The invention provides a joint fractal-based method for detecting a
small target under a sea
clutter background. The joint fractal-based method is higher in detection probability. The detection problem of a non-
additive model is transformed into a classification problem, i.e. whether a target exists or not is equivalent to belong to a class in which a pure sea
clutter exists, and a characteristic joint detection
algorithm is provided. A bilogarithmic graph is established by using a trend fluctuation method through sea
clutter data, a slope, namely a
Hurst index, is fitted by using a least square method within a scale-
free interval, and is used as a characteristic scalar, a
nodal increment of a keypoint in the bilogarithmic graph is used as another characteristic scalar, therefore, a double-scalar obtained by each group of sea clutter data corresponds to one point in the bilogarithmic graph, n groups of corresponding points (i=1,...n) of the pure sea clutter data are obtained by using the steps, a space optimal classification line
omega is obtained by using a convex
hull function, sea clutters of regions in which the target possibly exits are obtained by using the same steps, and finally, by using whether the points exist in the space optimal classification line
omega or not as a criterion, when the points exists in the space optimal classification line
omega, no target exists, and when the points are outside the space optimal classification line omega, the target exists.