USGS MIPS Autoalt Documentation

USGS MIPS Autoalt Documentation

This program is used to automatically detect the first bottom returns in a sidescan sonar image . Using user provided information and statistics obtained from the image, Autoalt attempts to identify the locations of the first bottom returns on both sides of nadir within the entire image. The pixel positions of the first bottom returns found are then converted to an altitude in meters (height of fish above the seafloor) and placed into the image's associated navigation file.

Files

This program requires as input one unsigned 8-bit or signed 16-bit image file. It will not generate an output image but modifies the same input image. An additional second input file may be entered where it will be the name of a work file to be used by AUTOALT.

Water column parameters

NPIXELS: This parameter is used to select the number of pixels to ignore at either side of nadir. Selecting an appropriate value keeps Autoalt from selecting any altitude values within the water column offset (i.e., such as noise). Note that NPIXELS must be greater than or equal to 1.
LCLEAN and RCLEAN: These parameters are used to select the left and right water column maximum DN values. Locations found left of nadir with dn values less than LCLEAN will be ignored and vice-versa. If the sonar image is 8-bit, LCLEAN and RCLEAN must be greater than or equal to 0 and must be less than or equal to 255. If the sonar image is 16-bit, LCLEAN and RCLEAN must be greater than or equal to -32768 and must be less than or equal to 32767.

Tolerances

LTOL and RTOL: These parameters are used to select the left and right side tolerance values. Each has a default (suggested) value based on statistics automatically calculated by Autoalt. For images with bright first bottom returns the tolerance should be high (at the DN value of the first return). For images with dark first bottom returns, the calculated value should be fairly close to the best tolerance value. If the sonar image is 8-bit, LTOL and RTOL must be greater than or equal to 1 and must be less than or equal to 255. If the sonar image is 16-bit, LTOL and RTOL must be greater than or equal to -32767 and must be less than or equal to 32767.

When inspecting the results of Autoalt, if the altitude values are located in the water column then the tolerances are too low. If the altitude values are located past the first return then the tolerances are too high.