Global Observing System Research Articles

Toward a Coordinated Global Observing System for Seagrasses and Marine Macroalgae

In coastal waters around the world, the dominant primary producers are benthic macrophytes, including seagrasses and macroalgae, that provide habitat structure and food for diverse and abundant biological communities and drive ecosystem processes. Seagrass meadows and macroalgal forests play key roles for coastal societies, contributing to fishery yields, storm protection, biogeochemical cycling and storage, and important cultural values. These socio-economically valuable services are threatened worldwide by human activities, with substantial areas of seagrass and macroalgal forests lost over the last half-century. Tracking the status and trends in marine macrophyte cover and quality is an emerging priority for ocean and coastal management, but doing so has been challenged by limited coordination across the numerous efforts to monitor macrophytes, which vary widely in goals, methodologies, scales, capacity, governance approaches, and data availability. Here, we present a consensus assessment and recommendations on the current state of and opportunities for advancing global marine macrophyte observations, integrating contributions from a community of researchers with broad geographic and disciplinary expertise. With the increasing scale of human impacts, the time is ripe to harmonize marine macrophyte observations by building on existing networks and identifying a core set of common metrics and approaches in sampling design, field measurements, governance, capacity building, and data management. We recommend a tiered observation system, with improvement of remote sensing and remote underwater imaging to expand capacity to capture broad-scale extent at intervals of several years, coordinated with stratified in situ sampling annually to characterize the key variables of cover and taxonomic or functional group composition, and to provide ground-truth. A robust networked system of macrophyte observations will be facilitated by establishing best practices, including standard protocols, documentation, and sharing of resources at all stages of workflow, and secure archiving of open-access data. Because such a network is necessarily distributed, sustaining it depends on close engagement of local stakeholders and focusing on building and long-term maintenance of local capacity, particularly in the developing world. Realizing these recommendations will produce more effective, efficient, and responsive observing, a more accurate global picture of change in vegetated coastal systems, and stronger international capacity for sustaining observations.

A multi-year record of atmospheric mercury species at a background mountain station in Andean Patagonia (Argentina): Temporal trends and meteorological influence

This work provides the first continuous measurements of atmospheric mercury (Hg) at the EMMA Station in Patagonia (Argentina), within the Southern Volcanic Zone of South America. This monitoring site was set up by the Global Mercury Observation System (GMOS project) and is located inside Nahuel Huapi National Park (41°07′43.33″S, 71°25′12.03″W; 800 m a.s.l) in a forested valley of the Andes upwind of San Carlos de Bariloche city.This study aimed at describing atmospheric Hg levels and trends of variation using concentration data of Gaseous Elemental Mercury (GEM) collected from October 2012 to July 2017 and, Gaseous Oxidized Mercury (GOM) and Particle-Bound Mercury (PBM) recorded from March 2014 until July 2017. During the studied period the mean GEM concentration was 0.86 ± 0.16 ng m−3; with the highest level in the austral spring (0.95 ± 0.13 ng m−3) and the lowest in the autumn (0.80 ± 0.15 ng m−3). Mean GOM concentration was 4.61 ± 4.00 pg m−3, displaying the highest level in autumn (5.47 ± 4.39 pg m−3) and the lowest in winter (1.24 ± 0.90 pg m−3). Mean PBM computed for the whole period was 3.74 ± 3.41 pg m−3; with the highest mean levels recorded in autumn (6.32 ± 3.41 pg m−3) and the lowest in spring (1.18 ± 0.92 pg m−3). Daytime levels of GEM, GOM and PBM were higher than nighttime concentrations, although in the case GOM and PBM similar levels were computed in autumn and summer, respectively. Westerly winds along with temperature and relative humidity influenced the dynamics of GEM, GOM and PBM at the EMMA Station. The HYSPLIT model showed that the area of the EMMA station was simultaneously affected by local and regional sources (forest fires and volcanoes) while the lowest values were recorded with the inflow of clean oceanic air masses coming from the free troposphere and corresponding to a long-range transport. Moreover, the Potential Source Contribution Function analysis showed that emissions in the Marine Boundary Layer, deriving from remote areas of Pacific Ocean, are sources of GEM and GOM.

