ISTP Metadata Guidelines: Dictionary Keywords

A project data dictionary contains information required to make the data independently useable to a wide community. For ISTP the Common Data Format (CDF), chosen as the data exchange format for key parameter and event data, carries much (but not all) of the data dictionary information using a set of standard global attributes describing the overall CDF content and a set of standard attributes for each variable in the CDF. The variable attributes contain descriptions, data types, minimum and maximum values, labels, units, time tags, and if required, dependencies, uncertainties, and offsets. However there is little consistency in variable names nor in the descriptions that are tied to each variable, to help other users of the data find and use the variables of interest. We have extended the ISTP project data dictionary to include dictionary keywords that identify variables as being a certain type such as time or magnetic_field regardless of the naming convention adopted by the investigators. Each variable in a CDF has defined dictionary keywords (class and subclass) that are stored in its associated DICT_KEY attribute.

List of Class Keywords

We provide a standard set of class keywords that include ‘sensor (science)’ and ‘supporting’ class words and their meanings, to be used to categorize the data variables of primary interest to investigators, among the several ISTP satellites and experiments. ISTP class keywords will be restricted to the approved values shown below. Sets of subclass keywords, with each set used to modify one of the class keywords, are also adopted and listed with the associated information below. Lists of common subclass keywords, valid for any variable, can also be found below.

Sensor Words                                Supporting Words

anisotropy                                  angle
current                                     energy
density                                     flag
electric_field                              frequency
magnetic_field                              label
particle_flux                               number
photon_flux                                 ratio
position                                    significance
potential                                   source
power                                       species
pressure                                    time
temperature                                 uncertainty
velocity                                    wavelength

*Common subclass keywords valid for any variable


The syntax for populating the Dictionary Keyword attribute DICT_KEY is class>subclass_subclass_subclass. Click here for examples.

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Associated information: More on Class words

The dictionary keywords and definitions (along with the other global and variable attributes) comprise the primary content of the ISTP project data dictionary. The class keywords were selected to be, as much as possible, a complete and orthogonal set. In the realm of space physics there are three broad classes of sensor data words: electric and magnetic field (DC values for vectors, AC values for power spectra), particle distributions (e.g., densities, flow speeds, flow direction angles, thermal speeds, temperatures, anisotropy, fluxes), images (e.g., remote sensing of the aurora, ionosphere and sun at various wavelength ranges measuring e.g., electromagnetic waves, temperatures, pressures). In addition, there are time words, orbit/attitude words, and flags of various types (e.g.,instrument mode). We choose the measured quantities such as magnetic_field, density, temperature, to be the sensor (science) class keywords that are of primary science interest. Supporting keywords are of secondary science interest such as the energy or time at which a measurement was made, or the label or flag associated with a measured quantity. The sensor (science) class words are listed separately from the supporting class words below. It is envisioned that the usage of the sensor (science) and supporting class keywords will be different. Sensor Words make up a short, standard list that enables automated searching for data of interest at a fairly high level. Supporting Words are at a lower level of interest, but may still be used for some types of searches. In the CDF model every variable must have one and only one class keyword defined, but may have any number of subclass keywords defined.

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Class word definitions and associated subclass words

ANGLE The geometric figure formed by two lines diverging from a point or two planes diverging from a common line or the space between two such lines or surfaces.

Subclass Words:       antenna       elevation      pitch
                      aspect        fov            pointing
                      axis          geometric      polar
                      azimuth       inclination    rotation
                                    phase          sector
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ANISOTROPY The variation of physical properties with direction, usually expressed as a ratio.

Subclass Words:          parallel

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CURRENT The rate of flow of electricity.

Subclass Words:          Hall       primary
                         load       secondary

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DENSITY The mass per unit volume of a substance, or the number of items per unit volume.

Subclass Words:          partial     mass      number

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ELECTRIC_FIELD The space surrounding an electric charge within which it is capable of exerting a perceptible force on another electric charge. The strength of an electric field at a given point is given in terms of the force exerted by the field on unit charge at that point.

Subclass Words:          AC             calibration
                         amplitude      DC
                         angle          potential 
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ENERGY The property of a system that is a measure of its capacity for doing work.

Subclass Words:          band             channel                
                         incident         reflected                

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FLAG An entity that signals the occurance of an event, or that indicates a particular status of a spacecraft or instrument or software program. The flag can be a number, letter, or word, and may have any of a variety of encoded meanings.

Subclass Words:          number            post_gap                
                         quality           status                

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FREQUENCY The number of cycles completed by a periodic function in unit time.

Subclass Words:           band                

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LABEL A term or phrase attached by way of classification or characterization.

Subclass Words:            [All other class words are also  
                           possible sub-class words]

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MAGNETIC_FIELD The field of force surrounding a magnetic pole or a current flowing through a conductor, in which there is a magnetic flux.

Subclass Words:           AC           calibration                
                          amplitude    DC                
                          angle        potential                 

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NUMBER A symbol or word, or a group of either of these, showing how many or what place in a sequence.

Subclass Words:           direction     frame       target
                          event         image       telescope
                          exposure      mode                
                          filter        sequence                

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PARTICLE_FLUX The number of particles passing through a specified area or volume in a specified time interval (and possibly in a specified energy range or in a specified range of directions).

Subclass Words:    differential    number            rate
                   directional     omni-directional  sample
                   integral        parallel          spectral
                   mass            perpendicular     thermal

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PHOTON_FLUX The number of photons passing through a specified area or volume in a specified time interval (and possibly in a specified energy or wavelength range or in a specified range of directions).

