Field Definitions are Available Here
Collection
string (500)
Keyword used to describe the general category of the collection. A collection can conceivably cover several categories.
EARTH SCIENCE
/ScienceKeywords/ScienceKeyword/CategoryKeyword
/gmi:MI_Metadata/gmd:identificationInfo/gmd:MD_DataIdentification/gmd:descriptiveKeywords/gmd:MD_Keywords/gmd:keyword/gco:CharacterString
Descriptive Information (ECHO)