# Cubesats Allow High Spatiotemporal Estimates of Satellite-Derived Bathymetry
## 4 Discussion
### Are PlanetScope Suitable for Data Inclusion in Navigation Maps?  
The results from the application of the calculated coefficients are very promising for the value of the PlanetScope imagery in estimating bathymetry and its subsequent integration in navigation charts compliant with the IHO requirements and the fit of them into ZDCs. The results are also comparable with the Copernicus Sentinel-2 based SDB from the same site, as has been shown by [16] using the Google Earth Engine platform. For the Zone of 0-10 m (Figure 4), the estimated R\({}^{2}\), using a 3 rd order polynomial equation, is 0.88, the SEz is 0.66 m, and the estimated RMSEz is 0.32 m while for the zone 10 m-25 m R\({}^{2}\) is 0.88 with SEz at 1.43, and RMSEz at 1.58 m. According to the IHO, the Zone of Confidence A1 requires data in the zone 0-10 m with a depth accuracy of \(\pm\) 0.6 m and a position accuracy of \(\pm\)5 m, while the zone A2 a depth accuracy of \(\pm\)0.6 m and a position accuracy of \(\pm\)20 m. For Zone B, it requires for the same depth as in A2, an accuracy of \(\pm\)1.2 m and a position accuracy of \(\pm\)50 m. For the depth zone 10-30 m, the ZOC A1 requires \(\pm\)0.8 m, the ZOC A2 requires \(\pm\)1.2 m and the ZOC B requires \(\pm\)1.6 m. The results from the current study suggest that the PlanetScope data can fit into the ZOC A2 and possibly into the ZOC A1. This fit is also supported by the position accuracy of the satellite images, according to the recent study of [31], which shows that the geolocation performance of the PlanetScope's Level 3A product is good and the absolute geolocation performance is set by a max RMSE\({}_{x}\) = 5.18 m, RMSE\({}_{y}\) = 4.21 m and CE(90) = 9.93 m, respectively.  
While the current study includes only one site and is targeted at understanding the behavior of the different selected PlanetScope CubeSat images from the same site covering one-month period, more studies are required to robustly conclude for the suitability of the employed Earth Observation data in the calculation of bathymetry. Studies that will include different satellites of very high-resolution data and high signal-to-noise ratio with images from the same period (e.g., within the same month) will allow a full benchmark on the radiometric quality of the PlanetScope data for the calculation of SDB. Other approaches like the cloud-based one presented in [19] will allow the full scientific and operational exploitation of the Planet archive for seabed mapping and monitoring without the laborious analysis per image and the visual inspection of the \"best image\" for further processing and analysis; this will be achieved through the utilization of multi-temporal (weekly, monthly, seasonal) PlanetScope image composites, which will reduce technological and environmental issues, both intra and inter-sensor, e.g., low signal-to-noise ratio, varying radiometric quality, atmospheric, water surface and column, and seabed conditions.  
There is an increasing need in the charting of shallow coastal waters across the globe at fine scales that will allow the creation of new navigation maps, but also the update of old productions. IHO has started to adopt the SDB approach and the IHO S-44 standards are currently under revision. The revised one will be updated to include the ability to exploit new technologies for the update of nautical charts when that is possible under the specifications required, as the use of traditional means, like the hydroacoustics, in shallow uncharted waters is dangerous for the equipment and the per km\({}^{2}\) charted area is much more costly in comparison to the SDB approach.