2.8. Product metadata keywords

The following metadata keywords are required to be present in all Herschel products. In the Data Processing system these keywords are referred to as "attributes":

Table 2.1. Herschel products attributes

Herschel DP keyword name Type Description FITS keyword
type String Product type identification TYPE
creator String The name and version of the software that created the product CREATOR
creationDate Fine time Date of product creation DATE
description String Full name of product DESC
instrument String Instrument name INSTRUME
modelName String Instrument Model Name MODELNAM
startDate Fine time Start date of observation DATE-OBS
endDate Fine time End date of observation DATE-END

Fine Time is the internal DP representation that holds the value of time. Fine time is defined as the atomic time (SI seconds) elapsed since the TAI epoch of 1 January 1958 UT2. In the DP system the resolution provided is microseconds. When the value of a Fine Time keyword is displayed on a GUI or exported to FITS, the parameter is transformed to a String value, formatted according to the rules as defined by the TIMESYS keyword. Per default, TIMESYS='UTC', so the format will then be YYYY-MM-DDTHH:MM:SS.ssssss.

In addition to the product attributes, observational products contain those metadata keywords that identify the product and the observation that is associated with. In particular, the main metadata keywords common to all instruments are:

Table 2.2. Main metadata keywords in observational products

Herschel DP keyword name Type Description FITS keyword
obsid Long Observation identifier OBS_ID
bbid Long Building block identifier BBID
observer String Name of observer OBSERVER
proposal String Proposal name PROPOSAL
aot String AOT identifier AOT
obsMode String Observation mode name OBS_MODE
cusMode String CUS observation mode CUSMODE
aorLabel String AOR label as entered in HSpot AOR
odNumber Long Mission operational day number ODNUMBER

The "obsid" uniquely identifies an observation for all mission phases. The "obsid" relates all observational products associated with an AOR.

The "bbid" identifies uniquely each building block in an observation. A Building Block is a unit of observation or key component of the observation from the instrument commanding point of view (e.g., a single filter, a single node). An observation execution is always defined as a flat sequence of Building Blocks. The bbid is particularly important in the Herschel product definitions because large products (e.g., Level 0, Level 0.5) are sliced per building block. That is, a product or context product is provided for each building block in the observation.

Both the "obsid" and the "bbid" are essential to link the uplink commanding and the downlink telemetry.

"observer", "proposal", "aot", "obsMode" and "aorLabel" are derived from the proposal information and AORs as entered in HSpot.

"cusMode" is an internal uplink keyword that associates the observation requested with the corresponding pipeline processing. CUS stands for Common Uplink System.

"odNumber" is the number that identifies the Operational Day in the mission since launch. An Operation Day is defined as the interval between the start of two contiguous satellite ground contact periods. The duration of an Operational Day is in average around 24 hours, but it can also be shorter or longer, depending on operational constraints. The "odNumber" is an important key for the identification of those Auxiliary products that are generated per OD.

A complete list of the compulsory metadata keywords in the Herschel observational products can be found in the PDS.

A complete list of metadata per instrument mode in the Observation Context Product can be found in Chapter 3 (HIFI), Chapter 4 (PACS) and Chapter 5 (SPIRE).