Doppler Observations Research Articles

High-resolution 3D winds derived from a modified WISSDOM synthesis scheme using multiple Doppler lidars and observations

Abstract. The WISSDOM (Wind Synthesis System using Doppler Measurements) synthesis scheme was developed to derive high-resolution 3-dimensional (3D) winds under clear-air conditions. From this variational-based scheme, detailed wind information was obtained from scanning Doppler lidars, automatic weather stations (AWSs), sounding observations, and local reanalysis datasets (LDAPS, Local Data Assimilation and Prediction System), which were utilized as constraints to minimize the cost function. The objective of this study is to evaluate the performance and accuracy of derived 3D winds from this modified scheme. A strong wind event was selected to demonstrate its performance over complex terrain in Pyeongchang, South Korea. The size of the test domain is 12×12 km2 extended up to 3 km a.m.s.l. (above mean sea level) height with a remarkably high horizontal and vertical resolution of 50 m. The derived winds reveal that reasonable patterns were explored from a control run, as they have significant similarity with the sounding observations. The results of intercomparisons show that the correlation coefficients between derived horizontal winds and sounding observations are 0.97 and 0.87 for u- and v-component winds, respectively, and the averaged bias (root mean square deviation, RMSD) of horizontal winds is between −0.78 and 0.09 (1.77 and 1.65) m s−1. The correlation coefficients between WISSDOM-derived winds and lidar QVP (quasi-vertical profile) are 0.84 and 0.35 for u- and v-component winds, respectively, and the averaged bias (RMSD) of horizontal winds is between 2.83 and 2.26 (3.69 and 2.92) m s−1. The statistical errors also reveal a satisfying performance of the retrieved 3D winds; the median values of wind directions are −5 to 5 (0 to 2.5)∘, the wind speed is approximately −1 to 3 m s−1 (−1 to 0.5 m s−1), and the vertical velocity is −0.2 to 0.6 m s−1 compared with the lidar QVP (sounding observations). A series of sensitivity tests with different weighting coefficients, radius of influence (RI) in interpolation, and various combination of different datasets were also performed. The results indicate that the present setting of the control run is the optimal reference to WISSDOM synthesis in this event and will help verify the impacts against various scenarios and observational references in this area.

Precise Position Estimation Using Smartphone Raw GNSS Data Based on Two-Step Optimization.

This paper presents a high-precision positioning method using raw global navigation satellite system (GNSS) observations from smartphones in the Google smartphone decimeter challenge (GSDC). Compared to commercial GNSS receivers, smartphone GNSS observations are noisy owing to antenna limitations, making it difficult to apply conventional high-precision positioning methods. In addition, it is important to exclude outliers in GSDC because GSDC includes data in environments where GNSS is shielded, such as tunnels and elevated structures. Therefore, this study proposes a smartphone positioning method based on a two-step optimization method, using factor graph optimization (FGO). Here, the velocity and position optimization process are separated and the velocity is first estimated from Doppler observations. Then, the outliers of the velocity estimated by FGO are excluded, while the missing velocity is interpolated. In the next position-optimization step, the velocity estimated in the previous step is adopted as a loose state-to-state constraint and the position is estimated using the time-differenced carrier phase (TDCP), which is more accurate than Doppler, but less available. The final horizontal positioning accuracy was 1.229 m, which was the first place, thus demonstrating the effectiveness of the proposed method.

GNSS Observation Generation from Smartphone Android Location API: Performance of Existing Apps, Issues and Improvement

Precise position information available from smartphones can play an important role in developing new location-based service (LBS) applications. Starting from 2016, and after the release of Nougat version (Version 7) by Google, developers have had access to the GNSS raw measurements through the new application programming interface (API), namely android.location (API level 24). However, the new API does not provide the typical GNSS observations directly (e.g., pseudorange, carrier-phase and Doppler observations) which have to be generated by the users themselves. Although several Apps have been developed for the GNSS observations generation, various data analyses indicate quality concerns, from biases to observation inconsistency in the generated GNSS observations output from those Apps. The quality concerns would subsequently affect GNSS data processing such as cycle slip detection, code smoothing and ultimately positioning performance. In this study, we first investigate algorithms for GNSS observations generation from the android.location API output. We then evaluate the performances of two widely used Apps (Geo++RINEX logger and GnssLogger Apps), as well as our newly developed one (namely UofC CSV2RINEX tool) which converts the CSV file to a Receiver INdependent Exchange (RINEX) file. Positioning performance analysis is also provided which indicates improved positioning accuracy using our newly developed tool. Future work finding out the potential reasons for the identified misbehavior in the generated GNSS observations is recommended; it will require a joint effort with the App developers.

