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All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Lunar Prospecting: Searching for Volatiles at the South Pole

The Resource Prospector is an in-situ resource utilization (ISRU) technology demonstration mission, planned for a 2021 launch to search for and analyze volatiles at the Lunar South Pole. The mission poses unique operational challenges. Operating at the Lunar South Pole requires navigating a surface with lighting, shadow and regolith characteristics unlike those of previous missions. The short round trip communications time enables reactive surface operations for science and engineering. Navigation of permanently shadowed regions with a solar powered rover creates risks, including power and thermal management, and requires constant real time decision making for safe entry, path selection and egress. The mission plan requires a faster rover egress from the lander than any previous NASA rover mission.

operations↗
NASA NTRS2016

On the Distance to the North Polar Spur and the Local CO-H2 Factor

Aims. Most models identify the X-ray bright North Polar Spur (NPS) with a hot interstellar (IS) bubble in the Sco-Cen star-forming region at approx. = to 130 pc. An opposite view considers the NPS as a distant structure associated with Galactic nuclear outflows. Constraints on the NPS distance can be obtained by comparing the foreground IS gas column inferred from X-ray absorption to the distribution of gas and dust along the line of sight. Absorbing columns towards shadowing molecular clouds simultaneously constrain the CO-H2 conversion factor. Methods. We derived the columns of X-ray absorbing matter N(sub Habs) from spectral fitting of dedicated XMM-Newton observations towards the NPS southern terminus (l(sup II) approx. = to 29 degrees, b(sup II) approx. = to +5 to +11 degrees). The distribution of the IS matter was obtained from absorption lines in stellar spectra, 3D dust maps and emission data, including high spatial resolution CO measurements recorded for this purpose. Results. N(sub Habs) varies from approx. = to 4.3 to approx. = to 1.3 x 10(exp 21) per sq cm along the 19 fields. Relationships between X-ray brightness, absorbing column and hardness ratio demonstrate a brightness decrease with latitude governed by increasing absorption. The comparison with absorption data, local and large-scale dust maps rules out a NPS near side closer than 300 pc. The correlation between N(sub Habs) and the reddening increases with the sightline length from 300 pc to 4 kpc and is the tightest with Planck tau(sub 353GHz) -based reddening, suggesting a much larger distance. N(H)/E(B-V)(sub tao) approx. = to 4.1 x 10(exp 21) per sq cm mag, close to Fermi-Planck determinations. N(sub Habs) absolute values are compatible with HI-CO clouds at -5 less than or equal to V(sub LSR) less than or equal to +25 to +45 km/s and a NPS potentially far beyond the Local Arm. A shadow cast by a b=+9 degree molecular cloud constrains X(sub CO) in that direction to less than or equal to 1.0 x 10(exp 20) sec/((sq cm)K km). The average X(sub CO) over the fields is less than or equal to 0.75 x 10(exp 20) sec/((sq cm)K km).

X-rays: ISM / radio lines: ISM / local insterstell↗
NASA NTRS2017

Evidence for Surface and Subsurface Ice Inside Micro Cold-Traps on Mercury's North Pole

The small obliquity of Mercury causes topographic depressions located near its poles to cast persistent shadows. Many [1, 9, 15] have shown these permanently shadowed regions (PSRs) may trap water ice for geologic time periods inside cold-traps. More recently, direct evidence for the presence of water ice deposits inside craters was remotely sensed in RADAR [5] and visible imagery [3]. Albedo measurements (reflectence at 1064 nm) obtained by the MErcury Space ENviroment GEochemistry and Ranging Laser Altimeter (MLA) found unusually bright and dark areas next to Mercury's north pole [7]. Using a thermal illumination model, Paige et al. [8] found the bright deposits are correlated with surface cold-traps, and the dark deposits are correlated with subsurface cold-traps. They suggested these anomalous deposits were brought to the surface by comets and were processed by the magnetospheric radiation flux, removing hydrogen and mixing C-N-O-S atoms to form a variety of molecules which will darken with time. Here we use a thermal illumination model to find the link between the cold-trap area fraction of a rough surface and its albedo. Using this link and the measurements obtained by MESSENGER we derive a surface and a subsurface ice distribution map on Mercury's north pole below the MESSENGER spatial resolution, approximately 500 m. We find a large fraction of the polar ice on Mercury resides inside micro cold-traps (of scales 10 - 100 m) distributed along the inter-crater terrain.

