cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.48577/jpl.wuc1vu
title: Optimal estimation of snow and ice surface parameters from imaging spectroscopy measurements

description: Snow and ice melt processes are key indicators of climate change, and may be assessed with remote sensing instruments. These processes decrease the surface reflectance with unique spectral patterns due to the accumulation of liquid water and light absorbing particles (LAP), making imaging spectroscopy a powerful tool to measure and map this phenomenon. Here we present a new method to retrieve snow grain size, liquid water fraction, and LAP mass mixing ratio from airborne and space borne imaging spectroscopy acquisitions. This methodology is based on a simultaneous retrieval of atmospheric and surface parameters using optimal estimation (OE), a retrieval technique which leverages prior knowledge and measurement noise in the inversion and models estimation uncertainties. The retrieval extends the surface model by exploiting statistical relationships between surface reflectance spectra and the snow properties to estimate their most probable quantities given the reflectance. To test this new algorithm we conducted a sensitivity analysis based on simulated EnMAP spectra, demonstrating accurate estimation performance of snow surface properties for orbital observations. An additional validation experiment of the extended surface model approach was conducted using in-situ measurements of algae mass mixing ratios and surface reflectance from the Greenland Ice Sheet yielding promising results. Finally, we evaluated the retrieval capacity for all snow properties with an AVIRIS-NG acquisition from the Greenland Ice Sheet demonstrating this approach’s potential and suitability for upcoming orbital imaging spectroscopy missions.
DOI: 10.48577/jpl.cueeot
title: The Chandra Deep Wide-Field Survey: A New Chandra Legacy Survey in the Boo ̈tes Field I. X-ray Point Source Catalog, Number Counts and Multi-Wavelength Counterparts

description: We present a new, ambitious survey performed with the Chandra X-ray Observatory of the 9.3 deg2 Bo¨otes field of the NOAO Deep Wide-Field Survey. The wide field probes a statistically representative volume of the Universe at high redshift. The Chandra Deep Wide-Field Survey exploits the excellent sensitivity and angular resolution of Chandra over a wide area, combining 281 observations spanning 15 years, for a total exposure time of 3.4 Ms, and detects 6891 X-ray point sources down to limiting fluxes of 4:7 10􀀀16, 1:5 10􀀀16, and Corresponding author: Alberto Masini amasini@sissa.it 2 MASINI ET AL. 910􀀀16 erg cm􀀀2 s􀀀1, in the 0:5􀀀7 keV, 0:5􀀀2 keV, and 2􀀀7 keV bands, respectively. The robustness and reliability of the detection strategy is validated through extensive, state-of-the-art simulations of the whole field. Accurate number counts, in good agreement with previous X-ray surveys, are derived thanks to the uniquely large number of point sources detected, which resolve 65:0 12:8% of the cosmic X-ray background between 0:5􀀀2 keV and 81:011:5% between 2􀀀7 keV. Exploiting the wealth of multi-wavelength data available on the field, we assign redshifts to 94% of the X-ray sources, estimate their obscuration and derive absorptioncorrected luminosities. We provide an electronic catalog containing all the relevant quantities needed for future investigations.
DOI: 10.48577/jpl.t6zcxs
title: Robust retrieval of soil moisture at field scale across wide-ranging SAR incidence angles for soybean, wheat, forage, oat and grass

