Atmosphere and climate
The instruments nobody's press office can edit.
GNSS signals bend. That bending tells you everything about the air in between.GNSS radio occultation for atmospheric profiling
When a GNSS signal grazes Earth's limb before reaching a low-orbit receiver, its path curves in proportion to atmospheric density. Inverting that curve yields precise vertical profiles of temperature, pressure, and water vapour from the surface to roughly 60 km altitude, with no calibration drift and near-global coverage every six hours.
COSMIC-2 / FORMOSAT-7Spire Global Lemur-2Metop GRAS (GNSS Receiver for Atmospheric Sounding)
Clouds block optical sensors. Water vapour absorbs its own signal.Tropospheric humidity retrieval from microwave sounders
Passive microwave sounders near 183 GHz retrieve tropospheric humidity profiles through cloud cover that defeats every optical instrument. This page explains the physics, the key instruments, and what the data honestly can and cannot resolve.
ATMS (Suomi-NPP / NOAA-20)MHS (Metop-A / B / C)AMSU-B (NOAA-15 / 16 / 17)
The sky looks clear. The column optical depth disagrees.Aerosol optical depth mapping from multispectral imagers
Aerosol optical depth (AOD) quantifies how much sunlight a column of atmosphere scatters or absorbs. Satellites retrieve it at multiple wavelengths, separating dust, smoke, and sulphate pollution by spectral fingerprint and Ångström exponent, with known limits over bright surfaces.
MODIS (Terra / Aqua)VIIRS (NOAA-20 / Suomi-NPP)TROPOMI (Sentinel-5P)
Dust crosses continents. The physics makes it visible from orbit.Saharan and Asian dust plume transport tracking
Mineral dust lofted from the Sahara and Asian deserts can travel thousands of kilometres, disrupting aviation, agriculture and public health. Satellites detect and track these plumes using UV absorbing aerosol index, thermal infrared brightness-temperature differences, and lidar backscatter profiles.
OMPS (Ozone Mapping and Profiler Suite) on Suomi-NPPSEVIRI on Meteosat-11CALIOP lidar on CALIPSO
Cities are warmer than their surroundings. Satellites can prove exactly how much.Urban heat island intensity mapping from thermal infrared
Land surface temperature retrieved from thermal infrared satellites reveals the urban heat island with quantified intensity. Landsat TIRS reaches 100 m resolution; MODIS and ECOSTRESS offer different trade-offs between revisit and detail.
Landsat 8/9 TIRSECOSTRESS (ISS)MODIS MOD11 LST (Terra/Aqua)
Clouds hide the ocean. Microwaves do not.Sea-surface temperature retrieval for oceanography and fisheries
Satellite SST combines thermal infrared precision with microwave all-weather coverage to track ocean heat at daily global scales. The physics of each method sets hard limits on what you can know, and where.
AVHRR on Metop-A/B/CVIIRS on Suomi-NPP and NOAA-20SLSTR on Sentinel-3A/B
The ocean rises three millimetres a year. Proving it took thirty years of physics.Sea-level rise measurement from radar altimetry
Nadir-pointing Ku-band radar altimeters on a continuous satellite series have measured global mean sea-level change since 1992 at millimetre-per-year precision, revealing thermal expansion, ice-melt contributions, and regional divergence from the global mean.
Sentinel-6 Michael Freilich (ESA/EUMETSAT/NASA/NOAA, launched 2020)Jason-3 (OSTM, CNES/EUMETSAT/NASA/NOAA, launched 2016)SARAL/AltiKa (ISRO/CNES, launched 2013)
Ice does not move quietly. Gravity notices first.Ice-sheet mass balance from satellite gravimetry
Twin satellites ranging each other to millimetre precision detect month-to-month shifts in Earth's gravity field caused by ice-mass loss over Greenland and Antarctica. The technique is the only operational method for whole-ice-sheet mass budgets, but its 300 km resolution floor means it cannot pinpoint which glacier is responsible.
GRACE-FO K-Band Ranging (KBR)GRACE (historical archive)ICESat-2 ATL11 (complementary)
The ice is thinning by centimetres. The physics is unambiguous.Ice-sheet surface elevation change from photon-counting lidar
ICESat-2's photon-counting lidar resolves ice-surface elevation change to a few centimetres per year, giving glaciologists and policymakers the most precise public record of ice-sheet geometry available from orbit.