Laser Altimeter↗
NASA NTRS2017

Payload Design for the Lunar Flashlight Mission

Recent reflectance data from LRO (Lunar Reconnaissance Orbiter) instruments suggest water ice and other volatiles may be present on the surface in lunar permanently shadowed regions, though the detection is not yet definitive. Understanding the composition, quantity, distribution, and form of water and other volatiles associated with lunar permanently shadowed regions (PSRs) is identified as a NASA Strategic Knowledge Gap (SKG). These polar volatile deposits are also scientifically interesting, having the potential to reveal important information about the delivery of water to the Earth-Moon system.

payload↗
NASA NTRS2016

Outer Radiation Belt Dropout Dynamics Following the Arrival of Two Interplanetary Coronal Mass Ejections

Magnetopause shadowing and wave-particle interactions are recognized as the two primary mechanisms for losses of electrons from the outer radiation belt. We investigate these mechanisms, sing satellite observations both in interplanetary space and within the magnetosphere and particle drift modeling. Two interplanetary shocks sheaths impinged upon the magnetopause causing a relativistic electron flux dropout. The magnetic cloud (C) and interplanetary structure sunward of the MC had primarily northward magnetic field, perhaps leading to a concomitant lack of substorm activity and a 10 day long quiescent period. The arrival of two shocks caused an unusual electron flux dropout. Test-particle simulations have shown 2 to 5 MeV energy, equatorially mirroring electrons with initial values of L 5.5can be lost to the magnetosheath via magnetopause shadowing alone. For electron losses at lower L-shells, coherent chorus wave-driven pitch angle scattering and ULF wave-driven radial transport have been shownto be viable mechanisms.

Alves, L. R.↗
NASA NTRS2016

Observations of Energetic Particle Escape at the Magnetopause: Early Results from the MMS Energetic Ion Spectrometer (EIS)

Energetic (greater than tens of keV) magnetospheric particle escape into the magnetosheath occurs commonly, irrespective of conditions that engender reconnection and boundary-normal magnetic fields. A signature observed by the Magnetospheric Multiscale (MMS) mission, simultaneous monohemispheric streaming of multiple species (electrons, H+, Hen+), is reported here as unexpectedly common in the dayside, dusk quadrant of the magnetosheath even though that region is thought to be drift-shadowed from energetic electrons. This signature is sometimes part of a pitch angle distribution evolving from symmetric in the magnetosphere, to asymmetric approaching the magnetopause, to monohemispheric streaming in the magnetosheath. While monohemispheric streaming in the magnetosheath may be possible without a boundary-normal magnetic field, the additional pitch angle depletion, particularly of electrons, on the magnetospheric side requires one. Observations of this signature in the dayside dusk sector imply that the static picture of magnetospheric drift-shadowing is inappropriate for energetic particle dynamics in the outer magnetosphere.

