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NASA NTRS2020

International VLBI Service for Geodesy and Astrometry 2017+2018 Biennial Report

Since its creation in 1999, the International VLBI Service for Geodesy and Astrometry (IVS) has documented its progress and current status in the form of annual or biennial reports. The first sixteen years were recorded in the form of annual reports, while starting with the years 2015+2016 the rhythm was changed to two years. Hence, the 2017+2018 Biennial Report constitutes the second installment of the two-yearly reporting scheme, documenting the work of the IVS components for the calendar years 2017 and 2018. As a testament to its usefulness, the general structure of the reporting has remained stable over the years: the individual components of the IVS contributed short reports describing their numerous activities, progress, and future plans. Without the continued input from the VLBI groups of the international geodetic and astrometric community, this publication could not be compiled and the IVS itself would not be able to flourish. So, once again many thanks to all IVS components who contributed to this Biennial Report.

Armstrong, Kyla L.↗
NASA NTRS2020

The Global Ecosystem Dynamics Investigation: High-Resolution Laser Ranging of the Earth’s Forests and Topography

Obtaining accurate and widespread measurements of the vertical structure of the Earth’s forests has been a longsought goal for the ecological community. Such observations are critical for accurately assessing the existing biomass of forests, and how changes in this biomass caused by human activities or variations in climate may impact atmospheric CO2 concentrations. Additionally, the three-dimensional structure of forests is a key component of habitat quality and biodiversity at local to regional scales. The Global Ecosystem Dynamics Investigation (GEDI) was launched to the International Space Station in late 2018 to provide high-quality measurements of forest vertical structure in temperate and tropical forests between 51.6 N & S latitude. The GEDI instrument is a geodetic-class laser altimeter/waveform lidar comprised of 3 lasers that produce 8 transects of structural information. Over its two-year nominal lifetime GEDI is anticipated to provide over 10 billion waveforms at a footprint resolution of 25 m. These data will be used to derive a variety of footprint and gridded products, including canopy height, canopy foliar profiles, Leaf Area Index (LAI), sub-canopy topography and biomass. Additionally, data from GEDI are used to demonstrate the efficacy of its measurements for prognostic ecosystem modeling, habit and biodiversity studies, and for fusion using radar and other remote sensing instruments. GEDI science and technology are unique: no other space-based mission has been created that is specifically optimized for retrieving vegetation vertical structure. As such, GEDI promises to advance our understanding of the importance of canopy vertical variations within an ecological paradigm based on structure, composition and function.

Dubayah, Ralph↗
NASA NTRSDate not supplied

Surviving and Thriving in Space and on Earth's Oceans - Human Logistics and Sustainability Comparisons and Considerations