Comprehensive Evaluation of Data-Related Factors on BDS-3 B1I + B2b Real-Time PPP/INS Tightly Coupled Integration

Owing to the developments of satellite-based and network-based real-time satellite precise products, the Precise Point Positioning (PPP) technique has been applied far and wide, especially since the PPP-B2b service was provided by the third-generation BeiDou Navigation Satellite System (BDS-3). However, satellite outages during dynamic application lead to significant degradation of the accuracy and continuity of PPP. A generally used method is integrating PPP with Inertial Measurement Units (IMUs) to enhance positioning performance. Previous works on this topic are usually based on IMU data at a high sampling rate and are mostly implemented in post-processing mode. This paper will carry out a compressive assessment of the impacts of different types of precise satellite products (real-time products from the CAS, DLR, GFZ, WHU, and the final one from GFZ), Doppler observations, and different sampling rates of IMU data on the performance of the tightly coupled integration of the BDS-3 B1I/B2b and the Inertial Navigation System (INS). Results based on a group of on-board experimental data illustrate that (1) the positioning accuracy with products supplied by the CAS and WHU are roughly consistent with those using the final products; (2) the Doppler observations can effectively improve the accuracies of velocity, attitude, and vertical position at the initial epochs and during the reconvergence periods, but have invisible influences on the overall positioning, velocity, and attitude determination; and (3) the impact of IMU data interval on the performance of PPP/INS tightly coupled integration is insignificant when there are enough available satellites. However, the divergent speed of position is visibly affected by the IMU sampling rate during satellite outage periods.

Revisiting the Space Weather Environment of Proxima Centauri b

Close-in planets orbiting around low-mass stars are exposed to intense energetic photon and particle radiation and harsh space weather. We have modeled such conditions for Proxima Centauri b, a rocky planet orbiting in the habitable zone of our closest neighboring star, finding a stellar wind pressure 3 orders of magnitude higher than the solar wind pressure on Earth. At that time, no Zeeman–Doppler observations of the surface magnetic field distribution of Proxima Cen were available and a proxy from a star with a similar Rossby number to Proxima was used to drive the MHD model. Recently, the first Zeeman–Doppler imaging (ZDI) observation of Proxima Cen became available. We have modeled Proxima b’s space weather using this map and compared it with the results from the proxy magnetogram. We also computed models for a high-resolution synthetic magnetogram for Proxima b generated by a state-of-the-art dynamo model. The resulting space weather conditions for these three scenarios are similar with only small differences found between the models based on the ZDI observed magnetogram and the proxy. We conclude that our proxy magnetogram prescription based on the Rossby number is valid, and provides a simple way to estimate stellar magnetic flux distributions when no direct observations are available. Comparisons with models based on the synthetic magnetogram show that the exact magnetogram details are not important for predicting global space weather conditions of planets, reinforcing earlier conclusions that the large-scale (low-order) field dominates, and that the small-scale field does not have much influence on the ambient stellar wind.

Options to optimize the orthopedic treatment protocol to prevent inflammatory complications at the immediate prosthetic stage in patients after multiple teeth extraction

