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- 2019
- low-temperature electronics
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Investigation of Tandem-x Penetration Depth Over the Greenland Ice Sheet
摘要： Ongoing global warming causes dramatic changes globally, especially with respect to Polar Regions. In this context, digital elevation data is of high importance for most glaciological applications. In this paper, we investigate TanDEM-X penetration depth over snow and ice on the Greenland ice sheet. In particular, the relation of backscatter intensity and interferometric coherence to penetration depth of the X-band InSAR signal is explored in order to improve the reliability of TanDEM-X elevation data. The analyses showed a distinct relationship of backscatter intensity, coherence and penetration depth. In addition, the influence of the height of ambiguity of the interferometric TanDEM-X data is presented. On an experimental test site in Northern Greenland, we demonstrated the estimation of TanDEM-X penetration depth based on backscatter intensity and interferometric coherence utilizing a linear regression model.
关键词： TanDEM-X,Interferometric Synthetic Aperture Radar (InSAR),Greenland ice sheet,penetration depth
更新于2025-09-10 09:29:36
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Calderón preconditioning of PMCHWT boundary integral equations for scattering by multiple absorbing dielectric particles
摘要： We consider the simulation of electromagnetic scattering by single and multiple isotropic homogeneous dielectric particles using boundary integral equations. Galerkin discretizations of the classical Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) boundary integral equation formulation provide accurate solutions for complex particle geometries, but are well-known to lead to ill-conditioned linear systems. In this paper we carry out an experimental investigation into the performance of Calder′on preconditioning techniques for single and multiple absorbing obstacles, which involve a squaring of the PMCHWT operator to produce a well-conditioned second-kind formulation. For single-particle scattering configurations we find that Calder′on preconditioning is actually often outperformed by simple "mass-matrix" preconditioning, i.e. working with the strong form of the discretized PMCHWT operator. In the case of scattering by multiple particles we find that a significant saving in computational cost can be obtained by performing block-diagonal Calder′on preconditioning in which only the self-interaction blocks are preconditioned. Using the boundary element software library Bempp (www.bempp.com) the numerical performance of the different methods is compared for a range of wavenumbers, particle geometries and complex refractive indices relevant to the scattering of light by atmospheric ice crystals.
关键词： Calder′on preconditioning,ice crystals,electromagnetic scattering,boundary element method
更新于2025-09-10 09:29:36
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A METHOD FOR ICE-THICKNESS DETECTING AND ICE-SECTION IMAGING BY USING FMCW-SAR ALGORITHM
摘要： Sea ice plays an important role in global climate. Many researches focus on the measurement of the sea ice thickness. In this paper, we present a method for the ice-detecting combining frequency-modulated continuous-wave (FMCW) technology and synthetic aperture radar (SAR) technology. It can provide a good resolution both in the range dimension and the azimuth one. Then a simulation is conducted to verify the accuracy and the feasibility of this algorithm. The physical properties of the sea ice, such as re?ection and scatter properties of the ice surface and the transmission characteristic when the electromagnetic wave travels through the ice, are considered in the simulation. The results of the simulation demonstrate that this algorithm has a good performance in ice penetrating.
关键词： FMCW-SAR,simulation,ice thickness detection,sea ice
更新于2025-09-09 09:28:46
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Measurements of Global Distributions of Polar Mesospheric Clouds during 2005–2012 by MIPAS/Envisat
摘要： We have analysed the MIPAS IR measurements of PMCs for the summer seasons in the Northern and Southern Hemispheres from 2005 to 2012. Measurements of PMCs using this technique are very useful because they are sensitive to the total ice volume independent of particle size. For the first time, MIPAS has provided coverage of the PMCs total ice volume from mid-latitudes to the poles. MIPAS measurements indicate the existence of a continuous layer of mesospheric ice, extending from about ～81 km up to about 88-89 km on average and from the poles to about 50–60? in each hemisphere, increasing in concentration with proximity to the poles. We have found that the ice concentration is larger in the Northern Hemisphere than in the Southern Hemisphere. The ratio between the ice water content (IWC) in both hemispheres is also latitude-dependent, varying from a NH/SH ratio of 1.4 close to the poles to a factor of 2.1 around 60?. This also implies that PMCs extend to lower latitudes in the NH. A very clear feature of the MIPAS observations is that PMCs tend to be at higher altitudes with increasing distance from the polar region (in both hemispheres), particularly equator-ward of 70?, and that they are about 1 km higher in the SH than in the NH. The difference between the mean altitude of the PMC layer and the mesopause altitude increases towards the poles and is larger in the NH than in the SH. The PMC layers are denser and wider when the frost point temperature occurs at lower altitudes. The layered water vapour structure caused by sequestration and by sublimation of PMCs is more pronounced at latitudes northernmost of 70 degrees. Finally, MIPAS observations have also shown a clear impact of the migrating diurnal tide on the diurnal variation of the PMCs ice concentration.