ICESat-2 ATLAS (Advanced Topographic Laser Altimeter System)CryoSat-2 SIRAL (Synthetic Aperture Interferometric Radar Altimeter)TanDEM-X global DEM
The ozone hole shrank. Proving it requires four decades of physics.Stratospheric ozone column monitoring for treaty verification
Total ozone column and vertical ozone profiles retrieved from UV backscatter and occultation instruments provide the long-term, calibrated record needed to verify Montreal Protocol compliance and track the stratosphere's slow recovery.
TROPOMI (Sentinel-5P)OMPS Nadir Mapper + Nadir Profiler (Suomi-NPP / NOAA-20)MLS (Aura)
Countries report their emissions. Satellites read the atmosphere independently.Atmospheric CO₂ and CH₄ column measurement for climate-treaty datasets
OCO-2, OCO-3, GOSAT-2 and TROPOMI retrieve column-averaged CO₂ and CH₄ from shortwave infrared spectra, giving treaty bodies an independent check on national greenhouse-gas inventories. The technique is powerful but cloud-biased and cannot directly invert surface fluxes without modelling.
OCO-2 (NASA, launched 2014)OCO-3 (NASA, ISS, launched 2019)GOSAT-2 (JAXA, launched 2018)
Lightning cannot hide. Geostationary sensors watch every flash, day and night.Global lightning climatology from optical sensors in geostationary orbit
High-frame-rate optical sensors in geostationary orbit detect the 777.4 nm oxygen triplet emission from lightning, enabling continuous global flash mapping tied to convective intensity and climate variability.
Geostationary Lightning Mapper (GLM) on GOES-16/17/18Lightning Imaging Sensor (LIS) on the International Space StationMTG Lightning Imager (LI) on Meteosat Third Generation
Volcanoes cannot hide their sulphur. Physics and UV spectra disagree.Volcanic SO₂ plume tracking and emission quantification
UV backscatter spectrometry on TROPOMI and OMPS retrieves sulphur dioxide column amounts daily at sub-kilometre to tens-of-kilometres scale, enabling near-real-time aviation hazard alerts and long-run climate forcing estimates, with honest caveats on altitude ambiguity and low-altitude degassing blind spots.
TROPOMI on Sentinel-5POMPS Nadir Mapper on Suomi-NPPGOME-2 on Metop-A/B/C
Soil hides its water. Physics at 1.4 GHz does not.Surface soil moisture retrieval for drought monitoring
L-band microwave radiometry measures the dielectric contrast between wet and dry soil to retrieve volumetric moisture in the top 5 cm, globally. SMOS and SMAP are the dedicated missions; Sentinel-1 SAR fills the resolution gap they cannot close.
SMAP L-band Radiometer (NASA)SMOS MIRAS (ESA)Sentinel-1 SAR (ESA, C-band)
Ozone is mostly stratospheric. The small tropospheric slice is what kills people.Tropospheric ozone column mapping for air-quality assessment
Satellites measure total ozone columns easily; isolating the tropospheric fraction that governs ground-level air quality is the hard part. This page explains how TROPOMI, OMI and companion sensors do it, and where the method breaks down.
TROPOMI / Sentinel-5POMI / AuraGOME-2 / MetOp series
Aerosols reach the stratosphere quietly. Their cooling signal is not quiet.Stratospheric aerosol layer monitoring after volcanic and wildfire injections
Volcanic eruptions and intense wildfires can inject sulphate and smoke above the tropopause, where aerosols persist for months and measurably depress surface temperatures. Limb-scatter and solar-occultation instruments track the layer's evolution, but each technique carries hard geometric and physical limits that matter for any serious monitoring programme.
SAGE III / ISSOSIRIS / OdinCALIOP / CALIPSO
Radiosondes cover 1% of Earth. Lidar covers the rest, once a day.Planetary boundary layer height retrieval from spaceborne lidar
The planetary boundary layer governs how pollutants disperse and how heat moves between surface and sky. Spaceborne lidar can estimate its depth globally, but sun-synchronous orbits, elevated aerosol layers and cloud contamination impose hard limits every analyst must understand.
