SEB for estimation of turbulent fluxes
...thus evapotranspiration (ET)...
Terrestrial processes are mainly driven by energy sourced from the Sun. Exchanges within the energy and water cycles, for example. To ensure energy conservation, solar radiation received at the [natural] near-land surface (thus available energy) is generally partitioned into turbulent fluxes. That is, sensible and latent heat energy fluxes. The latter is the energy used for the evaporation of water back into the atmosphere.
SEB methods in application include : SEBS, TSEB, SPARSE., among others. Here you can use the point-based SPARSE SEB algorithm proposed by Boulet et al. (2015).
...Method : RTM (source to surface temp. link)...
TB(θ)4 = ε surfTsurf(θ)4 + (1-ε surf)L↓ = b(θ)εgTg4 + (1 - b(θ))εvTv4 + (1-εsurf)L↓
where TB(θ) = (εsurfTsurf(θ)4 + (1-ε surf)L↓)0.25 is the non-isotropic brightness temperature, which is a function of the directional surface temperature (Tsurf(θ)) and emissivity (ε surf). b(θ) is the directional gap fraction.
...Methods : Radiative- (net radiation) and Energy (available energy & turbulent fluxes) Budgets...
The overall radiative balance/budget is expressed thusly,
Rn = S↓ - S↑ + L↓ - L↑
and the energy budget/balance is,
Rn - G0 = H + λE
where Rn is the net radiation, which is aggregrated from the incoming/downwelling short (S↓) and longwave (L↓) and outgoing/upwelling short (S↑) and longwave (L↑) radiation, respectively. All radiation flux terms are in [W.m-2]. The available energy (net radiation net of any storage/transport in/through the soil, G 0) is subsequently partitioned between the turbulent fluxes, i.e. the latent (λE) and sensible (H) heat fluxes.