A Global Ocean Observing System (GOOS), Delivered Through Enhanced Collaboration Across Regions, Communities, and New Technologies

Since OceanObs'09, the Global Ocean Observing System (GOOS) has evolved from its traditional focus on the ocean's role in global climate. GOOS now also encompasses operational services and marine ecosystem health, from the open ocean into coastal environments where much of the world's population resides. This has opened a field of opportunity for new collaborations-across regions, communities, and technologies-facilitating enhanced engagement in the global ocean observing enterprise to benefit all nations. Enhancement of collaboration is considered from the perspectives of regional alliances, global networks, national systems, in situ observing, remote sensing, oceanography, and meteorology. Reinvigoration of GOOS Regional Alliances has been important in connecting the power of this expanded remit to the needs of coastal populations and the capabilities of regional and national marine science communities. An assessment of progress is provided, including issues/challenges with the current structure, and opportunities to increase participation and impact. Meeting the expanded requirements of GOOS will entail new system networks. The Joint Technical Commission for Oceanography and Marine Meteorology Observations Coordination Group has been working with some communities to help assess their readiness, including high frequency radars, ocean gliders, and animal tracking. Much more needs to be done, with a range of strategies considered. Other opportunities include partnering with programs such as the Global Ocean Acidification Observing Network, engaging with mature and emerging national ocean observing programs, and learning from multinational projects such as Tropical Pacific Observing System 2020 and AtlantOS, which are bringing renewed rigor to the design and operation of regional observing systems. Consideration is given to the expansion and advancement that is coming in both in situ and remote sensing ocean observation platforms over the next decade. In combination they provide the potential to measure new Essential Ocean Variables routinely at global scale. Opportunities provided by the World Meteorological Organization Integrated Global Observing System (WIGOS) in fostering a comprehensive and integrated approach across meteorology and oceanography are also considered. The focus of WIGOS on providing accurate, reliable and timely weather, climate, and related environmental observations and products sits well with the expanded requirements of GOOS, in climate, operational services, and marine ecosystem health.

Animal-Borne Telemetry: An Integral Component of the Ocean Observing Toolkit

Animal telemetry is a powerful tool for observing marine animals and the physical environments that they inhabit, from coastal and continental shelf ecosystems to polar seas and open oceans. Satellite-linked biologgers and networks of acoustic receivers allow animals to be reliably monitored over scales of tens of meters to thousands of kilometers, giving insight into their habitat use, home range size, the phenology of migratory patterns and the biotic and abiotic factors that drive their distributions. Furthermore, physical environmental variables can be collected using animals as autonomous sampling platforms, increasing spatial and temporal coverage of global oceanographic observation systems. The use of animal telemetry, therefore, has the capacity to provide measures from a suite of essential ocean variables (EOVs) for improved monitoring of Earth's oceans. Here we outline the design features of animal telemetry systems, describe current applications and their benefits and challenges, and discuss future directions. We describe new analytical techniques that improve our ability to not only quantify animal movements but to also provide a powerful framework for comparative studies across taxa. We discuss the application of animal telemetry and its capacity to collect biotic and abiotic data, how the data collected can be incorporated into ocean observing systems, and the role these data can play in improved ocean management.

