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Difference between revisions of "Filling Out the Spectral Dictionary Classes"

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If your spectral object is a 2D or 3D array and the bin centers are provided as a data object in a different PDS archive product, use this class to reference that other product. This is filled out similarly to the ''[[#.3Cpds:Internal_Reference.3E|pds:Internal_Reference]]'' class detailed for the ''Slit_Parameters'' class, except that the ''<reference_type>'' value must be '''spectral_characteristics_to_bin_center_values'''.
 
If your spectral object is a 2D or 3D array and the bin centers are provided as a data object in a different PDS archive product, use this class to reference that other product. This is filled out similarly to the ''[[#.3Cpds:Internal_Reference.3E|pds:Internal_Reference]]'' class detailed for the ''Slit_Parameters'' class, except that the ''<reference_type>'' value must be '''spectral_characteristics_to_bin_center_values'''.
 
===== <comment> =====
 
 
''OPTIONAL''
 
 
As usual, any additional notes or caveats can be provided here.
 
  
  
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If your spectral object is a 2D or 3D array and the bin widths are provided as a data object in a different PDS archive product, use this class to reference that other product. This is filled out similarly to the ''[[#.3Cpds:Internal_Reference.3E|pds:Internal_Reference]]'' class detailed for the ''Slit_Parameters'' class, except that the ''&lt;reference_type&gt;'' value must be '''spectral_characteristics_to_bin_width_values'''.
 
If your spectral object is a 2D or 3D array and the bin widths are provided as a data object in a different PDS archive product, use this class to reference that other product. This is filled out similarly to the ''[[#.3Cpds:Internal_Reference.3E|pds:Internal_Reference]]'' class detailed for the ''Slit_Parameters'' class, except that the ''&lt;reference_type&gt;'' value must be '''spectral_characteristics_to_bin_width_values'''.
  
===== <comment> =====
+
==== <comment> ====
  
 
''OPTIONAL''
 
''OPTIONAL''
  
As usual, any additional notes or caveats can be provided here.
+
As usual, any additional notes or caveats about the look-up process can be provided here.

Revision as of 15:30, 30 May 2017

The Spectral Dictionary is a discipline dictionary, which means that its classes will appear in the <Discipline_Are> at the bottom of the <Observation_Area> in observational product labels (and in the <Context_Area>, if appropriate, in non-observational products). The classes in this dictionary describe the spectral characteristics of the data objects presented in the product.

The standard abbreviation for the Spectral Discipline Dictionary namespace is "sp:". Typically, every class and attribute from this dictionary would be prefixed with the "sp:" abbreviation, but this has been omitted in these pages in the interest of readability. See the "Namespace References" section of the "Schema Reference in PDS4 Labels" page for additional information on ways of typing attributes and classes to namespaces.

Update: 19 April 2017 - begin re-write for new Spectral Dictionary nearing the end of development

Contents

<Spectral_Characteristics>

REQUIRED

This is the wrapper class for spectral characteristics. Repeat it once for each spectral-type object you have in your observational product. The Spectral Discipline Dictionary can currently accommodate spectra measured in wavelength, wavenumber, and frequency that are presented as either image cubes, images, or tables (i.e., linear spectra where each row presents one point in the spectrum).

If you have a different type of spectrum, contact Anne Raugh at the Small Bodies Node at the University of Maryland for assistance.

<comment>

OPTIONAL

This is a free-format text field you can use to provide any additional explanation or caveats about the information that follows that would be helpful to an end user.

<pds:Local_Internal_Reference>

REQUIRED

Use this class to identify the spectral-type data object in this product for which this class provides the characteristics. Typically, an observational product will contain only a single spectral object (though it might be a spectral cube). This class is required even in that case.

Note that this class and its elements are in the pds: core namespace, rather than the Spectral Dictionary namespace, so you will need to make the appropriate change of namespace for this class. See "Schema Referencing in PDS4 Labels: Namespace References" for details.

<pds:comment>

OPTIONAL

This is a free-format text field that you can use if there is something about the relationship between the referenced spectrum and its characteristics that requires additional explanation.

<pds:local_identifier_reference>

REQUIRED

This attribute must contain a <local_identifier> string of a spectral data object described elsewhere in this label. Spelling and capitalization count.

<pds:local_reference_type>

OPTIONAL

This attribute must have one of these values:

  • spectral_characteristics_to_array_object
  • spectral_characteristics_to_table_object

The value you use must correspond to the type of the data object you're linking to. So if your local_identifier points to an Array_2D_Spectrum then the local_reference_type must be spectral_characteristics_to_array_object. If your local_identifier points to a linear spectrum in a Table_Character object, then the local_reference_type must be spectral_characteristics_to_table_object.

