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c88baa5
add atmospheric trajectory profile issue UAS NetCDF
amilan17 Jun 16, 2026
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minor corrections
amilan17 Jun 16, 2026
122244f
add platform type
amilan17 Jun 26, 2026
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Update c5-fm303-2026-atmos-traj.adoc
drdaphos Jun 26, 2026
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330 changes: 330 additions & 0 deletions c5-fm303-2026-atmos-traj.adoc
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## FM 303-2026 WMO-CF ATMOSPHERIC TRAJECTORY

### Regulations

[width="100%",cols="15%,85%",grid=none,frame=none]
|===
|*303.1*|*Scope*
|303.1.1 |This profile is intended for the reporting of meteorological, atmospheric chemistry and air quality observations along one or more trajectories from a single platform. The trajectory may follow an undulating profile.
|303.1.2 |The data shall be stored as either a single timeseries for the entire flight/trajectory, or using a multidimensional array representation for multiple trajectories.
|===
_Note: See https://cfconventions.org/Data/cf-conventions/cf-conventions-1.9/cfconventions.html#trajectory-data for further information on the multidimensional array representation._

[width="100%",cols="15%,85%",grid=none,frame=none]
|===
|303.1.3 |Only data for a single platform shall be included in the file.
|303.1.4 |Groups are not supported in this profile and groups other than the root group shall not be used.
|===

[width="100%",cols="15%,85%",grid=none,frame=none]
|===
|*303.2* |*Global scope / root group*
|303.2.1 |_Global attributes_
|303.2.1.1 |The rules for global attributes from the general regulations shall apply.
|303.2.1.2 |Table 303-1a lists the values that shall be used for the indicated mandatory attributes.
|303.2.2 |_Station / platform identifier_
|303.2.2.1 |The rules for station identifiers WMO-CF.4.5, WMO-CF.4.6, WMO-CF.6.10.6 and WMO-CF.6.10.7 shall be observed.
|303.2.2.2 |Table 303-1b lists additional global attributes that should be used to further identify the platform or station making the observations.
|303.2.3 |_Dimensions_
|303.2.3.1 |Files containing atmospheric profile trajectory data shall have the following dimensions:
|303.2.3.1.1 |`+obs+`, the `+obs+` dimension shall be used to indicate the total number of observations per trajectory within the file.
|303.2.3.1.2 |`+trajectory+`, the `+trajectory+` dimension shall be used to indicate the number of trajectories contained in the file and to index the observations to a trajectory. When there is a single trajectory in the file this dimension can be omitted.
|303.2.4 |_Coordinate Variables_
|303.2.4.1 |Table 303-2 lists the coordinate variables that shall be used with this profile.
|303.2.5 |_Trajectory identification_
|303.2.5.1 |When storing multiple trajectories in the same file, the trajectory dimension provides the identifier for a trajectory, and the number of trajectories in the file. See example 2.
|303.2.5.2 |Table 303-3 defines the variable and variable attributes that shall be used to identify the trajectories when more than one trajectory is included.
|303.2.6 |_Data variables_
|303.2.6.1 |The general regulations for data variables, including mandatory attributes, defined in regulation WMO-CF.5 shall apply.
|303.2.6.2 |For files containing a single trajectory the data variables shall have a single dimension `+obs+`.
|303.2.6.3 |For files containing multiple trajectories the data variables shall have two dimensions, `+trajectory+` followed by `+obs+`.
|303.2.6.4 |The NetCDF variable names shall be interpreted as the short name for the variable.
|303.2.6.5 |Table 303-4a provides a list of names that should be used for the indicated geophysical parameters reported.
|303.2.6.6 |Table 303-4b provides guidance on the attributes for those variables.
|303.2.6.7 |Multiple variables sharing the same short name shall follow the following naming convention: `+<measurement_short_name>_<n>+`, where `+<n>+` is incremented for each additional variable sharing the same short name. For example, `+humidity_1+` and `+humidity_2+` in the case of two humidity sensors on an observing platform.
|303.2.6.8 |Table 303-5a provides a list of names that should be used for reporting the platform trajectory and orientation.
|303.2.6.9 |_Ancillary variables_
|303.2.6.10 |The naming of the ancillary variables shall take the form `+<measurement_short_name>_<n>_<ancillary_variable>+`.
|303.2.6.11 |Table 303-7a lists the ancillary variables that should be reported for the observed / measured variables.
|303.2.6.12 |Table 303-7b lists the attributes that shall be included for those ancillary variables when reported.
|===