Designing the Global Observing System for Marine Life

Identifying the Backbone of a Global Observing System for Marine Life and Planning Its Implementation for the Next Decade; Santa Barbara, California, 5–7 March 2019

Ocean Observations Required to Minimize Uncertainty in Global Tsunami Forecasts, Warnings, and Emergency Response

It is possible that no catastrophe has mobilized the global ocean science and coastal emergency management communities more than the 2004 Indian Ocean tsunami. Though the Pacific tsunami threat was recognized, and a warning system had been in place since 1965, there was no warning system in the Indian Ocean, and almost 230,000 people perished. More broadly, the event highlighted critical gaps in global tsunami science and observation systems. In 2004, real-time coastal and deep-ocean observation systems were almost nonexistent. Tsunami sources were inferred based on rough seismic parameters. Since then, tremendous strides have been made under the auspices of IOC/UNESCO toward better understanding tsunami mechanisms, deploying advanced real-time tsunami observation systems, and establishing tsunami warning and mitigation systems for the four main ocean basins at risk from tsunamis. Nevertheless, significant detection, measurement, and forecast uncertainties remain to meet emergency response and community needs. A new generation of ocean sensing capabilities presents an opportunity to address several of these uncertainties. Ocean bottom pressures can be measured over dense, multisensor grids linking stand-alone buoy systems with emerging capabilities like fiber-optic cables. The increasing number of coastal sea-level stations can better verify forecasts and account for local variability. In addition, GNSS sensors may be able to provide solid-earth data needed to define seismic tsunami sources more precisely in the short timescales required. When combined with advances in seismology, other emerging techniques, and state-of-the-art modeling and computational resources, these capabilities will enable more timely and accurate tsunami detection and measurement to meet identified user needs and save lives. Because of these advances in detection and measurement, the opportunity exists to greatly reduce and/or quantify uncertainties associated with forecasting tsunamis. Providing more timely and accurate information related to tsunami location, arrival time, height, inundation, and duration would improve public trust and confidence and fundamentally alter tsunami emergency response. Additionally, this capability could be integrated with related fields (e.g., storm surge, sea-level rise, tide predictions, and ocean forecasting) to develop and deploy one continuous, real-time, accurate depiction of the always moving boundary that separates ocean from coast, wet from dry, and, sometimes, life from death.

Climate Change and Livelihood Vulnerability of the Local Population on Sagar Island, India

This paper attempts to assess the vulnerability to climate change of human communities in selected mouzas of Sagar Island, South 24 Parganas District of India. A primary household survey has been conducted to collect data on socio-demographic profile, livelihood strategy, health, food, water, social network, natural disaster and climate variation indicators, were selected for Livelihood Vulnerability Index (LVI) and Livelihood Vulnerability Index-Intergovernmental Panel on Climate Change (LVI-IPCC) analyses to measure and compare the vulnerability of mouzas (administrative unit) currently suffering from frequent flooding, coastal erosion and embankment breaching on an annual basis. Secondary data collected from the Indian Meteorological Department, the Water Resources Information System of India and the Global Sea Level Observing System have been used to identify dynamics of climate change by employing statistical and Geographic Information System (GIS) techniques. A GPS survey has been conducted to identify locations of embankment breaching, and satellite images obtained from the National Aeronautics and Space Administration and U.S. Geological Survey (NASA USGS) Government website have been applied to shoreline and land use change detection, using a supervised maximum likelihood classification. The results indicate that the study area has experienced increasing temperature, changing precipitation patterns, rise in sea level, higher storm surges, shoreline change, constant land loss, embankment breaching and changing land use, which have had impact on vulnerability, particularly of poorer people. The LVI (0.48 to 0.68) and LVI-IPCC (0.04 to 0.14) scores suggest that the populations of Dhablat, Bankimnagar, Sumatinagar, Muri Ganga and Sibpur mouzas are highly vulnerable (LVI scores of 0.60 to 0.68 and LVI-IPCC scores of 0.11 to 0.14) to climate change both because the communities are more exposed to it, and because poor access to food, health facilities and water makes them extremely sensitive to it and lowers their adaptive capacity. The findings of this study could be crucial to framing further development and adaptation strategies relating to climate change, and to safeguarding the estuarine ecosystem and the vulnerable population.

