Methodologies
The techniques that answer EO questions. Each methodology specifies what it requires - spectral range, resolution, cadence - and which sensors can implement it, demonstrated or by spec.
Techniques that exploit continuous or near-continuous spectral coverage across visible, NIR, and SWIR wavelengths to identify materials, gases, and surface composition from their spectral fingerprints.
- SWIR absorption - point-source 3 topics
Detects gas absorption features (CH4, CO2, CO) at SWIR wavelengths from a single point or facility source; good for industrial emissions monitoring and leak detection.
- SWIR absorption - regional flux 2 topics
Estimates area-integrated greenhouse gas flux over agricultural, wetland, or basin-scale regions; good for national inventory support and carbon accounting.
- SWIR absorption - global screening 2 topics
Wide-area survey for anomalous methane or CO2 concentrations at coarse spatial resolution; good for prioritising follow-up with finer sensors.
- Hyperspectral classification 4 topics
Identifies surface materials or land-cover classes from full spectral fingerprints; good for geology, vegetation stress, and mineralogy mapping.
Techniques that retrieve gas column densities and vertical composition profiles from the interaction of solar radiation with the atmosphere, the primary toolset for air quality, greenhouse gas, and stratospheric monitoring from orbit.
- Atmospheric limb/nadir sounding 2 topics
Retrieves vertical profiles of atmospheric composition (O3, H2O, NO2) from solar occultation or nadir radiance; good for air quality monitoring and stratospheric science.
- Tropospheric column mapping (NO2/SO2) 4 topics
Maps tropospheric NO2 and SO2 column density from UV-VIS backscatter; good for urban air quality, shipping emissions, and volcanic SO2 tracking.
Techniques based on a small number of discrete spectral bands, the workhorse of operational EO. Covers vegetation indices, ocean colour, and land-cover products that underpin the majority of commercial and governmental monitoring programmes.
- Vegetation index mapping 6 topics
Derives vegetation health, density, and phenology indicators (NDVI, EVI, SAVI) from red and NIR band ratios; good for crop monitoring, deforestation alerts, and land cover change detection.
- Ocean colour / water-leaving radiance 5 topics
Retrieves chlorophyll-a concentration, CDOM, and suspended sediment from spectrally resolved water-leaving radiance; good for marine primary production, harmful algal bloom detection, and coastal water quality.
Techniques that exploit microwave backscatter from active radar illumination, operating independently of sunlight and cloud cover. Ranges from millimetre-precision deformation measurement to rapid flood and damage mapping.
- InSAR - surface deformation 3 topics
Measures millimetre-scale ground surface displacement by comparing phase differences between repeat SAR passes; good for subsidence, earthquake deformation, and volcanic monitoring.
- Polarimetric SAR - target decomposition 4 topics
Decomposes backscatter into scattering mechanisms (surface, double-bounce, volume) using multi-polarisation data; good for forest structure estimation, urban mapping, and soil moisture retrieval.
- SAR backscatter - change detection 3 topics
Detects land-cover or structural change by comparing backscatter intensity across dates; good for flood mapping, deforestation alerts, and disaster damage assessment.
Techniques that measure emitted thermal radiation from the Earth's surface and atmosphere, enabling temperature retrieval and hotspot detection without requiring solar illumination.
- Land-surface temperature - emissivity retrieval 3 topics
Retrieves surface temperature and spectral emissivity from TIR radiance measurements; good for urban heat islands, drought stress monitoring, and surface energy balance studies.
- Thermal anomaly detection 3 topics
Identifies localised high-temperature events against background radiance; good for active fire detection, gas flare monitoring, and volcanic hotspot mapping.
Techniques based on time-of-flight laser pulses to measure precise surface elevation and vertical vegetation structure, the only spaceborne methodology that directly profiles canopy height and ice sheet topography at metre-scale vertical resolution.
Techniques that measure naturally emitted microwave radiation at centimetre-to-decimetre wavelengths, penetrating cloud cover and operating day and night. The primary source of global soil moisture, sea ice, and snow water equivalent records.
Techniques that use nadir-pointing radar pulses to measure the precise distance to the ocean or land surface, producing the longest unbroken satellite record of sea level change and enabling inland water level monitoring.
Techniques that exploit reflected navigation satellite signals as a low-cost bistatic radar source, retrieving surface roughness, soil moisture, ocean wind speed, and sea ice properties from signals originally transmitted for positioning.
Techniques that combine outputs from two or more sensor families to exploit complementary information, trading the individual limitations of spatial resolution, temporal frequency, spectral coverage, or weather independence against each other.
- Optical-SAR data fusion 3 topics
Combines optical reflectance and SAR backscatter to exploit complementary information; good for cloud-persistent monitoring, crop classification under cloud cover, and flood mapping in vegetated areas.
- Multi-sensor spatiotemporal fusion - gap-filling 3 topics
Reconstructs dense time-series by blending high-frequency coarse-resolution and low-frequency fine-resolution observations; good for crop phenology tracking and cloud-gap filling.
Techniques that isolate the faint chlorophyll fluorescence signal re-emitted by vegetation during active photosynthesis, providing a direct proxy for gross primary production that vegetation indices cannot match.