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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Remote sensing of the boundary layer

Limited information about the boundary layer stratification is obtained from remote infrared spectral measurements in the water vapor window region. A global map of the average strength of the water vapor spectral lines in the 9 micron window region derived from Nimbus 4 IRIS data is presented to indicate this boundary layer information. Presence of deep convective layer in the intertropical convergence zone and trade wind inversion over the subtropical oceanic high pressure systems are appropriately revealed in this map.

Prabhakara, C.↗
NASA NTRS2001

A Multilayer Dataset of SSM/I-Derived Global Ocean Surface Turbulent Fluxes

A dataset including daily- and monthly-mean turbulent fluxes (momentum, latent heat, and sensible heat) and some relevant parameters over global oceans, derived from the Special Sensor Microwave/Imager (SSM/I) data, for the period July 1987-December 1994 and the 1988-94 annual and monthly-mean climatologies of the same variables is created. It has a spatial resolution of 2.0deg x 2.5deg latitude-longitude. The retrieved surface air humidity is found to be generally accurate as compared to the collocated radiosonde observations over global oceans. The retrieved wind stress and latent heat flux show useful accuracy as verified against research quality measurements of ship and buoy in the western equatorial Pacific. The 1988-94 seasonal-mean wind stress and latent heat flux show reasonable patterns related to seasonal variations of the atmospheric general circulation. The patterns of 1990-93 annual-mean turbulent fluxes and input variables are generally in good agreement with one of the best global analyzed flux datasets that based on COADS (comprehensive ocean-atmosphere data set) with corrections on wind speeds and covered the same period. The retrieved wind speed is generally within +/-1 m/s of the COADS-based, but is stronger by approx. 1-2 m/s in the northern extratropical oceans. The discrepancy is suggested to be mainly due to higher COADS-modified wind speeds resulting from underestimation of anemometer heights. Compared to the COADS-based, the retrieved latent heat flux and sea-air humidity difference are generally larger with significant differences in the trade wind zones and the ocean south of 40degS (up to approx. 40-60 W/sq m and approx. 1-1.5 g/kg). The discrepancy is believed to be mainly caused by higher COADS-based surface air humidity arising from the overestimation of dew point temperatures and from the extrapolation of observed high humidity southward into data-void regions south of 40degS. The retrieved sensible heat flux is generally within +/-5 W/sq m of UWM/COADS, except for some areas in the extratropical oceans, where the differences in wind speed have large impact on the difference in sensible heat flux. The dataset of SSM/I-derived turbulent fluxes is useful for climate studies, forcing of ocean models, and validation of coupled ocean-atmosphere global models.

Chou, Shu-Hsien↗
NASA NTRS2017

Design Trade Study for a 4-Meter Off-Axis Primary Mirror Substrate and Mount for the Habitable-Zone Exoplanet Direct Imaging Mission

An extensive trade study was conducted to evaluate primary mirror substrate design architectures for the HabEx mission baseline 4-meter off-axis telescope. The study’s purpose is not to produce a final design, but rather to established a design methodology for matching the mirror’s properties (mass and stiffness) with the mission’s optical performance specifications (static dynamic wavefront error, WFE). The study systematically compares the effect of proven design elements (closed-back vs. open-back vs. partial-back; meniscus vs. flat back vs. shaped back; etc.), which can be implemented with proven space mirror materials (ULE and Zerodur), on static and dynamic WFE. Additionally, the study compares static and dynamic WFE of each substrate point design integrated onto three and six point mounts.

space↗
NASA NTRS1991

Sea level response to wind forcing in the tropical Atlantic

The circulation of the warm-water layer of the tropical Atlantic varies seasonally. This predominant signal is imposed by the annual migration of the Intertropical Covergence Zone separating two trade-wind regimes. As the migration varies interannually, so does the ocean circulation. A long-time objective of climate studies is to understand this interannual variability: to define its range, to fully explain the causal relationship between wind and ocean response, and eventually to understand how the resulting changes in sea surface temperature affect the wind field itself. Our initial objective is to observe and model the oceanic response.