Subclass Words:          brightness         integral
                         differential       incident
                         directional        omni-directional
                         filtered           reflected

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POSITION A location, distance, or direction with respect to some particular reference. The reference can be moving or fixed, such as the geographic coordinate system or a spacecraft body.

Subclass Words:         altitude      distance       radial
                        angle         elevation      range
                        antenna       height         RA
                        attitude      horizontal     row
                        azimuth       inclination    surface
                        column        latitude       target
                        declination   longitude      vertical
                        direction     projection                

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POTENTIAL Electrostatic, magnetostatic, or gravitational potential, at a point in the field: the work done in bringing unit positive charge, unit positive pole, or unit mass respectively from infinity (i.e., a place infinitely distant from the causes of the field) to the point.

Subclass Words:         antenna        Hall
                        bias           magnetic
                        electric       polar_cap
                        gravity        surface

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POWER The rate at which energy is expended or work is done.

Subclass Words:      amplitude      electric    radiant
                     antenna        emission    reflected
                     bandwidth      field       spectral
                     calibration    flux        transmittance
                     density        poynting                

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PRESSURE Force per unit area.

Subclass Words:       atmosphere      magnetic
                      derived         solar
                      dynamic         surface 

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RATIO The quotient of one quantity divided by another of the same kind, and usually expressed as a fraction.

Subclass Words:    albedo        electric_field   power
                   beta          energy           pressure
                   anisotropy    particle_flux    temperature
                   current       photon_flux      velocity
                   density       magnetic_field   spectral

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Subclass Words:          correlation                

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SOURCE The origin (mission, spacecraft, instrument, ground observatory, or other observing platform) of the data in question.

Subclass Words:       experiment          ground-based                
                      campaign            investigation                 

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SPECIES The identity of a particle or class of particles in detail, such as common name, chemical name, mass, charge state, atomic number, atomic weight, degree of ionization, mass per charge, etc.

Subclass Words:        electron      oxygen
                       ion           Z>3
                       proton        neutral
                       helium        particle
                       nitrogen      dust 

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TEMPERATURE The degree or intensity of heat or cold as measured on a thermometric scale. Also the equivalent temperature corresponding to the energy of thermal motion of plasma particles, or the equivalent temperature as computed in radio measurements.

Subclass Words:        characteristic        parallel
                       isotropic             perpendicular
                       operational           threshold 

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TIME The period between two events or measurements; a measurable interval, usually between a fixed reference (instant of time) such as 0 AD and the subject event or measurement.

Subclass Words:         bin          GMT           minute
                        clock        hour          PB5
                        cycle        interval      reference
                        date         Julian        relative
                        elapsed      local         second
                        epoch        magnetic      spacecraft
                        event        millisecond   UT

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UNCERTAINTY An estimate of the lack of precision in an observed or calculated value.

Subclass Words:        [All other class words are also 
                       possible sub-class words]                

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VELOCITY The rate of increase of distance traversed by a body in a particular direction (linear velocity) or the rate at which a body rotates about an axis (angular velocity). Speed is similarly defined with the omission of reference to direction.

Subclass Words:        doppler       horizontal      speed
                       drift         phase           thermal
                       group         rotation        vertical 

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WAVELENGTH The distance from a particular point of a wave to that same point in the next oscillation cycle of the wave. Also a range of wavelengths, such as infra-red, visible, radio, x-ray.

Subclass Words:        radio       band            primary
                       IR          bin             scan
                       visible     channel         resolution
                       UV          characteristic   
                       x-ray       filter                        
                       gamma ray   nominal                 

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Common Subclass Words

The following lists of words are valid for more than one class word. Note that some species and wavelength subclass keywords are also considered to be common because they can be used in conjuction with several of the class words.

GENERAL Subclass Words:   absolute    instrument   mean
                          average     interval     offset
                          center      maximum      spacecraft
                          component   measured     vector
                          derived     minimum      total

COORDINATE SYSTEM Subclass Words:      cartesian      GSM
                                       geographic     HDZ
                                       geomagnetic    HGI
                                       GCI            NEV
                                       GSE            polar

SOURCE Subclass Words:        electron      oxygen
                              ion           Z>3
                              proton        neutral
                              helium        particle
                              nitrogen      dust 

WAVELENGTH Subclass Words:        radio       
                                  gamma ray       

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Source  Exp   Variable          Value of DICT_KEY 
All     All   Epoch             time>Epoch_center_range
IMP 8   MAG   Time_PB5          time>PB5_center_range 
IMP 8   MAG   B_GSE_c           magnetic_field>GSE_cartesian_vector 
IMP 8   MAG   B_GSM_p           magnetic_field>GSM_polar_vector 
IMP 8   MAG   Rad_dist          position>radial_distance 
IMP 8   MAG   SC_pos_se         position>GSE_cartesian 
IMP 8   MAG   Mode              flag>mode 
IMP 8   MAG   DQF               flag>quality 
DARN    GBAY  vel               velocity>drift_components 
DARN    GBAY  post_flag         flag>post_gap 
DARN    GBAY  label_time        label>time 
DARN    GBAY  label_unit        label>unit 
Geotail EPIC  IDiffI_I          particle_flux>ion_differential 
Geotail EPIC  IDiffI_I_Uncert   uncertainty>ion_differential
Geotail EPIC  IDiffI_I_Energy   energy>ion_center_channel 
Geotail EPIC  IDiffI_I_Ch       label>ion_energy_channel
Geotail EPIC  IDiffI_I_Eplus    energy>ion_energy_plus 
Geotail EPIC  IDiffI_I_Eminus   energy>ion_energy_minus 

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