wiki:PointObservationConventions

Version 8 (modified by caron, 10 years ago) (diff)

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Chapter 9 Point Observation Data

Section 5 explains how to specify Coordinate Systems using coordinate variables and auxiliary coordinate variables. This section extends and modifies that framework for point observational data.

9.1 Overview

A point observation is a data measurement at a specific time and location. Each kind of measured data is placed in a data variable. The time and location values are placed into coordinate variables and auxiliary coordinate variables.

Point data files contain collections of point observation data of one of the following point feature types, which reflect the connectedness of common observational datasets in the earth sciences:

  • point: one or more parameters measured at one point in time and space
  • stationTimeSeries: a time-series of data points at the same location, with varying time
  • trajectory: a connected set of data points along a 1D curve in time and space
  • profile: a set of data points along a vertical line
  • stationProfile: a time-series of profiles at a named location
  • section: a collection of profiles which originate along a trajectory.

You cannot mix multiple types of data in the same file. A global attribute CF:featureType indicates the feature type used in a particular file, and its value must be one of the above names in order to be correctly processed as point observation data.

All point data must have lat, lon and time coordinate or auxiliary coordinate variables, which are identified according to sections 4 and 5 of this document. Some feature types allow the vertical coordinate to be optional, and some require it.

There are two main ways to represent point data in the classic netCDF model:

  • the multidimensional (rectangular array) representation is simpler but requires that the same amount of space be reserved for each feature stored in the file
  • the ragged array representation allows different features to be stored with different lengths in the file

The following subsections detail each point feature types and show examples of the possible representations of each.

Certain assumption are common to all representations:

  • the lat, lon and time coordinates must always exist; a vertical coordinate may exist
  • coordinates are identified with the "coordinates" attribute on the data variables, as specified in sections 4 and 5
  • coordinates may use missing values, but must do so in a consistent way
  • index numbering, if used, is always 0 based
  • variables are associated together by having a common, outer dimension

9.2 Point Data

To represent data at scattered, unconnected points, both data and coordinates use the same, single dimension. The 'coordinates' attribute is used on the data variables to unambiguously identify the time, lat, lon, and vertical auxiliary coordinate variables.

dimensions:
  obs = 1234 ;

variables:
  double time(obs) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(obs) ;
    lon:long_name = "longitude of the observation";
    lon:units = "degrees_east";
  float lat(obs) ;
    lat:long_name = "latitude of the observation" ;
    lat:units = "degrees_north" ;
  float alt(obs) ;
    alt:long_name = "altitude above MSL" ;
    alt:units = "m";
    alt:positive = "up";

  float humidity(obs) ;
    humidity:long_name = "specific humidity" ;
    humidity:coordinates = "time lat lon alt" ;
  float temp(obs) ;
    temp:long_name = "temperature" ;
    temp:units = "Celsius" ;
    temp:coordinates = "time lat lon alt" ;

attributes:
  :CF\:featureType = "point";

In this example, the humidity(i) and temp(i) data are associated with the coordinate values time(i), lat(i), lon(i), and optionally alt(i). The obs dimension may use the unlimited dimension or not. If the time coordinate is ordered, the obs dimension may be named time (making time a coordinate variable rather than an auxiliary variable).

9.3 Time series of Station Data

Point data may be taken at a set of named locations called stations. The set of observations at a particular station, if ordered by time, is a time series, and the file contains a collection of stationTimeSeries features.

Some assumption are common to all stationTimeSeries representations:

  • The outer dimension of the latitude and longitude coordinates (which must agree) is the 'station dimension'.
  • All variables that have the station dimension as their outer dimension are considered to be station information, and are called 'station variables'.
  • There must always be a station variable (of any type) with standard_name attribute "station_id", whose values uniquely identify the station.
  • The station_id variable may use missing values. This allows one to reserve more space than is needed for stations.
  • There may be station variables with standard_name attribute "station_desc", "station_altitude", and "station_wmoid"..

