BennartzScatIndex

This ObsFunction calculates a scattering index based on observations from two satellite microwave channels.

An offset is computed which varies with satellite zenith angle as

\[\text{Offset = bennartz_coeff_1 + bennartz_coeff_2*sensor_zenith_angle}\]

A scattering index is then computed as the difference between two channel brightness temperatures (BTs) minus the offset:

\[\text{S.I. = BT(channel_89ghz) - BT(channel_150ghz) - Offset}\]

Typically channels such as 89 GHz and 150 GHz are chosen where the sensitivity to scattering by ice particles increases with frequency.

Required parameters:

channel_89ghz

Channel number corresponding to 89 GHz (or nearby frequency depending on sensor channel specification) e.g. MHS channel 1 at 89 GHz.

channel_150ghz

Channel number corresponding to 150 GHz (or nearby frequency depending on sensor channel specification) e.g. MHS channel 2 at 157 GHz.

bennartz_coeff_1

First coefficient used to compute scattering index offset

bennartz_coeff_2

Second coefficient used to compute scattering index offset

Optional parameters:

apply_bias

Name of the bias correction group used to apply correction to ObsValue

Default (missing optional parameter) applies no bias correction

Reference:

R. Bennartz. Precipitation analysis using the Advanced Microwave Sounding Unit in support of nowcasting applications. Meteorol. Appl. 9, 177-189 (2002). DOI:10.1017/S1350482702002037

Example yaml:

Here is an example using this ObsFunction inside the Bounds Check filter for ATMS. The brightness_temperature filter variables are rejected if the output value of this ObsFunction is larger than the example maxvalue = -1.0.

- filter: Bounds Check
  filter variables:
  - name: brightness_temperature
    channels: 1-7, 16-22
  where:
  - variable:
      name: land_sea@MetaData
    is_in: 0  # land=0, sea=1, ice=2
  test variables:
  - name: BennartzScatIndex@ObsFunction
    options:
      channel_89ghz: 16    # ATMS 89.5 GHz channel
      channel_150ghz: 17   # ATMS 165.5 GHz channel
      bennartz_coeff_1: 0.158
      bennartz_coeff_2: 0.0163
      apply_bias: ObsBias
  maxvalue: -1.0
  action:
    name: reject