Future SLR station networks in the framework of simulated multi-technique terrestrial reference frames

Currently, the requirements of the Global Geodetic Observing System are not yet met by the latest global terrestrial reference frames (TRF). In this study, we assess potential TRF improvements by future SLR network designs partly already classified as “future stations” by the International Laser Ranging Service. We simulate the space geodetic techniques GPS, SLR, and VLBI within the time span 2008–2014 and evaluate the feasible improvements of the SLR-only and the multi-technique TRFs w.r.t. the current station networks. The station performance of the simulated 14 additional SLR stations is driven by the total cloud coverage from the numerical weather model ERA5. We find that the estimated station positions and velocities as well as the Earth rotation parameters, and the TRF-defining parameters origin and scale improve by 1–4% if a single additional station is added to the current SLR-only network. The solution with all 14 additional stations improves by about 22% in origin and 20% in scale w.r.t. the current SLR-only TRF. Single existing stations were excluded from the network resulting in deteriorations of 2–6%. Multi-technique TRFs improve by new co-located sites due to additional SLR stations by up to 1% for station positions, velocities, and the realization of the orientation.

The ILRS: approaching 20 years and planning for the future

The International Laser Ranging Service (ILRS) was established by the International Association of Geodesy (IAG) in 1998 to support programs in geodesy, geophysics, fundamental constants and lunar research, and to provide the International Earth Rotation Service with data products that are essential to the maintenance and improvement in the International Terrestrial Reference Frame (ITRF), the basis for metric measurements of changes in the Earth and Earth–Moon system. Other scientific products derived from laser ranging include precise geocentric positions and motions of ground stations, satellite orbits, components of Earth’s gravity field and their temporal variations, Earth Orientation Parameters, precise lunar ephemerides and information about the internal structure of the Moon. Laser ranging systems are already measuring the one-way distance to remote optical receivers in space and are performing very accurate time transfer between remote sites in the Earth and in Space. The ILRS works closely with the IAG’s Global Geodetic Observing System. The ILRS develops (1) the standards and specifications necessary for product consistency, and (2) the priorities and tracking strategies required to maximize network efficiency. The service collects, merges, analyzes, archives and distributes satellite and lunar laser ranging data to satisfy a variety of scientific, engineering, and operational needs and encourages the application of new technologies to enhance the quality, quantity, and cost effectiveness of its data products. The ILRS works with (1) new satellite missions in the design and building of retroreflector targets to maximize data quality and quantity, and (2) science programs to optimize scientific data yield. Since its inception, the ILRS has grown to include forty laser ranging stations distributed around the world. The ILRS stations track more than ninety satellites from low Earth orbit (LEO) to the geosynchronous orbit altitude as well as retroreflector arrays on the surface of the Moon. Applications have been expanded to include time transfer, asynchronous ranging for targets at extended ranges, free space quantum telecommunications, and the tracking of space debris. Laser ranging technology is moving to lower energy, higher repetition rates (kHz), single-photon-sensitive detectors, shorter pulse widths, shorter normal point intervals for faster data acquisition, and increased pass interleaving, automated to autonomous operation with remote access, and embedded software for real-time updates and decision making. An example of pass interleaving is presented for the Yarragadee station (see Fig. 4); tracking of LEO satellites is often accommodated during break in LEO and GNSS passes. New satellites arrays provide more compact targets and work continues on the development of lighter less expensive arrays for satellites and the moon. The service now provides operational ITRF products including daily/weekly station positions and daily resolution Earth orientation products; the flow of weekly combination of satellite orbit files for LAGEOS/Etalon-1 and -2 has recently been established. New products are under testing through a pilot project on systematic error monitoring currently underway. The article will give an overview of activities underway within the service, paths forward presently envisioned, and current issues and challenges.

