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Theoretical analysis and numerical experiments of variational adjoint approach for refractivity estimation
Author(s) -
Zhao XiaoFeng,
Huang SiXun,
Du HuaDong
Publication year - 2011
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/2010rs004417
Subject(s) - regularization (linguistics) , inversion (geology) , variational analysis , mathematics , refractive index , gradient descent , inverse problem , wavelength , refractive index profile , perturbation (astronomy) , mathematical analysis , mathematical optimization , computer science , optics , physics , geology , paleontology , structural basin , quantum mechanics , artificial intelligence , machine learning , artificial neural network
This paper puts forward possibilities of refractive index profile retrieval using field measurements at an array of radio receivers in terms of variational adjoint approach. The derivation of the adjoint model begins with the parabolic wave equation for a smooth, perfectly conducting surface and horizontal polarization conditions. To deal with the ill‐posed difficulties of the inversion, the regularization ideas are introduced into the establishment of the cost function. Based on steepest descent iterations, the optimal value of refractivity could be retrieved quickly at each point over height. Numerical experiments demonstrate that the method works well for low‐distance signals, while it is not accurate enough for long‐distance propagations. Through curve fitting processing, however, giving a good initial refractivity profile could generally improve the inversions.