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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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NASA NTRS2012

Polarimetric Retrievals of Surface and Cirrus Clouds Properties in the Region Affected by the Deepwater Horizon Oil Spill

In 2010, the Goddard Institute for Space Studies (GISS) Research Scanning Polarimeter (RSP) performed several aerial surveys over the region affected by the oil spill caused by the explosion of the Deepwater Horizon offshore platform. The instrument was deployed on the NASA Langley B200 aircraft together with the High Spectral Resolution Lidar (HSRL), which provides information on the distribution of the aerosol layers beneath the aircraft, including an accurate estimate of aerosol optical depth. This work illustrates the merits of polarization measurements in detecting variations of ocean surface properties linked to the presence of an oil slick. In particular, we make use of the degree of linear polarization in the glint region, which is severely affected by variations in the refractive index but insensitive to the waviness of the water surface. Alterations in the surface optical properties are therefore expected to directly affect the polarization response of the RSP channel at 2264 nm, where both molecular and aerosol scattering are negligible and virtually all of the observed signal is generated via Fresnel reflection at the surface. The glint profile at this wavelength is fitted with a model which can optimally estimate refractive index, wind speed and direction, together with aircraft attitude variations affecting the viewing geometry. The retrieved refractive index markedly increases over oil-contaminated waters, while the apparent wind speed is significantly lower than in adjacent uncontaminated areas, suggesting that the slick dampens high-frequency components of the ocean wave spectrum. The constraint on surface reflectance provided by the short-wave infrared channels is a cornerstone of established procedures to retrieve atmospheric aerosol microphysical parameters based on the inversion of the RSP multispectral measurements. This retrieval, which benefits from the ancillary information provided by the HSRL, was in this specific case hampered by prohibitive variability in atmospheric conditions (very inhomogeneous aerosol distribution and cloud cover). Although the results presented for the surface are essentially unaffected, we discuss the results obtained by typing algorithms in sorting the complex mix of aerosol types, and show evidence of oriented ice in cirrus clouds present in the area. In this context, polarization measurements at 1880 nm were used to infer ice habit and cirrus optical depth, which was found in the subvisual/threshold-visible regime, confirming the utility of the aforementioned RSP channel for the remote sensing of even thin cold clouds.

Polarization↗
NASA NTRS2013

Mission Design for Global Mapping Orbits at Primitive Bodies

Global mapping campaigns are part of most primitive body exploration missions. However, designing a mapping orbit without station keeping maneuvers is challenging due to the highly perturbed environment near small bodies. In this paper, we present a new design methodology to support mapping campaigns using 'quasi-terminator' orbits, a class of quasi-periodic orbits that exist in the vicinity of the well-known terminator orbits. The inherent stability of quasi-terminator trajectories and their wide variety of viewing geometries make them a very compelling option for mapping campaigns. A high-fidelity test case solution is also presented to prove the existence of these mapping orbits in full ephemeris.

quasi-periodic orbits↗
NASA NTRS2013

Design of Quasi-Terminator Orbits near Primitive Bodies

Quasi-terminator orbits are a class of quasi-periodic orbits around a primitive body that exist in the vicinity of the well-known terminator orbits. The inherent stability of quasi-terminator trajectories and their wide variety of viewing geometries make them a very compelling option for primitive body mapping missions. In this paper, we discuss orbit design methodologies for selection of an appropriate quasi-terminator orbit that would meet the needs of a specific mission. Convergence of these orbits in an eccentric, higher-fidelity model is also discussed with an example case at Bennu, the target of the upcoming NASA's OSIRIS-REx mission.

mapping↗
NASA NTRS2015

Stratospheric Benzene and Hydrocarbon Aerosols Detected in Saturn's Auroral Regions

