Searching for Data

Overview

You can search for Capella SAR data using the catalog service. Capella's catalog follows the Spatio Temporal Asset Catalog (STAC) specification. The catalog service allows you to search the Capella catalog using filters for location, time, collections, metadata properties, and scene ids. Items returned from a catalog search can be subsequently ordered and downloaded.

Search Filters

Before submitting a search, it's important to understand the various filters that can be used to refine results from a search.

BBOX Filter

"bbox": [-110,39.5,-105,40.5]

The bbox filter can be used to filter search results to items that intersect with a bounding box. Only features that have a geometry that intersects the bounding box are selected. The bounding box is provided as four or six numbers, depending on whether the coordinate reference system includes a vertical axis (elevation or depth):

• Lower left corner, coordinate axis 1
• Lower left corner, coordinate axis 2
• Lower left corner, coordinate axis 3 (optional)
• Upper right corner, coordinate axis 1
• Upper right corner, coordinate axis 2
• Upper right corner, coordinate axis 3 (optional)

The coordinate reference system of the values is WGS84 longitude/latitude unless a different coordinate reference system is specified in the parameter bbox-crs.

For WGS84 longitude/latitude the values are in most cases the sequence of minimum longitude, minimum latitude, maximum longitude and maximum latitude. However, in cases where the box spans the antimeridian the first value (west-most box edge) is larger than the third value (east-most box edge).

Intersects Filter

"intersects": {
    "type": "Point",
      "coordinates": [
      -113.5546875,
      51.17934297928927
    ]
  }

The intersects filter can be used to filter search results to items that intersect with a GeoJSON geometry that can be a point, line, or polygon. Note that only the geometry component of the GeoJSON is used. The coordinate reference system of the values is WGS84 longitude/latitude. For WGS84 longitude/latitude the values are in most cases the sequence of minimum longitude, minimum latitude, maximum longitude and maximum latitude. However, in cases where the box spans the antimeridian the first value (west-most box edge) is larger than the third value (east-most box edge).

Datetime Filter

"datetime": "2018-02-12T00:00:00Z/2018-03-18T12:31:12Z"

The datetime filter will constrain search results to scenes that have been collected within a certain period of time. This can be either a date-time or an interval, open or closed. Date and time expressions adhere to RFC 3339. Open intervals are expressed using double-dots.

• A date-time: "2018-02-12T23:20:50Z"
• A closed interval: "2018-02-12T00:00:00Z/2018-03-18T12:31:12Z"
• Open intervals: "2018-02-12T00:00:00Z/.." or "../2018-03-18T12:31:12Z"

Capella uses UTC time for items within the catalog.

Collections Filter

"collections": ["capella-geo","capella-slc"]

The collections filter will indicate that the search should only occur within a specific collection or collections. The filter requires an array of strings that correspond with the identifiers of the collections to be searched.

Ids Filter

"ids": ["CAPELLA_ARL_SM_SLC_VV_20190927234024_20190927234124", "CAPELLA_ARL_SL_SLC_VV_20190927234024_20190927234124"]

The ids filter allows a user to search for specific items within the catalog. The filter requires an array of strings that correspond with the identifiers of the products that the user would like to find. When this filter is used, other filters are ignored.

Query Filter

"query": {"sar:instrument_mode": {"eq": "stripmap"},"sar:product_type": {"eq":"GEO"}}

The query filter will be used to constrain results to scenes that match the specific properties described within the filter. This filter is defined using key/value pairs that describe which metadata property to filter and the comparison operation to perform for that property. The query filter can be used for most STAC metadata fields, including:

• sar:instrument_mode
• sar:pixel_spacing_range
• sar:pixel_spacing_azimuth
• sar:looks_range
• sar:looks_azimuth
• sar:looks_equivalent_number
• sar:resolution_range
• sar:resolution_azimuth
• capella:squint_angle
• sar:observation_direction
• capella:collect_id
• start_datetime
• end_datetime
• platform
• sar:product_type
• sat:orbit_state
• view:incidence_angle
• instruments

The comparison operation is defined using equals (eq), less-than (lt), less-than-equal-to (lte), greater-than (gt), or greater-than-equal-to (gte), and the value for comparison.

Submitting a Search

To submit a search to the catalog with full filtering capabilties, you will POST the desired search filters to the catalog search endpoint:

POST https://api.capellaspace.com/catalog/search
{
    "bbox": [],
    "intersects": {},
    "datetime": "",
    "collections": [],
    "ids": [], 
    "query": {},
    "sortby": [],
    "limit": 50
}

You can use sortby to sort the returned items by a particular metadata property. For example, you can sort the results by the start datetime of the collect in descending order:

"sortby": [{"field": "properties.datetime","direction": "desc"}, {"field": "collection","direction": "desc"}]

Alternatively, you can use a shorted form:

"sortby": "-properties.datetime"

You can also limit the number of results returned per page by using limit, where the value is an integer indicating the desired number of results. The default is 10.

Additional Information

For more information on submitting a search and the results of a search, see the API reference for the Catalog Service.