In Remote Sensing and GIS, DSM, DTM, DEM, CHM, and FHM are elevation-based digital surface representations derived from LiDAR, photogrammetry, stereo satellite imagery, or radar (e.g., InSAR). They are raster-based 3D models where each pixel stores an elevation (Z-value) relative to a vertical datum (e.g., Mean Sea Level).
DEM – Digital Elevation Model
Concept
A Digital Elevation Model (DEM) is a generic term for a raster grid representing elevation values of the Earth's surface.
It represents a continuous field surface
Each pixel contains a Z-value (elevation)
It may represent bare earth or surface, depending on data source
Terminologies
Raster resolution – spatial pixel size (e.g., 10 m, 30 m)
Vertical accuracy – elevation precision (± m)
Elevation datum – reference level (e.g., MSL, WGS84 ellipsoid)
Grid-based terrain model
Digital surface representation
Important Clarification
DEM is often used as an umbrella term
In many datasets, DEM ≈ DTM (bare earth)
Technically, DEM is the broader concept
Applications
Slope, aspect, curvature analysis
Watershed delineation
Terrain visualization
Contour generation
DSM – Digital Surface Model
Concept
A Digital Surface Model (DSM) represents the topmost reflective surface, including:
Buildings
Trees
Vegetation
Infrastructure
Ground
It captures the first return (top hit) in LiDAR data.
Terminologies
First return LiDAR
Top-of-canopy elevation
Surface elevation
Object-inclusive elevation model
Applications
3D city modelling
Urban morphology studies
Shadow and solar radiation analysis
Telecommunication planning
DTM – Digital Terrain Model
Concept
A Digital Terrain Model (DTM) represents the bare-earth terrain, excluding:
Buildings
Trees
Vegetation
Man-made structures
It is generated using ground-classified LiDAR points or filtering algorithms.
Terminologies
Ground return (last return)
Bare-earth extraction
Terrain filtering
Morphological filtering algorithms
Applications
Hydrological modelling
Flood simulation
Slope stability analysis
Landslide susceptibility mapping
Geomorphological studies
CHM – Canopy Height Model
Concept
A Canopy Height Model (CHM) represents the height of vegetation or objects above ground level.
Mathematical Expression:
It removes terrain elevation and isolates object height.
Terminologies
Normalized height model
Vegetation height extraction
Vertical canopy structure
Relative height model
Applications
Forest biomass estimation
Carbon stock assessment
Precision forestry
Habitat structure analysis
FHM – Forest Height Model
Concept
A Forest Height Model (FHM) is a specialized version of CHM focusing specifically on:
Forest canopy height
Stand-level tree height variation
Forest structural parameters
Applications
Forest inventory
Growth monitoring
Timber volume estimation
Ecological modelling
Differences
| Model | Represents | Includes Objects? | Data Basis | Primary Use |
|---|---|---|---|---|
| DEM | General elevation surface | Depends | Any elevation dataset | General terrain analysis |
| DSM | Top reflective surface | Yes | First return | Urban & surface modelling |
| DTM | Bare-earth terrain | No | Ground returns | Hydrology & geomorphology |
| CHM | Height above ground | Only object height | DSM − DTM | Vegetation studies |
| FHM | Forest canopy height | Vegetation only | Filtered CHM | Forestry |
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