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M. Mommert – One of the best experts on this subject based on the ideXlab platform.

  • tnos are cool a survey of the trans neptunian region xiv size Albedo characterization of the haumea family observed with herschel and spitzer
    Astronomy and Astrophysics, 2018
    Co-Authors: E. Vilenius, C. Kiss, M. Mommert, J A Stansberry, Thomas Muller, M Mueller, P Santossanz, Emmanuel Lellouch

    Abstract:

    Context. A group of trans-Neptunian objects (TNOs) are dynamically related to the dwarf planet 136108 Haumea. Ten of them show strong indications of water ice on their surfaces, are assumed to have resulted from a collision, and are accepted as the only known TNO collisional family. Nineteen other dynamically similar objects lack water ice absorptions and are hypothesized to be dynamical interlopers.

    Aims: We have made observations to determine sizes and geometric Albedos of six of the accepted Haumea family members and one dynamical interloper. Ten other dynamical interlopers have been measured by previous works. We compare the individual and statistical properties of the family members and interlopers, examining the size and Albedo distributions of both groups. We also examine implications for the total mass of the family and their ejection velocities.

    Methods: We use far-infrared space-based telescopes to observe the target TNOs near their thermal peak and combine these data with optical magnitudes to derive sizes and Albedos using radiometric techniques. Using measured and inferred sizes together with ejection velocities, we determine the power-law slope of ejection velocity as a function of effective diameter.

    Results: The detected Haumea family members have a diversity of geometric Albedos 0.3-0.8, which are higher than geometric Albedos of dynamically similar objects without water ice. The median geometric Albedo for accepted family members is pV = 0.48-0.18+0.28, compared to 0.08-0.05+0.07 for the dynamical interlopers. In the size range D = 175-300 km, the slope of the cumulative size distribution is q = 3.2-0.4+0.7 for accepted family members, steeper than the q = 2.0 ± 0.6 slope for the dynamical interlopers with D < 500 km. The total mass of Haumea's moons and family members is 2.4% of Haumea's mass. The ejection velocities required to emplace them on their current orbits show a dependence on diameter, with a power-law slope of 0.21-0.50. Herschel is an ESA space observatory with science instruments provided by a European-led Principal Investigator consortia and with important participation from NASA.

  • “TNOs are Cool”: A survey of the trans-Neptunian region XI. A Herschel-PACS view of 16 Centaurs
    Astronomy and Astrophysics – A&A, 2014
    Co-Authors: R. Duffard, N. Pinilla-alonso, P. Santos-sanz, E. Vilenius, J. L. Ortiz, T. Mueller, S. Fornasier, E. Lellouch, M. Mommert, C. Kiss

    Abstract:

    Context. Centaurs are the transitional population between trans-Neptunian objects (TNOs) and Jupiter-family comets. Their physical properties provide an insight into TNO properties, but only under restricted conditions since Centaurs are closer to the Sun and Earth. For this reason it is possible to access the smaller ones, which is more difficult to do with the TNO population. Aims. The goal of this work is to characterize a set of 16 Centaurs in terms of their size, Albedo, and thermal properties. We study the correlations, for a more extended sample obtained from the literature, of diameter, Albedo, orbital parameters, and spectral slopes. Methods. We performed three-band photometric observations using Herschel-PACS and used a consistent method for the data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70, 100, and 160 mu m. Additionally, we used Spitzer-MIPS flux densities at 24 and 70 pm when available. We also included in our Centaur sample scattered disk objects, a dynamical family of TNOs, using results previously published by our team, and some Centaurs observed only with the Spitzer-MIPS instrument. Results. We have determined new radiometric sizes and Albedos of 16 Centaurs. The first conclusion is that the Albedos of Centaur objects are not correlated with their orbital parameters. Similarly, there is no correlation between diameter and orbital parameters. Most of the objects in our sample are dark (pv \textless 7%) and most of them are small (D \textless 120 km). However, there is no correlation between Albedo and diameter, in particular for the group of small objects as Albedo values are homogeneously distributed between 4 to 16%. The correlation with the color of the objects showed that red objects are all small (mean diameter 65 km), while the gray ones span a wide range of sizes (mean diameter 120 km). Moreover, the gray objects tend to be darker, with a mean Albedo of 5.6%, compared with a mean of 8.5% (ranging from 5 to 15%) for the red objects.

