## 3 Results
### GPR Interpretation and Radar Facies  
At the top of each GPR profile there is a pair of black and white bands that are the direct signal between the transmitter and the reciever. The top band is the 'airwave,' which travels through the air at the speed of light. The second band is the 'groundwave,' which travels through the ground close to the surface at a lower velocity. The velocity of the radar waves in the surface shingle at Dungeness is determined as 0.12 m/ns using field measurements and curve fitting to hyperbolic reflections. Beneath the direct arrivals of the airway and groundwave are reflections from the depositional layers within the shingle. We used radar facies analysis to identify and interpret GPR reflection patterns. Radar facies are mappable, three-dimensional sedimentary units composed of reflections whose parameters differ from adjacent units [25; 26; 28]. At Dungeness, we identified four \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Progradation** & **Beach 1** & **Beach 2** & **Beach 3** & **Beach 4** & **Beach 5** & **Beach 6** & **Beach 7** \\ \hline
1940–1960 (m) & 40 & 30 & 27 & 28 & 28 & 26 & 29 \\ \hline
1960–1990 (m) & 48 & 33 & 21 & 14 & 22 & 14 & \(-\)5 \\ \hline
1990–2006 (m) & 48 & 43 & 25 & 27 & 26 & 34 & 19 \\ \hline
2006–2019 (m) & 11 & 20 & 16 & 11 & 9 & 16 & 25 \\ \hline Total 1940–2019 (m) & 146 & 120 & 89 & 81 & 84 & 90 & 69 \\ \hline Progradation rate & & & & & & & \\
1940–2019 (m/year) & 1.85 & 1.73 & 1.13 & 1.03 & 1.06 & 1.14 & 0.86 \\ \hline \end{tabular}
\end{table} 
Table 1: Beach accretion at Dungeness between 1940 and 2019, with average rates of progradation over this time. Figure 6: Graphic representation of beach accretion at Dungeness between 1940 and 2019. Note the reverse movement at Beach 7 between 1960 and 1990 when the beach was locally eroded, and the shoreline retreated by 5 m. Rates of progradation decrease from south to north along the direction of longshore drift. radar facies in the GPR profiles. Radar facies 1 (RF 1) are planar inclined reflections that dip towards the sea at an angle of around 15\({}^{\circ}\) and commonly extend for around 10 m. Radar facies 1 is the dominant reflection pattern on the GPR profile; the example shown in Figure 7C comes from 100-112 m on the GPR profile. RF 1 is commonly found beneath the swales and is interpreted as a beach prograde. Radar facies 2 (RF 2), high amplitude hyperbolic reflections (Figure 7B), are particularly well developed close to the landward end of the profile between 16 and 26 m. This is between the road that was built in 1935 and the 1940 shingle-sand contact picked from aerial photographs. Parabolic reflections are commonly formed where GPR profiles cross linear features such as pipelines or other buried objects. The location and spacing of the RF 2 hyperbolas on the GPR profile suggest that these reflections come from the remains of anti-tank and anti-personnel defences that were constructed along the beach in the second world war. Such structures can be seen in the 1940 aerial photographs on Google Earth ProTM. Parabolic reflections elsewhere in the profiles may also be from WWII defenses that were bulldozed into the sea at the end of the war, or they could be from other anthropogenic artifacts associated with fishing boats and a range of launch and recovery systems that have been deployed to move fishing boats on and off the beach at Dungeness. Radar facies 3 (RF 3) comprises short concave reflections. These are typically low amplitude and found within the beach ridges and on the modern active beach. On the modern beach, the concave reflections are associated with berms, and this observation is used to inform the interpretation of the concave reflections as berms preserved within the beach ridges. The examples shown in Figure 7D are from 140-152 m on the GPR profile of Beach 1 (Figure 7D).