Oceans, ice and polar
The poles are the planet's ledger.
The ocean is not binary. Ice concentration proves it.Sea-ice extent and concentration mapping
Passive microwave radiometry has tracked sea-ice extent and fractional concentration daily since 1979, but its 25 km resolution floor hides the leads and polynyas that matter most. Sentinel-1 SAR closes that gap at the cost of coverage and latency.
AMSR2 (JAXA GCOM-W1)SSMIS (DMSP F-17/F-18)Sentinel-1 A/B SAR (ESA)
Ice hides most of itself. Physics reveals the rest.Sea-ice thickness from radar and laser altimetry
Sea-ice thickness cannot be measured directly from orbit, so satellites measure freeboard and work backwards through isostatic balance. The method is powerful but depends critically on snow-load assumptions that vary across ice types and seasons.
CryoSat-2 SIRAL (ESA, launched 2010)ICESat-2 ATLAS (NASA, launched 2018)Sentinel-3 SRAL (ESA/EUMETSAT, launched 2016 and 2018)
Icebergs do not file flight plans. Physics still finds them.Iceberg detection and drift tracking
From Antarctic tabular giants to sub-10-metre growlers, satellite SAR and optical imagery can locate, classify and track icebergs across open ocean and sea-ice fields. The hazard to shipping lanes and subsea pipelines makes positional accuracy and revisit rate the critical variables.
Sentinel-1 SAR (C-band, ESA)RADARSAT-2 (C-band, MDA/CSA)Sentinel-2 MSI (ESA)
Ice doesn't file a notice of intent. Radar does.Polar shipping-route ice condition monitoring
Satellite SAR and passive-microwave data now give voyage planners near-daily ice charts along the Northern Sea Route and Northwest Passage. This page explains how those charts are made, what they miss, and when you need something more.
Sentinel-1 A/B (C-band SAR, ESA)RADARSAT Constellation Mission (C-band SAR, CSA)AMSR2 on GCOM-W1 (passive microwave, JAXA)
The ocean is mostly blue. Phytoplankton make it tell a different story.Ocean colour and marine primary productivity estimation
Ocean colour radiometry retrieves chlorophyll-a concentration from the spectral ratio of water-leaving radiance, turning subtle blue-to-green shifts into estimates of phytoplankton biomass and marine net primary productivity. Atmospheric correction dominates the challenge: more than 90 % of the signal at the sensor is atmosphere, not ocean.
Sentinel-3 OLCIMODIS-AquaNASA PACE OCI
Blooms look green from the air. Not all green is safe.Harmful algal bloom detection and extent mapping
Toxin-producing phytoplankton blooms threaten fisheries, drinking water and public health, yet cloud cover and coarse revisit rates make reliable single-pass detection difficult. Multi-sensor compositing and Sentinel-3 OLCI's 300 m ocean-colour products now give coastal managers a practical detection workflow.
Sentinel-3 OLCIMODIS-AquaNASA PACE OCI
Salt changes how the ocean radiates. Satellites can hear it.Sea-surface salinity mapping from L-band radiometry
L-band microwave radiometers measure ocean surface salinity by detecting shifts in seawater's dielectric constant, but the signal is faint, cold water blunts it further, and radio interference corrupts coastal swaths. Three missions now hold a decade of global salinity records.
SMOS MIRAS (ESA, launched 2009)Aquarius/SAC-D (NASA/CONAE, 2011–2015, archive only)SMAP L-band radiometer (NASA, launched 2015)
The ocean's hidden engines spin for months. Altimetry finds them.Ocean current and mesoscale eddy tracking from altimetry
Radar altimetry measures sea-surface height to within centimetres, revealing geostrophic currents and the mesoscale eddies that redistribute heat, carbon and marine life across ocean basins. Multi-mission merged products turn sparse along-track swaths into actionable gridded current fields.
Sentinel-6 Michael FreilichJason-3SARAL/AltiKa
Gravity does not lie, but the mantle beneath complicates the reading.Greenland ice-sheet mass balance and outlet glacier dynamics
Three satellite techniques, gravimetry, altimetry and SAR, together constrain how fast Greenland is losing ice and where. Each method has distinct error sources; reconciling them is the science.
