Dependence Of Albedo Research Articles

A Simple Model for Multiple Equilibria in Ice-Covered Oceans

Abstract The existence of multiple equilibria (ice-covered and ice-free states) is explored using a set of coupled, nondimensional equations that describe the heat and salt balances in basins, such as the Arctic Ocean, that are subject to atmospheric forcing and two distinct water mass sources. Six nondimensional numbers describe the influences of atmospheric cooling, evaporation minus precipitation, solar radiation, atmospheric temperature, diapycnal mixing, and the temperature contrast between the two water masses. It is shown that multiple equilibria resulting from the dependence of albedo on ice cover exist over a wide range of parameter space, especially so in the weak mixing limit. Multiple equilibria can also occur if diapycnal mixing increases to O(10−4) m2 s−1 or larger under ice-free conditions due to enhanced upward mixing of warm, salty water from below. Sensitivities to various forcing parameters are discussed. Significance Statement The purpose of this study is to better understand under what circumstances high-latitude seas, such as the Arctic Ocean, can exist in either an ice-covered or an ice-free state. The temperature and salinity of the ocean, as well as the heat exchange with the atmosphere, are drastically different depending on which state the ocean is in. The theory presented here identifies how forcing from the atmosphere and ocean dynamics determines whether the ocean is ice covered, ice free, or possibly either one.

Погодно-климатический аспект стратегии устойчивого развития экосистем горных территорий

Introduction. The results of an analysis of information about threats to the development of civilization from the consequences of global warming and the effectiveness of projects presented to society to prevent it are presented. Research methods and materials. The method of inductive-deductive content analysis of scientific publications on the problems of global warming and the effectiveness of known methods for adjusting the heat balance of the planet was used. Research results. The high sensitivity of the thermal balance of the earth’s shell to cloud albedo and the complex dependence of cloud albedo on combinations of different types of clouds and on the frequency of cyclone formation have been established. Discussion of research results. Projects presented by various initiative groups to prevent global warming are assessed as unpromising. Conclusions on the article. An alternative method for adjusting cloud albedo is presented based on the use of thermoacoustic instability of atmospheric moisture. The method uses not a material substrate, but a phase of acoustic vibrations to influence the atmosphere. As a result, the use of the method is not accompanied by an increase in the entropy of the terrestrial ecosystem. Suggestions for practical applications and directions for future research. The application of the acoustic method is carried out in the form of remote initiation in the atmosphere of direct and reverse thermoacoustic effects using narrowly directed acoustic radiation from a ground-based installation and is characterized by high scalability, constant readiness for use and the absence of supporting infrastructure.

Investigation of the effects of the Greek extreme wildfires of August 2021 on air quality and spectral solar irradiance

Abstract. In August 2021, a historic heatwave was recorded in Greece which resulted in extreme wildfire events that strongly affected the air quality over the city of Athens. Saharan dust was also transferred over Greece on certain days of the same period due to the prevailing southern winds. The impact of these events on air quality and surface solar radiation is investigated in this study. Event characterization based on active and passive remote sensing instrumentation has been performed. The study shows that significantly increased levels of air pollution were recorded from the end of July to the first week of August. The smoke led to unusually high aerosol optical depth (AOD) values (up to 3.6 at 500 nm), high Ångström exponent (AE) (up to 2.4 at 440–870 nm), and a strong and negative dependence of single-scattering albedo (SSA) on wavelength that was observed to decrease from 0.93 at 440 nm to 0.86 at 1020 nm, while the dust event led to high AOD (up to 0.7 at 500 nm), low AE (up to 0.9 at 440–870 nm), and a positive dependence of SSA on wavelength that was observed to increase from 0.89 at 440 nm to 0.95 at 1020. Furthermore, the smoke plume was also detected over the PANhellenic GEophysical observatory of Antikythera on 7 August, which is about 240 km away from Athens. Increased AOD values (up to ∼ 0.90 at 500 nm) associated with a high fine-mode AOD (up to ∼ 0.85 at 500 nm) and decrease in SSA with wavelength suggested the dominance of fine biomass burning aerosols. The impact of dust and smoke on solar irradiance revealed significant differences in the spectral dependence of the attenuation caused by the two different aerosol types. The attenuation of solar irradiance in the ultraviolet (UV-B) spectrum was found to be much lower in the case of dust compared to smoke for similar AOD500 values. Differences were less pronounced in the near-infrared and visible spectral regions. The large AODs during the wildfires resulted in a decrease in the noon UV index by up to 53 %, as well as in the daily effective doses for the production of vitamin D (up to 50 %), in the daily photosynthetically active radiation (up to 21 %) and in the daily global horizontal irradiance (up to 17 %), with serious implications for health, agriculture, and energy. This study highlights the wider impacts of wildfires that are part of the wider problem for Mediterranean countries, whose frequency is predicted to increase in view of the projected increasing occurrence of summer heatwaves.

