Visibility of targets on and below the ocean surface

摘要

A pair of images is obtained having pixel intensities substantially proportional to wave height for a majority of pixels. The images are aligned, orthorectified, and adjusted for relative reflectance in their respective spectral bands. The images are Fourier transformed, and then one image is propagated to the time of the other image. A deglinted image is calculated by taking the difference in wavenumber space, then inverse Fourier transforming. Alternatively, an equivalent formula can be obtained using convolutions. The propagation uses a gravity wave propagation function, which, in general, can be a function of depth, surface current, and wave direction which can be obtained from external data, assumed constant, or calculated from wave images depending on the particular circumstances.

主权项

1. A method for deglinting comprising
obtaining a first pair of images, R({right arrow over (x)}) and S({right arrow over (x)}), where {right arrow over (x)} is the two-dimensional (2D) spatial coordinate for pixels in each image, wherein a majority of pixel intensities have a near-linear relationship to surface wave height of a body of water, wherein the two images of the first pair are spatially registered, and wherein there is a time interval between the two images of the first pair; calculating a deglinted image using one of
S′({right arrow over (x)})=2−1[(FS({right arrow over (k)})−W({right arrow over (k)})β({right arrow over (k)})FR′({right arrow over (k)}))](the “Fourier transform” formula)orS′({right arrow over (x)})=(S({right arrow over (x)})−b({right arrow over (x)})*ω({right arrow over (x)})*ψ*R({right arrow over (x)})(the “convolution” formula),where
2−1 is the inverse 2D Fourier transform operator, FS({right arrow over (k)})=2 (S({right arrow over (x)})), FR({right arrow over (k)})=2 (R({right arrow over (x)})), 2 is the 2D Fourier transform operator, {right arrow over (k)} is the 2D frequency coordinate for a 2D Fourier transform of an image, FR′=Φ−1FR propagates FR to the time of FS, W({right arrow over (k)}) is a wavenumber mask restricting subtraction to wavenumbers with significant wave energy,
{right arrow over (ω)}({right arrow over (x)})=2−1(W({right arrow over (k)})), * is the convolution operator, β({right arrow over (k)}) is the ratio of the ocean surface reflected radiance in S relative to the radiance in R, which may be a constant or a function of {right arrow over (k)}, b({right arrow over (x)}) is also the ratio of ocean surface reflected radiance in S relative to the radiance in R, which may be a constant or a function of {right arrow over (x)}, Φ−1 is a gravity wave propagation function, ψ*R({right arrow over (x)}) propagates waves in R({right arrow over (x)}) to the time of S({right arrow over (x)}), Φ−1 and ψ are each functions of the depth, surface current (velocity) vector, and wave direction at each pixel location in said first pair of images, printing said deglinted image S′({right arrow over (x)}) or displaying said deglinted image S′({right arrow over (x)}) on an image display device.