groundAlbedo.f90 File Reference

Calculates visible and near-IR ground albedos. More...

Functions/Subroutines
subroutine	groundalbedo (ALVSG, ALIRG, ALVSGC, ALIRGC, ALGWV, ALGWN, ALGDV, ALGDN, THLIQ, FSNOW, ALVSU, ALIRU, FCMXU, AGVDAT, AGIDAT, FG, ISAND, ILG, IG, IL1, IL2, JL, IALG)

Detailed Description

Calculates visible and near-IR ground albedos.

Author

D. Verseghy, M. Lazare

Function/Subroutine Documentation

groundalbedo()

subroutine groundalbedo	(	real, dimension (ilg), intent(out)	ALVSG,
		real, dimension (ilg), intent(out)	ALIRG,
		real, dimension (ilg), intent(out)	ALVSGC,
		real, dimension (ilg), intent(out)	ALIRGC,
		real, dimension (ilg), intent(in)	ALGWV,
		real, dimension (ilg), intent(in)	ALGWN,
		real, dimension (ilg), intent(in)	ALGDV,
		real, dimension (ilg), intent(in)	ALGDN,
		real, dimension (ilg,ig), intent(in)	THLIQ,
		real, dimension (ilg), intent(in)	FSNOW,
		real, dimension (ilg), intent(in)	ALVSU,
		real, dimension (ilg), intent(in)	ALIRU,
		real, dimension (ilg), intent(in)	FCMXU,
		real, dimension(ilg), intent(in)	AGVDAT,
		real, dimension(ilg), intent(in)	AGIDAT,
		real, dimension (ilg), intent(in)	FG,
		integer, dimension (ilg, ig), intent(in)	ISAND,
		integer, intent(in)	ILG,
		integer, intent(in)	IG,
		integer, intent(in)	IL1,
		integer, intent(in)	IL2,
		integer, intent(in)	JL,
		integer, intent(in)	IALG
	)

Parameters

[out]	alvsg	Visible albedo of bare ground \([ ] (\alpha_{g, VIS})\)
[out]	alirg	Near-IR albedo of bare ground \([ ] (\alpha_{g, NIR})\)
[out]	alvsgc	Visible albedo of ground under vegetation canopy [ ]
[out]	alirgc	Near-IR albedo of ground under vegetation canopy [ ]
[in]	algwv	Visible albedo of wet soil for modelled area \([ ] (alpha_{g, NIR, wet})\)
[in]	algwn	Near-infrared albedo of wet soil for modelled area \([ ] (alpha_{g, NIR, wet})\)
[in]	algdv	Visible albedo of dry soil for modelled area \([ ] (alpha_{g, VIS, dry})\)
[in]	algdn	Near-infrared albedo of dry soil for modelled area \([ ] (alpha_{g, NIR, dry})\)
[in]	thliq	Volumetric liquid water content of soil layers \([m^3 m^{-3}]\)
[in]	alvsu	Visible albedo of urban part of modelled area \([ ] (alpha_{u, VIS})\)
[in]	aliru	Near-IR albedo of urban part of modelled area \([ ] (alpha_{u, NIR})\)
[in]	fcmxu	Fractional coverage of urban part of modelled area \([ ] (X_u)\)
[in]	agvdat	Assigned value of visible albedo of ground – optional [ ]
[in]	agidat	Assigned value of near-IR albedo of ground – optional [ ]
[in]	fg	Fractional coverage of bare soil on modelled area \([ ] (X_g)\)
[in]	fsnow	Fractional coverage of snow on modelled area [ ]
[in]	isand	Soil type flag based on sand content, assigned in subroutine soilProperties

If the ISAND flag for the surface soil layer is greater than or equal to zero (indicating mineral soil), first the urban area not covered by snow is evaluated. Next the visible and near-IR open ground albedos, \(\alpha_{g, VIS}\) and \(\alpha_{g, NIR}\), for each wavelength range, are calculated on the basis of the wet and dry ground albedos \(\alpha_{g, wet}\) and \(\alpha_{g, dry}\) which were assigned for the modelled area in soilProperties. Idso et al. (1975) found a correlation between the soil liquid moisture content in the top 10 cm of soil (represented in CLASS by that of the first soil layer, \(\theta_{1, 1}\)) and the total surface albedo \(\alpha_{g, T}\): for water contents less than 0.22 \(m^3 m^{-3}\), \(\alpha_{g, T}\) took on the value of \(\alpha_{g, dry}\); for liquid water contents greater than 0.26 \(m^3 m^{-3}\), \(\alpha_{g, T}\) took on the value of \(\alpha_{g, wet}\). For values of \(\theta_{1, 1}\) between these two limits, a linear relationship is assumed:

\([\alpha_{g, T} - \alpha_{g, dry} ] / [\theta_{l, 1} - 0.22] = [\alpha_{g, wet} - \alpha_{g, dry} ]/[0.26 - 0.22]\)

Thus, in groundAlbedo for each of the two wavelength ranges \(\alpha_{g}\) is calculated as follows:

\(\alpha_{g, T} = \alpha_{g, dry}\) \(\theta_{l, 1} \leq 0.22 \)
\(\alpha_{g, T} = \theta_{l, 1} [\alpha_{g, wet} - \alpha_{g, dry} ]/0.04 - 5.50 [\alpha_{g, wet} - \alpha_{g, dry} ] + \alpha_{g, dry} \) \(0.22 < \theta_{l, 1} < 0.26 \)
\(\alpha_{g, T} = \alpha{g, wet} \) \( 0.26 \leq \theta_{l, 1}\)

Afterwards, a correction is applied to \(\alpha_{g, VIS}\) and \(\alpha_{g, NIR}\) in order to account for the possible presence of urban surfaces over the modelled area. Visible and near-IR albedos are assigned for local urban areas, \(\alpha_{g, VIS}\) and \(\alpha_{g, NIR}\), as part of the background data (see the section on “Data Requirements”). A weighted average over the bare soil area \(X_g\) is calculated from the fractional snow-free urban area \(X_u\) as:

\(\alpha_{g, VIS} = [X_u \alpha_{u, VIS} + (X_g-X_u) \alpha_{g, VIS}] / X_g \)
\(\alpha_{g, NIR} = [X_u \alpha_{u, NIR} + (1.0-X_u) \alpha_{g, NIR}] / X_g \)

If the soil on the modelled area is not mineral, i.e. if the ISAND flag is less than zero, \(\alpha_{g, VIS}\) and \(\alpha_{g, NIR}\) are determined as follows:

If ISAND = -2, indicating organic soil, \(\alpha_{g, VIS}\) and \(\alpha_{g, NIR}\) are assigned values of 0.05 and 0.30 respectively from the lookup tables in the block data subroutine soilPropertiesD, corresponding to average measured values reported in Comer et al. (2000) [26].

If ISAND = -3, indicating rock at the surface, \(\alpha_{g, VIS}\) and \(\alpha_{g, NIR}\) are assigned the dry ground values from soilProperties.

If ISAND = -4, indicating continental ice sheet or glacier, \(\alpha_{g, VIS}\) and \(\alpha_{g, NIR}\) are assigned values of 0.95 and 073 from soilPropertiesD, reflecting values reported for Antarctica (e.g. Sellers, 1974).

The above calculations are all performed if the flag IALG is set to zero. If IALG is set to one, indicating that assigned ground albedos are to be used instead of calculated values, \(\alpha_{g, VIS}\) and \(\alpha_{g, NIR}\) are set to the assigned values AGVDAT and AGIDAT respectively.

Lastly, the ground values of visible and near-IR albedo under the vegetation canopy are currently set equal to the open values (this approach is under review).