NAME

       i.evapo.time   -  Computes  temporal  integration  of  satellite  ET  actual (ETa) following the daily ET
       reference (ETo) from meteorological station(s).

KEYWORDS

       imagery, evapotranspiration

SYNOPSIS

       i.evapo.time
       i.evapo.time --help
       i.evapo.time   eta=name[,name,...]    eta_doy=name[,name,...]    eto=name[,name,...]    eto_doy_min=float
       start_period=float end_period=float output=name  [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       --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:
       eta=name[,name,...] [required]
           Names of satellite ETa raster maps [mm/d or cm/d]

       eta_doy=name[,name,...] [required]
           Names of satellite ETa Day of Year (DOY) raster maps [0-400] [-]

       eto=name[,name,...] [required]
           Names of meteorological station ETo raster maps [0-400] [mm/d or cm/d]

       eto_doy_min=float [required]
           Value of DOY for ETo first day

       start_period=float [required]
           Value of DOY for the first day of the period studied

       end_period=float [required]
           Value of DOY for the last day of the period studied

       output=name [required]
           Name for output raster map

DESCRIPTION

       i.evapo.time  (i.evapo.time_integration) integrates ETa in time following a reference ET (typically) from
       a set of meteorological stations dataset.  Inputs:

           •   ETa images

           •   ETa images DOY (Day of Year)

           •   ETo images

           •   ETo DOYmin as a single value
       Method:

       1      each ETa pixel is divided by the same day ETo and become ETrF

       2      each ETrF pixel is multiplied by the ETo sum for the representative days

       3      Sum all n temporal [ETrF*ETo_sum] pixels to make a summed(ET) in [DOYmin;DOYmax]

       representative days calculation: let assume i belongs to range [DOYmin;DOYmax]
       DOYbeforeETa[i] = ( DOYofETa[i] - DOYofETa[i-1] ) / 2
       DOYafterETa[i] = ( DOYofETa[i+1] - DOYofETa[i] ) / 2

NOTES

       ETo images preparation: If you only have one meteorological station data set, the easiest way is:
       n=0
       for ETo_val in Eto[1] Eto[2] ...
       do
            r.mapcalc "eto$n = $ETo_val"
            `expr n = n + 1`
       done
       with Eto[1], Eto[2], etc being a simple copy and paste from your data file of all ETo values separated by
       an empty space from each other.

       If you have several meteorological stations data, then you need  to  grid  them  by  generating  Thiessen
       polygons or using different interpolation methods for each day.

       For  multi-year  calculations, just continue incrementing DOY values above 366, it will continue working,
       up to maximum input of 400 satellite images.

       This is an example of a temporal integration from a weather station as done by  Chemin  and  Alexandridis
       (2004)

References

       Chemin  and  Alexandridis,  2004.  Spatial  Resolution  Improvement  of  Seasonal  Evapotranspiration for
       Irrigated Rice, Zhanghe Irrigation District, Hubei Province, China.   Asian  Journal  of  Geoinformatics,
       Vol. 5, No. 1, September 2004 (PDF)

SEE ALSO

        i.eb.eta, i.evapo.mh, i.evapo.pt, i.evapo.pm, r.sun

AUTHOR

       Yann Chemin, International Rice Research Institute, The Philippines

SOURCE CODE

       Available at: i.evapo.time source code (history)

       Accessed: Monday Apr 01 03:09:08 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.3.2 Reference Manual

GRASS 8.3.2                                                                                 i.evapo.time(1grass)