### FM 303-2026 tables

*Table 303-1a. Mandatory global attributes and required values*

[width="100%",cols="38%,15%,47%",options="header",]
|===
|Global attribute |Type |Description / value
|Conventions |string |"CF-1.8, WMO-CF-1.0"
|wmo__cf_profile |string |"FM 303-2026"
|featureType |string |"trajectory"
|===

*Table 303-1b. Recommended global attributes*

[width="100%",cols="38%,62%",options="header",]
|===
|Global attribute |Description
|platform_name |Name or non-WMO identifier of the platform(s) that supported the sensor data used to create this dataset or product
|platform_type |Type of platform upon which the sensor used to create this dataset was mounted on
|flight_id |Human-readable unique identifier for dataset
|===

*Table 303-2a. Coordinate variables that shall be used in the trajectory profile (attributes are given in Table 303-2b)*

[width="100%",cols="15%,27%,18%,40%",options="header",]
|===
|Coordinate variable |Dimensions |Type (recommended) |Comments
|/lat |(obs) [single trajectory] +
(obs, trajectory) [multiple trajectories] |float |Latitude of the observations
|/lon |(obs) [single trajectory] +
(obs, trajectory) [multiple trajectories] |float |Longitude of the observations
|/altitude |(obs) [single trajectory] +
(obs, trajectory) [multiple trajectories] |any numeric |Vertical position of the platform relative to sea level, for example, altitude in meters above sea level
|/pressure |(obs) [single trajectory] +
(obs, trajectory) [multiple trajectories] |float (could also be int or double depending on precision) |Pressure level as an alternative to altitude above sea level (hPA)
|/time |(obs) [single trajectory] +
(obs, trajectory) [multiple trajectories] |double |Date and time of the observation
|===

*Table 303-2b. Attributes for the coordinate variables given in Table 303-2a*

[width="100%",cols="15%,22%,10%,53%",options="header",]
|===
|Variable path/name |Attribute |Type |Value
|/lat |standard_name |string |"latitude"
| |units |string |"degrees_north"
| |axis |string |"Y"
| |valid_min |float |0.0f - optional – replace with correct value
| |valid_max |float |0.0f - optional – replace with correct value
|/lon |standard_name |string |"longitude"
| |units |string |"degrees_east"
| |axis |string |"X"
| |valid_min |float |0.0f - optional – replace with correct value
| |valid_max |float |0.0f - optional – replace with correct value
|/altitude |standard_name |string |"altitude"
| |units |string |"km"
| |axis |string |"Z"
| |positive |string |"up"
| |long_name |string |"altitude_above_sea_level"
| |valid_min |float |0.0f - optional – replace with correct value
| |valid_max |float |0.0f - optional – replace with correct value
|/pressure |standard_name |string |"pressure"
| |units |string |"Pa"
| |axis |string |"Z"
| |positive |string |"up"
| |long_name |string |"air_pressure"
| |valid_min |float |0.0f - optional – replace with correct value
| |valid_max |float |0.0f - optional – replace with correct value
|/time |standard_name |string |"time"
| |units |string |"seconds since <reftime>" where <reftime> is an ISO8601 time string of the form YYYY-MM-DDThh:mm:ssZ
| |axis |string |"T"
| |calendar |string |"standard"
|===

*Table 303-3a. Variables defined to identify the trajectory an observation belongs to and that shall be included in atmospheric trajectory files (attributes are listed in Table 303-3b)*

[width="100%",cols="25%,14%,8%,53%",options="header",]
|===
|Variable path/name |Dimensions |Type |Comments
|/trajectory |(trajectory) |string |Identifier for trajectory
|===