9.3.1 Multidimensional representation

When the numbers of observations at each station are the same, one can use the multidimensional representation:

dimensions:
  station = UNLIMITED ;
  obs = 13 ;

variables:
  float lon(station) ;
    lon:long_name = "station longitude";
    lon:units = "degrees_east";
  float lat(station) ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;
  float alt(station) ;
    alt:long_name = "altitude above MSL" ;
    alt:units = "m" ;
    alt:positive= "up" ;
  char station_name(station, name_strlen) ;
    station_name:long_name = "station name" ;
    station_name:standard_name = "station_id";
  int station_info(station) ;
    station_info:long_name = "any kind of station info" ;

  double time(station, obs) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
    time:missing_value = -999.9;
  float humidity(station, obs) ;
    humidity:long_name = "specific humidity" ;
    humidity:coordinates = "time lat lon alt" ;
    humidity:_FillValue = -999.9;
  float temp(station, obs) ;
    temp:long_name = "temperature" ;
    temp:units = "Celsius" ;
    temp:coordinates = "time lat lon alt" ;
    temp:_FillValue = -999.9;

attributes:
    :CF\:featureType = "stationTimeSeries";

The humidity(s,i) and temp(s,i) data are associated with the coordinate values time(s,i), lat(s), lon(s), and optionally vertical(s). The station dimension may be the unlimited dimension or not.

The time coordinate may use a missing value, which indicates that data is missing for that station and obs index. This allows one to have a variable number of observations at different stations, at the cost of some wasted space. The data variables may also use missing data values, to indicate that just that data variable is missing. If all the time values are identical for all stations, you may use time(obs) or time(time) to indicate this.

Note that this is a generalization of Example 5.4, which assumes that all the stations have observations with the same time coordinates.

9.3.2 Ragged array (contiguous) representation

When the number of observations at each station vary, one can use the 'contiguous ragged array' representation if you are able to completely control the order in which the observations are written. Add a rowSize station variable specifying the number of observations for each station. The observations for each station are stored sequentially, first for the station with index = 0, then the station with index = 1, etc.

dimensions:
  station = 23 ;
  obs = 1234 ;

variables:
  float lon(station) ;
    lon:long_name = "station longitude";
    lon:units = "degrees_east";
  float lat(station) ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;
  float alt(station) ;
    alt:long_name = "altitude above MSL" ;
    alt:units = "m" ;
  char station_name(station, name_strlen) ;
    station_name:long_name = "station name" ;
    station_name:standard_name = "station_id";
  int station_info(station) ;
    station_info:long_name = "some kind of station info" ;
  int nobs(station) ;
    nobs:long_name = "number of observations for this station " ;
    nobs:standard_name = "ragged_rowSize" ;

  double time(obs) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float humidity(obs) ;
    humidity:long_name = "specific humidity" ;
    humidity:coordinates = "time lat lon alt" ;
    humidity:_FillValue = -999.9;
  float temp(obs) ;
    temp:long_name = "temperature" ;
    temp:units = "Celsius" ;
    temp:coordinates = "time lat lon alt" ;
    temp:_FillValue = -999.9;

attributes:
    :CF\:featureType = "stationTimeSeries";

Then for each station with index stn, its observations go from

  rowStart(stn) to rowStart(stn) + nobs(stn) - 1

where

  rowStart(stn) = 0 if stn = 0    
  rowStart(stn) = rowStart(stn-1) + nobs(stn-1) if i > 0

The rowSize variable contains the number of observations for each station, and is identified by having a standard_name of "ragged_rowSize". It must have the station dimension as its single dimension, and must be type integer.

The single dimension of the time coordinate is the obs dimension. All variables having the obs dimension as their outer dimension are observation variables. The obs dimension may use the unlimited dimension or not.

9.3.3 Ragged array (indexed) representation

When the number of observations at each station vary, and the observations cannot be written in order, one can use the 'indexed ragged array' representation. Add a parentIndex observation variable specifying the station index that the observation belongs to:

dimensions:
  station = 23 ;
  obs = UNLIMITED ;

variables:
  float lon(station) ;
    lon:long_name = "station longitude";
    lon:units = "degrees_east";
  float lat(station) ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;
  float alt(station) ;
    alt:long_name = "altitude above MSL" ;
    alt:units = "m" ;
  char station_name(station, name_strlen) ;
    station_name:long_name = "station name" ;
    station_name:standard_name = "station_id";
  int station_info(station) ;
    station_info:long_name = "some kind of station info" ;

  int stationIndex(obs) ;
    stationIndex:long_name = "which station this obs is for" ;
    stationIndex:standard_name = "ragged_parentIndex" ;
  double time(obs) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float humidity(obs) ;
    humidity:long_name = "specific humidity" ;
    humidity:coordinates = "time lat lon alt" ;
    humidity:_FillValue = -999.9;
  float temp(obs) ;
    temp:long_name = "temperature" ;
    temp:units = "Celsius" ;
    temp:coordinates = "time lat lon alt" ;
    temp:_FillValue = -999.9;

attributes:
    :CF\:featureType = "stationTimeSeries";

