ILRS Reference Point Determination Using Close Range Photogrammetry

A global geodetic reference system (GGRS) is realized by physical points on the Earth’s surface and is referred to as a global geodetic reference frame (GGRF). The GGRF is derived by combining several space geodetic techniques, and the reference points of these techniques are the physical points of such a realization. Due to the weak physical connection between the space geodetic techniques, so-called local ties are introduced to the combination procedure. A local tie is the spatial vector defined between the reference points of two space geodetic techniques. It is derivable by local measurements at multitechnique stations, which operate more than one space geodetic technique. Local ties are a crucial component within the intertechnique combination; therefore, erroneous or outdated vectors affect the global results. In order to reach the ambitious accuracy goal of 1 mm for a global position, the global geodetic observing system (GGOS) aims for strategies to improve local ties, and, thus, the reference point determination procedures. In this contribution, close range photogrammetry is applied for the first time to determine the reference point of a laser telescope used for satellite laser ranging (SLR) at Geodetic Observatory Wettzell (GOW). A measurement campaign using various configurations was performed at the Satellite Observing System Wettzell (SOS-W) to evaluate the achievable accuracy and the measurement effort. The bias of the estimates were studied using an unscented transformation. Biases occur if nonlinear functions are replaced and are solved by linear substitute problems. Moreover, the influence of the chosen stochastic model onto the estimates is studied by means of various dispersion matrices of the observations. It is shown that the resulting standard deviations are two to three times overestimated if stochastic dependencies are neglected.

Co-location of SLR and GNSS techniques onboard Galileo and GLONASS satellites

<p>All satellites of the Galileo and GLONASS navigation systems are equipped with laser retroreflector arrays for Satellite Laser Ranging (SLR). SLR observations to Global Navigation Satellite Systems (GNSS) provide the co-location of two space geodetic techniques onboard navigation satellites.</p><p>SLR observations, which are typically used for the validation of the microwave-GNSS orbits, can now contribute to the determination of the combined SLR+GNSS orbits of the navigation satellites. SLR measurements are especially helpful for periods when the elevation of the Sun above the orbital plane (β angle) is the highest. The quality of Galileo-IOV orbits calculated using combined SLR+GNSS observations improves from 36 to 30 mm for β> 60° as compared to the microwave-only solution. </p><p>Co-location of two space techniques allows for the determination of the linkage between SLR and GNSS techniques in space. Based on the so-called space ties, it is possible to determine the 3D vector between the ground-based co-located SLR and GNSS stations and compare it with the local ties which are determined using the ground measurements. The agreement between local ties derived from co-location in space and ground measurements is at the level of 1 mm in terms of the long-term median values for the co-located station in Zimmerwald, Switzerland.</p><p>We also revise the approach for handling the SLR range biases which constitute one of the main error sources for the SLR measurements. The updated SLR range biases consider now the impact of not only of SLR-to-GNSS observations but also the SLR observations to LAGEOS and the microwave GNSS measurements. The updated SLR range biases improve the agreement between space ties and local ties from 34 mm to 23 mm for the co-located station in Wettzell, Germany.</p><p>Co-location of SLR and GNSS techniques onboard navigation satellites allows for the realization of the terrestrial reference frame in space, onboard Galileo and GLONASS satellites, independently from the ground measurements. It may also deliver independent information on the local tie values with full variance-covariance data for each day with common measurements or can contribute to the control of the ground measurements as long as both GNSS and SLR-to-GNSS observations are available.</p>

The Big House

For centuries, Britain’s religious life benefited from the patronage of local grandees: in rural areas major landowners were obliged by custom and by law to support the churches, and in the growing towns and cities of the nineteenth century industrialists performed a similar role. Those social obligations collapsed abruptly in the early twentieth century with the decline of the Big House, the amalgamation of local firms into national and then international companies, the growth of democracy, and the rise of the welfare state. The personally religious wealthy continued to fund religion, but the breaking of local ties released those of little faith from any obligation to promote Christianity. That change seriously weakened the churches.

