Observing Sucrose Accumulation With Sentinel-1 Backscatter

In this study the impact of sucrose accumulation in Sentinel-1 backscatter observations is presented and compared to Planet optical observations. Sugarcane yield data from a sugarcane plantation in Xinavane, Mozambique are used for this study. The database contains sugarcane yield of 387 fields over two seasons (2018-2019 and 2019-2020). The relation between sugarcane yield and Sentinel-1 VV and VH backscatter observation is analyzed by using the Normalized Difference Vegetation Index (NDVI) data as derived from Planet Scope optical imagery as a benchmark. The different satellite observations were compared over time to sugarcane yield to understand how the relation between the observations and yield evolves during the growing season. A negative correlation between yield and Cross Ratio (CR) from Sentinel-1 backscatter was found while a positive correlation between yield and Planet NDVI was observed. An additional modeling study on the dielectric properties of the crop revealed how the CR could be affected by sucrose accumulation during the growing season and supported the opposite correlations. The results shows CR contains information on sucrose content in the sugarcane plant. This sets a basis for further development of sucrose monitoring and prediction using a combination of radar and optical imagery.

Retrieval of Phytoplankton Pigment Composition from Their In Vivo Absorption Spectra

Algal pigment composition is an indicator of phytoplankton community structure that can be estimated from optical observations. Assessing the potential capability to retrieve different types of pigments from phytoplankton absorption is critical for further applications. This study investigated the performance of three models and the utility of hyperspectral in vivo phytoplankton absorption spectra for retrieving pigment composition using a large database (n = 1392). Models based on chlorophyll-a (Chl-a model), Gaussian decomposition (Gaussian model), and partial least squares (PLS) regression (PLS model) were compared. Both the Gaussian model and the PLS model were applied to hyperspectral phytoplankton absorption data. Statistical analysis revealed the advantages and limitations of each model. The Chl-a model performed well for chlorophyll-c (Chl-c), diadinoxanthin, fucoxanthin, photosynthetic carotenoids (PSC), and photoprotective carotenoids (PPC), with a median absolute percent difference for cross-validation (MAPDCV) < 58%. The Gaussian model yielded good results for predicting Chl-a, Chl-c, PSC, and PPC (MAPDCV < 43%). The performance of the PLS model was comparable to that of the Chl-a model, and it exhibited improved retrievals of chlorophyll-b, alloxanthin, peridinin, and zeaxanthin. Additional work undertaken with the PLS model revealed the prospects of hyperspectral-resolution data and spectral derivative analyses for retrieving marker pigment concentrations. This study demonstrated the applicability of in situ hyperspectral phytoplankton absorption data for retrieving pigment composition and provided useful insights regarding the development of bio-optical algorithms from hyperspectral and satellite-based ocean-colour observations.

Measurements of Magnetic Fiber Dynamics in Magnetic Fields using Optical and Electrical Techniques

<p>The fabrication of piezoelectric ceramics (Piezoceramics) currently relies on a costly dice and fill process to create an array of aligned pillars. These pillars act as waveguides, improving the performance of the piezoceramic wafers over the bulk piezoceramic alone. It is theorised the creation of aligned pores in the piezoceramic may exhibit the same waveguiding effect, removing the need for the dice and fill process. A technique for creating these pores is in development at Callaghan Innovation, New Zealand, where nickel coated carbon fibers are added to the ceramic slurry, aligned with a magnetic field, and attracted to the bottom of a mold. The number of fibers and degree of alignment dictate the waveguiding effectiveness and hence the performance of the piezoceramic. Additionally the time taken for fibers to form an array in the bottom of the mold dictate the piezoceramics fabrication time. Thus it is crucial to be able to measure the alignment and magnetically assisted sedimentation of these fibers in-situ. However the ceramic slurry is opaque, hence the optical methods traditionally can not be implemented. This thesis describes the development and implementation of an electrical technique using the anisotropic conductance of fibers, for measuring fiber dynamics during the fabrication of piezoceramics. The results of this electrical technique are compared to both optical monitoring results in a transparent solution, and models for the motion of rigid cylinders in a fluid suspension. The change in conductance corresponding to fiber rotation was found to have a time constant corresponding to fiber rotation which is a scalar multiple of that of transmission microscopy and the mathematical modeling. This is a product of the geometry of the electrode configurations used to measure conductance. Furthermore, for fiber rotation, the fiber concentration in the solution changes the effective fluid viscosity due to hydrodynamic turbulence created by the rotating fibers. The conductance change corresponding to the magnetically assisted fiber settling is in good accordance with both the optical observations and mathematical modeling for 50 mPas solutions, however for 30 mPas solutions the modeling underestimates the settling time by 20%. The maximum fiber concentration to create a single layer of aligned fibers in the bottom of the mold was found to be 12 fibers=mm³. Exceeding this limit results in a secondary and tertiary layer of fibers forming directly below the fiber suspension injection location.</p>

