i.eb.z0m

Computes momentum roughness length (z0m) and surface roughness for heat transport (z0h) after Bastiaanssen (2004).

i.eb.z0m [-p] input=name [coef=float] [hv_max=float] [hmr=float] output=name [z0h=name] [--overwrite] [--verbose] [--quiet] [--qq] [--ui]

Example:

i.eb.z0m input=name output=name

grass.script.run_command("i.eb.z0m", input, coef=0.1, hv_max=1.5, hmr=0.02, output, z0h=None, flags=None, overwrite=False, verbose=False, quiet=False, superquiet=False)

Example:

gs.run_command("i.eb.z0m", input="name", output="name")

Parameters

Command linePython (grass.script)

input=name [required]
    Name of the NDVI map [-1.0;1.0], SAVI if -p flag
coef=float
    Value of the conversion factor from z0m and z0h (Bastiaanssen (2005) used 0.1), for -f flag
    Default: 0.1
hv_max=float
    Value of the vegetation height at max(NDVI) i.e. standard C3 crop could be 1.5m, not needed for -p flag
    Default: 1.5
hmr=float
    Value of the micro-relief height (h.m-r.) on flat bare ground, most references point to 2cm, not need for -p flag
    Default: 0.02
output=name [required]
    Name of the output z0m layer
z0h=name
    Name of the output z0h layer
-p
    Use SAVI input only with equation of Pawan (2004)
--overwrite
    Allow output files to overwrite existing files
--help
    Print usage summary
--verbose
    Verbose module output
--quiet
    Quiet module output
--qq
    Very quiet module output
--ui
    Force launching GUI dialog

input : str, required
    Name of the NDVI map [-1.0;1.0], SAVI if -p flag
    Used as: input, raster, name
coef : float, optional
    Value of the conversion factor from z0m and z0h (Bastiaanssen (2005) used 0.1), for -f flag
    Used as: 0.1
    Default: 0.1
hv_max : float, optional
    Value of the vegetation height at max(NDVI) i.e. standard C3 crop could be 1.5m, not needed for -p flag
    Used as: 0.1
    Default: 1.5
hmr : float, optional
    Value of the micro-relief height (h.m-r.) on flat bare ground, most references point to 2cm, not need for -p flag
    Used as: 0.1
    Default: 0.02
output : str, required
    Name of the output z0m layer
    Used as: output, raster, name
z0h : str, optional
    Name of the output z0h layer
    Used as: output, raster, name
flags : str, optional
    Allowed values: p
    p
        Use SAVI input only with equation of Pawan (2004)
overwrite: bool, optional
    Allow output files to overwrite existing files
    Default: False
verbose: bool, optional
    Verbose module output
    Default: False
quiet: bool, optional
    Quiet module output
    Default: False
superquiet: bool, optional
    Very quiet module output
    Default: False

DESCRIPTION

i.eb.z0m calculates the momentum roughness length (z0m) and optionally the surface roughness for heat transport (z0h) as per SEBAL requirements from Bastiaanssen (1995). Default: calculating from a NDVI with an deterministic equation, as seen in Bastiaanssen (1995). Flag -p : calculating from a SAVI with an empirical equation, as seen in Pawan (2004). This is a typical input to sensible heat flux computations of any energy balance modeling.

NOTES

The NDVI map input and the ndvi_max operation set, is only to get a linear relationship from NDVI to vegetation height. The latter being related to z0m by a factor 7. If you happen to have a vegetation height (hv) map, then z0m=hv/7 and z0h=0.1*z0m.

TODO

REFERENCES

Bastiaanssen, W.G.M., 1995. Regionalization of surface flux densities and moisture indicators in composite terrain; a remote sensing approach under clear skies in mediterranean climates. PhD thesis, Wageningen Agricultural Univ., The Netherland, 271 pp. (PDF)
Chemin, Y., 2012. A Distributed Benchmarking Framework for Actual ET Models, in: Irmak, A. (Ed.), Evapotranspiration - Remote Sensing and Modeling. InTech. (PDF, DOI: 10.5772/23571)

AUTHOR

Yann Chemin

SOURCE CODE

Available at: i.eb.z0m source code (history)
Latest change: Friday Feb 21 10:10:05 2025 in commit 7d78fe3