Opened 10 years ago

Last modified 14 months ago

#899 assigned enhancement

Better documentation and examples for i.eb.* and related modules requested

Reported by: huhabla Owned by: ychemin
Priority: minor Milestone: 7.6.2
Component: Docs Version: svn-trunk
Keywords: imagery, i.eb.*, r.sunhours Cc: grass-dev@…, ychemin
CPU: All Platform: All

Description

I would like to request a major documentation update for the new i.eb.* and related modules (i.sunhours, i.albedo, ...?). It would be great if we can see:

  • More detailed description of the specific usage for each module with examples
  • Better description of several abbreviations (eb, ETa, ETo, ETrF)
  • Knowledge transfer from the pointed literature into the module documentation, it was hard for me to find online available referred literature.
  • Integrative examples how to combine all these modules in a meaningful manner, this will make work much easier and will prevent errors in handling those modules.
  • Adding i.eb.* introduction and usage to the imagery introduction page
  • Several modules are referred, but they are only available in the addon wiki, if these modules are important, maybe they should go direct into grass7. If not, alternative processing method should be documented?

Many thanks in advances Soeren

Change History (15)

comment:1 Changed 6 years ago by ychemin

Cc: ychemin added
Owner: changed from grass-dev@… to ychemin
Status: newassigned

The radiation is coming from the planet's star, Earth has around 1800 W/m2 of incoming radiation from the sun (also called irradiance) at exo-atmospheric altitude.

Atmospheric transfer of irradiance is subject to atmosphere particles interactions, scattering, diffraction, reflection, etc.

When reaching the planetary surface, is it partially reflected in the shortwave by Albedo. Surface Albedo is the integrated 0.3-3 micro-meters reflectance, it reflects the shortwave energy coming from the sun by 5% on oceans, 15-25% on vegetation, 35-40% on sand/desert/beach, 60-80% on snow/clouds, roughly. This energy fraction is returned to atmosphere for complex interaction with gas particles again before leaving the atmosphere altogether.

As for the shortwave surface balance, the energy is also received in the longwave, but interacts with the grey-body characteristics of the surface elements. The blackbody to greybody fraction is ruled by emissivity, a hidden component in the thermal spectrum (search for Temperature-Emissivity Separation algorithms). On Earth, emissivity is always above 0.9 (mostly 0.96-0.98). The Stefan-Boltzman equation is dealing with blackbody energy, and multiplying it by Emissivity transforms it to greybody energy emitted.

Together, shortwave and longwave energy balance provide with the net radiation balance at the surface of the planetary body. This crucial term is the total energy available for thermodynamic fluxes to act on the surface of the planet. On a planet like Earth where there is a triple phase of a given molecule (H20, in gas, liquid, solid), energy available is used to transfer phases from lower energy to higher energy (sublimation, liquefaction, evaporation). Thermal transfers also happen as conduction (soil, rocks) and convection (atmosphere, oceans). The i.eb.* modules and models deal with conduction (i.eb.g0, for thermal conduction in soils), convection (i.eb.h_* especially, for thermal convection in atmosphere) and by residual method estimate the energy left for evaporation processes (i.eb.evapf, i.eb.eta are examples).

i.evapo.* modules/models are integrated models, from the oldest (Penman-Monteith i.evapo.pm, Priestley-Taylor i.evapo.pt, Hargreaves i.evapo.mh, etc) that are not based on energy balance, but are computing some form of evapotranspiration (ETo: Evapotranspiration for a reference of 20cm well-watered grass, see FAO no56 report of Richard Allen) to newer that area in some form or another linked to thermal processes (i.evapo.senay: uses a thermal index), biome thermal processes (i.evapo.zk: global model based on typical info from biomes Albedo/soil heat flux) or more thermodynamic processes (i.evapo.potrad: potential ET if not water stress, based on astronomical equations only). Most developed thermodynamic models are TSEB (i.evapo.tseb: Two Source Energy Balance, Schmugge, Kustas, etc., 2000), SEBS (i.evapo.sebs: Zhu et al, 2002), SEBAL (i.eb.h_SEBAL95, i.eb.g0, i.eb.evapfr, i.eb.eta: Bastiaanssen et al, 1998), and some newer models like RESET and others. The list of models using thermodynamic principles is large now, and any willing to submit a code for any of them is most welcome.

comment:2 Changed 6 years ago by neteler

Keywords: r.sunhours added; i.sunhours removed

Some ref added in r59348. Extra fixes in r59349.

TODO: Yann's text above should also be added, but where? a SVN diff would be appreciated.

comment:3 Changed 6 years ago by neteler

Some potential material coming up for the EGU 2014 in

http://svn.osgeo.org/grass/grass-promo/grassposter/2014_EGU_WD_Landscape/

comment:4 in reply to:  3 Changed 5 years ago by wenzeslaus

comment:5 Changed 5 years ago by neteler

Cc: grass-dev@… added
Component: ImageryDocs

comment:6 Changed 4 years ago by martinl

Milestone: 7.0.07.0.5

comment:7 Changed 4 years ago by martinl

Milestone: 7.0.57.3.0

comment:8 Changed 4 years ago by martinl

Milestone: 7.3.07.4.0

Milestone renamed

comment:9 Changed 2 years ago by neteler

Milestone: 7.4.07.4.1

Ticket retargeted after milestone closed

comment:10 Changed 2 years ago by neteler

Milestone: 7.4.17.4.2

comment:11 Changed 20 months ago by martinl

What is the state of this ticket?

comment:12 Changed 20 months ago by veroandreo

AFAICT, all i.eb.* modules in core have still a very minimal description and they all lack examples. These latter are pretty difficult to include (for someone not in the field) without a proper description of what the module does and what the parameters mean or how they are supposed to be obtained.

Maybe an i.eb general manual could give the basics of the process and then each module describe the specifics.

comment:13 Changed 20 months ago by martinl

Milestone: 7.4.27.6.0

All enhancement tickets should be assigned to 7.6 milestone.

comment:14 Changed 16 months ago by martinl

Milestone: 7.6.07.6.1

Ticket retargeted after milestone closed

comment:15 Changed 14 months ago by martinl

Milestone: 7.6.17.6.2

Ticket retargeted after milestone closed

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