In high-resolution sonar imagery, large variations in image background can make it difficult to reliably find targets. These variations result from irregular illumination of the sea floor, which is caused by sonar platform motion. Contributing to this problem is the fact that the spatial frequencies of the varying background can be similar to those of the target. Consequently, image-processing methods that attempt to segment image regions associated with target highlight (or shadow), are often fooled by bright (or dark) target-size patches of background. This typically results in an increase of the number of false alarms. This paper describes two image normalization methods: the Cross-Range Forward-Backward filter and the Serpentine Forward-Backward filter. Results are presented that show the impact of the image normalization on reducing false alarms.