Cohen, I. J.↗
NASA NTRS2017

Traverse Planning with Temporal-Spatial Constraints

We present an approach to planning rover traverses in a domain that includes temporal-spatial constraints. We are using the NASA Resource Prospector mission as a reference mission in our research. The objective of this mission is to explore permanently shadowed regions at a Lunar pole. Most of the time the rover is required to avoid being in shadow. This requirement depends on where the rover is located and when it is at that location. Such a temporal-spatial constraint makes traverse planning more challenging for both humans and machines. We present a mixed-initiative traverse planner which addresses this challenge. This traverse planner is part of the Exploration Ground Data Systems (xGDS), which we have enhanced with new visualization features, new analysis tools, and new automation for path planning, in order to be applicable to the Re-source Prospector mission. The key concept that is the basis of the analysis tools and that supports the automated path planning is reachability in this dynamic environment due to the temporal-spatial constraints.

temporal-spatial constraints↗
NASA NTRS2017

Robust Exploration and Commercial Missions to the Moon Using LANTR Propulsion and In-Situ Propellants Derived From Lunar Polar Ice (LPI) Deposits

Since the 1960s, scientists have conjectured that water icecould survive in the cold, permanently shadowed craters located at the Moons poles Clementine (1994), Lunar Prospector (1998),Chandrayaan-1 (2008), and Lunar Reconnaissance Orbiter (LRO) and Lunar CRater Observation and Sensing Satellite(LCROSS) (2009) lunar probes have provided data indicating the existence of large quantities of water ice at the lunar poles The Mini-SAR onboard Chandrayaan-1discovered more than 40 permanently shadowed craters near the lunar north pole that are thought to contain 600 million metric tons of water ice. Using neutron spectrometer data, the Lunar Prospector science team estimated a water ice content (1.5 +-0.8 wt in the regolith) found in the Moons polar cold trap sand estimated the total amount of water at both poles at 2 billion metric tons Using Mini-RF and spectrometry data, the LRO LCROSS science team estimated the water ice content in the regolith in the south polar region to be 5.6 +-2.9 wt. On the basis of the above scientific data, it appears that the water ice content can vary from 1-10 wt and the total quantity of LPI at both poles can range from 600 million to 2 billion metric tons NTP offers significant benefits for lunar missions and can take advantage of the leverage provided from using LDPs when they become available by transitioning to LANTR propulsion. LANTR provides a variablethrust and Isp capability, shortens burn times and extends engine life, and allows bipropellant operation The combination of LANTR and LDP has performance capability equivalent to that of a hypothetical gaseousfuel core NTR (effective Isp 1575 s) and can lead to a robust LTS with unique mission capabilities that include short transit time crewed cargo transports and routine commuter flights to the Moon The biggest challenge to making this vision a reality will be the production of increasing amounts of LDP andthe development of propellant depots in LEO, LLO and LPO. An industry-operated, privately financed venture, with NASA as its initial customer, might provide a possible blueprint for future development and operation With industry interested in developing cislunar space and commerce, and competitive forces at work, the timeline for developing this capability could well be accelerated, quicker than any of us can imagine, and just the beginning of things to come.

Nuclear Thermal Propulsion↗
NASA NTRS2017

H31G-1596: DeepSAT's CloudCNN: A Deep Neural Network for Rapid Cloud Detection from Geostationary Satellites

Cloud and cloud shadow detection has important applications in weather and climate studies. It is even more crucial when we introduce geostationary satellites into the field of terrestrial remote sensing. With the challenges associated with data acquired in very high frequency (10-15 mins per scan), the ability to derive an accurate cloud shadow mask from geostationary satellite data is critical. The key to the success for most of the existing algorithms depends on spatially and temporally varying thresholds,which better capture local atmospheric and surface effects.However, the selection of proper threshold is difficult and may lead to erroneous results. In this work, we propose a deep neural network based approach called CloudCNN to classify cloudshadow from Himawari-8 AHI and GOES-16 ABI multispectral data. DeepSAT's CloudCNN consists of an encoderdecoder based architecture for binary-class pixel wise segmentation. We train CloudCNN on multi-GPU Nvidia Devbox cluster, and deploy the prediction pipeline on NASA Earth Exchange (NEX) Pleiades supercomputer. We achieved an overall accuracy of 93.29% on test samples. Since, the predictions take only a few seconds to segment a full multispectral GOES-16 or Himawari-8 Full Disk image, the developed framework can be used for real-time cloud detection, cyclone detection, or extreme weather event predictions.

