======================================================================= IMP-8 EPE Data Files ======================================================================= These files contain data from the Energetic Particles Experiment (EPE) on the IMP-8 spacecraft. Each file contains 5.5-minute (330-second) averaged data for one of five EPE channels, designated L1, L2, L7, L8, or F. See descriptions under subheading EPE Instrument on IMP-8 Charged Particle Measurement Experiment (CPME) & Energetic Particle Experiment (EPE) home page. Last Changed: 09-Feb-98 (RBD) ======================================================================= ---------------------------------- I. IMP-8 EPE Data Sampling: ---------------------------------- The IMP-8 spacecraft spin period is approx. 2.64 seconds. Counts for channels L1, L2, L7, L8, and F are collected in 16 sectors during one 2.64 second spin, once every 20.48 seconds. During this sampling spin, each sector is sampled for approx. 2.64/16 = 0.165 seconds. During 5.5 minutes (330 seconds), the spacecraft spins approx. 16 times. Thus, in principle, over 5.5 minutes, the maximum sampling time for each sector is approx. 2.64 seconds, and the maximum sampling time summed over all 16 sectors is 42.24 seconds. However, in practice, this sampling time may be reduced or eliminated altogether due to missing data, telemetry gaps, data that has been flagged as bad by the processing software, etc. As a result, it is not unusual for the 5.5-minute averaged data sets to be missing one or more consecutive points every so often. ---------------------------------- II. EPE Count Rate Calculation: ---------------------------------- The count rate for each of the 16 sectors of a given channel is calculated by dividing the total number of counts during the total sampling time by the sampling time. For example, if sector 5 of channel L2 registers N = 230 counts during the time T = 2.64 seconds (i.e., assuming complete data sampling during 5.5-minutes), the count rate is R = N/T = (230 counts)/(2.64 seconds) = 87.1 counts/second, and the statistical uncertainty R_unc (1 standard deviation) is R_unc = R/sqrt(N) = (87.1 counts/second)/15.2 = 5.73 counts/second. The sector-averaged count rate and associated uncertainty are calculated similarly, using N and T as summed over 16 sectors. ---------------------------------- III. EPE Flux Calculation: ---------------------------------- The flux F is calculated by dividing the count rate R by the detector geometric factor G. For channel L2, G = 0.011 cm^2-ster, so in the above example, F = R/G = 87.1/0.011 = 7.92e03 counts/(cm^2-sec-ster), and the corresponding flux uncertainty F_unc is F_unc = R_unc/G = 5.22e02 counts/(cm^2-sec-ster). Note: Due to the relatively large energy width of the channels, we have not calculated the differential-in-energy fluxes. One can do so by simply dividing the fluxes as provided in our files by the difference between the upper and lower passband energies of the particular channel of interest. For example, for L2, one would divide by (0.80 MeV - 0.22 MeV) = 0.58 MeV, and the flux would have units of counts/(cm^2-sec-ster-MeV). ---------------------------------- IV. EPE Channel Parameters: ---------------------------------- ----------------------------------------------------------------------- Channel Energy (MeV) Species/Charge No. Sectors G (cm^2-ster) ----------------------------------------------------------------------- L1 0.050 - 0.22 Ions/Z>=1 16 1.114e-02 L2 0.22 - 0.80 Ions/Z>=1 16 1.114e-02 L7 0.03 - 0.10 Electrons 16 1.5e-02 L7 0.10 - 0.20 Electrons 16 9.0e-03 F > 0.015 Ions & Electrons 16 3.21e-02 ----------------------------------------------------------------------- ---------------------------------- V. Record description ---------------------------------- Each file contains fluxes for one of channels L1, L2, L7, L8, or F. X designates the particular channel name. Times given are the beginning of the averaging interval. Fluxes are in units of counts/(cm^2-sec-ster). Each record consists of 42 items, as described in the table below. Notes: (1) Data values of -99.00 denote missing or bad data. (2) Data values of 0.00 denote true zeros (i.e., zero counts during nonzero accumulation time). ----------------------------------------------------------------------- Column Name Description ----------------------------------------------------------------------- 1 year 4-digit year 2 doy day of year (1-365 or 366) 3 hr hour of day (0-23) 4 mn minute of hour (1-59) 5 sc second of hour (1-59) 6 dec_year decimal year = year + [(doy-1) + hr/24 + mn/1440 + sc/86400]/(365 or 366) 7 dec_doy decimal doy = doy + hr/24 + mn/1440 + sc/86400 8 dec_hr decimal hour = hr + mn/60 + sc/3600 9 X_sav_fx channel X sector-averaged flux (SEE NOTE BELOW)* 10 X_sav_fxu channel X sector-averaged flux uncertainty 11 X_s1_fx channel X, sector 1 flux 12 X_s1_fxu channel X, sector 1 flux uncertainty 13 X_s2_fx channel X, sector 2 flux 14 X_s2_fxu channel X, sector 2 flux uncertainty 15 X_s3_fx channel X, sector 3 flux 16 X_s3_fxu channel X, sector 3 flux uncertainty 17 X_s4_fx channel X, sector 4 flux 18 X_s4_fxu channel X, sector 4 flux uncertainty 19 X_s5_fx channel X, sector 5 flux 20 X_s5_fxu channel X, sector 5 flux uncertainty 21 X_s6_fx channel X, sector 6 flux 22 X_s6_fxu channel X, sector 6 flux uncertainty 23 X_s7_fx channel X, sector 7 flux 24 X_s7_fxu channel X, sector 7 flux uncertainty 25 X_s8_fx channel X, sector 8 flux 26 X_s8_fxu channel X, sector 8 flux uncertainty 27 X_s9_fx channel X, sector 9 flux 28 X_s9_fxu channel X, sector 9 flux uncertainty 29 X_s10_fx channel X, sector 10 flux 30 X_s10_fxu channel X, sector 10 flux uncertainty 31 X_s11_fx channel X, sector 11 flux 32 X_s11_fxu channel X, sector 11 flux uncertainty 33 X_s12_fx channel X, sector 12 flux 34 X_s12_fxu channel X, sector 12 flux uncertainty 35 X_s13_fx channel X, sector 13 flux 36 X_s13_fxu channel X, sector 13 flux uncertainty 37 X_s14_fx channel X, sector 14 flux 38 X_s14_fxu channel X, sector 14 flux uncertainty 39 X_s15_fx channel X, sector 15 flux 40 X_s15_fxu channel X, sector 15 flux uncertainty 41 X_s16_fx channel X, sector 16 flux 42 X_s16_fxu channel X, sector 16 flux uncertainty ----------------------------------------------------------------------- *IMPORTANT NOTE TO USERS: Due to solar photon contamination, some sectors of channels L1, L2, L7, L8, and F may register abnormally high counts. Some sectors show consistent photon contamination, and so can be eliminated from the sector-averaged fluxes. For example, sectors 9 and 10 are not included in the sector-averaged flux of channel L1, and sectors 8, 9, 10, and 11 are not included in the sector-averaged flux of channel L7. However, some other sectors suffer sporadic contamination by solar photons, and no attempt has been made to eliminate these sectors from the sector-averaged fluxes. USERS ARE CAUTIONED TO EXAMINE CAREFULLY THE INDIVIDUAL SECTORS OF A GIVEN CHANNEL BEFORE DRAWING ANY CONCLUSIONS BASED ON LARGE AND RAPID VARIATIONS IN THE SECTOR-AVERAGED FLUXES OF A GIVEN CHANNEL. =======================================================================