Water and hydrology
Reservoirs do not file honest reports. Radar altimeters do.
A gauge network costs millions. Physics costs nothing extra.Reservoir and lake surface-level monitoring by radar altimetry
Satellite radar altimetry and photon-counting lidar measure water-surface elevation in reservoirs and lakes to centimetre accuracy, with no in-country infrastructure required. Virtual-station time series now extend to bodies as small as 250 m across.
Sentinel-6 Michael Freilich (Poseidon-4 altimeter)SWOT KaRIn (Ka-band Radar Interferometer)ICESat-2 ATLAS (photon-counting lidar)
The river keeps no records. Satellites can start keeping them.River discharge estimation from satellite observations
Volumetric river flow can be inferred from space using width, surface velocity, slope and elevation as hydraulic proxies. Accuracy depends heavily on calibration data and unknown bathymetry, but the SWOT mission is reshaping what is possible in ungauged basins.
SWOT KaRIn (Ka-band Radar Interferometer)Sentinel-1 SAR (C-band, 5.6 cm wavelength)Sentinel-2 MSI (multispectral optical)
Clouds close optical sensors. Radar sees straight through both.Flood extent mapping with synthetic aperture radar
SAR backscatter maps flooded land within hours of acquisition, day or night, through cloud cover. Open water returns a specular, near-zero signal; the complication is flooded forest, which can appear bright and fool simple thresholds.
Sentinel-1 A/B (C-band, 5.405 GHz)ALOS-2 PALSAR-2 (L-band, 1.236 GHz)RADARSAT-2 (C-band, 5.405 GHz)
Models drift. Satellites correct them before the flood arrives.Satellite data assimilation for flood forecasting
Satellite-derived precipitation, soil moisture and river levels can be fed into hydrological forecast models as state updates, sharpening predictions hours before a flood peak. The physics is well understood; the operational challenge is latency.
GPM IMERGSMAP L-band radiometerSentinel-1 SAR (C-band)
Aquifers drain invisibly. Gravity tells the truth.Groundwater depletion detection using satellite gravimetry
GRACE and GRACE-FO measure month-to-month shifts in Earth's gravity field to reveal changes in terrestrial water storage, including groundwater. Signal decomposition isolates the aquifer signal, but the ~300 km resolution floor means attribution requires ancillary data.
GRACE-FO K-Band Ranging (KBR)GRACE (archive, 2002–2017)GLDAS (Global Land Data Assimilation System)
Optical sensors see snow's edge. Microwaves weigh what lies beneath.Snowpack extent and snow water equivalent from orbit
Satellite data delivers two complementary snowpack measurements: snow-covered area at 10–30 m resolution from optical sensors, and snow water equivalent from passive microwave brightness temperatures, each with hard physical limits the other partially compensates for.
Sentinel-2 MSILandsat 8/9 OLIMODIS Terra/Aqua
Ice thins silently. Differenced elevations make the loss legible.Glacier mass balance and volume change monitoring
The geodetic method compares digital elevation models from different epochs to quantify glacier surface-elevation change, then converts volume to mass. Satellite stereo imagery, SAR interferometry and laser altimetry now make this possible at near-global scale.
TanDEM-X InSAR (TerraSAR-X / TanDEM-X pair)ICESat-2 ATLASASTER VNIR stereo
Ice moves. The question is how fast, and whether that changed last week.Glacier surface velocity and ice-flow dynamics
SAR interferometry and optical feature tracking let analysts measure glacier surface motion from centimetres to kilometres per year. Sentinel-1, ALOS-2, Landsat and Sentinel-2 each cover different speed regimes, with honest limits around wet snow, crevassing and cloud.
Sentinel-1 C-band SAR (ESA)ALOS-2 PALSAR-2 L-band SAR (JAXA)Landsat 8/9 OLI (USGS/NASA)
Farmers report what they use. Thermodynamics reports what they take.Irrigation withdrawal detection and agricultural water accounting
Satellite-derived evapotranspiration lets water managers infer irrigation timing and volume from orbit, without a meter in the ground. GRACE-FO gravity data cross-checks cumulative groundwater abstraction at basin scale.