GOES-1↗
NASA NTRS2018

Radioisotope Power Systems to Enable Extended Lunar Science and In-Situ Resource Utilization Missions

The Moon's surface environment offers a significant challenge for most space systems and, particularly, for power technologies. First, the Moon's rotational synodic period is 27.3 days long because it is tidally-locked with Earth and thus matches its orbital period. However, for a point on the lunar surface with respect to the Sun returning to the same position in the sky, called a synodic day, is 29.5 days or 708 hours. Therefore, a lunar day is 354 hours of sunlight and 354 hours of darkness. Equatorial diurnal temperatures range from about 400K at noon to 100K during the night. Within craters and permanently shadowed regions (PSRs) temperatures can be a constant 40K or below. Sunlight in the lunar polar regions can range from total darkness in deep polar craters and at higher elevations, potentially nearly continuous conditions are possible. However local topographical features such as outcrops or more distant mountains and ridges would obscure the Sun even in these extended sunlit areas and thus create intermittent shadowed periods depending on seasonally varying Sun angle and the obscuring topographical features. Thus, the power system technology that a mission selects becomes a critical trade.

radioisotope↗
NASA NTRS2016

Mid and Thermal Infrared Remote Sensing at the Jet Propulsion Laboratory

The mid and thermal infrared (MTIR) for the Earth surface is defined between 3 and 14µm. In the outer solar system, objects are colder and their Planck response shifts towards longer wavelengths. Hence for these objects (e.g. icy moons, polar caps, comets, Europa), the thermal IR definition usually stretches out to 50µm and beyond. Spectroscopy has been a key part of this scientific exploration because of its ability to remotely determine elemental and mineralogical composition. Many key gas species such as methane, ammonia, sulfur, etc. also have vibrational bands which show up in the thermal infrared spectrum above the background response. Over the past few decades, the Jet Propulsion Laboratory has been building up a portfolio of technology to capture the MTIR for various scientific applications. Three recent sensors are briefly reviewed: The airborne Hyperspectral thermal emission spectrometer (HyTES), the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) and Mars Climate Sounder (MCS)/DIVINER. Each of these sensors utilize a different technology to provide a remote sensing product based on MTIR science. For example, HyTES is a push-brooming hyperspectral imager which utilizes a large format quantum well infrared photodetector (QWIP). The goal is to transition this to a new complementary barrier infrared photodetector (CBIRD) with a similar long wave cut-off and increased sensitivity. ECOSTRESS is a push-whisk Mercury Cadmium Telluride (MCT) based high speed, multi-band, imager which will eventually observe and characterize plant/vegetation functionality and stress index from the International Space Station (ISS) across the contiguous United States (CONUS). MCS/DIVINER utilizes thermopile technology to capture the thermal emission from the polar caps and shadow regions of the moon. Each sensor utilizes specific JPL technology to capture unique science. similar long wave cut-off and increased sensitivity. ECOSTRESS is a push-whisk Mercury Cadmium Telluride (MCT) based high speed, multi-band, imager which will eventually observe and characterize plant/vegetation functionality and stress index from the International Space Station (ISS) across the contiguous United States (CONUS). MCS/DIVINER utilizes thermopile technology to capture the thermal emission from the polar caps and shadow regions of the moon. Each sensor utilizes specific JPL technology to capture unique science.