GRACE-FO (Gravity Recovery and Climate Experiment Follow-On)CryoSat-2 SIRAL (Synthetic Aperture Interferometric Radar Altimeter)ICESat-2 ATLAS (Advanced Topographic Laser Altimeter System)
Ice shelves thin from below long before they break from above.Antarctic ice-shelf calving-front monitoring and basal melt
SAR imagery and laser altimetry reveal calving-front retreat, rift propagation and basal melt on Antarctic ice shelves year-round, through cloud and polar night. Together they quantify the processes that govern future sea-level rise.
Sentinel-1 A/B C-band SARRADARSAT-2 C-band SARICESat-2 ATLAS photon-counting lidar
The ground moves a few centimetres. Pipelines and carbon budgets notice.Permafrost active-layer dynamics from InSAR surface deformation
Repeat-pass SAR interferometry detects the seasonal heave and subsidence of permafrost active layers at centimetre scale, revealing where frozen ground is losing structural integrity and releasing stored carbon.
Sentinel-1 A/B (C-band, 5.6 cm wavelength)ALOS-2 PALSAR-2 (L-band, 23.6 cm wavelength)RADARSAT Constellation Mission (C-band)
Open water in a frozen sea announces itself loudly. Reading the signal is harder.Polynya detection and polar ocean heat-flux estimation
Polynyas are persistent or transient gaps in the sea-ice pack where the ocean loses heat to the atmosphere at extraordinary rates. Satellite passive microwave and thermal infrared sensors can locate them reliably, but separating thin new ice from open water demands careful multi-sensor reconciliation.
AMSR2 on GCOM-W1 (JAXA)MODIS Terra and AquaSuomi NPP and NOAA-20 VIIRS
Ice moves. The fractures it leaves behind tell the real story.Sea-ice drift and deformation velocity fields
Sequential SAR and passive-microwave imagery reveal how sea ice drifts, shears and piles up. Velocity fields derived from feature-tracking and cross-correlation expose lead openings, pressure ridges and divergence zones that static concentration maps cannot show.
Sentinel-1 A/B SAR (C-band, 5.4 GHz)RADARSAT-2 (C-band SAR)AMSR2 on GCOM-W1 (passive microwave, 6.9–89 GHz)
Ponds form in days. Their albedo effect lasts the whole melt season.Arctic melt-pond fraction and albedo feedback mapping
Surface melt ponds cut sea-ice albedo from roughly 0.8 to below 0.2, accelerating melt far faster than models predicted. Optical multispectral imagery at sub-10 m resolution can map pond fraction across the Arctic Basin, but cloud cover and polar logistics make this harder than it looks.
Sentinel-2 MSIWorldView-3Landsat 8/9 OLI
A lead looks like open water. It behaves like a chimney.Sea-ice lead detection and refreezing state classification
Linear fractures in pack ice transfer enormous heat to the atmosphere and set navigation risk. SAR polarimetry and altimeter waveforms can classify them by refreezing state, from open water through nilas to grey ice.
Sentinel-1 A/B (C-band SAR)CryoSat-2 SIRAL (Ku-band radar altimeter)RADARSAT Constellation Mission (C-band SAR)
Snow buries the signal. Two satellites disagree, productively.Snow depth on sea ice from passive microwave and altimetry
Snow on sea ice is the largest source of uncertainty in satellite thickness retrievals, yet it remains poorly measured. Passive-microwave spectral gradients and the freeboard residual between ICESat-2 and CryoSat-2 offer complementary, imperfect routes to a number.
ICESat-2 ATLAS (NASA, launched 2018)CryoSat-2 SIRAL (ESA, launched 2010)AMSR2 on GCOM-W1 (JAXA, launched 2012)
Old ice remembers its past. Satellites can read that memory.Multi-year versus first-year sea-ice classification
Multi-year ice and first-year ice look similar to the eye but behave very differently under a microwave sensor. Distinguishing the two, at basin scale and weekly cadence, is the sharpest available measure of whether the Arctic is losing its structural resilience.