BACKGROUND: Simultaneous multiple loss of teeth significantly increases the need for immediate orthopedic treatment in dental patients, often with the use of removable immediate dentures due to general somatic pathologies and local Dental Prostheses System features.
 AIM: The study aimed to optimize the orthopedic treatment protocol for patients after multiple teeth extractions.
 MATERIAL AND METHODS: As part of the study, the orthopedic preparation of 18 patients was conducted for further permanent prosthetics. Patients underwent tooth extraction in the upper or lower jaw amounting to the formation of included, combined, or terminal dentition defects. The following were used for patient treatment: a standard protocol for immediate prosthetics, a modified protocol, including an improved method of vital mucous membrane staining of the prosthetic bed in the surgical intervention area using standard and immediate original design prostheses. The treatment option effectiveness was evaluated based on the results of diagnostic monitoring of wound healing zones in the prosthetic bed area of immediate prostheses, including visual-palpation assessment, vital oral mucosa staining with an iodine-containing diagnostic solution to control inflammation, and a modified Doppler observation method.
 RESULTS: Study results revealed that all patients, who used standard immediate prostheses without considering the diagnostic control of inflammation areas, had objective signs of inflammation up to the 20th day of treatment with low microcirculation dynamics in the wound healing area. In 4 out of 6 patients using standard immediate prostheses, considering inflammation control, the vital staining indicators by day 20 indicated a possible trend toward chronic inflammation development in the prosthetic bed area, which was confirmed by an unstable microcirculation picture. The severity of inflammatory changes was insignificant in patients who received the original design of the immediate prosthesis, starting from the 7th day of observation and minimal by the 20th day. At this time the hemodynamics are physiologically normal.
 CONCLUSIONS: Based on the study results, the orthopedic rehabilitation protocols effectiveness, with the use of a modified design based on the immediate prosthesis and permanent diagnostic, mucous membrane staining of the prosthetic bed was established to detect inflammatory complications in the wound healing areas.

Considerations about L2- and L1-norm regularizations for ultrasound reverberation characteristics imaging and vectoral Doppler measurement.

The L1-norm regularization is applied to ultrasonic reverberation characteristics imaging and vectoral Doppler measurement, of which performances are compared with those of L2-norm regularizations. The L1 regularization yields the sharper image than the L2 regularization. Alternatively, for the Doppler measurement, the L1 regularization yields less accuracy than the L2 regularization. Clinical Relevance- This study will permit us to perform quantitative ultrasonic reverberation characteristics and accurate vectoral Doppler observation.

A Doppler enhanced TDCP algorithm based on terrain adaptive and robust Kalman filter using a stand-alone receiver

AbstractTime-differenced carrier phase (TDCP) is a commonly used method of precise velocimetry, but when the receiver is in a dynamic or complex observation environment, the estimation accuracy is reduced. Doppler velocimetry aims at estimating instantaneous velocity, and the accuracy is restricted by the accuracy of measurement. However, in such unfavourable cases, the Doppler measurement is more reliable than the carrier phase measurement. This paper derives the relationship between Doppler observation and TDCP observation, then proposes a Doppler enhanced TDCP algorithm, for the purpose of improving the velocity estimation accuracy in dynamic and complex observation environments. In addition, considering the error caused by the constant speed state update model in the robust Kalman filter (RKF), this paper designs a terrain adaptive and robust Kalman filter (TARKF). After three experimental tests, the improved TDCP algorithm can significantly increase the speed measurement accuracy to sub-metre per second, and the accuracy can be further improved after using TARKF.

Cold Atom Interferometry for Enhancing the Radio Science Gravity Experiment: A Phobos Case Study

Interplanetary missions have typically relied on Radio Science (RS) to recover gravity fields by detecting their signatures on the spacecraft trajectory. The weak gravitational fields of small bodies, coupled with the prominent influence of confounding accelerations, hinder the efficacy of this method. Meanwhile, quantum sensors based on Cold Atom Interferometry (CAI) have demonstrated absolute measurements with inherent stability and repeatability, reaching the utmost accuracy in microgravity. This work addresses the potential of CAI-based Gradiometry (CG) as a means to strengthen the RS gravity experiment for small-body missions. Phobos represents an ideal science case as astronomic observations and recent flybys have conferred enough information to define a robust orbiting strategy, whilst promoting studies linking its geodetic observables to its origin. A covariance analysis was adopted to evaluate the contribution of RS and CG in the gravity field solution, for a coupled Phobos-spacecraft state estimation incorporating one week of data. The favourable observational geometry and the small characteristic period of the gravity signal add to the competitiveness of Doppler observables. Provided that empirical accelerations can be modelled below the nm/s2 level, RS is able to infer the 6 × 6 spherical harmonic spectrum to an accuracy of 0.1–1% with respect to the homogeneous interior values. If this correlates to a density anomaly beneath the Stickney crater, RS would suffice to constrain Phobos’ origin. Yet, in event of a rubble pile or icy moon interior (or a combination thereof) CG remains imperative, enabling an accuracy below 0.1% for most of the 10 × 10 spectrum. Nevertheless, technological advancements will be needed to alleviate the current logistical challenges associated with CG operation. This work also reflects on the sensitivity of the candidate orbits with regard to dynamical model uncertainties, which are common in small-body environments. This brings confidence in the applicability of the identified geodetic estimation strategy for missions targeting other moons, particularly those of the giant planets, which are targets for robotic exploration in the coming decades.

