On determining parameters of the returned altimetry signal

2020 ◽  
Vol 954 (12) ◽  
pp. 10-19
Author(s):  
Yu.M. Neiman ◽  
L.S. Sugaipova

The authors summarize the principle underlying the modern satellite altimetry. Careful analysis of the shape of the reflected signal enables estimating the flight altitude of the satellite altimeter above sea level, and other important parameters of the sea surface in the area under study quite reliably. Important in doing so is the reflected signal power model used. The Brown-Hayne model seems to be the most common one. The values of these parameters are determined from measurements using certain optimization methods. It is especially noted that the problem in question can be successfully solved by methods based on modern theory of artificial neural networks. Numerical experiments using real altimetric data were carried out in MATLAB environment. In this regard, the basic concepts of this theory are described and the possibilities of its use as an effective approximation of any dependence are emphasized. The Levenberg-Marquardt method and the genetic algorithm of artificial neural networks show the same results, but the latter does not require setting initial values of parameters, only limits of their possible change.

2018 ◽  
Vol 35 (7) ◽  
pp. 1441-1455 ◽  
Author(s):  
Kalpesh Patil ◽  
M. C. Deo

AbstractThe prediction of sea surface temperature (SST) on the basis of artificial neural networks (ANNs) can be viewed as complementary to numerical SST predictions, and it has fairly sustained in the recent past. However, one of its limitations is that such ANNs are site specific and do not provide simultaneous spatial information similar to the numerical schemes. In this work we have addressed this issue by presenting basin-scale SST predictions based on the operation of a very large number of individual ANNs simultaneously. The study area belongs to the basin of the tropical Indian Ocean (TIO) having coordinates of 30°N–30°S, 30°–120°E. The network training and testing are done on the basis of HadISST data of the past 140 yr. Monthly SST anomalies are predicted at 3813 nodes in the basin and over nine time steps into the future with more than 20 million ANN models. The network testing indicated that the prediction skill of ANNs is attractive up to certain lead times depending on the subbasin. The ANN models performed well over both the western Indian Ocean (WIO) and eastern Indian Ocean (EIO) regions up to 5 and 4 months lead time, respectively, as judged by the error statistics of the correlation coefficient and the normalized root-mean-square error. The prediction skill of the ANN models for the TIO region is found to be better than the physics-based coupled atmosphere–ocean models. It is also observed that the ANNs are capable of providing an advanced warning of the Indian Ocean dipole as well as abnormal basin warming.


Author(s):  
Raúl Vicen Bueno ◽  
Manuel Rosa Zurera ◽  
María Pilar Jarabo Amores ◽  
Roberto Gil Pita ◽  
David de la Mata Moya

The Artificial Neural Networks (ANNs) are based on the behaviour of the brain. So, they can be considered as intelligent systems. In this way, the ANNs are constructed according to a brain, including its main part: the neurons. Moreover, they are connected in order to interact each other to acquire the followed intelligence. And finally, as any brain, it needs having memory, which is achieved in this model with their weights. So, starting from this point of view of the ANNs, we can affirm that these systems are able to learn difficult tasks. In this article, the task to learn is to distinguish between the presence or not of a reflected signal called target in a Radar environment dominated by clutter. The clutter involves all the signals reflected from other objects in a Radar environment that are not the desired target. Moreover, the noise is considered in this environment because it always exists in all the communications systems we can work with.


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