*3.1.2 RTS applications*

*Glaciers and the Polar Environment*

tracking of the hourly photographs.

*3.1.1 Point cloud analysis*

related references are reported when available.

corresponds to the glacier thickness in 2014.

guides it is necessary for the installation of new targets. Moreover, the Whymper Serac is continuously monitored by a 4800-m-far monoscopic camera. This survey is active since 2010 and the serac surface displacement is estimated with feature

Besides these continuous monitoring systems, in the past, several measurement campaigns have been conducted to increase the glacier understanding and to develop new monitoring techniques of glaciological close-range remote sensing. In **Table 1**, the complete list of the surveys conducted since 2010 is presented and the

DEMs obtained during LiDAR and TLS surveys and from photographic SfM acquired by drones and helicopter-borne cameras allow monitoring the morphology evolution of the glacier surface. In addition, the DEM of difference (DoD) calculation permits to estimate the surface elevation changes and the possible ice mass loss. From the DoD obtained with the DEMs acquired in October 2019 and June 2014 (helicopter-borne SfM and LiDAR respectively), one can observe the glacier thinning of more than 10 m on average (**Figure 3**). In the considered period, the terminus retreated by several tenths of metres and the bedrock remained exposed. In this part, the DoD shows a thickness loss of 30–40 m approximately, which

*DEM of difference (DoD) of the Montitaz Lobe. The DoD is calculated as the difference between the DEMs acquired on 1/10/2019 and 9/6/2014. The glacier outlines in both years are represented as dashed lines.*

**130**

**Figure 3.**

RTS measurements are continuously active since 2010 to monitor the surface velocity of the Whymper Serac. The survey is conducted with a Leica TM30 that operates in ATR mode. The prism network is composed of several stakes installed into the unstable portions, while a few prisms placed in the surrounding bedrock serve as reference points. Complete acquisition of the entire network lasts approximately 45 min and it is conducted every 2h. The sensor-to-target distance is of 4800 m on average, which is beyond the instrument operating limits declared by the manufacture in ATR mode (https://w3.leica-geosystems.com/downloads123/zz/ tps/tm30/brochures-datasheet/tm30\_technical\_data\_en.pdf). In addition, extreme atmospheric conditions linked to the high-mountain elevation occur frequently. This situation makes the Whymper Serac a critical scenario for RTS measurements and a robust processing method has been developed ad hoc [11]. However, the RTS data allowed forecasting 10 days in advance the serac break-off of 22/10/2014 [12]. The RTS data acquired before such an event are shown in **Figure 4**.
