A method for monitoring blade frequencies of a wind turbine and a monitoring system for performing the method are provided. The image is analyzed at multiple spatial scales and over multiple feature channels to determine the likely salience of different portions of the image. According to the above structure, it is possible to realize the duty adjustment and the optical power adjustment by using only one adjusting circuit so that it is possible to achieve a simplified, miniatuarized, and low cost optical transmission circuit. Another embodiment creates a variable external cross-section which provides hydraulic stresses that are in opposition to the surface tension and body force stresses and thus, reduces the influence of surface tension and body forces. The user-specified grammar can be pre-specified directly to the voice browser by the user or fetched by the browser from a remote location on the fly.