The human species has a yearning for exploration as evidenced by the extensive historical ocean voyages and expeditions which have led to a massive advancement in the scientific and geodetic knowledge about planet Earth. These global explorations via the oceans have also had strategic, economic, cultural and religious implications and impacts, which have drastically changed the state of humanity and its condition. The transportation network created by ships traveling across the oceans has been supplemented by other transportation networks on land and in the air, creating a global economy that, in general, has improved the human condition leading to better health, longer lives, lower child mortality, better education, political freedom, higher gross national product (GNP) and improved hygiene. The logical extension of this societal trend is to extend the transportation network and human civilization into outer space, beyond the cradle of planet Earth. Our solar system contains vast amounts of natural resources which can be harnessed and used to bootstrap a space economy and related infrastructure by using advanced technologies. Sailing journeys from hundreds of years ago required large vessels and large crews, (in comparison with today’s space capsules). Modern sailors of today are able to complete large voyages, in small vessels, with a minimal crew, comparable in magnitude to modern space travel. This paper will use a systems engineering approach (e.g. using the NASA Human Integration Design Handbook (HIDH), NASA-SP-2010-3407, 2010 and the “Advanced Life Support Baseline Values and Assumptions Document, (BVAD)” NASA-CR-2004-208941, 2004.), to examine and compare the logistics and sustainability aspects of a small crew traveling on Earth's oceans in sailing vessels versus humans traveling in space. The “Mālama Honua Worldwide Voyage” of the Hokule’a, a replica of an ancient Hawaiian double hulled sailing canoe, will be used as a case study. This is the best comparison case since the Polynesian exploration of the vast (and virtually empty) Pacific Ocean is the closest analogue to modern space travel. “"Both are voyages of exploration.” –Shuttle astronaut Lacy Veach. Minimizing waste and maximizing re-use and re-cycling will lead to more efficient logistics and sustainability. In addition, In-Situ Resource Utilization (ISRU) strategies, based on successful Earth based strategies used for many years by sailors will be considered and evaluated for their usefulness. For example, human logistics for a typical space mission are shown in Table 1 and Table 2 (Lopez et al, 2015). Studies show that typical human water consumption in space is projected to be 3.2 kg/day per crew member as shown in Table 2. Data from human sailing voyages around the globe will be examined. Anecdotal evidence indicates that knowledgeable and well-equipped modern sailors, who conserve water, can comfortably live using 1.5 to 5 kg/day per person. This paper will investigate key logistics and sustainability aspects of living in space and compare them quantitatively to similar aspects of living on ocean faring sailing vessels on Earth. Mutually beneficial observations, advanced technologies and modern considerations will be applied within confines of a remote sailing environment, which could be of immense value to both the space faring community and the ocean sailing community.

Space↗
NASA NTRS2019

Evidence for recent and ancient faulting at Mare Frigoris and implications for lunar tectonic evolution

Nearside basin-related extensional tectonism on the Moon was thought to have ended by about 3.6 billion years ago and mare basin-localized contractional deformation ended by about 1.2 billion years ago. Lunar Reconnaissance Orbiter Camera (LROC) high resolution (50–200 cm/pixel) images show the Moon's surface in unprecedented detail and have enabled us to find many previously unidentified tectonic landforms, forcing a reassessment of our views of tectonism in the maria. The morphology and stratigraphic relationships of these newly identified populations of tectonic landforms imply a more complex and longer-lasting history of deformation. We selected Mare Frigoris as an ideal location to perform a mapping survey where excellent imaging conditions, abundant tectonic landforms, and restricted mascon allow us to unravel the mare's tectonic evolution. Similar to previous surveys, we find that tectonism in the eastern portion of Mare Frigoris was controlled by ancient mascon induced flexure. In the western portion, however, we identify a parallel set of ancient compressional wrinkle ridges across the mare that is inconsistent with an origin by mare basin-centric mascon flexure or influence from the Mare Imbrium mascon. Instead, our results imply an ancient, regional, non-isotropic stress field over western Mare Frigoris. We also identify young wrinkle ridges and show that they have likely been active within the last 1 billion years, and some ridges as recently as within 40 million years. Finally, we identify a 300 km long series of lobate scarps coincident with one of the shallow moonquakes recorded during Apollo and use geodetic strain from the mapped global population of young lobate scarps to predict a level of seismicity consistent with the shallow moonquakes recorded during Apollo. In tandem with similarly young lobate scarps and small graben, as well as recorded shallow moonquakes, these young wrinkle ridges imply that some tectonism in and around Mare Frigoris has occurred in the geologically recent past and likely still continues today.

Nathan R. Williams↗
NASA NTRS2020

Reconstructing Magma Storage Depths for the 2018 Kilauean Eruption from melt inclusion CO2 Contents: The importance of Vapor Bubbles