Context. Saturn's polar upper atmosphere exhibits significant auroral activity; however, its impact on stratospheric chemistry (i.e. the production of benzene and heavier hydrocarbons) and thermal structure remains poorly documented. Aims. We aim to bring new constraints on the benzene distribution in Saturn's stratosphere, to characterize polar aerosols (their vertical distribution, composition, thermal infrared optical properties), and to quantify the aerosols' radiative impact on the thermal structure. Methods. Infrared spectra acquired by the Composite Infrared Spectrometer (CIRS) on board Cassini in limb viewing geometry are analysed to derive benzene column abundances and aerosol opacity profiles over the 3 to 0.1 mbar pressure range. The spectral dependency of the haze opacity is assessed in the ranges 680-900 and 1360-1440 cm(exp −1). Then, a radiative climate model is used to compute equilibrium temperature profiles, with and without haze, given the haze properties derived from CIRS measurements. Results. On Saturn's auroral region (80 deg S), benzene is found to be slightly enhanced compared to its equatorial and mid-latitude values. This contrasts with the Moses & Greathouse (2005, J. Geophys. Res., 110, 9007) photochemical model, which predicts a benzene abundance 50 times lower at 80◦S than at the equator. This advocates for the inclusion of ion-related reactions in Saturn's chemical models. The polar stratosphere is also enriched in aerosols, with spectral signatures consistent with vibration modes assigned to aromatic and aliphatic hydrocarbons, and presenting similarities with the signatures observed in Titan's stratosphere. The aerosol mass loading at 80 deg S is estimated to be 1−4 × 10(exp −5) g cm(exp −2), an order of magnitude less than on Jupiter, which is consistent with the order of magnitude weaker auroral power at Saturn.We estimate that this polar haze warms the middle stratosphere by 6 K in summer and cools the upper stratosphere by 5 K in winter. Hence, aerosols linked with auroral activity can partly account for the warm polar hood observed in Saturn's summer stratosphere.

satellites↗
NASA NTRS2016

Validation of Cloud Properties From Multiple Satellites Using CALIOP Data

The NASA Langley Satellite ClOud and Radiative Property retrieval System (SatCORPS) is routinely applied to multispectral imagery from several geostationary and polar-orbiting imagers to retrieve cloud properties for weather and climate applications. Validation of the retrievals with independent datasets is continuously ongoing in order to understand differences caused by calibration, spatial resolution, viewing geometry, and other factors. The CALIOP instrument provides a decade of detailed cloud observations which can be used to evaluate passive imager retrievals of cloud boundaries, thermodynamic phase, cloud optical depth, and water path on a global scale. This paper focuses on comparisons of CALIOP retrievals to retrievals from MODIS, VIIRS, AVHRR, GOES, SEVIRI, and MTSAT. CALIOP is particularly skilled at detecting weakly-scattering cirrus clouds with optical depths less than approx. 0.5. These clouds are often undetected by passive imagers and the effect this has on the property retrievals is discussed.

Yost, Christopher R.↗
NASA NTRS2016

Comparison of Areas in Shadow from Imaging and Altimetry in the North Polar Region of Mercury and Implications for Polar Ice Deposits

Earth-based radar observations and results from the MESSENGER mission have provided strong evidence that permanently shadowed regions near Mercury's poles host deposits of water ice. MESSENGER's complete orbital image and topographic datasets enable Mercury's surface to be observed and modeled under an extensive range of illumination conditions. The shadowed regions of Mercury's north polar region from 65 deg N to 90 deg N were mapped by analyzing Mercury Dual Imaging System (MDIS) images and by modeling illumination with Mercury Laser Altimeter (MLA) topographic data. The two independent methods produced strong agreement in identifying shadowed areas. All large radar-bright deposits, those hosted within impact craters greater than or equal to 6 km in diameter, collocate with regions of shadow identified by both methods. However, only approximately 46% of the persistently shadowed areas determined from images and approximately 43% of the permanently shadowed areas derived from altimetry host radar-bright materials. Some sizable regions of shadow that do not host radar-bright deposits experience thermal conditions similar to those that do. The shadowed craters that lack radar-bright materials show a relation with longitude that is not related to the thermal environment, suggesting that the Earth-based radar observations of these locations may have been limited by viewing geometry, but it is also possible that water ice in these locations is insulated by anomalously thick lag deposits or that these shadowed regions do not host water ice.

