Underwater Laser Systems For Rangin, Size Estimation, And 3-D Measurement

Abstract

structured lighting systems have been used to obtain range, scale, and orientation measures from video and still camera images. Application areas have included the construction of mosaic maps for geological surveying, photo surveys for establishing the environmental impact of offshore drilling, and various inspection tasks requiring size estimation, such as biological specimen observation and platform inspection. With earlier designed systems, the estimation size or range is obtained only after analysis of prerecorded data or by visual observation of patterns produced on video. In this paper we present a review of conventional photogrammetric techniques that have been used in oceanographic application, and describe the development of several computer based-systems which are capable of displaying range and size information automatically. One recently developed system utilizes a multibeam projection from a laser source to produce structured light patterns over portions of a scene which are viewed simultaneously by an underwater video camera. The video output is digitized, captured, and stored in a high speed digital memory and then analyzed on-line to produce a range estimate which is displayed on the video image as an overlay. A size estimate for objects within the video field can also be produced by manual placement of cursors within the image. Another system under development produces threedimensional maps of the image space using a scanned laser beam. The scene is viewed from a separate location with a position sensitive detector (PSD) to provide depth information via triangulation principles. The PSD provides an estimate of position of the apparent landing spot of the laser beam for each scan angle from which a depth estimate is calculated. The system is designed to scan an entire 20 X 20 degree field-of-view at distances from 0.5 to 2.5 meters. The entire field of view can be scanned and a 3-D image can be produced in less than 4 seconds with the present design. Further technological advancements are anticipated which should allow video rate opertaion. The paper will include detailed system descriptions, including elements of the optical and electronic design. Calibration data will be presented and performance will be reviewed. This work was supported in part by a grant from the Atlantic Foundation and by the Naval Civil Engineering Laboratory under Contract N47408-9 1C1209.