STEP 01
Orbit & Calibration
Precise orbit state vectors are applied to refine the satellite position, followed by radiometric calibration to convert raw digital numbers to σ⁰.
GEOAI CAPABILITY·BACKSCATTER NORMALISATION
Radiometric Terrain Correction
Normalises SAR backscatter against terrain geometry so pixel intensities reflect surface properties instead of slope and aspect, enabling consistent multi-temporal analysis.
OVERVIEW
What is Radiometric Terrain Correction?
Radiometric Terrain Correction (RTC) is a processing step that removes the radiometric distortions in SAR images caused by variations in terrain slope. Without it, the same forest, field, or flooded area produces very different backscatter values depending on which way the ground tilts relative to the satellite.
RTC normalises the radar backscatter coefficient (sigma-nought, σ⁰) by computing the local incidence angle at each pixel from elevation data, then projecting the values into terrain-corrected γ⁰ (gamma-nought), the backscatter per unit area on the local terrain surface. The corrected pixel is comparable across slopes, sensors, and acquisition geometries.
Sentient runs RTC across every SAR scene that enters the platform, so downstream models, change detection, biomass, flood mapping, work on a consistent radiometric baseline regardless of where the scene was acquired.
METHODOLOGY
RTC Processing Steps
STEP 02
DEM Co-registration
The DEM is reprojected into the SAR slant-range / azimuth coordinate system using the Range-Doppler terrain-correction approach, so every elevation sample lines up with its corresponding radar pixel.
STEP 03
Local Incidence Angle Computation
For each pixel, the local incidence angle (θ_loc) is computed as the angle between the radar look vector and the local surface normal derived from the DEM.
STEP 04
Radiometric Normalisation
Backscatter is normalised pixel-by-pixel using γ⁰ = σ⁰ × (sin θ_ref / sin θ_loc), where θ_ref is a chosen reference incidence angle. Slopes that previously appeared bright or dark for purely geometric reasons collapse to a comparable scale.
STEP 05
Geocoding & Output
The corrected γ⁰ values are resampled from radar geometry to a map projection (typically UTM), producing a geocoded, radiometrically terrain-corrected product ready for analysis.
APPLICATIONS
Where it shows up
Land Cover Classification
Normalised backscatter enables consistent classification across mountainous and flat terrain without topographic bias.
Forest Biomass Estimation
γ⁰ values correlate with above-ground biomass independently of terrain slope, enabling reliable forest-inventory mapping.
Flood Mapping
Terrain-corrected SAR distinguishes true water surfaces from radar shadow in valleys, reducing false-positive flood detections.
Time-Series Analysis
Consistent radiometry across acquisitions with different orbital passes enables robust multi-temporal change detection.
POWERS THESE PRODUCTS