Local Ties in the Social Networks of Older Adults

Objectives Family members and friends who live nearby may be especially well-positioned to provide social support and companionship for community-residing older adults, but prior research has not examined the distribution and characteristics of local ties in older adults’ networks. We hypothesize that local ties are newer, more frequently accessed, and more embedded in the network, and that social disadvantage and neighborhood conditions structure older adults’ access to local ties. Methods We use egocentric network data from 15,137 alters named by 3,735 older adults in Wave 3 of the National Social Life, Health, and Aging Project (NSHAP). We conduct dyadic analysis to compare characteristics of local and nonlocal ties. Logistic regression models estimate how personal and neighborhood characteristics are associated with naming local kin and local non-kin ties. Results Nearly half of the older adults named at least one local network tie, and about 60% of these local ties are non-kin. Local ties are newer, frequently accessed, and highly embedded in older adults’ networks. Local kin ties are most common among socially disadvantaged older adults. Local non-kin ties are most common among white older adults and those who live in areas with high levels of collective efficacy, although local non-kin ties are also associated with residence in high-poverty neighborhoods. Discussion Local ties may bring unique benefits for community-residing older adults, but their availability is likely structured by residential mobility, neighborhood context, disparities in resources, and support needs. Future research should consider their implications for health and well-being.

Assessment on atmospheric parameters at co-location sites

<p>Atmospheric ties are affected by the differences of atmospheric parameters of space geodetic techniques at co-location sites. Similar to local ties, they could be applied along with local ties for a combination of space geodetic techniques to improve the realization of terrestrial reference frames (TRF). Theoretically, atmospheric ties are affected by the height differences between antennas at the same site and meteorological conditions. Therefore, atmospheric ties could be determined by analytical equation based on meteorological information from in situ measurements or weather model. However, there is often a discrepancy between the expected zenith delay differences and those estimated from geodetic analysis, thus potentially degrading a combined atmospheric ties solution. In this study, we analyse the time series of zenith delays from co-located GNSS antennas at Wettzell (height differences below 3 meters), for 11 years (2008–2018). GNSS observations were analyzed with Bernese GNSS software version 5.2 with double-differencing technique and relative tropospheric delay and gradients were estimated with L1, L2, and the ionosphere-free (L3) linear combination thereof. Atmospheric ties were derived analytically employing meteorological data from Global Pressure and Temperature model 3 (GPT3) and ERA5 reanalysis, as well as corrections derived from ray tracing (Potsdam Mapping Functions, PMF). The comparison shows that zenith delay differences are dominated by equipment changes. The discrepancies between atmospheric ties and estimated zenith delay differences are frequency dependent, with the L1 solutions being the least biased. For these small vertical differences, seasonal signals are not significant for all frequencies.</p>

Short-Term Realization of the ITRS with GNSS/SLR/VLBI/DORIS

<p>International Terrestrial Reference Frame (ITRF) is the realization of the International Terrestrial Reference System (ITRS), which can be used for the variety applications such as earth research, surveying and mapping. 2000 National Geodetic Coordinate System (CGCS2000) has been established and widely applied as a long-term reference frame in China, however, a software for short-term reference frame establishment is also developed to provide high accuracy applications based on the fusion of GNSS/SLR/VLBI/DORIS. We analyzed the covariance from sinex format of the GNSS/SLR/VLBI/DORIS and the quality of local ties. The errors between the local ties and the ITRF2014 within 1cm was 89% in north direction and 85% east direction. We used inner constraints as the method of datum realization and Helmert variance component estimation for giving the weight of different space geodetic GNSS/SLR/VLBI/DORIS. Finaly, short-term terrestrial reference frame realization software can produce the weekly, monthly and annual frame products for high accuracy applications.</p>

