This is something that Rong Li brought to our attention in her work on the SIF code. There are two issues. One is that in datm we divide solar radiation evenly between the visible and near-IR bands using a ratio of 0.5. The other is that PAR is only part of the visible spectrum and not the entire amount.
The ratio between NIR and VIS is done for the offline model in datm. The ratio based on FluxNet sites is more like 0.43. The justification for this ratio in datm given in a comment is:
! relationship between incoming NIR or VIS radiation and ratio of
! direct to diffuse radiation calculated based on one year's worth of
! hourly CAM output from CAM version cam3_5_55However, if we modify NIR and VIS in the datm, that will have a whole list of downstream affects on the model that would likely be a big tuning exercise to workout.
@RongLi29 way to resolve this was to apply a factor inside of surface radation that only applies for what's being used as PAR. The factor is only appropriate when running I cases (with datm rather than CAM). So we'll need to have it apply for I cases, but not B or F cases.
@RongLi29 @danicalombardozzi
This is something that Rong Li brought to our attention in her work on the SIF code. There are two issues. One is that in datm we divide solar radiation evenly between the visible and near-IR bands using a ratio of 0.5. The other is that PAR is only part of the visible spectrum and not the entire amount.
The ratio between NIR and VIS is done for the offline model in datm. The ratio based on FluxNet sites is more like 0.43. The justification for this ratio in datm given in a comment is:
! relationship between incoming NIR or VIS radiation and ratio of ! direct to diffuse radiation calculated based on one year's worth of ! hourly CAM output from CAM version cam3_5_55However, if we modify NIR and VIS in the datm, that will have a whole list of downstream affects on the model that would likely be a big tuning exercise to workout.
@RongLi29 way to resolve this was to apply a factor inside of surface radation that only applies for what's being used as PAR. The factor is only appropriate when running I cases (with datm rather than CAM). So we'll need to have it apply for I cases, but not B or F cases.
@RongLi29 @danicalombardozzi