The humidity(i) and temp(i) data are associated with the coordinate values time(i), lat(s), lon(s), and optionally alt(s), where s = stationIndex(i). The stationIndex variable is identified by having a standard_name of "ragged_parentIndex". It must have the obs dimension as its single dimension, and must be type integer.

The single dimension of the time coordinate is the obs dimension. All variables having the obs dimension as their outer dimension are observation variables. The obs dimension may use the unlimited dimension or not.

9.3.4 Single station

When there is a single station in the file, one can can use the multidimensional representation with number of stations = 1. One can also use scalar coordinates. This case is identified when the lat and lon coordinates are scalar. In this case, no connecting variable between station and observations is required, since they all belong to the same station. However, the station_id variable is still required, and must be a scalar (or 1D char).

dimensions:
  obs = 1233 ;
  name_strlen = 23

variables:
  float lon ;
    lon:long_name = "station longitude";
    lon:units = "degrees_east";
  float lat ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;
  float alt ;
    alt:long_name = "altitude above MSL" ;
    alt:units = "m" ;
  char station_name(name_strlen) ;
    station_name:long_name = "station name" ;
    station_name:standard_name = "station_id";

  double time(obs) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
    time:missing_value = -999.9;
  float humidity(obs) ;
    humidity:long_name = "specific humidity" ;
    humidity:coordinates = "time lat lon alt" ;
    humidity:_FillValue = -999.9;
  float temp(obs) ;
    temp:long_name = "temperature" ;
    temp:units = "Celsius" ;
    temp:coordinates = "time lat lon alt" ;
    temp:_FillValue = -999.9;

attributes:
    :CF\:featureType = "stationTimeSeries";

9.3.5 Flattened representation

When factoring out the station information is not needed, one may use a 'flattened representation', in which the station information is repeated for each observation. The station_id variable is used to associate the observations into a time series.

dimensions:
  obs = UNLIMITED ;

variables:
  float lon(obs) ;
    lon:long_name = "station longitude";
    lon:units = "degrees_east";
  float lat(obs) ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;
  float alt(obs) ;
    alt:long_name = "altitude above MSL" ;
    alt:units = "m" ;
  int station_id(obs) ;
    station_name:long_name = "station" ;
    station_name:standard_name = "station_id";

  double time(obs) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float humidity(obs) ;
    humidity:long_name = "specific humidity" ;
    humidity:coordinates = "time lat lon alt" ;
    humidity:_FillValue = -999.9;
  float temp(obs) ;
    temp:long_name = "temperature" ;
    temp:units = "Celsius" ;
    temp:coordinates = "time lat lon alt" ;
    temp:_FillValue = -999.9;

attributes:
    :CF\:featureType = "stationTimeSeries";

The humidity(i) and temp(i) data are associated with the coordinate values time(i), lat(i), lon(i), and optionally alt(i). All observations with the same station_id are assumed to belong to that station.

In some observational networks, station location may change. However, for station feature types this should be infrequent and not overly consequential. In principle, a new station identifier should be assigned. In practice, occasional and small adjustments to station location may not matter for typical processing of data for visualization, and generic clients may not detect these changes, eg they may assume that the first location encountered is valid for all other observations at the same station. Specialized clients, of course, may be more careful in examining station location data, and nothing prevents data providers from using a factored representation as in 9.3.1, 9.3.2, and 9.3.3, and also putting location information into the observation record, as in the flattened representation in 9.3.5.

9.4 Trajectory Data

Point data may be taken along a flight path or ship path, constituting a connected set of points called a trajectory.

Some assumption are common to all trajectory representations:

  • There must always be a variable (of any type) with standard_name attribute "trajectory_id", whose values uniquely identify the trajectory.
  • The outer dimension of the trajectory_id variable is the 'trajectory dimension'.
  • All variables that have the trajectory dimension as their single dimension are considered to be information about that trajectory
  • The trajectory_id variable may use missing values. This allows one to reserve more space than is needed.

