SAR image sparse countermeasure attack method based on generator
Technical Field
The invention belongs to the field of automatic image identification and attack resistance, and mainly relates to the problems of improving the spoofing rate of SAR images against attacks and improving the concealment and universality of an attack method.
Background
Synthetic aperture radar (SYNTHETIC APERTURE RADAR, SAR) is a high resolution all-day, all-weather, multi-polarized, multi-band imaging radar technology that plays an important role in applications such as geographic investigation, climate change research, environmental monitoring, military information processing, etc. With the wide application of SAR in the remote sensing field, the extraction of target information from SAR data has become a research hotspot, wherein automatic target recognition (Automatic Target Recognition, ATR) of SAR images is a mature and effective method in the research of current recognition technology, and more researchers explore the application of deep learning in SAR-ATR.
However, since the linear or nonlinear operation in the neural network model has an amplifying effect on the micro-disturbance, if some positions on the SAR image are slightly modified, the confidence of the classification result of the SAR-ATR system is greatly affected, and even the neural network model can be wrongly identified. The act of spoofing DNN (Deep Neural Network) by adding interference is referred to as a challenge attack, and the images modified by the attack are referred to as challenge samples (ADVERSARIAL EXAMPLES, AEs), the presence of which indicates a defect in the neural network in identifying classification tasks. If the loopholes of the neural network are utilized, a general anti-attack method is designed to add weak interference on the SAR image, the obtained anti-sample data set can deceive various types of neural network models, the military SAR image of the own party can be protected from being correctly identified by the enemy, and the method has a certain military defense value.
The general anti-attack method needs to be suitable for spoofing various neural network models, and realize higher spoofing performance under the condition of slightly modifying the image as much as possible. The initial anti-attack Method is designed aiming at loopholes in the neural network learning process, for example, classical FGSM (FAST GRADIENT SIGN Method) attack utilizes learning thinking of gradient decline of the neural network, adds interference to input in the direction of the fastest gradient rise, realizes error classification of the neural network on images, and subsequent I-FGSM and MI-FGSM enhance the anti-attack performance by using iterative and momentum methods. However, the attack method changes almost every pixel point of the image, and has a too large interference range on the image, so that the obtained countermeasure sample set has a large difference from the original data, and the concealment performance is poor. And the attack method based on the gradient attacks the specific neural network, so that the dependence on the parameters of the model of the specific neural network is too great, and the generated countermeasure sample only obtains higher spoofing rate on a single model, so that other neural network models cannot be spoofed efficiently.
Aiming at the problem of overlarge anti-attack interference range, some researchers introduce the l 0 norm to limit the number of pixels of an attack image, for example JSMA (Jacobian-based SALIENCY MAP ATTACK) determines the influence value of different pixels of the image on target classification by using the gradient direction of the target predicted value, and then the interference on pixels with specific proportion realizes the interference on only part of pixels of the image, namely sparse anti-attack. Although the method realizes sparse attack by selecting important points, the method is designed aiming at a trained network model, is only suitable for a single network structure, and the generated anti-sample has poor spoofing effect on other neural network models, namely, has low transfer spoofing performance and does not have universal attack performance.
The method is characterized in that the first method is used for realizing good deception performance under the condition of controlling the interference intensity and range of interference images, namely, the deception performance and deception performance of an anti-sample set are both considered, and the second method is used for designing a general attack method, so that the generated anti-sample can deception different types of neural network models, and the universal deception capability of the anti-attack method is improved.
Disclosure of Invention
The method focuses on the concealment, deception and universality of the attack resistance method, and provides the SAR image sparse attack method based on the generator, which is used for controlling the quantity and intensity of interference, is independent of a specific neural network structure, and improves the deception rate and the transfer deception rate of the attack method while ensuring the concealment of the attack method.
The invention relates to a SAR image sparse countermeasure attack method based on a generator, which comprises the following steps:
s1, generating an intensity interference value of each pixel point of an SAR image through a generator to obtain an intensity interference image;
s2, generating a position interference image through key point extraction based on a quantization method combining the point group sliding difference value and the single-point surrounding difference value;
S3, multiplying the generated intensity interference image and the position interference image by elements to obtain an countermeasure sample, and updating parameters of the generator through a difference loss function.
Aiming at the problem of low deception rate and low transfer deception rate in the background technology, the method designs a generating method of an intensity interference image based on a generator and a generating method of a position image based on a key point, improves deception of the attacking method through nonlinear properties of a neural network, and improves transfer deception of the attacking method by providing structural constraint.
The foregoing description is only an overview of the present invention, and is intended to be implemented in accordance with the teachings of the present invention in order that the same may be more clearly understood and to make the same and other objects, features and advantages of the present invention more readily apparent.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of a generator-based SAR image sparse challenge attack method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram illustrating a calculation process of a point group sliding difference value according to an embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating a calculation process of a single-point surround difference value according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of correspondence between an optical image and an SAR image of an MSTAR dataset according to an embodiment of the present disclosure;
FIG. 5 is a schematic diagram of a process for extracting key points and removing isolated points according to an embodiment of the present invention;
FIG. 6 is a graph showing the variation of the attack rate with epoch for a method of attack when training a model under a training set in accordance with an embodiment of the present invention;
fig. 7 is a graph showing the difference between the position disturbance images obtained at different lambda values according to the embodiment of the present invention.
