ALARM Interface

Overview

The non-exportable version of WSF optionally includes many capabilities from the Advanced Low-Altitude Radar Model (ALARM) version 5.2 from the Air Force Research Laboratory. The following features are included:

• The atmospheric attenuation model.

• The clutter model.

• The propagation model.

Note

This model is only applicable to radars operating on the surface of the Earth (either land or water). It is not applicable to radars on air or space craft.

Items to Note

WSF will propagate certain values into the ALARM environment:

• The ALARM value of REFRACTIVITY is set to the WSF earth_radius_multiplier value from the transmitter (which defaults to 4/3 for WSF_RADAR_SENSOR).

• If the sensing player is of the ‘surface’ or ‘subsurface’ spatial domain (by using WSF_SURFACE_MOVER or WSF_SUBSURFACE_MOVER, or by using spatial_domain in the definition of the platform type, then the following is done:

  • The ALARM value of LAND_COVER is set to ‘water’.

  • The ALARM value of LAND_FORM is derived from the WSF global_environment command sea_state .

• If the sensing player is NOT of the ‘surface’ or ‘subsurface’ spatial domain (as defined in the previous item), then the following is done:

  • The ALARM value of LAND_COVER is derived from the WSF global_environment command land_cover .

  • The ALARM value of LAND_FORM is derived from the WSF global_environment command land_formation .

Note that the internal ALARM environment does not have as many land cover values as WSF. Some mapping will be performed.

Attenuation Model

The ALARM attenuation model is selected by including an attenuation command in the transmitter block that selects the ‘earce’ model:

sensor ...
   transmitter
      attenuation earce
      ...
   end_transmitter
   ...
end_sensor

Clutter Model

The ALARM clutter model is selected through one of two mechanisms:

• Including a clutter_model block in WSF_RADAR_SENSOR that selects the ‘alarm’ model.

• Defining a clutter_model type that selects the ‘alarm’ model and then referencing that model using the clutter_model command in WSF_RADAR_SENSOR.

An example of the first case is:

sensor EX_RADAR WSF_RADAR_SENSOR
   transmitter
      ...
   end_transmitter
   receiver
      ...
   end_receiver
   clutter_model alarm
      ... parameters ...
   end_clutter_model
end_sensor

An example of the second case is:

clutter_model EX_RADAR_CLUTTER alarm
   ... parameters ...
end_clutter_model

sensor EX_RADAR WSF_RADAR_SENSOR
   transmitter
      ...
   end_transmitter
   receiver
      ...
   end_receiver
   clutter_model EX_RADAR_CLUTTER
end_sensor

This very useful capability is used when it may be desirable to change clutter models without having to modify the radar definition. The mechanism for doing this is fully described in the clutter_model command.

Commands for the ‘alarm’ Clutter Model

By default the WSF-ALARM interface will use the global_environment to determine the clutter reflectivity, and that the only commands that might be needed are azimuth_angle_limit and azimuth_angle_increment (if you want to include side lobe clutter), and maximum_range (to increase run-time performance). If you specify reflectivity, reflectivity_delta or statistic, the reflectivity will be defined by the input values.

azimuth_angle_limit <angle-value>

The maximum off-boresight angle in azimuth for which clutter returns will be computed.

Note

This is the same as the ALARM input CLUT_AZ_WIDTH.

Note

If this input is not specified, or if it is set to 0, The model will use only one mainbeam sample for its calculation

Default 0.0 (One mainbeam sample is used).

azimuth_angle_increment <angle-value>

The azimuth angle increment used in computingclutter returns.

Note

This is the same as the ALARM input CLUT_ANGLE_INCR.

Note

If this input is not specified, or if it is set to 0, The model will use the azimuth beamwidth for its calculation

Default 0.0 (Full azimuth beamwidth is used).

maximum_range <length-value>

The maximum range at which clutter will be computed. Shorter ranges decrease execution time, especially for simulations utilizing terrain elevation data such as DTED.

Default (Twice the computed clutter horizon range).

Note

This is the same as the ALARM input CLUT_MAX_RANGE.

reflectivity <db-ratio-value>

The reflectivity value used when statistic is set to numerical.

Note

This is the same as the ALARM input CLUT_REFLECTIVITY.

Default 0.0

reflectivity_delta <db-ratio-value>

Delta clutter reflectivity value about reflectivity used only when statistic is set to numerical. The clutter reflectivity is uniformly randomly distributed over the range: reflectivity reflectivity_delta. This value is optional.

