PEACE moments Andrew Lahiff 29 November 2004 10 January 2005 24 January 2005
peacemoments - summary • Cluster & Double Star PEACE moments: number density, velocity, pressure, heat flow vector, temperature • GSE or B-field aligned coordinate systems • any distribution, any sensor combination • S/C potential corrections • plain ASCII, CEF & CDF output files • if you run it without thinking, i.e. looking at spectrograms, your results will probably be wrong - more on this later…
peacemoments - GUI There are 3 pages: • basic • S/C potential • integration Note: there are help bubbles
peacemoments - GUI There are 3 pages: • basic • S/C potential • integration
peacemoments - GUI There are 3 pages: • basic • S/C potential • integration
peacemoments - recent changes • v1.2 & below: - called exportIDFS, then Qtran: cdf qft read into peacemoments - temporary files were ASCII - this was very slow • now peacemoments can read data directly from the IDFS archive; temporary files are binary - this is much faster
peacemoments • written in C/C++; GUI in Perl/Tk. Needs: - SDDAS - Qtran for CDF output files - gnuplot for generating plots • the latest versions use • IDFS libraries (not in standard SDDAS installation) • “cIDFSSource” code from Joey Mukherjee (SwRI) to promote & read data from the database • available as an executable for Linux, Solaris & Mac OS X
peacemoments LEEA 3D velocity distribution function HEEA 3D velocity distribution function sweep mode, sun pulse times EFW PP potential GSE spin-axis angles FGM PP B-field vector .mom file moments .mom files gzipped and stored - used next time you calculate moments for the same time period (faster than getting data from database). IDFS routines - promotion & reading data from the IDFS archive
PEACE - distributions • 3D distributions: 3DR, 3DXP, 3DXE, 3DF; 2D: SPINPAD • 3DF - highest resolution • 15 degree polar res. • 22.5 degree azimuth res. • Double Star only has 3DF • SPINPAD determined on • the ground from PAD data LAR: Low Angular Resoution MAR: Medium Angular Resolution HAR: High Angular Resolution
peacemoments - distributions • SPINPAD • 3DR • 3DF • 3DX1P, 3DX1E, 3DX1 • 3DX1P + 3DX2P • 3DX1P + 3DR • 3DX1E + 3DR • also PEACE onboard (MOMS_L2), HIA PP, CODIF PP, WHISPER PP
peacemoments - sensor combinations • 1-sensor: L1L2B, TH1H2, H1H2, L1L2 • 2-sensor: TL1L2B, TH1H2B, TL1L2, H1H2B • normally use either TL1L2B or L1L2B (HEEA more likely to be saturated than LEEA) usually like this (but not always)
Double Star - sweep option 1 26 keV 1 keV 34 eV 1 eV Spin 1,3,5,7,… Spin 2,4,6,8,…
Double Star - alternating sweeps 26 keV 1 keV 34 eV 1 eV Spin 1,3,5,7,… Spin 2,4,6,8,…
Double Star - alternating sweeps Top moments covering full energy range - time resolution 8-seconds Can have similar “sensor combinations” to Cluster, e.g. TL1L2B, L1L2, … H Overlap L Bottom
Double Star - sensor combinations • use TL1L2B for alternating sweep mode • don’t use TH1H2B (peacemoments won’t actually let you) - frequently the overlap part of the ”high sweep preset” sweeps aren’t transmitted “H1H2” doesn’t exist
timetags • 3 options: • PEACE interval averaged • PEACE sunpulse • CSDS interval averaged (same as PP’s) tPP = tPEACE; sun + tduration (0.5 + (SPOS - 75/16)/1024) For CL, SPOS = 176 or 1200; for DS SPOS = 1104. Note: from v1.41, these timetags also apply to SPINPAD, PEACE onboard, HIA, CODIF & WHISPER
Available Data Listing - Cluster • peacemoments has an “Available Data Listing” command (this uses CPMODES) Example Output: 17th November 2002, CL-2 SPINPAD (LEEA) START: 2002-11-17 00:00:02.549 STOP: 2002-11-17 03:09:03.581 MAR 79 START: 2002-11-17 03:10:03.692 STOP: 2002-11-17 05:11:00.002 MAR 71 SPINPAD (HEEA) START: 2002-11-17 00:00:02.549 STOP: 2002-11-17 03:09:03.581 MAR 91 START: 2002-11-17 03:10:03.692 STOP: 2002-11-17 05:11:00.002 MAR 89 3DR (LEEA) START: 2002-11-17 00:00:02.549 STOP: 2002-11-17 03:09:03.581 3DR (HEEA) START: 2002-11-17 00:00:02.549 STOP: 2002-11-17 03:09:03.581 3DX1 (LEEA) START: 2002-11-17 03:10:03.692 STOP: 2002-11-17 05:09:51.950 [N] Note that each time interval listed has a single sweep mode and sweep preset.