DORIS Alcatel ground antenna: Evaluation of the phase center variation models

The DORIS ground antenna phase center variation (PCV) modeling is an important factor of the DORIS solution accuracy and affects also the DORIS solutions employed in the ITRF2020 realization. There are two different elevation dependent models available for the Alcatel antenna, called here 1.0 and 2.0. For the Starec antenna we have only one PCV model. We demonstrate the effect of the Alcatel PCV model selection, reaching a value around 15 mm in the estimated DORIS station height. The post-fit Doppler observation residual analysis proved a better performance of the residuals derived from the solution employing Alcatel PCV model 2.0, particularly in several specific elevation intervals over 50 degrees. The elevation dependent systematics in the residuals have been proven by the separation of the ascending and descending portions of the residuals. The residual mean calculated for the elevation intervals reached values with a mutually opposite sign for the ascending and descending observations. Moreover, we have compared the residuals of the Starec and Alcatel stations, whereas the Starec residual RMS was lower for elevations approximately under 50 degrees, the Alcatel residual RMS was lower for higher elevations. This result could relate to an eventual Starec PCV model imperfection at higher elevations.To check the compatibility of the Starec and Alcatel PCV models impact on the station height, we have performed the comparison of the measured vertical component of the DORIS-DORIS local ties to a value calculated from the DORIS observations. The pairs of the Alcatel-Starec stations were the object of interest. When repeating the experiment with both Alcatel models 1.0 and 2.0, we have found a similar level of agreement of the measured and observed/computed height difference, but with the opposite sign. The average difference reached 8.7 ± 2.5 mm for Alcatel PCV model 1.0 and −7.2 ± 2.4 mm for Alcatel PCV model 2.0.

EUREC<sup>4</sup>A's <i>Maria S. Merian</i> ship-based cloud and micro rain radar observations of clouds and precipitation

Abstract. As part of the EUREC4A field campaign, the research vessel Maria S. Merian probed an oceanic region between 6 to 13.8∘ N and 51 to 60∘ W for approximately 32 d. Trade wind cumulus clouds were sampled in the trade wind alley region east of Barbados as well as in the transition region between the trades and the intertropical convergence zone, where the ship crossed some mesoscale oceanic eddies. We collected continuous observations of cloud and precipitation profiles at unprecedented vertical resolution (7–10 m in the first 3000 m) and high temporal resolution (1–3 s) using a W-band radar and micro rain radar (MRR), installed on an active stabilization platform to reduce the impact of ship motions on the observations. The paper describes the ship motion correction algorithm applied to the Doppler observations to extract corrected hydrometeor vertical velocities and the algorithm created to filter interference patterns in the MRR observations. Radar reflectivity, mean Doppler velocity, spectral width and skewness for W-band and reflectivity, mean Doppler velocity, and rain rate for MRR are shown for a case study to demonstrate the potential of the high resolution adopted. As non-standard analysis, we also retrieved and provided liquid water path (LWP) from the 89 GHz passive channel available on the W-band radar system. All datasets and hourly and daily quicklooks are publically available, and DOIs can be found in the data availability section of this publication. Data can be accessed and basic variables can be plotted online via the intake catalog of the online book “How to EUREC4A”.

Long-Term Variation of Helioseismic Far-Side Images and What Causes It

A new time–distance far-side imaging technique was recently developed by utilizing multiple multi-skip acoustic waves. The measurement procedure is applied to 11 years of Doppler observations from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, and over 8000 far-side images of the Sun have been obtained with a 12-hour temporal cadence. The mean travel-time shifts in these images unsurprisingly vary with the solar cycle. However, the temporal variation does not show good correlations with the magnetic activity in their respective northern or southern hemisphere, but show very good anti-correlation with the global-scale magnetic activity. We investigate four possible causes of this travel-time variation. Our analysis demonstrates that the acoustic waves that are used for mapping the Sun’s far side experience surface reflections around the globe, where they may interact with surface or near-surface magnetic field and carry travel-time deficits with them. The mean far-side travel-time shifts from these acoustic waves therefore vary in phase with the Sun’s magnetic activity.