CALIOP / CALIPSOATLID / EarthCARECATS / ISS
Radiosondes cover the land. Aeolus covered everything else.Tropospheric wind profiling from spaceborne Doppler wind lidar
ESA's Aeolus mission was the first satellite to profile tropospheric winds globally using Doppler lidar, filling a decades-old data void over oceans and the Southern Hemisphere that degraded numerical weather prediction for half the planet.
ALADIN (Atmospheric LAser Doppler INstrument) aboard ESA AeolusAeolus Mie channel (particulate backscatter)Aeolus Rayleigh channel (molecular backscatter)
Clouds look opaque from the ground. From orbit, physics disagrees.Cloud-top height and pressure retrieval for aviation and climate
Cloud-top pressure determines aviation hazard altitudes and corrupts trace-gas retrievals when it is wrong. Three physically distinct satellite methods cover the full range from dense convective towers to near-invisible cirrus.
MODIS / Terra and AquaVIIRS / NOAA-20 and Suomi-NPPMISR / Terra
Clouds are mostly invisible to radar. Microwaves disagree.Cloud liquid water path retrieval from passive microwave radiometry
Passive microwave radiometers on AMSR2, GMI and SSMIS measure cloud liquid water path to roughly 10–20 g/m² over ocean, giving climate modellers and precipitation forecasters a variable optical sensors cannot reach. The method fails almost completely over land.
AMSR2 / GCOM-W1 (JAXA)GMI / GPM Core Observatory (NASA/JAXA)SSM/I and SSMIS / DMSP series (NOAA/DoD)
Rain gauges cover 1% of Earth's surface. Satellites cover the rest.Global precipitation rate estimation from merged microwave and IR
No single satellite samples the globe often enough to track precipitation continuously. Operational products fuse passive microwave swath observations with geostationary infrared data to produce near-global, half-hourly rain-rate fields, with known limits at high latitudes and over complex terrain.
GMI / GPM Core ObservatoryAMSR2 / GCOM-W1 (JAXA)SSMIS / DMSP constellation
Snowpack holds next spring's floods. Reading it from orbit is harder than it looks.Snow water equivalent mapping from passive microwave brightness temperatures
Passive microwave radiometers can estimate snow water equivalent across continental snowfields daily, but wet snow, deep mountain snowpacks and coarse footprints make the method unreliable precisely where water managers need it most.
AMSR2 / GCOM-W1 (JAXA)SSMIS / DMSP series (USAF / NOAA)SSM/I heritage archive (DMSP F8–F15)
Ice looks different at 19 GHz than at 37 GHz. That gap is the measurement.Sea-ice concentration mapping from passive microwave radiometry
Passive microwave radiometry has tracked Arctic and Antarctic sea-ice concentration continuously since 1979, making it the backbone of both climate-model validation and real-time shipping-route assessment. This page explains how the algorithms work, what they get wrong, and when the numbers should not be trusted.
AMSR2 / JAXA GCOM-W1SSMIS / DMSP F-16 to F-19MWRI / FY-3D (CMA)
Ice extent tells you where. Thickness tells you everything else.Sea-ice freeboard and thickness from radar and laser altimetry
Radar and laser altimeters measure the sliver of sea ice above the waterline; converting that freeboard to thickness requires assumed densities and carries real uncertainty. This page explains the physics, the sensors, and the honest limits of each approach.
SIRAL / CryoSat-2 (ESA)ATLAS / ICESat-2 (NASA)SRAL / Sentinel-3A and 3B (ESA/EUMETSAT)
Ice thins silently. Stereo optics make the loss legible.Mountain glacier mass balance from repeat optical stereo DEM differencing
For the world's ~200,000 mountain glaciers, the geodetic method, differencing repeat stereo DEMs and converting volume change to mass, offers the only practical regional-scale mass-balance estimate. Cloud, density assumptions, and coregistration error set the honest limits.
ASTER / TerraPléiades 1A/1BSPOT-6/7
The ground is sinking. Radar sees it before the pipeline does.Permafrost thaw subsidence monitoring with InSAR time series
Repeat-pass InSAR time series detect millimetre-scale vertical displacement in Arctic permafrost terrain, separating seasonal frost heave from irreversible thaw settlement to warn of infrastructure risk and carbon-release acceleration.