Available Data Listing - Double Star Example Output: 13:20 to 14:20 11th March 2004, TC-1 3DF (HEEA) ---------- START: 2004-03-11 13:20:00.156 STOP: 2004-03-11 14:19:56.630 MAR 91 63
Output: GSE • can select GSE or B-field aligned output • running the program with GSE output gives all of the following moments: * n * v * P * Q * T • plain ASCII, cef & cdf output files
Output: B-field aligned • running the program gives all of the following moments: * n * vpara vperp * Qpara Qperp * Ppara Pperp Pperp1 Pperp2 * Tpara Tperp Tperp1 Tperp2 P rotated so that the z-axis is parallel to the B-field Ppara = Pzz Pperp1 = Pxx Pperp2 = Pyy Pperp = (Pperp1 + Pperp2)/2 Also, T = P/(nk) where, e.g., vpara = B (v.B)/(B.B) vperp = v - vpara B is the FGM PP B-field vector.
Configuration files • can save/load configuration files - stores start & stop times & dates, distribution, sensor combination, S/C number, coordinate system, S/C potential offsets, etc. - preferences are not saved in these files (temperature units, timetag convention, etc) • preferences can be saved • ‘Calculate All in Current Directory’ command - calculates moments using all configuration files in the current directory
running from the command line • peacemoment can be run from the command line - example: peacemoments cl1_25Jan2005.cpm peacemoments_cmd 2002 025 0 0 2002 025 0 0 CL1 3DR TL1L2B ON 1 2 bins NONE CSDS_AVERAGED eV
Restricting the integration ranges • the energy, polar & azimuth integration ranges can be restricted • the lower & upper limits can be different for each spin if necessary - useful if you want to isolate beams • peacemoments reads in the limits from text files
Calculation of moments • moments (relative to the bulk flow) of the velocity distribution function, e.g.: n = ∫ f(v).d3v nu = ∫ f(v).v.d3v pij = m ∫ (vi - ui).(vj - uj).f(v).d3v q = (m/2) ∫ (v - u)2.(v - u).f(v).d3v Integration is over the whole of velocity space.
Calculation of moments • peacemoments calculates moments the same way as the on-board PEACE moments are calculated • standard moments (these do not contain the drift velocity): n = ∫ f(v).d3v nu = ∫ f(v).v.d3v Pij = m ∫ vi .vj . f(v).d3v Q = (m/2) ∫v2. v . f(v).d3v • relative moments: n = n u = u pij = Pij - m n ui uj q = Q - u Tr(P)/2 - u.P + m n u2 u
Calculation of moments • we only have 4 integrals to calculate: MOMENTi =∫ f(v).Mi(v)d3v where M1(v) = 1 M2(v) = v M3ij(v) = mvivj M4(v) = (m/2) v2v Note:
Calculation of moments • we know f(v) for a finite number of energy, polar & azimuth bins • e.g. for 3DR 15 energy bins covering Emin to Emax 6 polar bins covering 0 - 180 degrees 16 azimuth bins covering 0 - 360 degrees • rewrite each integral as a sum over integrals for each bin, e.g.
