The data then undergo level zero processing (per NASA's standard
terminology) as soon as all the data contained within the current 24 hour
time frame have been received. In level zero processing, duplicate data are
removed from the data stream, data are time ordered, and data quality and
accounting summaries are appended. The data are formatted into a 24-hour
Science Routine Data Set File (Level 0 data file). Production of Level 0 data
is now the responsibility of the ACE Science Center at Caltech.
In addition to formatting, level one processing includes those data processing steps which are judged to be of sufficient simplicity that they can be understood, defined, and coded before launch, and do not require iterated processing with increasing experience. Examples of such steps include decompression of compressed rate scaler data and proper time labeling of data which are buffered for a number of minor frames within the instrument before readout. A counter-example (a process which clearly does not belong in level one) is application of calibration data to convert digital pulse heights from detector signals to engineering units. Experience indicates that calibrations are often adjusted repeatedly to improve resolution based on extended iterative study of the instrument response.
In parallel with the level one processing, the level zero data is processed to yield Browse Parameters. Browse parameters are a subset of ACE measurements which allow monitoring of the solar wind and large-scale particle and magnetic field behavior. They also allow the selection of time intervals of particular interest for more intensive study. Since it is considered important to distribute first-order ACE results as soon as possible, the browse parameters are delivered to the public domain immediately, at the expense of full verification.
Click here for more detailed level 1 data
Data processing beyond Level 1 is the responsibility of the individual instrument teams. Level 2 processing includes such operations as application of calibration data and detector response maps, organization of data into appropriate energy and time bins, and application of ancillary data (for example, conversion of magnetic field vectors to useful coordinate systems using the spacecraft attitude data). The Science Center attempts to facilitate these efforts within its resources, especially when high-level processing involves multiple instrument teams. For example, much of the anisotropy/flow data for the particle instruments, in particular for the Electron, Proton, and Alpha-particle Monitor (EPAM), will be computed in terms of the direction of the magnetic field. Thus the EPAM team will need high level results from the MAG team to do high level EPAM analysis. The Science Center can facilitate data sharing and communications with its substantial data storage capabilities and its data formatting experience. Another example is the high level processing for the Cosmic Ray Isotope Spectrometer, CRIS. Four institutions are involved in this processing, each contributing expertise and experience in a different sub-assembly of this very complex instrument. Communications and iteration of the data processing are being facilitated by the Science Center for this team.
Each instrument team is required to deliver level two data back to the Science Center, which will then make the data available to the other instrument teams, the space science community (as required by NASA), and the NSSDC for long term archiving. Delivery of level two data back to the Science Center is expected to begin about three months after the spacecraft enters orbit about the L1 Lagrangian point. Thereafter, roughly a two month lag time is expected between receipt of level one data by the instrument teams and delivery of level two data back to the Science Center. However, these delivery schedules may require revision if instrument checkout and debugging take longer than expected. In addition, the level two dataset is expected to be evolutionary, in the sense that an instrument team may enhance their level two data with additional products in the future, as the sophistication of their analysis increases.
Access ACE Level 2 data.
Ancillary data is data provided by various sources in addition to what is
telemetered from the spacecraft. This includes
attitude and position solutions from Flight Dynamics
and onboard clock calibration data from the Flight
Operations team. These data are either folded into the Level 1 data at the
Science Center, and/or provided to the instrument teams in addition to the
Level 1 data.
Last Updated: Sep 24, 1998Return to ASC Home Page