Reducing loss of significance in the computation of Earth-based two-way Doppler observables for small body missions

Two-way Doppler measurement is a typical Earth-based radiometric technique for interplanetary spacecraft navigation and gravity science investigation. The most widely used model for the computation of two-way Doppler observables is Moyer’s differenced-range Doppler (DRD) formula, which is based on a Schwarzschild approximation of the Solar-System space-time. However, the computation of range difference in DRD formula is sensitive to round-off errors due to approximate numbers defined by the norm IEEE754 in all PCs. This paper presented two updated models and their corresponding detailed instructions for the computation of the two-way Doppler observables so as to impair the effects of this type of numerical error. These two models were validated by two case studies related to the Rosetta mission—asteroid Lutetia flyby and comet 67P/Churyumov-Gerasimenko orbiting case. In these two cases, the numerical noise from the updated models can be reduced by two orders-of-magnitude in the computed two-way Doppler observables. The results showed an accuracy from better than 6 × 10−3 mm s−1 at 1 s counting time interval to better than 3 × 10−5 mm s−1 at 60 s counting time interval.

A new real‐time cycle slip detection and repair approach based on BDS dual‐frequency carrier phase and Doppler observations

The Global Navigation Satellite System (GNSS) traditional dual-frequency cycle slip detection and repair methods such as the TurboEdit algorithm are restricted by the availability and accuracy of pseudorange observations. Doppler observations represent the instantaneous variation of the carrier phase during the integration time, which are immune to cycle slips. They are less affected by multipath effects compared with the pseudorange observations. Hence, a real-time cycle slip detection and repair approach for the BeiDou Navigation Satellite System (BDS) dual-frequency signals is proposed by combining the carrier phase and Doppler observations. The proposed method adopts the phase-Doppler combination and the geometry-free combination to detect cycle slips, and uses the simple rounding method or the dual-frequency least-square ambiguity decorrelation adjustment (LAMBDA) method to repair cycle slips. The validity of the proposed method is verified by the static and kinematic observation data under 1 s sampling interval and steady ionosphere. The results show that the new method can successfully detect all the small, insensitive, and large cycle slips. Moreover, the fixing rates of the simple rounding method under static and kinematic conditions are above 94% and 83%, respectively, while those of the dual-frequency LAMBDA method are both 100%.

Research on single-epoch RTK positioning method based on Doppler relative velocimetry

In the traditional single-epoch kinematic positioning, the positioning performance is relatively poor due to the less prior constraint information and lower success rate of ambiguity fixation. Accordingly, this paper proposes a single-epoch kinematic positioning method using Doppler relative velocity information constraint, that is, using Doppler observation information of rover station and base station for relative velocity measurement, and then using rover’s prior coordinates and velocity information to predict the coordinates of the current epoch, considering the advantages of higher accuracy of this method for coordinate update and more robustness of traditional single-point positioning, the corresponding strategy for single-epoch ambiguity resolution is further introduced to improve the positioning performance. The experimental results show that the proposed method can improve the accuracy of the float solution and ambiguity fixation rate, especially when the satellite geometry is poor and the observation conditions are obscured.

Venus Atmospheric Dynamics at Two Altitudes: Akatsuki and Venus Express Cloud Tracking, Ground-Based Doppler Observations and Comparison with Modelling