description: Abstract: Surface soil moisture is estimated by inverting physical scattering models for low- crops using L-band airborne SAR data over the incidence angle range from 30 to 50. The forward simulation is accurate with 1.7, 1.8, and 2.3 dB rmse for grass, wheat (including oat and forage), and soybean respectively assessed over 38 fields and during the full growth period for soybean. Dominant scattering mechanisms revealed by the model are found consistent across the incidence angle range: surface (VV) and double bounce (HH) for grass, double bounce for both polarization of wheat, and surface (young plant) and volume (mature plant) for both polarization of soybean. The model fidelity is robust across incidence angles between 30 and 50, benefiting from rigorously simulating the three scattering mechanisms and successfully simulating the effect of vegetation and roughness.The soil moisture estimates are accurate to unbiased rmse of 0.041, 0.059 and 0.060 m3/m3 and correlation of 0.71, 0.83, and 0.69 for grass, wheat, and soybean fields, respectively over the soil moisture dynamic range up to 0.5 m3/m3, and soybean’s full growth cycle. Vegetation water content and surface roughness are retrieved simultaneously to the soil moisture solutions, thus constraining the inversion of soil moisture. The retrieval performance is fairly uniform across the incidence angle, partly because of the reliable forward modeling across the incidence angle and also thanks to the reliable retrieval strategy. The robustness against the incidence angle supports frequent global mapping.The use of both HH and VV offers superior soil moisture retrievals than single-channel VV or HH input perfoms, by 0.034 m3/m3 unbiased rmse for grass and by 0.01 m3/m3 for wheat and soybean. The VV-based retrieval performed better than HH for grass and soybean, where surface scattering was important, but either choice resulted in similar retrieval accuracy for double-bounce dominanted wheat. No need for quad-pol and multi-angular observations would allow the retrieval approach to be applicable for spaceborne global mapping.
DOI: 10.48577/jpl.6zir65
title: High-fidelity comet 67P ephemeris and predictions based on Rosetta data

description: Because of observational biases and outgassing, comets are notoriously challenging interms of trajectory estimation and ephemeris predictions. We used tracking data collected by ESA’s Rosetta mission at 67P/Churyumov-Gerasimenko to derive 10-meterlevel constraints on the distance between the Earth and 67P in 2014 and 2016, which,together with high-quality ground-based astrometry, provide unprecedented information on a comet’s trajectory. Based on these data, we reconstruct the trajectory of67P from 2012 to 2018 by modeling nongravitational perturbations with a rotating jetmodel, informed by measured physical properties of the comet. Using this trajectoryreconstruction as reference, we characterize the astrometric error of publicly availableoptical observations of 67P and show how their quality significantly degrades withbrightness and proximity to the Sun. Moreover, we assessed the accuracy of predictionsmade with different nongravitational perturbation models and data treatments. Whileeach comet is unique and it is difficult to provide a general recipe, the reliability of anephemeris can benefit from the availability of high-quality data with quantified uncertainties and can be gauged by comparing different ephemeris solutions and tracking asolution’s stability and predictive performance as new observations are added to the fit.
DOI: 10.48577/jpl.53vkd1
title: A Low-noise Photonic Heterodyne Synthesizer and Application to Millimeter-wave Radar

description: Microwave photonic systems have created new paradigms for ultra-wideband electronic signal processing and frequency synthesis with record-low phase noise levels. Despite the intrinsic bandwidth of optical systems operating at ~200 THz carrier frequencies, many existing schemes for high-performance photonics-based microwave generation lack wideband tunability, and experience tradeoffs between noise level, system complexity, and operation frequency. An alternative approach uses direct frequency down-mixing of two tunable semiconductor lasers on a fast photodiode. This form of optical heterodyning produces widely-tunable operation, but experimental realizations have been hindered by the relatively high noise of free-running lasers. Here, we demonstrate a heterodyne synthesizer based on ultralow-noise self-injection-locked lasers, enabling highly-coherent, photonics-based microwave and millimeter-wave generation. Continuously-tunable operation is realized from 1-104 GHz, with constant phase noise of -109 dBc/Hz at 100 kHz offset from carrier across this frequency range. This tuning range is limited only by photodiode availability. To explore its practical utility, we leverage this photonic source as the local oscillator within a 95-GHz frequency-modulated continuous wave (FMCW) radar. Through field testing, we observe dramatic reduction in phase-noise-related Doppler and ranging artifacts as compared to the radar's existing electronic synthesizer. These results establish strong potential for coherent heterodyne millimeter-wave generation, opening the door to a wide variety of future applications including high-dynamic range remote sensing, wideband wireless communications, and THz spectroscopy.
DOI: 10.48577/jpl.hpzrqs
title: A Moments View of Climatology and Variability of the Asian Summer Monsoon Anticyclone

