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Synthetic Aperture Radar (SAR) backscatter is the coherent combination of the scattering from multiple individual scatterers within the radar resolution cell, which results into a 2-D radar image. Tomographic SAR (TomoSAR) takes advantage of multiple SAR acquisitions to provide 3-D vertical structure of the imaged target. Over forests, parameters such as canopy structure, canopy density, leaf area and phenology contribute to different SAR scattering mechanisms along the vertical dimension of the trees. Tomography has been demonstrated in various earlier works for forest bio-physical parameter estimation using airborne data. In this research work, multi-polarimetric space-borne TanDEM-X tomograms are examined for the first time over a multi-species Indian tropical forest. Multiple TanDEM-X acquisitions are focused using Capon beamforming at five polarimetric channels — HH, HV, VV, HH − VV and HH + VV. Four distinct forest species compartments are selected representing different canopy structure and density. The tomograms obtained in different polarizations for these species are analyzed in detail to understand the scattering patterns across different forest species. Field surveys carried out in several forest locations provide in situ observations of forest height and vertical structure. It was observed that canopy gaps and leaf density play a crucial role for X-band SAR signal penetration through ground. For dense canopy species the backscatter contributions are spread through the canopy, while in case of sparse canopy species, the ground scattering is dominant. Vertical profiles obtained at surveyed plot locations are plotted in all polarizations, and provide a good agreement with field observations. Further, the obtained TomoSAR backscatter layers have a good correlation with field measured above-ground biomass (AGB). The AGB is modeled from TomoSAR with the HH-pol TomoSAR backscatter layer at 27 m canopy height leading to an AGB estimation with correlation r = 0.76 and RMSE of 50.4 t/ha. • First space-borne multi-polarimetric tomograms over Indian tropical forests • Analysis of effect of species on X-band TanDEM-X tomograms presented • SAR scattering along height of tropical forest visualized for different species • Potential of single-baseline space-borne SAR systems explored [ABSTRACT FROM AUTHOR]

When a non-conducting plastic block is irradiated with high-energy electrons, the thermalised electrons are trapped in the block if the range of the incident electrons is less than its thickness. These stored charges set up an electrostatic field in the block that can affect the trajectories of the incident electrons. The strength and the shape of the field depend on the intrinsic properties of the material as well as on the irradiation geometry. For this study, we selected various commercial electrical insulators such as polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene (PE), Teflon (PTFE), polyvinylchloride (PVC) and nylon. We measured the influence of the electrostatic field on depth-dose distribution in these materials using GafChromic® film dosimeters, and the subsequent leakage of the stored charge. This is an extension of our previous work on PMMA. The effect on the depth-dose distribution was most pronounced in PMMA, while in PTFE and PE it was minimal. On the other hand, PC showed an intermediate behaviour. Nylon and PVC electrically broke down at low doses. We have attempted an explanation of this behaviour of the various plastics based on radiation-induced conductivity, the measured leakage charge and also on their intrinsic electrical properties such as dielectric constant and dielectric strength. [Copyright &y& Elsevier]

In a former work inorganic phosphor particles NaYF 4 :Yb3+, Er3+ were found to exhibit a radiation dose dependency of their luminescence decay time upon near-infrared excitation. This material is now presented in the form of an ultra-thin dosimeter to measure depth dose curves. They were derived by electron beam irradiation of 1.6 μm thin dosimeters through a stepped stack of absorber polymer films followed by optical decay time evaluation. The suitability of the phosphor dosimeters for depth curve measurement is proven by good agreement in normalized dose results with film dosimeter (Risø B3 strips) after medium-energy electron-beam irradiation. But the approach qualifies especially for use at low-energies, where original measurement results from as close as 3–4 μm (water equivalent) from the surface are obtained for 80, 140 and 200 keV e-beam irradiations. They align well with results from Monte Carlo simulations. Thus, an approach is proposed for discussion which may allow the experimental evaluation of the first μm of depth dose curves after low-energy electron beam irradiation. • Dose dependency of phosphor luminescence decay time. • Fabrication of 1.6 μm ultra-thin dosimeter film. • Depth dose profiles through stack of absorbing polymer films for low-energy e-beam. • Unprecedented proximity to surface with first data point at 3.4 μm depth. • Good agreement between measurement and Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

In 2015 and 2016, the AfriSAR campaign was carried out as a collaborative effort among international space and National Park agencies (ESA, NASA, ONERA, DLR, ANPN and AGEOS) in support of the upcoming ESA BIOMASS, NASA-ISRO Synthetic Aperture Radar (NISAR) and NASA Global Ecosystem Dynamics Initiative (GEDI) missions. The NASA contribution to the campaign was conducted in 2016 with the NASA LVIS (Land Vegetation and Ice Sensor) Lidar, the NASA L-band UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar). A central motivation for the AfriSAR deployment was the common AGBD estimation requirement for the three future spaceborne missions, the lack of sufficient airborne and ground calibration data covering the full range of ABGD in tropical forest systems, and the intercomparison and fusion of the technologies. During the campaign, over 7000 km2 of waveform Lidar data from LVIS and 30,000 km2 of UAVSAR data were collected over 10 key sites and transects. In addition, field measurements of forest structure and biomass were collected in sixteen 1-hectare sized plots. The campaign produced gridded Lidar canopy structure products, gridded aboveground biomass and associated uncertainties, Lidar based vegetation canopy cover profile products, Polarimetric Interferometric SAR and Tomographic SAR products and field measurements. Our results showcase the types of data products and scientific results expected from the spaceborne Lidar and SAR missions; we also expect that the AfriSAR campaign data will facilitate further analysis and use of waveform lidar and multiple baseline polarimetric SAR datasets for carbon cycle, biodiversity, water resources and more applications by the greater scientific community. • In 2016, the international collaborative air and field campaign AfriSAR took place • The data provides calibration and validation for NASA GEDI, NISAR and ESA BIOMASS • NASA collected coincident L-band SAR (UAVSAR) and waveform Lidar (LVIS) data • We produced SAR- and Lidar derived canopy height, biomass and vertical profile datasets • We provide an overview of the airborne mission, data products and applications [ABSTRACT FROM AUTHOR]

Abstract: The radical cation of (phenoxymethyl)oxirane is generated by pulse radiolysis in dichloromethane solution and by direct action of radiation on the title compound. In the pure system its UV–vis spectrum is characterized by two bands at 340 and 430nm, such that the electronic structure corresponds to a dipole bearing the positive charge on the phenoxy side. At the same time, the phenoxy-oxirane bridge is weakened. Then, the radical cation fragments into a phenoxonium ion and an oxyranylmethyl radical . The latter immediately rearranges to an allyloxyl radical by ring opening. It is then conceived that the action of onium salts, as radiation curing initiators of phenoxy-oxirane derivatives, occurs after epoxy ring opening. [Copyright &y& Elsevier]