Asteroid Polarimetric Phase Behavior in the Near-infrared: S- and C-complex Objects

We present the first results of our survey of asteroid polarization phase curves in the near-infrared J and H bands using the WIRC+Pol instrument on the Palomar 200-inch telescope. We confirm through observations of standard stars that WIRC+Pol can reach the 0.1% precision needed for asteroid phase curve characterization, and we show that C-complex asteroids could act as an alternate calibration source, as they show less wavelength variation than stellar polarized standards. Initial polarization phase curve results for S-complex asteroids show a shift in behavior as a function of wavelength from visible to near-infrared bands, extending previously observed trends. Full near-infrared polarization phase curve characterization of individual asteroids will provide a unique constraint on surface composition of these objects by probing the wavelength dependence of albedo and index of refraction of the surface material.

Modelling surface temperature and radiation budget of snow-covered complex terrain

Abstract. The surface temperature controls the temporal evolution of the snowpack, playing a key role in metamorphism and snowmelt. It shows large spatial variations in mountainous areas because the surface energy budget is affected by the topography, for instance because of the modulation of the short-wave irradiance by the local slope and the shadows and the short-wave and long-wave re-illumination of the surface from surrounding slopes. These topographic effects are often neglected in large-scale models considering the surface to be flat and smooth. Here we aim at estimating the surface temperature of snow-covered mountainous terrain in clear-sky conditions in order to evaluate the relative importance of the different processes that control the spatial variations. For this, a modelling chain is implemented to compute the surface temperature in a kilometre-wide area from local radiometric and meteorological measurements at a single station. The first component of this chain is the Rough Surface Ray-Tracing (RSRT) model. Based on a photon transport Monte Carlo algorithm, this model quantifies the incident and reflected short-wave radiation on every facet of the mesh describing the snow-covered terrain. The second component is a surface scheme that estimates the terms of the surface energy budget from which the surface temperature is eventually estimated. To assess the modelling chain performance, we use in situ measurements of surface temperature and satellite thermal observations (Landsat 8) in the Col du Lautaret area, in the French Alps. The results of the simulations show (i) an agreement between the simulated and measured surface temperature at the station for a diurnal cycle in winter within 0.2 ∘C; (ii) that the spatial variations in surface temperature are on the order of 5 to 10 ∘C in the domain and are well represented by the model; and (iii) that the topographic effects ranked by importance are the modulation of solar irradiance by the local slope, followed by the altitudinal variations in air temperature (lapse rate), the re-illumination by long-wave thermal emission from surrounding terrain, and the spectral dependence of snow albedo. The changes in the downward long-wave flux because of variations in altitude and the absorption enhancement due to multiple bounces of photons in steep terrain play a less significant role. These results show the necessity of considering the topography to correctly assess the energy budget and the surface temperature of snow-covered complex terrain.