Katz, Eli Joel↗
NASA NTRS2012

NASA Human Spaceflight Architecture Team Lunar Destination Activities

NASA's Human Spaceflight Architecture Team (HAT) Lunar Destination Team has been developing a number of "Design Reference Missions" (DRM) to inform exploration architecture development, transportation approaches, and destination elements and operations. There are four destinations being considered in the HAT studies: Cis-Lunar, Lunar, Near Earth Asteroids and Mars. The lunar destination includes all activities that occur on the moon itself, but not low lunar orbit operations or Earth Moon LaGrange points which are the responsibility of the HAT Cis-Lunar Team. This paper will review the various surface DRMs developed as representative scenarios that could occur in a human lunar return. The approaches have been divided into two broad categories: a seven day short stay mission with global capabilities and a longer extended duration stay of 28 days which is limited to the lunar poles as a landing zone. The surface elements, trade studies, traverses, concept of operations and other relevant issues and methodologies will be presented and discussed in the context and framework of the HAT ground rules and assumptions which are constrained by NASA's available transportation systems. An international collaborative effort based on the 2011 Global Exploration Roadmap (GER) will also be examined and evaluated.

Connolly, J. F.↗
NASA NTRS2010

Quantitative Measures of Immersion in Cloud and the Biogeography of Cloud Forests

Sites described as tropical montane cloud forests differ greatly, in part because observers tend to differ in their opinion as to what constitutes frequent and prolonged immersion in cloud. This definitional difficulty interferes with hydrologic analyses, assessments of environmental impacts on ecosystems, and biogeographical analyses of cloud forest communities and species. Quantitative measurements of cloud immersion can be obtained on site, but the observations are necessarily spatially limited, although well-placed observers can examine 10 50 km of a mountain range under rainless conditions. Regional analyses, however, require observations at a broader scale. This chapter discusses remote sensing and modeling approaches that can provide quantitative measures of the spatiotemporal patterns of cloud cover and cloud immersion in tropical mountain ranges. These approaches integrate remote sensing tools of various spatial resolutions and frequencies of observation, digital elevation models, regional atmospheric models, and ground-based observations to provide measures of cloud cover, cloud base height, and the intersection of cloud and terrain. This combined approach was applied to the Monteverde region of northern Costa Rica to illustrate how the proportion of time the forest is immersed in cloud may vary spatially and temporally. The observed spatial variation was largely due to patterns of airflow over the mountains. The temporal variation reflected the diurnal rise and fall of the orographic cloud base, which was influenced in turn by synoptic weather conditions, the seasonal movement of the Intertropical Convergence Zone and the north-easterly trade winds. Knowledge of the proportion of the time that sites are immersed in clouds should facilitate ecological comparisons and biogeographical analyses, as well as land use planning and hydrologic assessments in areas where intensive on-site work is not feasible.

Lawton, R. O.↗
NASA NTRS1980

Inference of the boundary layer structure over the oceans from satellite infrared measurements

Remote infrared spectral measurements in the 8-13 micron m window region, at a resolution about 3 cm/1, contain useful information about the water vapor and temperature stratification of the atmosphere within the first few kilometers above the water surface. Two pieces of information are retrieved from the spectral measurements: precipitable water vapor in the atmosphere, from the depth of the line structure between 8 and 9 micron m due to water vapor lines; and sea surface temperature, from the variation of brightness temperature between 11 and 13 micron m. Together, these two pieces of information can signify either the presence of a deep moist convective layer or the prevalence of stable conditions, such as caused by temperature inversions, which inhibit moist convection. A simple infrared radiative transfer model of the 9 micron m water vapor lines was developed to validate the method. With the help of this model and the Nimbus 4 infrared interferometer spectrometer data, a gross picture of the planetary boundary layer for different seasons over the global oceans is deduced. The important regions of the trade wind inversion and the intertropical convergence zones over all the oceans are clearly identified with this method. The derived information is in reasonable agreement with some observed climatological patterns over the oceans.

Prabhakara, C.↗
NASA NTRS2020

An Overview of CMIP5 and CMIP6 Simulated Cloud Ice, Radiation Fields, Surface Wind Stress, Sea Surface Temperatures and Precipitation over Tropical and Subtropical Oceans