Johnson, William R.↗
NASA NTRS2018

Subaru/HiCIAO HK(sub S) Imaging of LKHa 330: Multi-Band Detection of the Gap and Spiral-Like Structures

We present H- and K s-bands observations of the LkHα 330 disk with a multi-band detection of the large gap and spiral-like structures. The morphology of the outer disk (r ~ 0."3) at PA = 0°–45° and PA° = 180–290° is likely density wave-induced spirals, and comparison between our observational results and simulations suggests a planet formation. We have also investigated the azimuthal profiles at the ring and the outer-disk regions as well as radial profiles in the directions of the spiral-like structures and semimajor axis. Azimuthal analysis shows a large variety in wavelength and implies that the disk has non-axisymmetric dust distributions. The radial profiles in the major-axis direction (PA = 271°) suggest that the outer region (r ≥ 0."25) may be influenced by shadows of the inner region of the disk. The spiral-like directions (PA = 10° and 230°) show different radial profiles, which suggests that the surfaces of the spiral-like structures are highly flared and/or have different dust properties. Finally, a color map of the disk shows a lack of an outer eastern region in the H-band disk, which may hint at the presence of an inner object that casts a directional shadow onto the disk.

H- and Ks-bands observations↗
NASA NTRS2017

Thermal Modeling of Mars Ground for Surface Missions

Thermal analysis packages are capable of including ground temperature effects for orbital and surface thermal analyses. In particular, Thermal Desktop® offers the option of specifying ground temperatures as a function of time for planetary surface modeling. While suitable for many cases, this approach is not sufficient if an object has local interactions with the ground that could significantly affect the ground temperature. Ground modeling is necessary for the Mars 2020 rover thermal design and analysis since shadowing and heat dissipation from the rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) can result in significant temperature deviations of the local ground. The Mars 2020 thermal team is explicitly modeling the Martian ground so that these local temperature effects can be captured. The upper portion of the ground is modeled, and material and optical properties of the ground are varied in order to match data collected from orbiting science instruments. Atmospheric surface temperature, sky temperatures, and solar loads from a Mars General Circulation Model (GCM) are used as boundary conditions, resulting in a ground surface temperature profile consistent with the GCM predictions. The rover model is then placed on this modeled ground so that the effects of shadowing and MMRTG dissipation on the ground temperature can be captured.

Farias, Edgardo↗
NASA NTRS2019

Preparing General Mission Analysis Tool for Operational Maneuver Planning of the Advanced Composition Explorer Mission

The General Mission Analysis Tool (GMAT) is an open-source space mission design, analysis and trajectory optimization tool. GMAT is developed by a team of NASA, private industry, public and private contributors. GMAT is designed to model, optimize and estimate spacecraft trajectories in flight regimes ranging from low Earth orbit to lunar applications, interplanetary trajectories and other deep space missions. GMAT has also been flight qualified to support operational maneuver planning for the Advanced Composition Explorer (ACE) mission. ACE was launched in August, 1997 and is orbiting the Sun-Earth L1 libration point. The primary science objective of ACE is to study the composition of both the solar wind and the galactic cosmic rays. Operational orbit determination, maneuver operations and product generation for ACE are conducted by NASA Goddard Space Flight Center (GSFC) Flight Dynamics Facility (FDF). This paper discusses the entire engineering lifecycle and major operational certification milestones that GMAT successfully completed to obtain operational certification for the ACE mission. Operational certification milestones such as gathering of the requirements for ACE operational maneuver planning, gap analysis, test plans and procedures development, system design, pre-shadow operations, training to FDF ACE maneuver planners, shadow operations, Test Readiness Review (TRR) and finally Operational Readiness Review (ORR) are discussed. These efforts have demonstrated that GMAT is flight quality software ready to support ACE mission operations in the FDF.

mission design↗
NASA NTRS2020

JSC-Rocknest: A Large-Scale Mojave Mars Simulant (MMS) Based Soil Simulant for In-Situ Resource Utilization Water-Extraction Studies

