Precipitation is a well-recognized pillar in global water and energy balances. An accurate and timely understanding of its characteristics at the global, regional, and local scales is indispensable ...for a clearer understanding of the mechanisms underlying the Earth’s atmosphere–ocean complex system. Precipitation is one of the elements that is documented to be greatly affected by climate change.
In its various forms, precipitation comprises a primary source of freshwater, which is vital for the sustainability of almost all human activities. Its socio-economic significance is fundamental in managing this natural resource effectively, in applications ranging from irrigation to industrial and household usage.
Remote sensing of precipitation is pursued through a broad spectrum of continuously enriched and upgraded instrumentation, embracing sensors which can be ground-based (e.g., weather radars), satellite-borne (e.g., passive or active space-borne sensors), underwater (e.g., hydrophones), aerial, or ship-borne.
Precipitation is a well-recognized pillar in global water and energy balances. An accurate and timely understanding of its characteristics at the global, regional, and local scales is indispensable ...for a clearer understanding of the mechanisms underlying the Earth’s atmosphere–ocean complex system. Precipitation is one of the elements that is documented to be greatly affected by climate change.
In its various forms, precipitation comprises a primary source of freshwater, which is vital for the sustainability of almost all human activities. Its socio-economic significance is fundamental in managing this natural resource effectively, in applications ranging from irrigation to industrial and household usage.
Remote sensing of precipitation is pursued through a broad spectrum of continuously enriched and upgraded instrumentation, embracing sensors which can be ground-based (e.g., weather radars), satellite-borne (e.g., passive or active space-borne sensors), underwater (e.g., hydrophones), aerial, or ship-borne.
Stereo methods using GOES‐17 and Himawari‐8 applied to the Hunga Tonga‐Hunga Ha'apai volcanic plume on 15 January 2022 show overshooting tops reaching 50–55 km altitude, a record in the satellite ...era. Plume height is important to understand dispersal and transport in the stratosphere and climate impacts. Stereo methods, using geostationary satellite pairs, offer the ability to accurately capture the evolution of plume top morphology quasi‐continuously over long periods. Manual photogrammetry estimates plume height during the most dynamic early phase of the eruption and a fully automated algorithm retrieves both plume height and advection every 10 min during a more frequently sampled and stable phase beginning 3 hr after the eruption. Stereo heights are confirmed with Global Navigation Satellite System Radio Occultation bending angles, showing that much of the plume was lofted 30–40 km into the atmosphere. Cold bubbles are observed in the stratosphere with brightness temperature of ∼173 K.
Plain Language Summary
The Hunga Tonga‐Hunga Ha'apai volcano in the South Pacific erupted violently on 15 January 2022. A volcanic plume from the eruption was lofted into the stratosphere to altitudes that are unprecedented in the era of satellite observations. We observed the highest part of the plume at 55 km and tracked the motion of the plume in 3D in the vicinity of the volcano for a 7‐hr period, every 10 min, using imagery from the geostationary GOES‐17 and Himawari‐8 satellites that are positioned at different locations on the equator. The apparent shift in the plume as seen from two different vantage points contains information about the plume height and the apparent movement of the plume as it is repeatedly observed by one satellite contains information about the plume velocity. We confirmed our height observations using radio occultation measurements that NOAA uses to profile the atmosphere. Radio waves are normally bent as they pass through the atmosphere from satellite to satellite, nearly grazing the Earth's surface, but when radio waves pass through the volcanic plume, there is an anomalously large change in bending angle.
Key Points
The Hunga Tonga‐Hunga Ha'apai eruption of 15 January 2022, lofted material above 30 km to record‐breaking heights of ∼55 km
Our stereo‐winds code retrieved height and motion vectors from GOES‐17 and Himawari‐8 every 10 min shortly after the eruption
Radio occultation bending angles confirm plume altitudes
Using the first full annual cycle of Cyclone Global Navigation Satellite System (CyGNSS) observations, we investigated the limitations and capabilities of CyGNSS observations for soil moisture (SM) ...estimates (0–5 cm). A relative signal‐to‐noise ratio (rSNR) value from a CyGNSS‐derived delay‐Doppler map is introduced to improve the temporal resolution of SM derived from Soil Moisture Active Passive (SMAP) data. We then evaluated the CyGNSS‐derived rSNR using ground‐based SM measurements and the triple collocation method with SMAP and modeled SM products. We found that CyGNSS can provide useful SM estimates over moderately vegetated regions (correlation coefficient of the individual data: 0.77) but shows degraded performance over arid and densely vegetated regions (correlation coefficient of the individual data: 0.68 and 0.67). However, when rSNR data is combined with SM data from SMAP, daily SM estimates can be achieved. These results show that synergistic use of CyGNSS observations can improve on SM estimates from current satellite systems.