Landsat 8/9 TIRSSentinel-3 SLSTRMODIS MOD16 ET
Optical sensors see reed beds. SAR sees the water underneath them.Wetland inundation dynamics and long-term change detection
Mapping wetland inundation requires sensors that see through vegetation, not just over it. This page explains how multi-temporal SAR and the Landsat-derived Global Surface Water dataset together give the most complete picture of seasonal flooding and long-term wetland loss.
Sentinel-1 C-band SAR (ESA)ALOS-2 PALSAR-2 L-band SAR (JAXA)Landsat 5/7/8/9 archive (USGS/NASA)
Sediment cannot hide: physics betrays every plume from orbitWater turbidity and suspended sediment concentration mapping
Suspended particles scatter red and near-infrared light in ways satellites can measure and calibrate to concentration. This page explains which sensors work at which scales, where the physics breaks down, and what the data can honestly tell a water manager.
Sentinel-2 MSISentinel-3 OLCIMODIS Aqua/Terra
Water looks clean until the physics of light says otherwise.Harmful algal bloom and cyanobacteria detection in inland and coastal waters
Satellite ocean-colour sensors can detect toxic algal blooms days before conventional monitoring networks raise an alarm, but sensor choice, water type and dissolved organics all determine whether the signal is real or an artefact.
Sentinel-3 OLCISentinel-2 MSIMODIS Aqua
A reservoir fills quietly. The downstream state notices last.Monitoring upstream dam construction and its hydrological consequences
Optical, SAR and altimetry data can reveal dam construction and impoundment in transboundary basins before any official announcement, giving downstream governments an independent hydrological record.
Sentinel-1 SAR (C-band, ESA)Sentinel-2 MSI (ESA)Planet SuperDove
Lakes freeze on a schedule. That schedule is changing.Lake ice phenology: freeze-up, break-up and ice thickness
Passive microwave, SAR and optical sensors together track when lakes freeze, when they clear, and how thick the ice grows. These dates are among the longest-running climate indicators in the observational record.
AMSR2 (JAXA GCOM-W)Sentinel-1 SAR (C-band, 5.405 GHz)MODIS Terra and Aqua
Satellites measure the water you cannot see leaving the land.Basin-scale evapotranspiration and water-balance closure
Actual evapotranspiration is the largest unmeasured flux in most catchments. Combining thermal infrared land-surface temperature, vegetation indices, GPM rainfall and GRACE-FO gravity change lets analysts close the water balance and expose unaccounted abstractions.
Landsat 8/9 TIRSMODIS MOD11 LSTGPM IMERG
Rivers move. The archive remembers every position since 1972.River planform change and lateral channel migration
Multi-epoch optical imagery, anchored by the Landsat archive, lets analysts map lateral channel migration, cutoff events, and braiding-pattern shifts across decades. The same record exposes unreported human interventions that alter natural migration rates.
Landsat 1–9 (USGS/NASA)Sentinel-2 MSI (ESA Copernicus)Planet SuperDove
L-band sees salt where optical sensors see only colour.Coastal lagoon and estuarine salinity mapping from orbit
L-band microwave radiometry detects ionic concentration in surface water, but its 40 km footprint misses most lagoons. Fusing SMOS/SMAP with Sentinel-2 optical indices extends usable salinity estimates into water bodies too small for the radiometer alone.
SMOS MIRAS (ESA)SMAP Radiometer (NASA)Sentinel-2 MSI (ESA)
Gauges measure one point. Satellites measure the whole river.River water-surface width retrieval for discharge proxy
High-resolution optical and SAR imagery can extract river channel width at scale, which hydraulic geometry converts to a discharge proxy. SWOT now adds simultaneous water-surface slope, tightening the estimate considerably, though ungauged basins remain genuinely hard.
SWOT KaRInSentinel-1 SAR (C-band)Planet SuperDove
A lake can vanish in hours. The archive remembers every decade.Permafrost thermokarst lake expansion and drainage monitoring
Thermokarst lakes expand as ground ice melts and drain catastrophically when ice-wedge networks fail. Multi-decadal Landsat records, Sentinel-1 InSAR subsidence maps and ICESat-2 elevation data together quantify permafrost degradation rates and infrastructure risk across Arctic regions.