The Nonlinear Radiative Feedback Effects in the Arctic Warming

The analysis of radiative feedbacks requires the separation and quantification of the radiative contributions of different feedback variables, such as atmospheric temperature, water vapor, surface albedo, cloud, etc. It has been a challenge to include the nonlinear radiative effects of these variables in the feedback analysis. For instance, the kernel method that is widely used in the literature assumes linearity and completely neglects the nonlinear effects. Nonlinear effects may arise from the nonlinear dependency of radiation on each of the feedback variables, especially when the change in them is of large magnitude such as in the case of the Arctic climate change. Nonlinear effects may also arise from the coupling between different feedback variables, which often occurs as feedback variables including temperature, humidity and cloud tend to vary in a coherent manner. In this paper, we use brute-force radiation model calculations to quantify both univariate and multivariate nonlinear feedback effects and provide a qualitative explanation of their causes based on simple analytical models. We identify these prominent nonlinear effects in the CO2-driven Arctic climate change: 1) the univariate nonlinear effect in the surface albedo feedback, which results from a nonlinear dependency of planetary albedo on the surface albedo, which causes the linear kernel method to overestimate the univariate surface albedo feedback; 2) the coupling effect between surface albedo and cloud, which offsets the univariate surface albedo feedback; 3) the coupling effect between atmospheric temperature and cloud, which offsets the very strong univariate temperature feedback. These results illustrate the hidden biases in the linear feedback analysis methods and highlight the need for nonlinear methods in feedback quantification.

Improving Spatial Coverage of Satellite Aerosol Classification Using a Random Forest Model

The spatial coverage of satellite aerosol classification was improved using a random forest (RF) model trained with observational data including target (aerosol type) and input (satellite measurement) variables. The AErosol RObotic NETwork (AERONET) aerosol-type dataset was used for the target variables. Satellite input variables with many missing data or low mean-decrease accuracy were excluded from the final input variable set, and good performance in aerosol-type classification was achieved. The performance of the RF-based model was evaluated on the basis of the wavelength dependence of single-scattering albedo (SSA) and fine-mode-fraction values from AERONET. Typical SSA wavelength dependence for individual aerosol types was consistent with that obtained for aerosol types by the RF-based model. The spatial coverage of the RF-based model was also compared with that of previously developed models in a global-scale case study. The study demonstrates that the RF-based model allows satellite aerosol classification with improved spatial coverage, with a performance similar to that of previously developed models.

A First Approach to Aerosol Classification Using Space-Borne Measurement Data: Machine Learning-Based Algorithm and Evaluation

A new method was developed for classifying aerosol types involving a machine-learning approach to the use of satellite data. An Aerosol Robotic NETwork (AERONET)-based aerosol-type dataset was used as a target variable in a random forest (RF) model. The contributions of satellite input variables to the RF-based model were quantified to determine an optimal set of input variables. The new method, based on inputs of satellite variables, allows the classification of seven aerosol types: pure dust, dust-dominant mixed, pollution-dominant mixed aerosols, and pollution aerosols (strongly, moderately, weakly, and non-absorbing). The performance of the model was statistically evaluated using AERONET data excluded from the model training dataset. Model accuracy for classifying the seven aerosol types was 59%, improving to 72% for four types (pure dust, dust-dominant mixed, strongly absorbing, and non-absorbing). The performance of the model was evaluated against an earlier aerosol classification method based on the wavelength dependence of single-scattering albedo (SSA) and fine-mode-fraction values from AERONET. Typical wavelength dependences of SSA for individual aerosol types are consistent with those obtained for aerosol types by the new method. This study demonstrates that an RF-based model is capable of satellite aerosol classification with sensitivity to the contribution of non-spherical particles.

Methane retrieved from TROPOMI: improvement of the data product and validation of the first 2 years of measurements

