Early hydrographic surveys consisted of depths measured by sounding pole and hand lead line, with positions determined by 3-level sextant fixes to mapped reference factors. Guide lines were ropes, or lines, with depth markings and lead weights hooked up. Developing vertical control includes putting benchmarks to measure water depth relative https://jeffreyooycf.p2blogs.com/31416186/an-unbiased-view-of-hydrographic-survey