The Spectra dictionary contains classes that describe the spectral characteristics of Array (and Array subclass) data objects, and of the instruments that acquired them. The Axis_Bin_Set class describes the spectral characteristics of each band along a spectral axis of an Array. This class is used in cases where the spectral information is not uniform along the spectral axis. The Axis_Uniformly_Sampled class provides attributes describing the spectral characteristics of an axis of an Array object, in cases where the spectral sampling interval is regular. The Bin class specifies the characteristics of an individual bin along a spectral or other binned axis in an Array object. The Filter class identifies the filter associated with a specific band or bin along a spectral axis in an Array object. The filter may be identified by either name, identifier, or number or some combination of these. The Local_Internal_Reference class is used to cross-reference other classes or objects within the product. The Spectral_Characteristics class provides information about the spectral characteristics of an Array object. The Spectral_Lookup class references a 2-dimensional lookup map providing spectral characteristics for a corresponding spectral Array object. The referenced lookup map may either be internal to the referencing product, or an external stand-alone product. The bin_width_desc attributes provides a description of the method used to calculate the bin_width of a bin along a spectral axis in an Array object. The description should include information on the shape (e.g. gaussian, square wave, etc.) and what the bin_width value means (i.e., standard deviation of a gaussian function or full-width at half max (FWHM)). The bin_sequence_number provides the sequential numbering of bins along an axis in an Array object. The bin_width attribute provides the width of a bin along a spectral axis in an Array object, in the specified units. The method used to calculate the width must be specified using the bin_width_desc attribute. The center_value attribute provides the wavelength, wave number, or frequency describing the center of a bin along the band axis of a spectral data object. When describing data from a spectrometer, the value corresponds to the peak of the response function for a particular detector and/or grating position. The comment attribute is a character string expressing one or more remarks or thoughts relevant to the object. The detector_number attribute provides the spectrometer detector number corresponding to a band of a spectral qube. Detector numbers are usually assigned consecutively from 1, in order of increasing wavelength. The filter_name attribute provides the commonly-used name of the instrument filter through which an image or measurement was acquired or which is associated with a given instrument mode. The filter_number attribute provides the numeric identifier of an instrument filter through which an image or measurement was acquired or which is associated with a given instrument mode. Within the bin class of a spectral data object, it identifies the filter through which data in the given band were acquired. The first_center_value attribute provides the wavelength, wave number, or frequency describing the center of the first bin along the spectral axis of a spectral data object. The grating_position attribute of a spectral qube describes the grating position which corresponds to the band. Grating positions are usually assigned consecutively from 0, and increasing position causes increasing wavelength for each detector. The last_center_value attribute provides the wavelength, wave number, or frequency describing the center of the last bin along the spectral axis of a spectral data object. The local_identifier_reference attribute provides the local_identifier of the digital object described by the referencing class. Note that a local_identifier attribute, with the same value as this local_identifier_reference, must be present within the label. The local_reference_type attribute provides the name of an association between an entity identified by a local_identifier_reference and another corresponding entity identified by a local_identifier The sampling_parameter_type attribute indicates the nature of the parameter specified along the spectral axis in an Array object. The original_bin_number attribute of a spectral Array object is used when the current data object is a subset of some original data object. The original_bin_number for each band identifies the bin_sequence_number of the corresponding band in the original data object. The sampling_interval attribute provides the spacing of points at which data are sampled and at which a value for an instrument or data parameter is available. This sampling interval can be either the original (raw) sampling or the result of some resampling process. The sampling parameter (wavelength, frequency, etc.) is identified by the sampling_parameter_type attribute. The scaling_factor attribute is the scaling factor to be applied to each stored value in order to recover an original value. The observed value (Ov) is calculated from the stored value (Sv) thus: Ov = (Sv * scaling_factor) + value_offset. The default value is 1. The Units_of_Spectra class provides a union of the three unit classes: Units_of_Frequency, Units_of_Length, and Units_of_Wavenumber. The value_offset attribute is the offset to be applied to each stored value in order to recover an original value. The observed value (Ov) is calculated from the stored value (Sv) thus: Ov = (Sv * scaling_factor) + value_offset. The default value is 0.