9.4.1 Multidimensional representation

When storing multiple trajectories in the same file, and the number of observations in each trajectory is the same, one can use the multidimensional representation:

dimensions:
  obs = 1000 ;
  trajectory = 77 ;

variables:
  char trajectory(trajectory, name_strlen) ;
   trajectory:standard_name = "station_id";
   trajectory:long_name = "trajectory name" ;
  int trajectory_info(trajectory) ;
    trajectory_info:long_name = "some kind of trajectory info" 

  double time(trajectory, obs) ;
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(trajectory, obs) ;
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(trajectory, obs) ;
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;

  float z(trajectory, obs) ;
    z:long_name = "height above mean sea level" ;
    z:units = "km" ;
    z:positive = "up" ; 

  float O3(trajectory, obs) ;
    O3:long_name = "ozone concentration" ;
    O3:units = "1e-9" ;
    O3:coordinates = "time lon lat z" ;

  float NO3(trajectory, obs) ;
    NO3:long_name = "NO3 concentration" ;
    NO3:units = "1e-9" ;
    NO3:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "trajectory";

The NO3(t,i) and O3(t,i) data are associated with the coordinate values time(t,i), lat(t,i), lon(t,i), and alt(t,i). The trajectory dimension may be the unlimited dimension or not. All variables that have trajectory as their only dimension are considered to be information about that trajectory.

The time coordinate may use a missing value, which indicates that data is missing for that trajectory and obs index. This allows one to have a variable number of observations for different trajectories, at the cost of some wasted space. The data variables may also use missing data values.

9.4.2 Single Trajectory

When a single trajectory is stored in a file, one can use a variation of 9.4.1 which removes the trajectory dimension:

dimensions:
  time = 42;

variables:
  char trajectory(name_strlen) ;
    trajectory:standard_name = "trajectory_id";

  double time(time) ;
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(time) ;
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(time) ;
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;
  float z(time) ;
    z:long_name = "height above mean sea level" ;
    z:units = "km" ;
    z:positive = "up" ; 

  float O3(time) ;
    O3:long_name = "ozone concentration" ;
    O3:units = "1e-9" ;
    O3:coordinates = "time lon lat z" ;

  float NO3(time) ;
    NO3:long_name = "NO3 concentration" ;
    NO3:units = "1e-9" ;
    NO3:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "trajectory";

The NO3(n) and O3(n) data is associated with the coordinate values time(n), z(n), lat(n), and lon(n). When the time coordinate is ordered, it is appropriate to use a coordinate variable for time, i.e. time(time). The time dimension may be unlimited or not.

Note that structurally this looks like unconnected point data as in example 9.2.1. The presence of the CF:featureType = "trajectory" global attribute indicates that in fact the points are connected along a trajectory.

Note that this is the same as Example 5.5.

9.4.3 Ragged array (contiguous) representation

When the number of observations for each trajectory varies, and one can control the order of writing, one can use the contiguous ragged array representation. One stores the set of observations for each trajectory contiguously along the obs dimension, and adds a rowSize variable specifying the number of observations for each trajectory:

dimensions:
  obs = 3443;
  trajectory = 77 ;

variables:
  char trajectory(trajectory, name_strlen) ;
     trajectory:standard_name = "trajectory_id";
  int rowSize(trajectory) ;
    rowSize:long_name = "number of obs for this trajectory " ;
    rowSize:standard_name = "ragged_rowSize" ;

  double time(obs) ;
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(obs) ;
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(obs) ;
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;
  float z(obs) ;
    z:long_name = "height above mean sea level" ;
    z:units = "km" ;
    z:positive = "up" ; 

  float O3(obs) ;
    O3:long_name = "ozone concentration" ;
    O3:units = "1e-9" ;
    O3:coordinates = "time lon lat z" ;

  float NO3(obs) ;
    NO3:long_name = "NO3 concentration" ;
    NO3:units = "1e-9" ;
    NO3:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "trajectory";

The O3(i) and NO3(i) data are associated with the coordinate values time(i), lat(i), lon(i), and alt(i). All observations for one trajectory are contiguous along the obs dimension, and should be time ordered. All variables that have trajectory as their single dimension are considered to be information about that trajectory. The obs dimension may use the unlimited dimension or not.

The rowSize variable contains the number of observations for each trajectory, and is identified by having a standard_name of "ragged_rowSize". It must have the trajectory dimension as its single dimension. The observations are associated wit the trajectory using the same algorithm as in 9.3.2.

