Below are two sets of metadata which will be stored in the new archive in regard to Images and the Image Sets to which they belong. Included where relevant are the equivalent fields in the Virtual Observatory ObsCore Data Model, a potential source from which to obtain the data, and a comment. The images table was written specifically with the idea of spatial images in mind. Other data products (spectra, time series, etc) would have different amounts of granularity in the header information available.
Images Database Table:
| Column Name | Units | VO Equivalent | Source | Comments |
|---|---|---|---|---|
| sourcename | target_name | OBJECT Keyword | ||
| ra | deg | s_ra | Center of Ra Axis | |
| dec | deg | s_dec | Center of Dec Axis | |
| image_field_of_view | deg | s_fov | Average of NAXISn*CRDELn of the spatial Axes | |
| spatial_region | s_region | Derived from spatial Data | STC-S String Defined in the TAP (Dowler, et al 2010) | |
| ra_element_count | s_xel1 | Relevant NAXISn Keyword | ||
| ra_pixel_size | abs(Relevant CDELTn) | |||
| dec_element_count | s_xel2 | Relevant NAXISn Keyword | ||
| dec_pixel_size | abs(Relevant CDELTn) | |||
| spatial_resolution | arcsec | s_resolution | sqrt(BMAJ*BMIN) | Geometric mean of the synthesized beam axes. |
| beam_axis_ratio | BMAJ/BMIN | Ratio of the synthesized beam axes. | ||
| starttime | MJD | t_min | These values should be obtained by some larger-scale process. VlassMgr, in the case of quicklook images. | |
| endtime | MJD | t_max | ||
| exposure_time | s | t_exptime | ||
| min_frequency | Hz | em_min | Minimum of Spectral Axis | |
| max_frequency | Hz | em_max | Maximum of Spectral Axis | |
| rest_frequency | Hz | RESTFRQ Keyword | Used for transformations | |
| band_code | weblog | Requires outside information source for accuracy. | ||
polarization_id | pol_states | Polarization CRVALn value | CASA uses the CRVALn value to convey polarization information, with [1,2,3,4] mapped to [I,Q,U,V]. Default to 'None' in case of other values. | |
| telescope | instrument_name | TELESCOP Keyword | This must accommodate images for multiple instruments (i.e. VLA + Single Dish) | |
| file_id | automatically generated | link to information about the physical file | ||
| image_id | obs_id | automatically generated | Unique Identifier for the Image | |
| image_units | o_ucd | BTYPE & BUNIT Keywords | Description of the physical quantity measured in the image | |
| max_intensity | image_units | image table values | ||
| min_intensity | image_units | image table values | ||
| rms_noise | image_units | weblog | Both of these will need to come from the last stage of the imaging process, to maintain accuracy. For quicklook images, that is stage7. That may change (and will likely be different for the Single Epoch products). | |
| thumbnail | weblog, find the matching thumbnail image generated. | |||
| tags | Internal tagging system to facilitate searches. |
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