NICER Level 0, 1, 2, 3 Processing Levels


THe NICER software provides various processing tools that to various processing levels. This document describes what these levels refer to.

Read this thread if you want to: Understand NICER Level 0, 1, 2, and 3 Processing.

Last update: 2022-10-19


Throughout the NICER software, the user may encounter references to various levels of processing. These may refer to "Level 2" or "Level2" and so on.

These processing levels were defined during the mission design phase, and correspond to approximate levels of quality and complexity. This document describes the various NICER processing levels in more detail.

NICER Processing Levels

Level0. In NICER parlance, Level0 refers to the raw data received by the NICER science data pipeline system. This data is typically formatted on the spacecraft into CCSDS packets, which means that large data products are broken into small pieces that need to be reassembled at a later level. Data delivered to the pipeline may also be not in time order, and may contain duplicate information. The typical science user does not see or interact with Level0 data: this data is archived within the NICER science data pipeline, and not HEASARC.

Level1 At the NICER Level1 processing level, data have been assembled into archivable FITS format. Unlike Level0 data, data are in time order and any duplicated information has been removed. However, the data are not calibrated or screened.

In the case of NICER data the event data with the path name xti/event_uf/ni9999999999_0mpuN_uf.evt are the Level1 data, one file for each MPU (where N is an MPU number and 9999999999 is an observation ID number).

Level1 data is archived at HEASARC and is the lowest level of data science user typically sees. NICER's science data pipeline uses internal software to convert Level0 to Level1 data which is not available to scientists.

Level 1a Level "1a" data are fully calibrated but lightly screened.

The NICER event data with path name xti/event_cl/ni9999999999_0mpuN_ufa.evt are fully calibrated files, but have not been completely screened for non-X-ray events or bad data times. These are also known as "ufa" files, the "uf" standing for "unfiltered" and "a" standing for "Level 1a."

The NICER processing task nicerl2 generates Level 1a and Level 2 files. Level 1a files are not typically fuilly archived but can be reproduced by running nicerl2.

Level2 or Level 2. Level2 data area in FITS format and fully calibrated and screened.

The NICER event data with path name xti/event_cl/ni9999999999_0mpu7_cl.evt are fully calibrated Level 2 files. These are also known as the "cl" (or cleaned) event files the "cl" standing for "clean."

The NICER processing task nicerl2 generates Level 1a and Level 2 files. Level 2 files are archived.

Level3 or Level 3. Level3 data are high level products in FITS format.

High level products are light curves and spectra, as well as auxiliary information such as responses and backgrounds. The high level spectral task nicerl3-spect produces NICER spectra and auxiliary products, and the task nicerl3-lc produces light curves.

For NICER's early mission, standard Level3 products were not available. Staring in late 2022 the standard scripts became available and NICER began archiving Level3 products.


  • 2022-10-20 - initial draft