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Airborne Imaging System

#1167


Airborne Optical System for Imaging and Ranging in Shallow Water

Tech Area / Field

  • PHY-OPL/Optics and Lasers/Physics

Status
3 Approved without Funding

Registration date
24.12.1997

Leading Institute
Institute of General Physics named after A.M. Prokhorov RAS, Russia, Moscow

Project summary

The purpose of the Project is development of an airborne lidar facility for mapping and tracing comparatively large foreign objects on and under (at a depth of several meters) the water surface. Solution of this problem is extremely important for ship navigation in narrow channels, harbors, and straits. Collisions with such objects may lead to great ecological disasters in areas significant both economically and politically. Most promising method for solving the problem is related to scanning the area by a laser beam and subsequently analyzing the area images taken by a passive technique. Such a scanning should be carried out from a flying platform which coordinates are fixed by positioning systems. The laser-illuminated images are to be processed in real time in order to detect dangerous objects. The prompt maps generated by a computer are put in memory and transmitted by radio to prevent ship accidents.

The novelty of the proposed technical approach is due to a unique solid-state laser to be used. To attain extreme laser radiation features at high repetition rate, phase conjugation (PC) via stimulated Brillouin scattering (SBS) is used resulting in a diffraction - limited laser beam. The peculiarity of the lidar facility to be designed is a dual-channel data acquisition and processing system. One of the receiving channels is intended for 2D-object imaging at/under the water surface, while the another channel has to measure coordinates of the detected target, including the along-sight distance to the object and its depth in water. The laser source power is enough for recording the beam scattered by an object at the depth up to 50 m (in clean water). Additionally, an original processor will be implemented into the lidar facility to provide prompt and reliable image recording and data processing.

Technical approach

Subsurface objects floating in water can be visualized only with the use of laser illumination, since merely the laser light at an appropriate wavelength penetrates from the atmosphere into water to a sufficient depth with minimum attenuation. The laser with both high peak and average powers of radiation can be used as an onboard platform light source. The received images temporally gated and amplified in brightness, are digitized by a Charge Couple Device (CCD) array and processed preliminarily in a buffer where the neighboring frames are compared (the amplitudes are subtracted in each pixel). The noncoincident frames indicate a possible object at/under the water surface and these should be delivered to a main computer for more detailed processing (selecting the images layer by layer) to determine a nature of the object detected.

Expected results

As a result of the Project completion, the prototype shall be built of an onboard facility designed to search for, visualize, and on line map comparatively large objects at the water body surface. Software for imaging and identification of dangerous objects in water should be also developed. Technological achievements used in the facility design are based on novel research data and allow us to reach limiting technical parameters. In particular, a powerful Nd:YAG laser will be especially developed and constructed with features which so far have not been attainable for airborne light sources. These features are due to a unique combination of the technique of so-called phase conjugation via stimulated Brillouin scattering with a novel design of the optical resonator which are supposed to be used in the laser. Application of the both approaches in the laser emitter will allow us to meet diffraction - limited, high peak power green beams capable of penetrating up to 50 m into the water depth in clean sea areas. Even at such depth the laser pulse will have enough power for the light scattered by an underwater object be detected by an airborne optical receiver for further processing. All that characterizes the proposed facility as unique.

The economic benefit of using the proposed airborne setup is obvious. Airborne data collection eliminates the problems associated with shipborne survey of shallow, dangerous, or route-complex waters such as reef areas and narrow straits. Cost-effectiveness of the laser airborne range/imaging system is illustrated by the following example. With the aircraft speed of about 100 m/s the total surveyed area can be rapidly covered by overlapping aircraft tacks. This provides significant advantage over conventional shipborne sonar probing only a small surface portion at each ship tack. Even for ship-accessible sea areas the example shows more than tenfold saving of time (or the same gain in efficiency of data collection) and other resources.

When comparing the system with laser illumination of water to conventional photo and TV aerial survey (at daytime and middle latitudes), estimates show the efficiency of laser mapping to be 5 - 10 times better. Besides the active irradiation allows one to map the water surface both at night and under usually inhomogeneous natural illumination of the area under inspection.

The proposed facility will meet the state-of-art technical performances in the field of laser technology and data processing. Meanwhile its cost when using Russian components will prove three-fivefold less than that manufactured on the West.

Potential foreign collaborator


Name of Institution: Groupe d'Etudes Sous-marines de 1'Atlantique
Address: BP42 - 29240 Brest Naval - France
Telephone: + 33 (0) 2.98.22.53.69
Fax: + 33 (0) 2.98.22.72.13
Director of GESMA & GERBAM Doctor F. Regis ARTIN-LAUZER

Potential role of foreign collaborator

Technical characteristics of the Project were preliminarily agreed with the collaborator in order to start a commercialization of the onboard facility after preparation of its prototype. In particular, we plan to undertake joint flight tests of the instrument, as well as joint modernization and use of this type equipment.


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