Detailed Description
The technical solutions of the present invention will be clearly and completely described in connection with the embodiments, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Method embodiment
According to an embodiment of the invention, a generator-based SAR image sparse challenge method is provided, and fig. 1 is a flowchart of the generator-based SAR image sparse challenge method in the embodiment of the invention. As shown in fig. 1, the method specifically includes:
(1) Generating an intensity interference value of each pixel point of the SAR image through a generator to obtain an intensity interference image;
(2) Generating a position interference image through key point extraction based on a quantization method combining the point group sliding difference value and the single-point surrounding difference value;
(3) And multiplying the generated intensity interference image and the position interference image by elements to obtain a countering sample, and updating parameters of the generator through a difference loss function.
Fig. 2 is a schematic diagram of a calculation process of a point group sliding difference value according to an embodiment of the present invention. As shown in fig. 2, the formula for calculating the point group sliding difference d slide is as follows:
Wherein the method comprises the steps of Representing pixel points satisfying (x-x i)2+(y-yj)2≤r2), w (x, y) representing a weight function, selecting a two-dimensional gaussian function as a weight for highlighting the weight of the center point, and I (x, y) representing the pixel value size of the image at the point (x, y).
The point group sliding difference value represents the overall change condition of a part of the image taking a certain pixel as the center during sliding, if the pixel point is positioned at a boundary position such as a contour, the pixel value change between different point groups is larger during the point group sliding, and then the point group sliding difference value d slide is larger, so that whether the pixel point is positioned on the boundary of a target can be quantified.
FIG. 3 is a schematic diagram illustrating a calculation process of a single-point surround difference value according to an embodiment of the present invention. As shown in fig. 3, the formula for calculating the single-point surround difference d surround is as follows:
Where I 1(xi,yj) represents the pixel value of 8 pixels surrounding the first week (x i,yj), I 2(xi,yj) represents the pixel value of 16 pixels surrounding the second week (x i,yj), s 1 and s 2 are adjustment parameters.
The single-point surrounding difference d surround indicates the variation difference between a pixel point and its neighboring pixels, and can determine whether the pixel point is a mutation point with larger variation from the surrounding points.
Fig. 4 is a schematic diagram of an optical image of an MSTAR dataset corresponding to an SAR image according to an embodiment of the present invention. As shown in fig. 4, the MSTAR data set adopted in the experiment is a public data set acquired by the synthetic aperture radar, and the polarization mode of the radar signal and HH in the X-band is adopted, so that the MSTAR data set is widely used by the automatic target recognition research technology of the SAR image. The MSTAR dataset contains 10 categories in total, and can be divided into 3 major categories, wherein 2S1 and ZSU belong to the artillery category, BMP2, BDRM2, BTR70, BTR60, D7 and ZIL131 belong to the truck category, and T62 and T72 belong to the tank category. The experiment selects a training set in the MSTAR data set for training, totalizes 2747 pictures, and tests with a test set in the MSTAR data set, totalizes 2425 pictures.
FIG. 6 is a graph showing the fraud rate as a function of epoch when training a model under a training set in accordance with an embodiment of the present invention. As shown in FIG. 6, the training process is totally 6 epochs, the convergence rate of training is greatly improved because the attack range is limited in the key area of the image, the spoofing rate of 99.8% is already reached at the 3 rd epochs, and the generator parameters can meet the requirement of high spoofing performance. After the training process is finished, the generator model parameters obtained through training are experimentally saved for subsequent generation of the countermeasure sample. The method has the advantages that once model training is completed, the generator can generate universal challenge samples, and corresponding challenge samples with universal deception capability can be output only by inputting original images.
Fig. 7 is a graph comparing differences between position disturbance images obtained at different lambda values according to an embodiment of the present invention. As shown in fig. 7, the ratio of λ 1 to λ 2 affects the importance of the difference between the sliding of the point group and the surrounding difference of the single point, so that the ratio of the contour point to the mutation point in the extracted key points is changed, the values of λ 1 and λ 2 are respectively set to be three groups of λ 1=0.5,λ2=0.5、λ1=0.6,λ2 =0.4 and λ 1=0.7,λ2 =0.3 in the experiment, the influence of the key point extraction on the attack method is compared, and the key point extraction images with different parameters are drawn as shown in fig. 7. Under the condition that the value of lambda 1 is smaller and the value of lambda 2 is larger, the proportion of the abrupt change point is increased, more points with larger differences from surrounding points are extracted from the image, clutter interference points of the background in the image are easily extracted as key points affecting identification, under the condition that the value of lambda 1 is larger and the value of lambda 2 is smaller, more contour points are extracted, even contour information is misjudged because the pixel value of the points around the real contour is smaller, the extracted key points are limited in a small area, and the follow-up efficient addition of interference in the area with the largest influence on classification is also not facilitated, so that the attack efficiency is improved.
It will be appreciated by those skilled in the art that the modules or steps of the invention described above may be implemented in a general purpose computing device, they may be concentrated on a single computing device, or distributed across a network of computing devices, they may alternatively be implemented in program code executable by computing devices, so that they may be stored in a memory device for execution by computing devices, and in some cases, the steps shown or described may be performed in a different order than that shown or described, or they may be separately fabricated into individual integrated circuit modules, or multiple modules or steps within them may be fabricated into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.
It should be noted that the above embodiments are merely for illustrating the technical solution of the present invention, and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solution described in the above embodiments may be modified or some or all of the technical features may be equivalently replaced, and these modifications or substitutions may not make the essence of the corresponding technical solution deviate from the scope of the present solution.