9.4.4 Ragged array (indexed) representation

When the number of observations at each trajectory vary, and the observations cannot be written in order, one can use the indexed ragged array representation. Add a parentIndex field specifying the trajectory index that the observation belongs to:

dimensions:
  obs = UNLIMITED ;
  trajectory = 77 ;

variables:
  char trajectory(trajectory, name_strlen) ;
     trajectory:standard_name = "trajectory_id";

  int trajectory_index(obs) ;
    trajectory_index:long_name = "index of trajectory this obs belongs to " ;
    trajectory_index:standard_name = "ragged_parentIndex" ;
  double time(obs) ;
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(obs) ;
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(obs) ;
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;
  float z(obs) ;
    z:long_name = "height above mean sea level" ;
    z:units = "km" ;
    z:positive = "up" ; 

  float O3(obs) ;
    O3:long_name = "ozone concentration" ;
    O3:units = "1e-9" ;
    O3:coordinates = "time lon lat z" ;

  float NO3(obs) ;
    NO3:long_name = "NO3 concentration" ;
    NO3:units = "1e-9" ;
    NO3:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "trajectory";

The O3(i) and NO3(i) data are associated with the coordinate values time(i), lat(i), lon(i), and alt(i). All observations for one trajectory will have the same trajectory index value, and should be time ordered. The obs dimension may use the unlimited dimension or not.

The parentIndex variable is identified by having a standard_name of "ragged_parentIndex". It must have the obs dimension as its single dimension.

9.5 Profile Data

A series of connected observations along a vertical line, like an atmospheric or ocean sounding, is called a profile. The lat,lon locations are factored out into the profile.

Some assumption are common to all profile representations:

  • There must always be a variable (of any type) with standard_name attribute "profile_id", whose values uniquely identify the profile.
  • The outer dimension of the profile_id variable is the 'profiledimension'.
  • All variables that have the profile dimension as their single dimension are considered to be information about that profile
  • The profile_id variable may use missing values. This allows one to reserve more space than is needed.

9.5.1 Multidimensional representation

When storing multiple profiles in the same file, and the numbers of vertical levels in each profile are the same, one can use the multidimensional representation:

dimensions:
  z = 42 ;
  profile = 142 ;

variables:
  int profile(profile) ;
     profile:standard_name = "profile_id";
  double time(profile);
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(profile);
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(profile);
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;

  float alt(profile, z) ;
    alt:long_name = "height above mean sea level" ;
    alt:units = "km" ;
    alt:positive = "up" ; 

  float pressure(profile, z) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat alt" ;

  float temperature(profile, z) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat alt" ;

  float humidity(profile, z) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat alt" ;

attributes:
  :CF\:featureType = "profile";

The pressure(p,i), temperature(p,i), and humidity(p,i) data is associated with the coordinate values time(p), alt(p,i), lat(p), and lon(p). If the vertical coordinates are the same for all profiles, one can use z(z) instead of alt(profile,z). The time coordinate may depend on z also, eg time(profile,z).

When there are a variable number of observations for different profiles, use alt(profile, z) with missing values.

9.5.2 Single Profile

When a single profile is stored in a file, one can use a variation of the 9.5.1 which removes the profile dimension:

dimensions:
  z = 42 ;

variables:

  int profile ;
    profile:standard_name = "profile_id";
  double time;
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon;
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat;
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;

  float alt(z) ;
    alt:long_name = "height above mean sea level" ;
    alt:units = "km" ;
    alt:positive = "up" ; 

  float pressure(z) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat z" ;

  float temperature(z) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat z" ;

  float humidity(z) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "profile";

The pressure(i), temperature(i), and humidity(i) data is associated with the coordinate values time, alt(i), lat, and lon. The time coordinate may depend on z also, eg may be time(z).

