## Advanced / Configuration Setup / Dynamic Sampling

This menu creates the optional LAGSET.CFG file which is used to configure a dynamic sampler. A dynamic sampler is defined as a moving sampler that can pass through the model simulation domain, either passively with the wind (Lagrangian mode) or by using a pre-defined velocity vector (Forced mode). In the current version the dynamic sampler transport is always vertically isobaric regardless of the vertical motion method selected for the pollutant transport. The dynamic sampler samples model produced values that are generated internally on a snapshot concentration grid.

The first menu tab defaults to the configuration for one sampler. If multiple samplers are required, then enter the number in this menu. After pressing the Configure Samplers button, another menu comes up to select the sampler number to configure. Pressing the sampler number button brings up the menu shown below. Each defined sampler must be configured according to the following instructions.

The dynamic sampler configuration file must be located in the model's startup directory to be found and the name should always be in uppercase. The following is an example of the contents of LAGSET.CFG for one dynamic sampler. Multiple samplers would repeat the last seven line sequence.

1 : number of dynamic samplers

40.0 -90.0 500.0 : release location and height (agl)

0.0 0.0 : force vector - direction, speed (m/s)

95 10 16 00 00 : release start - year month day hour minute

95 10 16 00 00 : sampling start - year month day hour minute

00 : sample averaging (min)

60 : disk file output interval (min)

'LAGOUT.TXT' : sampler output file

Number of dynamic samplers: Due to file unit number restrictions, the current version only supports 9 simultaneous sampler definitions. The following seven lines need to be repeated for every defined sampler.

Release location and height: The location is the latitude-longitude point at which the trajectory of the sampler path is started. Although the subsequent vertical motion is isobaric, the initial starting height must be defined in meters above ground-level. Note that the isobaric sampler trajectory will not be identical to the HYSPLIT trajectory model isobaric trajectory because of differences in how the vertical motion is computed between the two models.

Force vector: If the direction (downwind) and speed (m/s) set to zero, then the model computes the sampler trajectory according to the meteorological input data wind velocity. If any of these values are not zero, then the sampler trajectory is computed using these values for its entire length. To simulate a more complex aircraft sampling path, each leg of the flight pattern requires its own sampler definition. For instance, an aircraft flying east with have a direction vector of 090.

Release start: The release time of the sampler gives the date and time that sampler starts from the previously defined release location. Note that in the current version, zero's for this field (relative start time) are not supported.

Sampling start: The sampler may proceed on its trajectory for quite some time before sampling is started. The sampler start time must be greater than or equal to the release start time.

Sample averaging (minutes): At every computational time step the model determines the sampler position in the concentration grid and accumulates the concentration value in memory. When the sampler accumulation time reaches the sample averaging time, all sums are reset to zero. A sample averaging time of zero means that the sample is only accumulated for one model integration time step.

Disk file output interval (minutes): At the disk output interval, the sampler concentration values are written to the output file defined on the next input line. The value written is the accumulated concentration divided by the accumulated minutes. The disk output interval is independent from the sample averaging time.

Sampler output file: The directory and file name should be enclosed in single quotes. If the file is defined without a directory it is written to the model startup directory.

Concentration Grid Configuration

Note that dynamic sampling will only work if the sampler trajectory passes through a concentration grid covering the region of interest. That means that a concentration grid of sufficient resolution, in both the horizontal and vertical is required for a sampler to capture the pollutant. However too much resolution (too fine a grid) may mean that there could be an insufficient number of pollutant particles to provide a uniform distribution and therefore the sampling could provide unrepresentative results. The concentration grid is required to be defined as a snapshot grid. In the current version, only one pollutant species per simulation is supported.

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