description: A comprehensive investigation of the climatology of and interannual variabilityand trends in the Asian summer monsoon anticyclone (ASMA) is presented,based on a novel area and moments analysis. Moments include centroidlocation, aspect ratio, angle, and “excess kurtosis” (measuring how farthe shape is from elliptical) for an equivalent ellipse with the same area asthe ASMA. Key results are robust among the three modern reanalyses studied.The climatological ASMA is nearly elliptical, with its major axis alignedalong its centroid latitude and a typical aspect ratio of 5–8. The ASMAcentroid shifts northward with height, northward and westward during development,and in the opposite direction as it weakens. New evidence finding noobvious climatological bimodality in the ASMA reinforces similar suggestionsfrom previous studies using modern reanalyses. Most trends in ASMAmoments are not statistically significant. ASMA area and duration, however,increased significantly during 1979–2018; the 1958–2018 record analyzedfor one reanalysis suggests that these trends may have accelerated in recentdecades. ASMA centroid latitude is significantly positively (negatively) correlatedwith subtropical jet core latitude (altitude), and significantly negativelycorrelated with concurrent ENSO; these results are consistent with and extendprevious work relating monsoon intensity, ENSO, and jet shifts. ASMA areais significantly positively correlated with the MEI ENSO index two monthspreviously. These results improve our understanding of the ASMA using consistentlydefined diagnostics of its size, geometry, interannual variability, andtrends that have not previously been analyzed.
DOI: 10.48577/jpl.sbwbyk
title: Observation of Rotating MHD Modes in the Plume of a High-Current Hollow Cathode

description: High current hollow cathodes are widely used in electric propulsion as well as for laboratory plasma generation applications. The plasma region just outside of the high-current cathode is characterized by the presence of many fluctuations, which can develop coherent plasma structures affecting the operation and life of the cathode. The properties of plasma oscillations have been investigated in the exterior region of a high-current hollow cathodes operating at 25-150 A of discharge current with an applied axial magnetic field. Electrostatic and magnetic probes were used to measure the electromagnetic fluctuations, and correlation analysis between each of the probes signals provides spatiotemporal characterization of the generated waves. The results of this investigation reveal the presence of a coherent magnetohydrodynamic azimuthal mode with fundamental frequency of 58 kHz. This mode has features of a helical kink instability with azimuthal wave number m = 1 and axial wavenumber 〖k 〗_z= 50 m^(-1) that is readily observed in high-speed Fast-Cam images. The occurrence of this mode, the frequency, and the wavenumber at onset are found to be predicted well by ideal MHD theory, considering the boundary condition of a nonline-tying cylindrical anode. Investigation of the MHD mode properties at different discharge currents and mass flow rate shows additional features that could qualitatively agree with resistive MHD modes. In particular, when the plasma has a finite conductivity associated with anomalous resistivity in the cathode plume, a gradual emergence of modes at relatively low discharge currents are observed.
DOI: 10.48577/jpl.gjlh0b
title: Thermal Forcing of Near Surface Temperatures by Martian Water Ice Clouds

description: No abstract available.
DOI: 10.48577/jpl.ii0dep
title: Chandra Observations of Candidate Sub-Parsec Binary Supermassive Black Holes

description: We present analysis of Chandra X-ray observations of seven quasars that were identified as candi- date sub-parsec binary supermassive black hole (SMBH) systems in the Catalina Real-Time Transient Survey (CRTS) based on apparent periodicity in their optical light curves. Simulations predict close- separation accreting SMBH binaries will have different X-ray spectra than single accreting SMBHs, including harder or softer X-ray spectra, ripple-like profiles in the Fe K-α line, and distinct peaks in the spectrum due to the separation of the accretion disk into a circumbinary disk and mini-disks around each SMBH. We obtained Chandra observations to test these models and assess whether these quasars could contain binary SMBHs. We instead find that the quasar spectra are all well fit by simple absorbed power law models, with the rest frame 2-10 keV photon indices, Γ, and the X-ray-to-optical power slopes, αOX, indistinguishable from the larger quasar population. This may indicate that these seven quasars are not truly sub-parsec binary SMBH systems, or it may simply reflect that our sample size was too small to robustly detect any differences. Alternatively, the X-ray spectral changes might only be evident at higher energies than probed by Chandra. Given the available models and current data, no firm conclusions are drawn. These observations will help motivate and direct further work on theoretical models of binary SMBH systems, such as modeling systems with thinner accretion disks and larger binary separations.
DOI: 10.48577/jpl.qxwpus
title: Australian New Year's PyroCb impact on Stratospheric Composition