9.5.3 Ragged array (contiguous) representation

When the number of vertical levels for each profile varies, one can use the contiguous ragged array representation. One stores the set of observation for each profile contiguously along the obs dimension, and adds a rowSize variable specifying the number of observations for each profile:

dimensions:
  obs = UNLIMITED ;
  profiles = 142 ;

variables:
  int profile(profile) ;
    profile:standard_name = "profile_id";
  double time(profile);
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(profile);
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(profile);
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ; 
  int rowSize(profile) ;
    rowSize:long_name = "number of obs for this profile " ;
    rowSize:standard_name = "ragged_rowSize" ;

  float z(obs) ;
    z:long_name = "height above mean sea level" ;
    z:units = "km" ;
    z:positive = "up" ;

  float pressure(obs) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat z" ;

  float temperature(obs) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat z" ;

  float humidity(obs) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "profile";

The pressure(i), temperature(i), and humidity(i) data is associated with the coordinate values time(p), z(i), lat(p), and lon(p), where p is found by reading the rowSize variable values. The time coordinate may depend on z also, eg time(p,z).

9.5.4 Ragged array (indexed) representation

When the number of vertical levels for each profile varies, and one cant write them contiguously, one can use the indexed ragged array representation. Add a parentIndex field specifying the profile index that the observation belongs to:

dimensions:
  obs = UNLIMITED ;
  profiles = 142 ;

variables:
  int profile(profile) ;
    profile:standard_name = "profile_id";
  double time(profile);
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(profile);
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(profile);
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ; 

  int parentIndex(obs) ;
    parentIndex:long_name = "index of profile " ;
    parentIndex:standard_name = "ragged_parentIndex" ;

  float z(obs) ;
    z:long_name = "height above mean sea level" ;
    z:units = "km" ;
    z:positive = "up" ;

  float pressure(obs) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat z" ;

  float temperature(obs) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat z" ;

  float humidity(obs) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "profile";

The pressure(i), temperature(i), and humidity(i) data is associated with the coordinate values time(p), z(i), lat(p), and lon(p), where p=parentIndex(i). The time coordinate may depend on z also, eg time(p,z).

9.6 Station Profile Data

When profiles are taken at a set of stations, one gets a time series of profiles at each station, called a stationProfile.

The same assumptions are made as with stationTimeSeries data:

  • The outer dimension of the latitude and longitude coordinates (which must agree) is the 'station dimension'.
  • All variables that have the station dimension as their outer dimension are considered to be station information, and are called 'station variables'.
  • There must always be a station variable (of any type) with standard_name attribute "station_id", whose values uniquely identify the station.
  • The station_id variable may use missing values. This allows one to reserve more space than is needed for stations.
  • There may be station variables with standard_name attribute "station_desc", "station_altitude", and "station_wmoid"..

9.6.1 Multidimensional representation

When storing time series of profiles at multiple stations in the same file, if there are the same number of time points for all stations, and te same number of vertical levels for every profile, one can use the multidimensional representation:

dimensions:
  station = 22 ;
  profile = 3002 ;
  z = 42 ;

variables:
  float lon(station) ;
    lon:long_name = "station longitude";
    lon:units = "degrees_east";
  float lat(station) ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;
  char station_name(station, name_strlen) ;
    station_name:long_name = "station name" ;
  int station_info(station) ;
    station_name:long_name = "some kind of station info" ;

  float alt(station, profile , z) ;
    alt:long_name = "height above mean sea level" ;
    alt:units = "km" ;
    alt:positive = "up" ; 

  double time(station, profile ) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
    time:missing_value = -999.9;

  float pressure(station, profile , z) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat alt" ;

  float temperature(station, profile , z) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat alt" ;

  float humidity(station, profile , z) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat alt" ;

attributes:
 :CF\:featureType = "stationProfile";

The pressure(s,p,i), temperature(s,p,i), and humidity(s,p,i) data is associated with the coordinate values time(s,p), z(s,p,i), lat(s), and lon(s).

The time coordinate may depend on z also, eg time(station,profile,z). If all of the profiles use the same z coordinate, alt(station, profile, z) may be factored out into z(z).

When there are varying number of profiles for different stations, use time(station, profile) with missing values. When there are varying number of levels for different profiles, use alt(station, profile, z) with missing values.

