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

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

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 brightnessTemperature 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: brightnessTemperature
    channels: 1-7, 16-22
  where:
  - variable:
      name: MetaData/landOrSeaQualifier
    is_in: 0  # land=0, sea=1, ice=2
  test variables:
  - name: ObsFunction/BennartzScatIndex
    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