AMSR2 on GCOM-W1 (JAXA)Sentinel-1 A/B C-band SAR (ESA)SSMIS on DMSP (NOAA/USAF)
A single tracked berg is a curiosity. A population is a water budget.Iceberg size-distribution and volume estimation from SAR
SAR amplitude imagery from Sentinel-1 and RADARSAT Constellation Mission can detect icebergs down to roughly 100 m in calm seas, enabling the population statistics that govern freshwater flux and iron fertilisation across polar oceans.
Sentinel-1 A/B (C-band SAR, 5.4 GHz)RADARSAT Constellation Mission (C-band SAR)TerraSAR-X / TanDEM-X (X-band SAR, 9.65 GHz)
The visible tip is the easy part. The keel is the problem.Iceberg freeboard and keel-depth estimation from altimetry
Satellite altimetry measures how high an iceberg sits above sea level. Combined with ice-density assumptions, that freeboard converts to total draft, often exceeding 200 metres, with direct consequences for subsea pipelines, cables and drilling infrastructure.
ICESat-2 ATLAS (NASA)CryoSat-2 SIRAL (ESA)WorldView stereo pairs (Maxar)
Ice meets ocean. The front line keeps moving.Tidewater glacier calving-front position and retreat rates
Tidewater glaciers outside the polar ice sheets are retreating at measurable, trackable rates. SAR and optical satellites delineate calving fronts through polar night and cloud, turning terminus positions into sea-level budget inputs.
Sentinel-1 A/B SAR (C-band, 5.4 GHz)Sentinel-2 MSI (10 m optical, 13 bands)Landsat 8/9 OLI (15–30 m optical)
Lakes form in days. They can vanish in hours.Supraglacial lake formation and rapid drainage on ice sheets
Supraglacial lakes on the Greenland and Antarctic ice sheets can drain catastrophically through moulins, injecting meltwater to the bed and accelerating ice flow. Multispectral reflectance retrieves lake area and depth; ICESat-2 elevation data confirms drainage events that optical imagery alone can miss.
Sentinel-2 MSILandsat 8/9 OLIICESat-2 ATLAS
Ice moves. The question is how fast, and why it just accelerated.Ice-sheet and glacier surface velocity from InSAR and offset tracking
SAR interferometry and pixel-offset tracking convert repeat-pass radar imagery into ice-flow velocity fields, exposing acceleration events, surge cycles and dynamic instability months before visible change reaches the terminus.
Sentinel-1 A/B (C-band SAR, ESA)ALOS-2 PALSAR-2 (L-band SAR, JAXA)RADARSAT-2 (C-band SAR, MDA)
Ice hides its plumbing. Altimetry reads the pressure gauge.Subglacial lake detection and volume change from altimetry
Active subglacial lakes beneath Antarctica and Greenland inflate and drain over months to years, deforming the ice surface by centimetres to metres. Repeat-track laser and radar altimetry from ICESat-2 and CryoSat-2 isolates these anomalies from background firn and dynamic signals.
ICESat-2 ATLAS (NASA, 2018–present)CryoSat-2 SIRAL (ESA, 2010–present)ERS-2 RA (ESA, 1995–2011, historical archive)
The ice sheet is sinking. The question is whether ice is leaving or air is.Firn compaction and densification correction for ice-sheet altimetry
Surface-elevation change measured by satellite altimetry conflates dynamic ice loss with firn compaction driven by temperature and snowfall variability. Separating the two requires firn models constrained by GRACE-FO gravity and multi-mission altimetry, where model uncertainty remains the dominant error source.
CryoSat-2 SIRALICESat-2 ATLASGRACE-FO KBR/LRI
Cloud hides the ocean surface. Physics does not hide the front.Polar ocean sea-surface temperature fronts and water-mass boundaries
Thermal infrared and microwave radiometry map the SST fronts that control nutrient upwelling and krill distribution across the Southern Ocean, but persistent cloud cover demands multi-sensor compositing strategies and honest acknowledgement of what each sensor cannot see.
