Limitations and Constraints
The topometer-acquired data were then compared with GNSS surveys based on a similar measuring protocol (Fig. 15.5a). For the same bearings and measuring pace, the topometer data correlated closely with the GNSS survey data. The topometer’s vertical error margin can be estimated at ±0.5 cm (Sinane 2013) for each measurement. The method’s main drawback is that occasional reading errors are aggregated. The longer the profile, the higher the risk of compounding errors.
Such discrepancies in measurements, particularly in the lower parts of profiles (Fig. 15.5b), have been noted by other studies using this type of instrument (Emery 1961; Delgado and Lloyd 2004; Sinane 2010, 2013). To reduce errors related to the rod’s subsiding into the sand, a larger leg was added to the ends of each target rod to keep them from sinking in. Errors arising from operator readings or rounding-off can be reduced by using a finer graduation, such as half-centimetres or millimetres. Once again, however, this deviation trend in profiles as compared with reference profiles (GNSS) is more pronounced in some, though not all, of the longest profiles (Fig. 15.5a) and, when it does occur, only very slightly affects the relevant profiles’ morphology (Fig. 15.5b), so qualitative comparisons between the morphotypes can be maintained (Sinane 2010, 2013).
Obviously, this type of instrument is not as accurate as GNSS nor can data obtained with it be as thoroughly processed, but it is nevertheless highly appropriate, because it is easy to use and can be readily reproduced by the communities themselves in participatory observatories. The lack of any data at all on coastal areas is particularly detrimental to communities and research organisations do not have sufficient funds to conduct major field surveys. Involving communities in producing data not only helps them break away from the fence-sitting, ossifying and disempowering mind-set they are sometimes caught up in but also allows them to become active players in reducing their climate-change vulnerability and knowledge and skills that are useful and relevant for day-to-day use in coastal areas can be sustainably passed on to them.
Fig. 15.5 Comparisons between GNSS and “topometer” data in different profiles