Plain Language Summary
Accurate climate forecasting affects our daily lives. Large‐scale farmers depend on weather forecasts to decide when to plant their crops. Bad timing can impact the whole years' harvest and thus the farmers' livelihoods. Even more importantly, people who live in floodplains and hurricane zones trust their lives to accurate weather forecasts. For these reasons and more, hydrologists need up‐to‐date knowledge of Earth's climate systems. And one of the most important sources of data may surprise you. The amount of moisture in just the first 8 mm of topsoil affects all of Earth's climate systems. Currently, National Aeronautics and Space Administration keeps track of soil moisture levels with a satellite called Soil Moisture Active Passive. However, it only provides soil moisture data every 2–3 days. We believe that we can do better, and we believe that we can do it with preexisting satellite systems. In 2017, National Aeronautics and Space Administration (NASA) launched eight microsatellites, called Cyclone Global Navigation Satellite System (CyGNSS), to predict cyclone paths. We have found that while the CyGNSS satellites are predicting cyclone paths, they can simultaneously measure changes in soil moisture around 5 times per day. Augmenting the Soil Moisture Active Passive data with CyGNSS would give us detailed prediction of weather changes in near‐real time, protecting livelihoods and lives.
Key Points
CyGNSS‐derived signal‐to‐noise ratio data were utilized for soil moisture estimation
CyGNSS data can fill the gap of missing spatial and temporal values in existing satellite‐based soil moisture retrieval systems
By combining CyGNSS and SMAP data sets, reliable daily soil moisture estimates from space can be achieved
Low earth orbit (LEO) satellite communications are expected to be incorporated in future wireless networks, in particular 5G and beyond networks, to provide global wireless access with enhanced data ...rates. Massive multiple-input multiple-output (MIMO) techniques, though widely used in terrestrial communication systems, have not been applied to LEO satellite communication systems. In this paper, we propose a massive MIMO transmission scheme with full frequency reuse (FFR) for LEO satellite communication systems and exploit statistical channel state information (sCSI) to address the difficulty of obtaining instantaneous CSI (iCSI) at the transmitter. We first establish the massive MIMO channel model for LEO satellite communications and simplify the transmission designs via performing Doppler and delay compensations at user terminals (UTs). Then, we develop the low-complexity sCSI based downlink (DL) precoder and uplink (UL) receiver in closed-form, aiming to maximize the average signal-to-leakage-plus-noise ratio (ASLNR) and the average signal-to-interference-plus-noise ratio (ASINR), respectively. It is shown that the DL ASLNRs and UL ASINRs of all UTs reach their upper bounds under some channel condition. Motivated by this, we propose a space angle based user grouping (SAUG) algorithm to schedule the served UTs into different groups, where each group of UTs use the same time and frequency resource. The proposed algorithm is asymptotically optimal in the sense that the lower and upper bounds of the achievable rate coincide when the number of satellite antennas or UT groups is sufficiently large. Numerical results demonstrate that the proposed massive MIMO transmission scheme with FFR significantly enhances the data rate of LEO satellite communication systems. Notably, the proposed sCSI based precoder and receiver achieve the similar performance with the iCSI based ones that are often infeasible in practice.
ABSTRACT We explore the past evolution of Saturn's moons using direct numerical integrations. We find that the past Tethys-Dione 3:2 orbital resonance predicted in standard models likely did not ...occur, implying that the system is less evolved than previously thought. On the other hand, the orbital inclinations of Tethys, Dione, and Rhea suggest that the system did cross the Dione-Rhea 5:3 resonance, which is closely followed by a Tethys-Dione secular resonance. A clear implication is that either the moons are significantly younger than the planet or their tidal evolution must be extremely slow (Q > 80,000). As an extremely slow evolving system is incompatible with intense tidal heating of Enceladus, we conclude that the moons interior to Titan are not primordial, and we present a plausible scenario for the system's recent formation. We propose that the midsized moons re-accreted from a disk about 100 Myr ago, during which time Titan acquired its significant orbital eccentricity. We speculate that this disk has formed through orbital instability and massive collisions involving the previous generation of Saturn's midsized moons. We identify the solar evection resonance perturbing a pair of midsized moons as the most likely trigger of such an instability. This scenario implies that most craters on the moons interior to Titan must have been formed by planetocentric impactors.