The potential links between ice water path (IWP), radiation, circulation, sea surface temperature (SST) and precipitation over the Pacific and Atlantic Oceans resulting from the falling ice radiative effects (FIREs) are examined from present day model outputs of CMIP5 and CMIP6. The latter is divided into two subsets with (SON6) and without FIREs (NOS6) as more models with FIREs are included in CMIP6 than in CMIP5. Improvement in floating cloud ice (~20 g m-2) is noticeable over convective regions in CMIP6 relative to CMIP5. The inclusion of FIREs in SON6 subset may contribute to reduce biases of overestimated outgoing longwave radiation and downward surface shortwave and overestimated reflected shortwave at the top of the atmosphere (TOA) by magnitudes of 4?8 W m-2 over convective regions against CERES, compared to NOS6 subset. The reduced biases in radiative fluxes in convective regions stabilize the atmosphere and lead to circulation, SST, cloud and precipitation changes over the trade-wind regions, as seen from improved radiative fluxes (4?15 W m-2), surface wind stress biases, SST (0.2?0.8 K) and precipitation (1 mm day-1) biases. The significant improvement from NOS6 to SON6 leads to improved multi-model means for CMIP6 relative to CMIP5 for radiation fields over the trade wind regions but the degradation over convective zones is attributed to NOS6 subset. The results suggest that other sources of uncertainty and deficiencies in climate models may play significant roles for reducing discrepancies although FIREs, via radiation-circulation coupling, may be one of the factors that help to reduce regional biases.

Jui-Lin F Li↗
NASA NTRS2014

Implementation of Active Thermal Control (ATC) for the Soil Moisture Active and Passive (SMAP) Radiometer

NASA's Earth Observing Soil Moisture Active and Passive (SMAP) Mission is scheduled to launch in November 2014 into a 685 kilometer near-polar, sun-synchronous orbit. SMAP will provide comprehensive global mapping measurements of soil moisture and freeze/thaw state in order to enhance understanding of the processes that link the water, energy, and carbon cycles. The primary objectives of SMAP are to improve worldwide weather and flood forecasting, enhance climate prediction, and refine drought and agriculture monitoring during its three year mission. The SMAP instrument architecture incorporates an L-band radar and an L-band radiometer which share a common feed horn and parabolic mesh reflector. The instrument rotates about the nadir axis at approximately 15 revolutions per minute, thereby providing a conically scanning wide swath antenna beam that is capable of achieving global coverage within three days. In order to make the necessary precise surface emission measurements from space, the electronics and hardware associated with the radiometer must meet tight short-term (instantaneous and orbital) and long-term (monthly and mission) thermal stabilities. Maintaining these tight thermal stabilities is quite challenging because the sensitive electronics are located on a fast spinning platform that can either be in full sunlight or total eclipse, thus exposing them to a highly transient environment. A passive design approach was first adopted early in the design cycle as a low-cost solution. With careful thermal design efforts to cocoon and protect all sensitive components, all stability requirements were met passively. Active thermal control (ATC) was later added after the instrument Preliminary Design Review (PDR) to mitigate the threat of undetected gain glitches, not for thermal-stability reasons. Gain glitches are common problems with radiometers during missions, and one simple way to avoid gain glitches is to use the in-flight set point programmability that ATC affords to operate the radiometer component away from the problematic temperature zone. A simple ThermXL model (10 nodes) was developed to exercise quick trade studies among various proposed control algorithms: Modified P control vs. PI control. The ThermXL results were then compared with the detailed Thermal Desktop (TD) model for corroboration. Once done, the simple ThermXL model was used to evaluate parameter effects such as temperature digitization, heater size and gain margin, time step, and voltage variation of power supply on the ATC performance. A Modified P control algorithm was implemented into the instrument flight electronics based on the ThermXL results. The thermal short-term stability margin decreased by 10 percent with ATC and a wide temperature error band (plus or minus 0.1 degrees Centigrade) compared to the original passive thermal design. However, a tighter temperature error band (plus or minus 0.1 degrees Centigrade) increased the thermal short-term stability margin by a factor of three over the passive thermal design. The current ATC design provides robust thermal control, tighter stability, and greater in-flight flexibility even though its implementation was prompted by non-thermal performance concerns.

Mikhaylov, Rebecca↗
NASA NTRS1979

Remote sensing of seasonal distribution of precipitable water vapor over the oceans and inference of boundary layer structure

Over the ocean satellite infrared spectral measurements in the 18 micrometer water vapor band and the 11 micrometer window region were used to derive precipitable water vapor, w, in the atmosphere and the sea surface temperature, SST. Seasonal maps of w on the oceans derived from these data reveal the dynamical influence of the large scale atmospheric circulation. With the help of a model for the vertical distribution of water vapor, the configuration of the atmospheric boundary layer over the oceans can be inferred from w when the information of SST is combined. The gross seasonal mean structure of the boundary layer inferred in this fashion reveals the broad areas of the trade wind inversion and the convectively active areas such as the intertropical convergence zones.

