space Research (INPE) in Brazil, and the Japan Aerospace Exploration Agency (JAXA). Launched in May 2002, its main focus is studying Earth’s water cycle, including clouds, precipitation, air–sea moisture exchange, radiation, and sea ice.
Aqua launched with six instruments. The most relevant for atmospheric humidity are the Atmospheric Infrared Sounder (AIRS), which measures infrared radiation to retrieve temperature and humidity profiles; the Advanced Microwave Sounding Unit-A (AMSU), which provides microwave atmospheric sounding; and the Humidity Sounder for Brazil (HSB, operated until February 2003), which was designed to measure atmospheric humidity using microwave channels.
Advanced Microwave Scanning Radiometer (AMSR)
AMSR is a series of instruments developed by the Japan Aerospace Exploration Agency (JAXA) and carried on a variety of missions. The first instrument AMSR, operated onboard ADEOS-II from 2002 - 2003, followed by AMSR-E onboard Aqua, which operated from 2002 - 2011. The observations continue with AMSR-2 onboard GCOM-W, launched in 2012, and AMSR-3 onboard GOSAT-GW, launched in 2025.
Himawari-8 and -9
Himawari-8 and Himawari-9 are identical geostationary weather satellites operated by the Japan Meteorological Agency (JMA). Launched in 2014 and 2016 respectively, they support weather forecasting and environmental monitoring across East Asia and the western Pacific.
Each satellite carries the Advanced Himawari Imager (AHI), a 16-channel visible and infrared instrument providing full-disc observations every ten minutes. Its infrared channels observe water vapour at different atmospheric levels and track clouds and water-vapour features to support atmospheric wind measurements and numerical weather prediction.
References
1) Joseph Gentilli, “Atmospheric humidity and precipitation,” 2 May 2026, URL: https://www.britannica.com/science/climate-meteorology/Atmospheric-humidity-and-precipitation
2) CEOS Database/Symbios, “Atmospheric Humidity Fields Measurements Made by Earth Observation Satellites,” URL: https://database.eohandbook.com/measurements/measurements.aspx?measurementTypeID=2
3) Met Office, “Understanding humidity,” URL: https://weather.metoffice.gov.uk/learn-about/weather/types-of-weather/humidity
4) Chris Deziel, “How Does Humidity Affect Weather?,” 24 March 2022, URL: https://www.sciencing.com/humidity-affect-weather-10033063/
5) Royal Meteorological Society, “What is humidity and how is it measured?,” 14 August 2013, URL: https://www.rmets.org/metmatters/what-humidity-and-how-it-measured
6) Miranti Indri Hastuti, “How Satellites ‘See’ the Atmosphere: From Observations to Weather Prediction,” 20 May 2026, URL: https://research.reading.ac.uk/met-darc/2026/05/20/how-satellites-see-the-atmosphere-from-observations-to-weather-prediction/
7) NASA/JPL, “Water Vapor,” URL: https://airs.jpl.nasa.gov/data/guides-docs/climcaps-science/climcaps-science-guide/geophysical-products/water-vapor
8) NASA/JPL, “CLIMCAPS Instrument Configurations,” URL: https://airs.jpl.nasa.gov/data/guides-docs/climcaps-science/climcaps-science-guide/instrument-configs
9) EUMETSAT, “IASI All Sky Temperature and Humidity Profiles,” URL: https://user.eumetsat.int/catalogue/EO:EUM:DAT:0576
10) NOAA/NASA GOES-R Series, “Data Products: Cloud and Moisture Imagery,” URL: https://www.goes-r.gov/products/baseline-cloud-moisture-imagery.html
11) NOAA/NESDIS STAR, “Cloud and Moisture Imagery,” URL: https://www.star.nesdis.noaa.gov/goesr/product_cp_imagery.php
12) ESA Climate Office, “Data,” URL: https://climate.esa.int/en/projects/water-vapour/data/
13) Schröder, Marc; Danne, Olaf; Falk, Ulrike; Niedorf, Anja; Preusker, Rene; Trent, Tim; Brockmann, Carsten; Fischer, Jürgen; Hegglin, Michaela; Hollmann, Rainer; Pinnock, Simon, “A combined high resolution global TCWV product from microwave and near infrared imagers - COMBI,” 2023, URL: https://wui.cmsaf.eu/safira/action/viewDoiDetails?acronym=COMBI_V001