<spectral_bin_type>

REQUIRED

This attribute indicates the unit of measure for the spectral bin dimensions. It must be one of the following vaues:

  • frequency
  • wavelength
  • wavenumber

The bin descriptions you provide in the subsequent classes and attributes must correspond to the spectral_bin_type specified here.


<Target_Parameters>

OPTIONAL

This class provides known spectral attributes of the target observed (as identified in the <Target_Identification> area of the label). The class may be omitted if it is not needed.

<apparent_magnitude>

OPTIONAL

This attribute provides the apparent magnitude of the target at the time of the observation. This attribute mustbe accompanied by the apparent_magnitude_band_name attribute, following.

<apparent_magnitude_band_name>

OPTIONAL

This attribute provides the band name or filter ID in which the apparent_magnitude was measured. It must be used in conjunction with that attribute.


<Observation_Parameters>

REQUIRED

This class is required to be present and includes various attributes related to the observing circumstances.

<number_of_exposures>

REQUIRED

This attribute indicates the number of individual exposures or distinct integrations were combined to produce the spectrum in the data object.

<net_integration_time>

REQUIRED

The net_integration_time is the sum total of the exposure/integration times for all exposures combined to produce this spectrum.

<spectral_resolution_frequency> or <spectral_resolution_wavelength> or <spectral_resolution_wavenumber>

REQUIRED

One of these attributes must be provided to indicate the smallest possible distinguishable interval in frequency for the instrument in units corresponding to the spectral_bin_type indicated in the parent class. If the spectral resolution is unknown, use the corresponding type of spectral resolution, but set it to

<solar_analog_star_name>

OPTIONAL

The solar_analog_star_name attribute provides a name in a standard format (i.e., one that is recognized by the SIMBAD system) for the solar analog star used to reduce the raw spectral data to the reflectance units presented in this spectrum. You may repeat this attribute if needed.


<Slit_Parameters>

REQUIRED

This class contains attributes to characterize the slit and its projection on the sky. At the least, you must supply the angular slit width.

<slit_position_angle>

OPTIONAL

The slit_position_angle attribute provides the angle the long axis of the slit makes with respect to celestial north, measured eastward of celestial north in the range 0-180 degrees.

<slit_width_angle>

REQUIRED

The slit_width_angle is the angle subtended on the sky by the short dimension of a simple slit.

<slit_length_angle>

OPTIONAL

The slit_length_angle attribute provides the angle subtended on the sky by the long dimension of a simple slit.

<slit_description>

OPTIONAL

The slit_description attribute provides a free-format text field where you can provide a description of the slit shape. This should only be used for cases where the slit is something other than a simple, rectangular slit. For complex slit descriptions, provide a reference to a detailed document using the (optional) <pds:Internal_Reference> class, following.

<pds:Internal_Reference>

OPTIONAL

Use this class to link to a document that provides a detailed description of the slit. This could be a text description, a graphic representation, or a larger document (an instrument SIS for example) that includes this information. Use the pds:comment field to indicate a specific section or page if you are referencing a part of a larger document. This class may be repeated, if needed.

Note that, like the <pds:Local_Internal_Reference> above, this class and its attributes are in the pds: namespace.

<pds:lid_reference> or <pds:lidvid_reference>

REQUIRED

Either a logical identifier without a version number (a "LID"), or a logical identifier with a version number (a "LIDVID"), must be provided for the product you wish to reference. You may not provide both, or repeat this attribute.

<pds:reference_type>

REQUIRED

This attribute must have the value spectral_characteristics_to_document.

<pds:comment>

OPTIONAL

This is a free-format text field in which you can provide additional explanation for why you're referencing the previously mentioned product. If the relevant information is actually in a subsection of the document (rather than comprising the whole document) a section number or page range reference would be an excellent thing to include here.


<Bin_Description>

This class provides three different ways to define the spectral bin characteristics: implicitly, as a uniformly sampled set; explicitly, as individual bin descriptions provided in the label; or externally, in another data object in this product or even in a separate product altogether. You are required to provide at least a minimal text description of the bins. To pass review, most data products will require a more precise description. Check with your PDS node consultant if you have any questions or doubts.

<bin_width_desc>

REQUIRED

This is a free-format text field for describing the spectral bins. It is required to be present and non-null. It does not need to be exhaustive - it just needs to provide a user with the essential details needed to understand the spectrum. So do include things like bandpass shape or how the bins were defined for analysis and data reduction. If the situation is complicated but well-documented, use the <Reference_list> class in the upper part of the product label to include an explicit reference to the explanatory document. If the situation is complicated but not well-document, please consider writing that document and then referencing it.