  • “TNOs are Cool”: A survey of the trans-Neptunian region IV. Size/Albedo characterization of 15 scattered disk and detached objects observed with Herschel-PACS
    Astronomy and Astrophysics – A&A, 2012
    Co-Authors: P. Santos-sanz, C. Kiss, E. Vilenius, S. Fornasier, E. Lellouch, M. Mommert, A. Pal, T. G. Mueller, J. Stansberry, A. Delsanti

    Abstract:

    Context. Physical characterization of trans-Neptunian objects, a primitive population of the outer solar system, may provide constraints on their formation and evolution. Aims. The goal of this work is to characterize a set of 15 scattered disk (SDOs) and detached objects, in terms of their size, Albedo, and thermal properties. Methods. Thermal flux measurements obtained with the Herschel-PACS instrument at 70, 100 and 160 mu m, and whenever applicable, with Spitzer-MIPS at 24 and 70 mu m, are modeled with radiometric techniques, in order to derive the objects’ individual size, Albedo and when possible beaming factor. Error bars are obtained from a Monte-Carlo approach. We look for correlations between these and other physical and orbital parameters. Results. Diameters obtained for our sample range from 100 to 2400 km, and the geometric Albedos (in V band) vary from 3.8% to 84.5%. The unweighted mean V geometric Albedo for the whole sample is 11.2% (excluding Eris); 6.9% for the SDOs, and 17.0% for the detached objects (excluding Eris). We obtain new bulk densities for three binary systems: Ceto/Phorcys, Typhon/Echidna and Eris/Dysnomia. Apart from correlations clearly due to observational bias, we find significant correlations between Albedo and diameter (more reflective objects being bigger), and between Albedo, diameter and perihelion distance (brighter and bigger objects having larger perihelia). We discuss possible explanations for these correlations.

C. Kiss – One of the best experts on this subject based on the ideXlab platform.

  • tnos are cool a survey of the trans neptunian region xiv size Albedo characterization of the haumea family observed with herschel and spitzer
    Astronomy and Astrophysics, 2018
    Co-Authors: E. Vilenius, C. Kiss, M. Mommert, J A Stansberry, Thomas Muller, M Mueller, P Santossanz, Emmanuel Lellouch

    Abstract:

    Context. A group of trans-Neptunian objects (TNOs) are dynamically related to the dwarf planet 136108 Haumea. Ten of them show strong indications of water ice on their surfaces, are assumed to have resulted from a collision, and are accepted as the only known TNO collisional family. Nineteen other dynamically similar objects lack water ice absorptions and are hypothesized to be dynamical interlopers.

    Aims: We have made observations to determine sizes and geometric Albedos of six of the accepted Haumea family members and one dynamical interloper. Ten other dynamical interlopers have been measured by previous works. We compare the individual and statistical properties of the family members and interlopers, examining the size and Albedo distributions of both groups. We also examine implications for the total mass of the family and their ejection velocities.

    Methods: We use far-infrared space-based telescopes to observe the target TNOs near their thermal peak and combine these data with optical magnitudes to derive sizes and Albedos using radiometric techniques. Using measured and inferred sizes together with ejection velocities, we determine the power-law slope of ejection velocity as a function of effective diameter.

    Results: The detected Haumea family members have a diversity of geometric Albedos 0.3-0.8, which are higher than geometric Albedos of dynamically similar objects without water ice. The median geometric Albedo for accepted family members is pV = 0.48-0.18+0.28, compared to 0.08-0.05+0.07 for the dynamical interlopers. In the size range D = 175-300 km, the slope of the cumulative size distribution is q = 3.2-0.4+0.7 for accepted family members, steeper than the q = 2.0 ± 0.6 slope for the dynamical interlopers with D < 500 km. The total mass of Haumea's moons and family members is 2.4% of Haumea's mass. The ejection velocities required to emplace them on their current orbits show a dependence on diameter, with a power-law slope of 0.21-0.50. Herschel is an ESA space observatory with science instruments provided by a European-led Principal Investigator consortia and with important participation from NASA.

  • “TNOs are Cool”: A survey of the trans-Neptunian region XI. A Herschel-PACS view of 16 Centaurs
    Astronomy and Astrophysics – A&A, 2014
    Co-Authors: R. Duffard, N. Pinilla-alonso, P. Santos-sanz, E. Vilenius, J. L. Ortiz, T. Mueller, S. Fornasier, E. Lellouch, M. Mommert, C. Kiss

    Abstract:

