ParSymG: a parallel clustering approach for unsupervised classification of remotely sensed imagery

Symmetry is a common feature in the real world.It may be used to improve a classification by using the point symmetry-based distance as a measure of clustering.However,it is time consuming to calculate the point symmetry-based distance.Although an efficient parallel point symmetry-based K-means algorithm(ParSym)has been propsed to overcome this limitation,ParSym may get stuck in sub-optimal solutions due to the K-means technique it used.In this study,we proposed a novel parallel point symmetry-based genetic clustering(ParSymG)algorithm for unsupervised classification.The genetic algorithm was introduced to overcome the sub-optimization problem caused by inappropriate selection of initial centroids in ParSym.A message passing interface(MPI)was used to implement the distributed master–slave paradigm.To make the algorithm more time-efficient,a three-phase speedup strategy was adopted for population initialization,image partition,and kd-tree structure-based nearest neighbor searching.The advantages of ParSymG over existing ParSym and parallel K-means(PKM)alogithms were demonstrated through case studies using three different types of remotely sensed images.Results in speedup and time gain proved the excellent scalability of the ParSymG algorithm.

Analytic derivation of Monin-Obukhov similarity function for open atmospheric surface layer

The Monin-Obukhov(MO)similarity functionφm of the atmospheric surface layer(ASL)describing the deviation from the log law of the canonical turbulent boundary layer because of thermal stratification has been traditionally determined empirically.This study presents a unified analytic expression derived from a symmetry-based theory of wall turbulence,called structural ensemble dynamics(SED),which postulates a generalized dilation symmetry principle expressing the effect of the wall on turbulence,leading to an analytic multi-regimes expression for the mixing length.For ASL in unstable and stable conditions(i.e.,UC and SC),a unified two-regime formula of the mixing length is proposed,leading to aφm,similar to the Businger-Dyer(BD)formula;with a simplified model energy balance equation,φm is completely specified with no free parameter.Furthermore,the theory allows the study of the open ASL’s underlying additional physical processes such as bottom-up or top-down flux due to pressure variations Tp.Assuming that Tp is decomposed into shear-like and buoyancy-like components,we propose new explanations for two important features of typical ASL:a significantly smaller Karman constant of 0.36 and a varyingφm for SC mean speed profiles.The theory is validated by the data obtained at Kansas and also at Qingtu Lake Observation Array in Northern China for a variety of heat flux conditions.In conclusion,due to pressure variations,we assert that ASL is intrinsically open and that the current theory offers a new basis for its quantification.