Metadata
Browse images are typically created as a by-product of an image acquisition postprocessing system from the processing of satellite imagery, or navigation data from an aerial imagery campaign. Such systems typically output the browse image as well as a table that contains the metadata about the individual frames. Such tables may exist as CSV files, databases, or structured XML. This workflow assumes that such a metadata table exists, and that it is converted into a feature class compatible with ArcGIS. There are many tools within ArcGIS that can be used to create and restructure such tables.
In this workflow, this metadata table will be used to populate a mosaic dataset to manage and serve the browse imagery. This workflow assumes that there is a one-to-one relationship between a record in the metadata table and a browse image. Typically the footprint of each scene is available as part of the feature class; if not, the footprint must be computed.
Depending on your organization and the type of data to be managed, it is recommended to include additional metadata in the mosaic dataset (more than in the existing metadata table), especially where the browse imagery and its application support multiple sensors. New data fields can be added to the mosaic dataset as necessary to support key metadata defined by your organization.
The following is a list of suggested metadata, with recommended names for commonly used metadata fields. Since some search applications may search on multiple image services, this list is optimized for compatibility with these applications by using standardized field names and definitions. Any additional metadata available with the browse imagery can also be maintained. Some metadata fields may not be necessary for search or query, and if they significantly increase the size of the attribute table, it may be best to put them in an external file and reference these in a MetadataURL field. The data manager decides which metadata fields will be maintained live with the browse imagery, versus any metadata that can be stored in external files for infrequent access.
FieldName | FieldType | Length | Value | Description |
|---|---|---|---|---|
Name | Text | 50 | Unique name of scene, for example, Scene ID. Required field. | |
Raster | Text | 120 | Path to browse image file in server directory structure. Required when using raster type = Table. | |
SensorName | Text | 20 | Name of the sensor (not the satellite; see SatelliteName), for example, ETM+. | |
SatelliteName | Text | 25 | Name of the satellite, for example, Landsat7. | |
CloudCover | Double | 0...100; <NULL> | Estimated percent cloud cover in the full scene, as an integer from 0 to 100. | |
SatElevation | Double | 0...90; <NULL> | Angle of vector to satellite in degrees positive upward from the horizon as seen by an observer on the earth within the scene's footprint. | |
SatAzimuth | Double | 0...360; <NULL> | Angle of vector to satellite in degrees positive clockwise from true north as seen by an observer on the earth within the scene's footprint. | |
SunElevation | Double | 0...90; <NULL> | Angle of sun in degrees positive upward from the horizon as seen by an observer on the earth within the scene's footprint. | |
SunAzimuth | Double | 0...360; <NULL> | Angle of sun in degrees positive clockwise from true north as seen by an observer on the earth within the scene's footprint. | |
AcquisitionDate | Date/Time | UTC date and time of the acquisition. | ||
DayOfYear | Long | 1...366, <NULL> | Numerical integer representation of day of year (Jan 1 = 1, Feb 1=32, and so on). Can be calculated from AcquisitionDate. Used to search for seasonal data. | |
MetadataURL | Text | 120 | URL or link to external metadata file with detailed and/or original metadata, available for infrequent access. | |
GSD | Double | Approximate pixel size in meters of source data. Highest resolution in cases where scene has multiple sizes. | ||
BrowseURL | Text | 80 | Internet URL to browse image file. | |
ProductName | Text | 25 | This is a standard field name in all mosaic datasets, but it is typically unused. For browse imagery, the product typically refers to a level of processing (for example, L1A, L2B) available. If this field is available in the metadata table, the data manager should decide if it should be ingested. | |
Download_URL | Text | 80 | Link to the full-resolution image (for download). |
If the metadata from the existing database does not include the high-priority fields listed above, it is recommended that those fields (where appropriate) be added into the table before ingestion into the mosaic dataset. It is also recommended that extraneous or redundant fields be removed from the data stored in the attribute table and included with the external metadata, since they increase the size of the tables. Similarly reconsider the size of each field so they are not larger than necessary. Reducing the size of the tables can speed up the performance of web applications when searching metadata.