The Magnetic Field Experiment (MAG) consists of twin vector fluxgate magnetometers controlled by a common CPU. The sensors are mounted on booms extending 4.19 meters from the center of the spacecraft at opposite sides along the +/-Y axes of the spacecraft. The instrument returns 6 magnetic field vector measurements each second, divided between the two sensors, with onboard snapshot and FFT buffers to enhance the high-frequency resolution.
For more information about the MAG instrument,
visit the MAG Home
Page, at Bartol Research Institute.
Time Data
All level 2 data records for all ACE instruments contain timing information
in the same format. The format of the timing information is described
here.
MAG level 2 data contains one extra time data item: the spacecraft clock time (32-bit unsigned int), which counts minor frames since the start of the mission.
Interplanetary Magnetic Field Data
MAG level 2 data is organized into 27 day time periods (Bartels Rotations -
roughly one solar rotation period).
For each Bartels Rotation, the level 2 data contains time averages of
the magnetic field data over the following time periods:
Release notes for MAG level 2 data - provided by the MAG instrument team. All users of MAG data should read these notes.
A data value of -999.9 indicates bad or missing data for the given time period.
Magnetic field vectors are given in the RTN and GSE coordinate systems.
For daily and Bartels rotation averages, only Bmag data is valid. For Br, Bt, Bn, Delta, Lambda, Bgse_x, Bgse_y, and Bgse_z, the fill value (-999.9) is output. Individual vector components on timescales longer than 1 hour are considered to be potentially misleading and have questionable value at 1 AU. For this reason, they are not computed. Values of <|B|> may be more useful, but the user is cautioned to examine the dBrms value for these intervals as large values of dBrms may indicate significant changes in the magnetic field during the averaging interval.
Data error is less than 0.1 nT (where nT is nano-Tesla).
The averaged Mag data, which are all float32, are: Br - The r component of the magnetic field vector in the RTN coordinate system in nT Bt - The t component of the magnetic field vector in the RTN coordinate system in nT Bn - The n component of the magnetic field vector in the RTN coordinate system in nT Bmag - The <|B|> magnetic field magnitude in nT Delta - The angle in degrees with 0 at Br/Bt plane + toward Bn (-90 to +90 degrees), i.e. the RTN latitude Lambda - The angle in degrees with 0 at Br and + toward Bt (0 to 360 degrees), i.e. the RTN longitude Bgse_x - The x component of the magnetic field vector in the GSE coordinate system in nT Bgse_y - The y component of the magnetic field vector in the GSE coordinate system in nT Bgse_z - The z component of the magnetic field vector in the GSE coordinate system in nT dBrms - RMS values of underlying high-resolution measurements in nT. This is the rms variation of the vector over the time interval, calculated as follows: 1) calculate the average magnitude of each of the three components of the vector, over the time interval. 2) for each component, average the square of the difference between the measurement and the average 3) add the averages from the three components 4) take the square-root of the result. i.e. dBrms = sqrt(sum_i <( B_i -)^2>) For the 16-second averages, dBrms is calculated using the the highest resolution data (3 vectors/second, from one of the two sensors). For the 4-minute and hourly averages, the 16-second averages are used as input to the calculations. sigma_B - The variance of |B| over the time interval, in nT. i.e. sigma_B = sqrt(<(|B|-<|B|>)^2>). If sigma_B/<|B|> is small, there was little variation during the time period. If sigma_B/<|B|> is large , there was much variation during the time period. sigma_B is only calculated for the 4-minute and hourly averages. It is calculated using the 16-second averages as input.
Quality information about the Mag data, float32 except as noted:
fraction_good
- Fraction of the timing period for which there was data
available for the time period.
N_vectors- (in int32) Number of 16 second vectors that were included
in the average.
The data quality for the period (int32); data of type 2 have been excised,
i.e. replaced with fill data (-999.9):
Quality = 0 Normal data
= 1 Spacecraft Maneuver & subsequent high-nutation period (~4 hr)
= 2 Bad data/missing data
ACE spacecraft position, in
GSE coordinate system (float32):
pos_gse_x - The x-component of the spacecraft position, in GSE, in km. pos_gse_y - The y-component of the spacecraft position, in GSE, in km. pos_gse_z - The z-component of the spacecraft position, in GSE, in km.
Our Email Address: asc@srl.caltech.edu
Last Updated: 11 November, 1998