Landsat TM / ETM+ / OLISentinel-1 SAR (C-band, 5.6 cm)ALOS-2 PALSAR-2 (L-band, 23.6 cm)
The riverbed is visible from orbit. Turbid water hides it again.Satellite-derived bathymetry for optically shallow rivers and lakes
In clear, shallow water, sunlight penetrates to the bed and returns through the water column carrying depth information in its spectral ratios. Sentinel-2 and WorldView imagery can resolve that signal to roughly 10 m depth, provided turbidity stays below about 5 NTU.
Sentinel-2 MSIWorldView-2 / WorldView-3Planet SuperDove
The surface tells you where water enters. Only boreholes confirm it arrives.Groundwater recharge zone identification using multi-source satellite data
Combining Sentinel-1 backscatter, Sentinel-2 land cover, TanDEM-X terrain and GRACE-FO gravity trends narrows the search for productive recharge zones. Satellite data constrains the hypothesis; borehole validation closes it.
GRACE-FOSentinel-1 SAR (C-band, 5.405 GHz)Sentinel-2 MSI
Soil hides its water. Physics does not.Surface and root-zone soil moisture retrieval at basin scale
Active microwave and passive L-band sensors read dielectric contrast to estimate surface soil moisture at basin scale. Exponential filter methods push those estimates to root-zone depth, where irrigation and drought decisions are actually made.
SMAP Radiometer (NASA, L-band 1.41 GHz)Sentinel-1 SAR (ESA, C-band 5.4 GHz)ASCAT on MetOp (EUMETSAT, C-band)
Floodwaters retreat in days. The damage record must be made in hours.Post-flood crop and infrastructure damage assessment
SAR coherence loss and optical NDVI change detection together identify damaged cropland, collapsed structures and debris-covered roads after a flood. Pre-event baseline archives are the critical dependency that determines whether the analysis is possible at all.
Sentinel-1 SAR (C-band, ESA)Sentinel-2 MSI (ESA)Planet SuperDove
A lake's surface hides its interior. Thermal infrared does not.Lake and reservoir water-surface temperature and thermal stratification
Thermal infrared radiometry from Landsat TIRS, MODIS and ECOSTRESS retrieves skin-layer water temperature to within roughly 0.5 K under clear skies, revealing stratification onset, upwelling and cold dam releases. Cloud cover and a 100 m resolution floor are the binding constraints.
Landsat 8/9 TIRSMODIS Terra and AquaECOSTRESS (ISS-mounted)
Brown water tells a story; reading it from orbit is the hard part.Dissolved organic carbon and coloured dissolved organic matter in inland waters
CDOM shifts the water-leaving reflectance spectrum in measurable ways, letting satellites estimate dissolved organic carbon export from peatlands and forests. Retrieval accuracy depends heavily on separating CDOM from sediment and phytoplankton signals.
Sentinel-2 MSILandsat 8/9 OLIPACE OCI
Ice jams form in hours. Cloud cover is no excuse for missing them.River ice breakup, ice-jam flood detection and timing
River ice jams can raise water levels by several metres within hours, yet most sub-Arctic gauge networks are too sparse to catch them early. SAR satellites see through cloud and polar darkness, distinguishing ice types by roughness signature to give near-real-time flood warning.
Sentinel-1 A/B (C-band SAR, 5.4 GHz)RADARSAT-2 (C-band SAR, 5.4 GHz)ALOS-2 PALSAR-2 (L-band SAR, 1.27 GHz)
Upstream states control the gauges. They do not control physics.Transboundary river flow monitoring without in-country gauge access
When data-sharing agreements fail, satellite observations of water-surface slope, inundation width and total water storage can reconstruct cross-border river discharge independently of any upstream gauge network.
SWOT KaRInSentinel-1 SAR (C-band)GRACE-FO
The seabed leaks. Thermal physics makes it visible.Submarine groundwater discharge detection at the coast
Submarine groundwater discharge is invisible to the eye but leaves cold or warm thermal scars and salinity shadows detectable from orbit. Satellite methods locate candidate SGD zones; quantifying flux still requires boots and radon counters on the ground.