*Table 303-3b. Attributes for the trajectory variables listed in Table 303-3a*

[width="100%",cols="25%,22%,9%,44%",options="header",]
|===
|Variable path/name |Attribute |Type |Value
|/trajectory |cf_role |string |"trajectory_id"
| |long_name |string |"trajectory name"
|===

*Table 303-4a. Example geophysical variables. Dimensions shall be (obs) [single trajectory] or (trajectory, obs) [multiple trajectories]*

[width="100%",cols="55%,20%,25%",options="header",]
|===
|Variable |Type |Value / units
|air_temperature |float or double |K
|air_pressure |float or double |Pa
|elapsed_time |float or double |s
|relative_humidity |float or double |%
|dew_point_temperature |float or double |K
|humidity_mixing_ratio |float or double |kg kg^-1^
|wind_speed |float or double |m s^-1^
|wind_direction |float or double |degree
|y_wind |float or double |m s^-1^ (positive north)
|x_wind |float or double |m s^-1^ (positive east)
|vertical_wind_component |float or double |m s^-1^ (positive up)
|upward_air_velocity |float or double |m s^-1^
|turbulent_kinetic_energy |float or double |m^2^ s^-2^
|eddy_dissipation_rate |float or double |m^2/3^ s^-1^
|cloud_liquid_water_mixing_ratio |float or double |kg kg^-1^
|===

*Table 303-4b. Example attributes for each geophysical variable*

[width="100%",cols="20%,22%,58%",options="header",]
|===
|Variable |Attribute |Description
|geophysical variable |standard_name |CF compliant standard name
| |units |CF compliant appropriate unit
| |scale_factor |If the data uses a scale factor other than 1. The data type should be the data type of the variable.
| |add_offset |If the data uses an add offset other than 0, The data type should be the data type of the variable.
| |_FillValue |If there could be missing values in the data
| |valid_min |0.0f - optional – replace with correct value
| |valid_max |0.0f - optional – replace with correct value
| |coordinates |e.g., "time lat lon z"
| |instrument_variable |Refers to name of variable containing information on the instrument from which this variable was collected.
| |platform_variable |Refers to name of variable containing information on the platform from which this variable was collected.
| |ancillary_variables |Identify the variable name(s) of the flag(s) and other ancillary variables relevant to this variable. Use a space-separated list.
|===

*Table 303-5a. Example platform variables. Dimensions shall be (obs) [single trajectory] or (trajectory, obs) [multiple trajectories]*

[width="100%",cols="55%,20%,25%",options="header",]
|===
|Variable |Type |Value / units
|platform_pitch |float or double |degree
|platform_pitch_rate |float or double |degree s^-1^
|platform_yaw |float or double |degree
|platform_yaw_rate |float or double |degree s^-1^
|platform_roll |float or double |degree
|platform_roll_rate |float or double |degree s^-1^
|platform_speed_wrt_ground |float or double |m s^-1^
|platform_course |float or double |degree
|platform_speed_wrt_air |float or double |m s^-1^
|platform_speed_wrt_ground_upward |float or double |m s^-1^
|platform_eastward_ground_speed |float or double |m s^-1^
|platform_northward_ground_speed |float or double |m s^-1^
|===

*Table 303-6a. Conditional/ancillary variables that should be reported for each measured/observed variable (attributes are given in Table 303-6b; <prefix> has been used to represent <measurand_short_name>_<n>)*

[width="100%",cols="42%,8%,50%",options="header",]
|===
|Variable name |Type |Comments
|/<prefix>_sensor |string |Name of sensor
|/<prefix>_sensor_make |string |Manufacturer of sensor
|/<prefix>_sensor_model |string |Model of sensor
|/<prefix>_sensor_serial_number |string |Sensor serial number
|/<prefix>_sensor_calibration_date |string |Last calibration date of sensor
|===

*Table 303-6b. Attributes for the ancillary variables defined in Table 303-6a (<prefix> has been used to represent <measurand_short_name>_<n>)*

