**5. Conclusions and future work**

Finally, **Methods 2** and **3** have been verified for six-look images. The estimates are presented in Table 7 for 7x7 blocks. **Method 2** produces obvious overestimation (only one estimate is within the required interval and other ones exceed the upper limit). In turn, **Method 3** provides all four estimates accurate enough although underestimation is observed for all four processed images. Thus, **Method 3** operating in 7x7 blocks provides the best or nearly the best accuracy

10(a) 0.033 0.042 0.043 10(b) 0.034 0.048 0.055 10(c) 0.033 0.045 0.051 10(d) 0.038 0.053 0.061 Table 6. Blind estimates of speckle variance for six-look real-life SAR images obtained by

Block size 5x5 7x7 9x9

(c) (d) Fig. 10. Multi-look SAR elementary images (512x512 pixels) of urban region in Canada

**Figure 10.** Multi-look SAR elementary images (512x512 pixels) of urban region in Canada

(a) (b)

The presented results clearly show that for estimation techniques based on scatter-plots and robust fitting it is often not enough to carry out robust fitting. Image pre-processing able to

Finally, **Methods 2** and **3** have been verified for six-look images. The estimates are presented in Table 7 for 7x7 blocks. **Method 2** produces obvious overestimation (only one estimate is

for all considered simulated and real-life images.

Image presented in Figure

322 Computational and Numerical Simulations

**Method 1** 

Some aspects of SAR image simulation have been considered. In particular, it has been stressed that spatial correlation of speckle is to be taken into account. One algorithm to do this is described.

Three methods for blind estimation of noise statistical characteristics in SAR images have been first tested for simulated images. It has been shown that there are several factors influencing their performance. These factors are image content (complexity), the method used and its parameters. It is not always possible to provide blind estimates within desired limits especially for highly textural (complex structure) images. Then, these methods have been verified for real life TerraSAR-X images of limited size of 512x512 pixels. Preliminary tests have clearly demonstrated the presence of essential spatial correlation of speckle, especially for multi-look images. This is taken into account in setting parameters of BENC methods. The block size of 7x7 pixels is recommended for practical use.

The BENC methods based on scatter-plots without image pre-processing produce, on the average, worse accuracy than the method based on mode determination for local estimates' distribution. If pre-processing is applied, BENC methods (as **Method 3**) are able to produce acceptable accuracy for most images. Estimation accuracy for single-look images is mostly acceptable. However, there are more problems with speckle variance estimation for multi-look images. Thus, in future, special attention should be paid to considering multi-look image case. In this sense, the methods based in obtaining noise-informative maps (Uss et al. 2011; Uss et al., 2012) seem to be attractive although they are not so fast as the methods considered above.

This work has been partly supported by French-Ukrainian program Dnipro (PHC DNIPRO 2013, PROJET N° 28370QL).
