Page 68 - Summer 2021

ECHO CLASSIFICATION
statistically varying echo from the sea surface and (2) the “target” echoes from the ships or rigs. Through understand- ing the characteristics of the echoes that are specific to each type of scatterer, those differences were exploited using echo statistics to discriminate between the echoes from the ships/
rigs and the sea surface (Figure 7).
Laser Classification of Tissue Surfaces
The variability of echoes from a laser signal is typically referred to as “speckle.” The speckle provides information for the classification of surfaces. In the medical community, lasers have been used for Laser Speckle Contrast Imaging (LSCI) as a metric for classification (Heeman et al., 2019).
This imaging exploits the variability of the echo normal- ized by (i.e., contrasted with) the averaged echo. Current and potential future applications include ophthalmology (retina scans) and dermatology (characterization of burns) as well as diagnosing surfaces of organs during surgery. It is especially useful in the objective characterization of changes in tissue conditions in these applications.
The Future
The information contained in the statistical variability of echoes is being exploited across a wide range of applications, acoustic and electromagnetic. Although some applications have been operational for a long time, others are currently at much earlier stages, such as in medical ultrasound. Potential advancements in the use of echo statistics include opera- tionalizing what is currently being explored in the research phase. In addition, there should be more crossover among different fields on their respective proven techniques, such as methods involving generic statistical functions and those involving physics-based methods.
Acknowledgments
We thank Natalie Renier for creating or adapting the fig- ures. The writing of this article was supported by National Science Foundation Grant No. OCE MRI 1626087.
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