In-orbit results of the Coupled Dark State Magnetometer aboard the China Seismo-Electromagnetic Satellite

The China Seismo-Electromagnetic Satellite (CSES) was launched in February 2018 into a polar, sun-synchronous, low Earth orbit. It provides the first demonstration of the Coupled Dark State Magnetometer (CDSM) measurement principle in space. The CDSM is an optical scalar magnetometer based on the coherent population trapping (CPT) effect and measures the scalar field with the lowest absolute error aboard CSES. Therefore, it serves as the reference instrument for the measurements done by the fluxgate sensors within the High Precision Magnetometer instrument package. In this paper several correction steps are discussed in order to improve the accuracy of the CDSM data. This includes the extraction of valid 1 Hz data, the application of the sensor heading characteristic, the handling of discontinuities, which occur when switching between the CPT resonance superpositions, and the removal of fluxgate and satellite interferences. The in-orbit performance is compared to the Absolute Scalar Magnetometer aboard the Swarm satellite Bravo via the CHAOS magnetic field model. Additionally, an uncertainty of the magnetic field measurement is derived from unexpected parametric changes of the CDSM in orbit in combination with performance measurements on the ground.

In-orbit results of the Coupled Dark State Magnetometer aboard the China Seismo-Electromagnetic Satellite

The China Seismo-Electromagnetic Satellite (CSES) was launched in February 2018 into a polar, sun-synchronous, low Earth orbit. It provides the first demonstration of the Coupled Dark State Magnetometer (CDSM) measurement principle in space. The CDSM is an optical scalar magnetometer based on the Coherent Population Trapping (CPT) effect and measures the scalar field with the lowest absolute error aboard CSES. Therefore, it serves as the reference instrument for the measurements done by the fluxgate sensors within the High Precision Magnetometer instrument package. In this paper several correction steps are discussed in order to improve the accuracy of the CDSM data. This includes the extraction of valid 1 Hz data, the application of the sensor heading characteristic, the handling of discontinuities at CPT resonance transitions as well as the removal of fluxgate and satellite interferences. The in-orbit performance is compared to the Absolute Scalar Magnetometer aboard the SWARM satellite Bravo via the CHAOS-6 magnetic field model. Additionally, an uncertainty of the magnetic field measurement is derived from unexpected parametric changes of the CDSM in orbit in combination with performance measurements on ground.

Gravitational lenses and the inhomogeneous universe

The theory of static gravitatonal lenses is discussed using the optical scalar formalism and the ray-bending approximation to this formalism. The advantages of each approach are discussed, with particular emphasis on the use of the bending approximation for discretely observable lenses, say multiply imaged quasars, and the optical scalar equations for cumulative effects of inhomogeneities for distant objects in the universe.The effect of a locally lumpy distribution on the past null cone of a typical observer is discussed. This is of particular interest in deciding the limits to which one can hope to do cosmology through the use of optical and other telescopes. The optical-scalar-equation driving terms can be replaced by appropriately defined mean driving terms for subsets of observable objects, and coupled with corresponding probabilities, these calculations can yield estimates of the "thickness" of the observer's past null cone as a function of the red shift. This imposes a limit on the use of standard observations in determining the structure of the universe, simply owing to the "fuzzy" structure of the perceived past null cone.