We present new results of our studies of zonal and meridional winds in both hemispheres of Venus, using ground- and space-based coordinated observations. The results obtained from telescope observations were retrieved with a Doppler velocimetry method. The wind velocities retrieved from space used an improved cloud-tracked technique based on the phase correlation between images. We present evidence that the altitude level sensed by our Doppler velocimetry method is approximately four kilometres higher (~4 km) than that using ground-tracked winds (using 380 or 365 nm). Since we often take advantage of coordinated space and ground observations simultaneously, this altitude difference will be very relevant in order to estimate the vertical wind shear at the related heights in future observation campaigns. We also explored a previous coordinated campaign using Akatsuki observations and its Ultraviolet Imager (UVI) at 283 and 365 nm filters, which showed that cloud-tracked winds showed a difference of about 10–15 ms−1, as in the case of the comparison between the Doppler velocimetry winds and the 365 nm cloudtracked winds. The results’ comparison also strongly suggested that the cloud-tracked winds based on the 283 nm filter’s images were sensing at about the same atmospheric altitude level as the Doppler winds. The observational results were compared with the ground-to-thermosphere 3D model developed at the Laboratoire de Meteorologie Dynamique (IPSL-Venus General Circulation Model (VGCM)) and AFES-Venus General Circulation Model (GCM), at several pressure levels (and related heights). The analysis and results showed the following: (1) additional confirmation of the coherence and complementarity in the results provided by these techniques on both the spatial and temporal time scales of the two methods; (2) we noticed in the following that the results from the two different Akatsuki/UVI filters (283 and 365 nm) showed an average difference of about 10–15 ± 5 ms−1, and we suggest this may be related to SO2 atmospheric fluctuations and the particular conditions in the coordinated observing time window; (3) we present evidence indicating that, in the context of our observations, visible Doppler methods (highly self-consistent) seem to sense wind speeds at a vertical level closer to or within the range sensed by the UVI 283 nm filter images (again, in the context of our observations); (4) modelling predicted wind profiles suggests that the layers of the atmosphere of Venus sensed by the methods referred to in Point 3 differ by approximately four km in altitude (~4 ± 2 km) regarding the cloud-tracked winds retrieved using 365 or 380 nm images.

Radar-Based Bayesian Estimation of Ice Crystal Growth Parameters within a Microphysical Model

Abstract The potential for polarimetric Doppler radar measurements to improve predictions of ice microphysical processes within an idealized model–observational framework is examined. In an effort to more rigorously constrain ice growth processes (e.g., vapor deposition) with observations of natural clouds, a novel framework is developed to compare simulated and observed radar measurements, coupling a bulk adaptive-habit model of vapor growth to a polarimetric radar forward model. Bayesian inference on key microphysical model parameters is then used, via a Markov chain Monte Carlo sampler, to estimate the probability distribution of the model parameters. The statistical formalism of this method allows for robust estimates of the optimal parameter values, along with (non-Gaussian) estimates of their uncertainty. To demonstrate this framework, observations from Department of Energy radars in the Arctic during a case of pristine ice precipitation are used to constrain vapor deposition parameters in the adaptive habit model. The resulting parameter probability distributions provide physically plausible changes in ice particle density and aspect ratio during growth. A lack of direct constraint on the number concentration produces a range of possible mean particle sizes, with the mean size inversely correlated to number concentration. Consistency is found between the estimated inherent growth ratio and independent laboratory measurements, increasing confidence in the parameter PDFs and demonstrating the effectiveness of the radar measurements in constraining the parameters. The combined Doppler and polarimetric observations produce the highest-confidence estimates of the parameter PDFs, with the Doppler measurements providing a stronger constraint for this case.

An Emergency Positioning System Fusing GEO Satellite Doppler Observation and INS for SOTM

This article presents a newly invented emergency positioning system deployed on a satellite communication on-the-move (SOTM) platform, which can extend the SOTM communication function to the positioning function. Inherent to the SOTM system's high reliability, this emergency positioning system can effectively estimate the vehicle's position by fusing a geosynchronous orbit (GEO) satellite Doppler frequency observation and inertial navigation system (INS) of a SOTM-mounted moving vehicle when the global navigation satellite system (GNSS) is unavailable. It is a great challenge to use GEO Doppler frequency measurement with weak observability to correct the INS's cumulative error to estimate the position of the vehicle. In this article, the traditional inertial measurement unit (IMU) pre-integration model is improved to meet the needs of large-scale and high-precision navigation. In addition, we use graph optimization (GO) to estimate all states in the trajectory, which can effectively improve the observability of the error and reduce the nonlinear influence. We evaluated the system on a Ku-band SOTM platform, and the experimental results indicate that the system can achieve a convergent positioning accuracy of tens of meters. This method can provide emergency positioning in the case of GNSS interference.

Prospective longitudinal cohort study of uterine arteries Doppler in singleton pregnancies obtained by IVF/ICSI with oocyte donation or natural conception.