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel 5 Precursor (S5-P) satellite provides methane (CH4) measurements with high accuracy and exceptional temporal and spatial resolution and sampling. TROPOMI CH4 measurements are highly valuable to constrain emissions inventories and for trend analysis, with strict requirements on the data quality. This study describes the improvements that we have implemented to retrieve CH4 from TROPOMI using the RemoTeC full-physics algorithm. The updated retrieval algorithm features a constant regularization scheme of the inversion that stabilizes the retrieval and yields less scatter in the data and includes a higher resolution surface altitude database. We have tested the impact of three state-of-the-art molecular spectroscopic databases (HITRAN 2008, HITRAN 2016 and Scientific Exploitation of Operational Missions – Improved Atmospheric Spectroscopy Databases SEOM-IAS) and found that SEOM-IAS provides the best fitting results. The most relevant update in the TROPOMI XCH4 data product is the implementation of an a posteriori correction fully independent of any reference data that is more accurate and corrects for the underestimation at low surface albedo scenes and the overestimation at high surface albedo scenes. After applying the correction, the albedo dependence is removed to a large extent in the TROPOMI versus satellite (Greenhouse gases Observing SATellite – GOSAT) and TROPOMI versus ground-based observations (Total Carbon Column Observing Network – TCCON) comparison, which is an independent verification of the correction scheme. We validate 2 years of TROPOMI CH4 data that show the good agreement of the updated TROPOMI CH4 with TCCON (−3.4 ± 5.6 ppb) and GOSAT (−10.3 ± 16.8 ppb) (mean bias and standard deviation). Low- and high-albedo scenes as well as snow-covered scenes are the most challenging for the CH4 retrieval algorithm, and although the a posteriori correction accounts for most of the bias, there is a need to further investigate the underlying cause.

Regional features of intraseasonal temperature variability in the regions of Northern Eurasia with global climate change

Polymodal (bimodal) features of the probability density functions (PDFs) for long term series of surface air temperature anomalies in transitional (fall, spring) seasons are studied based on daily data from meteorological observations in various North Eurasian regions using a stochastic energy balance model. The observed PDFs are characterized by bimodality with the minimums laying near 0° C. Changes of weather regimes since the middle of 20th century until recent years are analyzed. The increase in probability of negative temperatures for both transitional seasons in the 21st century compared to the 20th century can be linked to global changes in atmosphere circulation patterns and, particularly, to intensification of cold air outbreaks occurrence in spring seasons. “Indian summer” (the effect of recurrent warming in fall seasons) phenomenon is stronger in the 20th century PDF, while the bimodality of PDF around 0° C can signify the nonlinear dependence of albedo on SAT.

Daily spectral ocean surface albedo (OSA) parameterization in case of clearness index (Kt) and phytoplankton variability in Malacca Strait

In this study, we examined the albedo's dependence on clearness index (Kt) based on measured global radiation data and phytoplankton variability influence represented by chlorophyll (a) concentration at the upper layers over the Malacca Strait. Half-hourly global solar radiation (5°26′53″ N, 100°11′36″ E) measurement over the period from January to October 2017 was analyzed to investigate the correlation between clearness index and ocean surface albedo (OSA) in case of phytoplankton influence in Malacca Strait coastal waters. Three days (January 29, February 26 and March 22, 2017) with high irradiation values were selected for daily OSA variability study. The parameterization includes bio-optical analytical modelling based on apparent optical properties and photosynthetically active range (PAR) estimation. Daily timescale analysis of spectral albedo in Malacca Strait enables detail examination for the chlorophyll maximum absorption wavelength (λ = 440 nm) parameterization. OSA diurnal variability was estimated using Jin et al. scheme, which is based on the separation of albedo components (direct and diffuse). Hourly changes in radiation (including Kt) and solar position properties provide valuable information to investigate the pathways of daily spectral albedo in case of small concentrations of chlorophyll (a) and clearness index parameterization.

The Dark Planets of the WASP-47 Planetary System

Abstract Exoplanet discoveries have demonstrated a vast range of planetary system architectures. The demographic of compact planetary systems are especially interesting from the perspective of planetary formation and the evolution of orbital dynamics. Another interesting demographic is that of giant planets in eccentric orbits, since these planets have likely had a dynamical history involving planet–planet scattering events. The WASP-47 system is particularly fascinating since it combines these two demographics, having both compact planetary orbits and a giant planet on an eccentric orbit within the system the habitable zone. Here we provide an analysis of the WASP-47 system from the perspective of atmospheric detection and characterization. We discuss the system architecture and the potential for additional long-period planets. We simulate expected phase variations as a function of planet orbital phase for the system due to the combined effect of the planets. We present an analysis of precision photometry of WASP-47 from the K2 mission, phased on each of the planets. The analysis rules out the detection of phase signatures for the two inner-most planets, enabling constraints upon their albedos and atmospheric properties. Our study concludes that WASP-47b is an example of a “dark” planet with a tentative geometric albedo of 0.016 and a 1σ upper limit of 0.17. The WASP-47e data are consistent with a broad range of albedos, but also show early evidence of having a relatively low albedo. The growing number of dark, short-period giant planets provide the framework of an ideal sample for studying low albedo dependence on atmospheric composition.

