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Prevent numerical instability in pt_downscale_radiations #132

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Prevent numerical instability in pt_downscale_radiations #132

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19 changes: 14 additions & 5 deletions TopoPyScale/topo_scale.py
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Original file line number Diff line number Diff line change
Expand Up @@ -265,9 +265,13 @@ def pt_downscale_radiations(row, ds_solar, horizon_da, meta, output_dir):
down_pt['LW'] = row.svf * surf_interp['aef'] * sbc * down_pt.t ** 4

kt = surf_interp.ssrd * 0
sunset = ds_solar.sunset.astype(bool).compute()
mu0 = ds_solar.mu0
sunset = ds_solar.sunset.astype(bool).compute()
SWtoa = ds_solar.SWtoa
mu0 = ds_solar.mu0
# prevent numerical instability with the mu0 (in denominator of formulas at lines 304 and 307) when sun is very close to horizon (cos(75) ~= 0.25)
mu0_stable = mu0.where(mu0 > 0.25, 0.25)



# pdb.set_trace()
kt[~sunset] = (surf_interp.ssrd[~sunset] / tstep_seconds) / SWtoa[~sunset] # clearness index
Expand All @@ -281,12 +285,17 @@ def pt_downscale_radiations(row, ds_solar, horizon_da, meta, output_dir):
down_pt['SW_diffuse'] = row.svf * surf_interp.SW_diffuse

surf_interp['SW_direct'] = surf_interp.SW - surf_interp.SW_diffuse
# prevent the case in which SWtoa < SW_direct, which would cause negative ka at line 292.
surf_interp['SW_direct'][surf_interp['SW_direct'] > SWtoa] = SWtoa[surf_interp['SW_direct'] > SWtoa]



# scale direct solar radiation using Beer's law (see Aalstad 2019, Appendix A)
ka = surf_interp.ssrd * 0
# pdb.set_trace()
ka[~sunset] = (g * mu0[~sunset] / down_pt.p) * np.log(SWtoa[~sunset] / surf_interp.SW_direct[~sunset])
# Illumination angle
down_pt['cos_illumination_tmp'] = mu0 * np.cos(row.slope) + np.sin(ds_solar.zenith) * \
down_pt['cos_illumination_tmp'] = mu0_stable * np.cos(row.slope) + np.sin(ds_solar.zenith) * \
np.sin(row.slope) * np.cos(ds_solar.azimuth - row.aspect)
down_pt['cos_illumination'] = down_pt.cos_illumination_tmp * (
down_pt.cos_illumination_tmp > 0) # remove selfdowing ccuring when |Solar.azi - aspect| > 90
Expand All @@ -300,10 +309,10 @@ def pt_downscale_radiations(row, ds_solar, horizon_da, meta, output_dir):
shade = (horizon > ds_solar.elevation)
down_pt['SW_direct_tmp'] = down_pt.t * 0
down_pt['SW_direct_tmp'][~sunset] = SWtoa[~sunset] * np.exp(
-ka[~sunset] * down_pt.p[~sunset] / (g * mu0[~sunset]))
-ka[~sunset] * down_pt.p[~sunset] / (g * mu0_stable[~sunset])) # avoid exploding denominator by using mu0_stable
down_pt['SW_direct'] = down_pt.t * 0
down_pt['SW_direct'][~sunset] = down_pt.SW_direct_tmp[~sunset] * (
down_pt.cos_illumination[~sunset] / mu0[~sunset]) * (1 - shade)
down_pt.cos_illumination[~sunset] / mu0_stable[~sunset]) * (1 - shade) # avoid exploding denominator by using mu0_stable
down_pt['SW'] = down_pt.SW_diffuse + down_pt.SW_direct

# currently drop azimuth and level as they are coords. Could be passed to variables instead.
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