**Basis for MAG Data Rates**

**Survey:**

The key factors determining the survey data rate for the magnetometer
(MAG) are the number of components needed for determining the magnetic
field direction (3 components) and the need to resolve EMIC waves, and
important radiation belt particle scattering mechanism. To provide good
pitch angle resolution and wave data with some overlap with the Wave
search coil magnetometer, the sampling of MAG will be at 32 samples/s.
This will provide good wave coverage up to about 15 Hz. This corresponds
roughly the hydrogen cyclotron frequency at 3 R~E~ geocentric. To cover
lower altitudes a higher rate is needed. For survey data, this will be
accomplished by transmitting one 0.025-30 Hz spectrogram once every 40
s.

**High Rate:**

To compliment survey rate data, MAG will be sampled at the rate of 64
vecotrs/s in high-rate and burst modes. The two rates are the same for
MAG. This will provide continuous waveform coverage of important low
frequency waves such as EMIC waves down to 2 R~E~ geocentric distance,
covering a frequency range of DC to 30 Hz. This also provides good
overlap with the Waves search coil magnetometer, allowing for good cross
calibration to ensure optimal accuracy of both instruments.

**MAG Measurement Requirements per AO Objectives: Drivers on MAG Data
Rates**

**1.1.a-1**

Quasi-DC 3D magnetic field vectors needed for pitch and first adiabatic
invariant calculations. Sampling at 16 samples per second gives 5 degree
resolution as the payload spins.

**1.1.a-2**

Measuring the magnetic component of EMIC waves requires frequency
response below the 10Hz limit of the Waves instrumentation. Sampling at
32 samples/s will give 15 Hz as an upper cutoff at corresponds to the
hydrogen cyclotron frequency at 3 R~E~ geocentric. Sampling to 64 Hz in
burst mode gives good overlap between experiments and resolves the
hydrogen gyrofrequency down to altitudes just above 2 R~E~ geocentric.

**1.1.b-4**

Measurements of magnetic field vectors with sufficient resolution to
determine characteristics of the injection fronts including structures
within the larger front. Maximum burst rate of 64 samples/s yields 16 ms
resolution.

**1.1.c-1**

Same as 1.1.a-2

**2a-1**

3D magnetic field vectors to characterize EMIC waves with spectra up to
30 Hz every

40 s.

**2a-2**

Same as 1.1.a-2

**3c-1**

Characterization of low frequency waves above 10 Hz. MAG sampled at
either 32 sampels/s (up to 15 Hz) or in burst at 64 samples/s (up to 30
Hz).

**3e-1**

Same as 3c-1

**4.1.b**

Measure 3D magnetic field vectors at up to 64 samples/s to determine
wave modes of importance. This includes overlap with Waves to give
continuous coverage of low-frequency waves.

**4.2.c**

Sames a 4.1.b

**4.3.b**

Measure 3D agnetic fields of the waves and structures which are
efficient at violating the third invariant which are capable of
transporting energetic particles earthward at 32 samples/s.

**5d-2**

Survey B wave properties \\including spectrum. One DC-30 Hz spectrum
every 40 s provides coverage of lwest frequency waves.

**5e-2**

same as 5c-2

**6c-1**

To determine how inner magnetospheric VLF waves are associated with
variations in the ring current and other plasma populations measure 3D
magnetic field vectors 32 samples/s. Burst at 64 samples/s extends the
frequency coverage.

**7e-1**

Determine how substorm injection phenomena affect ring current
development by measuring vector B at 10 samples/s.

**7f-1**

Same as 7e-1

**8b-2**

Measure 3D magnetic field vector from dc to TBD Hz. Sensitivity: 0.05
nT. Absolute accuracy 10 nT; Range 1 nT to 40,000 nT.

**8c**

same as 8b-2

**8d**

same as 8b-2

**Driving Requirements**

(Note: where requirement appears in multiple objectives, only one
objective is cited.)

Number of components: 3D magnetic field - **1.1.a-1**

Frequency Range (EMIC, VLF Hiss, Chorus): DC-15 Hz (nominal); DC-32 Hz
(burst) - **1.1.a-2**

**EMFISIS/MAG Data Rates**

The EMFISIS magnetometer can be sampled at a variety of rates, but we
currently envision only two primary modes of operation.

**Survey Data:**

For routine operations to support both EMFISIS science objectives (with
sufficient sampling to overlap with the Waves search coil magnetometer)
and to provide background field orientation for particle instruments,
the magnetometer will be sampled 32 times per second. Each vector
component requires 16 bits. In addition, EMFISIS will telemeter one
spectrogram of MAG data up to its highest frequency once every 40 s.
This yields:

[Data component Rate (bps)]{.underline}

3 vector components x 32 samples/second 1536

[1 40 frequency spectrogram .covering 0.025-30 Hz 16]{.underline}

TOTAL RAW SURVEY RATE: 1552

TOTAL COMPRESSED SURVEY RATE (50% compression): 1149

Compressed rate corresponds to 37 Mbits/orbit

**High Rate or Burst Data:**

In high rate or burst data rates, the maximum sample rate for the
magnetometer of 64 samples/s is telemetered. This eliminates the need
for spectrograms.

[Data component: Rate (bps)]{.underline}

[3 vector components x 64 samples/second 3072]{.underline}

TOTAL SURVEY RATE: 3072

TOTAL COMPRESSED SURVEY RATE: 2304

Compressed rate corresponds to 75 Mbits/orbit