description: AbstractFollowing the Australian New Year's pyrocumulonimbus complex between 29-Dec-2019 and 4-Jan-2020, the Aura Microwave Limb Sounder (MLS) observed a plume with unprecedented enhancements of H2O and biomass-burning products (CO, HCN, CH3Cl, CH3CN, and CH3OH) in the lower/middle stratosphere, accompanied by depressions in stratospheric species (O3 and HNO3). The plume persisted for 110 days, circling the globe twice while ascending to 5.62 hPa (35 km). Air masses drawn o the main plume moved toward the developing Antarctic polar vortex but do not appear to have penetrated it. Comparison of species in the plume requires consideration of their measurements' spatial resolutions and background abundances. The apparent decay of some long-lived plume constituents is largely attributable to their coarsening spatial resolution with height, which reduces observed peak values. Differing HCN/H2O signatures indicate that multiple early plumes originated from different stratospheric injection events.
DOI: 10.48577/jpl.4omgmk
title: Evaluation of AIRS and CrIS SST measurements relative to three globally gridded SST products between 2013 and 2019.

description: Globally gridded sea surface temperatures (SST) are useful for providing boundary conditions for atmospheric models and for the long-term monitoring of satellite derived SSTs. The Real Time Global (RTG) SST from NOAA has been used for the past decade to evaluate the stability and accuracy of the AIRS calibrated radiances since 2002. In order to find an alternate and improved SST product, we evaluated SST products provided by the Canadian Meteorological Centre (CMC) and the UKMetOffice (OSTIA). We analyzed the mean, standard deviation and trend of the daily SST derived from clear sky AIRS and CrIS radiances relative to daily matchups with gridded SST products for the 2013 and 2019 period. During this time the standard deviation of the difference between AIRS and the RTG was 0.55K and increasing. In contrast, the standard deviation of the difference between the AIRS, the CMC and the OSTIA dropped steadily to below 0.4 K, a level previously only seen in SST products relative to the Argo buoys. Unexplained biases between the observed and the gridded SSTs at the 100 mK level are consistent with already existing estimates of the AIRS and CrIS absolute calibration accuracy. However, the AIRS and CrIS observations also independently confirm artifacts in all three SST products, increasing with distance from the equator, with the CMC artifacts being the smallest. We selected the CMC as the replacement for the RTG. In the 2013-2019 data, the CMC artifacts for the 30S-30N oceans create a 4 mK/yr trend artifact.
DOI: 10.48577/jpl.hxcd3y
title: Modeling the Impact of COVID-19 on Air Quality in Southern California: Implications for Future Control Policies

description: In response to the Coronavirus Disease 2019 (COVID-19), California issued statewide stay-at-home orders, bringing about abrupt and dramatic reductions in air pollutant emissions. This crisis offers us an unprecedented opportunity to evaluate the effectiveness of emission reductions on air quality. Here we use the Weather Research and Forecasting model with Chemistry (WRF-Chem) in combination with surface observations to study the impact of the COVID-19 lockdown measures on air quality in southern California. Based on activity level statistics and satellite observations, we estimate the sectoral emission changes during the lockdown. Due to the reduced emissions, the population-weighted concentrations of fine particulate matter (PM2.5) decrease by 15% in southern California. The emission reductions contribute 68% of the PM2.5 concentration decrease before and after the lockdown, while meteorology variations contribute the remaining 32%. Among all chemical compositions, the PM2.5 concentration decreases due to emission reductions is dominated by nitrate and primary components. For O3 concentrations, the emission reductions cause a decrease in rural areas but an increase in urban areas; the increase can be offset by a 70% emission reduction in anthropogenic volatile organic compounds (VOC). These findings suggest that a strengthened control on primary PM2.5 emissions and a well-balanced control on nitrogen oxides and VOC emissions are needed to effectively and sustainably alleviate PM2.5 and O3 pollution in southern California.
DOI: 10.48577/jpl.ohaty2
title: Past and Ongoing Pacific Sea Level Change

