Subject: Data Format Description for the IMP-J MAG15 Datatype in NDADS From: J. H. King Organization: National Space Science Data Center Entered as B46481 in NSSDC's Technical Reference File, January 12, 1998. Corrected Word 22 day number definition Jan. 10, 2001. ============================================================================ Data Format for Tri-Axis Magnetometer 15 Second Magnetic Field Vectors and footnotes. Note that this format applies to MAG15, both IBM-binary version before July 21, 1991, and to VMS-binary version thereafter. Logical record size = 272 bytes ITEM Description (Type)(Size) Units Notes ============================================================================ 1* Year I*4 Last two digits only 2* Day-of-year I*4 days January 1 = 0 (before 1992) January 1 = 1 (1992 - ) 3* Milliseconds of day I*4 millisec Elapsed Millisec. 4* Data Quality Flag I*4 5* Orbit number I*4 6* Bit Rate Flag I*4 7* Pseudo Sequence Count I*4 8* Fill = Zero (0) I*4 9* Housekeeping Data I*4 See footnote 1 10 Field Magnitude (F1) R*4 nT F1 = 1/n sum[F_i] for i=1,N (Averaged over 15.36 where F_i is seconds) computed over 1.28 seconds 11 Field Magnitude (F2) R*4 nT See footnote 2 12 Field Latitude R*4 degrees -90 degs < theta < +90 degs. (or inclination theta) (averaged over 15.36 seconds) See footnote 4 13 Field Longitude R*4 degrees 0 degs < phi < 360 degs (or azimuthal angle) phi (averaged over 15.36 See footnote 4 seconds) 14 Variance XX from Avgs R*4 nT^2 Variance Matrix over 15.36sec. 15 Variance YY from Avgs R*4 nT^2 |V_xx | 16 Variance ZZ from Avgs R*4 nT^2 |V_yx V_yy | 17 Variance YX from Avgs R*4 nT^2 |V_zx V_zy V_zz | 18 Variance ZX from Avgs R*4 nT^2 See footnote 3 19 Variance ZY from Avgs R*4 nT^2 20 N I*4 Number of seqs. over which stats. were computed. N_max = 384 21 ND I*4 Number of detail points over which stats. were computed. ND_max = 384 22 Trajectory (day-of- I*4 day January 1 = 0 (all years) year) 23 Trajectory (millisec I*4 millisec of day) 24 Geomagnetic Latitude R*4 degrees of spacecraft 25 Geomagnetic Longitude R*4 degrees of spacecraft 26 X Geocentric SE pos. R*4 kilometers of spacecraft 27 Y Geocentric SE pos. R*4 kilometers of spacecraft 28 Z geocentric SE pos. R*4 kilometers of spacecraft 29 Radial Distance R*4 kilometers 30 Y Solar MagnetosphericR*4 kilometers position of spacecraft 31 Z Solar MagnetosphericR*4 kilometers position of spacecraft 32 Geomagnetic Latitude R*4 degrees of Sun 33 Geomagnetic Longitude R*4 degrees of Sun 34 X Moon's Posit. in R*4 kilometers geomagnetic SE 35 Y Moon's Posit. in R*4 kilometers geomagnetic SE 36 Z Moon's Posit. in R*4 kilometers geomagnetic SE 37 Items 37 through 45 R*4 Element given in Rotation Matrix following order: from SE to SM 1st row, 1st col. 38 R*4 1st row, 2nd col. 39 R*4 1st row, 3rd col. 40 R*4 2nd row, 1st col. 41 R*4 2nd row, 2nd col. 42 R*4 2nd row, 3rd col. 43 R*4 3rd row, 1st col. 44 R*4 3rd row, 2nd col. 45 R*4 3rd row, 3rd col. 46 Items 46 through 54 R*4 Element given in Rotation Matrix following order: from CI to SE 1st row, 1st col. CI=Celestial Inertial 47 R*4 1st row, 2nd col. 48 R*4 1st row, 3rd col. 49 R*4 2nd row, 1st col. 50 R*4 2nd row, 2nd col. 51 R*4 2nd row, 3rd col. 52 R*4 3rd row, 1st col. 53 R*4 3rd row, 2nd col. 54 R*4 3rd row, 3rd col. 55 Month I*4 VMS version only unused in IBM version 56 Day of Month I*4 VMS version only unused in IBM version 57 Angle of RA of Spin R*4 degrees vector of spacecraft in CI 58 Angle of dec. of Spin R*4 degrees vector of spacecraft in CI 59 Field Latitude,theta_SE,R*4 degrees in SE coordinates (avgd. over 15.36 seconds) 60 Field Latitude,theta_SM,R*4 degrees in SM coordinates (avgd. over 15.36 seconds) 61 Field Longitude,phi_SE,R*4 degrees in SE coordinates (avgd. over 15.36 seconds) 62 Field Longitude,phi_SM,R*4 degrees in SM coordinates (avgd. over 15.36 seconds) 63 B_X_SE Avgd. over R*4 nT 15.36 seconds 64 B_Y_SE Avgd. over R*4 nT 15.36 seconds 65 B_Z_SE Avgd. over R*4 nT 15.36 seconds 66 B_X_SM Avgd. over R*4 nT 15.36 seconds 67 B_Y_SM Avgd. over R*4 nT 15.36 seconds 68 B_Z_SM Avgd. over R*4 nT 15.36 seconds * Items 1 - 9 are for the last sequence included in the 15.36 second statistical computation. FOOTNOTES Footnote 1 ---------- 15 14 3 2 1 0 2 2 2 2 2 2 ------------------------------------------------------------------------- | | | | | | | | | | | | | | | | | | | | 1 | 2 | * | * | * | * | * | * | * | * | * | * | 3 | 3 | 4 | 4 | | | | | | | | | | | | | | | | | | | ------------------------------------------------------------------------- * Not used 1) ENCODER A = 0 2) EXPA = 0 ENCODER B = 1 EXPB = 1 3) 10 = NORMAL is identical with 0 DEGREES 01 = FLIPPED is identical with 90 DEGREES 4) 11 = 12 gamma 10 = 36 gamma 01 = 12 gamma 00 = 108 gamma Footnote 2 ---------- F2 = SQRT( (1/N sum[X_i])^2 + (1/N sum[Y_i])^2 + (1/N sum[Z_i])^2) for i=1,N where X_i, Y_i and Z_i are 1.28 seconds average field component values. Footnote 3 ---------- e.g., V_XX = (N sum[X_i^2] - sum[X_i] sum[X_i])/N(N-1) for i=1,N , and V_ZY = (N sum[Z_i Y_i] - sum[Z_i] sum[Y_i])/N(N-1) for i=1,N , etc. Footnote 4 ---------- The quasi-payload coordinate system is spacecraft centered with X_p hat toward the Sun, Z_p hat aligned with the spin axis and positive at or near North-SE (usually within 2 degrees), and (X_p hat) x (Y_p hat) = Z_p hat. =============================================================================