An improved air mass factor calculation for nitrogen dioxide measurements from the Global Ozone Monitoring Experiment-2 (GOME-2)

Abstract. An improved tropospheric nitrogen dioxide (NO2) retrieval algorithm from the Global Ozone Monitoring Experiment-2 (GOME-2) instrument based on air mass factor (AMF) calculations performed with more realistic model parameters is presented. The viewing angle dependency of surface albedo is taken into account by improving the GOME-2 Lambertian-equivalent reflectivity (LER) climatology with a directionally dependent LER (DLER) dataset over land and an ocean surface albedo parameterisation over water. A priori NO2 profiles with higher spatial and temporal resolutions are obtained from the IFS (CB05BASCOE) chemistry transport model based on recent emission inventories. A more realistic cloud treatment is provided by a clouds-as-layers (CAL) approach, which treats the clouds as uniform layers of water droplets, instead of the current clouds-as-reflecting-boundaries (CRB) model, which assumes that the clouds are Lambertian reflectors. On average, improvements in the AMF calculation affect the tropospheric NO2 columns by ±15 % in winter and ±5 % in summer over largely polluted regions. In addition, the impact of aerosols on our tropospheric NO2 retrieval is investigated by comparing the concurrent retrievals based on ground-based aerosol measurements (explicit aerosol correction) and the aerosol-induced cloud parameters (implicit aerosol correction). Compared with the implicit aerosol correction utilising the CRB cloud parameters, the use of the CAL approach reduces the AMF errors by more than 10 %. Finally, to evaluate the improved GOME-2 tropospheric NO2 columns, a validation is performed using ground-based multi-axis differential optical absorption spectroscopy (MAXDOAS) measurements at different BIRA-IASB stations. At the suburban Xianghe station, the improved tropospheric NO2 dataset shows better agreement with coincident ground-based measurements with a correlation coefficient of 0.94.

Seasonal dynamics of albedo across European boreal forests: Analysis of MODIS albedo and structural metrics from airborne LiDAR

Uncertainties in estimation of albedo-related radiative forcing cause ambiguity in evaluation of net climate effects of forests and forest management. Numerous studies have reported local relations between forest structure and albedo in the boreal zone. However, more research is needed to establish these relations for geographically extensive areas, and to examine seasonal courses of albedo to understand the effects of forest structure on mean annual shortwave energy balance. Remote sensing is a viable option for accomplishing these goals, but there are many challenges related to e.g. long periods of cloud cover and low solar elevations in high latitudes. We used the new MODIS Collection 6 (MCD43A3) daily albedo product, and analyzed MODIS albedo dependence on airborne LiDAR-based forest structure in 22 study sites in Estonia, Finland, Sweden, and Russia (57°–69° N, 12°–57° E). Wall-to-wall LiDAR data allowed us to take into account the effective spatial resolution of MODIS, which notably improved correlations between albedo and forest structure. Use of the best quality backup algorithm (magnitude inversion) together with main algorithm results in the MODIS albedo product did not reduce the correlations compared to using main algorithm only. We quantified the effects of landscape-level forest structure (forest height, canopy cover, fraction of young forest) and fraction of broadleaved deciduous forest on mean annual albedo. We showed that because the forest structure-albedo relations are the strongest in snow-covered periods, and because the snow-covered period is longest in the north, the effect of forest structure on mean annual albedo increases towards the north. On the other hand, the effect of broadleaved fraction did not show such latitudinal trend. Our results indicate that even within a single climatic zone the optimal forest management solution to mitigate climate change depends on geographic location.

Three-wavelength cavity-enhanced albedometer for measuring wavelength-dependent optical properties and single-scattering albedo of aerosols.

