Numerical study on c-axis orientations of sea ice surface grown under calm sea conditions using a particle method and Voronoi dynamics

Kawano, Yoshiki; Ohashi, Tetsuya

doi:10.1016/j.coldregions.2014.12.012

Cited by 5 publications

(2 citation statements)

References 27 publications

(47 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As shown in Figures 7e,h and 8, the majority of the volume scattering powers are decomposed by the two strategies to the vertical components, indicating the brine inclusions within young ice of the study area are preferentially vertically tilted; this is consistent with the previous studies of young ice [52]. Nevertheless, based on the second and third rows of Figure 7 and the quantitative statistics in Figure 8, it is found that when using the two strategies, besides the brine inclusions with vertical tilt, there are also some brine inclusions that show a preference for horizontal random tilt, this is consistent with the geometric selection mechanism, in which the c-axes of polycrystalline formations within sea ice gradually align with depth [53,73]. Therefore, rather than using a simple vertically tilted volume scattering model, it is necessary to adaptively select volume models according to the orientation of ice particles.…”

Section: Discussionsupporting

confidence: 90%

“…Nonetheless, the degree of alignment of c-axis to the horizontal plane is also dependent on the depth. The directions of c-axes of polycrystalline formations within the upper layer of sea ice are actually various [73], but they are gradually aligned horizontally within the layer below, with depth. The mechanism of the transition process of c-axis orientations from random to horizontal is known as the geometric selection [53].…”

Section: Dataset In Prydz Baymentioning

confidence: 99%

See 1 more Smart Citation

Solid Angle Geometry-Based Modeling of Volume Scattering with Application in the Adaptive Decomposition of GF-3 Data of Sea Ice in Antarctica

Li,

Lu,

Zhang

2023

Remote Sensing

View full text Add to dashboard Cite

Over the last two decades, spaceborne polarimetric synthetic aperture radar (PolSAR) has been widely used to penetrate sea ice surfaces to achieve fully polarimetric high-resolution imaging at all times of day and in a range of weather conditions. Model-based polarimetric decomposition is a powerful tool used to extract useful physical and geometric information about sea ice from the matrix datasets acquired by PolSAR. The volume scattering of sea ice is usually modeled as the incoherent average of scatterings of a large volume of oriented ellipsoid particles that are uniformly distributed in 3D space. This uniform spatial distribution is often approximated as a uniform orientation distribution (UOD), i.e., the particles are uniformly oriented in all directions. This is achieved in the existing literature by ensuring the canting angle φ and tilt angle τ of particles uniformly distributed in their respective ranges and introducing a factor cos⁡τ in the ensemble average. However, we find this implementation of UOD is not always effective, while a real UOD can be realized by distributing the solid angles of particles uniformly in 3D space. By deriving the total solid angle of the canting-tilt cell spanned by particles and combining the differential relationship between solid angle and Euler angles φ and τ, a complete expression of the joint probability density function pφ,τ that can always ensure the uniform orientation of particles of sea ice is realized. By ensemble integrating the coherency matrix of φ,τ-oriented particle with pφ,τ, a generalized modeling of the volume coherency matrix of 3D uniformly oriented spheroid particles is obtained, which covers factors such as radar observation geometry, particle shape, canting geometry, tilt geometry and transmission effect in a multiplicative way. The existing volume scattering models of sea ice constitute special cases. The performance of the model in the characterization of the volume behaviors was investigated via simulations on a volume of oblate and prolate particles with the differential reflectivity ZDR, polarimetric entropy H and scattering α angle as descriptors. Based on the model, several interesting orientation geometries were also studied, including the aligned orientation, complement tilt geometry and reflection symmetry, among which the complement tilt geometry is specifically highlighted. It involves three volume models that correspond to the horizontal tilt, vertical tilt and random tilt of particles within sea ice, respectively. To match the models to PolSAR data for adaptive decomposition, two selection strategies are provided. One is based on ZDR, and the other is based on the maximum power fitting. The scattering power that reduces the rank of coherency matrix by exactly one without violating the physical realizability condition is obtained to make full use of the polarimetric scattering information. Both the models and decomposition were finally validated on the Gaofen-3 PolSAR data of a young ice area in Prydz Bay, Antarctica. The adaptive decomposition result demonstrates not only the dominant vertical tilt preference of brine inclusions within sea ice, but also the subordinate random tilt preference and non-negligible horizontal tilt preference, which are consistent with the geometric selection mechanism that the c-axes of polycrystallines within sea ice would gradually align with depth. The experiment also indicates that, compared to the strategy based on ZDR, the maximum power fitting is preferable because it is entirely driven by the model and data and is independent of any empirical thresholds. Such soft thresholding enables this strategy to adaptively estimate the negative ZDR offset introduced by the transmission effect, which provides a novel inversion of the refractive index of sea ice based on polarimetric model-based decomposition.

show abstract

Section: Discussionsupporting

confidence: 90%

Section: Dataset In Prydz Baymentioning

confidence: 99%