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