To homogenize the database, each calibration site is automatically assigned with an unique site identifier. This ID is built using information provided during submission and has the following format: 

SSSS-YY 

where: 

• SSSS: is a unique short site identifier defined by the site maintainer during the submission of the proposal for a new site. I in a fixed length identified of 4 (four) alpha numerical characters. Only capital letters and digits are allowed. In case of conflict with existing sites, site maintainer will be notified and modification will be agreed.
  
• YY: is the primary target type identifier for the site. A calibration target can, in general, include different target types. The primary target type is the most common one in the site of the one which better represents the primary purpose of the calibration site. The primary target type identifier is an enumeration with a fixed length of 2 characters. It can have one of the following values: 
  • AT – for Artificial Targets 
  • DT – for Distributed Targets (e.g. rain forest or deserts) 

Each calibration target is also automatically assigned with an unique target identifier, facilitating the submission and displaying of surveys. This ID is built using information provided during submission and has the following format: 

SSSS-TT-DDDD

where:

• SSSS: is a unique short site identifier defined by the site maintainer during the submission of the proposal for a new site. It is a fixed length identified of 4 (four) alpha numerical characters. Only capital letters and digits are allowed.
• TT: is the target type identifier. It is an enumeration with a fixed length of 2 characters. It can have one of the following values:
  • TP – for Transponders (active artificial targets). This also includes Polarimetric Active Radar Calibrators PARCs)
  • CR – for Corner Reflectors (passive artificial targets)
  • LB – for Low Backscatter targets (e.g. calm sea)
  • SI – for Snow/Ice
  • FR – Forest
  • DE – Desert
  • PS – Persistent Scatterer
• DDDD: is the short target identifier provided by the site maintainer when the proposal for the inclusion of the target in the SARCalNet database is submitted. It must be unique within the calibration site. The short target identifier is numerical identifier having a fixed length of 4 digits (padded with leading zeros if necessary). The guideline, in this case, is to use progressive numbers starting from “1”.

The SARCalNet database is built using a database engine with geo-spatial extensions (currently the xcube geoDB, developed in the context of the Euro Data Cube initiative). The database supports to store any geo-referenced vector data in “collections” and offers a flexible API.

 The SARCalNet Calibration DB allows to extract information for the calibration sites, the calibration targets (e.g. coarse location, description and characterization). Moreover, in the case of artificial targets only, information about the surveys that are conducted on the targets themselves can be retrieved (surveys include, e.g., the accurate geolocation and pointing of targets, as well as information which may vary with time).

The information is strictly related to the fields to be provided in the submission templates (see here) and can be downloaded in different formats (csv, kml, GeoJSON). Downloads are available:

•  From the “Calibration Sites” overview page (here). In this case, the download (calibration_sites.zip) includes:
  • A summary file for all sites matching querying criteria (sites.***)
  • Separate files for specific information of each site (identified by unique site ID), containing, e.g., rough target position (<site_unique_id>_targets.***)
  • Separate files for specific information of each site surveys (identified by unique site ID), containing all available surveys for the site (<site_unique_id>_surveys.***)

• From a specific calibration site page, in the download area, information on the site can be retrieved in a zip file (<site_unique_id>.zip), containing:
  • A file for specific information of the site (identified by unique site ID, i.e., <site_unique_id>.***)
  • A file with information of all the targets of the site (<site_unique_id>_targets.***)
  • A file with the precise surveys for the site, when available (<site_unique_id>_surveys.***)
  • Specific surveys for targets can also be downloaded in machine readable format from “Survey” area (surveys_<survey_date>.***), containing all the targets of a certain survey.

Calibration sites and targets might receive different levels of endorsement (and associated labels) depending on the completeness of provided information. Currently, the following labels are available: 

• “Fully Endorsed”: All targets comply with all mandatory and optional requirements, no inconsistencies or blocking points are found during expert quality check and the data will be shared in the SARCalNet database.  
• “Endorsed”: All targets comply with all mandatory requirements, no inconsistencies or blocking points are found during expert quality check and the data will be shared in the SARCalNet database.   
• “Informational”: Targets do not comply with all mandatory requirements, but expert assessment is that provided information can be relevant for certain users. 
• “Externally endorsed”: All targets comply with all mandatory requirements, no inconsistencies or blocking points are found during expert quality check. The data will not be shared entirely in the SARCalNet database some of them are directly distributed by the maintainer. Specific information on how to access or how to request data shall be provided in this case, and published in the calibration site web page on the SARCalNet portal. 
• “Rejected”: Targets do not comply with mandatory requirements and information is not fit to be published in the SARCalNet website. In this case, the site will be removed from the database. 
• “Dismissed”: the information of the site /target are no longer regularly updated but the historical data are still fully valid. 

Before the curation is completed, the site is labelled “Under review” and is still visible in the database. For details on the curation procedure, see the SARCalNet Handbook in here.

The SARCalNet data policy is based on the Creative Common CC systems (see here). Upon submission, SARCalNet calibration site maintainers shall select one of the available CC types summarized below:

• CC0: no rights reserved and data users may freely build upon, enhance and reuse the data for any purposes without restriction under copyright or database law.
• CC-BY: This license lets others distribute, remix, tweak, and build upon licensor data, even commercially, as long as they credit licensor for the original creation.
• CC-BY-SA-4.0: This license lets others remix, tweak, and build upon licensor data even for commercial purposes, as long as they credit licensor and license their new creations under the identical terms.
• CC-BY-NC: This license lets others remix, tweak, and build upon the licensor data non- commercially, and although their new data/works must also acknowledge licensor and be non-commercial, they don’t have to license their derivative works on the same terms.
• CC-BY-NC-SA: This license lets others remix, tweak, and build upon licensor data non- commercially, as long as they credit licensor and license their new creations under the identical terms.
• CC-BY-ND: This license lets others reuse the data for any purpose, including commercially; however, it cannot be shared with others in adapted form, and credit must be provided to licensor.
• CC-BY-NC-ND: This license allows others to download licensor data and share them with others as long as they credit licensor, but they can’t change them in any way or use them commercially.

The information of the license of each calibration site in provided in the calibration site dedicated pages.

Note: If no copyright applies to the data and this is documented publicly by the copyright owner, the license file can be skipped. This should be justified in the self-assessment form.