Spatial interpolation of point data

• Interpolation of Hourly scalars to Sub-daily Basins
  • Meteorological Service of Canada (MSC) scalars
  • Hourly Basin to 6-hourly Basin interpolation
• 6-hourly Precipitation to Basins
• References

Interpolation of Hourly scalars to Sub-daily Basins

Below is an itemized description of the interpolation process, with open data access. All interpolated (i.e., “vector”) data are automatically updated and maintained using the ORMGP-FEWS system system.

workflow: preprocessMSCtoBasinsHourly.xml

Meteorological Service of Canada (MSC) scalars

1. Scrape MSC for recent data, executed from FEWS.
2. Import scraped MSC hourly scalars into FEWS.

3. Export hourly MSC NetCDF file (*.nc) from FEWS, from 1989-10-01

   _exportMSChourlyNetcdf.nc $T_a, p_a, r, \text{vis}, u, u_\alpha$

4. Interpolate to 10km sub-watersheds, using a python script executed from config file pyMSChourliesToBasin.xml that executes: ncMSCtoHourlyBasinNetCDF.py.
   • Air temperature $(T_a)$, relative humidity $(r)$ and wind speeds $(u)$ are interpolated using a radial basis function (RBF) (with a cubic kernel and a smoothing factor $\lambda=1/1000$ to prevent singular matrices).
   • Air/barometric pressure $(p_a)$ are first corrected for elevation then interpolated using the same cubic RBF.
   • Wind directions $(u_\alpha)$ are split into their x-y components, each interpolated separately using a cubic RBF before returned to an angle. A sample result is shown below:
5. Interpolated $(T_a, r, u)$ are applied to compute potential evaporation flux [m/s] (Novák, 2012):

\[E_a=7.46\times 10^{-9} \cdot (a + ub) d_a\] \[d_a=(1-r) \cdot e_s(T_a)\]

1. Save to NetCDF (.nc) for import back to FEWS.

   _exportMSChourlyNetcdf_interp.nc $T_a, p_a, r, u, E_a$ hourly basins

Hourly Basin to 6-hourly Basin interpolation

1. Hourly aggregation to 6-hourly time intervals (00:00 06:00 12:00 18:00 UTC) is performed in FEWS using the:
   • MeanToMean aggregation routine for $Ta, p_a, r, u$, and
   • Accumulative aggregation routine for $E_a$.

   These data have a set expiry.

2. Export 6-hourly, basin-interpolated $P_\text{HRDPA}, T_a, p_a, r, u$ to NetCDF.

   yyyyMMddHHmm-6hourlyBasin.nc

   to be altered to $P_\text{HRDPA}, P_R, P_S, T_a, p_a, r, u, E_a$

6-hourly Precipitation to Basins

The 6-hourly CaPA-RDPA precipitation $(P)$ field is a gridded raster that is routinely scraped of open web resources and proportioned to the sub-watersheds using our ORMGP-FEWS system, using the Interpolation: SpatialAverage transformation.

References

Novák, V., 2012. Evapotranspiration in the Soil-Plant-Atmosphere System. Springer Science+Business Media Dordrecht. 253pp.