Prabhakara, C.↗
NASA NTRS2021

Assessing Relay Communications for Mars Sample Return Surface Mission Concepts

The Mars Sample Return (MSR) Campaign is a 3-mission campaign concept supported by NASA and ESA to return samples from the Mars surface. MSR will, for the firsttime ever, present a need to communicate with multiple surfaceassets that are co-located on Mars in a coordinated effort toaccomplish the unified objective of fetching, transporting, andreturning samples from Mars. Currently, Mars surface assetsrelay data to and from Earth using a number of orbiters inwhat’s known as the Mars Relay Network (MRN). This networkis characterized by a small number of surface assets distributedacross the Martian globe and a larger number of orbiters toprovide relay services. As of June 2020, there are two surfaceassets for which five orbiters are providing relay. During theMSR Campaign, there will be two rovers and a lander that allwill require relay communication from a small number of Marsorbiters to meet the aggressive MSR timeline. The inversion ofthe current MRN paradigm, a system of many surface assetsrequiring relay and few orbiters to provide relay, necessitatesthe unique challenge of optimally allocating relay passes tomaximize the operational capability of all assets. The allocationmust consider a large number of trade variables includingMars asset operational requirements and Earth ground systemconstraints, including staffing schedules, operations planningacross time zones, and more. To address these telecommunicationchallenges, the Mars Asset Relay Mission Link AllocationDesign Environment (MARMLADE) tool was developed. Itis a MATLAB-based tool to assign orbiter passes or Direct-From-Earth (DFE) links to each of the three surface assets andquantify the operational efficiency of each surface asset.MARMLADE uses a data set of simulated Mars relay orbitergeometry and telecommunication capabilities provided by JPL’sTelecom Orbit Analysis and Simulation Tool (TOAST) softwareto compute which asset should get each pass based on a seriesof heuristics and predictions of all assets’ states. WithinMARMLADE, the user can provide inputs including the optionfor time-based pass splitting, fixed FWD data rate capabilities,DFE communication capabilities, and link parameters allowingfor the assessment of complex operations and hardware tradesusing surface mission operational efficiency as a primary figureof merit. As the MSR mission concepts continue to mature,MARMLADE is being used to assess ability of all MSR elementsto meet the surface mission timeline requirements and to provide relay link allocations to each of the MSR surface assets.

Lee, Charles↗
NASA NTRS2021

Assessing Relay Communications for Mars Sample Return Surface Mission Concepts

The Mars Sample Return (MSR) Campaign would be a 3-mission campaign concept supported by NASA and ESA to return samples from the Mars surface. MSR would, for the first time ever, present a need to communicate with multiple surface assets that are co-located on Mars in a coordinated effort to accomplish the unified objective of fetching, transporting, and returning samples from Mars. Currently, Mars surface assets relay data to and from Earth using a number of orbiters in what’s known as the Mars Relay Network (MRN). This network is characterized by a small number of surface assets distributed across the Martian globe and a larger number of orbiters to provide relay services. As of June 2020, there are two surface assets for which five orbiters are providing relay. During the MSR Campaign, there would be two rovers and a lander that all would require relay communication from a small number of Mars orbiters to meet the aggressive MSR timeline. The inversion of the current MRN paradigm, a system of many surface assets requiring relay and few orbiters to provide relay, necessitates the unique challenge of optimally allocating relay passes to maximize the operational capability of all assets. The allocation must consider a large number of trade variables including Mars asset operational requirements and Earth ground system constraints, including staffing schedules, operations planning across time zones, and more. To address these telecommunication challenges, the Mars Asset Relay Mission Link Allocation Design Environment (MARMLADE) tool was developed. It is a MATLAB-based tool to assign orbiter passes or Direct-From-Earth (DFE) links to each of the three surface assets and quantify the operational efficiency of each surface asset.MARMLADE uses a data set of simulated Mars relay orbiter geometry and telecommunication capabilities provided by JPL’s Telecom Orbit Analysis and Simulation Tool (TOAST) software to compute which asset should get each pass based on a series of heuristics and predictions of all assets’ states. Within MARMLADE, the user can provide inputs including the option for time-based pass splitting, fixed FWD data rate capabilities, DFE communication capabilities, and link parameters allowing for the assessment of complex operations and hardware trades using surface mission operational efficiency as a primary figure of merit. As the MSR mission concepts continue to mature, MARMLADE is being used to assess ability of all MSR elements to meet the surface mission timeline requirements and to provide relay link allocations to each of the MSR surface assets.This paper will describe the motivation and design of the MARMLADE tool and how it is being used to perform campaign and mission level trades, generate requirements, and support development of the MSR surface mission scenarios.