MESSENGER↗
NASA NTRS2016

Recent Variability Observations of Solar System Giant Planets: Fresh Context for Understanding Exoplanet and Brown Dwarf Weather

Over the past several years a number of high cadence photometric observations of solar system giant planets have been acquired by various platforms. Such observations are of interest as they provide points of comparison to the already expansive set of brown dwarf variability observations and the small, but growing, set of exoplanet variability observations. By measuring how rapidly the integrated light from solar system giant planets can evolve, variability observations of substellar objects that are unlikely to ever be resolved can be placed in a fuller context. Examples of brown dwarf variability observations include extensive work from the ground (e.g., Radigen et al. 2014), Spitzer (e.g., Metchev et al. 2015), Kepler (Gizis et al. 2015), and HST (Yang et al. 2015).Variability has been measured on the planetary mass companion to the brown dwarf 2MASS 1207b (Zhou et al. 2016) and further searches are planned in thermal emission for the known directly imaged planets with ground based telescopes (Apai et al. 2016) and in reflected light with future space based telescopes. Recent solar system variability observations include Kepler monitoring of Neptune (Simon et al. 2016) and Uranus, Spitzer observations of Neptune (Stauffer et al. 2016), and Cassini observations of Jupiter (West et al. in prep). The Cassini observations are of particular interest as they measured the variability of Jupiter at a phase angle of approximately 60 deg, comparable to the viewing geometry expected for space based direct imaging of cool extrasolar Jupiters in reflected light. These solar system analog observations capture many of the characteristics seen in brown dwarf variability, including large amplitudes and rapid light curve evolution on timescales as short as a few rotation periods. Simon et al. (2016) attribute such variations at Neptune to a combination of large scale, stable cloud structures along with smaller, more rapidly varying, cloud patches. The observed brown dwarf and exoplanet variability may well arise from comparable cloud structures. In my presentation I will compare and contrast the nature of the variability observed for the various solar system and other substelar objects and present a wish list for future observations.

giant planets↗
NASA NTRS2017

Solar Energetic Particle Warnings from a Coronagraph

We report here the concept of using near-real time observations from a coronagraph to provide early warning of a fast coronal mass ejection (CME) and the possible onset of a solar energetic particle (SEP) event. The 1 January 2016, fast CME, and its associated SEP event are cited as an example. The CME was detected by the ground-based K-Cor coronagraph at Mauna Loa Solar Observatory and by the SOHO Large Angle and Spectrometric Coronagraph. The near-real-time availability of the high-cadence K-Cor observations in the low corona leads to an obvious question: Why has no one attempted to use a coronagraph as an early warning device for SEP events? The answer is that the low image cadence and the long latency of existing spaceborne coronagraphs make them valid for archival studies but typically unsuitable for near-real-time forecasting. The January 2016 event provided favorable CME viewing geometry and demonstrated that the primary component of a prototype ground-based system for SEP warnings is available several hours on most days. We discuss how a conceptual CME-based warning system relates to other techniques, including an estimate of the relative SEP warning times, and how such a system might be realized.

St Cyr, O. C.↗
NASA NTRS2014

The Surface Compositions of Pluto and Charon

The surface of Pluto as it is understood on the eve of the encounter of the New Horizons spacecraft (mid-2015) consists of a spatially heterogeneous mix of solid N2, CH4, CO, C2H6, and an additional component that imparts color, and may not be an ice. The known molecular ices are detected by near-infrared spectroscopy. The N2 ice occurs in the hexagonal crystalline b-phase, stable at T greater than 35.6 K. Spectroscopic evidence for wavelength shifts in the CH4 bands attests to the complex mixing of CH4 and N2 in the solid state, in accordance with the phase diagram for N2 + CH4. Spectra obtained at several aspects of Plutos surface as the planet rotates over its 6.4-day period show variability in the distribution of CH4 and N2 ices, with stronger CH4 absorption bands associated with regions of higher albedo, in correlation with the visible rotational light curve. CO and N2 ice absorptions are also strongly modulated by the rotation period; the bands are strongest on the anti-Charon hemisphere of Pluto. Longer term changes in the strengths of Plutos absorption bands occur as the viewing geometry changes on seasonal time-scales, although a complete cycle has not been observed. The non-ice component of Plutos surface may be a relatively refractory material produced by the UV and cosmic-ray irradiation of the surface ices and gases in the atmosphere, although UV does not generally penetrate the atmospheric CH4 to interact with the surface. Laboratory simulations indicate that a rich chemistry ensues by the irradiation of mixtures of the ices known to occur on Pluto, but specific compounds have not yet been identified in spectra of the planet. Charons surface is characterized by spectral bands of crystalline H2O ice, and a band attributed to one or more hydrates of NH3. Amorphous H2O ice may also be present; the balance between the amorphization and crystallization processes on Charon remains to be clarified. The albedo of Charon and its generally spatially uniform neutral color indicate that a component, not yet identified, is mixed in some way with the H2O and NH3nH2O ices. Among the many known small bodies in the transneptunian region, several share characteristics with Pluto and Charon, including the presence of CH4, N2, C2H6, H2O ices, as well as components that yield a wide variety of surface albedo and color. The New Horizons investigation of the Pluto-Charon system will generate new insight into the physical properties of the broader transneptunian population, and eventually to the corresponding bodies expected in the numerous planetary systems currently being discovered elsewhere in the Galaxy.

