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NAME

i.eb.hsebal95 - Performs sensible heat flux iteration (SEBAL 95).

KEYWORDS

imagery, heat flux, energy balance

SYNOPSIS

i.eb.hsebal95
i.eb.hsebal95 --help
i.eb.hsebal95 [-tacz] temperature=name elevation=name windvelocity2m=name ndvi=name albedo=name netradiation=name soilheatflux=name [iteration=integer] [row_wet=integer] [col_wet=integer] [row_dry=integer] [col_dry=integer] output=name [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-t
Temperature histogram check (careful!)
-a
Automatic wet/dry pixel (careful!)
-c
Coordinates of manual dry/wet pixels are in image projection and not row/col
-z
set negative evapo to zero
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog

Parameters:

temperature=name [required]
Name of Surface Skin Temperature input map [K]
elevation=name [required]
Name of dem input map [m a.s.l.]
windvelocity2m=name [required]
Name of Wind speed at 2m height input map [m/s]
ndvi=name [required]
Name of NDVI input map [-]
albedo=name [required]
Name of Albedo input map [-]
netradiation=name [required]
Name of instantaneous Net Solar Radiation input map [W/m2]
soilheatflux=name [required]
Name of instantaneous Soil Heat Flux input map [W/m2]
iteration=integer
Value of the number of SEBAL95 loops (default is 10)
row_wet=integer
Row value of the wet pixel
col_wet=integer
Column value of the wet pixel
row_dry=integer
Row value of the dry pixel
col_dry=integer
Column value of the dry pixel
output=name [required]
Name of output sensible heat flux layer [W/m2]

Table of contents

DESCRIPTION

i.eb.h_sebal95 computes the sensible heat flux [W/m2] after Bastiaanssen, 1995 in [1].

i.eb.h_sebal95 given the vegetation height (hc), humidity (RU), wind speed at two meters height (WS), temperature (T), digital terrain model (DEM), and net radiation (NSR) raster input maps, calculates the sensible heat flux map (h0).

Optionally the user can activate a flag (-z) that allows him setting to zero all of the negative evapotranspiration cells; in fact these negative values motivated by the condensation of the air water vapour content, are sometime undesired because they can produce computational problems. The usage of the flag -n detect that the module is run in night hours and the appropriate soil heat flux is calculated.

The algorithm implements well known approaches: the hourly Penman-Monteith method as presented in Allen et al. (1998) for land surfaces and the Penman method (Penman, 1948) for water surfaces.

Land and water surfaces are idenfyied by Vh:
- where Vh less than 0 vegetation is present and evapotranspiration is calculated;
- where Vh=0 bare ground is present and evapotranspiration is calculated;
- where Vh more than 0 water surface is present and evaporation is calculated;

For more details on the algorithms see [1].

Parameters:

DEM=name
Input elevation raster [m a.s.l.]. Required.
T=name
Input temperature raster [°C]. Required.
RH =name
Input relative humidity raster [%]. Required.
WS =name
Input wind speed at two meters raster [m/s]. Required.
NSR =name
Input net solar radiation raster [MJ/(m2*h)]. Required.
Vh =name
Input vegetation heigth raster [m]. Required.
ETP =name
Output evapotranspiration raster [mm/h]. Required.

NOTES

Net solar radiation map in MJ/(m2*h) can be computed from the combination of the r.sun, run in mode 1, and the r.mapcalc commands.

The sum of the three radiation components outputted by r.sun (beam, diffuse, and reflected) multiplied by the Wh to Mj conversion factor (0.0036) and optionally by a clear sky factor [0-1] allows the generation of a map to be used as an NSR input for the i.evapo.pm command.
example:
r.sun elev_in=dem asp_in=aspect slope_in=slope lin=2 albedo=alb_Mar \ incidout=out beam_rad=beam diff_rad=diffuse refl_rad=reflected day=73 time=13:00 dist=100;
r.mapcalc 'NSR=0.0036*(beam+diffuse+reflected)';

SEE ALSO

REFERENCES

[1] Bastiaanssen, W.G.M., 1995. Estimation of Land surface paramters by remote sensing under clear-sky conditions. PhD thesis, Wageningen University, Wageningen, The Netherlands.

[2] Allen, R.G., L.S. Pereira, D. Raes, and M. Smith. 1998. Crop Evapotranspiration: Guidelines for computing crop water requirements. Irrigation and Drainage Paper 56, Food and Agriculture Organization of the United Nations, Rome, pp. 300

[3] Penman, H. L. 1948. Natural evaporation from open water, bare soil and grass. Proc. Roy. Soc. London, A193, pp. 120-146.

AUTHOR

Yann Chemin
International Rice Research Institute, Los Banos, The Philippines.
International Water management Institute, Colombo, Sri Lanka.

Contact: Yann Chemin

SOURCE CODE

Available at: i.eb.hsebal95 source code (history)

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