Last modified 19 years ago Last modified on 06/09/05 12:26:04

Spectral Range

The electromagnetic wavelength interval or equivalent over which observations are made is the fundamental discriminator among many types of solar image and other data. The model needs to apply to both narrow-band ("monochromatic" or single-line) and broad-band data. Different branches of the field use different units depending on their spectral band -- frequency at the lowest ranges (of frequency), wavelength at intermediate ranges, energy at the highest. Again for the sake of simplicity we define a single model, assuming that the necessary conversions can be simply made.


type: menu
FITS keyword: WV_TYPE

The class of spectral data, relating to both the nominal spectral

bandpass and the spectral target. Three values are recognized:


Indicates that the spectral range of the measurement is large

compared to the width of absorption/emission lines within the range, and encompasses multiple lines as well as continuum (unless blanketed)


The spectral range of the measurement is of the same order or less

than the width of the target line, and is centered on a wavelength within the wings of the line.


The spectral range of the measurement is of the same order or less

than the typical width of lines in the neighborhood, but is centered on a continuum wavelength, outside of any significant lines. This designation is used to distinguish narrow-band continuum (or "white-light") data from true broad-band data. For data of this description, the matching spectral range should be much broader than the instrumental bandpass, on the understanding that the data are proxies for broadband measurements.

The exact definition of the bandpass (e.g. FWHM) is not prescribed, but is left up to the terminology of the data provider. In the absence of a provider definition, FWHM should be used.


type: number
unit: Ångström (10nm)
FITS keyword: WV_MIN


type: number
unit: Ångström (10nm)
FITS keyword: WV_MAX

The nominal minimum (maximum) of the observing spectral bandpass

associated with the data. As discussed above, for narrowband continuum data, the range should be much larger than the instrumental bandpass; it should correspond to the spectral range over which the data are useful as a proxy, typically an octave or more.


type: number
FITS keyword: WV_NBAND

The number of wavelength bands in the observation


type: number
unit: Ångström (10nm) / pixel
FITS keyword: WV_STP

The spectral dispersion