    Context. Centaurs are the transitional population between trans-Neptunian objects (TNOs) and Jupiter-family comets. Their physical properties provide an insight into TNO properties, but only under restricted conditions since Centaurs are closer to the Sun and Earth. For this reason it is possible to access the smaller ones, which is more difficult to do with the TNO population. Aims. The goal of this work is to characterize a set of 16 Centaurs in terms of their size, Albedo, and thermal properties. We study the correlations, for a more extended sample obtained from the literature, of diameter, Albedo, orbital parameters, and spectral slopes. Methods. We performed three-band photometric observations using Herschel-PACS and used a consistent method for the data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70, 100, and 160 mu m. Additionally, we used Spitzer-MIPS flux densities at 24 and 70 pm when available. We also included in our Centaur sample scattered disk objects, a dynamical family of TNOs, using results previously published by our team, and some Centaurs observed only with the Spitzer-MIPS instrument. Results. We have determined new radiometric sizes and Albedos of 16 Centaurs. The first conclusion is that the Albedos of Centaur objects are not correlated with their orbital parameters. Similarly, there is no correlation between diameter and orbital parameters. Most of the objects in our sample are dark (pv \textless 7%) and most of them are small (D \textless 120 km). However, there is no correlation between Albedo and diameter, in particular for the group of small objects as Albedo values are homogeneously distributed between 4 to 16%. The correlation with the color of the objects showed that red objects are all small (mean diameter 65 km), while the gray ones span a wide range of sizes (mean diameter 120 km). Moreover, the gray objects tend to be darker, with a mean Albedo of 5.6%, compared with a mean of 8.5% (ranging from 5 to 15%) for the red objects.

  • “TNOs are Cool”: A survey of the trans-Neptunian region IV. Size/Albedo characterization of 15 scattered disk and detached objects observed with Herschel-PACS
    Astronomy and Astrophysics – A&A, 2012
    Co-Authors: P. Santos-sanz, C. Kiss, E. Vilenius, S. Fornasier, E. Lellouch, M. Mommert, A. Pal, T. G. Mueller, J. Stansberry, A. Delsanti

    Abstract:

    Context. Physical characterization of trans-Neptunian objects, a primitive population of the outer solar system, may provide constraints on their formation and evolution. Aims. The goal of this work is to characterize a set of 15 scattered disk (SDOs) and detached objects, in terms of their size, Albedo, and thermal properties. Methods. Thermal flux measurements obtained with the Herschel-PACS instrument at 70, 100 and 160 mu m, and whenever applicable, with Spitzer-MIPS at 24 and 70 mu m, are modeled with radiometric techniques, in order to derive the objects’ individual size, Albedo and when possible beaming factor. Error bars are obtained from a Monte-Carlo approach. We look for correlations between these and other physical and orbital parameters. Results. Diameters obtained for our sample range from 100 to 2400 km, and the geometric Albedos (in V band) vary from 3.8% to 84.5%. The unweighted mean V geometric Albedo for the whole sample is 11.2% (excluding Eris); 6.9% for the SDOs, and 17.0% for the detached objects (excluding Eris). We obtain new bulk densities for three binary systems: Ceto/Phorcys, Typhon/Echidna and Eris/Dysnomia. Apart from correlations clearly due to observational bias, we find significant correlations between Albedo and diameter (more reflective objects being bigger), and between Albedo, diameter and perihelion distance (brighter and bigger objects having larger perihelia). We discuss possible explanations for these correlations.

Crystal B Schaaf – One of the best experts on this subject based on the ideXlab platform.

  • Albedo and reflectance anisotropy retrieval from avhrr operated onboard noaa and metop satellites algorithm performance and accuracy assessment for europe
    Remote Sensing of Environment, 2015
    Co-Authors: Melanie Sutterlin, Crystal B Schaaf, Stefan Wunderle, R Stockli, Fabia Husler, Christoph Neuhaus

    Abstract:

    In this study, the land surface Albedo together with its Bidirectional Reflectance Distribution Function (BRDF) are retrieved for the years 2000 to 2012 from Local Area Coverage (LAC) surface reflectance data gathered by the Advanced Very High Resolution Radiometer (AVHRR) over Europe. For the retrieval the MODerate resolution Imaging Spectroradiometer (MODIS) BRDF/Albedo processing scheme is employed. The comparatively high revisit frequency and high variability in angular sampling of the AVHRR sensors operated simultaneously onboard the different National Oceanic and Atmospheric Administration (NOAA) and Meteorological Operational (MetOp) satellites contribute substantially to the success and quality of BRDF retrieval. The performance of the BRDF model for AVHRR data is assessed by comparison to MODIS BRDF retrievals, and the AVHRR BRDF reflectance data is validated against BRDF reflectance data from MODIS and in situ data gathered at three field sites in Switzerland. The comparison shows that the AVHRR BRDF retrievals are of high quality across most of Europe. The higher angular sampling of AVHRR allows for more full model retrievals of best quality and generates less fill values compared to MODIS. For most of the years investigated, the absolute accuracy of the AVHRR Albedos is found to be within 0.05 throughout the complete seasonal cycle with a minimum bias at the peak of the growing season. However, they systematically underestimate the field-measured Albedos, predominantly in winter due to spatial scale mismatch in combination with site heterogeneity and because the expression for the calculation of satellite-based blue-sky Albedo does not account for multiple scattering. A slightly increased underestimation also occurs during vegetation senescence, presumably because of the narrow to broadband conversion employing only two bands. Overall, the results confirm the potential of AVHRR to produce multi-decadal data sets of reflectance anisotropy and Albedo for use in climate monitoring and modeling studies. This offers a promising and unique opportunity to produce a BRDF/Albedo climate data record from AVHRR dating back to 1985.

