authority: folia
slug: rem
name: Relative Elevation Model
domain: land
subdomain: topography
authority_id: folia:rem
parent: elevation
aliases:
  - relative-elevation-model
  - detrended-dem
  - detrended-dtm
external_ids:
  cf_standard_name: null
canonical_units: m
external_validations:
  product:
    id: riverrem
    docs_url: https://github.com/OpenTopography/RiverREM
  stac:
    extension: raster
    field: raster:bands
    docs_url: https://github.com/stac-extensions/raster
description: |
  Elevation expressed relative to the water surface of a nearby river,
  rather than relative to sea level. Produced by detrending a bare-earth
  DTM: sample DTM heights along the river centreline, interpolate a
  smooth trend surface across the valley, then subtract it from the DTM.
  The result flattens the regional slope so that abandoned channels,
  meander scrolls, terraces, and floodplain micro-topography stand out,
  and it colour-maps directly to height-above-river for flood context.
  Distinct from HAND (height above nearest drainage), which measures
  vertical distance to the drainage network along flow paths. A REM is a
  derived product, not a measured one: it is one detrend transform away
  from a DTM (which is itself one classify-and-grid transform away from a
  lidar point cloud). Folia has no detrend op yet — this concept names
  the output that recipe should produce. Common tools: RiverREM
  (OpenTopography), WhiteboxTools, manual interpolation in QGIS.
theme: terrain
consumed_by: []
produced_by: []
demos: []
example_recipes:
  - title: "REM from a 3DEP DTM via RiverREM"
    tool: python
    requires: [dtm]
    snippet: |
      from riverrem.REMMaker import REMMaker
      rem = REMMaker(dem="dtm_3dep_10m.tif", out_dir="out")
      rem.make_rem_viz()  # detrends against the OSM-derived river centreline
    docs_url: https://github.com/OpenTopography/RiverREM
status: documented
sources:
  - https://github.com/OpenTopography/RiverREM
  - https://opentopography.org/blog/new-package-automates-river-relative-elevation-model-rem-generation