An improved atmospheric weighted mean temperature model and its impact on GNSS precipitable water vapor estimates for China

The atmospheric weighted mean temperature, $${T_{\text{m}}}$$Tm, is an important parameter for retrieving precipitable water vapor (PWV) from global navigation satellite system (GNSS) signals. There are few empirical, high-precision $${T_{\text{m}}}$$Tm models for China, which limit the real-time and high-precision application of GNSS meteorology over China. The GPT2w (Global Pressure and Temperature 2 Wet) model, as a state-of-the-art global empirical tropospheric delay model, can provide values for $${T_{\text{m}}}$$Tm, surface temperature, surface pressure, and water vapor pressure. However, several studies have noted that the GPT2w model has significant systematic errors in the calculation of $${T_{\text{m}}}$$Tm for China, mainly due to the neglect of the $${T_{\text{m}}}$$Tm lapse rate. We develop an improved $${T_{\text{m}}}$$Tm model for China, IGPT2w, by refining the $${T_{\text{m}}}$$Tm derived from GPT2w using both gridded $${T_{\text{m}}}$$Tm data and ellipsoidal height grid data from the Global Geodetic Observing System (GGOS) Atmosphere. Both gridded $${T_{\text{m}}}$$Tm data from the GGOS Atmosphere and radiosonde data from 2015 are used to test the performance of IGPT2w in China. The results are compared with the GPT2w model and the widely used Bevis formula. The results show that IGPT2w yields significant performance against other models in $${T_{\text{m}}}$$Tm estimation over China, especially in western China, where the significant systematic errors of the GPT2w model are largely eradicated. IGPT2w has $${\sigma _{{\text{PWV}}}}$$?PWV and $${\sigma _{{\text{PWV}}}}/{\text{PWV}}$$?PWV/PWV values of 0.29 mm and 1.38% when used to retrieve GNSS-PWV, respectively. Thus, the IGPT2w has significant potential for real-time GNSS-PWV sounding in China, especially when used to retrieve GNSS-PWV values for the study of PWV transportation in the Tibetan Plateau.

Putting It All Together: Adding Value to the Global Ocean and Climate Observing Systems With Complete Self-Consistent Ocean State and Parameter Estimates

In 1999, the consortium for Estimating the Circulation and Climate of the Ocean (ECCO) set out to synthesize the hydrographic data collected by the World Ocean Circulation Experiment (WOCE) and satellite sea surface height measurements into a complete and coherent description of the ocean afforded by an ocean general circulation model. Twenty years later, the versatility of ECCO's estimation framework enables production of global and regional ocean and sea-ice state estimates that incorporate not only the initial suite of data and its successors, but nearly all data streams available today. New observations include measurements from Argo floats, marine mammal-based hydrography, satellite retrievals of ocean bottom pressure and sea surface salinity, and ice-tethered profiler data in polar regions. The framework also produces improved estimates of uncertain inputs, including initial conditions, surface atmospheric state variables, and mixing parameters. The freely available state estimates and related efforts are property-conserving, allowing closed budget calculations that are a requisite to detect, quantify, and understand the evolution of climate-relevant signals as mandated by the Coupled Model Intercomparison Project Phase 6 (CMIP6) protocol. The solutions can be reproduced by users through provision of the underlying modeling and assimilation machinery. Regional efforts have spun off that offer increased spatial resolution to better resolve relevant processes. Emerging foci of ECCO are on global sea level change, in particular contributions from polar ice sheets, and the increased use of biogeochemical and ecosystem data to constrain global cycles of carbon, nitrogen and oxygen. Challenges in the coming decade include provision of uncertainties, informing observing system design, globally increased resolution, and moving toward coupled Earth system estimation with consistent momentum, heat and freshwater fluxes between the ocean, atmosphere, cryosphere and land.

