= Virtual measurements =
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Since -r3707 a virtual-measurement module is available in PALM. The module enables an easy setup of virtual measurements in the model domain emulating 'real-world' observations. Virtual measurement locations are placed within the model domain according to the UTM coordinates of the 'real-world' observations. This way, not only point and profile measurements can be emulated in the model, but also complex trajectories such as spiral-shaped flight measurements or bicycle/pedestrian measurements. With masked data output this would be hardly possible. 
Please note, to correctly setup the virtual measurement locations the origin UTM coordinates of the lower-left edge of the model domain ([../iofiles/pids#origin_x origin_x], [../iofiles/pids#origin_y origin_y]) within the static input file should be as accurate as possible. 

For different measurement sites the variables which should be sampled can be prescribed individually. Variables will be sampled at each model time step at all given coordinates and adjacent grid points.
The sampled data is written into binary files. PALM-4U comes with a post-processor (please see https://palm.muk.uni-hannover.de/trac/browser/palm/trunk/UTIL/combine_virtual_measurements), which merges data from the binary files and gives a single NetCDF file with all virtually sampled data for each prescribe site. 

In order to setup the measurement locations, a measurement setup file is required. This file contains all information about the measurement coordinates, the type of the measurement, and further attributes. For a description of required attributes and variables, as well as an example input file, please see #virtual_measurement_input [../iofiles/pids#virtual_measurement_input here].    

'''NAMELIST group name:''' [=#virtual_measurement_parameters '''{{{virtual_measurement_parameters}}}''']

||='''Parameter Name'''  =||='''[[../fortrantypes|FORTRAN]]\\[[../fortrantypes|Type]]'''  =||='''Default\\Value'''  =||='''Explanation'''  =||
|----------------
{{{#!td style="vertical-align:top; width: 150px"
[=#use_virtual_measurement '''use_virtual_measurement'']
}}}
{{{#!td style="vertical-align:top; width: 50px"
L
}}}
{{{#!td style="vertical-align:top; width: 75px"
.F.
}}}
{{{#!td
Control flag to enable virtual measurements.
}}}
|----------------
{{{#!td style="vertical-align:top; width: 150px"
[=#vm_time_start '''vm_time_start'']
}}}
{{{#!td style="vertical-align:top; width: 50px"
R
}}}
{{{#!td style="vertical-align:top; width: 75px"
0.0
}}}
{{{#!td
Start time of the virtual measurements.
}}}