Measurements of Magnetic Fiber Dynamics in Magnetic Fields using Optical and Electrical Techniques

<p>The fabrication of piezoelectric ceramics (Piezoceramics) currently relies on a costly dice and fill process to create an array of aligned pillars. These pillars act as waveguides, improving the performance of the piezoceramic wafers over the bulk piezoceramic alone. It is theorised the creation of aligned pores in the piezoceramic may exhibit the same waveguiding effect, removing the need for the dice and fill process. A technique for creating these pores is in development at Callaghan Innovation, New Zealand, where nickel coated carbon fibers are added to the ceramic slurry, aligned with a magnetic field, and attracted to the bottom of a mold. The number of fibers and degree of alignment dictate the waveguiding effectiveness and hence the performance of the piezoceramic. Additionally the time taken for fibers to form an array in the bottom of the mold dictate the piezoceramics fabrication time. Thus it is crucial to be able to measure the alignment and magnetically assisted sedimentation of these fibers in-situ. However the ceramic slurry is opaque, hence the optical methods traditionally can not be implemented. This thesis describes the development and implementation of an electrical technique using the anisotropic conductance of fibers, for measuring fiber dynamics during the fabrication of piezoceramics. The results of this electrical technique are compared to both optical monitoring results in a transparent solution, and models for the motion of rigid cylinders in a fluid suspension. The change in conductance corresponding to fiber rotation was found to have a time constant corresponding to fiber rotation which is a scalar multiple of that of transmission microscopy and the mathematical modeling. This is a product of the geometry of the electrode configurations used to measure conductance. Furthermore, for fiber rotation, the fiber concentration in the solution changes the effective fluid viscosity due to hydrodynamic turbulence created by the rotating fibers. The conductance change corresponding to the magnetically assisted fiber settling is in good accordance with both the optical observations and mathematical modeling for 50 mPas solutions, however for 30 mPas solutions the modeling underestimates the settling time by 20%. The maximum fiber concentration to create a single layer of aligned fibers in the bottom of the mold was found to be 12 fibers=mm³. Exceeding this limit results in a secondary and tertiary layer of fibers forming directly below the fiber suspension injection location.</p>

The Remarkable Spin-down and Ultrafast Outflows of the Highly Pulsed Supersoft Source of Nova Herculis 2021

Nova Her 2021 (V1674 Her), which erupted on 2021 June 12, reached naked-eye brightness and has been detected from radio to γ-rays. An extremely fast optical decline of 2 magnitudes in 1.2 days and strong Ne lines imply a high-mass white dwarf. The optical pre-outburst detection of a 501.42 s oscillation suggests a magnetic white dwarf. This is the first time that an oscillation of this magnitude has been detected in a classical nova prior to outburst. We report X-ray outburst observations from Swift and Chandra that uniquely show (1) a very strong modulation of supersoft X-rays at a different period from reported optical periods, (2) strong pulse profile variations and the possible presence of period variations of the order of 0.1–0.3 s, and (3) rich grating spectra that vary with modulation phase and show P Cygni–type emission lines with two dominant blueshifted absorption components at ∼3000 and 9000 km s−1 indicating expansion velocities up to 11,000 km s−1. X-ray oscillations most likely arise from inhomogeneous photospheric emission related to the magnetic field. Period differences between reported pre- and post-outburst optical observations, if not due to other period drift mechanisms, suggest a large ejected mass for such a fast nova, in the range 2 × 10−5–2 × 10−4 M ⊙. A difference between the period found in the Chandra data and a reported contemporaneous post-outburst optical period, as well as the presence of period drifts, could be due to weakly nonrigid photospheric rotation.