<Uniformly_Sampled_[unit]>

OPTIONAL

This class occurs in three flavors, one for each possible value of <spectral_bin_type>. Use the version of the class and its attributes corresponding to that value - indicated by the string "[unit]" in the descriptions that follow. The class provides the parameters needed to calculate the bin dimensions, in the specified unit, at each point along the spectral dimension of the data object.

<axis_name>

REQUIRED (for Array Spectra)

For spectra presented as 2D or 3D arrays, this attribute is required to be present and must contain the value of an <axis_name> attribute from the referenced data object. It is the name of the axis representing the spectral dimension in the corresponding object.

For spectra presented as tables, the rows correspond to the spectral dimension and this attribute is prohibited.

<sampling_interval_[unit]>

REQUIRED

This attribute provides the spacing from bin center to bin center in the indicated unit of measure.

<sampling_scale>

REQUIRED

This attribute indicates the type of scale used for sampling. It must have one of two values: Linear or Logarithmic. In the latter case, you must specify the base of the log using <sampling_base>.

<sampling_base>

see description

This attribute is required to be present if the preceding sampling_scale attribute is Logarithmic, otherwise it is forbidden. The value should be a number, so for the natural log a numeric approximation of e to an appropriate precision (e.g., "2.7182818") should be used.

<bin_width_[unit]>

REQUIRED

The width of one spectral bin in the appropriate units. How "width" is determined should have been indicated by the required bin_width_desc at the top of the Uniformly_Sampled_[unit] class.

<first_center_[unit]>

REQUIRED

This attribute provides the value, in the corresponding unit, at the center of the first spectral bin.

<last_center_[unit]>

REQUIRED

This attributes provides the value, in the corresponding unit, at the center of the last spectral bin.

<comment>

OPTIONAL

This free-format text field is provided as a place to note any peculiarities or caveats not otherwise noted about the bins and their definition.


<Axis_Bin_Set_[unit]>

OPTIONAL

This is the class to use if your spectral bins are not uniform but it is reasonable to provide individual bin parameters in the product label. This is often the case, for example, if your spectrum is a composite of points obtained by discrete detectors or observations through a series of filters, or has been resampled or selected from another (hopefully archival) spectrum product. If your bins are so numerous or complex that describing them individually in the label is not practical, you should probably be looking into the <Spectral_Lookup> class, following.

The Axis_Bin_Set class occurs in three flavors, one for each possible value of <spectral_bin_type>. Use the version of the class and its attributes corresponding to that value - indicated by the string "[unit]" in the descriptions that follow. This class provides parameters for defining each individual bin along the spectral axis of a 2D or 3D array structure. It is not used for tables, where typically (and preferably) bin parameters are included as columns in the table structure itself.

<axis_name>

REQUIRED

This attribute must contain the value of an <axis_name> attribute from the referenced data object. It is the name of the axis representing the spectral dimension in the corresponding object.

<Bin_[unit]>

REQUIRED

This sub-class is repeated once for each spectral bin along the named axis. It defines the dimensions of a single bin in the corresponding spectral units.

Note that it is difficult, if not impossible, to validate schematically that bins are being described in their physical sequence along the axis, but this should certainly be the case and reviewers and end-users will expect it.

<bin_sequence_number>

REQUIRED

Detailed bin descriptions make for a long and difficult-to-read string of XML. This attribute is used to help map bin descriptions to sequential positions along the spectral axis. It should start with "1" an increment for each bin described.

<center_[unit]>

REQUIRED

This attribute contains the spectral value at the center of the bin being described.

<bin_width_[unit]>

REQUIRED

This is the width of the particular bin. How the bin width was measured or otherwise determined should be described at least briefly in the <bin_width_desc> attribute at the top of the Bin_Description class.

<detector_number>

OPTIONAL

If you spectrum is a composite from several detectors, this attribute can be used to provide an identifying sequence number. Documentation elsewhere in the label or in the archive submission should map the sequence numbers here to specific detectors.

<grating_position>

OPTIONAL

Use this attribute to indicate that the spectral bin corresponds to a specific grating position. Typically, grating positions begin at zero and increase with wavelength (or equivalent).

<original_bin_number>

OPTIONAL

If your spectrum has been resampled or otherwise extracted from another spectrum product - preferably one that is or will also be in the PDS archives - you can use this attribute to indicate the original bin sequence number in that other product.

