Vocabulary: http://www.ivoa.net/rdf/product-type
Authors: Baptiste Cecconi <baptiste.cecconi@obspm.fr>, Yan Grange <grange@astron.nl>
Date: 2021-06-16

New Term: #dynamic-spectrum
Action: Addition
Label: Dynamic Spectrum
Description: Consecutive spectral measurements through time, 
organized as a time series of successive spectra of the same 
target or field of view.

Relationships: rdfs:subPropertyOf(two-d-array)

Used-in: http://vogate.obs-nancay.fr/tableinfo/nda.epn_core
Used-in: http://dorotka.ufa.cas.cz/tableinfo/thmsm.epn_core
Used-in: http://cdpp-epntap.irap.omp.eu/tableinfo/amdadb.epn_core
To-be-used-in: https://vo.astron.nl/browse/__system__/obscore

Rationale:
The term #dynamic-spectrum is mostly use in low frequency radio 
astronomy. A #dynamic-spectrum data product is a 2D product, with
a time axis and a spectral axis. Community-specific clients can 
use this term to select adequate plotting style (such as, e.g., 
the "waterfall" style). In TOPCAT, the corresponding plotting 
style would be the "spectrogram" option of its "Time Plot" window.

NB: The EPNcore short name for #dynamic-spectrum is `ds`.