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Performance of miniaturized atomic clocks in static laboratory and dynamic flight environments (2020)

Jain, Ankit ; Krawinkel, Thomas ; Schön, Steffen ; [weitere]

Springer Berlin Heidelberg

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Publikationsdatum: 2023-06-16

Beschreibung: Miniaturized atomic clocks with high frequency stability as local oscillators in global navigation satellite system (GNSS) receivers promise to improve real-time kinematic applications. For a number of years, such oscillators are being investigated regarding their overall technical applicability, i.e., transportability, and performance in dynamic environments. The short-term frequency stability of these clocks is usually specified by the manufacturer, being valid for stationary applications. Since the performance of most oscillators is likely degraded in dynamic conditions, various oscillators are tested to find the limits of receiver clock modeling in dynamic cases and consequently derive adequate stochastic models to be used in navigation. We present the performance of three different oscillators (Microsemi MAC SA.35m, Spectratime LCR-900 and Stanford Research Systems SC10) for static and dynamic applications. For the static case, all three oscillators are characterized in terms of their frequency stability at Physikalisch-Technische Bundesanstalt, Germany's national metrology institute. The resulting Allan deviations agree well with the manufacturer's data. Furthermore, a flight experiment was conducted in order to evaluate the performance of the oscillators under dynamic conditions. Here, each oscillator is replacing the internal oscillator of a geodetic-grade GNSS receiver and the stability of the receiver clock biases is determined. The time and frequency offsets of the oscillators are characterized with regard to the flight dynamics recorded by a navigation-grade inertial measurement unit. The results of the experiment show that the frequency stability of each oscillator is degraded by about at least one order of magnitude compared to the static case. Also, the two quartz oscillators show a significant g-sensitivity resulting in frequency shifts of − 1.2 × 10−9 and + 1.5 × 10−9, respectively, while the rubidium clocks are less sensitive, thus enabling receiver clock modeling and strengthening of the navigation performance even in high dynamics.

Beschreibung: Bundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360

Beschreibung: Gottfried Wilhelm Leibniz Universität Hannover (1038)

Schlagwort(e): ddc:526 ; Allan variance ; Miniaturized atomic clocks ; Frequency stability ; Flight navigation ; GNSS

Sprache: Englisch

Materialart: doc-type:article

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Using quantum optical sensors for determining the Earth’s gravity field from space (2020)

Müller, Jürgen ; Wu, Hu ; Müller, Jürgen; Institut für Erdmessung (IfE), Leibniz Universität Hannover, Hannover, Germany ; [weitere]

Springer Berlin Heidelberg

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Publikationsdatum: 2023-07-03

Beschreibung: Quantum optical technology provides an opportunity to develop new kinds of gravity sensors and to enable novel measurement concepts for gravimetry. Two candidates are considered in this study: the cold atom interferometry (CAI) gradiometer and optical clocks. Both sensors show a high sensitivity and long-term stability. They are assumed on board of a low-orbit satellite like gravity field and steady-state ocean circulation explorer (GOCE) and gravity recovery and climate experiment (GRACE) to determine the Earth’s gravity field. Their individual contributions were assessed through closed-loop simulations which rigorously mapped the sensors’ sensitivities to the gravity field coefficients. Clocks, which can directly obtain the gravity potential (differences) through frequency comparison, show a high sensitivity to the very long-wavelength gravity field. In the GRACE orbit, clocks with an uncertainty level of 1.0 × 10−18 are capable to retrieve temporal gravity signals below degree 12, while 1.0 × 10−17 clocks are useful for detecting the signals of degree 2 only. However, it poses challenges for clocks to achieve such uncertainties in a short time. In space, the CAI gradiometer is expected to have its ultimate sensitivity and a remarkable stability over a long time (measurements are precise down to very low frequencies). The three diagonal gravity gradients can properly be measured by CAI gradiometry with a same noise level of 5.0 mE/√Hz. They can potentially lead to a 2–5 times better solution of the static gravity field than that of GOCE above degree and order 50, where the GOCE solution is mainly dominated by the gradient measurements. In the lower degree part, benefits from CAI gradiometry are still visible, but there, solutions from GRACE-like missions are superior.

Beschreibung: Deutsche Forschungsgemeinschaft

Beschreibung: http://icgem.gfz-potsdam.de/tom_longtime

Beschreibung: https://earth.esa.int/web/guest/-/goce-data-access-7219

Beschreibung: ftp://podaac.jpl.nasa.gov/allData/grace/L1B/JPL/

Schlagwort(e): ddc:526 ; Quantum optical sensors ; Optical clocks ; Relativistic geodesy ; Atomic gradiometry ; Gravity field