surface composition↗
NASA NTRS2018

Validation of MODIS 3 km Land Aerosol Optical Depth from NASA's EOS Terra and Aqua Missions

In addition to the standard resolution product (10km), the MODerate resolution Imaging Spectroradiometer (MODIS) Collection 6 (C006) data release included a higher resolution (3km). Other than accommodations for the two different resolutions, the 10 and 3km Dark Target (DT) algorithms are basically the same. In this study, we perform global validation of the higher-resolution aerosol optical depth (AOD) over global land by comparing against AErosol RObotic NETwork (AERONET) measurements. The MODIS-AERONET collocated data sets consist of 161410 high-confidence AOD pairs from 2000 to 2015 for Terra MODIS and 2003 to 2015 for Aqua MODIS. We find that 62.5 and 68.4% of AODs retrieved from Terra MODIS and Aqua MODIS, respectively, fall within previously published expected error bounds of +/-(0.05+0.2 × AOD), with a high correlation (R = 0.87). The scatter is not random, but exhibits a mean positive bias of ∼ 0.06 for Terra and ∼ 0.03 for Aqua. These biases for the 3km product are approximately 0.03 larger than the biases found in similar validations of the 10km product. The validation results for the 3km product did not have a relationship to aerosol loading (i.e., true AOD), but did exhibit dependence on quality flags, region, viewing geometry, and aerosol spatial variability. Time series of global MODIS-AERONET differences show that validation is not static, but has changed over the course of both sensors' lifetimes, with Terra MODIS showing more change over time. The likely cause of the change of validation over time is sensor degradation, but changes in the distribution of AERONET stations and differences in the global aerosol system itself could be contributing to the temporal variability of validation.

Gupta, Pawan↗
NASA NTRS2018

Initial Assessment of Radiometric Performance of N20 VIIRS Reflective Solar Bands Using Vicarious Approaches

The newly launched (November 18, 2017) polar-orbiting satellite of the Joint Polar Satellite System (JPSS-1), now transitioned to NOAA-20, is the follow-on mission to the SNPP (Suomi National Polar-orbiting Partnership) satellite, launched six years ago. NOAA-20 leads SNPP by a half orbit or about 50 minutes. The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor onboard both NOAA-20 and SNPP spacecraft with nearly identical band spectral responses. Similar to the heritage sensor MODIS, VIIRS has on-board calibration components including a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB), and a space view (SV) as background reference for calibration. This study provides an initial assessment of calibration of the NOAA-20 VIIRS reflective solar bands (RSB) by inter-comparison with measurements from SNPP VIIRS using various vicarious approaches. The first approach is based on a double difference method using observations from simultaneous nadir overpasses (SNO) with Aqua MODIS. The second is from the collected reflectances over the widely used Liby-4 desert site from 16-day repeatable orbits so each data point has the same viewing geometry relative to the site. The third approach is to use the frequent overpasses over the Dome C snow site. Results of this study provide useful information on NOAA-20 VIIRS post-launch calibration assessment and preliminary analysis of its calibration stability and consistency for the first 6 months

Wu, Aisheng↗
NASA NTRS2018

PACE Technical Report Series, Volume 7: Ocean Color Instrument (OCI) Concept Design Studies

