Pv = (OGVI_S-0.15) / (0.9 - 0.15)

Soil emissivity
emis_s_S8 = if (OGVI_S <= 0.15) then (-0.051 * Oa08_reflectance_M) + 0.98 else 0
emis_s_S9 = if (OGVI_S <= 0.15) then (-0.032 * Oa09_reflectance_M) + 0.983 else 0

Mixed vegetation emissivity
emis_m_S8 = if (OGVI_S > 0.15) and (OGVI_S < 0.9) then 0.969 * (1 - Pv) + (0.99 * Pv) else 0
emis_m_S9 = if (OGVI_S > 0.15) and (OGVI_S < 0.9) then 0.977 * (1 - Pv) + (0.99 * Pv) else 0

Vegetation emissivity
emis_v = if (OGVI_S >= 0.9) then 0.99 else 0

Total emissivity
emis_total_S8 = emis_s_S8 + emis_m_S8 + emis_v
emis_total_S9 = emis_s_S9 + emis_m_S9 + emis_v

Effective emissivity
emis_mean = (emis_total_S8_S - emis_total_S9_S) / 2

Differential emissivity
emis_diff = emis_total_S8_S - emis_total_S9_S

Water vapour to g*cm2
water_vapour = IWV_S_S / 10