The role of biomass burning as derived from the tropospheric CO vertical profiles measured by IAGOS aircraft in 2002–2017

Abstract. This study investigates the role of biomass burning and long-range transport in the anomalies of carbon monoxide (CO) regularly observed along the tropospheric vertical profiles measured in the framework of the In-service Aircraft for a Global Observing System (IAGOS). Considering the high interannual variability of biomass burning emissions and the episodic nature of long-range pollution transport, one strength of this study is the amount of data taken into account, namely 30 000 vertical profiles at nine clusters of airports in Europe, North America, Asia, India and southern Africa over the period 2002–2017. As a preliminary, a brief overview of the spatiotemporal variability, latitudinal distribution, interannual variability and trends of biomass burning CO emissions from 14 regions is provided. The distribution of CO mixing ratios at different levels of the troposphere is also provided based on the entire IAGOS database (125 million CO observations). This study focuses on the free troposphere (altitudes above 2 km) where the long-range transport of pollution is favoured. Anomalies at a given airport cluster are here defined as departures from the local seasonally averaged climatological vertical profile. The intensity of these anomalies varies significantly depending on the airport, with maximum (minimum) CO anomalies of 110–150 (48) ppbv in Asia (Europe). Looking at the seasonal variation of the frequency of occurrence, the 25 % strongest CO anomalies appear reasonably well distributed throughout the year, in contrast to the 5 % or 1 % strongest anomalies that exhibit a strong seasonality with, for instance, more frequent anomalies during summertime in the northern United States, during winter/spring in Japan, during spring in south-east China, during the non-monsoon seasons in south-east Asia and south India, and during summer/fall in Windhoek, Namibia. Depending on the location, these strong anomalies are observed in different parts of the free troposphere. In order to investigate the role of biomass burning emissions in these anomalies, we used the SOFT-IO (SOft attribution using FlexparT and carbon monoxide emission inventories for In-situ Observation database) v1.0 IAGOS added-value products that consist of FLEXible PARTicle dispersion model (FLEXPART) 20-day backward simulations along all IAGOS aircraft trajectories, coupled with anthropogenic Monitoring Atmospheric Composition and Climate (MACC)/CityZEN EU projects (MACCity) and biomass burning Global Fire Assimilation System (GFAS) CO emission inventories and vertical injections. SOFT-IO estimates the contribution (in ppbv) of the recent (less than 20 days) primary worldwide CO emissions, tagged per source region. Biomass burning emissions are found to play an important role in the strongest CO anomalies observed at most airport clusters. The regional tags indicate a large contribution from boreal regions at airport clusters in Europe and North America during the summer season. In both Japan and south India, the anthropogenic emissions dominate all throughout the year, except for the strongest summertime anomalies observed in Japan that are due to Siberian fires. The strongest CO anomalies at airport clusters located in south-east Asia are induced by fires burning during spring in south-east Asia and during fall in equatorial Asia. In southern Africa, the Windhoek airport was mainly impacted by fires in Southern Hemisphere Africa and South America. To our knowledge, no other studies have used such a large dataset of in situ vertical profiles for deriving a climatology of the impact of biomass burning versus anthropogenic emissions on the strongest CO anomalies observed in the troposphere, in combination with information on the source regions. This study therefore provides both qualitative and quantitative information for interpreting the highly variable CO vertical distribution in several regions of interest.

Sustainable Observations of Plankton, the Sea’s Food Foundation

Workshop on Developing an Implementation Plan for a Sustained, Multidisciplinary Global Observing System of Plankton Communities; Santa Cruz, California, 25–27 June 2018

Modernizing and Expanding the NASA Space Geodesy Network to Meet Future Geodetic Requirements.

NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System (GNSS) ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC 2010, 2018). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame (TRF) to have an accuracy of 1 millimeter and stability of 0.1 millimeters per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations co-located at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA's Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the new geodetic stations.