Do uterine arteries Doppler studies show different pulsatility index (UtA-PI) measurements in IVF/ICSI pregnancies with oocyte donation (OD) as compared to natural conceptions? In IVF/ICSI pregnancies with OD, UtA-PI is reduced by an average of about 40% as compared to pregnancies with natural conception. OD pregnancies present worse pregnancy outcomes as compared to natural conception, particularly for increased incidence of pre-eclampsia (PE). Recent evidence shows that IVF/ICSI pregnancies with frozen blastocyst transfer also present higher prevalence of PE and 15% lower UtA-PI as compared to pregnancies after fresh blastocyst transfers. Prospective, longitudinal matched cohort study performed in the Fetal Medicine and Obstetric Departments of San Raffaele Hospital in Milan, between 2013 and 2018. The analysis is based on 584 Doppler observations collected from 296 women with different method of conception (OD n = 122; natural conception n = 174). IVF/ICSI viable singleton pregnancies with OD and natural conception control pregnancies matched for BMI and smoking, performing repeated UtA-PI measurements at 11-34 weeks. Miscarriages, abnormalities, twins, significant maternal diseases and other types of ARTs were excluded. Log mean left-right UtA-PI was used for analysis with linear mixed model (LMM) and correction for significant confounders. Pregnancy outcome was also analyzed. Participants after OD were older and more frequently nulliparous (mean age: OD 43.4, 95% CI from 42.3 to 44.6; natural conception 35.1, 95% CI from 34.5 to 35.7; P-value < 0.001; nulliparous: OD 96.6%; natural conception 56.2%; P-value < 0.001). Mean pulsatility index was lower in OD (UtA-PI: natural conception 1.22; 95% CI from 1.11 to 1.28; OD 1.04; 95% CI from 0.96 to 1.12; P-value < 0.001). A significant effect of parity, gestational age (GA) modeled with a cubic polynomial and BMI was described in the LMM. The mean Log UtA-PI was on average 37% lower in OD as compared to natural conception pregnancies at LMM (P-value < 0.001). We also found a significant interaction between longitudinal UtA-PI Doppler and GA. Therefore, at 11 weeks' gestation the Log UtA-PI was 42% lower and, at 34 weeks, the differences reduced to 32%. GA at delivery and birth weight were statistically lower in OD group; however, birthweight centile was not statistically different. Preeclampsia was 11-fold more common in the OD group (0.6% and 6.6%, P-value = 0.003). No other significant difference in pregnancy outcome was shown in the study groups (gestational diabetes mellitus, small or large for GA). It was not possible to properly match for maternal age and to blind the assessment given the major differences between cohorts; however, we did not find significant within-groups effects related to maternal age. Future research is needed to reassess outcomes and correct them for maternal characteristics (e.g. cardiovascular function). This finding reproduces our previous discovery of lower UtA-PI in frozen as compared to fresh blastocyst transfer. The vast majority of OD is obtained by the use of cryopreservation. We speculate that increased uterine perfusion may be the physiological response to compensate dysfunctions both in the mother and in the placenta. This is a non-funded study. The authors do not declare competing interest. N/A.

An improved real-time cycle slip correction algorithm based on Doppler-aided signals for BDS triple-frequency measurements

Doppler, which is an instantaneous GNSS observable signal, has been proven effective in determining velocity and acceleration due to its high availability and accuracy. We propose a real-time triple-frequency cycle slip correction (CSC) method based on Doppler-aided signals because Doppler shift is time-independent and immune to cycle slips. When the sampling interval is less than 1 s, cycle slips on triple-frequency can be detected and repaired using pure Doppler data with high reliability; however, this method cannot be used when the sampling interval exceeds 1 s because the integral cumulative error of Doppler increases significantly. For such cases, a modified triple-frequency CSC approach has been developed based on the raw phase and smoothed code data that was refined using the Doppler signal. To suppress the effect of the integral Doppler error, a balance factor is introduced to adjust the contributions of the raw code and Doppler observables. After the refinement of the GNSS data, three independent combinations need be selected to detect and repair cycle slips with triple-frequency observations. Four constrained criteria have been proposed to select optimal combinations that can reduce the residual ionospheric delay (RID) and measurement noise to a low level. Finally, experiments were carried out to test the performance of the new method using real triple-frequency BDS observations (GPST: 3:15:00–5:55:00, March 23, 2018). The results show that pure Doppler can detect and repair cycle slips effectively with small intervals, and modified Hatch-Melbourne-Wübbena (HMW) method based on Doppler-aided signals can achieve 99.7% success rate in cycle slip correction with large intervals (up to 30 s).