Level-1#

VODF Level-1 contains data products related to specific observations, and in particular to events detected by a given instrument as well as IRF that describe how the parameters of those events map to physical quantities. This data level may contain extra information on the instrument pointing, provenance information, stable time intervals or instrumental good time intervals, systematics error or quality estimation of the IRF. It also covers related information such as time-series tables of data quality, instrumental or atmospheric conditions.

Level-1 data is assumed to be already pre-processed by the instrument that produces it. The pre-processing must include all calibration and reconstruction necessary to reduce the raw data of the instrument into a set of physical estimated parameters per detected particle.

Note

VODF Level-1 is equivalent to data level 3 (DL3) defined by CTAO, also called “science-ready data”. In CTAO, levels DL0-DL2 constitute the raw and pre-processed data levels that are out of scope for VODF.

Data Model#

@startuml hide circles hide methods skinparam ClassBackgroundColor white/aliceblue skinparam ClassHeaderBackgroundColor lightblue skinparam backgroundcolor transparent <style> package { LineColor gray FontColor gray } </style> package IVOA { class ObsCore { } } package VODF.L1 { class DataRelease { + data_release_id + time_interval + facility + processing_configuration + processing_pipeline_version } class Observation #line.bold { + obs_id + time_interval + spatial_region : SkyRegion + instrument_name + ... } Observation "1" -- "0..1" Pointing Pointing <|-- NominalPointing Pointing <|-- TimeSeriesPointing DataRelease "1..*" -- "1" ObservationCollection ObservationCollection "1" -- "1..*" Observation ObsCore -r- Observation : "maps to <" Observation "1" -- "0..1" EventList Observation "0..*" *-- "0..1" IRF Observation "1" -- "1..*" OnTime OnTime <|-- SingleOnTime OnTime <|-- TimeSeriesOnTime EventList "1" -- "0..*" Event Event "properties" -- "dimensions" IRFComponent IRF "1" *-- "1..*" IRFComponent } @enduml

VODF Level-1 Data Model#

Observations#

The Observation forms the core of the Level-1 data model. Note that we use the term “Observation” more generally than one might expect: an observation is not simply related to the act of recording data with a telescope, but rather to the process of recording and processing the data. Therefore each new Data Release results in new Observations. This might seem strange, but it ensures there is a unique link to data products when the lower-level processing of them changes or improves. One way to think about it is that VHE instruments are not purely hardware, but a combination of hardware and software, and the details of the low-level data processing changes the characteristics of the instrument. With improvements to this low-level processing, the sensitivity, angular resolution, energy resolution, and other factors can change. A second consequence of observations being software-defined is that the minimal duration is therefore up to the observatory. It can be directly related to one data acquisition interval, but can also be a subset or concatenation of many.

A critical point is that an Observation is the minimum unit of what may be discovered by users knowing only the instrument name, a data release name, a time interval, and a sky region.

Data Releases#

TBD

Data Products#