ALOS-2 PALSAR-2 (L-band, JAXA)Sentinel-1 A/B C-band IW (ESA/Copernicus)NISAR (NASA/ISRO, forthcoming)
Facilities report their emissions. Physics reports what actually escapes.Methane point-source detection and quantification from hyperspectral imagers
Hyperspectral imagers in the shortwave infrared can detect individual methane plumes from oil and gas facilities, landfills and coal mines, attributing emissions to specific sources with quantified uncertainty.
GHGSat-D/C seriesEMIT (ISS)TROPOMI / Sentinel-5P
Smokestacks cannot hide from UV backscatter. Cloud cover can.Tropospheric NO₂ column mapping for urban and industrial emission inventories
TROPOMI and OMI retrieve tropospheric NO₂ columns daily at city-to-complex scale, giving regulators and industry an independent check on ground-based emission inventories. Retrieval physics, honest resolution limits, and cloud-screening trade-offs explained.
TROPOMI / Sentinel-5POMI / AuraGEMS / GEO-KOMPSAT-2B
Vegetation cannot hide its chemistry from an ultraviolet spectrometer.Formaldehyde column retrieval as a proxy for biogenic VOC emissions
Formaldehyde in the troposphere betrays the oxidation of isoprene and other biogenic VOCs. TROPOMI and GOME-2 retrieve its column daily at continental scale, giving emission modellers a top-down check on bottom-up inventories, provided fire interference is properly removed.
TROPOMI / Sentinel-5PGOME-2 / MetOp-A, B and COMI / Aura
Fires end in days. Their chemical signature drifts for weeks.Carbon monoxide column tracking for biomass-burning plume transport
Carbon monoxide is the most useful long-range tracer of incomplete combustion, surviving long enough to cross ocean basins. Thermal-infrared sounders and near-infrared spectrometers each see different altitude slices, and combining them gives the most complete picture of plume transport.
MOPITT / TerraIASI / MetOp-A, -B, -CTROPOMI / Sentinel-5P
Lightning doesn't lie: updraft intensity written in photons every millisecondConvective initiation and storm tracking from geostationary lightning mappers
Total lightning trends from geostationary optical mappers give forecasters a real-time proxy for convective updraft strength, often preceding severe weather by 10–20 minutes. This page covers the physics, the sensors, and the honest limits of the method.
GLM on GOES-16 / GOES-17 / GOES-18 (NOAA)LMI on FY-4A (CMA, China)MTG Lightning Imager on MTG-I1 (EUMETSAT, forthcoming operational)
The planet absorbs more than it emits. Measuring that gap is harder than it sounds.Top-of-atmosphere and surface radiation budget from broadband radiometers
Earth's energy imbalance, currently around 0.9 W/m² by CERES analyses, is the root signal of long-term climate change. Broadband radiometers on Terra, Aqua, NOAA-20 and Meteosat measure it, but a ~2 W/m² absolute calibration uncertainty means the trend matters more than any single epoch value.
CERES (Clouds and the Earth's Radiant Energy System) on Terra and AquaCERES on NOAA-20 (JPSS-1)GERB (Geostationary Earth Radiation Budget) on Meteosat Second Generation
The Sun varies by 0.1%. Climate science cannot afford to ignore it.Total solar irradiance monitoring for climate forcing datasets
Total solar irradiance has been measured from orbit continuously since 1978, but stitching 13+ instruments into one drift-free record is harder than measuring the Sun itself. This page explains how cavity radiometers work, what the 11-year cycle actually delivers to the climate system, and where the calibration bodies are buried.
TIM / SORCE (NASA, 2003–2020)TIM / TSIS-1 (NASA, ISS, 2018–present)VIRGO / SOHO (ESA/NASA, 1996–present)
The signal arrives late. That delay is the forecast.Precipitable water vapour mapping from GNSS tropospheric delay
Ground-based GNSS networks convert tropospheric signal delay into precipitable water vapour at sub-hourly intervals, feeding numerical weather prediction with observations that radiosondes and satellites alone cannot match in density or timing.
IGS Global GNSS NetworkEUREF Permanent GNSS Network (EPN)CYGNSS (NASA, 8-satellite constellation)
Smoke absorbs UV. Dust does too. Telling them apart is the hard part.Absorbing aerosol index and black carbon column retrieval
The absorbing aerosol index flags light-absorbing particles from space using UV backscatter, but cannot alone separate black carbon from mineral dust. Ancillary data and transport modelling are needed to make the signal actionable.