The 2018 Lower East Rift Zone (LERZ) eruption of Kīlauea Volcano and the accompanying collapse of the summit caldera marked the most destructive phase of activity on Hawai’i in the last 200 years. The integration of petrological data extracted from lava samples collected throughout the eruption with geodetic data examining the caldera collapse event, and estimates of the co-erupted flux of SO2 from the main eruptive fissure (Fissure 8), provides an exceptional opportunity to determine the reservoir geometry and magma transport paths supplying Kīlauea’s LERZ. The forsterite contents of erupted olivines and the degree of disequilibrium with their carrier melts indicate that two distinct olivine populations were erupted from Fissure 8. Melt inclusion entrapment pressures reveal that more evolved olivines (Fo<81.5) crystallized at ~2 km depth within the shallower Halema’uma’u reservoir, while more primitive olivines (Fo>81.5)crystallized within the deeper South Caldera reservoir at ~3–5 km depth. Crucially, primitive olivines experienced extensive post-entrapment crystallization, driving the growth of a vapor bubble. Raman spectroscopy reveals that this bubble contains up to 99% of the total inclusionCO2 budget (median=93%). Measurements of CO2 in only the glass phase would have underestimated entrapment depths by up to 60× (median=11×), and the importance of the SC reservoir as a source of magma to Fissure 8 would have been overlooked. Overall, we demonstrate that Raman measurements of bubbles, along with careful choice of suitably-calibrated H2O-CO2 solubility model, is vital to place accurate constraints on the depths of magma storage regions supplying volcanic eruptions.

SIMS↗
NASA NTRS2020

Improved LOLA Elevation Maps for South Pole Landing Sites: Error Estimates and Their Impact on Illumination Conditions

We present new high-resolution topographic models of 4 high-priority lunar south pole landing sites based exclusively on the laser altimetry data acquired by the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter. By iteratively adjusting the LOLA tracks to the LOLA-based digital elevation model (LDEM) in a self-consistent fashion, we reduce the orbital geolocation errors by over a factor of 10 such that the new ground track geolocation uncertainty is ~10–20 ​cm horizontally and ~2–4 ​cm vertically over each 16 ​× ​16 km region. These new and improved 5 ​m/pix LDEMs will be useful to constrain higher-resolution topographic models derived from imagery, which are not as well controlled geodetically and which can be hindered by shadows. We developed a method to estimate surface height uncertainty in the new LDEMs, which accounts for the reduced orbital errors and interpolation errors by assuming a fractal behavior for the short-scale topography. The LDEM surface height and slope uncertainties have typical RMS values of ~0.30–0.50 ​m and ~1.5–2.5°, respectively. Finally, we examine how height uncertainties propagate to variations in horizon elevation and thus the predicted illumination conditions at these polar latitudes, and we show how this error characterization can inform landing site studies.

Michael K Barker↗
NASA NTRSDate not supplied

Mapping Inundation from Hurricane Florence (2018) with L-Band Synthetic Aperture Radar, Commercial Imagery, and Ancillary Data via Machine Learning Classification

During and after flooding events, mapping the extent of floodwaters aids in the distribution of resources, recovery efforts, and damage assessment practices. Development of a land cover classification system focused on mapping inundation after major hurricane events using synthetic aperture radar (SAR) data could allow for the production of near-real-time inundation mapping, enabling government and emergency response entities to get a preliminary idea of a developing situation. Complimentary optical and SAR images from domestic and foreign entities are brought together through activations of the International Charter: Space and Major Disasters to support response efforts, from true-color, near-infrared, and thermal remote sensing data obtained by NASA, NOAA, and international satellites to the collection of high-resolution true color aerial photography by NOAA and the National Geodetic Survey. In response to Hurricane Florence of 2018, NASA JPL collected numerous swaths of quad-pol L-band SAR data with the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) instrument observing the record-setting river stages across North and South Carolina. The resulting fully-polarized SAR images allow for mapping of inundation extent at a high spatial resolution with a unique advantage over optical imaging stemming from the sensor’s ability to penetrate cloud cover and dense vegetation. In this study, true-color NOAA aerial and commercial satellite imagery are used in conjunction with four UAVSAR data swaths centered on the Lumberton and Cape Fear River basins in southeastern North Carolina to develop a Random Forest classification model focused on mapping open water and floodwater otherwise obscured by vegetation or lingering cloud cover. Ancillary building footprint, transportation route, and population data will also be incorporated into the classification scheme to estimate the societal impacts of flooding based on the proximity of features to detected inundation. Preliminary results from the Hurricane Florence case study will be discussed in addition to the limitations of available validation data for assessment of the classifier’s accuracy.

