NSSDCA ID: PSFP-00681
Availability: Archived at NSSDC, accessible from elsewhere
This description was generated automatically using input from the Planetary Data System.
This data set consists of all of the ion moments data generated from the Cassini Plasma Spectrometer (CAPS) ion mass spectrometer singles or time-of-flight uncalibrated data. The data set contains the derived ion moments data as follows: Ion Moments (ION_MOMT) Density, Temperature, Average Flow Speed, Average Flow Velocity Ions included are H+, H2+, and W+ (water group ions: O+, OH+, H2O+) The uncalibrated data were acquired in a mix of CAPS operating modes beginning with the first instrument checkout in January 1999 and containing throughout the Cassini Tour and through the end of prime mission. The data set covers the time period from 1999-004T03:07:47 UT until end of prime mission (July 2008). In addition, it will cover data received during extended missions. Sampling rates were variable and depended upon the downlink capabilities and other activities on-board. For times when CAPS is not producing data due to being turned off or due to communication issues, the data set will not contain data. Additionally, there will be no data during times when the calculations are not possible. ION Moment File Discussion ========== The data provided in this file are the moments of the ion distribution (density, temperature, and flow velocity) derived from measurements from the CAPS/IMS (Ion Mass Spectrometer) [YOUNGETAL2004]. The final adopted geometric factors, efficiencies, and other relevant instrument parameters used to derive these moments are available in the CAPS PDS User's Guide [WILSONETAL2012] and are slightly different than those used in the study of Thomsen et al. [THOMSENETAL2010]. The final values are based on calculations, laboratory calibrations, simulations, and comparison of in-flight data with measurements from other instruments, including CAPS/ELS (Electron Spectrometer [LEWISETAL2008, LEWISETAL2010]) and RPWS (Radio and Plasma Wave Investigation [GURNETTETAL2004]). When the Ion Method Flag is 1, i.e., numerical integration of the Singles (SNG) measurements, the partition of SNG counts into three different species bins (H+, H2+, W+) is based on concurrent measurements of the ion composition available from the Time-of-Flight (TOF) data product from the same instrument (W+ represents the sum of the 'water-group' ion species O+, OH+, H2O+, and H30+). This partition and the numerical integration algorithm are described in detail in Thomsen et al. [THOMSENETAL2010] and Thomsen and Delapp [THOMSENETAL2005]. While the calculation of the moments (n,T,V) is is done independently for each species [THOMSENETAL2010], for the PDS submission we report only a single velocity vector, which is calculated as a mass- and density- weighted average of the velocities derived for the three species: AveV = sum (m_i * n_i * V_i) / sum (m_i * n_i) where i=H+, H2+, W+ (note that the _ indicates that what follows is a subcript) and where m_i and n_i are the ion mass and density of the ith species (m_W+ is taken to be 16, although in practice it makes very little difference whether one takes either extreme, i.e., 16 or 19). This weighting is based on our experience [e.g., THOMSENETAL2010] that the heavy-ion velocities are more reliable when they are available (hence the weighting by m_i), but if they are not well-determined due to low counts, the light-ion values are to be preferred (hence the weighting by n_i). The reported temperatures represent averages of the values perpendicular and parallel to the magnetic field. Because the ion flows within the Saturnian magnetosphere are typically transonic, an accurate measurement of the plasma properties requires that the flow be in the field of view. Analysis of CAPS measurements has determined that the magnetospheric flows typically lie near the corotation direction [e.g., THOMSENETAL2010]. Therefore, the PDS file includes a flag to tell whether or not the corotation direction lies within the CAPS FOV. In addition, the numerical moments algorithm does not work if the spacecraft is rolling or if the instrument is not actuating. Under such conditions, the moments are flagged as 'bad'. Therefore, there are three values for the quality flag: 'Not-bad; corotation direction in FOV', 'Not-bad; corotation direction not in the FOV', and 'Bad (s/c rolling and/or CAPS not actuating)'. Data ==== The data are stored in multiple data files and have been organized in folders, first by higher order data type and then by year. Each file contains a maximum of 24 hours of data. Note that data is included in the file based on the start time, and not the end time of the data. Format of the data files can be found in the CAPS instrument archive specification [FURMANETAL2013]. The format can also be found in the .LBL files in the FM/HIGHERORDER/IONMOMT/YYYY specific directory, co-located with the data. Ancillary Data ============== Ancillary data can be found in the ANC data file provided with the CAPS UNCALIBRATED data set. References ======== [FURMANETAL2005] CAPS standard data products and archive volume software interface specification, Version 1.9, JPL SIS ID: IO-AR-017, Southwest Research Institute, San Antonio, TX 78250, 2005. [ARRIDGEETAL2009] The effect of spacecraft radiation sources on electron moments from the Cassini CAPS electron spectrometer, Planetary and Space Science, 57, 854-869, doi:10.1016/j.pss.2009.02.011, 2009. [GURNETTETAL2004] The Cassini Radio and Plasma Wave Investigation, Space Sci. Rev. 114, 395-463, 2004. [LEWISETAL2008] Derivation of density and temperature from the Cassini Huygens CAPS electron spectrometer, Planetary and Space Science, 56, 901-912, doi: 10.1016/j.pss.2007.12.017, 2008. [LEWISETAL2010] The calibration of the Cassini-Huygens CAPS Electron Spectrometer, Plan. and Space Sci., 58, 427?436, doi:10.1016/j.pss.2009.11.008, 2010. [THOMSENETAL2005] Numerical moments computation for CAPS/IMS, Los Alamos National Laboratory Report LA-UR-05-1542, 2005. [THOMSENETAL2010] Survey of ion plasma parameters in Saturn's magnetosphere, J. Geophys. Res., 115, A10220, doi:10.1029/2010JA015267, 2010. [WILSONETAL2012] PDS User's Guide for Cassini Plasma Spectrometer (CAPS), 2012. [YOUNGETAL2004] Cassini Plasma Spectrometer Investigation, Space Sci. Rev. 114, 1-112, 2004.
These data are available on-line from the Planetary Data System (PDS) at:
https://pds-ppi.igpp.ucla.edu/data/CO-S_SW-CAPS-5-DDR-ION-MOMENTS-V1.0/
Questions and comments about this data collection can be directed to: Dr. Edwin V. Bell, II
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. David T. Young | Data Provider | Southwest Research Institute | dyoung@srwi.edu |
Dr. Judith D. Furman | General Contact | Southwest Research Institute | jfurman@swri.edu |