Ocean worlds are prevalent in the solar system. Focusing on Enceladus, Titan, Europa, and Ganymede, I use rotating convection theory and numerical simulations to predict ocean currents and the ...potential for ice‐ocean coupling. When the influence of rotation is relatively strong, the oceans have multiple zonal jets, axial convective motions, and most efficient heat transfer at high latitudes. This regime is most relevant to Enceladus and possibly to Titan and may help explain their long‐wavelength topography. For a more moderate rotational influence, fewer zonal jets form, Hadley‐like circulation cells develop, and heat flux peaks near the equator. This regime is predicted for Europa, where it may help drive geologic activity via thermocompositional diapirism in the ice shell, and is possible for Titan. Weak rotational influence allows concentric zonal flows and overturning cells with no preferred orientation. Predictions for Ganymede's ocean span multiple regimes.
Plain Language Summary
The outer solar system is host to a large number of diverse satellites, many of which likely have global oceans beneath their outer icy shells. I use theoretical arguments and numerical models to make predictions about ocean currents and heat transfer across such oceans. Our results suggest that strong ocean currents exist in Enceladus, Titan, Europa, and Ganymede and cause the transfer of heat to vary with latitude that may modify the overlying ice shell.
Key Points
Ocean dynamics are important for the habitability of icy ocean worlds
Strong ocean currents likely exist in Enceladus, Titan, Europa, and Ganymede
Convective heat transfer in the ocean is predicted to vary with latitude, which would modify the thermophysical structure of the ice shell
This book presents fundmentals of orbit determination--from weighted least squares approaches (Gauss) to today's high-speed computer algorithms that provide accuracy within a few centimeters. ...Numerous examples and problems are provided to enhance readers' understanding of the material.
*Covers such topics as coordinate and time systems, square root filters, process noise techniques, and the use of fictitious parameters for absorbing un-modeled and incorrectly modeled forces acting on a satellite. *Examples and exercises serve to illustrate the principles throughout each chapter. *Detailed solutions to end-of-chapter exercises available to instructors.
China's BeiDou navigation system (BDS) has evolved from the demonstration navigation satellite system (BDS‐1) to the regional navigation satellite system (BDS‐2). Now, the global BeiDou navigation ...system (BDS‐3) is in construction and is proceeding well. The design and functions of BDS‐3 are quite different from those of both BDS‐1 and BDS‐2. In this paper, the general design, the coordinate reference system, and the system time basis of BDS‐3 are introduced. Several new payloads designed to accomplish different objectives are described as well as the platforms on which they are hosted. Since BDS‐3 consists of several different constellations, the general service capabilities and special service functions provided by these different constellations are described. The performances of the initial BDS‐3 platforms are evaluated based on the available eight‐medium Earth orbit (MEO) satellite configuration. The results of satellite orbit determination and prediction with and without the BDS‐3 inter‐satellite links (ISL) are compared and analyzed.
Recently, low earth orbit (LEO) satellite-based systems have attracted tremendous attention and various technologies have been developed for payload miniaturization and optical communications. In ...addition, mega-constellation architectures are expected to be deployed with LEO satellites for global broadband networks. In this article, we present a thorough analysis of mega-constellation architecture in terms of a change in the number of visible satellites and antenna steering capability to investigate the impact of increase in the constellation size and adoption of optical intersatellite links. The network architecture is evaluated with respect to satellite antenna steering capability and the satellite visibility considering the very narrow beam divergence of optical communications. We analyze the impact of a change in relative positions among the satellites due to continuous satellite movement in the constellation. The results offer guidelines for designing a novel visibility matrix using a time-varying satellite topology. This could defuse the problem of the conventional studies using fixed visibility matrices. The proposed time-varying visibility matrix achieves better performance than the previous preassigned links in terms of end-to-end link distance and hop count of LEO satellite networks.
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