Seafloor Surveying by Divers

Plane surveying is becoming as important in seafloor construction as it is on land, so diver surveyor tools are being developed. This technology review found underwater diver surveying sorely deficient compared to land survey accuracy and utility. Seafloor surveying is divided into: (1) sea surface location determination; (2) establishment of ocean bottom control; and (3) seafloor traverse and profile. Stage 1 is handled most accurately with triangulation at near shore locations and by VHF radio navigation systems at intermediate distances from shore. Stage 2 has been accomplished best with acoustics for carrying a plumb line to the seafloor and marking it there; however, less expensive devices show promise. In stage 3, a tape is optimum for distance measurement (0.3% of distance), but too often important corrections are ignored; the most accurate angle measurements (10 min) have been made with lasers and comparatively accurate relative elevations have been measured with photogrammetry to ¼ in. (6.35 mm), with control at 30 ft (9.1 m) increments horizontally.