Landsat 8/9 TIRSECOSTRESS (ISS-mounted)SMAP L-band radiometer
Peat breathes. Radar listens to every centimetre of it.Peatland water-table depth estimation by InSAR surface deformation
Peatlands rise and fall with their water table. Repeat-pass InSAR translates that surface motion into water-table depth estimates, giving hydrologists a spatially continuous record where dipwells are sparse.
Sentinel-1 A/B (C-band, 5.6 cm wavelength)ALOS-2 PALSAR-2 (L-band, 23.6 cm wavelength)TanDEM-X (X-band, 3.1 cm wavelength)
The ground sinks slowly. InSAR notices before the city does.Land subsidence from groundwater over-extraction detected by InSAR
Excessive groundwater pumping compacts aquifer sediments and causes surface subsidence measurable to millimetres per year by satellite radar interferometry. Sentinel-1 time-series reveal subsidence bowls across major urban aquifers, but translating deformation rates into extraction volumes requires hydrogeological modelling.
Sentinel-1 (ESA, C-band SAR, 5.6 cm wavelength)ALOS-2 PALSAR-2 (JAXA, L-band SAR, 23.6 cm wavelength)COSMO-SkyMed (ASI, X-band SAR, 3.1 cm wavelength)
Mangroves drown or desiccate by centimetres. Satellites count the difference.Mangrove tidal inundation frequency and hydroperiod mapping
Inundation frequency and hydroperiod duration control mangrove species zonation and canopy vigour more than any other variable. Multi-temporal Sentinel-1 SAR stacks, cross-validated with Sentinel-2 reflectance, resolve the tidal gradient within the fringe at scales relevant to management decisions.
Sentinel-1 SAR (C-band, ESA)Sentinel-2 MSI (ESA)Landsat 8/9 OLI (USGS/NASA)
The snowpack melts on physics. Forecasters who ignore the canopy pay later.Snowmelt runoff timing and volume forecasting from satellite snow cover
Spring flood peaks and hydropower revenues hinge on when the snowpack releases. Satellite snow-cover area, degree-day melt models and SMAP soil-moisture state can constrain runoff timing and volume weeks in advance, but forest canopy masking and cloud cover impose real limits that any honest forecast must account for.
MODIS Terra/AquaSentinel-2 MSISentinel-1 SAR (C-band)
The terminus retreats in days. The sea-level signal lasts centuries.Iceberg calving front position and calving flux monitoring
Marine-terminating glacier fronts shift on timescales of days to decades, controlling both sea-level contribution and fjord oceanography. Sentinel-1 SAR, Sentinel-2 optical imagery and ICESat-2 lidar together make automated, year-round calving front monitoring operationally feasible.
Sentinel-1 SAR (C-band, ESA)Sentinel-2 MSI (ESA)ICESat-2 ATL06 (NASA)
A plant that doubles in a fortnight cannot wait for clear skiesInvasive aquatic vegetation mapping: water hyacinth and floating macrophytes
Water hyacinth and floating macrophytes spread fast enough to close navigation channels and crash fisheries within weeks. Sentinel-2 red-edge bands, Planet SuperDove daily revisit and Sentinel-1 SAR together provide the spectral discrimination and cloud-penetrating coverage the problem demands.
Sentinel-2 MSIPlanet SuperDoveSentinel-1 SAR (C-band)
Sediment fills reservoirs silently. Satellites can read the tide gauge.Reservoir sedimentation and storage capacity loss from orbit
Repeat satellite altimetry, optical surface-area mapping and ICESat-2 photon-counting lidar combine to track how sediment infill shrinks live storage, without a single diver or echo sounder.
ICESat-2 ATL03 / ATL13Sentinel-3 SRALSentinel-2 MSI
Water escapes invisibly. Phase shifts in radar do not.Irrigation canal and pipeline leakage detection by InSAR soil-moisture anomaly
Persistent-scatterer and small-baseline InSAR time-series detect millimetre-scale ground deformation caused by soil saturation or void formation next to leaking buried irrigation infrastructure, confirmed by L-band backscatter and passive microwave soil-moisture products.