Calculation of moments • Therefore: becomes where
Calculation of moments • Assume f(, , v) doesn’t vary much inside each bin, therefore becomes • These integrals are carried out analytically. • For more information see Extracting the Bulk Parameters of a Particle Distribution by R.A. Gowen & M.A. Birdseye
Spacecraft potential corrections (1) • when carrying out the energy integration: - ignore any energy bins if VSC > Elower (here VSC is the S/C potential) This removes the photoelectrons. - remaining energy bins are rescaled Elower Elower - VSC Eupper Eupper - VSC This removes the acceleration of the electrons by the S/C potential.
Spacecraft potential corrections (2) • can use EFW PP probe potential, or an ASCII file • two S/C potential offsets - offset 1: difference between EFW probe and spacecraft potential (value from EFW team, typically 1 eV) VSC = VEFW + Voffset 1 - offset 2: for removing photoelectrons above the EFW probe potential (either in bins or eV). Cuts off the integration at a higher energy. • Important to set offset 2 correctly. Usually leave offset1 at default value. Increasing offset 1: Increases VSC • Increasing offset 2: • removes more • energy bins above VSC
User-defined S/C potential file • if there’s no EFW data: • ask someone from Cassini for help • look at spectrogram & determine the potential by eye • if the potential for another S/C exists & is similar: efwgenerate 2002-025 10:00:00 2002-025 12:00:00 CL1 generates an ASCII file containing EFW data
User-defined S/C potential file • making your own S/C potential ASCII file: 2002-01-25 10:00:00 10.0 2002-01-25 12:00:00 15.0 2002-01-25 10:00:00 10.0 2002-01-25 10:59:59 10.0 2002-01-25 11:00:00 15.0 2002-01-25 12:00:00 15.0 V 10:00:00 12:00:00 V 10:00:00 11:00:00 12:00:00
SPINPAD 2-sec resolution moments • when HEEA and LEEA cover the same energy range • this has slightly better time resolution than 3DR!
It’s sometimes easy… (1) • in this example (offset1 = 1 & offset2 = 0), i.e. VSC = VEFW + 1 PEACE HIA
It’s sometimes easy… (3) • in this example (offset1 = 1 & offset2 = 0), i.e. VSC = VEFW + 1 PEACE (TH1H2B) PEACE (TL1L2B) HIA
…but this is more common PEACE HIA
Comparisons with CIS If PEACE and CIS disagree: • CIS might be in the wrong mode (look at the status bytes) • you need to adjust the S/C potential offset to ensure photoelectrons have been removed completely • …
Removing photoelectrons (1) • removal of all photoelectrons (this can’t easily be automated) an example spectrogram for < 100 eV • using just EFW probe potential won’t remove all photoelectrons • offset 2 in peacemoments needs to be used to remove photoelectrons above • the EFW probe potential • need to be careful if there are cold electrons
Removing photoelectrons (2) 1. 2. 3. • may need to use Steve Schwartz’ QTMC software to fill in the gap between the S/C potential and the lowest energy • measured by peace • need to be careful if there are cold electrons
Removing photoelectrons (2) Importance of setting offset 2 correctly • Example 1: green & blue cuvers overlap
Removing photoelectrons (4) Importance of setting offset 2 correctly • Example 2:
Removing photoelectrons (6) • peacemoments can generate SpectroScalar layouts showing PEACE data & EFW potential - meant to encourage users to look at spectrograms! - use “lower band edge” not “centre” energies!
Vz problem in 3D & on-board moments PEACE HIA HEEA usually worse than LEEA CL-1 CL-3
HEEA-LEEA velocity mirror effect Vz problem also can be seen here! PEACE (TH1H2B) PEACE (TL1L2B) HIA
HEEA saturation • sometimes HEEA can be saturated - use TL1L2B instead of TH1H2B - use L1L2B instead of TH1H2(if LEEA & HEEA cover same energy range) HEEA LEEA
PEACE secondary electrons • need to work out what to do about them…