关键词： MIPAS,Polar Mesospheric Clouds,ENVISAT,Hemispheric Dependence,Diurnal Variation,Ice Volume Density
更新于2025-09-09 09:28:46
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ISMAR: an airborne submillimetre radiometer
摘要： The International Submillimetre Airborne Radiometer (ISMAR) has been developed as an airborne demonstrator for the Ice Cloud Imager (ICI) that will be launched on board the next generation of European polar-orbiting weather satellites in the 2020s. It currently has 15 channels at frequencies between 118 and 664 GHz which are sensitive to scattering by cloud ice, and additional channels at 874 GHz are being developed. This paper presents an overview of ISMAR and describes the algorithms used for calibration. The main sources of bias in the measurements are evaluated, as well as the radiometric sensitivity in different measurement scenarios. It is shown that for downward views from high altitude, representative of a satellite viewing geometry, the bias in most channels is less than ±1 K and the NE(cid:49)T is less than 2 K, with many channels having an NE(cid:49)T less than 1 K. In-?ight calibration accuracy is also evaluated by comparison of high-altitude zenith views with radiative-transfer simulations.
关键词： ISMAR,radiometric sensitivity,Ice Cloud Imager,submillimetre radiometer,calibration,airborne demonstrator
更新于2025-09-09 09:28:46
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - First Assessment of Hy-2A Altimeter Data Over Antarctica and Greenland Using Crossover Analysis
摘要： The radar altimeter onboard China’s HY-2A satellite was launched in August 2011 and it can provide the surface elevation measurements from 80.6 oN to 80.6 oS. In this letter, the precision of the HY-2A elevation measurements over the Antarctica ice sheet (AIS) and the Greenland ice sheet (GrIS) is assessed through crossover analysis. We process the HY-2A sensor geophysical dataset records (SGDR) data from June 1, 2014 to June 14, 2014. The OCOG, Ice-1 and Ice-2 algorithms are applied to retrack the waveforms of HY-2A altimeter over the AIS and GrIS. Crossover analysis shows that the Ice-2 algorithm performs best among the three algorithms. The precision of the HY-2A altimeter elevations are found to vary as a function of the threshold of the surface slope from ~56 cm to ~63 cm over the AIS, and from ~29 cm to ~50 cm over the GrIS.
关键词： crossover analysis,radar altimeter,HY-2A satellite,elevation measurements,ice sheets
更新于2025-09-09 09:28:46
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Polarimetry of Water Ice Particles Providing Insights on Grain Size and Degree of Sintering on Icy Planetary Surfaces
摘要： The polarimetry of the light scattered by planetary surfaces is a powerful tool to provide constraints on their microstructure. To improve the interpretation of polarimetric data from icy surfaces, we have developed the POLarimeter for ICE Samples complementing the measurement facilities of the Ice Laboratory at the University of Bern. The new setup uses a high precision Stokes polarimeter to measure the degree of polarization in the visible light scattered by surfaces at moderate phase angles (from 1.5° to 30°). We present the photometric and polarimetric phase curves measured on various surfaces made of pure water ice particles having well-controlled size and shape (spherical, crushed, and frost). The results show how the amplitude and the shape of the negative polarization branch change with the particles sizes and the degree of metamorphism of the ice. We found that fresh frost formed by water condensation on cold surfaces has a phase curve characterized by resonances (Mie oscillations) indicating that frost embryos are transparent micrometer-sized particles with a narrow size distribution and spherical shape. Comparisons of these measurements with polarimetric observations of the icy satellites of the Solar System suggest that Europa is possibly covered by relatively coarser (~40–400 μm) and more sintered grains than Enceladus and Rhea, more likely covered by frost-like particles of few micrometers in average. The great sensitivity of polarization to grain size and degree of sintering makes it an ideal tool to detect hints of ongoing processes on icy planetary surfaces, such as cryovolcanism.