On the multi-technique combination with atmospheric ties

<p align="justify"><span>We explore a new strategy to combine geodetic observations employing the existing and future systems. Imposing atmospheric ties on the combination at either the observation or normal equation level introduces a physical interpretation to the estimated atmospheric delay parameters, </span><span>that is, </span><span>zenith delays and gradients. In essence, besides combining station coordinates via local ties, we combine atmospheric delays via atmospheric ties. The purpose of this work is to assess the advantages and caveats of such a combination approach, on legacy, state-of-the-art, and next generation geodetic systems. We simulate 10 years of observations of all space geodetic techniques that currently contribute to the realization of the international terrestrial reference system; that is, very long baseline interferometry (VLBI), satellite laser ranging (SLR), global navigation satellite systems (GNSS), and Doppler orbitography and radiopositioning integrated by satellite (DORIS). The noise we inject in the simulated observations is technique-specific and - besides a thermal contribution - stems from three-state clock models and ray-traced delays from the latest ECMWF reanalysis, ERA5. To make the simulations more realistic, we estimate the probability of potential observations being successful by utilizing ERA5 fields, for example cloud fields for SLR. To avoid overoptimistic uncertainty estimates, we have accounted for the correlation between observations based on ERA5 fields. In a bias-free setup, we find that the improvement of employing atmospheric ties in addition to local ties to fuse multi-sensor observations, on the combined station coordinates and atmospheric delays is statistically significant for all techniques except for GNSS. We attribute the latter to the relatively good observing geometry. We also find that employing atmospheric ties reveals unaccounted systematic errors stemming from erroneous auxiliary data that are necessary for the reduction of geodetic observations, </span><span>such as </span><span>pressure </span><span>measurements, </span><span>cable </span><span>calibrations, </span><span>and range biases. Performing the observation combination with atmospheric ties improves the combined solution, </span><span>especially </span><span>for sparse observing geometry, and facilitates the detection of unaccounted systematic errors.</span></p>

Coherent Time and Frequency for an Improved Global Geodetic Observing System

<p>The toolbox of space geodesy contains a number of measurement techniques, which are globally distributed. In this diverse network fundamental stations are playing an important role as they are forming the backbone of the global geodetic observing system. They provide the ties for the combination of the techniques.</p><p>Until recently these ties were only considering the spatial relationship between the measurement techniques. Upon closer inspection it turns out that clocks are also playing an important role. Variable delays within the main techniques of space geodesy, namely SLR, VLBI, GNSS and DORIS are limiting the stability of the measurements and hence the entire observing system. This leads to the rather paradox situation, that each technique has to adjust the clock offsets independently. Although all main measurements systems on an observatory are usually based on the same clock, each technique provides different offsets, thus weakening the local ties. This reflects the fact that the clock adjustments are also contaminated with (variable) system specific delays. Increasing the coherence of time on these GGOS observatories disentangles erroneous system delays from local ties, thus strengthening the entire observing system. </p><p>We have designed and built such a coherent time and frequency distribution system for the Geodetic Observatory Wettzell. It is based on a mode-locked fs- pulse laser, fed into a network of actively delay controlled two-way optical pulse transmission links. This utilizes the ultra low noise properties of optical frequency combs, both in the optical and electronic regime. Together with a common central inter- and intra- technique reference target time can provide consistency for the complex instrumentation of SLR and VLBI systems in situ, which was not possible before. This talk outlines the concept and its potential for GGOS.</p>

Local Ties that Bind? Exploring Noncombat Contact and Understandings of Military Duty in Afghanistan

Contemporary “population-oriented” military intervention and the objectives of protecting, supporting, and fighting alongside host-nation authorities and populations pose new challenges to Western armed forces’ traditionally combat-oriented understanding of duty. The article argues that military personnel who engage in unarmed and nonthreatening interaction—noncombat contact—with host citizens are more likely to develop a stronger sense of duty—perceived obligations—toward the host-nation population. Interviews with US Army officers with experiences from Afghanistan show that noncombat contact with Afghan citizens led to increased willingness to safeguard the interests and well-being of the Afghan population and adapt the mission accordingly.