Extending OCI hyperspectral radiance measurements in the ultraviolet to 320 nm on the blue spectrograph enables quantitation of atmospheric total column ozone (O3) for use in ocean color atmospheric correction algorithms. The strong absorption by atmospheric ozone below 340 nm enables the quantification of total column ozone. Other applications are possible but were not investigated due to their exploratory nature and lower priority.The first step in the atmospheric correction processing, which converts top-of-the-atmosphere radiances to water-leaving radiances, is removal of the absorbance by atmospheric trace gases such as water vapor, oxygen, ozone and nitrogen dioxide. Details of the atmospheric correction process currently used by the Ocean Biology Processing Group (OBPG) and will be employed for PACE with appropriate modifications, are described by Mobley et al. [2016]. Atmospheric ozone absorbs within the visible to near-infrared spectrum between ~450 nm and 800nm and most appreciably between 530 nm and 650 nm, a spectral region critical for maintaining NASA's chlorophyll-a climate data record and for PACE algorithms planned to characterize phytoplankton community composition and other ocean color products.While satellite-based observations will likely be available during PACE's mission lifetime, the difference in acquisition time with PACE, the coarseness in their spatial resolution, and differences in viewing geometries will introduce significant levels of uncertainties in PACE ocean color data products.

Cetinic, Ivona↗
NASA NTRS2019

The Search for the Gamma Lyrid Progenitor

On 5 February 2015, a previously unknown meteor shower, the γ Lyrids were observed for the first time. Because of the Sun-Earth-Moon viewing geometry, however, stream members were observed almost exclusively by the Canadian Meteor Orbit Radar (CMOR). The γ Lyrids did not appear again until 2018, and that outburst was stronger than in 2015. This study analyzed the 2015 and 2018 CMOR data in order to determine the orbital parameters of the stream in an attempt to determine the γ Lyrid parent body. Of primary importance is to determine if the γ Lyrids will recur in a predictable manner. Two bodies, with dramatically different orbital parameters and evolutionary behaviors, emerged as the leading candidates: 2003 EH1 and 1854 R1.

Grazier, Kevin R.↗
NASA NTRS2019

On the Curious Pulsation Properties of the Accreting Millisecond Pulsar IGR J17379-3747

(NICER) monitoring campaign of the 468 Hz accreting millisecond X-ray pulsar IGR J17379–3747. From a detailed spectral and timing analysis of the coherent pulsations we find that they show a strong energy dependence, with soft thermal emission lagging about 640 μs behind the hard, Comptonized emission. Additionally, we observe uncommonly large pulse fractions, with measured amplitudes in excess of 20% sinusoidal fractional amplitude across the NICER passband and fluctuations of up to ∼70%. Based on a phase-resolved spectral analysis, we suggest that these extreme properties might be explained if the source has an unusually favorable viewing geometry with a large magnetic misalignment angle. Due to these large pulse fractions, we were able to detect pulsations down to quiescent luminosities (~5 x 10(exp 33) erg/s).

Bult, Peter↗
NASA NTRS2019

A Fast All-Sky Radiation Model for Solar Applications with Narrowband Irradiances on Tilted Surfaces (FARMS-NIT): Part II. The Cloudy-Sky Model

The Fast All-sky Radiation Model for Solar applications with Narrowband Irradiances on Tilted surfaces (FARMSNIT) reported in Part I of this study is enhanced to include the requirements for cloudy-sky conditions. Surface radiances in 2002 narrow-wavelength bands from 0.28 to 4.0 μm are analytically computed by solving the radiative transfer equation for five independent photon paths accounting for clear-sky absorption, Rayleigh scattering, and cloud absorption and scattering. The Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS) is used to provide the optical thickness of the clear-sky atmosphere. Unlike Part I, which approximates the computation of aerosol scattering using the single-scattering phase function, the cloud transmittance and reflectance are efficiently retrieved from a comprehensive look-up table pre-computed by a 32-stream DIScrete Ordinates Radiative Transfer (DISORT) model for possible cloud conditions as well as solar and viewing geometries. A resolution analysis is performed to assess the optimal balance between the computational efficiency and accuracy in the development of the look-up table. Model simulations by DISORT and TMYSPEC are used to evaluate the performance of FARMS-NIT under cloudy-sky conditions. Compared to DISORT, FARMS-NIT yields 2–3% uncertainties on average, but it substantially reduces the computational time because of the independent computation of cloud properties and the implementation of the look-up table. In contrast to TMYSPEC, which uses successive steps to empirically compute plane-of-array (POA) irradiances and spectral irradiances, FARMS-NIT directly solves spectral radiances from the radiative transfer equation, which profoundly increases the accuracy in surface irradiances, especially over inclined photovoltaics (PV) panels.

