Coastal cliff is almost a vertical elongated structure with a wave-cut notch and a landslip. Cliffs are geological formations of limestone, sandstone, chalk, rock shelters and granite. Cliff surface weathering causes an almost unpredictable and unstoppable detachment between constitutes formations with eventual collapse. The absence of regular coastal cliffs monitoring infrastructure may cause cliff hazard and can decline the biodiversity of freshwater and terrestrial ecosystems. The Terrestrial Laser Scanners TLS is unarguable with high spatial resolution in understanding the structural framework of the coastal cliff. Regular surveys by the TLSs are also limited by cost, handiness and erroneous data from surrounding illumination not traveling in the same wavelength as the laser beam. There are more regulations globally on the use of drones to health, safety, environmental and military factors. It is difficult to automate a flight plan with the drone at very close range to the cliff at such angles that could capture hidden sections due to irregular protruding and instability of the coastal cliff. Coastal cliff monitoring would require frequent surveys to be able to understand change effects and patterns. Regular surveys are also required to overcome the effects of shadow cast and other atmospheric uncertainties. This study develops a rapid, low-cost and precise digital photogrammetry methodology using the pole as a platform and mobile phone as a sensor. The most favorable survey distance and vertical camera angle to the cliff surface are developed. This study also determines the best time Interval for executing a pole survey using the Integrated Sensor Orientation (ISO) from very cheap single frequency inbuilt GNSS sensors in the mobile phone. Time series surveys were carried out on a section of the Penarth coastal cliff Wales, the United Kingdom that is 73 meters in length with an average height of 33 meters. The different point clouds had a theoretical overlap of 100% using the finely register already aligned entities tool in the open-source cloud compare software with the maximum deviation of 0.15cm in the planimetric coordinates of adjoining points in the four different point cloud. Change analysis performed identifies areas of cut, fill and segments that are of threats in all point clouds. The photogrammetric technique developed is very cheap, simple, reliable and can be executed by one person. Results obtained indicate the applicability of this methodology for second-order deformation study.
