1i.evapo.time(1) GRASS GIS User's Manual i.evapo.time(1)
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6 i.evapo.time - Computes temporal integration of satellite ET actual
7 (ETa) following the daily ET reference (ETo) from meteorological sta‐
8 tion(s).
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11 imagery, evapotranspiration
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14 i.evapo.time
15 i.evapo.time --help
16 i.evapo.time eta=name[,name,...] eta_doy=name[,name,...]
17 eto=name[,name,...] eto_doy_min=float start_period=float end_pe‐
18 riod=float output=name [--overwrite] [--help] [--verbose] [--quiet]
19 [--ui]
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21 Flags:
22 --overwrite
23 Allow output files to overwrite existing files
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25 --help
26 Print usage summary
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28 --verbose
29 Verbose module output
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31 --quiet
32 Quiet module output
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34 --ui
35 Force launching GUI dialog
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37 Parameters:
38 eta=name[,name,...]Â [required]
39 Names of satellite ETa raster maps [mm/d or cm/d]
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41 eta_doy=name[,name,...]Â [required]
42 Names of satellite ETa Day of Year (DOY) raster maps [0-400] [-]
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44 eto=name[,name,...]Â [required]
45 Names of meteorological station ETo raster maps [0-400] [mm/d or
46 cm/d]
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48 eto_doy_min=float [required]
49 Value of DOY for ETo first day
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51 start_period=float [required]
52 Value of DOY for the first day of the period studied
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54 end_period=float [required]
55 Value of DOY for the last day of the period studied
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57 output=name [required]
58 Name for output raster map
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61 i.evapo.time (i.evapo.time_integration) integrates ETa in time follow‐
62 ing a reference ET (typically) from a set of meteorological stations
63 dataset. Inputs:
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65 • ETa images
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67 • ETa images DOY (Day of Year)
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69 • ETo images
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71 • ETo DOYmin as a single value
72 Method:
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74 1 each ETa pixel is divided by the same day ETo and become ETrF
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76 2 each ETrF pixel is multiplied by the ETo sum for the representa‐
77 tive days
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79 3 Sum all n temporal [ETrF*ETo_sum] pixels to make a summed(ET) in
80 [DOYmin;DOYmax]
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82 representative days calculation: let assume i belongs to range
83 [DOYmin;DOYmax]
84 DOYbeforeETa[i] = ( DOYofETa[i] - DOYofETa[i-1] ) / 2
85 DOYafterETa[i] = ( DOYofETa[i+1] - DOYofETa[i] ) / 2
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88 ETo images preparation: If you only have one meteorological station
89 data set, the easiest way is:
90 n=0
91 for ETo_val in Eto[1] Eto[2] ...
92 do
93 r.mapcalc "eto$n = $ETo_val"
94 `expr n = n + 1`
95 done
96 with Eto[1], Eto[2], etc being a simple copy and paste from your data
97 file of all ETo values separated by an empty space from each other.
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99 If you have several meteorological stations data, then you need to grid
100 them by generating Thiessen polygons or using different interpolation
101 methods for each day.
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103 For multi-year calculations, just continue incrementing DOY values
104 above 366, it will continue working, up to maximum input of 400 satel‐
105 lite images.
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108 i.eb.eta, i.evapo.mh, i.evapo.pt, i.evapo.pm, r.sun
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111 Yann Chemin, International Rice Research Institute, The Philippines
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114 Available at: i.evapo.time source code (history)
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116 Accessed: Saturday Oct 28 18:19:02 2023
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121 © 2003-2023 GRASS Development Team, GRASS GIS 8.3.1 Reference Manual
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125GRASS 8.3.1 i.evapo.time(1)