Abstract. Although the number of terrestrial global navigation satellite system (GNSS) receivers supported by the International GNSS Service (IGS) is rapidly growing, the worldwide rather inhomogeneously distributed observation sites do not allow the generation of high-resolution global ionosphere products. Conversely, with the regionally enormous increase in highly precise GNSS data, the demands on (near) real-time ionosphere products, necessary in many applications such as navigation, are growing very fast. Consequently, many analysis centers accepted the responsibility of generating such products. In this regard, the primary objective of our work is to develop a near real-time processing framework for the estimation of the vertical total electron content (VTEC) of the ionosphere using proper models that are capable of a global representation adapted to the real data distribution.The global VTEC representation developed in this work is based on a series expansion in terms of compactly supported B-spline functions, which allow for an appropriate handling of the heterogeneous data distribution, including data gaps. The corresponding series coefficients and additional parameters such as differential code biases of the GNSS satellites and receivers constitute the set of unknown parameters. The Kalman filter (KF), as a popular recursive estimator, allows processing of the data immediately after acquisition and paves the way of sequential (near) real-time estimation of the unknown parameters. To exploit the advantages of the chosen data representation and the estimation procedure, the Bspline model is incorporated into the KF under the consideration of necessary constraints. Based on a preprocessing strategy, the developed approach utilizes hourly batches of GPS and GLONASS observations provided by the IGS data centers with a latency of 1 h in its current realization.Two methods for validation of the results are performed, namely the self consistency analysis and a comparison with Jason-2 altimetry data. The highly promising validation results allow the conclusion that under the investigated conditions our derived near real-time product is of the same accuracy level as the so-called final post-processed products provided by the IGS with a latency of several days or even weeks.

No abstract

There are various global and regional methods that have been proposed for the modeling of ionospheric vertical total electron content (VTEC). Global distribution of VTEC is usually modeled by spherical harmonic expansions, while tensor products of compactly supported univariate Bsplines can be used for regional modeling. In these empirical parametric models, the coefficients of the basis functions as well as differential code biases (DCBs) of satellites and receivers can be treated as unknown parameters which can be estimated from geometry-free linear combinations of global positioning system observables. In this work we propose a new semi-parametric multivariate adaptive regression B-splines (SP-BMARS) method for the regional modeling of VTEC together with satellite and receiver DCBs, where the parametric part of the model is related to the DCBs as fixed parameters and the non-parametric part adaptively models the spatio-temporal distribution of VTEC. The latter is based on multivariate adaptive regression B-splines which is a non-parametric modeling technique making use of compactly supported B-spline basis functions that are generated from the observations automatically. This algorithm takes advantage of an adaptive scale-by-scale model building strategy that searches for best-fitting B-splines to the data at each scale. The VTEC maps generated from the proposed method are compared numerically and visually with the global ionosphere maps (GIMs) which are provided by the Center for Orbit Determination in Europe (CODE). The VTEC values from SP-BMARS and CODE GIMs are also compared with VTEC values obtained through calibration using local ionospheric model. The estimated satellite and receiver DCBs from the SP-BMARS model are compared with the CODE distributed DCBs. The results show that the SP-BMARS algorithm can be used to estimate satellite and receiver DCBs while adaptively and flexibly modeling the daily regional VTEC.

No abstract

2007 yılında hizmete giren ve Samsun'dan Sarp sınır kapısına kadar uzanan Karadeniz Sahil Yolu (KSY), Giresun-Piraziz arasındaki bölgede bazı yerlerde karadan, bazı yerlerde deniz doldurularak inşa edilmiştir. KSY bazı yerlerde plajları daraltırken, yol kapsamında inşa edilen mahmuz şeklindeki dalgakıranların etkisiyle mevcut plajlar deniz yönünde genişlemiş, hatta yeni plajlar oluşmuştur. Mahmuz bulunmasına rağmen bazı yerlerde plaj oluşumu gerçekleşmemiş veya diğer yerlere göre daha yavaş bir oluşum söz konusudur. Kıyı boyunca farklı durumların gelişmesinde T mahmuz şeklindeki dalgakıranların ve balıkçı barınaklarının etkisi ile birlikte akarsularla sediment taşınımı, akarsu ağızlarında akarsu ile dalga etkileşimi ve özellikle deniz batimetrisi önemli parametrelerdir. Batimetrinin derin olduğu yerlerde (örneğin Piraziz sahili) ve büyük akarsu (Batlama ve Pazar Suyu) ağızlarında mahmuzlara rağmen plaj oluşumunun gerçekleşmemesi veya oluşum hızının çok yavaş olması bu iki faktörün etkisindendir. Plaj oluşum hızının en yüksek olduğu Giresun şehir plajları 2006 yılından 2020 yılına kadar alansal olarak iki buçuk kat genişlemiş ve kıyı çizgisi 60-85 m ilerlemiştir. Bu süre içinde yıllık ortalama ilerleme hızı 4,3 m ile 6 m arasında değişmektedir. Bu plajın tamamında kıyı çizgisindeki ilerleme hızı son üç-beş yıldaki gibi devam ederse en geç 2028 yılında kıyı çizgisinin mahmuz uçlarına ulaşacağı tahmin edilmektedir.