This attribute only takes a single integer and mat not be repeated. If the relationship to the original data is more complex than that, please explain in the optional <comment> field provided. If you are referring to a source product that is also in the PDS, please remember to reference it in the Reference_List section in the top part of the product label.

<Filter>

OPTIONAL

If your spectral bin corresponds to the bandpass of a filter, use this class to identify the filter. Filters specific to missions, projects, or observatories should be described in documentation also included in the PDS archives (and references in the Reference_List section of this product label). Standard ground-based filter sets should be identified using the full, formal name wherever possible (i.e., "Johnson V", not just "V").

<filter_name>

OPTIONAL

The name of the filter - either the full name for standard ground-based filters, or the name by which the filter can be found in archived documentation. While this attribute is optional, at least one of <filter_name> and <filter_number> must be specified.

<filter_number>

OPTIONAL

This attribute contains a numeric filter identifier. While this attribute is optional, at least one of <filter_name> and <filter_number> must be specified.

<comment>

OPTIONAL

This text field is for any notes or caveats about this particular filter you'd care to provide for users.

<comment>

OPTIONAL

This attribute, which occurs at the bottom of the <Bin_[unit]> class (in case you've lost track), is for any notes or caveats about this particular bin that you'd like to provide for users.


<Spectral_Lookup>

OPTIONAL

Often the spectral bin parameters for 2D and 3D spectral arrays are supplied as parallel arrays withe explicit values for each pixel. These parameter arrays may be included in the same data product, or as one or more separate products. It is also common for spectra provided as tables to include bin parameters as additional fields in the table object. In either event, this class is provided to link to the data objects that provide the essential bin parameters.

<Bin_Center_Lookup>

REQUIRED

This class provides a link to the values at the center of each spectral bin. Note that exactly one of the following subclasses must be included.

<bin_center_field_name>

see description

This attribute is required if the spectrum object is a table. It contains the value of the <name> attribute of one field in the table - the field containing the center value (in the unit indicated by <spectral_bin_type> at the top of the Spectral_Characteristics class) for each row/bin. It may not be used with spectral arrays.

<pds:Local_Internal_Reference>

OPTIONAL

If your spectral object is a 2D or 3D array, and the bin centers are provided as a separate array but are included as part of this data product (could be in the same data file as the spectrum or a separate one - as long as they are both described by this label), the you should use this class to indicate the <local_identifier> of the array corresponding to the bin centers. You will, of course, have to include a unique <local_identifier> attribute in that array object to reference.

This class is filled out similarly to the pds:Local_Internal_Reference class mentioned at the top of this page, except that the <reference_type> value must be spectral_characteristics_to_bin_center_values.

<pds:Internal_Reference>

OPTIONAL

If your spectral object is a 2D or 3D array and the bin centers are provided as a data object in a different PDS archive product, use this class to reference that other product. This is filled out similarly to the pds:Internal_Reference class detailed for the Slit_Parameters class, except that the <reference_type> value must be spectral_characteristics_to_bin_center_values.


<Bin_Width_Lookup>

REQUIRED

This class provides a link to the values at the center of each spectral bin. Note that no more than one of the following subclasses may be included.

<bin_width_field_name>

OPTIONAL

This attribute should be provided wherever possible when the spectrum object is a table. It contains the value of the <name> attribute of one field in the table - the field containing the bin width for each row/bin. It may not be used with spectral arrays.

If the bin widths are not explicitly included in the table, this field may be omitted. In that case, because the containing Bin_Width_Lookup class is required, you should use the optional <comment> field (below) to state directly what, if anything, is known about the bin widths in addition to whatever is already stated in the <bin_width_desc&gt at the top of the Spectral_Characteristics class.

<pds:Local_Internal_Reference>

OPTIONAL

If your spectral object is a 2D or 3D array, and the bin widths are provided as a separate array but are included as part of this data product (could be in the same data file as the spectrum or a separate one - as long as they are both described by this label), the you should use this class to indicate the <local_identifier> of the array corresponding to the bin widths. You will, of course, have to include a unique <local_identifier> attribute in that array object to reference.

This class is filled out similarly to the pds:Local_Internal_Reference class mentioned at the top of this page, except that the <reference_type> value must be spectral_characteristics_to_bin_width_values.

<pds:Internal_Reference>

OPTIONAL

If your spectral object is a 2D or 3D array and the bin widths are provided as a data object in a different PDS archive product, use this class to reference that other product. This is filled out similarly to the pds:Internal_Reference class detailed for the Slit_Parameters class, except that the <reference_type> value must be spectral_characteristics_to_bin_width_values.

<comment>

OPTIONAL

As usual, any additional notes or caveats about the look-up process can be provided here.