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DSM DTM DEM CHM FHM

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 

ModelRepresentsIncludes Objects?Data BasisPrimary Use
DEMGeneral elevation surfaceDependsAny elevation datasetGeneral terrain analysis
DSMTop reflective surfaceYesFirst returnUrban & surface modelling
DTMBare-earth terrainNoGround returnsHydrology & geomorphology
CHMHeight above groundOnly object heightDSM − DTMVegetation studies
FHMForest canopy heightVegetation onlyFiltered CHMForestry


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