Alexander M Melancon↗
NASA NTRS1994

Seismology and Space-Based Geodesy

The spatial and temporal distributions of strain accoumulation and release involved in various tectonic and earthquake processes can be inferred from high-precision geodetic measurements of the correcponding crustal deformation at the Earth's surface.

Global↗
NASA NTRS1998

A Geodynamic Framework for Eastern Mediterranean Kinematics

We use a finite element model incorporating plate motion boundary conditions, fault constraints, and space geodetic velocities to calculate eastern Mediterranean plate kinematics and to estimate the motion of the region's major faults.

Plate↗
NASA NTRS1996

Combinations of Earth Orientation Measurements: SPACE94, COMB94, and POLE94

A Kalman filter has been used to combine independent measurements of the Earth's orientation taken by the space-geodetic observing techniques of lunar laser ranging, satellite laser ranging, very long baseline interferometry, and the Global Positioning System. Prior to their combination, the data series were adjusted to have the same bias and rate, the stated uncertainties of the measurements were adjusted, and data points considered to be outliers were deleted. The resulting combination, SPACE94, consists of smoothed, interpolated polar motion and UT1-UTC values spanning October 6.0, 1976, to January 27.0, 1995, at 1-day intervals.

Kalman↗
NASA NTRS1995

Combinations of Earth Orientation Measurements: COMB94 and POLE94

A Kalman filter has been used to combine Earth orientation measurements taken by optical astrometry with SPACE94, a previously determined combination of Earth orientation measurements taken by space-geodetic techniques. This created two series of combined, smoothed, and interpolated polar motion: COMB94 covering 1962-1995 at 5-day intervals, and POLE94 covering 1900 to 1995 at 30.4375-day intervals.

Earth↗
NASA NTRS2018

Design Principles for Smallsat SARs

Synthetic Aperture Radar (SAR) is by now a mature remote sensing technique to obtain spatially-resolved radar measurements of terrain. Currently, SAR image data are readily available from an ever-expanding multitude of SAR satellites in Earth orbit. Many spaceborne SAR systems currently in use or planned for the near-term are multifunctional: their designs tend to maximize the menu of image modes available to the end user. They also follow fairly conventional design principles, laid down decades ago, that lead almost inevitably to large antennas and even larger spacecraft. This raises the question: how does one go about designing a SAR system that fits in a Smallsat (<200 kg) form factor? The design principles for Smallsat SARs outlined in this paper have been developed over a twenty-year period in architecting Earth-orbiting SARs such as NASA/JPL’s NISAR and ESA’s Biomass mission, as well as planetary SAR mission concepts. Example mission concepts following this approach will be presented at the end of the paper. These include an S-Band Smallsat geodetic constellation to measure surface deformation, as called for by the 2018 National Academy Decadal Survey for Earth Observation from Space. Another example is a Ka-band cubesat-sized system designed to detect changes on Earth’s surface.

Freeman, Anthony↗
NASA NTRSDate not supplied

Optical Characterization of CLPS MiniatureLaser Retroreflector Arrays

Laser retroreflector arrays (LRAs) consisting of corner cube retroreflectors (CCRs) can act as fiducial markers for decades of laser ranging on the Moon and other planetary bodies. Upcoming lunar lander missions from government space agencies and commercial partners offer a unique opportunity to support lunar science and exploration through the deployment of small LRAs on lander decks. Placement of an LRA on the deck of a lander or rover enables tracking with an orbital laser altimeter to aprecision on the order of centimeters. When mounted alongside a suite of scientific instruments the LRA enables precise geolocation of those instruments in the lunar geodetic frame. Finally, optical markers such as LRAs can support precision autonomous navigation and landing regardless of lighting conditions, an especially valuable capability for lunar polar exploration where long shadows complicate terrain relative nagivation using imaging methods.

Daniel R. Cremons↗
NASA NTRS2021

Altimetry for the Future: Building on 25 Years of Progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion.

Saleh Abdalla↗