关键词： sintering,icy planetary surfaces,grain size,polarimetry,water ice particles
更新于2025-09-09 09:28:46
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Near-infrared optical investigations of snow, ice, and water layers on diffuse reflecting surfaces
摘要： While most experiments on water or ice utilize rather complex, elaborate, and expensive apparatus in order to obtain reliable optical data, here we present a simple and affordable setup that enables us to perform near-infrared measurements on water, ice, and snow on top of rough diffuse reflecting surfaces such as concrete, stone, pavement, or asphalt. By using the properties of diffuse scattering instead of specular reflection, we are able to determine the imaginary part of the refraction index of water without using any liquid cells. In addition, we demonstrate that the snow spectra can be well described by newly developed two-dimensional ray tracing simulations.
关键词： snow,ice,water layers,optical investigations,near-infrared,diffuse reflecting surfaces
更新于2025-09-09 09:28:46
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PHIPS–HALO: the airborne Particle Habit Imaging and Polar Scattering probe – Part 1: Design and operation
摘要： The number and shape of ice crystals present in mixed-phase and ice clouds influence the radiation properties, precipitation occurrence and lifetime of these clouds. Since clouds play a major role in the climate system, influencing the energy budget by scattering sunlight and absorbing heat radiation from the earth, it is necessary to investigate the optical and microphysical properties of cloud particles particularly in situ. The relationship between the microphysics and the single scattering properties of cloud particles is usually obtained by modelling the optical scattering properties from in situ measurements of ice crystal size distributions. The measured size distribution and the assumed particle shape might be erroneous in case of non-spherical ice particles. There is a demand to obtain both information correspondently and simultaneously for individual cloud particles in their natural environment. For evaluating the average scattering phase function as a function of ice particle habit and crystal complexity, in situ measurements are required. To this end we have developed a novel airborne optical sensor (PHIPS-HALO) to measure the optical properties and the corresponding microphysical parameters of individual cloud particles simultaneously. PHIPS-HALO has been tested in the AIDA cloud simulation chamber and deployed in mountain stations as well as research aircraft (HALO and Polar 6). It is a successive version of the laboratory prototype instrument PHIPS-AIDA. In this paper we present the detailed design of PHIPS-HALO, including the detection mechanism, optical design, mechanical construction and aerodynamic characterization.
关键词： mixed-phase clouds,PHIPS-HALO,precipitation,ice crystals,ice clouds,optical properties,radiation properties,climate system,microphysical properties,airborne optical sensor
更新于2025-09-04 15:30:14
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An Investigation of Optically Very Thin Ice Clouds from Ground-Based ARM Raman Lidars
摘要： Optically very thin ice clouds from the Cloud-Aerosol Lidar and Infrared Path?nder Satellite Observations (CALIPSO) and ground-based Raman lidars (RL) at the atmospheric radiation measurement (ARM) sites of the Southern Great Plains (SGP) and Tropical Western Paci?c (TWP) are analyzed. The optically very thin ice clouds, with ice cloud column optical depths below 0.01, are about 23% of the transparent ice-cloudy pro?les from the RL, compared to 4–7% from CALIPSO. The majority (66–76%) of optically very thin ice clouds from the RLs are found to be adjacent to ice clouds with ice cloud column optical depths greater than 0.01. The temporal structure of RL-observed optically very thin ice clouds indicates a clear sky–cloud continuum. Global cloudiness estimates from CALIPSO observations leveraged with high-sensitivity RL observations suggest that CALIPSO may underestimate the global cloud fraction when considering optically very thin ice clouds.
关键词： remote sensing,ice cloud detection,ice cloud optical depth,lidars
更新于2025-09-04 15:30:14