Sentinel-1 IW SLC (C-band, 5.6 cm)ALOS-2 PALSAR-2 (L-band, 23.6 cm)NISAR L-band SAR (launch 2024, ISRO/NASA)
Your hydraulic model is only as honest as its roughness map.Floodplain vegetation roughness mapping for hydraulic model parameterisation
Spatially distributed Manning's n values are the weakest link in most 2-D flood models. Combining TanDEM-X canopy height, GEDI waveform structure and Sentinel-1 SAR backscatter cuts the number of hand-drawn roughness zones without replacing field calibration.
TanDEM-X WorldDEMGEDI L2A / L2BSentinel-1 SAR (C-band)
Rainfall disappears two ways. Only one of them refills your aquifer.Blue-water and green-water partitioning at basin scale
Splitting the terrestrial water budget into blue water (runoff and groundwater) and green water (evapotranspiration) tells water managers where consumption is going and whether abstraction is sustainable. The method fuses GRACE-FO gravity, GPM rainfall and MODIS/VIIRS ET, and works best for basins above roughly 10,000 km².
GRACE-FO (Gravity Recovery and Climate Experiment Follow-On)GPM IMERG (Global Precipitation Measurement Integrated Multi-satellitE Retrievals)MODIS MOD16 ET
Lakes shrink slowly, then suddenly. The archive remembers both.Lake shoreline recession and drought-driven surface-area decline
Multi-decadal Landsat records combined with Sentinel-2 imagery and satellite altimetry let analysts separate genuine long-term lake decline from seasonal noise, quantifying shoreline retreat and surface-area loss with documented accuracy.
Landsat 4-9 (Collection 2)Sentinel-2 MSISentinel-3 SRAL (radar altimeter)
The lake looks green. That colour is doing chemistry you cannot ignore.Water colour as a proxy for dissolved oxygen and eutrophication state
Hyperspectral and multispectral sensors retrieve chlorophyll-a, phycocyanin and dissolved organics from spectral reflectance, giving water managers an eutrophication signal without field crews. Dissolved oxygen itself is invisible to satellites; the proxy works until stratification or rapid mixing breaks the relationship.
NASA PACE OCISentinel-3 OLCISentinel-2 MSI
Snow looks white. Soot, dust and algae disagree.Snow and glacier albedo decline from light-absorbing particle deposition
Black carbon, mineral dust and glacier algae darken snow and ice surfaces, cutting albedo and feeding additional melt. MODIS, Sentinel-2 and Landsat quantify the spatial pattern; radiative-transfer modelling converts albedo anomalies into absorbed-energy estimates.
MODIS MOD10A1 / MYD10A1VIIRS VNP10A1Sentinel-2 MSI
The tide retreats. A decade of radar tells you what it left behind.Tidal flat inundation frequency and sediment accretion dynamics
Dense Sentinel-1 SAR time-series and Sentinel-2 optical composites reconstruct inundation frequency curves and surface elevation on intertidal flats, revealing sediment accretion or erosion rates relevant to coastal flood defence and blue-carbon accounting.
Sentinel-1 IW GRD (C-band SAR)Sentinel-2 MSITanDEM-X CoSSC (X-band interferometric SAR)
Every rainfall product is wrong. The question is which errors you can afford.Satellite-gauge-radar precipitation merging for hydrological forcing
No single precipitation source captures rain accurately across terrain, climate zones and storm types. Merging GPM IMERG, ground radar and gauge networks with quantified uncertainty is now the operational standard for hydrological forcing.
GPM IMERG (NASA/JAXA)TRMM 3B42 (historical, NASA/JAXA)Meteosat SEVIRI (EUMETSAT)
No gauge, no problem. But no illusions either.Ungauged basin hydropower potential assessment from satellite observations
Satellite-derived slope, width, and modelled discharge can estimate gross hydropower potential in basins with no ground records. Uncertainties run 30–50 %, making the method a triage tool, not a bankable study.
ICESat-2 ATL13 (inland water surface elevation)Sentinel-2 MSIPlanetScope SuperDove