The Johnson Space Center-Rocknest (JSC-RN) simulant was developed in response to a need by NASA's Advanced Exploration Systems (AES) In-Situ Resource Utilization (ISRU) project for a simulant to be used in component and system testing for water extraction from Mars regolith. JSC-RN was designed to be chemically and mineralogically similar to material from the aeolian sand shadow named Rocknest in Gale Crater, particularly the 1-3 wt.% low temperature (<450 ºC) water release as measured by the Sample Analysis at Mars (SAM) instrument on the Curiosity rover. Sodium perchlorate, goethite, pyrite, ferric sulfate, regular and high capacity granular ferric oxide, and forsterite were added to a Mojave Mars Simulant (MMS) base in order to match the mineralogy, evolved gases, and elemental chemistry of Rocknest. Mineral and rock components were sent to the United States Geological Survey (USGS) in Denver for mixing. Approximately 800 kg of JSC-RN was sent back to NASA in 5 gallon buckets, which were subsampled and characterized. All samples of the USGS-produced simulants had similar evolved gas profiles as a small prototype batch of JSC-RN made in JSC laboratories, with the exception of HCl, and were similar in terms of mineralogy and total chemistry. Also, all JSC-RN subsamples were homogenous and had similar mineralogy, total chemistry, and low-temperature evolved gas profiles as the Rocknest aeolian sand shadow examined with Curiosity’s instrument suite on Mars. In particular, the low temperature water releases were similar and the amount of water evolved from JSC-RN at <450 ºC was similar to the water content of Rocknest based on SAM water peak integrations. Overall, JSC-RN is ideally suited for ISRU studies of water extraction of global martian soil due to its excellent agreement with measured properties of martian soils and its proven feasibility for large-scale production.

Simulant↗
NASA NTRSDate not supplied

VIPER – Volatiles Investigating Polar Exploration Rover: Mission Overview

VIPER is a low cost, lunar volatiles detection and measurement mission that will be delivered to the lunar south pole by one of NASA’s Commercial Lunar Payload Services partners and will characterize the nature of the volatiles in the area and extrapolate this data to create global lunar water resource maps. It will be the first mining expedition on another world while simultaneously addressing fundamental planetary science questions. Prospecting for lunar water at the poles is the next step in understanding the resource potential and addressing key theories about water emplacement and retention. It now appears that potentially economically significant amounts of water ice exists at the poles of the Moon, however, the distribution of this water is still not understood at a level sufficient to fully evaluate economic models. The water ice (and other potential volatiles), the “ore body”, needs to be understood at the scales of 10s to 100s of meters to evaluate localization, extraction and processing techniques. To accomplish this, VIPER will survey permanently-shadowed regions, semi-permanent shadowed regions, and even semi and full sunlit areas in order to have a comprehensive survey of polar region volatiles, to best inform future mission architectures. In order to characterize the volatiles, a payload suite consisting of a neutron spectrometer, mass spectrometer, near infrared spectrometer and a 1-meter drill will be hosted on the VIPER mobile lunar rover platform. Since VIPER is a relatively low cost, schedule-constrained, risk-tolerant mission, there are architectural limitations that require unique mission planning constraints to enable exploration of the lunar south pole region. These regions offer unique challenges such as uncertain terrain conditions, rock and crater hazards, lunar dust, multipath communications effects, extreme thermal environments and multiple overlapping planning constraints. Mission design/traverse planning, system design capabilities and mission operations are all highly linked through initial development phases. We will describe the current mission overview and the unique approaches taken by the VIPER project based on our programmatic framework and unique mission environment.