The spectral dependence of aerosol light absorption (αabs) and single-scattering albedo-[ω, defined as the ratio of the scattering (αscat) and extinction coefficients (αext = αabs + αscat)]-has proven effective in classifying dominant aerosol types. It is also helpful in understanding aerosol sources, transformation, climate and environmental effects, testing aerosol models, and improving the retrieval accuracy of satellite and remote sensing data. Despite the significant progress that has been made with measurement of light absorption and ω, many of the reported instruments either operate at a fixed wavelength or can only measure a single optical parameter. Quantitative multi-parameter wavelength-dependent measurement remains a challenge. In this work, a three-wavelength cavity-enhanced albedometer was developed. The albedometer can measure multiple optical parameters, αext, αscat, αabs, and ω, at λ = 365, 532, and 660 nm, in real time. The instrument's performance was evaluated using four different type laboratory generated aerosols, including polystyrene latex spheres (PSL, non-absorbing); ammonium sulfate (AS, non-absorbing); suwannee river fulvic acid (SRFA, slightly absorbing; a proxy for light absorbing organic aerosol); and nigrosin (strongly absorbing).

Recovering the colour-dependent albedo of exoplanets with high-resolution spectroscopy: from ESPRESSO to the ELT

The characterization of planetary atmospheres is a daunting task, pushing current observing facilities to their limits. The next generation of high-resolution spectrographs mounted on large telescopes -- such as ESPRESSO@VLT and HIRES@ELT -- will allow us to probe and characterize exoplanetary atmospheres in greater detail than possible to this point. We present a method that permits the recovery of the colour-dependent reflectivity of exoplanets from high-resolution spectroscopic observations. Determining the wavelength-dependent albedo will provide insight into the chemical properties and weather of the exoplanet atmospheres. For this work, we simulated ESPRESSO@VLT and HIRES@ELT high-resolution observations of known planetary systems with several albedo configurations. We demonstrate how the cross correlation technique applied to theses simulated observations can be used to successfully recover the geometric albedo of exoplanets over a range of wavelengths. In all cases, we were able to recover the wavelength dependent albedo of the simulated exoplanets and distinguish between several atmospheric models representing different atmospheric configurations. In brief, we demonstrate that the cross correlation technique allows for the recovery of exoplanetary albedo functions from optical observations with the next generation of high-resolution spectrographs that will be mounted on large telescopes with reasonable exposure times. Its recovery will permit the characterization of exoplanetary atmospheres in terms of composition and dynamics and consolidates the cross correlation technique as a powerful tool for exoplanet characterization.

Albedo of a Small Ice-Covered Boreal Lake: Daily, Meso-Scale and Interannual Variability on the Background of Regional Climate

In winter, the reflective properties of ice-and-snow-covered lakes and the surrounding surface covered with snow differ little. Estimation of the albedo becomes especially important in spring when the reflectivity of the ice-covered lakes differs markedly from the surrounding snow-free surface. The measurements of the snow and ice albedo in situ are necessary to ensure adequate analysis of remote sensing data and monitoring of the state of the land ice. A wide range of surface albedo of small boreal ice-covered Lake Vendyurskoe (North-Western Russia) is calculated from observational data of solar radiation obtained in 1995–2000 and 2002–2017. A noticeable variability of albedo due to spring melting and changes in weather conditions is described. Climatic variability (North Atlantic Oscillation (NAO) index, the average monthly air temperature and sum of precipitation in December-March) is analyzed in the context of possible influence on the maximal thickness of snow and white ice, and, consequently, on the spring lake albedo dynamics. In current work to estimate the external heat flux that comes from the atmosphere to the surface of the lake and presumably determines the dynamics of albedo during spring melting, a simple parameter was used: the accumulated sum of positive temperatures, starting from March 1. The obtained prognostic equation of the cubic dependence of albedo on the named parameter demonstrates a different rate of albedo decrease in the melting of snow, white, and congelation ice.