Note

This is the same as the ALARM input CLUT_DELTA_REFLECT.

Default 0.0

statistic [ mean | statistical | maximum | minimum | numerical ]

Default mean

Note

This is the same as the ALARM input CLUT_STATISTIC.

random_seed <integer>

The random number seed, only used when statistic is set to statistical, or numerical, with reflectivity_delta set. Random Seed : must be a large number (> 1000).

Note

This is the same as the ALARM input CLUT_SEED.

Default 1234567

sigmac <frequency-value>

Standard deviation of the Gaussian portion of the clutter PSD. Often referred to as the root mean squared clutter frequency spread. A suggested value is 10 Hz for land, and 50 Hz for sea (See ALARM documentation for details).

Note

This is the same as the ALARM input SIGMAC.

Note

This input is not currently used.

decay_constant <frequency-value>^2

The quadratic decay constant for the inverse quadratic portion of the clutter power spectral density (PSD). A suggested value is 10-6 Hz2 (See ALARM documentation for details).

Note

This is the same as the ALARM input CLUT_DECAY.

Note

This input is not currently used.

use_legacy_data <boolean-value>

Specified whether to use an older set of tables of clutter strength. This older table set was used prior to the release of WSF 1.7.5.

Default disabled

use_native_terrain_masking <boolean-value>

Specifies whether to use the native AFSIM terrain masking calculation, instead of ALARM’s.

Note

his command may also be specified in a ALARM propagation block; it is valid for both ALARM clutter and propagation masking calculations.

Default disabled

Propagation Model

The ALARM propagation model is selected through one of two mechanisms:

• Including a propagation_model block in a transmitter block of a WSF_RADAR_SENSOR that selects the ‘alarm’ model.

• Defining a propagation_model type that selects the ‘alarm’ model and then referencing that model using the propagation_model command in the transmitter block of a WSF_RADAR_SENSOR.

An example of the first case is:

sensor EX_RADAR WSF_RADAR_SENSOR
   transmitter
      ...
      propagation_model alarm
         ... parameters ...
      end_propagation_model
   end_transmitter
   receiver
      ...
   end_receiver
end_sensor

An example of the second case is:

propagation_model EX_RADAR_PROPAGATION alarm
   ... parameters ...
end_propagation_model

sensor EX_RADAR WSF_RADAR_SENSOR
   transmitter
      ...
      propagation_model EX_RADAR_PROPAGATION
   end_transmitter
   receiver
      ...
   end_receiver
end_sensor

This very useful capability is used when it may be desirable to change clutter models without having to modify the radar definition. The mechanism for doing this is fully described in the propagation_model command.

Commands for the ‘alarm’ Propagation Model

Note that by default the WSF-ALARM interface will use the global_environment to determine the conditions at reflection points. If you specify any command except propagation or diffraction, the model will use the input values rather than conditions dictated by the global environment.

propagation <boolean-value>

Specify if the multipath propagation model should be used.

Default true

Note

This is the same as the ALARM input PROPAGATION_SW.

diffraction <boolean-value>

Indicate if the spherical Earth/knife-edge diffraction model should be used.

Default true

Note

This is the same as the ALARM input DIFFRACTION_SW.

soil_moisture <real-value>

The percent [0 .. 100] of moisture in the soil.

Note

This is the same as the ALARM input SOIL_MOISTURE.

soil_moisture_fraction <real-value>

The fraction [0 .. 1] of moisture in the soil.

stddev_surface_height <length-value>

Note

This is the same as the ALARM input STDDEV_SURFACE_HEIGHT.

terrain_dielectric_constant <real-value>

epsilon_one <real-value>

Note

This is the same as the ALARM input EPSILON_ONE.

terrain_conductivity <real-value>

sigma_zero <real-value>

Note

This is the same as the ALARM input SIGMA_ZERO.

terrain_scattering_coefficient <real-value>

roughness_factor <real-value>

Note

This is the same as the ALARM input ROUGHNESS_FACTOR.

sea_relaxation <real-value>

Note

This is the same as the ALARM input SEA_RELAXATION.

sea_wind_speed <speed-value>

Note

This is the same as the ALARM input SEA_WIND_SPEED.

water_temperature <temperature-value>

Note

This is the same as the ALARM input WATER_TEMP.

water_type [ sea | lake ]

Default sea

Note

This is the same as the ALARM input WATER_TYPE.