MODIS Terra/AquaVIIRS (Suomi-NPP / NOAA-20)AMSR2 (GCOM-W1)
The ocean's thermostat is invisible. Physics and floats make it legible.Ocean mixed-layer depth estimation from altimetry and in-situ fusion
Mixed-layer depth governs how much heat the ocean stores and how much CO₂ it absorbs. Satellite altimetry and SST, fused with Argo float profiles via optimal interpolation, produce gridded MLD fields at near-global scale, though coverage thins sharply in under-floated basins.
Sentinel-6 Michael Freilich (radar altimeter)Jason-3 (radar altimeter)MODIS (Terra and Aqua, SST)
The ice retreats. The fetch grows. The waves follow.Significant wave height and swell propagation in polar seas
Shrinking sea ice opens vast new ocean fetches in the Arctic and Southern Ocean, driving wave heights that infrastructure and shipping routes were never designed for. Radar altimeters and SAR wave-mode imagery now give us the numbers.
Sentinel-6 Michael Freilich (Poseidon-4 altimeter)Jason-3 (Poseidon-3B altimeter)Sentinel-1 (wave mode, IW and WV sub-modes)
Phytoplankton blooms betray iron. Standard algorithms miss both.Southern Ocean chlorophyll and iron-fertilisation response mapping
The Southern Ocean is chronically iron-limited, yet icebergs and shelf sediments seed localised blooms detectable from orbit. Retrieving chlorophyll-a reliably demands sensors and algorithms built for optically complex, cloud-plagued sub-Antarctic waters.
Sentinel-3 OLCIMODIS-AquaPACE OCI
Ice thinner than 50 cm hides nothing from a thermal camera.Thin ice thickness from thermal infrared heat-flux inversion
For ice below roughly 50 cm, surface temperature betrays thickness through conductive heat flux. MODIS, VIIRS and Sentinel-3 SLSTR make the measurement possible; cloud and wind make it hard.
MODIS Terra / AquaVIIRS (Suomi-NPP / NOAA-20)Sentinel-3 SLSTR
The lake appears in summer. By autumn, it may be gone entirely.Thermokarst lake expansion and drainage in permafrost terrain
Thawing ground ice creates thermokarst lakes that grow, migrate and drain on timescales from decades to hours. Multispectral time-series analysis over the Landsat archive quantifies area change, new formation and abrupt drainage events across Arctic and sub-Arctic terrain.
Landsat 4-9 (USGS/NASA)Sentinel-2 MSI (ESA Copernicus)Planet SuperDove
The carbon is buried. The signal is not.Permafrost terrain carbon-pool mapping from SAR and optical fusion
Permafrost soils hold roughly twice the carbon currently in the atmosphere, yet mapping those stocks remotely is genuinely hard. SAR backscatter and optical vegetation indices together constrain the problem, within honest limits.
ALOS-2 PALSAR-2Sentinel-1 A/B C-band SARSentinel-2 MSI
Rivers freeze on a schedule. They thaw on a trend.Arctic river ice breakup and freshwater discharge timing
Spring ice breakup on the Ob, Yenisei, Lena and Mackenzie determines when billions of tonnes of freshwater enter the Arctic Ocean, reshaping salinity stratification and the following autumn's sea-ice formation. SAR backscatter transitions and MODIS/VIIRS optical time series make breakup dates detectable within days, even under cloud.
Sentinel-1 SAR (C-band, ESA)MODIS Terra and AquaVIIRS (Suomi-NPP and NOAA-20)
Ridged ice is 10% of the surface. It dominates the hazard.Sea-ice pressure ridge detection and deformation intensity mapping
Pressure ridges concentrate ice volume and under-ice drag in a small fraction of the pack. SAR texture analysis and ICESat-2 freeboard data let analysts map ridge density and sail height at operationally useful resolution.
