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.

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

       Last changed: $Date: 2014-12-27 23:51:00 +0100 (Sat, 27 Dec 2014) $

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