Climate studies require long data records extending the lifetime of a single remote sensing satellite mission. Precise satellite altimetry exploring global and regional evolution of the sea level has ...now completed a two decade data record. A consistent long-term data record has to be constructed from a sequence of different, partly overlapping altimeter systems which have to be carefully cross-calibrated. This cross-calibration is realized globally by adjusting an extremely large set of single- and dual-satellite crossover differences performed between all contemporaneous altimeter systems. The total set of crossover differences creates a highly redundant network and enables a robust estimate of radial errors with a dense and rather complete sampling for all altimeter systems analyzed. An iterative variance component estimation is applied to obtain an objective relative weighting between altimeter systems with different performance. The final time series of radial errors is taken to estimate (for each of the altimeter systems) an empirical auto-covariance function. Moreover, the radial errors capture relative range biases and indicate systematic variations in the geo-centering of altimeter satellite orbits. The procedure has the potential to estimate for all altimeter systems the geographically correlated mean errors which is not at all visible in single-satellite crossover differences but maps directly to estimates of the mean sea surface.
In this paper, combline substrate integrated waveguide (SIW) filters using electric and magnetic couplings are thoroughly studied. Thus, a negative coupling scheme consisting on an open-ended ...coplanar probe is proposed and analyzed in detail. Several in-line 3-pole filters at C-band are designed, manufactured and measured showing how the presented approach can be used for implementing direct couplings while enabling an important size reduction and improved spurious-free band compared to conventional magnetic irises. A fully-packaged quasi-elliptic 4-pole filter is also designed at 5.75 GHz showing how the negative coupling structure can be used for introducing transmission zeros by means of cross-couplings between non-adjacent resonators. Finally, average and peak power handling capabilities of these filters have been also analyzed from a multiphysics point of view. Measured results validate the theoretical predictions confirming that combline SIW filters can handle significant levels of continuous and peak power, providing at the same time easy integration, compact size and advanced filtering responses.
The TICON (TIdal CONstants) dataset contains harmonic constants of 40 tidal constituents computed for 1,145 tide gauges distributed globally. The tidal estimations are based on publicly available sea ...level records of the second version of the Global Extreme Sea Level Analysis (GESLA) project and were derived through a least squares‐based harmonic analysis on the single time series. A preliminary screening was performed on all records to exclude doubtful observations. Only the records containing more than 70% of valid measurements were processed, that correspond to 89.7% of the total 1,276 original public GESLA records. The results are stored in a text file, and include additional information on the position of the stations, the starting and ending years of the analysed record, the estimated error of the fit, a code that corresponds to the source of the record and additional information on the single time series. In ocean tide models, data from in situ stations are used for validation purposes, and TICON is a useful and easy‐to‐handle data set that allows the users to select the records according to different criteria most suitable for their purposes. The data are provided with DOI identification in the PANGAEA repository.
Since the launch of the first altimetry satellites, ocean tide models have been improved dramatically for deep and shallow waters. However, issues are still found for areas of great interest for ...climate change investigations: the coastal regions. The purpose of this study is to analyze the influence of the ALES coastal retracker on tide modeling in these regions with respect to a standard open ocean retracker. The approach used to compute the tidal constituents is an updated and along-track version of the Empirical Ocean Tide model developed at DGFI-TUM. The major constituents are derived from a least-square harmonic analysis of sea level residuals based on the FES2014 tide model. The results obtained with ALES are compared with the ones estimated with the standard product. A lower fitting error is found for the ALES solution, especially for distances closer than 20 km from the coast. In comparison with in situ data, the root mean squared error computed with ALES can reach an improvement larger than 2 cm at single locations, with an average impact of over 10% for tidal constituents K 2 , O 1 , and P 1 . For Q 1 , the improvement is over 25%. It was observed that improvements to the root-sum squares are larger for distances closer than 10 km to the coast, independently on the sea state. Finally, the performance of the solutions changes according to the satellite’s flight direction: for tracks approaching land from open ocean root mean square differences larger than 1 cm are found in comparison to tracks going from land to ocean.