description: Satellite altimeters have provided near-global coverage of the ocean with a continuous record now approaching three decades in length. These observations have led to definitive evidence of an increase in global mean sea level, while offering a clear depiction of the spatial variability in sea level change around the world. As a result of the increasing length of the altimeter record, studies have sought to understand and detect the emergence of a forced or anthropogenic response in sea level. The central idea behind these studies is that the altimeter record is now long enough that the influence of interannual to decadal variability is reduced and does not serve to obscure underlying regional trends in the way that it did for the early part of the altimeter record. Two locations - the western tropical Pacific and the northeastern Pacific off the west coast of the United States - are particularly noteworthy for their sea level variations during the altimeter era, exhibiting large departures from the global average albeit in opposite directions. In this study, we examine satellite altimeter-measured sea level in these two regions. The goals are to understand the evolution of the sea level trend over the past 26-years, and determine what can be inferred about future sea level change from the satellite altimeter record. We find that in both regions, the altimetry record is still too short to rule out natural variability contributions to the trend on the order of 1 mm/year. Using longer records from tide-gauge observations and Earth system models, an assessment of the potential future changes in both regions is made for both regions.
DOI: 10.48577/jpl.9kncke
title: The depth of Jupiter’s Great Red Spot revealed from Juno gravity overflights

description: The gravity signature of Jupiter’s Great Red Spot (GRS) is examined in the Juno data20 by combining twelve encounters of the spacecraft with the planet, including two directoverflights of the vortex. The data suggest the presence of localized density anomalies,which cause a detectable shift in the spacecraft velocity along the line-of-sight. We usetwo different approaches to infer the GRS depth: a mascon method, where the densityperturbations are modeled with disk-shaped mass concentrations, and a Slepian method,25 which defines the gravitational signature of the GRS in terms of orthonormal functions ina limited domain. Both approaches yield consistent results, implying that the anticycloneis shallower than 500 km. Furthermore, at the 1σ level it is found to be 300±100 km deep.
DOI: 10.48577/jpl.svp75u
title: Smart Power Supply Calibration System

description: Abstract- This paper details the development of an automated procedure to conduct calibrations of power supplies at Jet Propulsion Laboratory, California Institute of Technology (JPL). The fundamentals of power supply calibrations is given, and discussion on the method by which this custom software handles that calibration. Additionally, this technique provides real time uncertainty quantification of the calibrations. This automated system has demonstrated a time savings over existing automated techniques in use today.
DOI: 10.48577/jpl.cdc5vz
title: Model selection in atmospheric remote sensing with application to aerosol retrieval from DSCOVR/EPIC. Part 1: Theory

description: The retrieval of aerosol and cloud properties such as their optical thickness and/or 1 layer/top height requires the selection of a model that describes their microphysical properties. 2 We demonstrate that, if there is not enough information for appropriate microphysical model 3 selection, the solution accuracy can be improved if the model uncertainty is taken into account 4 and appropriately quantified. For this purpose, we design a retrieval algorithm accounting for the 5 uncertainty in model selection. The algorithm is based on (i) the computation of each model solution 6 using the iteratively regularized Gauss-Newton method, (ii) the linearization of the forward model 7 around the solution, and (iii) the maximum marginal likelihood estimation and the generalized 8 cross-validation to estimate the optimal model. The algorithm is applied to the retrieval of aerosol 9 optical thickness and aerosol layer height from synthetic measurements corresponding to the EPIC 10 instrument onboard the DSCOVR satellite. Our numerical simulations have shown that the heuristic 11 approach based on the maximum solution estimate, which is frequently used in the literature, is 12 completely unrealistic when both the aerosol model and surface albedo are unknown.