Sentinel-1 SAR (C-band, 5.405 GHz)RADARSAT-2 SAR (C-band, 5.405 GHz)ICESat-2 ATL07 (photon-counting lidar, 532 nm)
Clouds at 20 km altitude destroy ozone before spring even arrives.Polar stratospheric cloud occurrence and ozone-column depletion mapping
Polar stratospheric clouds form in the winter vortex and catalyse the chlorine reactions that hollow out the ozone column each spring. Satellite lidar, microwave limb-sounding and nadir UV spectrometry now make that destruction legible from orbit.
CALIPSO CALIOP lidarAura MLS (Microwave Limb Sounder)Sentinel-5P TROPOMI
The ice forms. The salt escapes. The ozone pays the price.Coastal polynya sea-salt aerosol production and atmospheric loading
Coastal polynyas expose open water in the depths of polar winter, generating frost flowers and sea-salt aerosol that load the troposphere with bromine and drive ozone depletion events. Fusing AMSR2 brightness temperatures, Sentinel-1 SAR backscatter and MERRA-2 wind reanalysis makes the flux quantifiable.
AMSR2 (GCOM-W1)Sentinel-1 SAR (C-band, 5.405 GHz)MERRA-2 reanalysis (NASA GMAO)
Pore space is the last line of defence before an ice shelf drowns itself.Antarctic ice-shelf firn-air content and surface-melt vulnerability assessment
Firn-air content determines whether meltwater ponds on an ice shelf or soaks away harmlessly. Radar altimeter waveform analysis and passive microwave melt-day counts now let analysts map that pore space across entire Antarctic shelves, flagging which ones are approaching the threshold where hydrofracture becomes plausible.
CryoSat-2 SIRAL (Ku-band radar altimeter)SSMIS on DMSP (passive microwave radiometer)ICESat-2 ATL06 (photon-counting laser altimeter)
Ocean-colour sensors stop at the ice edge. Biology does not.Under-ice and marginal-ice-zone phytoplankton bloom detection
Phytoplankton blooms initiate beneath sea ice weeks before open water appears, yet ocean-colour satellites cannot see through ice. Detecting them demands a fusion of marginal-ice-zone chlorophyll retrievals, light-transmission modelling constrained by melt-pond and snow data, and validation from biogeochemical Argo floats.
PACE OCI (NASA, launched 2024)MODIS-AquaAMSR2 on GCOM-W1 (JAXA)
The ice sheet is retreating. The tides are the witness.Ice-sheet grounding-line migration from tidal InSAR differential phase
Double-differential InSAR detects the tidal flexure zone where grounded ice becomes floating ice, resolving grounding-line position to within a few hundred metres. Retreat of this boundary is among the most direct early indicators of marine ice-sheet instability.
Sentinel-1 IW mode (C-band SAR)ERS-1 / ERS-2 tandem archive (C-band SAR)TanDEM-X (X-band SAR)
Ships cannot sound what ice forbids. Gravity can.Ice-covered polar ocean bathymetry from satellite gravity inversion
Satellite radar altimetry over open-water leads measures marine gravity anomalies that, when inverted, reveal seafloor topography beneath Arctic and Southern Ocean ice at roughly 5 km resolution, filling gaps that echo-sounding ships may never close.
CryoSat-2 SIRALICESat-2 ATL12 (ocean-surface height product)Geosat geodetic mission archive (1985–1986)
The ice reflects less light. The planet absorbs more heat.Spectral and broadband albedo retrieval across sea-ice surface types
Arctic sea-ice albedo varies from roughly 0.85 over fresh snow to below 0.15 over open melt ponds. Satellite retrieval of that range, corrected for sun angle and surface anisotropy, is the primary observational input to ice-albedo feedback quantification.
MODIS MCD43 (Terra and Aqua)OLCI (Sentinel-3A and 3B)CERES (Terra and Aqua)
The cliff is frozen solid. Until it isn't.Permafrost coastline erosion rates and cliff-face thaw monitoring
Arctic permafrost coasts can retreat more than 10 metres in a single storm season. Multi-temporal optical shoreline extraction and SAR coherence analysis now make those losses measurable from orbit, at the pace the problem demands.
Planet SuperDoveSentinel-2 MSISentinel-1 SAR (C-band)