The phrase "be witnessed by something" can be replaced with a number of synonyms, depending on the context of the sentence. Some of the most commonly used synonyms for this phrase include "be observed by," "be seen by," and "be noted by." Other possible synonyms might include "be detected by," "be watched by," or "be monitored by." Depending on the tone and formality of the writing, some synonyms might be more appropriate than others. For instance, "be monitored by" might be the best choice in a more formal document, while "be seen by" might work better in a more casual or conversational context.