Sentinel-5P TROPOMIAura OMINOAA-20 OMPS
Cirrus hides it. Physics at 6.3 µm does not.Upper tropospheric humidity retrieval from infrared sounders
Water vapour in the 200–500 hPa layer controls longwave radiative feedback and marks convective outflow. Thermal infrared sounders retrieve it globally, but optically thick cirrus remains a hard limit.
IASI on MetOp-A/B/CCrIS on Suomi-NPP and NOAA-20SEVIRI on Meteosat Third Generation (MTG)
The ocean's salt content is readable from orbit. Barely.Sea-surface salinity retrieval from L-band microwave radiometry
L-band passive microwave radiometry detects ocean salinity through tiny shifts in seawater emissivity, enabling global SSS mapping. Sensitivity is real but modest, and cold water, rough seas, and coastal proximity all degrade it.
SMOS (ESA, launched 2009)Aquarius/SAC-D (NASA/CONAE, 2011–2015)SMAP (NASA, launched 2015)
A one-degree cooling at 17 km rewrites stratospheric water vapour budgets.Cold-point tropopause temperature monitoring from radio occultation
The cold-point tropopause temperature is the narrowest bottleneck in Earth's atmosphere: it sets how much water vapour reaches the stratosphere, shaping ozone chemistry and radiative forcing. GNSS radio occultation profiles it with roughly 200 m vertical resolution, all-weather, globally.
COSMIC-2 / FORMOSAT-7Spire Global GNSS-RO constellationMetop GRAS (GNSS Receiver for Atmospheric Sounding)
The stratosphere is nearly dry. When it is not, someone needs to know.Stratospheric water vapour profiling from limb-sounding instruments
Limb-sounding instruments observe the atmosphere tangentially, resolving water vapour mixing ratios from roughly 15 to 80 km altitude at 1–3 km vertical resolution. This page covers microwave emission and solar occultation techniques, their role in radiative forcing and ozone chemistry, and what the 2022 Hunga Tonga eruption revealed about the limits and value of the method.
Aura MLS (Microwave Limb Sounder, NASA, launched 2004)ACE-FTS on SCISAT (Canadian Space Agency, launched 2003)MIPAS on Envisat (ESA, 2002–2012, heritage)
The ocean stores heat invisibly. Physics lets us read the receipt.Ocean heat content estimation from altimetry and in-situ fusion
Sea-surface height anomaly from radar altimetry, fused with Argo float temperature profiles, constrains depth-integrated ocean heat content through the steric sea-level relationship. The method underpins Earth energy imbalance assessments but carries real uncertainty below 2000 m and in mesoscale-active boundary currents.
Jason-3 / Sentinel-6 Michael FreilichSWOT (NASA/CNES, launched 2022)CryoSat-2 (ESA)
A fire burns for hours. Polar satellites visit twice a day.Fire radiative power and combustion rate estimation from geostationary imagers
Geostationary imagers sample active fires every 10–15 minutes, enabling fire radiative power integration over entire burn events and near-real-time smoke emission estimates for atmospheric chemistry models.
SEVIRI on Meteosat Second Generation (MSG)ABI on GOES-16 and GOES-18AHI on Himawari-9
Waves too small for climate models, too consequential to ignoreStratospheric gravity wave momentum flux from limb and occultation observations
Atmospheric gravity waves carry momentum from weather systems into the stratosphere and mesosphere, yet most climate models cannot resolve them directly. Satellite limb and occultation observations now make their signatures measurable, if imperfectly.
COSMIC-2 / FORMOSAT-7Aura MLS (Microwave Limb Sounder)AIRS on Aqua
Water hides under canopies. Radar sees through both.Coastal wetland inundation and methane emission proxy mapping with SAR
SAR backscatter and coherence reveal flooded ground beneath tidal marsh and mangrove canopies, providing inundation extent as a spatial proxy for anaerobic methane production. The method is powerful but indirect: emission estimates carry large uncertainty and depend on ancillary temperature and vegetation data.
Sentinel-1 C-band SAR (ESA)ALOS-2 PALSAR-2 L-band SAR (JAXA)NISAR (NASA/ISRO, planned launch 2025)