**4. Conclusions**

This synthesis showed that the new topographic measurement techniques implemented in coastal geomorphology over the last 25 years had enabled a clear gain in productivity in topographic measurements. The density of measurements has considerably increased, for example, for areas of several hectares, from 0.1 points/m2 to 1–2 points/m<sup>2</sup> with LiDAR and several hundred points/m2 with photogrammetry. This greater density of points resulted in the calculation of DTMs or DSMs with a higher spatial resolution (1 m/pixel with LiDAR measurements, 5 cm/pixel for photogrammetric measurements) on which small-scale landforms and topographic changes that could not be distinguished at a coarser resolution can be detected. With the development of these new techniques, it is therefore nowadays possible to work on shoreline morphodynamics at a very fine scale. For example, aeolian sand accumulation landforms on the upper beach and dune blowouts associated with pedestrian trampling are visible on a photogrammetric DSM but not on a LiDAR DTM (**Figure 12**: on the left, extract of the LiDAR DTM, and on the right, the photogrammetry DSM).

This improvement in spatial resolution is also associated with a decrease in measurement error margins (±20 cm horizontally and 2 cm vertically for aircraft LiDAR measurements, ±3 cm in both dimensions for low-height photogrammetric UAV surveys), which results in a higher accuracy of the DTMs produced.

**Table 1** compares the advantages and disadvantages of the three techniques. The financial costs are not discussed here.

In the coming years, coastal geomorphologists are waiting for a technique that will automatically distinguish bare areas from vegetated areas, so that DTMs can be easily calculated. The simultaneous use of LiDAR and multi- and hyperspectral sensors on board aircraft [52] or UAVs [31] is an interesting prospect. These multi- and hyperspectral images, processed with remote sensing methods, allow to

**107**

**Table 1.**

*Recent Advances in Coastal Survey Techniques: From GNSS to LiDAR and Digital…*

map vegetation and soil moisture. This is particularly interesting for analyzing the dynamics of embryo dunes, which is closely linked to the development of pioneer vegetation [53] or monitoring the stabilization or restoration of established coastal

*Comparison of DSM calculated from LiDAR data (on the left) and low-height photogrammetry (on the* 

Fit for small to medium study zones Only provide topographical

Low measurement density Time consuming measurements

Sensitive to weather conditions Long processing time of the data and high computing power required Huge amount of data to be stored Provide DSM, difficult to compute

Measurement campaign difficult to

Medium accuracy measurement Sensitive to weather conditions Long processing time of the data and high computing power required Huge amount of data to be stored

measurement

DTM

organize Low repeatability

**Technique Advantages Disadvantages**

Not really sensitive to weather conditions

Small to medium amount of data to be stored

Fit for small to medium study zones (short

Measurement campaign easy to organize (depending on local regulations)

GNSS Measurement campaign very easy to organize High repeatability

Provide DTM

High repeatability High measurement density High accuracy measurement Provide full orthophotographs for

photointerpretation

Airborne LiDAR Fit for large study zones (extensive flight

Can provide DTM

range)

*Advantages and disadvantages of the three techniques.*

High accuracy measurements Short processing time of the data

flight time and limited range)

Medium measurement density

*DOI: http://dx.doi.org/10.5772/intechopen.91964*

dunes [54].

**Figure 12.**

UAV

photogrammetry

*right).*

*Recent Advances in Coastal Survey Techniques: From GNSS to LiDAR and Digital… DOI: http://dx.doi.org/10.5772/intechopen.91964*

map vegetation and soil moisture. This is particularly interesting for analyzing the dynamics of embryo dunes, which is closely linked to the development of pioneer vegetation [53] or monitoring the stabilization or restoration of established coastal dunes [54].

#### **Figure 12.**

*Spatial Variability in Environmental Science - Patterns, Processes, and Analyses*

of sand was observed. Sediment accumulation was about 69 × 103

m3

the study site, with a total gain of nearly 90 × 103

foreshore, corresponding to only 0.04 m3

to 1–2 points/m<sup>2</sup>

the photogrammetry DSM).

financial costs are not discussed here.

responding volume changes are very limited: about +83 × 103

average accumulation rate of about 0.13 m3

and 15.7 × 103

36.5 × 103

m3

**4. Conclusions**

points/m2

dunes during the following period (2011–2012), which corresponds to a constant

ods. Subsequently, storms in late 2013 [50] resulted in widespread coastal retreat associated with the erosion of coastal dunes west of Bray-Dunes (**Figure 11**). About

Marchand, respectively, between 2012 and 2014. However, the Perroquet Dune, east of Bray-Dunes, remained fairly stable or even accumulated slightly during this storm period. Although coastal dune erosion was significant during the 2012–2014 period, a comparison of the 2008 and 2014 DTMs shows an accumulation in the dunes almost everywhere along the coast (**Figure 11A**) due to the supply of aeolian sand from the beach. Such vertical accretion is visible even where coastal dune erosion has occurred (e.g., Dune Dewulf), suggesting that wind-blown sand may also

The upper part of the beach was also characterized by accretion along most of

/m2 .

This synthesis showed that the new topographic measurement techniques implemented in coastal geomorphology over the last 25 years had enabled a clear gain in productivity in topographic measurements. The density of measurements has considerably increased, for example, for areas of several hectares, from 0.1

photogrammetry. This greater density of points resulted in the calculation of DTMs or DSMs with a higher spatial resolution (1 m/pixel with LiDAR measurements, 5 cm/pixel for photogrammetric measurements) on which small-scale landforms and topographic changes that could not be distinguished at a coarser resolution can be detected. With the development of these new techniques, it is therefore nowadays possible to work on shoreline morphodynamics at a very fine scale. For example, aeolian sand accumulation landforms on the upper beach and dune blowouts associated with pedestrian trampling are visible on a photogrammetric DSM but not on a LiDAR DTM (**Figure 12**: on the left, extract of the LiDAR DTM, and on the right,

This improvement in spatial resolution is also associated with a decrease in measurement error margins (±20 cm horizontally and 2 cm vertically for aircraft LiDAR measurements, ±3 cm in both dimensions for low-height photogrammetric

**Table 1** compares the advantages and disadvantages of the three techniques. The

In the coming years, coastal geomorphologists are waiting for a technique that will automatically distinguish bare areas from vegetated areas, so that DTMs can be easily calculated. The simultaneous use of LiDAR and multi- and hyperspectral sensors on board aircraft [52] or UAVs [31] is an interesting prospect. These multi- and hyperspectral images, processed with remote sensing methods, allow to

UAV surveys), which results in a higher accuracy of the DTMs produced.

maximum accumulation (>0.5 m) measured in the eastern part of the study site (**Figure 11B**). As for the dunes, sand accumulation on the upper beach occurred mainly between 2008 and 2012, while slight erosion occurred locally between 2012 and 2014. Comparison of the 2008 and 2014 DTMs shows characteristic patterns of topographic change of intertidal bars and troughs on the foreshore. The cor-

m3

with LiDAR and several hundred points/m2

have been transported landward as the dune front eroded and retreated.

/m2

m3

between 2008 and 2014, with

over the whole

with

m3

/year in the dunes during both peri-

were eroded from the Dune Dewulf and the Dune

in the coastal

**106**

*Comparison of DSM calculated from LiDAR data (on the left) and low-height photogrammetry (on the right).*


#### **Table 1.** *Advantages and disadvantages of the three techniques.*