VIPER↗
NASA NTRSDate not supplied

Case Study for Lunar ISRU Systems Utilizing Polar Water

In-Situ Resource Utilization (ISRU) is key to long term presence at any extraterrestrial destination. Current NASA direction is to achieve a sustainable presence on the lunar surface by 2028. Mission plans currently target the lunar South Pole to leverage the extended periods of solar illumination and allows for potential access to water ice in the permanently shadowed areas around the poles. With water, it is possible to produce both fuel and oxidizer to fully refuel a vehicle. In order to address ISRU infusion into mission planning, a study of an end-to-end ISRU propellant production system was initiated to assess ISRU architectures and obtain mass and power estimates for each. The results of these case studies will be presented. For this study, The ISRU system architecture involved two sites; the mine site in a shadowed crater where water ice is excavated and extracted from the regolith and the propellant production site at an illuminated ridge where the water is processed into liquefied O2 and H2 propellants. Fixed hardware would be emplaced at each site, with two alternating water tankers to transport water between them. Notional lunar sites were identified for this architecture for baseline environmental parameters. Technology solutions for each subsystem were selected based on those with the highest fidelity models or those that have empirical laboratory data to anchor to. While power needs were identified for each location, a power solution was not prescribed, therefore the masses presented do not include surface power systems. The baseline case in this study assumed that 10 mT of oxygen, along with enough hydrogen to support a propulsion mixture ratio of 6, must be produced in 225 days. Therefore 15 mT of water would need to be collected and processed. The baseline solution resulted in a system mass of5 mT and a total required power of 68kW. The majority of the mass was split between the ridge site system and the two water tankers (2.6 mTand 1.8mTrespectively). The majority of the required power was with three subsystems at approximately 20 kW each: hydrogen liquefaction, electrolysis, and the water extractor subsystem. Trades for four key variables are also presented, namely production rate, water concentration, dry overburden depth, and number of water transport trips. This can be compared to a system that targets oxygen from the minerals in the surface regolith material. A carbothermal reduction reactor system was used for this comparison. The use of direct solar thermal energy to process the regolith and the ease of access of the resource resulted in significantly lower values for the oxygen case: approximately 2.7 mT and 11.8 kW. However, the mass trade would favor the water case over successive missions where the hydrogen up-mass of 2 mT per mission will accrue against the oxygen system.1Aerospace Research Engineer, Chemical and Thermal Propulsion Systems Branch, Senior Member.2Mechanical Engineer, Propulsion and Power Division/Energy Conversion Systems, 2101 Nasa Pkwy/Mailcode EP3 Houston, TX 77058, AIAA member.

Lunar↗
NASA NTRS2020

Variability of Lidar-Derived Particle Properties Over West Africa Due to Changes in Absorption: Towards an Understanding

Measurements performed in western Africa (Senegal) during the SHADOW field campaign are analyzed to show that spectral dependence of the imaginary part of the complex refractive index (CRI) of dust can be revealed by lidar-measured particle parameters. Observations in April 2015 provide good opportunity for such study, because, due to high optical depth of the dust, exceeding 0.5, the extinction coefficient could be derived from lidar measurements with high accuracy and the contribution of other aerosol types, such as biomass burning, was negligible. For instance, in the second half of April 2015, AERONET observations demonstrated a temporal decrease in the imaginary part of the CRI at 440 nm from approximately 0.0045 to 0.0025. This decrease is in line with a change in the relationship between the lidar ratios (the extinction-to-backscattering ratio) at 355 and 532 nm (S(355) and S(532)). For instance in the first half of April, S(355)∕S(532) is as high as 1.5 and the backscatter Angstrom exponent, A(β), is as low as −0.75, while after 15 April S(355)/S(532)=1.0 and A(β) is close to zero. The aerosol depolarization ratio δ(532) for the whole of April exceeded 30 % in the height range considered, implying that no other aerosol, except dust, occurred. The performed modeling confirmed that the observed S(355)∕S(532) and Aβ values match the spectrally dependent imaginary part of the refractive index as can be expected for mineral dust containing iron oxides. The second phase of the SHADOW campaign was focused on evaluation of the lidar ratio of smoke and estimates of its dependence on relative humidity (RH). For five studied smoke episodes the lidar ratio increases from 44±5 to 66±7 sr at 532 nm and from 62±6 to 80±8 sr at 355 nm, when RH varied from 25 % to 85 %. Performed numerical simulations demonstrate that observed ratio S(355)∕S(532), exceeding 1.0 in the smoke plumes, can indicate an increase in the imaginary part of the smoke particles in the ultraviolet (UV) range.

Lidar-Derived Particle Properties↗