[width="100%",cols="39%,22%,9%,30%",options="header",]
|===
|Variable name |Attribute |Type |Value
|/<prefix>_sensor_calibration_date |standard_name |string |"time"
| |units |string |"seconds since <reftime>" where <reftime> is an ISO8601 time string of the form YYYYMMDDThh:mm:ss
| |axis |string |"T"
| |calendar |string |"standard"
|===

*Table 303-7a. Conditional/optional ancillary variables defined and that should be reported for each measured/observed variable when the described conditions are met (attributes are given in Table 303-7b; <prefix> has been used to represent <measurand_short_name>_<n>)*

[width="100%",cols="46%,8%,46%",options="header",]
|===
|Variable path/name |Type |Comments
|/<prefix>_sensor_installed_height |float |Value to be added to sensor_height to get vertical position of sensor relative to ground level
|/<prefix>_sensor_measurement_method |string |The method used by the sensor to measure the parameter, e.g. "capacitive humidity sensor"
|===

*Table 303-7b. Attributes for the ancillary variables defined in Table 303-7a (<prefix> has been used to represent <measurand_short_name>_<n>)*

[width="100%",cols="46%,25%,9%,20%",options="header",]
|===
|Variable path/name |Attribute |Type |Value
|/<prefix>_sensor_installed_height |units |string |"meters"
|/<prefix>_sensor_measurement_method |wmo__parameter_name |string |
| |wmo__parameter_uri |string |
|===


### FM 303-2026 examples

*Example 1: A single trajectory recording temperature and relative humidity*

[source]
----
dimensions:
obs = 42;
variables:
double time(obs) ;
time:standard_name = "time";
time:long_name = "time" ;
time:units = "days since 1970-01-01 00:00:00" ;
float lon(obs) ;
lon:standard_name = "longitude";
lon:long_name = "longitude" ;
lon:units = "degrees_east" ;
float lat(obs) ;
lat:standard_name = "latitude";
lat:long_name = "latitude" ;
lat:units = "degrees_north" ;
float z(obs) ;
z:standard_name = "altitude";
z:long_name = "height above mean sea level" ;
z:units = "km" ;
z:positive = "up" ;
z:axis = "Z" ;
float temp(obs) ;
temp:standard_name = "air_temperature";
temp:long_name = "bulk temperature of the air" ;
temp:units = "K" ;
temp:coordinates = "time lon lat z" ;
float rh(obs) ;
rh:standard_name = "relative_humidity";
rh:long_name = "relative humidity – percentage water vapour content of air" ;
rh:units = "%" ;
rh:coordinates = "time lon lat z" ;
attributes:
:featureType = "trajectory";
----

*Example 2: Trajectories recording temperature and relative humidity in a multidimensional array representation*

[source]
----
dimensions:
obs = 1000 ;
trajectory = 12 ;
variables:
string trajectory(trajectory) ;
trajectory:cf_role = "trajectory_id";
trajectory:long_name = "trajectory name" ;
int trajectory_info(trajectory) ;
trajectory_info:long_name = "some kind of trajectory info"
double time(trajectory, obs) ;
time:standard_name = "time";
time:long_name = "time" ;
time:units = "days since 1970-01-01 00:00:00" ;
float lon(trajectory, obs) ;
lon:standard_name = "longitude";
lon:long_name = "longitude" ;
lon:units = "degrees_east" ;
float lat(trajectory, obs) ;
lat:standard_name = "latitude";
lat:long_name = "latitude" ;
lat:units = "degrees_north" ;
float z(trajectory, obs) ;
z:standard_name = "altitude";
z:long_name = "height above mean sea level" ;
z:units = "km" ;
z:positive = "up" ;
z:axis = "Z" ;
float temp(trajectory, obs) ;
temp:standard_name = "air_temperature";
temp:long_name = "bulk temperature of the air" ;
temp:units = "K" ;
temp:coordinates = "time lon lat z" ;
float rh(trajectory, obs) ;
rh:standard_name = "relative_humidity";
rh:long_name = "relative humidity – percentage water vapour content of air" ;
rh:units = "%" ;
rh:coordinates = "time lon lat z" ;
attributes:
:featureType = "trajectory";
----