|This survey job is to collect the seawall topography for further analysis and research, as maintaining the strong and stable seawalls is of utmost significance in times of rising sea levels, or future disaster threats. It seems quite easy to go with conventional ground measurements for this seawall topography because surveyors could manage to access the shoulder, the slope and even the foot of the seawalls (see Fig. 5) while putting operator safety aside. Yet, the sturdy seawall was well engineered to be concave on its seaward side between the shoulder and the slope so that the waves would be deflected upward instead of striking the armor body hard. And as a result, it might be difficult to measure the concave downward (see Fig. 6) by GNSS RTK, even with the latest tilt sensing technology. Furthermore, there are still some blind spots, like the turnings, which might be invisible to total station and terrestrial laser scanner, especially when such tripod-mounted instruments are forced to set up on the 2 beach corners or onto the seawall shoulders. Obviously, failures to conduct some measurements might lead to certain data gaps and insufficient data reference. On the other hand, accumulative errors would inevitably occur in case of repeated station movements. All in all, it’s really hard to manifest the surface of uneven seawall slopes, composed of many irregular rocks, by measuring one group of dots after another.
(Note: the 2 pictures below were borrowed from internet.)