| 1 | == Spectral Range == |
| 2 | |
| 3 | The electromagnetic wavelength interval or equivalent over which |
| 4 | observations are made is the fundamental discriminator among many |
| 5 | types of solar image and other data. The model needs to apply to both |
| 6 | narrow-band ("monochromatic" or single-line) and broad-band data. |
| 7 | Different branches of the field use different units depending on their |
| 8 | spectral band -- frequency at the lowest ranges (of frequency), wavelength |
| 9 | at intermediate ranges, energy at the highest. Again for the sake of |
| 10 | simplicity we define a single model, assuming that the necessary |
| 11 | conversions can be simply made. |
| 12 | |
| 13 | |
| 14 | |
| 15 | ==== Wave_Type ==== |
| 16 | |
| 17 | |
| 18 | type: ''menu''[[BR]] |
| 19 | FITS keyword: ''WV_TYPE''[[BR]] |
| 20 | |
| 21 | The class of spectral data, relating to both the nominal spectral |
| 22 | bandpass and the spectral target. Three values are recognized: |
| 23 | |
| 24 | ''' broad ''' |
| 25 | |
| 26 | |
| 27 | Indicates that the spectral range of the measurement is large |
| 28 | compared to the width of absorption/emission lines within the range, |
| 29 | and encompasses multiple lines as well as continuum (unless blanketed) |
| 30 | |
| 31 | ''' line ''' |
| 32 | |
| 33 | |
| 34 | The spectral range of the measurement is of the same order or less |
| 35 | than the width of the target line, and is centered on a wavelength within |
| 36 | the wings of the line. |
| 37 | |
| 38 | ''' narrow ''' |
| 39 | |
| 40 | |
| 41 | The spectral range of the measurement is of the same order or less |
| 42 | than the typical width of lines in the neighborhood, but is centered on |
| 43 | a continuum wavelength, outside of any significant lines. This designation |
| 44 | is used to distinguish narrow-band continuum (or "white-light") data from |
| 45 | true broad-band data. For data of this description, the matching spectral |
| 46 | range should be much broader than the instrumental bandpass, on the |
| 47 | understanding that the data are proxies for broadband measurements. |
| 48 | |
| 49 | The exact definition of the bandpass (''e.g.'' FWHM) is not prescribed, |
| 50 | but is left up to the terminology of the data provider. In the absence of |
| 51 | a provider definition, FWHM should be used. |
| 52 | |
| 53 | |
| 54 | ==== Wave_Minimum ==== |
| 55 | |
| 56 | |
| 57 | type: ''number''[[BR]] |
| 58 | unit: ''Ångström (10nm)''[[BR]] |
| 59 | FITS keyword: ''WV_MIN'' |
| 60 | |
| 61 | ==== Wave_Maximum ==== |
| 62 | |
| 63 | |
| 64 | type: ''number''[[BR]] |
| 65 | unit: ''Ångström (10nm)''[[BR]] |
| 66 | FITS keyword: ''WV_MAX'' |
| 67 | |
| 68 | The nominal minimum (maximum) of the observing spectral bandpass |
| 69 | associated with the data. As discussed above, for narrowband continuum |
| 70 | data, the range should be much larger than the instrumental bandpass; |
| 71 | it should correspond to the spectral range over which the data are |
| 72 | useful as a proxy, typically an octave or more. |
| 73 | |
| 74 | |
| 75 | ==== Wave_Bands ==== |
| 76 | |
| 77 | |
| 78 | type: ''number''[[BR]] |
| 79 | FITS keyword: ''WV_NBAND''[[BR]] |
| 80 | |
| 81 | The number of wavelength bands in the observation |
| 82 | |
| 83 | |
| 84 | ==== Wave_Step ==== |
| 85 | |
| 86 | |
| 87 | type: ''number''[[BR]] |
| 88 | unit: ''Ångström (10nm) / pixel''[[BR]] |
| 89 | FITS keyword: ''WV_STP''[[BR]] |
| 90 | |
| 91 | The spectral dispersion |