9.6.2 Profile time series at a single station

If there is only one station in a file, one can use a variation of the Multidimensional representation which removes the station dimension:

dimensions:
  profile = 30 ;
  z = 42 ;

variables:
  float lon ;
    lon:long_name = "station longitude";
    lon:units = "degrees_east";
  float lat ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;
  char station_name(name_strlen) ;
    station_name:long_name = "station name" ;
  int station_info(station) ;
    station_name:long_name = "some kind of station info" ;

  float alt(profile , z) ;
    alt:long_name = "height above mean sea level" ;
    alt:units = "km" ;
    alt:positive = "up" ; 

  double time(profile ) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
    time:missing_value = -999.9;

  float pressure(profile , z) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat alt" ;

  float temperature(profile , z) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat alt" ;

  float humidity(profile , z) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat alt" ;

attributes:
 :CF\:featureType = "stationProfile";

The pressure(i,j), temperature(i,j), and humidity(i,j) data are associated with the coordinate values time(p), alt(p,i), lat, and lon. The time coordinate may depend on z also, eg time(profile,z). If all of the profiles use the same z coordinate, alt(profile, z) may be factored out into z(z).

9.6.3 Ragged array of station profile time series

When the number of profiles and levels for each station varies, one can use the ragged array representation. This uses the contiguous ragged array representation for profiles (9.5.3), and adds the (factored out) station information with station indexes (9.2.4):

dimensions:
  obs = UNLIMITED ;
  profiles = 1420 ;
  stations = 42;

variables:
  float lon(station) ;
    lon:long_name = "station longitude";
    lon:units = "degrees_east";
  float lat(station) ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;
  float alt(station) ;
    alt:long_name = "altitude above MSL" ;
    alt:units = "m" ;
  char station_name(station, name_strlen) ;
    station_name:long_name = "station name" ;
    station_name:standard_name = "station_id";
  int station_info(station) ;
    station_info:long_name = "some kind of station info" ;

  int profile(profile) ;
    profile:standard_name = "profile_id";
  double time(profile);
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  int stationIndex(profile) ;
    stationIndex:long_name = "which station this obs is for" ;
    stationIndex:standard_name = "ragged_parentIndex" ;
  int rowSize(profile) ;
    rowSize:long_name = "number of obs for this profile " ;
    rowSize:standard_name = "ragged_rowSize" ;

  float z(obs) ;
    z:long_name = "height above mean sea level" ;
    z:units = "km" ;
    z:positive = "up" ;

  float pressure(obs) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat z" ;

  float temperature(obs) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat z" ;

  float humidity(obs) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "stationProfile";

The profile is associated with a station using the stationIndex(profile). For each profile, the observations must be written contiguously.

The pressure(i), temperature(i), and humidity(i) data is associated with the coordinate values time(p), z(i), lat(s), and lon(s). The time coordinate may depend on z also, eg time(obs) instead of time(profile).

9.6.4 Flattened representation of multidimensional profiles

A variation of multidimensional profiles (9.5.1) allows these to be associated into a station time series. The station information (lat, lon, id) is repeated in each profile:

dimensions:
  z = 42 ;
  profile = 142 ;

variables:
  int profile(profile) ;
     profile:standard_name = "profile_id";
  double time(profile);
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(profile);
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(profile);
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;
  char station_name(profile, name_strlen) ;
    station_name:long_name = "station name" ;
    station_name:standard_name = "station_id";

  float alt(profile, z) ;
    alt:long_name = "height above mean sea level" ;
    alt:units = "km" ;
    alt:positive = "up" ; 

  float pressure(profile, z) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat alt" ;

  float temperature(profile, z) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat alt" ;

  float humidity(profile, z) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat alt" ;

attributes:
  :CF\:featureType = "stationProfile";

This is the same as 9.5.1, except that a station_id variable is added for each profile, which associates the profile to a station. The station information is repeated for each profile and should be the same for all profiles with the same station_id.

9.7 Section Profile Data

When profiles are taken along a trajectory, one gets a time series of profiles called a section. This looks like a collection of profiles (see 9.5), except that the profile locations are assumed to be a connected set of points along the trajectory.

9.7.1 Multidimensional representation

If there are the same number of profiles for all trajectories, and the same number of vertical levels for every profile, one can use the multidimensional representation:

dimensions:
  section = 22 ;
  profile = 33;
  z = 42 ;

variables:
  int section(section) ;
    section:standard_name = "section id" ;
  float lon(section, profile) ;
    lon:units = "degrees_east";
  float lat(section, profile) ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;

  float alt(section, profile , z) ;
    alt:long_name = "height above mean sea level" ;
    alt:units = "km" ;
    alt:positive = "up" ; 

  double time(section, profile ) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
    time:missing_value = -999.9;

  float pressure(section, profile , z) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat alt" ;

  float temperature(section, profile , z) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat alt" ;

  float humidity(section, profile , z) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat alt" ;

attributes:
 :CF\:featureType = "section";

The pressure(s,p,i), temperature(s,p,i), and humidity(s,p,i) data is associated with the coordinate values time(s,p), alt(s,p,i), lat(s,p), and lon(s,p).