Xie, Yu↗
NASA NTRS2019

Generating Accurate and Consistent Top-Of-Atmosphere Reflectance Products from the New Generation Geostationary Satellite Sensors

GeoNEX is a collaborative project by scientists from NASA, NOAA, JAXA, and other organizations around the world with the purpose of generating a suite of Earth-monitoring products using data streams from the latest geostationary (GEO) sensors including the GOES-16/17 ABI and the Himawari-8/9 AHI. An accurate and consistent top-of-atmosphere (TOA) reflectance product, in particular the bidirectional reflectance factor (BRF), is the starting point in the scientific processing chain. We describe the main considerations and corresponding algorithms in generating the GeoNEX TOA BRF product. First, a special advantage of geostationary data streams is their high temporal resolution (~10 minutes per full-disk scan), providing a key source of information for many downstream products. To fully utilize this high temporal frequency demands a high georegistration accuracy for every acquired image. Our analysis shows that there can be substantial georegistration uncertainties in both GOES and Himawari L1b data which we addressed by implementing a phase-based correction algorithm to remove residual errors. Second, geostationary sensors have distinct illumination-view geometry features in that the solar angle changes for every pixel. Therefore, to accurately derive a BRF requires a solar position algorithm and the estimation of the pixel-wise acquisition time within an uncertainty of 10 seconds. Third, we discuss the measures we adopted to check and correct residual radiometric calibration issues of individual sensors to enable time-series analysis as well as the cross calibration between different satellite sensors (including those from low-Earth orbit). Finally, we also explain the rationale for the choice of the global grid/tile system of the GeoNEX TOA BRF product.

Wang, Weile↗
NASA NTRS2019

Spectral Polarization Distribution Models (PDMs) for NASA CLARREO Pathfinder’s Inter-Calibration Applications

Solar radiation scattered by Earth surfaces of various scene types such as oceans, deserts, tree leaves etc and atmospheric molecules and particles is polarized and the amount of polarization depends on the surface composition and particle physical properties. This can be a source of measurement errors in satellite data if a non-polarimetric radiometric sensor is sensitive to the polarization state of light. To obtain highly accurate spectral solar radiation data from the Earth-atmosphere system for the space-borne inter-calibration studies as proposed in NASA's Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission and the CLARREO Pathfinder (CPF) mission, the spectral polarization state of the reflected solar light at the top of atmosphere (TOA) must be known with sufficient accuracy. The degree of polarization (DOP) and the angle of linear polarization (AOLP) of the light at the TOA as functions of incident and viewing geometry and scene type construct the Polarization Distribution Models (PDMs) for correction of polarization-induced error of satellite data. In this work, algorithms for modeling the spectral polarization state of reflected sunlight from various types of Earth, including oceans, deserts, vegetated land surfaces and these scene types with all kinds of clouds, are developed. By comparing the model results with the PARASOL satellite data, our numerical results demonstrate that the model can provide a reliable approach for making the spectral PDMs for wavelengths between 320 and 2300 nm for satellite inter-calibration applications as proposed in the CLARREO and the CLARREO CPF missions.

Sun, Wenbo↗
NASA NTRSDate not supplied

TPSAS-NF1676L-17894-DND

Are domain-aggregated, long-term climate trends in retrieved reflected solar cloud properties detectable despite instrument related and algorithm-related aliasing errors? Science Question: By how much do changes in instrument calibration distort reflected solar cloud property decadal trends? Objective: Quantify how changes in calibration error feed into cloud property changes. Science Question: By how much do reflected solar cloud property retrieval assumptions distort trends in retrieved cloud properties? Objective: Quantify how the plane-parallel assumption in reflected solar satellite cloud retrievals distorts cloud optical thickness decadal trends by determining how and if the large-scale 3D optical thickness bias changes over time. - The three panel procedure below will be performed for each time (month), (zonal) region, set of solar and viewing geometries.

Yolanda Roberts↗