Minimize ASM

Absolute Scalar Magnetometer (ASM)

Figure 2: ASM sensor

ASM sensor

The Absolute Scalar Magnetometer (ASM) measures the magnetic field intensity at the tip of the boom. The ASM is an absolute instrument, i.e. it is not subject to changes of its intrinsic parameters over time. It uses the PPS as the absolute, external reference. [AD-6] contains descriptions of the ASM intrinsic processing algorithms for both the nominal scalar mode and the experimental vector mode. Both modes generate scalar (magnetic field intensity) data; the processing of these is described in this chapter, including the system level algorithms for stray field correction. Vector data from the ASM vector mode (as well as burst mode data) are only provided as Level 1a data (the ASMXAUX_1B Level 1b Product contains additional data suited for the Level 1a ASM vector data).

ASM Algorithm Overview

The overall processing is sketched in the Figure below. First, the raw output (Level 1a.ASM. Sci.E, rate: 1 Hz, timestamps t0,ASM) from the ASM is converted to physical units (nT), corrected for the Bloch-Siegert effect, and corrected for delays in timestamps (from t0,ASM to tASM). This constitutes the Level 1bInst.ASM data, the ASM instrument Level 1b scalar product containing the perturbated magnetic field intensity measurements at corrected time instants, tASM. Note: this includes stray fields from the ASM itself.

Then outlier detection and/or rejection is performed. Followed by corrections for magnetic disturbances (stray fields) of the ASM itself, of the VFM, and of the rest of the spacecraft. These disturbances need to be filtered according to the intrinsic filter of the ASM instrument (see [AD-7] for a detailed description of ASM processing). This constitutes the fully calibrated and corrected scalar magnetic measurements, FASM, at instrument time instants (tASM). These data are then adjusted for the group delay of the ASM intrinsic filter, i.e. the measurements are shifted in time from tASM to tout,ASM.

Finally, these data are interpolated to yield the scalar elements of the Level 1b.Mag-L product at UTC seconds. The interpolation process also bridges small gaps (a few samples) in the ASM data stream typically caused by missing telemetry (missing ISP) or outlier rejection.

Figure 3: ASM processing overview

ASM processing overview

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