This document defines NASA's Earth Observing System (EOS) Clearinghouse (ECHO) metadata model, one of several supported formats for submitting metadata to NASA's Earth Science Data and Information Systems (ESDIS) Common Metadata Repository (CMR). The document was originally written as a set of requirements and recommendations for ingesting science metadata into the ECHO system, which has been subsumed by CMR. Though the ECHO system itself is now retired, the data model specification remains valid.
The following three metadata constructs are utilized in the ECHO metadata specification:
- Collection—A grouping of science data that all come from the same source, such as a modeling group or institution. Collections have information that is common across all the granules they contain.
- Granule—The smallest aggregation of data that can be independently managed (described, inventoried, and retrieved). Granules have their own metadata model and support values associated with the additional attributes defined by the owning collection.
- Browse—An image that provides a high-level view of the associated granule or collection metadata item. Browse images are not spatially enabled, but are very useful during data discovery and cross-referencing to other granules or collections.
ECHO's metadata model was derived from NASA's Earth Observing System Data and Information System (EOSDIS) Core System (ECS) metadata model with some extensions. ECS data model in turn was developed in parallel to the Federal Geographic Data Committee (FGDC) model. Metadata conformant with ECS or generally with FGDC can be mapped to ECHO. Together with the International Organization for Standardization (ISO) 19115 standards for science metadata and NASA's Global Change Master Directory (GCMD) Directory Interchange Format (DIF), the ECHO metadata model formed the basis for the more extensive Unified Metadata Model (UMM) used by CMR.
Conformance to the model is verified by XML schemas.
The ECHO Metadata Standard is an approved standard recommended for use in NASA Earth Science Data Systems in January 2010.
Updates to the ECHO metadata and API are available in the "Current specification" link and are to be considered the most recent recommended version.
NASA Earth Science Community Recommendations for Use (2010)
The ECHO metadata model has its heritage from the well-established EOS Data and Information System (DIS) Core System (ECS) data model and is robust and able to represent most NASA’s earth science data types. It is one of the formats supported for submitting metadata to CMR.
The current Unified Metadata Model is much more extensive, with the capability to describe data variables and services in addition to collections, granules and imagery. There are currently no plans to further evolve the ECHO-10 metadata model.
The ECHO metadata model has been optimized for remote sensing data, and therefore may be less suited to other NASA data types currently being cataloged, such as in situ data acquired in field experiments.
From the review community’s perspective, the single biggest hindrance to the adoption of ECHO as a proposed standard seems to have been that this would encourage the NASA earth science data systems community to “standardize” on a home-grown metadata model, rather than move toward an existing international standard for earth science metadata. As one reviewer stated, ECHO “is only used within NASA, and it is optimized for remote sensing data”.