SetSeaIceEmiss

From the internal Met Office report, “Fast Models for Land Surface Emissivity” (Hewison & English, 1999):

This is a semi-empirical model that uses Fresnel’s formulae to calculate the specular reflectivity (emissivity) of a dielectric surface, whose permittivity can be described by a single Debye relaxation, neglecting the ionic conductivity term, as this is negligible for frequencies above 20 GHz.

A more detailed description is contained in Airborne retrievals of snow and ice surface emissivity at millimeter wavelengths (Hewison & English, 1999).

This obsfunction requires observation Metadata (surface classification) from the ATOVS and AVHRR Pre-processing Package (AAPP) and returns an emissivity for applicable ice profiles.

Based on UK Met Office Ops_SatRad_SeaIceEmiss procedure.

Required input variables:

GeoVaLs

GeoVaLs/ice_area_fraction

ObsSpace

MetaData/sensorZenithAngle MetaData/surfaceClassAAPP MetaData/surfaceQualifier

Input parameters:

polarization index (required)

Vector of (integer) polarization indices for each instrument channel to be calculated.

0 corresponds to the average of the vertical and horizontal polarization

1 corresponds to ‘nominal vertical at nadir, rotating with view angle’

2 corresponds to ‘nominal horizontal at nadir, rotating with view angle’

3 corresponds to ‘vertical’

4 corresponds to ‘horizontal’

See yaml example for an appropriate array to use for a combined AMSU-A/B instrument (20 channels).

channel frequency (required)

Vector of channel frequencies (float), in GHz, to be used in the emissivity calculation.

See yaml example for an appropriate array to use for a combined AMSU-A/B instrument (20 channels).

orbit height (required)

Nominal satellite height, in km (scalar float). Used for satellite viewing angle calculation.

Example YAML

- filter: Variable Assignment
  assignments:
  - name: SeaIceEmiss@MetaData
    function:
      name: SetSeaIceEmiss@ObsFunction
      channels: &channels 1-20
      options:
        channels: *channels
        polarization index: [1, 1, 1, 1, 2,
                             2, 1, 2, 2, 2,
                             2, 2, 2, 2, 1,
                             1, 1, 1, 1, 1]
        channel frequency: [23.8,  31.4,  50.3,   52.8,   53.596,
                            54.4,  54.94, 55.5,   57.29,  57.29,
                            57.29, 57.29, 57.29,  57.29,  89.0,
                            89.0, 150.0,  183.31, 183.31, 183.31]
        orbit height: 827.0
    type: float