  • an algorithm for the retrieval of 30 m snow free Albedo from landsat surface reflectance and modis brdf
    Remote Sensing of Environment, 2011
    Co-Authors: Yanmin Shuai, Feng Gao, Jeffrey G Masek, Crystal B Schaaf

    Abstract:

    We present a new methodology to generate 30-m resolution land surface Albedo using Landsat surface reflectance and anisotropy information from concurrent MODIS 500-m observations. Albedo information at fine spatial resolution is particularly useful for quantifying climate impacts associated with land use change and ecosystem disturbance. The derived white-sky and black-sky spectral Albedos may be used to estimate actual spectral Albedos by taking into account the proportion of direct and diffuse solar radiation arriving at the ground. A further spectral-to-broadband conversion based on extensive radiative transfer simulations is applied to produce the broadband Albedos at visible, near infrared, and shortwave regimes. The accuracy of this approach has been evaluated using 270 Landsat scenes covering six field stations supported by the SURFace RADiation Budget Network (SURFRAD) and Atmospheric Radiation Measurement Southern Great Plains (ARM/SGP) network. Comparison with field measurements shows that Landsat 30-m snow-free shortwave Albedos from all seasons generally achieve an absolute accuracy of ±0.02–0.05 for these validation sites during available clear days in 2003–2005, with a root mean square error less than 0.03 and a bias less than 0.02. This level of accuracy has been regarded as sufficient for driving global and regional climate models. The Landsat-based retrievals have also been compared to the operational 16-day MODIS Albedo produced every 8-days from MODIS on Terra and Aqua (MCD43A). The Landsat Albedo provides more detailed landscape texture, and achieves better agreement (correlation and dynamic range) with in-situ data at the validation stations, particularly when the stations include a heterogeneous mix of surface covers.

  • assessing the coupling between surface Albedo derived from modis and the fraction of diffuse skylight over spatially characterized landscapes
    Remote Sensing of Environment, 2010
    Co-Authors: Crystal B Schaaf, P Lewis, A H Strahler, Curtis E Woodcock, Miguel O Roman, Gail P Anderson, J L Privette, Michael J Barnsley

    Abstract:

    Abstract In this effort, the MODerate Resolution Imaging Spectroradiometer (MODIS) (Collection V005) Bidirectional Reflectance Distribution Function (BRDF)/Albedo algorithm is used to retrieve instantaneous surface Albedo at a point in time and under specific atmospheric conditions. These retrievals are then used to study the role that the fraction of diffuse skylight plays under realistic scenarios of anisotropic diffuse illumination and multiple scattering between the surface and atmosphere. Simulations of the sky radiance using the MODTRAN®5.1 radiative transfer model were performed under different aerosol optical properties, illumination conditions, and surface characteristics to describe these effects on surface Albedo retrievals from MODIS. This technique was examined using a validation scheme over four measurement sites with varied aerosol levels and landscapes, ranging from croplands to tundra ecosystems, and over extended time periods. Furthermore, a series of geostatistical analyses were performed to examine the types of spatial patterns observed at each measurement site. In particular, Enhanced Thematic Mapper Plus (ETM+) retrievals of surface Albedo were acquired to analyze the change in variogram model parameters as a function of increased window-size. Results were then used to assess the degree to which a given point measurement is able to capture the intrinsic variability at the scale of MODIS observations. Assessments of MODIS instantaneous Albedos that account for anisotropic multiple scattering, over snow-free and snow-covered lands and at all diurnal solar zenith angles, show a slight improvement over the Albedo formulations that treat the downwelling diffuse radiation as isotropic. Comparisons with field measurements show biases improving by 0.004–0.013 absolute units (root-mean-squared error) or 0.1%–2.0% relative error.