SARAL uses the same orbit as ERS and Envisat and can be used to extend inland water height time series derived from these missions. This article investigates the potential of SARAL for this ...application over the Great Lakes and the Amazon basin. SARAL/AltiKa is the first altimeter using Ka-band that is rarely influenced by ionospheric effects but susceptible for atmospheric water. Our investigations show clear waveform disruptions for SARAL due to precipitation. It is demonstrated that the quality of water heights improved when using alternative retracker products, for example, the ice-1 product. The improvement depends on the weather and yields up to 3.8 cm for wet conditions. The advantage of the smaller footprint of SARAL is demonstrated for land-water transitions where SARAL provides better water level heights up to 6 km to the lakeshore whereas Envisat is limited to about 11 km. SARAL provides also more reliable water level heights for narrow Amazon rivers than Envisat. Furthermore, the hooking effect is decreased for SARAL. Comparing water level time series of SARAL-only, Envisat-only, and multi-mission with in-situ data demonstrates that SARAL has the potential to extend Envisat long-term time series and to decrease the RMS by about 10% for large lakes and 40% for selected rivers.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This paper demonstrates the use of a ceramic stereolithography-based additive manufacturing process to fabricate higher-order mode dielectric resonators. In this work, dielectric resonators with ...concentric rings around a combline rod structure are 3D-printed using alumina. The integration of the concentric rings for the use of the TE112 mode allows for a more compact cavity structure and a higher unloaded quality factor when compared to a simple dielectric combline resonator with a similar S-parameter response. The achievable improvements in quality factor for the TE112-mode resonators utilising concentric rings are compared through simulations and experimental results. The measured results demonstrate an increased average in the unloaded quality factor of <inline-formula> <tex-math notation="LaTeX">\text{Q}_{u}\approx ~2172 </tex-math></inline-formula> which is approximately 44%. Additionally, the application of the 3D-printed resonators is further demonstrated in a TE112 singlet, doublet, and dual-mode filter configuration.
The trend in transmitter systems is to move the digital domain closer toward the antenna using digital modulators and drivers to reduce circuit complexity and to save power. One promising approach is ...the use of RF pulse width modulation (RF PWM). Unfortunately purely digital discrete time RF PWM suffers from aliasing problems which limit the achievable resolution. For a 40 MHz bandwidth signal at 2.6 GHz carrier frequency for example the achievable signal quality is limited to ~ 43 dBc. This paper describes the root cause of this effect, an error in the determination of the cross points, due to the sampled nature of the signal and proposes a method to compensate for it. It is shown that by interpolating the signal and estimating the cross points the signal quality can be significantly improved. The interpolation is simplified by interpolating the decomposed outphasing signals instead of the full signal. This has the advantage that a constant instead of a phase modulated reference function can be used. It is shown that by simple cross point estimation the signal quality can already be improved to 65 dBc. When either considering a second modulator or when using a delta sigma like noise shaping architecture the signal quality can be further enhanced to 75 dBc.
A model of diurnal and semi-diurnal variations in Earth rotation parameters (ERP) is constructed based on altimetry-measured tidal heights from a multi-mission empirical ocean tide solution. ...Barotropic currents contributing to relative angular momentum changes are estimated for nine major tides in a global inversion algorithm that solves the two-dimensional momentum equations on a regular 0.5
∘
grid with a heavily weighted continuity constraint. The influence of 19 minor tides is accounted for by linear admittance interpolation of ocean tidal angular momentum, although the assumption of smooth admittance variations with frequency appears to be a doubtful concept for semi-diurnal mass terms in particular. A validation of the newly derived model based on post-fit corrections to polar motion and universal time (
Δ
UT1) from the analysis of Very Long Baseline Interferometry (VLBI) observations shows a variance reduction for semi-diurnal
Δ
UT1 residuals that is significant at the 0.05 level with respect to the conventional ERP model. Improvements are also evident for the explicitly modeled K
1
, Q
1
, and K
2
tides in individual ERP components, but large residuals of more than 15
μ
as remain at the principal lunar frequencies of O
1
and M
2
. We attribute these shortcomings to uncertainties in the inverted relative angular momentum changes and, to a minor extent, to violation of mass conservation in the empirical ocean tide solution. Further dedicated hydrodynamic modeling efforts of these anomalous constituents are required to meet the accuracy standards of modern space geodesy.
This study proposes a linear approach for propagating uncertainties in the multiline thru-reflect-line (TRL) calibration method for vector network analyzers. The multiline TRL formulation we are ...proposing applies the law of uncertainty propagation as outlined in the ISO Guide to the Expression of Uncertainty in Measurement (GUM) to both measurement and model uncertainties. In addition, we conducted a Monte Carlo analysis using a combination of measured and synthetic data to model various uncertainties, such as measurement noise, reflect asymmetry, line mismatch, and line length offset. The results of our linear uncertainty formulation demonstrate agreement with the Monte Carlo analysis and provide a more efficient means of assessing the uncertainty budget of the multiline TRL calibration.
This brief presents a fully passive RF wake-up receiver (WuRX) fabricated in a 130 nm CMOS process with a matched small loop antenna. The WuRX consists of a high-sensitivity RF energy harvester that ...supplies the circuitry necessary for passive WuRX functionality. The circuit consists of an on-chip voltage reference, current reference, power-on reset, low-dropout regulator, relaxation oscillator, envelope detector, comparator, and a digital processor. The WuRX supports an input bitrate of 26 kbps and has a user-defined 12-bit wake-up pattern. Measurements at 830 MHz reveal a wake-up sensitivity of -30.7 dBm and a 1 V harvested output sensitivity of -31 dBm. The RF-powered fully-passive WuRX paves the way for autonomous batteryless sensor nodes.
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