On the Potential for Remote Observations of Coastal Morphodynamics from Surf-Cameras
Round 1
Reviewer 1 Report
Conlin et al 2022 study the applicability of surfcam images for studying coastal morphodynamics. In contrast to previous work on this topic, they explore the potential to use such imagery for enabling quantitative analyses in a fully remote way. To do so, they very cleverly make use of freely-available lidar data for identifying ground control points and Google Earth for estimating camera position. This results in geo-rectified surfcam images with observational uncertainties lie within the range of those of as more traditional nearshore remote sensing techniques. Application to a shoreline change analysis shows that this technique is viable for analysing shoreline changes that are larger than the observational uncertainty, which coincides with seasonal and storm-related changes at this particular site.
With their work, the authors provide a valuable addition to the suite of nearshore remote sensing possibilities available to study coastal morphodynamics at a large spatial scale with a high temporal resolution. They outline their work in an excellent and well-written manner and provide all relevant considerations with respect to accuracy and uncertainty underlying their assumptions and the processed images. As such, I have no major concerns and highly recommend to publish this work. Below I outline some minor suggestions that may be incorporated by the authors, as well as some minor corrections.
Figure 4 : This figure is referred to in line 354, when addressing reprojection errors, but it might be more suitable to refer to Fig. 4 somewhere in lines 328-334. Here, the horizontal and vertical offsets are addressed. Also, it would help the reader if the authors would elaborate on Figure 4, also in relation to line 284, where it is stated that the principal point coordinates ended up being negative.
In lines 485-489 and 528-529 the authors mention that provided sufficient remote-GCPs and limited lens distortion this technique could be applied anywhere in the world. This is indeed an exciting prospect. However, an important data source for this study is the availability of (freely-available) lidar data. This might be the case along the US coasts, but in other parts of the world the lack of this data could hamper the application of this technique. Do the authors have any idea what the coverage of such data is? Also, could the authors elaborate on alternatives for such data?
L147 & 231 transformations & transformation
Author Response
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Reviewer 2 Report
the work is clearly exposed. the topic has been known in the literature for several years, but the authors have exploited the full potential of recreational coastal webcams. They used a consolidated methodology using rtk to georeference the GCPs and algorithms widely used in the bibliography.
the results and discussions are presented in a clear and orderly manner. the images are clear and useful for the purpose.
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Reviewer 3 Report
The work deals with an interesting topic: the use of surfcams to monitor the coast, which requires the calibration of the cameras (here through GCPs obtained from lidar).
However, i am afraid that the focus of the paper, which is the camera calibration, is performed in such a way that i do not find that the work can be published. The calibration ignores the distortion of the lens, which is not acceptable and justifies, in my opinion, not only the bad performance far from the center of the image, but also other behaviors. There are, nowadays (published in this same journal), works that satisfactorily perform the full camera calibration (extrinsic+intrinsic) from GCPs and the horizon line.
I would suggest to improve the calibration procedure so that the the novelty of the work (the use of lidar and surfcams) could be highlighted.
Author Response
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Reviewer 4 Report
Dear authors, you are presenting a magnificent manuscript. I do not have any corrections.
All the best.
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