BgdDepartureAnomaly.rst

BgdDepartureAnomaly

This ObsFunction calculates the background departure anomaly difference between two channels, such as:

Anomaly(i) = (O(i)-B(i) - MEAN(O-B))_ch1 - (O(i)-B(i) - MEAN(O-B))_ch2

With i the ith location under consideration, O the Tb from observation, B the Tb from the background, and MEAN(O-B) the mean departure over all valid observations on all processors.

Because hydrometeors are known to scatter radiation more efficiently with increasing microwave frequency, the anomaly tends to be positive at 36.5 GHz and negative at 89 GHz. The difference between these anomalies, largest in the H-polarised channels, is typically used to diagnose cloudy scenes.

Required parameters:

channel_low_freq

Lower frequency channel number Example: AMSR2 channel 11 corresponding to 36.5 GHz H-pol

channel_high_freq

Higher frequency channel number Example: AMSR2 channel 13 corresponding to 89 GHz H-pol

Optional parameters:

ObsBias

Name of the bias correction group used to apply correction to ObsValue. Default (missing optional parameter) applies no bias

testHofX

Name of the HofX group used to replace the default group (default is HofX)

Example yaml:

Here is an example using this ObsFunction inside the Bounds Check filter for AMSR-2. The brightness_temperature filter variables are rejected if the output value of this ObsFunction is larger than the example maxvalue = 5.

- filter: Bounds Check
  test variables:
  - name: BgdDepartureAnomaly@ObsFunction
    options:
      channel_low_freq: 11
      channel_high_freq: 13
      ObsBias: ObsBias
  maxvalue: 5
  action:
    name: reject