Community Global Observing System Simulation Experiment (OSSE) Package (CGOP): Assessment and Validation of the OSSE System Using an OSSE–OSE Intercomparison of Summary Assessment Metrics

AbstractObserving system simulation experiments (OSSEs) are used to simulate and assess the impacts of new observing systems planned for the future or the impacts of adopting new techniques for exploiting data or for forecasting. This study focuses on the impacts of satellite data on global numerical weather prediction (NWP) systems. Since OSSEs are based on simulations of nature and observations, reliable results require that the OSSE system be validated. This validation involves cycles of assessment and calibration of the individual system components, as well as the complete system, with the end goal of reproducing the behavior of real-data observing system experiments (OSEs). This study investigates the accuracy of the calibration of an OSSE system—here, the Community Global OSSE Package (CGOP) system—before any explicit tuning has been performed by performing an intercomparison of the OSSE summary assessment metrics (SAMs) with those obtained from parallel real-data OSEs. The main conclusion reached in this study is that, based on the SAMs, the CGOP is able to reproduce aspects of the analysis and forecast performance of parallel OSEs despite the simplifications employed in the OSSEs. This conclusion holds even when the SAMs are stratified by various subsets (the tropics only, temperature only, etc.).

The next generation of satellite laser ranging systems

Satellite laser ranging (SLR) stations in the International Laser Ranging Service (ILRS) global tracking network come in different shapes and sizes and were built by different institutions at different times using different technologies. In addition, those stations that have upgraded their systems and equipment are often operating a complementary mix of old and new. Such variety reduces the risk of systematic errors across all ILRS stations, and an operational advantage at one station can inform the direction and choices at another station. This paper describes the evolution of the ILRS network and the emergence of a new generation of SLR station, operating at kHz repetition rates, firing ultra-short laser pulses that are timestamped by epoch timers accurate to a few picoseconds. It discusses current trends, such as increased automation, higher repetition rate SLR and the challenges of eliminating systematic biases, and highlights possibilities in new technology. In addition to meeting the growing demand for laser tracking support from an increasing number of SLR targets, including a variety of Global Navigation Satellite Systems satellites, ILRS stations are striving to: meet the millimetre range accuracy science goals of the Global Geodetic Observing System; make laser range measurements to space debris objects in the absence of high optical cross-sectional retro-reflectors; further advances in deep space laser ranging and laser communications; and demonstrate accurate laser time transfer between continents.

Evaluation of the IAGOS-Core GHG package H<sub>2</sub>O measurements during the DENCHAR airborne inter-comparison campaign in 2011

Abstract. As part of the DENCHAR (Development and Evaluation of Novel Compact Hygrometer for Airborne Research) inter-comparison campaign in northern Germany in 2011, a commercial cavity ring-down spectroscopy (CRDS) based gas analyzer (G2401-m, Picarro Inc., US) was installed on a Learjet to measure atmospheric water vapor, CO2, CH4, and CO. The CRDS components were identical to those chosen for integration aboard commercial airliners within the IAGOS (In-service Aircraft for a Global Observing System) project. Since the quantitative capabilities of the CRDS water vapor measurements were never evaluated and reviewed in detail in a publication before, the campaign allowed for an initial assessment of the long-term IAGOS water vapor measurements by CRDS against reference instruments with a long performance record (Fast In-situ Stratospheric Hygrometer (FISH) and CR-2 frost point hygrometer (Buck Research Instruments L.L.C., US), both operated by Research Centre Jülich). For the initial water calibration of the instrument it was compared against a dew point mirror (Dewmet TDH, Michell Instruments Ltd., UK) in the range from 70 000 to 25 000 ppm water vapor mole fraction. During the inter-comparison campaign the analyzer was compared on the ground over the range from 2 to 600 ppm against the dew point hygrometer used for calibration of the FISH reference instrument. A new, independent calibration method based on the dilution effect of water vapor on CO2 was evaluated. Comparison of the in-flight data against the reference instruments showed that the analyzer is reliable and has a good long-term stability. The flight data suggest a conservative precision estimate for measurements made at 0.4 Hz (2.5 s measurement interval) of 4 ppm for H2O < 10 ppm, 20 % or 10 ppm (whichever is smaller) for 10 ppm < H2O < 100 ppm, and 5 % or 30 ppm (whichever is smaller) for H2O > 100 ppm. Accuracy of the CRDS instrument was estimated, based on laboratory calibrations, as 1 % for the water vapor range from 25 000 ppm down to 7000 ppm, increasing to 5 % at 50 ppm water vapor. Accuracy at water vapor mole fractions below 50 ppm was difficult to assess, as the reference systems suffered from lack of data availability.