Lee, Charles↗
NASA NTRSDate not supplied

Surface Transportation of the Common Habitat from Lander to Habitation Zone

The Common Habitat Architecture is a feasibility study surrounding the use of an SLS core stage liquid oxygen tank as the pressure vessel for a long-duration habitat intended for use in multiple gravity environments. The Common Habitat is used within this study as the primary habitation element in both Moon and Mars surface base camps. The Common Habitat Architecture offloads the Common Habitat from its lander and transports it to a Habitation Zone instead of leaving the habitat integrated with the lander. In this study, the Landing Zone is assumed to be approximately 3.5 kilometers from the Habitation Zone. Given the physical size and estimated 90-ton mass of the Common Habitat, a four-week trade study encompassing Moon and Mars lander identification, offloading, surface transport, and emplacement was conducted in February 2021 to assess whether there are any credible options for landing the Common Habitat on the Moon or Mars and deliver it to its intended point of use. Constrained to use only public data, the study applied subject matter expert opinion to each component of the study. The surface transportation component of the trade study assumes the habitat has been successfully offloaded from its lander and is at a point of handover to the surface transportation system. It is assumed that there are no crew present, and all human operations are performed remotely by Mission Control personnel. Three core cargo handling elements from prior NASA studies were used as the basis from which to derive surface transportation options – the Chariot, the All-Terrain Hex-Limbed Extra-Terrestrial Explorer, and the Lightweight Surface Manipulator System. Variations and hybrid combinations of these elements were used to develop transportation options for the Moon and Mars, given different habitat masses. Ultimately, several potentially feasible solutions were identified, and a solution was recommended that is common to both the Moon and Mars, with the potential to use a dissimilar system as a backup during lunar Common Habitat delivery. Next steps for sizing and additional development and analysis of the recommended surface transportation system are included as forward work.

Surface Mobility↗
NASA NTRS2017

Coronagraph Design Optimization for Segmented Aperture Telescopes

The goal of directly imaging Earth-like planets in the habitable zone of other stars has motivated the design of coronagraphs for use with large segmented aperture space telescopes. In order to achieve an optimal trade-o between planet light throughput and di racted starlight suppression, we consider coronagraphs comprised of a stage of phase control implemented with deformable mirrors (or other optical elements), pupil plane apodization masks (gray scale or complex valued), and focal plane masks (either amplitude only or complex-valued, including phase only such as the vector vortex coronagraph). The optimization of these optical elements, with the goal of achieving 10 or more orders of magnitude in the suppression of on-axis (starlight) di racted light, represents a challenging non-convex optimization problem with a nonlinear dependence on control degrees of freedom. We develop a new algorithmic approach to the design optimization problem, which we call the "Auxiliary Field Optimization" (AFO) algorithm. The central idea of the algorithm is to embed the original optimization problem, for either phase or amplitude (apodization) in various planes of the coronagraph, into a problem containing additional degrees of freedom, speci cally ctitious "auxiliary" electric elds which serve as targets to inform the variation of our phase or amplitude parameters leading to good feasible designs. We present the algorithm, discuss details of its numerical implementation, and prove convergence to local minima of the objective function (here taken to be the intensity of the on-axis source in a "dark hole" region in the science focal plane). Finally, we present results showing application of the algorithm to both unobscured o -axis and obscured on-axis segmented telescope aperture designs. The application of the AFO algorithm to the coronagraph design problem has produced solutions which are capable of directly imaging planets in the habitable zone, provided end-to-end telescope system stability requirements can be met. Ongoing work includes advances of the AFO algorithm reported here to design in additional robustness to a resolved star, and other phase or amplitude aberrations to be encountered in a real segmented aperture space telescope.