Influence of turbidity and aeration on the albedo of mountain streams

AbstractStream surface albedo plays a key role in the energy balance of rivers and streams that are exposed to direct solar radiation. Most physically based analyses and models have incorporated a constant stream albedo between 0.03 and 0.10, based primarily on measurements from low‐gradient streams with low suspended sediment concentrations. However, albedo should vary with solar elevation angle, suspended sediment concentration, aeration, and fraction of direct versus diffuse radiation. The objective of this study was to quantify the dependence of albedo of mountain streams on the controlling factors and to develop a predictive model for use in physically based analysis and modelling of stream temperature, especially for future climate and land‐use scenarios. Stream surface albedo was measured at nine sites with a variety of gradients and suspended sediment characteristics in the southern Coast Mountains of British Columbia, Canada. As expected, albedo of low‐gradient, non‐white water (flatwater) streams increased with solar elevation angle, suspended sediment concentration, and proportion of diffuse to direct solar radiation, ranging between 0.025 during cloudy periods over clear water to 0.25 for turbid water at elevation angles of less than 20°. Albedo was enhanced in steep reaches or at channel steps and cascades where flow was visibly aerated, with a range of 0.09 to 0.33. In clear weather, albedo exhibited notable diurnal variability at flatwater sampling sites. For example, during late summer, surface albedo typically fluctuated between 0.08 and 0.15 on a daily basis at a flatwater site on the highly turbid, glacier‐fed Lillooet River. Multiple regression models explained approximately 60% and 40% of the variance under cross validation for flatwater and white water data subsets, respectively, with corresponding root mean square errors of approximately 0.02 and 0.06.

Laboratory measurements of light polarization on samples targeted for the lunar regolith

We carried out multi-band (B, V, and R bands) polarimetric measurements of several soil samples targeted for the lunar regolith (JSC-1A, Fe2O3, SiC, and JSC-1Mars). Our laboratory experiments are intended to provide some constraints to the theoretical and numerical studies of the light scattering off the particulate surface of airless bodies in the solar system. Among our samples, the lunar soil simulant JSC-1A has the closest αmax to the typically observed value on the lunar surface, ∼100°, where αmax is the phase angle at which the polarization has the maximum value. In the other samples, αmax is higher than 120° or significantly wavelength dependent. The empirical relationship between the grain size, maximum polarization and albedo for the lunar regolith overestimates the actual grain sizes of some of our samples by a factor of up to ∼6. The measured polarization degrees and albedos of the JSC-1A sample are similar to the typical observed values of the lunar maria. We also find that the wavelength dependence of both polarization degree and albedo is larger for smaller-grain samples.

Improved calibration of reflectance data from the LRO Lunar Orbiter Laser Altimeter (LOLA) and implications for space weathering

The Lunar Orbiter Laser Altimeter (LOLA) experiment on Lunar Reconnaissance Orbiter (LRO) is a laser altimeter that also measures the strength of the return pulse from the lunar surface. These data have been used to estimate the reflectance of the lunar surface, including regions lacking direct solar illumination. A new calibration of these data is presented that features lower uncertainties overall and more consistent results in the polar regions. We use these data, along with newly available maps of the distribution of lunar maria, also derived from LRO instrument data, to investigate a newly discovered dependence of the albedo of the lunar maria on latitude (Hemingway et al., [2015]). We confirm that there is an increase in albedo with latitude in the lunar maria, and confirm that this variation is not an artifact arising from the distribution of compositions within the lunar maria, using data from the Lunar Prospector Neutron Spectrometer. Radiative transfer modeling of the albedo dependence within the lunar maria is consistent with the very weak to absent dependence of albedo on latitude in the lunar highlands; the lower abundance of the iron source for space weathering products in the lunar highlands weakens the latitude dependence to the extent that it is only weakly detectable in current data. In addition, photometric models and normalization may take into account the fact that the lunar albedo is latitude dependent, but this dependence can cause errors in normalized reflectance of at most 2% for the majority of near-nadir geometries.We also investigate whether the latitude dependent albedo may have obscured detection of small mare deposits at high latitudes. We find that small regions at high latitudes with low roughness similar to the lunar maria are not mare deposits that may have been misclassified owing to high albedos imposed by the latitude dependence. Finally, we suggest that the only modest correlations among space weathering indicators defined for the lunar samples may be due to mixing of soils from distinct latitudes.