NASA's Satellite Laser Ranging Systems for the 21st Century.

For over 40 years, NASA's global network of satellite laser ranging (SLR) stations has provided a significant percentage of the global orbital data used to define the International Terrestrial Reference Frame (ITRF). The current NASA legacy network is reaching its end-of-life and a new generation of systems must be ready to take its place. Scientific demands of sub-millimeter precision ranging and the ever-increasing number of tracking targets give aggressive performance requirements to this new generation of systems. Using lessons learned from the legacy systems and the successful development of a prototype station, a new network of SLR stations, called the Space Geodesy Satellite Laser Ranging (SGSLR) systems, is being developed. These will be the state-of-the-art SLR component of NASA's Space Geodesy Project (SGP). Each of SGSLR's nine subsystems has been designed to produce a robust, kilohertz laser ranging system with 24/7 operational capability and with minimal human intervention. SGSLR's data must support the aggressive goals of the Global Geodetic Observing System (GGOS), which are 1 millimeter (mm) position accuracy and 0.1 mm per year stability of the ITRF. This paper will describe the major requirements and accompanying design of the new SGSLR systems, how the systems will be tested, and the expected system performance.

A modified approach for automated reference point determination of SLR and VLBI telescopes

Abstract The International Terrestrial Reference Frame (ITRF) is derived by combining several space geodetic techniques. Basically, a meaningful combination of the geodesic space techniques is impossible without further geometrical information, i. e. local-ties. Local-tie vectors are defined between the geometrical reference points of space geodetic techniques at co-location stations. These local-ties are introduced during the inter-technique combination process, to overcome the weak physical connection between the space geodetic techniques. In particular, the determination of the reference point of radio telescopes or laser telescopes is a challenging task and requires indirect methods. Moreover, the Global Geodetic Observing System (GGOS) strives for an automated and continued reference point determination with sub-millimeter accuracy, because deviations in local-ties bias global results. This investigation presents a modified approach for automated reference point determination. The new approach extends the prior work of Lösler but evades the synchronization between the terrestrial instrument and the telescope. Thus, synchronization errors are omitted and the technical effort is reduced. A proof of concept was carried out at Geodetic Observatory Wettzell in 2018. Using a high-precision, mobile laser-tracker, the reference point of the Satellite Observing System Wettzell (SOS-W) was derived. An extended version of the in-house developed software package HEIMDALL was employed for a mostly automated data collection. To evaluate the estimated reference point, the derived results are compared with the results of two approved models.

Prospective study of high geodetic resolution to future VGOS reference point determination

The fast slewing rate and wide band of the VLBI2010 Global Observing System (VGOS) telescopes are beneficial to procure more observations and to obtain VLBI reference points (RPs) of high precisions. Meanwhile, with the development of synchronous tracking of fixed targets on telescopes during the observing, the RPs also can be determined in near real time based on a frame defined by other techniques. These opportunities provide us a possibility to explore the high geodetic resolution of VGOS telescopes. We design a thermal variation in RP as true values, and schedule a synchronous session of VGOS and target point (TP) series observing. Then VGOS delays and TP series are simulated and solved via piecewise functions. The results show that the accuracy of vertical component of the RP could be determined at an accuracy of 0.5 ± 0.3 mm in an hour using TP series, whereas the vertical components of RP solved by using VGOS delay measurements have a greater uncertainty due to the random error in the simulated atmosphere and bad radio source sky coverage in a shorter time interval. Some details in the data processing and accuracy evaluation are also introduced.