Redding, Dave↗
NASA NTRS2008

Terrestrial Planet Finder Interferometer: 2007-2008 Progress and Plans

This paper provides an overview of technology development for the Terrestrial Planet Finder Interferometer (TPF-I). TPF-I is a mid-infrared space interferometer being designed with the capability of detecting Earth-like planets in the habitable zones around nearby stars. The overall technology roadmap is presented and progress with each of the testbeds is summarized. The current interferometer architecture, design trades, and the viability of possible reduced-scope mission concepts are also presented.

formation flying↗
NASA NTRS2011

Hybrid RF / Optical Communication Terminal with Spherical Primary Optics for Optical Reception

Future deep space communications are likely to employ not only the existing RF uplink and downlink, but also a high capacity optical downlink. The Jet Propulsion Laboratory (JPL) is currently investigating the benefits of a ground based hybrid RF and deep space optical terminal based on limited modification of existing 34 meter antenna designs. The ideal design would include as large an optical aperture as technically practical and cost effective, cause minimal impact to RF performance, and remain cost effective even when compared to a separate optical terminal of comparable size. Numerous trades and architectures have been considered, including shared RF and optical apertures having aspheric optics and means to separate RF and optical signals, plus, partitioned apertures in which various zones of the primary are dedicated to optical reception. A design based on the latter is emphasized in this paper, employing spherical primary optics and a new version of a "clamshell" corrector that is optimized to fit within the limited space between the antenna sub-reflector and the existing apex structure that supports the subreflector. The mechanical design of the hybrid accommodates multiple spherical primary mirror panels in the central 11 meters of the antenna, and integrates the clamshell corrector and optical receiver modules with antenna hardware using existing attach points to the maximum extent practical. When an optical collection area is implemented on a new antenna, it is possible to design the antenna structure to accommodate the additional weight of optical mirrors providing an equivalent aperture of several meters diameter. The focus of our near term effort is to use optics with the 34 meter DSS-13 antenna at Goldstone to demonstrate spatial optical acquisition and tracking capability using an optical system that is temporarily integrated into the antenna.

optical communications↗
NASA NTRS1982

A simple atmospheric model of relevance to El Nino

A linear, equatorial, beta-plane atmosphere model with heating parameterized in terms of SST anomalies is developed and used to simulate surface wind anomalies in the equatorial Pacific during El Nino. The model results show some similarity to observations with respect to movement of the major convergence zones, and equatorial wind anomaly patterns in the central and western Pacific. There is considerable discrepancy between the model results and observations in much of the eastern Pacific, especially in the South Pacific high and southeast trades regions. The results suggest that some additional mechanisms may be responsible for these apparently sizeable and spatially coherent fluctuations, but that a direct link between wind anomalies and SST anomalies may indeed exist in much of the equatorial Pacific.

Zebiak, S. E.↗
NASA NTRS2020

Cramer-Rao Lower Bound for SoOp-R-Based Root-Zone Soil Moisture Remote Sensing

Signals of opportunity (SoOp) reflectometry (SoOp-R) is a maturing field for geophysical remote sensing as evidenced by the growing number of airborne and spaceborne experiments. As this approach receives more attention, it is worth analyzing SoOp-R’s capabilities to retrieve subsurface soil moisture (SM) by leveraging communication and navigation satellite transmitters. In this research, the CRLB is used to identify the effects of variable SoOp-R parameters on the best achievable estimation error for root-zone soil moisture (RZSM). This study investigates the use of multiple frequency, polarization, and incidence angle measurement configurations on a two-layered dielectric profile. The results also detail the effects of variable SM conditions on the capability of SoOp-R systems to predict subsurface SM. The most prevalent observation is the importance of using at least two frequencies to limit uncertainties from subsurface SM estimates. If at least two frequencies are used, the CRLB of a profile is retrievable within the root-zone depending on the surface SM content as well as the number of independent measurements of the profile. For a depth of 30 cm, it is observed that a CRLB corresponding to 4% RZSM estimation accuracy is achievable with as few as 2 dual-frequency-based SoOp-R measurements. For this depth, increasing number of measurements provided by polarization and incidence angle allow for sensing of increasingly wet SM profile structures. This study, overall, details a methodology by which SoOp-R receiver system can be designed to achieve a desired CRLB using a trade-off study between the available measurements and SM profile.

Signals of Opportunity (SoOp)↗