The time coordinate may depend on z also, eg time(section,profile,z). If all of the profiles use the same z coordinate, alt(section, profile, z) may be factored out into z(z).

When there are varying number of profiles for different sections, use time(section, profile) with missing values. When there are varying number of levels for different profiles, use alt(section, profile, z) with missing values.

9.7.2 Single section in the file

If there is only one section in the file, one can use a variation of the 9.7.1 which removes the section dimension:

dimensions:
  profile = 33;
  z = 42 ;

variables:
  int section ;
    section:standard_name = "section id" ;
  float lon(profile) ;
    lon:units = "degrees_east";
  float lat(profile) ;
    lat:long_name = "station latitude" ;
    lat:units = "degrees_north" ;

  float alt(profile , z) ;
    alt:long_name = "height above mean sea level" ;
    alt:units = "km" ;
    alt:positive = "up" ; 

  double time(profile ) ;
    time:long_name = "time of measurement" ;
    time:units = "days since 1970-01-01 00:00:00" ;
    time:missing_value = -999.9;

  float pressure(profile , z) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat alt" ;

  float temperature(profile , z) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat alt" ;

  float humidity(profile , z) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat alt" ;

attributes:
 :CF\:featureType = "section";

9.7.3 Ragged array of section data

When the number of profiles and levels for each station varies, one can use the ragged array representation. This uses the contiguous ragged array representation for profiles (9.5.3), and adds section information with section indexes:

dimensions:
  obs = UNLIMITED ;
  profiles = 142 ;
  sections= 3;

variables:
  int section ;
    section:standard_name = "section id" ;

  int profile(profile) ;
    profile:standard_name = "profile_id";
  double time(profile);
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(profile);
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(profile);
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ; 
  int rowSize(profile) ;
    rowSize:long_name = "number of obs for this profile " ;
    rowSize:standard_name = "ragged_rowSize" ;
  int sectionIndex(profile) ;
    sectionIndex:long_name = "which section this profileis for" ;
    sectionIndex:standard_name = "ragged_parentIndex" ;

  float z(obs) ;
    z:long_name = "height above mean sea level" ;
    z:units = "km" ;
    z:positive = "up" ;

  float pressure(obs) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat z" ;

  float temperature(obs) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat z" ;

  float humidity(obs) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat z" ;

attributes:
  :CF\:featureType = "section";

The profile is associated with a section using the sectionIndex(profile). For each profile, the observations must be written contiguously.

The pressure(i), temperature(i), and humidity(i) data is associated with the coordinate values time(p), z(i), lat(p), and lon(p). The time coordinate may depend on z also, eg time(obs) instead of time(profile).

9.7.4 Flattened representation of multidimensional profiles

A variation of multidimensional profiles (9.5.1) allows these to be associated into a section. The station information:

dimensions:
  z = 42 ;
  profile = 142 ;

variables:
  int profile(profile) ;
     profile:standard_name = "profile_id";
  double time(profile);
    time:long_name = "time" ;
    time:units = "days since 1970-01-01 00:00:00" ;
  float lon(profile);
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(profile);
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;
  int sectionId(profile) ;
    sectionIndex:long_name = "which section this profile is for" ;
    sectionIndex:standard_name = "section_id" ;

  float alt(profile, z) ;
    alt:long_name = "height above mean sea level" ;
    alt:units = "km" ;
    alt:positive = "up" ; 

  float pressure(profile, z) ;
    pressure:long_name = "pressure level" ;
    pressure:units = "hPa" ;
    pressure:coordinates = "time lon lat alt" ;

  float temperature(profile, z) ;
    temperature:long_name = "skin temperature" ;
    temperature:units = "Celsius" ;
    temperature:coordinates = "time lon lat alt" ;

  float humidity(profile, z) ;
    humidity:long_name = "relative humidity" ;
    humidity:units = "%" ;
    humidity:coordinates = "time lon lat alt" ;

attributes:
  :CF\:featureType = "stationProfile";

This is the same as 9.5.1, except that a section_id variable is added for each profile, which associates the profile to a section.